A method of controlling heat loss in an aerosol-generating system comprising an internal and external heater

Abstract

A method of controlling aerosol production in an aerosol-generating system (150), the aerosol- generating system comprising: an internal heater (214) configured to heat an aerosol- generating substrate (204) from inside the aerosol-generating substrate; and an external heater (66) configured to heat the aerosol-generating substrate (204) from outside the aerosol- generating substrate; the method comprising, during a consumer usage session: controlling a supply of power to the internal heater (214) to heat the internal heater; and controlling a supply of power to the external heater (66) such that the temperature of the external heater does not exceed a maximum temperature of 120 degrees Celsius.

Description

[0001] A METHOD OF CONTROLLING HEAT LOSS IN AN AEROSOL-GENERATING SYSTEM COMPRISING AN INTERNAL AND EXTERNAL HEATER

[0002] The present disclosure relates to a method of controlling aerosol production in an aerosolgenerating system. The described method is particularly applicable to handheld electrically-heated aerosol-generating systems that are configured to heat an aerosol-generating substrate to generate an aerosol and deliver the aerosol into the mouth of a consumer. The present disclosure further relates to a aerosol-generating system employing such a method.

[0003] Electrically heated aerosol-generating systems that heat an aerosol-generating substrate to produce an aerosol without burning the aerosol-generating substrate are known in the art. Some known aerosol-generating systems comprise an aerosol-generating device and an aerosol-generating article comprising the aerosol-generating substrate. In use, the aerosol-generating device heats the aerosol-generating substrate of the aerosol-generating article to form an aerosol.

[0004] It is desirable in such electrically-heated aerosol-generating systems to ensure as far as possible that combustion of the substrate does not occur, even in extreme environmental conditions and under extreme usage patterns. It is therefore desirable to control the temperature of the heating element or elements in the device to reduce the risk of combustion while still heating to a sufficient temperature to ensure a desirable aerosol.

[0005] It is also desirable in aerosol-generating systems to be able to produce aerosol which is consistent over time. In systems in which an exhaustible substrate is heated continuously or repeatedly over time this can be difficult, as the properties of the aerosol forming substrate can change significantly with continuous or repeated heating, both in relation to the amount and distribution of aerosol-forming constituents remaining in the substrate and in relation to substrate temperature. In particular, a consumer of a continuous or repeated heating device can experience a fading of flavour, taste, and feel of the aerosol as the substrate is depleted of the aerosol former that coveys key constituents such as nicotine and flavouring. To provide a consistent aerosol delivery over time, the first delivered aerosol needs to be substantially comparable to a final delivered aerosol during operation.

[0006] Some known aerosol-generating system comprise an internal heater for heating the aerosol-generating substrate from within the aerosol-generating substrate. However, using an internal heater to heat an outer portion of the aerosol-generating substrate sufficiently to form an aerosol may require heating the internal heater to a sufficiently high temperature that there is a risk of the internal heater overheating or burning an inner portion of the aerosol-generating substrate close to the internal heater. Thus, the use of an internal heater typically leads to an outer portion of the aerosol-generating substrate, furthest from the internal heater during use, not being heated to a sufficiently high temperature to form an aerosol. This means that theouter portion of the aerosol-generating substrate is typically wasted.

[0007] Some known aerosol-generating devices comprise an external heater for heating the aerosol-generating substrate from outside the aerosol-generating substrate. However, using an external heater to heat an inner portion of the aerosol-generating substrate sufficiently to form an aerosol may require heating the external heater to a sufficiently high temperature that there is a risk of the external heater overheating or burning the outer portion of the aerosolgenerating substrate close to the external heater. Thus, the use of an external heater typically leads to an inner portion of the aerosol-generating substrate, furthest from the external heater during use, not being heated to a sufficiently high temperature to form an aerosol. This means that the inner portion of the aerosol-generating substrate is typically wasted.

[0008] Some known aerosol-generating devices comprise both an internal and external heater and are configured to provide more than one heating profile for heating the aerosolgenerating substrate. Heating profiles may depend on consumer requirements or a particular aerosol-generating article being used in the system. For example, a particular heating profile may be configured not to use the external heater to externally heat the aerosol-generating substrate. Instead, such a heating profile may be configured to only use the internal heater to internally heat the aerosol-generating substrate. In such a scenario, the external heater, which is typically made from a thermally conductive material, can undesirably act as a heat sink for heat generated internally by the internal heater. This can result in heat loss from the aerosolgenerating substrate and consequently adversely affect aerosol production.

[0009] It would be desirable to provide a method of controlling aerosol production in an aerosol-generating system that reduces the risk of combustion of the aerosol-generating substrate. It would also be desirable to provide a method of aerosol production that reduces heat loss from the aerosol-generating substrate when internally heating the aerosolgenerating substrate provides consistent aerosol production over the duration of operation.

[0010] According to an aspect of the present disclosure, there is provided a method of controlling aerosol production in an aerosol-generating system. The aerosol-generating system may comprise an internal heater configured to heat an aerosol-generating substrate from inside the aerosol-generating substrate. The aerosol-generating system may comprise an external heater configured to heat the aerosol-generating substrate from outside the aerosol-generating substrate. The method may comprise, during a consumer usage session, controlling a supply of power to the external heater such that the temperature of the external heater does not exceed a maximum temperature. The maximum temperature may be 120 degrees Celsius.

[0011] According to an aspect of the present disclosure, there is provided a method of controlling aerosol production in an aerosol-generating system, the aerosol-generating systemcomprising: an internal heater configured to heat an aerosol-generating substrate from inside the aerosol-generating substrate; and an external heater configured to heat the aerosolgenerating substrate from outside the aerosol-generating substrate; the method comprising: during a consumer usage session, controlling a supply of power to the external heater such that the temperature of the external heater does not exceed a maximum temperature of 120 degrees Celsius.

[0012] As used herein, the term “usage session” refers to a time period during which an aerosol-generating system is producing aerosol so that a consumer is able to take a puff on the aerosol-generating system to extract aerosol from an aerosol-generating substrate. A usage session excludes any pre-heating and calibration processes, which may occur before a usage session in order to prepare an aerosol-generating system for puffing. The usage session may include a plurality of puffs, preferably at least 5 puffs. Once the aerosolgenerating substrate is depleted, the aerosol-generating article may be replaced and another usage session may be started. With the exception of any pre-heating and calibration processes, the method steps described herein take place during a usage session unless otherwise stated.

[0013] An advantage of controlling a supply of power to the external heater or to the internal heater or to both the internal and external heater during a usage session is that the effects of heating control on aerosol production are realised whilst the consumer is able to take puffs on the aerosol-generating system. As a result, the consumer experience in terms of the amount and quality of aerosol produced can be adjusted in real-time so that the desired experience can be provided to the consumer whilst the aerosol-generating system is in use. In contrast, if a significant amount of heating control occurs during a pre-heating phase when a user is not able to take puffs on the aerosol-generating system, then the full benefits of adjusting the heating are not experienced by the consumer.

[0014] An advantage of controlling a supply of power to the external heater such that the temperature of the external heater does not exceed a maximum temperature of 120 degrees Celsius is that it may reduce the risk of combustion or pyrolysis of the aerosol-generating substrate. This maximum temperature is significantly below the maximum external heater temperature used in conventional aerosol-generating systems. Despite this lower maximum external heating temperature, the inventors have found that the method provides consistent delivery of aerosol over the duration of the consumer usage session. In particular, the method provides substantially comparable amounts of aerosol and aerosol constituents at the end of a consumer usage session as it does at the start.

[0015] Another advantage of controlling a supply of power to the external heater such that the temperature of the external heater does not exceed a maximum temperature of 120 degreesCelsius is that it reduces heat loss from the aerosol-generating substrate during internal heating. By heating the external heater, the temperature difference between the internal heater and the external heater is reduced, which reduces heat transfer to the external heater and reduces the ability of the external heater to act as a heat sink. As a result, more heat is retained in the aerosol-generating substrate, which helps to maintain consistent and acceptable aerosol production. The external heater is heated to a relatively low temperature compared to the temperature of the internal heater. The external heater is merely heated to a temperature that helps to reduce heat loss to the external heater and reduce the external heater’s ability to act as a heat sink. Therefore, the above-described method does not use a significant amount of energy to heat the external heater and helps to improve the overall efficiency of the system by reducing heat loss.

[0016] The maximum temperature of the external heater may be less than 110 degrees Celsius. The maximum temperature of the external heater may be less than 100 degrees Celsius. The maximum temperature of the external heater may be approximately 95 degrees Celsius. These maximum temperature ranges further reduce the risk of combustion or pyrolysis of the aerosol-generating substrate and also reduce heat loss from the aerosolgenerating substrate during internal heating.

[0017] The maximum temperature of the external heater may be between 80 degrees Celsius and 120 degrees Celsius. The maximum temperature of the external heater may be between 85 degrees Celsius and 110 degrees Celsius. The maximum temperature of the external heater may be between 90 degrees Celsius and 100 degrees Celsius. These maximum temperature ranges further reduce the risk of combustion or pyrolysis of the aerosolgenerating substrate and also reduce heat loss from the aerosol-generating substrate during internal heating.

[0018] The supply of power to the external heater may be controlled such that the temperature of the external heater increases to the maximum temperature over the duration of the usage session.

[0019] The supply of power to the external heater may be controlled such that, during a first external heating phase, the temperature of the external heater increases at a first rate of change. The supply of power to the external heater may be controlled such that during a second external heating phase, the temperature of the external heater increases at a second rate of change. The first rate of change may be greater than the second rate of change. An advantage of the first rate of change being greater than the second rate of change is that it may help to bring the external heater to its desired temperature more quickly so that heat loss to the external heater is reduced earlier in the consumer usage session.

[0020] It will appreciated that the first and second rates of change are not necessarily constantand that there may be some variation in the rate at which the temperature of the external heater increases and possibly a sub-period or portion of the first or second external heating phases during which the temperature does not increase but is held constant. Therefore, the first and second rates of change may be average rates of change over the first and second external heating phases.

[0021] The supply of power to the external heater may be controlled such that, during the first external heating phase, the external heater is heated to a first temperature. The first temperature of the external heater may be at least 60 degrees Celsius. The first temperature of the external heater may be at least 70 degrees Celsius. The first temperature of the external heater may be at least 80 degrees Celsius. The first temperature of the external heater may be approximately 85 degrees Celsius.

[0022] The first temperature of the external heater may be between 60 degrees Celsius and 100 degrees Celsius. The first temperature of the external heater may be between 70 degrees Celsius and 90 degrees Celsius.

[0023] The first external heating phase may have a duration of less than 45 seconds. The first external heating phase may have a duration of less than 40 seconds. The first external heating phase may have a duration of less than 35 seconds. The first external heating phase may have a duration of approximately 30 seconds. These relatively short durations for the first external heating phase help to bring the external heater to its desired temperature more quickly to reduce heat loss to the external heater.

[0024] The external heater may be heated to at least 80 percent of the maximum temperature during the first external heating phase. The external heater may be heated to at least 85 percent of the maximum temperature during the first external heating phase. The external heater may be heated to approximately 90 percent of the maximum temperature during the first external heating phase. Advantageously, by heating to a relatively high percentage of the maximum temperature, the temperature difference between internal and external heater can be significantly reduced to help to reduce heat loss to the external heater.

[0025] The first external heating phase may be less than 15 percent of the duration of the consumer usage session. The first external heating phase may be less than 10 percent of the duration of the consumer usage session. These relatively short durations for the first external heating phase help to bring the external heater to its desired temperature more quickly to reduce heat loss to the external heater.

[0026] The supply of power to the external heater may be controlled such that, during the second external heating phase, the external heater is heated to a second temperature. The second temperature of the external heater may be the maximum temperature of the external heater.The temperature of the external heater may be held constant during a first portion of the second external heating phase. The temperature of the external heater may be held constant at the first temperature of the external heater during the first portion of the second external heating phase. The first portion of the second external heating phase may correspond to at least a portion of a first internal heating phase when the temperature of the internal heater is held substantially constant.

[0027] The first portion of the second external heating phase may have a duration of at least 120 seconds. The first portion of the second external heating phase may have a duration of at least 135 seconds. The first portion of the second external heating phase may have a duration of at least 150 seconds. The first portion of the second external heating phase may have a duration of at least 165 seconds. The first portion of the second external heating phase may have a duration of approximately 175 seconds.

[0028] The first portion of the second external heating phase may have a duration of between 120 seconds and 200 seconds. The first portion of the second external heating phase may have a duration of between 135 seconds and 195 seconds. The first portion of the second external heating phase may have a duration of between 150 seconds and 190 seconds. The first portion of the second external heating phase may have a duration of between 165 seconds and 185 seconds. The first portion of the second external heating phase may have a duration of between 170 seconds and 180 seconds.

[0029] The temperature of the external heater may increase during a second portion of the second external heating phase. The temperature of the external heater may increase to the second or maximum temperature during a second portion of the second external heating phase. The second portion of the second external heating phase may correspond to at least a portion of a second internal heating phase when the temperature of the internal heater is increasing. An advantage of increasing the temperature of the external heater during a second portion of the second external heating phase when the temperature of the internal heater is increasing is that it helps to reduce the resulting increase in temperature difference between the internal and external heaters as the temperature of the internal heater increases. This helps to reduce heat loss to the external heater.

[0030] The second portion of the second external heating phase may have a duration of at least 110 seconds. The second portion of the second external heating phase may have a duration of at least 125 seconds. The second portion of the second external heating phase may have a duration of at least 140 seconds. The second portion of the second external heating phase may have a duration of at least 155 seconds. The second portion of the second external heating phase may have a duration of approximately 165 seconds.

[0031] The second portion of the second external heating phase may have a duration ofbetween 110 seconds and 185 seconds. The second portion of the second external heating phase may have a duration of between 125 seconds and 180 seconds. The second portion of the second external heating phase may have a duration of between 140 seconds and 175 seconds. The second portion of the second external heating phase may have a duration of between 155 seconds and 175 seconds.

[0032] The method may further comprise controlling a supply of power to the internal heater to heat the internal heater.

[0033] The supply of power to the internal heater may be controlled such that the temperature of the internal heater is maintained at a constant temperature during a first internal heating phase. The constant temperature of the internal heater may be less than 350 degrees Celsius. The constant temperature of the internal heater may be less than 345 degrees Celsius. The constant temperature of the internal heater may be less than 340 degrees Celsius. The constant temperature of the internal heater may be less than 335 degrees Celsius. The constant temperature of the internal heater may be approximately 330 degrees Celsius.

[0034] The constant temperature of the internal heater may be between 320 degrees Celsius and 350 degrees Celsius. The constant temperature of the internal heater may be between 320 degrees Celsius and 345 degrees Celsius. The constant temperature of the internal heater may be between 320 degrees Celsius and 340 degrees Celsius. The constant temperature of the internal heater may be between 320 degrees Celsius and 335 degrees Celsius.

[0035] Although the above temperature ranges are relatively low temperatures for the internal heater, they still allow sufficient aerosol to be produced at least in the first phases of the consumer usage session. The level of heating can then be increased in the later phases of the consumer usage session to maintain aerosol production or increase the levels of aerosol production, if desired.

[0036] The constant temperature may correspond to a target temperature for the internal heater.

[0037] The temperature of the internal heater may correspond to a target conductance for the internal heater. The target conductance may be equal to a percentage of a conductance span between a first conductance value associated with a first calibration temperature of the internal heater and a second conductance value associated with a second calibration temperature of the internal heater.

[0038] The constant temperature may correspond to a target conductance of less than 48 percent of the conductance span. The constant temperature may correspond to a target conductance of less than 40 percent of the conductance span. The constant temperature may correspond to a target conductance of less than 25 percent of the conductance span. Theconstant temperature may correspond to a target conductance of less than 17 percent of the conductance span. The constant temperature may correspond to a target conductance of approximately 9 percent of the conductance span.

[0039] The constant temperature may correspond to a target conductance between 5 percent and 48 percent of the conductance span. The constant temperature may correspond to a target conductance between 5 percent and 40 percent of the conductance span. The constant temperature may correspond to a target conductance between 5 percent and 25 percent of the conductance span. The constant temperature may correspond to a target conductance between 5 percent and 17 percent of the conductance span.

[0040] The supply of power to the internal heater may be controlled such that the temperature of the internal heater may increase during a second internal heating phase.

[0041] The temperature of the internal heater may increase in a series of steps. Advantageously, a series of temperature steps allows the temperature of the internal heater to be gradually increased to compensate for aerosol depletion during the previous step or earlier in the consumer usage session.

[0042] The series of temperature steps may comprise at least three consecutive temperature steps. The series of temperature steps may comprise four or more consecutive temperature steps.

[0043] One or more temperature step, or alternatively each temperature step, may provide a temperature increase of at least 5 degrees Celsius. One or more temperature step, or alternatively each temperature step, may provide a temperature increase of at least 7.5 degrees Celsius. One or more temperature step, or alternatively each temperature step, may provide a temperature increase of at least 10 degrees Celsius.

[0044] The temperature increase of one or more temperature steps may correspond to conductance increase of 4 percent of the conductance span. The temperature increase of one or more temperature steps may correspond to conductance increase of 6 percent of the conductance span. The temperature increase of one or more temperature steps may correspond to conductance increase of 8 percent of the conductance span.

[0045] One or more temperature step, or alternatively each temperature step, may have a duration between 20 seconds and 60 seconds. One or more temperature step, or alternatively each temperature step, may have a duration between 30 seconds and 50 seconds. One or more temperature step, or alternatively each temperature step, may have a duration of approximately 40 seconds.

[0046] The temperature of the external heater may be less than the temperature of the internal heater for the duration of the usage session. This may help in reducing the risk of overheating the aerosol-generating substrate, in particular, it may help reduce the risk of combustion orpyrolysis of the aerosol-generating substrate.

[0047] The consumer usage session may have an overall duration of less than 420 seconds. The consumer usage session may have an overall duration of less than 400 seconds. The consumer usage session may have an overall duration of less than 380 seconds. The consumer usage session may have an overall duration of approximately 365 seconds.

[0048] According to an aspect of the present disclosure, there is provided a method of controlling aerosol production in an aerosol-generating system, the aerosol-generating system comprising: an internal heater configured to heat an aerosol-generating substrate from inside the aerosol-generating substrate; and an external heater configured to heat the aerosolgenerating substrate from outside the aerosol-generating substrate; the method comprising, during a consumer usage session: supplying a first amount of power to the internal heater to heat the internal heater; supplying a second amount of power to the external heater, the second amount of power being equivalent to an amount of power dissipated from the aerosolgenerating substrate to the external heater during another consumer usage session in which the external heater is not powered.

[0049] The second amount of power supplied to the external heater may be such that the temperature of the external heater does not exceed a maximum temperature of 120 degrees Celsius, or optionally does not exceed a maximum temperature of 110 degrees Celsius, or further optionally does not exceed a maximum temperature of 100 degrees Celsius, or yet further optionally does not exceed a maximum temperature of 95 degrees Celsius.

[0050] The method of this aspect of the disclosure may further comprise any of the steps described above with respect to the previous aspect of the disclosure, which are not repeated here in the interests of conciseness.

[0051] Optionally, controlling a supply of power to the internal heater may comprise controlling a supply of an alternating electric current to an inductor that is inductively coupled to the internal heater, which may be a susceptor, such that the internal heater is inductively heated.

[0052] Optionally, controlling a supply of power to the external heater may comprise controlling a supply of a direct electric current to the external heater, which may be a resistive heating element, such that the external heater is resistively heated.

[0053] Prior to commencement of the consumer usage session, the method may further comprise performing a calibration process for measuring one or more calibration values associated with the internal heater. This is step may be particularly applicable where the internal heater comprises a susceptor and, in the discussion of the calibration process herein, the terms “internal heater” and “susceptor” are used interchangeably. Controlling the power provided to the susceptor may comprise controlling the power such that the temperature of the susceptor is adjusted based on the one or more calibration values.The one or more calibration values may comprise a first conductance value associated with a first calibration temperature of the susceptor and a second conductance value associated with a second calibration temperature of the susceptor. Controlling the power provided to the susceptor may comprise maintaining a conductance value associated with the susceptor between the first conductance value and the second conductance value.

[0054] The one or more calibration values may comprise a first resistance value associated with a first calibration temperature of the susceptor and a second resistance value associated with a second calibration temperature of the susceptor. Controlling the power provided to the susceptor may comprise maintaining a resistance value associated with the susceptor between the first resistance value and the second resistance value.

[0055] The susceptor may comprise a first susceptor material having a first Curie temperature and a second susceptor material having a second Curie temperature. The second Curie temperature may be lower than the first Curie temperature. The second calibration temperature may correspond to the second Curie temperature of the second susceptor material.

[0056] Controlling the power provided to the susceptor may comprise controlling the power such that the temperature of the susceptor is between the first calibration temperature and the second calibration temperature.

[0057] The first calibration temperature may be between 150 degrees Celsius and 350 degrees Celsius and the second calibration temperature may be between 200 degrees Celsius and 400 degrees Celsius. A temperature difference between the first calibration temperature and the second calibration temperature may be at least 50 degrees Celsius.

[0058] The calibration process may be performed prior to a consumer usage session each time a consumer activates the aerosol-generating system. Accordingly, the calibration values used to control the heating process are more accurate and reliable than if the calibration process were performed at manufacturing. This is especially important if the susceptor forms part of a separate aerosol-generating article that does not form part of the aerosol generating device. In such circumstances calibration at manufacturing is not possible. Furthermore, performing the calibration process each time the aerosol-generating system is activated helps to adjust for any changes in ambient conditions, such as ambient temperature and humidity.

[0059] Performing the calibration process may comprise the steps of: (i) controlling the power provided to the susceptor to cause an increase of the temperature of the susceptor; (ii) monitoring at least a current value of the inductive heating arrangement; (iii) interrupting provision of power to the inductive heating arrangement when the at least the current value reaches a maximum, wherein the current value at the maximum corresponds to the second calibration temperature of the susceptor; and (iv) when the current value associated with thesusceptor reaches a minimum, controlling the power provided to the susceptor to cause an increase of the temperature of the susceptor, wherein the current value at the minimum corresponds to the first calibration temperature of the susceptor. Monitoring the at least a current value of the inductive heating arrangement may further comprise monitoring a voltage value of the inductive heating arrangement.

[0060] The method may further comprise repeating steps (i) to (iv) when the conductance value associated with the susceptor reaches the minimum. Subsequent to repeating steps (i) to (iv): a conductance value corresponding to the current value at the maximum may be stored as the second calibration value and a conductance value corresponding to the current value at the minimum may be stored as the first calibration value. Alternatively, a resistance value corresponding to the current value at the maximum may be stored as the second calibration value and a resistance value corresponding to the current value at the minimum may be stored as the first calibration value.

[0061] Prior to commencement of the consumer usage session, the method may further comprise performing a pre-heating process to heat the internal heater. This is step may be particularly applicable where the internal heater comprises a susceptor and, in the discussion of the pre-heating process herein, the terms “internal heater” and “susceptor” are used interchangeably. During pre-heating, the susceptor may be heated to the first calibration temperature. The pre-heating process may have a predetermined duration. The pre-heating process allows for heat to spread within the substrate before launching the calibration process, thereby further improving the reliability of the calibration values.

[0062] Performing the preheating process may comprise: controlling the power provided to the susceptor to cause an increase of the temperature of the susceptor; monitoring a at least a current value of the inductive heating arrangement; and interrupting provision of power to the inductive heating arrangement when the current value reaches a minimum, wherein the current value at the minimum corresponds to the first calibration temperature of the susceptor.

[0063] If the current value reaches a minimum during the predetermined duration of the preheating process, the method may comprise interrupting the provision of power to the inductive heating arrangement to cause a decrease of the temperature of the susceptor and subsequently resuming the provision of power to the inductive heating arrangement to cause an increase of the temperature of the susceptor to the first calibration temperature. Interrupting the provision of power to the inductive heating arrangement and resuming providing power to the inductive heating arrangement is repeated for the predetermined duration of the preheating process. The method may further comprise, if the current value of the susceptor does not reach a minimum during the predetermined duration of the pre-heating process, ceasing operation of the aerosol-generating device.Performing the preheating process may comprise: controlling the power provided to the susceptor to cause an increase of the temperature of the susceptor; monitoring a conductance value or a resistance value associated with the susceptor; and interrupting provision of power to the inductive heating arrangement when the conductance value reaches a minimum or when the resistance value reaches a maximum, wherein the conductance value at the minimum or the resistance value at the maximum corresponds to the first calibration temperature of the susceptor.

[0064] If, during the predetermined duration of the pre-heating process, the conductance value reaches a minimum or the resistance value reaches a maximum, the method may further comprise interrupting the provision of power to the inductive heating arrangement to cause a decrease of the temperature of the susceptor and subsequently resuming the provision of power to the inductive heating arrangement to cause an increase of the temperature of the susceptor to the first calibration temperature. Interrupting the provision of power to the inductive heating arrangement and the resuming providing power to the inductive heating arrangement may be repeated for the predetermined duration of the preheating process. If, during the predetermined duration of the pre-heating process, the conductance value does not reach a minimum or the resistance value does not reach a maximum, the method may further comprise ceasing operation of the aerosol-generating device.

[0065] Performing the steps of the pre-heating process for the pre-determined duration enables heat to spread within the substrate in time to reach the minimum conductance value measured during the calibration process no matter what the physical condition of the substrate (for example, if the substrate is dry or humid). This ensures reliability of the calibration process. Further, the susceptor is preferably comprised in an aerosol-generating article that is configured to be inserted into the aerosol-generating device. Aerosol-generating articles that are not configured to be used with the aerosol-generating device will not exhibit the same behaviour as authorized aerosol-generating articles. Specifically, for aerosol-generating articles that are not configured to be used with the aerosol-generating device, the minimum current / conductance value or the maximum resistance value will not be observed during the pre-determined duration of the pre-heating process. Accordingly, this may help to prevent the use of non-authorized aerosol-generating articles. Furthermore, the pre-heating process may reduce a time needed for aerosol production once the consumer usage session commences.

[0066] According to an aspect of the present disclosure, there is provided an aerosolgenerating system. The aerosol-generating system may comprise an internal heater configured to heat an aerosol-generating substrate from inside the aerosol-generating substrate. The aerosol-generating system may comprise an external heater configured to heat the aerosol-generating substrate from outside the aerosol-generating substrate. Theaerosol-generating system may comprise control circuitry. The control circuitry may be configured to carry out any of the above-described methods.

[0067] According to an aspect of the present disclosure, there is provided an aerosolgenerating system comprising: an internal heater configured to heat an aerosol-generating substrate from inside the aerosol-generating substrate; an external heater configured to heat the aerosol-generating substrate from outside the aerosol-generating substrate; and control circuitry, the control circuitry being configured to carry out any of above-described methods.

[0068] The aerosol-generating system may comprise an aerosol-generating device and an aerosol-generating article comprising the aerosol-generating substrate. The aerosolgenerating device may comprise the external heater. The aerosol-generating device or article may comprise the internal heater.

[0069] The device may comprise the control circuitry. The system, for example the device of the system, may comprise at least one power supply. Future references to “a power supply” or “the power supply” should be considered references to the at least one power supply. References herein to a supply of power may refer to a supply of power from the power supply. Controlling a supply of power to the internal heater or to the external heater may comprise or be controlling a supply of power, for example controlling one or both of current and voltage, from the at least one power supply to the internal heater or to the external heater. References herein to increasing or decreasing a temperature of the internal heater may be a result of controlling a supply of power to one or both of the internal heater and the external heater. References herein to increasing or decreasing a temperature of the external heater may be a result of controlling a supply of power to the external heater.

[0070] The internal heater may be or comprise a susceptor. In this case, the terms “controlling a supply of power to the internal heater” and “controlling a supply of power to the susceptor” may be used interchangeably.

[0071] The external heater may be or comprise a resistive heating element. In this case, the terms “controlling a supply of power to the external heater” and “controlling a supply of power to the resistive heating element” may be used interchangeably.

[0072] In a first arrangement, the device comprises the external heater and the article comprises the internal heater.

[0073] In a second arrangement, the device comprises the external heater and the device comprises the internal heater.

[0074] In both the first and second arrangements, the internal heater or susceptor may be inductively heated by an inductor. The inductor may be part of the aerosol-generating device. A direct electric current or DC power may be supplied by the control circuitry to the external heater or resistive heating element to resistively heat the resistive heating element. Analternating electric current or AC power may be supplied by the control circuitry to the inductor to inductively heat the susceptor to allow the susceptor to act as the internal heater.

[0075] The device may be configured to engage with, for example receive at least a portion of, the article. The device may comprise a housing. The device may comprise a chamber or cavity. The chamber may be configured to receive at least a portion of the article. The chamber may have a base. The chamber may have an open end. The open end may oppose the base. The device may be configured to receive at least the portion of the article into the chamber through the open end of the chamber. When the article is at least partially received in the chamber, the aerosol-generating substrate of the article may be completely received within the chamber. That is, when the article is at least partially received in the chamber, an entirety of the aerosol-generating substrate of the article may be within the chamber.

[0076] Where the device comprises the internal heater, the internal heater may extend from the base of the chamber or cavity. The internal heater may extend into the chamber, for example towards the open end of the chamber. The internal heater may be shaped as a pin, blade, or rod for penetrating an aerosol-generating substrate of an article inserted into the chamber.

[0077] The aerosol-generating device may comprise a heater assembly. The heater assembly may be configured to be received in a housing of an aerosol-generating device. The heater assembly may comprise the external heater. The heater assembly may comprise a jacket defining a chamber for receiving at least a portion of an aerosol-generating article. The heater assembly may comprise an inductor assembly comprising a sleeve at least partially surrounding the jacket. The inductor assembly may comprise an inductor coupled to the sleeve.

[0078] The jacket may comprise a jacket body. The jacket may comprise the external heater in the form of a heating element. Advantageously, the external heater may be configured to externally heat the aerosol-generating substrate of the aerosol-generating article. In particular, the external heater may be configured to heat a periphery of the chamber. When an aerosolgenerating article is received within the chamber, the external heater may be configured to heat an external or outer portion of the aerosol-generating substrate. Advantageously, if the internal heater is configured to heat an internal or inner portion of the aerosol-generating substrate, this arrangement may ensure that the aerosol-generating substrate is substantially uniformly heated.

[0079] The heating element of the external heater may be arranged on an outer surface of the jacket body. The heating element may at least partially surround the chamber. The heating element may surround the chamber.

[0080] The heating element may be a helical coil. The heating element may be arranged in aserpentine shape. The heating element may be folded or curved to at least partially surround the chamber.

[0081] The heating element may be a resistive heating element. Advantageously, a resistive heating element may be easily powered by a direct current from a power supply in an aerosolgenerating device. The heating element may comprise a resistive heating track arranged on a flexible substrate. The flexible substrate may comprise polyimide. By providing the resistive heating track on a flexible substrate, manufacture of the heater assembly may be simplified, as the resistive heating element may only require wrapping around the jacket.

[0082] When an alternating current is supplied to the inductor, for example when the heater assembly of the present disclosure is a component part of an aerosol-generating device, an alternating magnetic field is generated in the chamber by the inductor. Depending on the configuration of the resistive heating element of the external heater, this alternating magnetic field may induce an alternating current in the resistive heating element. An alternating current induced in the resistive heating element may be particularly disadvantageous as the control circuitry would require filters to ensure the induced alternating current in the resistive heating element does not cause damage to any electronic components electrically connected to the resistive heating element. Furthermore, an induced alternating current in the resistive heating element would generate electrical noise and make it difficult to monitor the voltage and current of the external heater, for example, as part of a feedback loop.

[0083] To overcome this, the resistive heating element of the external heater may be configured such that a total current induced in the heating element by an alternating magnetic field within the chamber is substantially zero. In particular, the resistive heating element is arranged such that any alternating current induced in the resistive heating element in a direction towards the negative terminal of the resistive heating element is equal to the current induced in the resistive heating element in a direction towards the positive terminal of the resistive heating element. As a result, a total alternating current induced in the resistive heating element between the positive terminal and the negative terminal of the resistive heating element is at least significantly reduced, and may be approximately zero. Here, the positive and negative terminals of the resistive heating element refer to the terminals used to receive a direct electric current to supply power to the resistive heating element. For example, in one such suitable arrangement, the resistive heating element may comprise two substantially parallel tracks extending from the first end of the resistive heating element to the second end of the resistive heating element.

[0084] A resistance between a first end and a second end of the resistive heating element of the external heater may be between 100 milliohms and 2000 milliohms, preferably between 200 milliohms and 1500 milliohms, preferably still between 500 milliohms and 1000 milliohms,and even more preferably between 700 milliohms and 900 milliohms. Such values have been found to provide particularly suitable resistive heating of the resistive heating element.

[0085] The resistive heating element may comprise any suitable electrically conductive material. The resistive heating element may comprise a metal. The resistive heating element may comprise a material having a low magnitude of a temperature coefficient of resistance. The temperature coefficient of resistance may be defined by the rate of change of resistance with respect to a change of temperature. A low magnitude of a temperature coefficient of resistance may be defined by the magnitude of the temperature coefficient of resistance being less than 0.004 K'1at 298 K. The resistive heating element may comprise at least one of stainless steel, copper, gold, nickel, platinum, palladium, and silver. The resistive heating element may comprise graphene or a semiconductor. The resistive heating element may comprise a silver-palladium alloy. Advantageously, a silver-palladium alloy provides a suitable resistivity to achieve a desired resistance between the first end and the second end of the resistive heating element. A silver-palladium alloy may also comprise a particularly low magnitude of a temperature coefficient of resistance. Advantageously, the resistance between the first end and the second end of a resistive heating element comprising a silver-palladium alloy will not vary significantly enough during operation to affect the operation of the resistive heating element.

[0086] The chamber may be substantially cylindrical. The chamber may comprise a substantially circular cross section.

[0087] The jacket body may comprise an electrically insulating material. Advantageously, the electrically insulating material may prevent current from the resistive heating element flowing through the jacket. Furthermore, the electrically insulating material ensures that no eddy currents are induced in the jacket body by the inductor element during use of the heater assembly in an aerosol-generating device.

[0088] The jacket body may comprise a proximal portion, a central portion, and a distal portion. The central portion may be positioned between the proximal portion and the distal portion. The proximal portion and the distal portion may comprise a polymer. The proximal portion and the distal portion may comprise polyether ether ketone (PEEK). Advantageously, PEEK is resistant to the temperatures experienced by the proximal portion and the distal portion during use of the heater assembly in an aerosol-generating device.

[0089] The heating element of the external heater may be arranged on an outer surface of the central portion. The central portion may comprise a ceramic. The ceramic may be alumina or zirconia. Advantageously, alumina and zirconia have low coefficients of thermal expansion, so will not expand significantly when heated during use. The central portion may be a thermally conductive central portion. The thermal conductivity of the thermally conductive central portionmay be at least 20 Wnr1K’1, preferably at least 30 Wm’1K’1, and preferably still approximately 40 Wm’1K’1. Advantageously, a thermally conductive ceramic allows for a preferable rate of heat transfer from a resistive heating element located on an outer surface of the central portion to an internal surface of the central portion which partially defines the chamber, whilst being electrically insulating.

[0090] The jacket may comprise a jacket insulating layer at least partially surrounding the jacket body. Advantageously, the jacket insulating layer increase the thermal insulation around the jacket, reducing the heat transferred from the jacket heating element out to the sleeve. This may reduce the temperature of any surrounding housing of an aerosol-generating device during use of the heater assembly in such an aerosol-generating device, thereby increasing comfort for a consumer’s hands. The jacket insulating layer may comprise Kapton™. The jacket insulating layer may surround the resistive heating element. The jacket insulating layer may surround the central portion.

[0091] The aerosol-generating system, for example the aerosol-generating device, may comprise an air inlet. The aerosol-generating system, for example, the aerosol-generating article or a mouthpiece of the device, may comprise an air outlet. The aerosol-generating system, for example the aerosol-generating article, may comprise an airflow path. The air flow path may connect the air inlet and the air outlet. In use, for example in response to a puff on the article or any mouthpiece of the system, air may flow through the air inlet and then through the article and then through the air outlet. After flowing through the air outlet, the air may flow into a mouth of a consumer.

[0092] The jacket may comprise an inner surface. The inner surface may define the chamber. The jacket may comprise at least one groove defined on the inner surface of the jacket. The at least one groove may extend parallel to a longitudinal axis of the jacket. The at least one groove may comprise a plurality of grooves. The chamber may comprise a proximal opening configured to receive the aerosol-generating article therethrough. The chamber may comprise a closed distal end. Advantageously, the at least one groove defined on the inner surface of the jacket provides, during use, an airflow pathway from the proximal opening, through the at least one groove to the distal end of the chamber. The proximal or upstream end of the grooves provide an air inlet to the aerosol-generating system. Accordingly, no other airflow inlets are necessary in the heater assembly or the housing of an aerosol-generating device in which the heater assembly is arranged.

[0093] The sleeve may comprise an electrically insulating material. The sleeve may comprise a plastics material. The sleeve may comprise a different material to the jacket. The sleeve may comprise a liquid crystal polymer (LCP).

[0094] The inductor may comprise an inductor coil. The inductor coil may be a helical coil.The inductor coil may be arranged on a surface of the sleeve. The inductor coil may be arranged on an outer surface of the sleeve. The inductor coil may be wound about a winding axis parallel to a longitudinal axis of the sleeve. Advantageously, winding the inductor coil about the sleeve may reducing manufacturing time.

[0095] The inductor coil may be formed from a coiled conductor. The conductor may be flat. The conductor may have a cross sectional area perpendicular to the direction of extension of the conductor between the first end and the second end of the inductor coil or perpendicular to the direction of flow of an alternating current within the inductor coil during use that is substantially rectangular in shape. The cross sectional area may have a width and a height. The width may be greater than the height, preferably at least 10 times greater than the height. Advantageously, such an inductor coil comprising a flat conductor has been found to be suitable to provide a varying magnetic field for inductive heating of a susceptor element, whilst reducing resistive losses in the inductor coil.

[0096] The inductor may at least partially surround the chamber. The inductor element may surround the chamber. The inductor element may comprise a first and a second electrical connector. The first and second electrical connectors may be embedded within the sleeve. The sleeve may be moulded around the first and second electrical connectors. The sleeve may be injection moulded. Advantageously, this allows the first and second electrical connectors to be electrically insulated from the inductor element. The remaining portion of the inductor element may be wrapped around the outer surface of the sleeve. The first and second electrical connectors may extend parallel to the longitudinal axis of the sleeve. The first and second electrical connectors may each comprise flat filaments.

[0097] The electrical resistance between the first end and the second end of the inductor may be less than 250 milliohms. The electrical resistance between the first end and the second end of the inductor element may be less than 150 milliohms. The electrical resistance between the first end and the second end of the inductor element may be approximately 100 milliohms. The resistance of the resistive heating element may be greater than the resistance of the inductor element. The resistance of the resistive heating element may be at least 2 times greater than the resistance of the inductor coil. Advantageously, the relatively low resistance of the inductor element results in less power dissipated as heat in the inductor element compared to the equivalent power dissipated as heat in the jacket heating element.

[0098] The sleeve may comprise a sleeve insulating layer at least partially surrounding the sleeve. The sleeve insulating layer may comprise Kapton™. The sleeve insulating layer may at least partially surround the inductor. Advantageously, the sleeve insulating layer may reduce the rate of heat transfer from the sleeve to other components of an aerosol-generating device when the heater assembly is received within an aerosol-generating device. This wouldmake the aerosol-generating device more comfortable for a consumer to hold.

[0099] The inductor may comprise metal. The inductor may comprise copper. The inductor may consist of copper. Advantageously, copper has a low resistivity, so the inductor has a relatively low resistance. The inductor may comprise a different material to the resistive heating element.

[0100] Where the internal heater comprises a susceptor, the susceptor, which may also be referred to as a susceptor element, may comprise or consist of one or more susceptor materials. The susceptor may comprise a first susceptor material having a first Curie temperature and a second susceptor material having a second Curie temperature. The first and second susceptor materials are preferably two separate materials that are joined together and therefore are in physical contact with each other, whereby it is ensured that both susceptor materials have the same temperature due to thermal conduction. The first susceptor material may be one of aluminium, iron, and stainless steel, and wherein the second susceptor material is nickel or a nickel alloy. The two susceptor materials are preferably two layers or strips that are joined along one of their major surfaces. The susceptor may further comprise yet an additional third layer of susceptor material. The third layer of susceptor material is preferably made of the first susceptor material. The thickness of the third layer of susceptor material is preferably less than the thickness of the layer of the second susceptor material.

[0101] The aerosol-generating system may comprise a power supply or power source. The power supply may be a DC power supply or power source. The power supply may be or comprise a battery. The battery may be rechargeable. The battery may be a Lithium-based battery, for example a Lithium-Cobalt, a Lithium-lron-Phosphate, a Lithium Titanate or a Lithium-Polymer battery, or a Nickel-metal hydride or Nickel cadmium battery. The power supply may be another form of charge storage device such as a capacitor. The power supply may have sufficient capacity to allow for the continuous generation of aerosol for a period of at least six minutes, corresponding to the typical time taken to smoke a conventional cigarette.

[0102] The control circuitry may comprise a DC / AC converter connected to the DC power source. The control circuitry may be configured to operate at high frequency. For the purpose of this application, the term “high frequency” may be understood to denote a frequency ranging from 1 to 30, or 1 to 10, or 5 to 7 Megahertz. The DC / AC converter may comprise a Class-E power amplifier including a first transistor switch and an LC load network. Class-E power amplifiers are generally known and are described in detail, for example, in the article “Class-E RF Power Amplifiers”, Nathan O. Sokal, published in the bimonthly magazine QEX, edition January / February 2001, pages 9-20, of the American Radio Relay League (ARRL), Newington, CT, U.S.A.. The LC load network may comprise a shunt capacitor and a series connection of a capacitor and the inductor coil.The control circuitry may comprise any suitable controller or electrical components. The control circuitry may comprise a memory. Information for performing the method described herein may be stored in the memory. The control circuitry may comprise a microprocessor. The microprocessor may be a programmable microprocessor, a microcontroller, or an application specific integrated chip (ASIC) or other electronic circuitry capable of providing control.

[0103] The control circuitry may be configured to determine the temperature of the external heater or resistive heating element, for example, during resistive heating. The control circuitry may comprise a sensor for determining the temperature of the external heater. The sensor may be a temperature sensor. Alternatively, or in addition, the controller may be configured to determine a temperature of the external heater by measuring or calculating its electrical resistance. The control circuitry may be configured to determine a potential difference V across the heater and a current I flowing through the heater. The electrical resistance may then be calculated by dividing the potential difference V by the current I. The control circuitry may use the resistance directly as an indication of temperature or may convert the resistance to temperature based on a known relationship between temperature and resistance or a resistance-temperature dataset. Similarly, the temperature of the external heater may be determined by measuring or calculating its electrical conductance, which is the reciprocal of electrical resistance.

[0104] The control circuitry may comprise a memory for storing a plurality of heating profiles for heating the aerosol-generating substrate. The plurality of heating profiles comprises at least an extended duration heating profile, an uplift profile and a boost profile.

[0105] The control circuitry may be configured to identify an aerosol-generating article based on an article identifier arranged on or in the aerosol-generating article. Based on the identity of the aerosol-generating article, the control circuitry may be configured to determine a selection from the plurality of heating profiles that is available to heat the aerosol-generating substrate.

[0106] The selection may comprise two or more heating profiles from the plurality of heating profiles. The selection may comprise three or more heating profiles from the plurality of heating profiles.

[0107] The control circuitry may further comprise a user interface to enable a user to select a heating profile from the selection.

[0108] The aerosol-generating system may further comprise a sensor assembly arranged to detect an article identifier arranged on or in the aerosol-generating article. The sensor assembly may be configured to output a signal corresponding to the article identifier. The sensor assembly may be communicatively connected to the control circuitry. The controlcircuitry may be configured to identify the aerosol-generating article based on the signal received from the sensor assembly.

[0109] The sensor assembly may comprise an optoelectronic emitter and an optoelectronic sensor.

[0110] As used herein, the term “optoelectronic emitter” refers to an electronic device that is able to emit or produce light including visible light, that is, light that can be detected by a human eye, and additionally or alternatively other invisible forms of radiation, including but not limited to, ultraviolet and infrared.

[0111] As used herein, the term “optoelectronic sensor” refers to an electronic device that is able to detect or otherwise sense light including visible light and additionally or alternatively other invisible forms of radiation, including but not limited to, ultraviolet and infrared.

[0112] The optoelectronic emitter may be a white light emitting diode (LED), that is, an LED capable of emitting all, or substantially all, visible wavelengths of light.

[0113] The optoelectronic sensor may comprise a colour sensor.

[0114] The housing of the device may be elongate. The housing may comprise any suitable material or combination of materials. Examples of suitable materials include metals, alloys, plastics or composite materials containing one or more of those materials, or thermoplastics that are suitable for food or pharmaceutical applications, for example polypropylene, polyetheretherketone (PEEK) and polyethylene.

[0115] The aerosol-generating article may comprise, or be in the form of, a cartridge.

[0116] The aerosol-generating article may appear substantially similar to a conventional cigarette. The aerosol-generating article may have a substantially cylindrical rod shape. The aerosol-generating article may comprise a plurality of elements sequentially arranged in coaxial alignment. The aerosol-generating article may comprise a front plug or upstream element. The upstream element may be a plug of cylindrical filter material. The aerosolgenerating article may comprise a substrate element. The substrate element may comprise the aerosol-generating substrate. The substrate element may comprise the internal heater. The internal heater may be in the form of a susceptor. The susceptor may be in direct physical contact with the aerosol-generating substrate. The aerosol-generating article may comprise a support element. The support element may be in the form of a hollow acetate tube having a central air passage. The aerosol-generating article may comprise an aerosol-cooling element. The aerosol-cooling element may be in the form of a hollow acetate tube having a thinner wall than the support element. The aerosol-generating article may comprise a mouthpiece. The mouthpiece may comprise a filter element. The aerosol-generating article may comprise a wrapper, for example, a paper wrapper. One or more or all of the upstream element, the substrate element, the support element, the aerosol-cooling element, and themouthpiece may be circumscribed by the wrapper.

[0117] Optionally, the upstream element is arranged at a most upstream or distal end of the article. Optionally, the substrate element is arranged downstream of the upstream element. Optionally, the support element is arranged downstream of the substrate element. Optionally, the aerosol-cooling element is arranged downstream of the support element. Optionally, the mouthpiece is arranged downstream of one or both of the support element and the aerosolcooling element. Optionally, the mouthpiece is arranged at a most downstream or proximal end of the article. Optionally, the most downstream end of the article, which may be referred to as a mouth end of the article, may be configured for insertion into a mouth of a consumer. A consumer may be able to inhale on, for example directly on, the mouth end of the article.

[0118] One or more of the upstream element, the substrate element, the support element, the aerosol-cooling element, and the mouthpiece may be substantially cylindrical in shape. One or more of the upstream element, the substrate element, the support element, the aerosolcooling element, and the mouthpiece may have a diameter of between 3.5 mm and 10 millimetres. Optionally, the upstream element has a length of between 2 and 10 millimetres. Optionally, the substrate element within the article has a length of between 5 and 20 millimetres. Optionally, the support element has a length of between 2 and 20 millimetres. Optionally, the aerosol-cooling element has a length of between 2 and 20 millimetres. Optionally, the mouthpiece has a length of between 5 and 20 millimetres.

[0119] The article may have a length of between 30 mm and 120 mm, for example between 40 mm and 80 mm, for example about 45 mm. The article may have a diameter of between 3.5 mm and 10 mm, for example between 4 mm and 8.5 mm, for example between 4.5 mm and 7.5 mm.

[0120] The aerosol-generating article may comprise an article identifier for providing an identity of the aerosol-generating article. The article identifier may comprise visible ink, ultra violet (UV) ink, infra red (IR) ink, phosphorescent ink, fluorescent ink. The article identifier may comprise one or more circumferential bands printed on an external surface of the aerosolgenerating article.

[0121] Optionally, the aerosol-generating substrate may be a solid aerosol-generating substrate. However, the aerosol-generating substrate may comprise both solid and liquid components. Alternatively, the aerosol-generating substrate may be a liquid aerosolgenerating substrate.

[0122] Optionally, the aerosol-generating substrate comprises nicotine. Optionally, the aerosol-generating substrate comprises tobacco. Alternatively or in addition, the aerosolgenerating substrate may comprise a non-tobacco containing aerosol-forming material.

[0123] If the aerosol-generating substrate is a solid aerosol-generating substrate, the solidaerosol-generating substrate may comprise, for example, one or more of: powder, granules, pellets, shreds, spaghettis, strips or sheets containing one or more of: herb leaf, tobacco leaf, fragments of tobacco ribs, reconstituted tobacco, homogenised tobacco, extruded tobacco and expanded tobacco. The solid aerosol-generating substrate may be in loose form, or may be provided in a suitable container or cartridge. Optionally, the solid aerosol-generating substrate may contain additional tobacco or non-tobacco volatile flavour compounds, to be released upon heating of the substrate. The solid aerosol-generating substrate may also contain capsules that, for example, include the additional tobacco or non-tobacco volatile flavour compounds and such capsules may melt during heating of the solid aerosol-generating substrate.

[0124] As used herein, homogenised tobacco refers to material formed by agglomerating particulate tobacco. Homogenised tobacco may be in the form of a sheet. Homogenised tobacco material may have an aerosol-former content of greater than 5 percent on a dry weight basis. Homogenised tobacco material may alternatively have an aerosol former content of between 5 percent and 30 percent by weight on a dry weight basis. Sheets of homogenised tobacco material may be formed by agglomerating particulate tobacco obtained by grinding or otherwise comminuting one or both of tobacco leaf lamina and tobacco leaf stems. Alternatively, or in addition, sheets of homogenised tobacco material may comprise one or more of tobacco dust, tobacco fines and other particulate tobacco by-products formed during, for example, the treating, handling and shipping of tobacco. Sheets of homogenised tobacco material may comprise one or more intrinsic binders, that is tobacco endogenous binders, one or more extrinsic binders, that is tobacco exogenous binders, or a combination thereof to help agglomerate the particulate tobacco; alternatively, or in addition, sheets of homogenised tobacco material may comprise other additives including, but not limited to, tobacco and non-tobacco fibres, aerosol-formers, humectants, plasticisers, flavourants, fillers, aqueous and non-aqueous solvents and combinations thereof.

[0125] In one example, the aerosol-generating substrate may comprise a gathered crimpled sheet of homogenised tobacco material. As used herein, the term ‘crimped sheet’ denotes a sheet having a plurality of substantially parallel ridges or corrugations. Preferably, when the aerosol-generating article has been assembled, the substantially parallel ridges or corrugations extend along or parallel to the longitudinal axis of the aerosol-generating article. This advantageously facilitates gathering of the crimped sheet of homogenised tobacco material to form the aerosol-generating substrate. However, it will be appreciated that crimped sheets of homogenised tobacco material for inclusion in the aerosol-generating article may alternatively or in addition have a plurality of substantially parallel ridges or corrugations that are disposed at an acute or obtuse angle to the longitudinal axis of the aerosol-generatingarticle when the aerosol-generating article has been assembled. In certain embodiments, the aerosol-generating substrate may comprise a gathered sheet of homogenised tobacco material that is substantially evenly textured over substantially its entire surface. For example, the aerosol-generating substrate may comprise a gathered crimped sheet of homogenised tobacco material comprising a plurality of substantially parallel ridges or corrugations that are substantially evenly spaced-apart across the width of the sheet.

[0126] The aerosol-generating substrate may further comprise an aerosol former. Examples of suitable aerosol formers include, but are not limited to: polyhydric alcohols, such as propylene glycol, triethylene glycol, 1,3-butanediol and glycerine; esters of polyhydric alcohols, such as glycerol mono-, di- or triacetate; and aliphatic esters of mono-, di- or polycarboxylic acids, such as dimethyl dodecanedioate and dimethyl tetradecanedioate. Preferred aerosol formers are polyhydric alcohols or mixtures thereof, such as propylene glycol, triethylene glycol, 1,3-butanediol and, most preferred, glycerine. The aerosolgenerating substrate may comprise one or more aerosol formers.

[0127] As used herein, the term “aerosol-generating article”, or simply “article” for short, may refer to an article able to generate, or release, an aerosol, for example when heated.

[0128] As used herein, the term “aerosol-generating substrate” may refer to a substrate capable of releasing an aerosol or volatile compounds that can form an aerosol. Such volatile compounds may be released by heating the aerosol-generating substrate. The aerosolgenerating substrate may comprise one or more aerosol formers or aerosol-forming materials. An aerosol-generating substrate may be adsorbed, coated, impregnated or otherwise loaded onto a carrier or support. An aerosol-generating substrate may conveniently be part of an aerosol-generating article.

[0129] As used herein, the term “aerosol former” may refer to any suitable known compound or mixture of compounds that, in use, facilitates formation of an aerosol and that is substantially resistant to thermal degradation at the operating temperature of the aerosolgenerating article.

[0130] As used herein, the term “aerosol-generating device” refers to a device that interacts with an aerosol-generating substrate to generate an aerosol. An aerosol-generating device may interact with one or both of an aerosol-generating article comprising an aerosolgenerating substrate, and a cartridge comprising an aerosol-generating substrate. In some examples, the aerosol-generating device may heat the aerosol-generating substrate to facilitate release of volatile compounds from the substrate.

[0131] As used herein, the term “susceptor” may refer to an element comprising a material that is capable of converting the energy of a magnetic field into heat. When a susceptor is located in an alternating magnetic field, the susceptor is heated. Heating of the susceptor maybe the result of at least one of hysteresis losses and eddy currents induced in the susceptor, depending on the electrical and magnetic properties of the susceptor material.

[0132] As used herein, the term “inductively couple” may refer to the heating of a susceptor when penetrated by an alternating magnetic field. The heating may be caused by the generation of eddy currents in the susceptor. The heating may be caused by magnetic hysteresis losses.

[0133] As used herein, the term “puff” may refer to the action of a consumer drawing an aerosol into their body through their mouth or nose.

[0134] As used herein, the terms ‘“distal”, “upstream” “proximal” and “downstream” describe the relative positions of components, or portions of components, of an aerosol-generating device and aerosol generating article. Aerosol generating articles and devices according to the present disclosure have a proximal end through which, in use, an aerosol exits the article or device for delivery to a consumer, and have an opposing distal end. In use, a consumer draws on the proximal end of the aerosol generating article. The terms upstream and downstream are relative to the direction of aerosol or air movement through the aerosol generating article or aerosol-generating device when a consumer draws on the proximal end of the aerosol-generating article. The proximal end of the aerosol-generating article is downstream of the distal end of the aerosol-generating article. The proximal end of the aerosol-generating article may also be referred to as the downstream end of the aerosolgenerating article and the distal end of the aerosol-generating article may also be referred to as the upstream end of the aerosol-generating article.

[0135] Features described in relation to one of the above examples may equally be applied to other examples of the present disclosure.

[0136] The invention is defined in the claims. However, below there is provided a non-exhaustive list of non-limiting examples. Any one or more of the features of these examples may be combined with any one or more features of another example, embodiment, or aspect described herein.

[0137] Example Ex1: A method of controlling aerosol production in an aerosol-generating system, the aerosol-generating system comprising at least one heater configured to heat an aerosol-generating substrate; the method comprising, during a consumer usage session, controlling a supply of power to the at least one heater.

[0138] Example Ex2: A method according to example Ex1, wherein the aerosol-generating system comprises an internal heater configured to heat an aerosol-generating substrate from inside the aerosol-generating substrate.

[0139] Example Ex3: A method according to example Ex1 or Ex2, wherein the aerosolgenerating system comprises an external heater configured to heat the aerosol-generatingsubstrate from outside the aerosol-generating substrate.

[0140] Example Ex4: A method according to example Ex3, further comprising, during a consumer usage session, controlling a supply of power to the external heater such that the temperature of the external heater does not exceed a maximum temperature.

[0141] Example Ex5: A method according to example Ex4, wherein the maximum temperature of the external heater is less than 120 degrees Celsius.

[0142] Example Ex6: A method according to example Ex5, wherein the maximum temperature of the external heater is less than 110 degrees Celsius.

[0143] Example Ex7: A method according to example Ex6, wherein the maximum temperature of the external heater is less than 100 degrees Celsius.

[0144] Example Ex8: A method according to example Ex4, wherein the maximum temperature of the external heater is between 80 degrees Celsius and 120 degrees Celsius.

[0145] Example Ex9: A method according to example Ex8, wherein the maximum temperature of the external heater is between 85 degrees Celsius and 100 degrees Celsius.

[0146] Example Ex10: A method according to example Ex9, wherein the maximum temperature of the external heater is between 90 degrees Celsius and 100 degrees Celsius.

[0147] Example Ex11: A method according to any of examples Ex4 to Ex10, wherein the supply of power to the external heater is controlled such that the temperature of the external heater increases for at least a period of time during the usage session.

[0148] Example Ex12: A method according to example Ex11 , wherein the supply of power to the external heater is controlled such that the temperature of the external heater increases to the maximum temperature over the duration of the usage session.

[0149] Example Ex13: A method according to example Ex11 or Ex12, wherein the supply of power to the external heater is controlled such that, during a first external heating phase, the temperature of the external heater increases at a first rate of change.

[0150] Example Ex14: A method according to example Ex13, wherein the supply of power to the external heater is controlled such that, during a second external heating phase, the temperature of the external heater increases at a second rate of change.

[0151] Example Ex15: A method according to example Ex13, wherein the first rate of change is greater than the second rate of change.

[0152] Example Ex16: A method according to any of examples Ex11 to Ex15, wherein the supply of power to the external heater may be controlled such that, during the first external heating phase, the external heater is heated to a first temperature.

[0153] Example Ex17: A method according to example Ex16, wherein the first temperature of the external heater is at least 60 degrees Celsius.

[0154] Example Ex18: A method according to example Ex17, wherein the first temperature ofthe external heater is at least 70 degrees Celsius.

[0155] Example Ex19: A method according to example Ex18, wherein the first temperature of the external heater is at least 80 degrees Celsius.

[0156] Example Ex20: A method according to example Ex16, wherein the first temperature of the external heater is between 60 degrees Celsius and 100 degrees Celsius.

[0157] Example Ex21: A method according to example Ex20, wherein the first temperature of the external heater is between 70 degrees Celsius and 90 degrees Celsius.

[0158] Example Ex22: A method according to any of examples Ex13 to Ex21 , wherein the first external heating phase has a duration of less than 45 seconds.

[0159] Example Ex23: A method according to example Ex20, wherein the first external heating phase has a duration of less than 40 seconds.

[0160] Example Ex24: A method according to example Ex23, wherein the first external heating phase has a duration of less than 35 seconds.

[0161] Example Ex25: A method according to example Ex24, wherein the first external heating phase has a duration of approximately 30 seconds.

[0162] Example Ex26: A method according to any of examples Ex16 to Ex25, wherein the supply of power to the external heater is controlled such that, during the second external heating phase, the external heater is heated to a second temperature.

[0163] Example Ex27: A method according to example Ex26, wherein the second temperature of the external heater is the maximum temperature of the external heater.

[0164] Example Ex28: A method according to any of examples Ex2 to Ex27, further comprising controlling a supply of power to the internal heater to heat the internal heater.

[0165] Example Ex29: A method according to example Ex28, further comprising providing a delay between supplying power to the internal heater and subsequently supplying power to the external heater.

[0166] Example Ex30: A method according to example Ex29, wherein the delay is less than 90 seconds.

[0167] Example Ex31: A method according to example Ex30, wherein the delay is 60 seconds or less.

[0168] Example Ex32: A method according to any of examples Ex28 to Ex31, wherein the supply of power to the internal heater is controlled such that the temperature of the internal heater is maintained at a constant temperature during a first internal heating phase.

[0169] Example Ex33: A method according to example Ex32, wherein the constant temperature of the internal heater is less than 350 degrees Celsius.

[0170] Example Ex34: A method according to example Ex33, wherein the constant temperature of the internal heater is less than 345 degrees Celsius.Example Ex35: A method according to example Ex34, wherein the constant temperature of the internal heater is less than 340 degrees Celsius.

[0171] Example Ex36: A method according to example Ex35, wherein the constant temperature of the internal heater is less than 335 degrees Celsius.

[0172] Example Ex37: A method according to example Ex36, wherein the constant temperature of the internal heater is approximately 330 degrees Celsius.

[0173] Example Ex38: A method according to example Ex32, wherein the constant temperature of the internal heater is between 320 degrees Celsius and 350 degrees Celsius.

[0174] Example Ex39: A method according to example Ex38, wherein the constant temperature of the internal heater is between 320 degrees Celsius and 345 degrees Celsius.

[0175] Example Ex40: A method according to example Ex39, wherein the constant temperature of the internal heater is between 320 degrees Celsius and 340 degrees Celsius.

[0176] Example Ex41: A method according to example Ex40, wherein the constant temperature of the internal heater is between 320 degrees Celsius and 335 degrees Celsius.

[0177] Example Ex42: A method according to any of examples Ex28 to Ex31, wherein the supply of power to the internal heater is controlled such that the temperature of the internal heater increases during a second internal heating phase.

[0178] Example Ex43: A method according to example Ex40, wherein the temperature of the internal heater increases in a series of steps.

[0179] Example Ex44: A method according to example Ex40, wherein the series of temperature steps comprises at least three consecutive temperature steps.

[0180] Example Ex45: A method according to example Ex44, wherein the series of temperature steps comprises four or more consecutive temperature steps.

[0181] Example Ex46: A method according to any of examples Ex43 to Ex45, wherein one or more temperature step, or optionally each temperature step, provides a temperature increase of at least 5 degrees Celsius.

[0182] Example Ex47: A method according to example Ex46, wherein one or more temperature step, or optionally each temperature step, provides a temperature increase of at least 7.5 degrees Celsius.

[0183] Example Ex48: A method according to example Ex47, wherein one or more temperature step, or optionally each temperature step, provides a temperature increase of at least 10 degrees Celsius.

[0184] Example Ex49: A method according to any of examples Ex43 to Ex48, wherein one or more temperature step, or optionally each temperature step, has a duration between 20 seconds and 60 seconds.

[0185] Example Ex50: A method according to example Ex49, wherein one or moretemperature step, or optionally each temperature step, has a duration between 30 seconds and 50 seconds.

[0186] Example Ex51: A method according to example Ex50, wherein one or more temperature step, or optionally each temperature step, has a duration of approximately 40 seconds.

[0187] Example Ex52: A method according to any of examples Ex3 to Ex51, wherein the temperature of the external heater is less than the temperature of the internal heater for the duration of the usage session.

[0188] Example Ex53: An aerosol-generating system comprising: at least one heater configured to heat an aerosol-generating substrate; and control circuitry; wherein the control circuitry is configured to carry out a method according to any of Examples Ex1 to Ex52.

[0189] Example Ex54: An aerosol-generating system according to Example Ex53, wherein the at least one heater comprises an internal heater configured to heat an aerosol-generating substrate from inside the aerosol-generating substrate.

[0190] Example Ex55: An aerosol-generating system according to Example Ex53 or Ex54, wherein the at least one heater comprises an external heater configured to heat the aerosolgenerating substrate from outside the aerosol-generating substrate.

[0191] Example Ex56: An aerosol-generating system according to Example Ex54 or Ex55, wherein the internal heater comprises a susceptor.

[0192] Example Ex57: An aerosol-generating system according to Example Ex55, wherein the external heater comprises a resistive heating element.

[0193] Examples will now be further described with reference to the figures in which:

[0194] Figure 1 A shows a schematic side cross-sectional view of an example heater assembly for an aerosol-generating device;

[0195] Figure 1B shows an axial cross-sectional view of the heater assembly of Figure 1A along line 1-1.

[0196] Figure 2 shows the assembly of part of the jacket of another example heater assembly. Figure 3A shows a schematic side cross-sectional view of an example aerosolgenerating device comprising the heater assembly of Figure 1A.

[0197] Figure 3B shows a schematic side cross-sectional view of an example aerosolgenerating system comprising an aerosol-generating article and the aerosol-generating device of Figure 3A;

[0198] Figure 4 is a block diagram showing an inductive heating arrangement of the aerosolgenerating device described in relation to Figures 3A and 3B;

[0199] Figure 5A is a schematic diagram of an electrical circuit for the heating arrangement of Figure 4.Figure 5B is a schematic diagram showing an equivalent circuit for the ohmic load of Figure 5A.

[0200] Figure 6 is a graph of DC current vs. time illustrating the remotely detectable current changes that occur when a susceptor material undergoes a phase transition associated with its Curie point;

[0201] Figure 7 illustrates a heating profile of the susceptor during operation of the aerosolgenerating device;

[0202] Figure 8 shows an example heating profile of a consumer usage session of an aerosolgenerating system when controlled by a first example method of controlling aerosol production;

[0203] Figure 9 shows another example heating profile of a consumer usage session of an aerosol-generating system when controlled by a second example method of controlling aerosol production;

[0204] Figure 10 shows another example heating profile for a consumer usage session of an aerosol-generating system when controlled by a third example method of controlling aerosol production;

[0205] Figure 11 A shows an aerosol-generating article having an article identifier;

[0206] Figure 11 B shows a schematic side cross-sectional view of an example aerosolgenerating system comprising the aerosol-generating article of Figure 11 A and an example aerosol-generating device;

[0207] Figure 12 shows three scenarios in which the identity of the aerosol-generating article determines a selection of heating profiles that are available to heat the aerosol-generating article;

[0208] Figure 13 shows another example heating profile of a consumer usage session of an aerosol-generating system when controlled by a fourth example method of controlling aerosol production;

[0209] Figure 14 shows another example heating profile of a consumer usage session of an aerosol-generating system when controlled by a fifth example method of controlling aerosol production.

[0210] Referring to Figures 1 A and 1 B, an example heater assembly 50 comprises an inductor assembly 10 and a jacket 60 received within the inductor assembly 10. The inductor assembly 10 comprises a cylindrical and hollow sleeve 12 formed from a liquid crystal polymer (LCP). The sleeve 12 defines a sleeve cavity 13. The sleeve 12 and sleeve cavity 13 extend between a proximal end 14 and a distal end 15 of the inductor assembly 10, defining a longitudinal axis 19 down the centre of the sleeve cavity 13. The sleeve 12 is injection moulded around a first electrical connector 20 and a second electrical connector 21. The first electrical connector 20and the second electrical connector 21 are therefore embedded within the sleeve 12, and extend parallel to the longitudinal axis 19. The first electrical connector 20 and the second electrical connector 21 comprise exposed ends 24, 25 at the distal end of the sleeve. The exposed ends 24, 25 are configured to be electrically connected to a power supply.

[0211] An inductor in the form of an inductor coil 16 is helically would around an outer surface of the sleeve 12. The inductor coil 16 comprises a plurality of windings 18. The inductor coil 16 is a continuous and flat filament, as each winding 18 of the filament of the inductor coil 16 has a thickness perpendicular to the longitudinal axis 19 which is less than a width parallel to the longitudinal axis 19. In other words, the cross-section of each winding 18 is rectangular in shape. The winding axis of the inductor coil 16 is the longitudinal axis 19.

[0212] A first end of the inductor coil 16 is connected to the first electrical connector 20 by an electrical connection 22, for example by soldering the first end of the inductor coil 16 to the first electrical connector 20. A second end of the inductor coil 16, opposite to the first end, is connected to the second electrical connector 21 by an electrical connection 23, for example by soldering the second end of the inductor coil 16 to the second electrical connector 21. The electrical connections 22, 23 are facilitated by holes in the outer surface of the sleeve 12 adjacent to the first and second ends of the inductor coil 16.

[0213] The inductor coil 16 is formed of copper, and the electrical resistance between the first end and the second end of the inductor coil 16 is approximately 100 milliohms.

[0214] A sleeve insulating layer 30 is wrapped around the sleeve 12 and the inductor coil 16 to surround the sleeve 12 and the inductor coil 16. The sleeve insulating layer 30 comprises at least one layer, and is formed from a polyimide film, such as Kapton™.

[0215] The axial cross-sectional view of Figure 1B shows the hollow cylindrical shape of the sleeve 12 and the sleeve insulating layer 30. As is illustrated in Figure 1B, the first electrical connector 20 comprises a flat filament, as the filament of the first electrical connector 20 has a thickness perpendicular to the longitudinal axis 19 which is less than a width perpendicular to the longitudinal axis 19. The second electrical connector 21 also comprises a flat filament, as the filament of the first electrical connector 21 has a thickness perpendicular to the longitudinal axis 19 which is less than a width perpendicular to the longitudinal axis 19, although this is not illustrated in Figure 2.

[0216] The jacket 60 is received within the sleeve cavity 13 of the inductor assembly 10. The jacket 60 comprises a jacket body formed from a proximal portion 62, a central portion 63 and a distal portion 61. The proximal portion 62 defines a hollow cylinder which is open at both ends, and is formed from polyether ether ketone (PEEK). The central portion 63 also defines a hollow cylinder which is open at both ends, and is formed from a thermally conductive and electrically insulating ceramic such as alumina or zirconia. The distal portion 61 defines ahollow cylinder which is open only ata proximal end and is closed at a distal end, and is formed from polyether ether ketone (PEEK).

[0217] The proximal portion 62 abuts the proximal end 14 of the sleeve cavity 13, and extends towards the distal end 15 of the sleeve cavity 13. The proximal portion 62 is press-fit to the central portion 63. The central portion 63 is press-fit to the distal portion 61. The distal portion 61 abuts the distal end 15 of the sleeve cavity 13, and extends towards the proximal end 14 of the sleeve cavity 13. Whilst press-fitting of the distal portion 61, central portion 63 and proximal portion 62 to one-another is described, other forms of attaching such as snap-fitting or tolerance fitting may also be used.

[0218] Together as the jacket body, the distal portion 61, central portion 63 and proximal portion 62 define a central and substantially cylindrical chamber 68 for receiving at least part of an aerosol-generating article (not shown). The proximal portion 62 therefore defines a proximal opening for receiving an aerosol-generating article therethrough.

[0219] The jacket 60 also defines a plurality of protrusions 69 extending into the chamber 68 from the distal end of the distal portion 61 of the jacket 60. As will be further described below, the plurality of protrusions 69 function to maintain a gap between an end of an aerosolgenerating article and the distal end of the jacket 60 when the aerosol-generating article is fully inserted into the chamber 68. In the example shown in Figures 1 A and 1 B, the jacket 60 defines three protrusions 69 spaced equidistantly about the longitudinal axis 19. The skilled person will appreciate that the jacket 60 may define more or fewer protrusions 69 and the arrangement of the protrusions 69 at the distal end of the jacket 60 may be varied. The plurality of protrusions 69 may be integrally formed with the distal portion 61.

[0220] The jacket 60 further comprises a plurality of grooves or airflow channels 67 extending in a longitudinal direction along the inner surface of the jacket 60. The plurality of grooves 67 are formed on the inner surfaces of the proximal portion 62, the central portion 63, and the distal portion 61, and are aligned to form continuous grooves 67 extending in a longitudinal direction from the proximal end of the jacket 60 to the distal end of the jacket 60. In order to ensure once connected the inner surfaces of the proximal portion 62, the central portion 63, and the distal portion 61 are aligned to form continuous grooves 67, the proximal portion 62, the central portion 63, and the distal portion 61 may only be connected in a singular relative rotational orientation to one another about the longitudinal axis 19. The longitudinal direction is parallel to the longitudinal axis 19. Each groove 67 extends in a straight line. The plurality of grooves 67 allow for air to flow from the proximal end of the jacket 60 to the distal end of the jacket 60 when the aerosol-generating article is inserted into the chamber 68.

[0221] The axial cross-sectional view of the heater assembly 50 of Figure 1 B illustrates the grooves 67 formed on the inner surface of the jacket 60, and the three protrusions 69extending into the chamber 68 from the distal end of the distal portion 61 of the jacket 60. The jacket 60 further comprises an external heater in the form of a resistive heating element 66. The resistive heating element 66 is arranged on an outer surface of the central portion 63. The resistive heating element 66 is formed from a silver-palladium alloy resistive heating track on a flexible polyimide substrate. The resistive heating element 66 is therefore wrapped around the outer surface of the central portion 63 to at least partially surround the chamber 68.

[0222] The resistive heating element 66 comprises two substantially parallel tracks extending from a first end of the resistive heating element to a second end of the resistive heating element, which are arranged such that a total current induced in the resistive heating element 66 by an alternating magnetic field within the chamber 68 is substantially zero. In particular, the resistive heating element is arranged such that any alternating current induced in the resistive heating element 66 in a direction towards a negative terminal of the resistive heating element is equal to the current induced in the resistive heating element 66 in a direction towards a positive terminal of the resistive heating element 66. As a result, a total alternating current induced in the resistive heating element between the positive terminal and the negative terminal of the resistive heating element is at least significantly reduced, and may be approximately zero.

[0223] The jacket 60 further comprises an insulating layer 64. The insulating layer 64 surrounds the central portion 63 and the resistive heating element 66, but does not contact the central portion 63 or the resistive heating element 66. Instead, the insulating layer 64 is fixed to the distal portion 61 and the proximal portion 62 to form an insulating zone 65 between the insulating layer 64 and the resistive heating element 66. The insulating layer 64 therefore surrounds only a portion of the distal portion 61 and the proximal portion 62. The insulating zone 65 in this embodiment is filled with an aerogel, though it can be understood that the insulating zone 65 may be filled with any other insulating material such as a polyimide, or filled only with air. The insulating layer 64 comprises at least one layer, and is formed from a polyimide film, such as Kapton™. During manufacturing, the insulating layer 64 is wrapped around the jacket 60, and is glued to the distal portion 61 and the proximal portion 62.

[0224] The jacket 60 is inserted into the sleeve cavity 13, and is press-fit or snap-fit to the sleeve 10 to form the heater assembly 50. Once assembled, the inductor coil 16 surrounds the chamber 68.

[0225] Figure 2 shows the assembly of part of the jacket of another example heater assembly. In particular, Figure 2 shows the proximal portion 62, the central portion 63 and the distal portion 61 of the jacket 60. The proximal portion 62 is assembled to the central portion 63. When a force 83 is applied to the central portion 63, a proximal lip 88 at the proximal end ofthe central portion 63 is pressed into a correspondingly shaped recess 89 in the proximal portion 62. The recess 89 and the proximal lip 88 are shaped and sized such that the tolerance between the recess 89 and the proximal lip 88 ensures a press-fit or tolerance fit between the central portion 63 and the proximal portion 62. The resistive heater 66 is located on the outer surface of the central portion 63 and spaced from the proximal lip 88, such that once the central portion 63 and the proximal portion 62 are connected, the resistive heater 66 does not contact the proximal portion 62. The distal portion 61 is assembled to the central portion 63 in a similar manner.

[0226] The proximal portion 62 and distal portion 61 comprise grooves or airflow channels 67 extending in a longitudinal direction along the inner surface of the proximal portion 62 and distal portion 61. In the example of Figure 2, the grooves 67 extend along only a portion of the length of the inner surface of the proximal portion 62 and distal portion 61. However, it will be appreciated that the grooves 67 could be formed on the inner surfaces of the proximal portion 62, the central portion 63, and the distal portion 61, and that the grooves 67 could extend along the entire length of these components and be aligned to form continuous grooves extending in a longitudinal direction from the proximal end of the jacket 60 to the distal end of the jacket 60, as shown in the example heater assembly of Figures 1A and 1B.

[0227] Figure 3A shows a schematic side cross-sectional view of an example aerosolgenerating device 100 comprising the heater assembly 50 of Figure 1A. The aerosolgenerating device 100 comprises a housing 101, within which the heater assembly 50 is received such that the housing 101 at least partially surrounds the heater assembly 50. The proximal end of the chamber 68 is open to the outside of the aerosol-generating device 100, in order to receive an aerosol-generating article.

[0228] The aerosol-generating device 100 also comprises control circuitry 102 and a power supply 103. The power supply 103 is electrically connected to the inductor coil 16 and to the resistive heating element 66 via the control circuitry 102. The electrical connection between the resistive heating element 66 and the control circuitry 102 is not illustrated for clarity purposes.

[0229] The power supply 103 comprises a DC power supply, and preferably a battery, such as a lithium-ion battery. As an alternative, the power supply 103 may be another form of charge storage device, such as a capacitor. The power supply 103 may require recharging. For example, the power supply 103 may have sufficient capacity to allow for the continuous generation of aerosol from an aerosol-generating article for a period of around six minutes or for a period that is a multiple of six minutes.

[0230] The control circuitry 102 is configured to provide a direct electric current or DC power from the power supply 103 to the external heater or resistive heating element 66 to generateheat in the resistive heating element 66 by Joule, or resistive, heating. The control circuitry 102 is configured to provide a direct electric current from the power supply 103 to the resistive heating element 66 to heat the resistive heating element 66 to at least 80°C. The external heater or resistive heating element 66 is therefore configured to externally heat the chamber 68, as heat is provided to the chamber 68 from a location outside the chamber 68.

[0231] The control circuitry 102 is also configured to convert a direct electric current from the power supply 103 to an alternating electric current and provide the alternating electric current to the inductor coil 16 to generate an alternating magnetic field within the chamber 68, which can be used to heat an internal heater such as a susceptor. As the power supply 103 comprises a DC power supply, the control circuitry comprises a DC / AC converter in order to provide an alternating electric current from the DC power supply to the inductor coil 16. Suitable control circuitry for providing an alternating electric current is described in more detail below with reference to Figures 3 and 4A.

[0232] The control circuitry 102 comprises a microcontroller, preferably a programmable microcontroller. The microcontroller is programmed to regulate the supply of power from the power supply 103 to the inductor coil 16 via the DC / AC converter, and to the resistive heating element 66, in order to control the temperature of the external heater or resistive heating element 66 and the temperature of an internal heater or susceptor element heated by the inductor coil 16.

[0233] In particular, the microcontroller is configured to control the supply of power from the power supply 103 to an internal heater or susceptor via the inductor coil 16 and the DC / AC converter in order to follow a pre-determined inductive heating profile by adjusting the frequency of an alternating current provided to the inductor coil 16 or by using pulse-width modulation. The control circuitry 102 is further configured to provide an inductive heating feedback signal from the inductor coil 16 to the microcontroller in order to follow the predetermined inductive heating profile. The microcontroller is also configured to control the supply of power from the power supply 103 to the external heater or resistive heating element 66 in order to follow a pre-determined resistive heating profile by using pulse-width modulation. The control circuitry 102 is further configured to provide a resistive heating feedback signal from the resistive heating element 66 to the microcontroller in order to follow the predetermined resistive heating profile. As mentioned above, the resistive heating element 66 is configured to reduce the alternating current induced in the resistive heating element 66 by the alternating magnetic filed produced by the inductor. This reduces the amount of electrical noise in the resistive heating feedback signal, allowing for the microcontroller to more precisely follow the pre-determined resistive heating profile.

[0234] Figure 3B shows a schematic side cross-sectional view of an example aerosol-generating system 150 comprising an aerosol-generating article 200 and the aerosolgenerating device 100 of Figure 3A. The aerosol-generating article 200 is received in the chamber 68 of the aerosol-generating device 100.

[0235] The aerosol-generating article 200 is a substantially rod-shaped. The article 200 comprises five elements sequentially arranged in coaxial alignment: an upstream element or front plug 202 comprising a cylindrical plug of filter material at a distal end of the article 200, a substrate element 203, a support element 206 in the form of a first hollow acetate tube with a central air passage, an aerosol-cooling element 208 in the form of a second thinner hollow acetate tube, and a mouthpiece 210 comprising a further cylindrical plug of filter material arranged at a proximal end of the article 200.

[0236] The substrate element 203 comprises an aerosol-generating substrate 204 and an internal heater in the form of a susceptor 214 which is in direct physical contact with the aerosol-generating substrate 204. The susceptor 214 is in the form of an elongate strip and has a length that is approximately the same as the length of the substrate element 203, and is located along a central axis of the substrate element 203. The susceptor 214 comprises at least two different materials. In particular, the susceptor 214 comprises at least two layers: a first layer of a first susceptor material disposed in physical contact with a second layer of a second susceptor material. The first susceptor material and the second susceptor material may each have a Curie temperature. In this case, the Curie temperature of the second susceptor material is lower than the Curie temperature of the first susceptor material. The first material may not have a Curie temperature. The first susceptor material may be aluminium, iron or stainless steel. The second susceptor material may be nickel or a nickel alloy. The susceptor 214 may be formed by electroplating at least one patch of the second susceptor material onto a strip of the first susceptor material. The susceptor may be formed by cladding a strip of the second susceptor material to a strip of the first susceptor material.

[0237] The five elements of the article 200 typically have a substantially cylindrical shape with substantially the same outer diameter. In addition, the five elements are circumscribed by an outer wrapper 212 to hold the elements together and to maintain the desired circular cross-sectional shape of the rod-like article 200. The wrapper 212 preferably is made of paper.

[0238] During use, a portion of the aerosol-generating article 200 is inserted into the chamber 68 so that the aerosol-generating substrate 204 and the internal heater or susceptor 214 are positioned inside the chamber 68 and are surrounded by the inductor coil 16 and the external heater or resistive heating element 66. The control circuitry 102 converts a direct electric current from the power supply 103 to an alternating electric current and provides the alternating electric current to the inductor coil 16 to generate an alternating magnetic field that inductively heats the susceptor 214, which heats an inner region of the aerosol-generatingsubstrate 204 to generate an aerosol. The level of inductive coupling between the inductor coil 16 and the susceptor 214, and consequently, the heating of the susceptor 214, is dependent on the frequency of the alternating current supplied to the inductor coil 16. The control circuitry 102 also provides a direct electric current from the power supply 103 to the external heater or resistive heating element 66 to generate heat in the resistive heating element 66 by Joule, or resistive, heating. The heat from the resistive heating element 66 travels through the central portion 63 of the jacket 60 to an outer region of the aerosolgenerating substrate 304, which heats the outer region of the aerosol-generating substrate 304 to generate an aerosol.

[0239] Airflow through the aerosol-generating system 200 during use is illustrated by the dashed line 216 in Figure 3B. When a consumer draws on the mouthpiece 210 of the aerosolgenerating article 200, a negative pressure is generated in the chamber 68. The negative pressure draws air into the chamber 68 via the open end of the chamber. The air entering the chamber 68 then flows through the plurality of grooves 67 defined in the inner wall of the jacket 60. When the airflow reaches the distal end of the chamber 68, the air enters the aerosolgenerating article 200 through the front plug 202 and flows through the aerosol-generating substrate 204. Airflow into the aerosol-generating article 200 is facilitated by the gap maintained between the distal end of the aerosol-generating article 200 and the distal end of the chamber 68 by the plurality of protrusions 69. As the airflow passes through the aerosolgenerating substrate 204, aerosol generated by heating of the aerosol-generating substrate 304 is entrained in the airflow. The aerosol then flows along the length of the aerosolgenerating article 200 and through the mouthpiece 210 to the consumer.

[0240] In the example aerosol-generating system 150 of Figure 3B, the susceptor 214 is a component part of the aerosol-generating article 200. However, it will be appreciated that in another example system, the aerosol-generating device may comprise one or more susceptors configured to be heated by the inductor coil 16. The one or more susceptors may be provided in the chamber 68 in the form of blades or needles or pins. For example, the one or more susceptors may be provided at the distal end of the jacket 60 extending parallel to the longitudinal axis 19 towards the proximal end of the jacket 60. The one or more susceptor elements may be configured to penetrate the aerosol-generating substrate 204 when the aerosol-generating article 200 is received within the chamber 68.

[0241] Figure 4 is a block diagram illustrating an exemplary configuration of components and circuitry for generating and providing an alternating current to an inductor coil of an aerosolgenerating device, such as the inductor coil 16 of the aerosol-generating device 100 of Figures 3A and 3B. A DC power source 310 is coupled to a heating arrangement 320. The heating arrangement 320 comprises a controller 330, a DC / AC converter 340, a matching network 350and an inductor coil 240. The DC power source 310 of Figure 4 corresponds to the power supply 103 of the aerosol-generating device 100 of Figures 3A and 3B. The controller 330, DC / AC converter 340 and matching network 350 correspond to, and are comprised in, the control circuitry 102 of the aerosol-generating device 100 of Figures 3A and 3B. The inductor coil 240 corresponds to the inductor coil 16 of the aerosol-generating device 100 of Figures 3A and 3B.

[0242] The DC power source 310 is configured to provide DC power to the heating arrangement 320. Specifically, the DC power source 310 is configured to provide a DC supply voltage VDC and a DC current lDc to the DC / AC converter 340. Preferably, the power source 310 is a battery, such as a lithium ion battery. As an alternative, the power source 310 may be another form of charge storage device such as a capacitor. The power source 310 may require recharging. For example, the power source 310 may have sufficient capacity to allow for the continuous generation of aerosol for a period of around six minutes or for a period that is a multiple of around six minutes. In another example, the power source 310 may have sufficient capacity to allow for a predetermined number of puffs or discrete activations of the heating arrangement.

[0243] The DC / AC converter 340 preferably comprises a Class-E power amplifier. The DC / AC converter 340 is configured to supply the inductor coil 240 with a high frequency alternating current. As used herein, the term "high frequency alternating current" means an alternating current having a frequency of between about 500 kilohertz and about 30 megahertz. The high frequency alternating current may have a frequency of between about 1 megahertz and about 30 megahertz, such as between about 1 megahertz and about 10 megahertz, or such as between about 5 megahertz and about 8 megahertz.

[0244] Although the DC / AC converter 340 is illustrated as comprising a Class-E power amplifier, it will be appreciated that the DC / AC converter 340 may use any suitable circuitry that converts DC current to AC current. For example, the DC / AC converter 340 may comprise a class-D power amplifier comprising two transistor switches. As another example, the DC / AC converter 340 may comprise a full bridge power inverter with four switching transistors acting in pairs.

[0245] In the example of Figure 4, the inductor 240 receives the alternating current from the DC / AC converter 340 via a matching network 350 for optimum adaptation to the load. However, the matching network 350 is not essential. The matching network 350 may comprise a small matching transformer. The matching network 350 may improve power transfer efficiency between the DC / AC converter 340 and the inductor 240.

[0246] Figure 5A schematically illustrates example electrical circuitry for use in supplying the inductor coil 240 of Figure 4 with electric energy. As mentioned above, the DC / AC converter340 of Figure 4 preferably comprises a Class-E power amplifier. The Class-E power amplifier comprises a transistor switch 410 comprising a Field Effect Transistor 420, for example a Metal-Oxide-Semiconductor Field Effect Transistor, a transistor switch supply circuit indicated by the arrow 430 for supplying a switching signal (gate-source voltage) to the Field Effect Transistor 420, and an LC load network 440 comprising a shunt capacitor C1 and a series connection of a capacitor C2 and inductor coil L2. Inductor coil L2 corresponds to inductor coil 240 of Figure 4. In addition, DC power source 310, comprising a choke inductor L1, is shown for supplying the DC supply voltage VDC, with the DC current lDc being drawn from the DC power source 310 during operation. The ohmic resistance R represents the total ohmic load 450, which is the sum of the ohmic resistance Rcoii of the inductor coil L2 and the ohmic resistance Road of the susceptor element, as shown in more detail in Figure 5B. The DC power source 310 corresponds to the DC power source 310 of Figure 4.

[0247] The transistor switch supply circuit 430 may supply a switching voltage having a rectangular profile to the Field Effect T ransistor 420. As long as the Field Effect T ransistor 420 is conducting (in an "on"-state), it essentially constitutes a short circuit (low resistance) so that the entire current flows through the choke Li and the Field Effect Transistor 420. When the Field Effect Transistor 420 is non-conducting (in an "off’-state), the entire current flows into the LC load network 440 since the Field Effect Transistor 420 essentially represents an open circuit (high resistance). Switching the Field Effect Transistor 420 between conducting (“on”) and non-conducting (“off”) states inverts the supplied DC voltage VDC and DC current lDc into an AC voltage AC and AC current lAc flowing in the inductor coil L2, having frequency f.

[0248] Figure 6 illustrates the relationship between the DC current lDc drawn from the power source 310 of Figure 4 over time as the temperature of the susceptor (indicated by the dashed line in Figure 6) increase. The susceptor may be, for example, the susceptor 214 of Figure 2B. The DC current lDc drawn from the power source 310 is measured at an input side of the DC / AC converter 340. For the purpose of this illustration, it may be assumed that the voltage VDC of the power source 310 remains approximately constant. As the susceptor 214 is inductively heated, the apparent resistance of the susceptor 214 increases. This increase in resistance is observed as a decrease in the DC current lDc drawn from the power source 310, which at constant voltage decreases as the temperature of the susceptor 214 increases. The high frequency alternating magnetic field provided by the inductor 240 of Figure 4 induces eddy currents in close proximity to the susceptor surface, an effect that is known as the skin effect. The resistance in the susceptor 214 depends in part on the electrical resistivity of the first susceptor material, the resistivity of the second susceptor material and in parton the depth of the skin layer in each material available for induced eddy currents, and the resistivity is in turn temperature dependent. As the second susceptor material reaches its Curie temperature,it loses its magnetic properties. This causes an increase in the skin layer available for eddy currents in the second susceptor material, which causes a decrease in the apparent resistance of the susceptor 214. The result is a temporary increase in the detected DC current lDc when the skin depth of the second susceptor material begins to increase, the resistance begins to fall. This is seen as the valley or local minimum 490 in the DC current curve in Figure 6. The current continues to increase until the maximum skin depth is reached, which coincides with the point where the second susceptor material has lost its spontaneous magnetic properties. This point is called the Curie temperature and is seen as the hill or local maximum 492 in the DC current curve in Figure 6. At this point the second susceptor material has undergone a phase change from a ferro-magnetic or ferri-magnetic state to a paramagnetic state. At this point, the susceptor 214 is at a known temperature (the Curie temperature, which is an intrinsic material-specific temperature). If the inductor 240 continues to generate an alternating magnetic field (i.e. power to the DC / AC converter 340 is not interrupted) after the Curie temperature has been reached, the eddy currents generated in the susceptor 214 will run against the resistance of the susceptor 214, whereby Joule heating in the susceptor 214 will continue, and thereby the resistance will increase again (the resistance will have a polynomial dependence of the temperature, which for most metallic susceptor materials can be approximated to a third degree polynomial dependence for our purposes) and current will start falling again as long as the inductor 240 continues to provide power to the susceptor 214.

[0249] Therefore, as can be seen from Figure 6, the apparent resistance of the susceptor 214 (and correspondingly the current lDc drawn from the power source 310) may vary with the temperature of the susceptor 214 in a strictly monotonic relationship over certain ranges of temperature of the susceptor 214. The strictly monotonic relationship allows for an unambiguous determination of the temperature of the susceptor 214 from a determination of the apparent resistance or apparent conductance, which is the reciprocal of resistance (1 / R). This is because each determined value of the apparent resistance is representative of only one single value of the temperature, so that there is no ambiguity in the relationship. The monotonic relationship of the temperature of the susceptor 214 and the apparent resistance allows for the determination and control of the temperature of the susceptor 214 and thus for the determination and control of the temperature of the aerosol-generating substrate. The apparent resistance of the susceptor 214 can be remotely detected by monitoring at least the DC current lDc drawn from the DC power source 310.

[0250] At least the DC current lDc drawn from the power source 310 is monitored by the controller 330 in Figure 4. Preferably, both the DC current lDc drawn from the power source 310 and the DC supply voltage VDC are monitored. The controller 330 regulates the supply of power provided to the heating arrangement 320 based on a conductance value or a resistancevalue, where conductance is defined as the ratio of the DC current lDc to the DC supply voltage VDC and resistance is defined as the ratio of the DC supply voltage VDC to the DC current IDC. The heating arrangement 320 of Figure 4 may comprise a current sensor (not shown) to measure the DC current IDC. The heating arrangement may optionally comprise a voltage sensor (not shown) to measure the DC supply voltage VDC. The current sensor and the voltage sensor are located at an input side of the DC / AC converter 340 in Figure 4. The DC current be and optionally the DC supply voltage DC are provided by feedback channels to the controller 330 to control the further supply of AC power PAC to the inductor 240.

[0251] The controller 330 may control the temperature of the susceptor 214 by maintaining the measured conductance value or the measured resistance value at a target value corresponding to a target operating temperature of the susceptor 214. The controller 330 may use any suitable control loop to maintain the measured conductance value or the measured resistance value at the target value, for example by using a proportional-integral-derivative control loop.

[0252] In order to take advantage of the strictly monotonic relationship between the apparent resistance (or apparent conductance) of the susceptor 214 and the temperature of the susceptor 214, during consumer operation for producing an aerosol, the conductance value or the resistance value associated with the susceptor 214 and measured at the input side of the DC / AC converter 340 is maintained between a first calibration value corresponding to a first calibration temperature and a second calibration value corresponding to a second calibration temperature. The second calibration temperature is the Curie temperature of the second susceptor material (the hill in the current plot in Fig. 6). The first calibration temperature is a temperature greater than or equal to the temperature of the susceptor at which the skin depth of the second susceptor material begins to increase (leading to a temporary lowering of the resistance). Thus, the first calibration temperature is a temperature greater than or equal to the temperature at maximum permeability of the second susceptor material. The first calibration temperature is at least 50 degrees Celsius lower than the second calibration temperature. At least the second calibration value may be determined by calibration of the susceptor, as will be described in more detail below. The first calibration value and the second calibration value may be stored as calibration values in a memory of the controller 330. Since the conductance (resistance) will have a polynomial dependence on the temperature, the conductance (resistance) will behave in a non-linear manner as a function of temperature. However, the first and second calibration values may be chosen so that this dependence may be approximated as being linear between the first calibration value and the second calibration value because the difference between the first and the second calibration values is small, and the first and the second calibration values are in the upper part of the operational temperaturerange. Therefore, to adjust the temperature to a target operating temperature, the conductance is regulated according to the first calibration value and the second calibration value, through linear equations. For example, if the first and the second calibration values are conductance values, the target conductance value corresponding to the target operating temperature may be given by:

[0253] ^

[0254]

[0255] Target ^Lower + AG) Equation 1

[0256] where AG is the difference between the first conductance value and the second conductance value and x is a percentage of AG.

[0257] The controller 330 may control the provision of power to the heating arrangement 320 by adjusting the duty cycle of the switching transistor 410 of the DC / AC converter 340. For example, during heating, the DC / AC converter 340 continuously generates alternating current that heats the susceptor 214, and simultaneously the DC supply voltage VDC and the DC current lDc may be measured, preferably every millisecond for a period of 100 milliseconds. If the conductance is monitored by the controller 330, when the conductance reaches or exceeds a value corresponding to the target operating temperature, the duty cycle of the switching transistor 410 is reduced. If the resistance is monitored by the controller 330, when the resistance reaches or goes below a value corresponding to the target operating temperature, the duty cycle of the switching transistor 410 is reduced. For example, the duty cycle of the switching transistor410 may be reduced to about 9%. In otherwords, the switching transistor 410 may be switched to a mode in which it generates pulses only every 10 milliseconds for a duration of 1 millisecond. During this 1 millisecond on-state (conductive state) of the switching transistor 410, the values of the DC supply voltage VDC and of the DC current lDc are measured and the conductance is determined. As the conductance decreases (or the resistance increases) to indicate that the temperature of the susceptor 214 is below the target operating temperature, the gate of the transistor 410 is again supplied with the train of pulses at the chosen drive frequency for the system.

[0258] The power may be supplied by the controller 330 to the inductor 240 in the form of a series of successive pulses of electrical current. In particular, power may be supplied to the inductor 240 in a series of pulses, each separated by a time interval. The series of successive pulses may comprise two or more heating pulses and one or more probing pulses between successive heating pulses. The heating pulses have an intensity such as to heat the susceptor 214. The probing pulses are isolated power pulses having an intensity such not to heat the susceptor 214 but rather to obtain a feedback on the conductance value or resistance value and then on the evolution (decreasing) of the susceptor temperature. The controller 330 maycontrol the power by controlling the duration of the time interval between successive heating pulses of power supplied by the DC power supply to the inductor 240. Additionally or alternatively, the controller 330 may control the power by controlling the length (in other words, the duration) of each of the successive heating pulses of power supplied by the DC power supply to the inductor 240.

[0259] Alternatively, or additionally, the controller 330 may control the provision of power to the heating arrangement 320 by adjusting the frequency or amplitude or both the frequency and amplitude of the AC current provided by the DC / AC converter 340 to adjust the degree of inductive coupling between the inductor 240 and susceptor 214. Where the heating arrangement 320 is implemented by the circuit of Figure 5, the controller may also control the supply of DC current to the inductor 240 to control external heating.

[0260] The controller 330 is programmed to perform a calibration process in order to obtain the calibration values at which the conductance is measured at known temperatures of the susceptor 214. The known temperatures of the susceptor may be the first calibration temperature corresponding to the first calibration value and the second calibration temperature corresponding to the second calibration value. Preferably, the calibration process is performed each time the consumer operates the aerosol-generating device 100, for example each time the consumer inserts an aerosol-generating article 200 into an aerosol-generating device 100.

[0261] During the calibration process, the controller 330 controls the DC / AC converter 340 to continuously or continually supply power to the inductor 240 in order to heat the susceptor 214. The controller 330 monitors the conductance or resistance associated with the susceptor 214 by measuring the current lDc drawn by the power supply and, optionally the power supply voltage VDC. AS discussed above in relation to Figure 6, as the susceptor 214 is heated, the measured current decreases until a first turning point 490 is reached and the current begins to increase. This first turning point 490 corresponds to a local minimum conductance value (a local maximum resistance value). The controller 330 may record the local minimum value of conductance (or local maximum of resistance) as the first calibration value. The controller may record the value of conductance or resistance at a predetermined time after the minimum current has been reached as the first calibration value. The conductance or resistance may be determined based on the measured current lDc and the measured voltage VDC. Alternatively, it may be assumed that the power supply voltage DC, which is a known property of the power source 310, is approximately constant. The temperature of the susceptor 214 at the first calibration value is referred to as the first calibration temperature. Preferably, the first calibration temperature is between 150 degrees Celsius and 350 degrees Celsius. More preferably, when the aerosol-generating substrate comprises tobacco, the first calibrationtemperature is 320 degrees Celsius. The first calibration temperature is at least 50 degrees Celsius lower than the second calibration temperature.

[0262] As the controller 330 continues to control the power provided by the DC / AC converter 340 to the inductor 240, the measured current increases until a second turning point 492 (see Figure 6) is reached and a maximum current is observed (corresponding to the Curie temperature of the second susceptor material) before the measured current begins to decrease. This turning point corresponds to a local maximum conductance value (a local minimum resistance value). The controller 330 records the local maximum value of the conductance (or local minimum of resistance) as the second calibration value. The temperature of the susceptor 214 at the second calibration value is referred to as the second calibration temperature. Preferably, the second calibration temperature is between 200 degrees Celsius and 400 degrees Celsius. When the maximum is detected, the controller 330 controls the DC / AC converter 340 to interrupt provision of power to the inductor 240, resulting in a decrease in temperature of the susceptor 214 and a corresponding decrease in conductance.

[0263] Due to the shape of the graph of Figure 6, this process of continuously heating the susceptor 214 to obtain the first calibration value and the second calibration value may be repeated at least once. After interrupting provision of power to the inductor 240, the controller 330 continues to monitor the conductance (or resistance) until a third turning point corresponding to a second minimum conductance value (a second maximum resistance value) is observed. When the third turning point is detected, the controller 330 controls the DC / AC converter 340 to continuously provide power to the inductor 240 until a fourth turning point corresponding to a second maximum conductance value (second minimum resistance value) is detected. The controller 330 stores the conductance value or the resistance value at or just after the third turning point as the first calibration value and the conductance value or the resistance value at the fourth turning point current as the second calibration value. The repetition of the measurement of the turning points corresponding to minimum and maximum measured current significantly improves the subsequent temperature regulation during consumer operation of the device for producing an aerosol. Preferably, controller 330 regulates the power based on the conductance or resistance values obtained from the second maximum and the second minimum, this being more reliable because the heat will have had more time to distribute within the aerosol-generating substrate and the susceptor 214.

[0264] In order to further improve the reliability of the calibration process, the controller 310 may be optionally programmed to perform a pre-heating process before the calibration process. For example, if the aerosol-generating substrate is particularly dry, the calibration may be performed before heat has spread within the aerosol-generating substrate, reducingthe reliability of the calibration values. If the aerosol-generating substrate is more moist, the susceptor 214 takes more time to reach the valley temperature due to water content in the substrate.

[0265] To perform the pre-heating process, the controller 330 is configured to continuously provide power to the inductor 240. As described above, the current starts decreasing with increasing temperature of the susceptor 214 until the minimum is reached. At this stage, the controller 330 is configured to wait for a predetermined period of time to allow the susceptor 214 to cool before continuing heating. The controller 330 therefore controls the DC / AC converter 340 to interrupt provision of power to the inductor 240. After the predetermined period of time, the controller 330 controls the DC / AC converter 340 to provide power until the minimum is reached. At this point, the controller controls the DC / AC converter 340 to interrupt provision of power to the inductor 240 again. The controller 330 again waits for the same predetermined period of time to allow the susceptor 214 to cool before continuing heating. This heating and cooling of the susceptor 214 is repeated for the predetermined duration of time of the pre-heating process. The predetermined duration of the pre-heating process is preferably 11 seconds. The predetermined combined durations of the pre-heating process followed by the calibration process is preferably 20 seconds.

[0266] If the aerosol-generating substrate is dry, the first minimum of the pre-heating process is reached within the pre-determined period of time and the interruption of power will be repeated until the end of the predetermined time period. If the aerosol-generating substrate is moist, the first minimum of the pre-heating process will be reached towards the end of the predetermined time period. Therefore, performing the pre-heating process for a predetermined duration ensures that, whatever the physical condition of the substrate, the time is sufficient for the substrate to reach the minimum temperature, in order to be ready to feed continuous power and reach the first maximum. This allows a calibration as early as possible, but still without risking that the substrate would not have reached the valley beforehand.

[0267] Further, the aerosol-generating article 200 may be configured such that the minimum is always reached within the predetermined duration of the pre-heating process. If the minimum is not reached within the pre-determined duration of the pre-heating process, this may indicate that the aerosol-generating article 200 comprising the aerosol-generating substrate is not suitable for use with the aerosol-generating device 100. For example, the aerosol-generating article 200 may comprise a different or lower-quality aerosol-generating substrate than the aerosol-generating substrate intended for use with the aerosol-generating device 100. As another example, the aerosol-generating article 200 may not be configured for use with the heating arrangement 320 of Figure 4, for example, if the aerosol-generating article 200 and the aerosol-generating device 100 are manufactured by different manufacturers. Thus, thecontroller 330 may be configured to generate a control signal to cease operation of the aerosol-generating device 100.

[0268] The pre-heating process may be performed in response to receiving a consumer input, for example, consumer activation of the aerosol-generating device 100. Additionally or alternatively, the controller 330 may be configured to detect the presence of an aerosolgenerating article 200 in the aerosol-generating device 100 and the pre-heating process may be performed in response to detecting the presence of the aerosol-generating article 200 within the chamber 68 of the aerosol-generating device 100.

[0269] Figure 7 is a graph of conductance against time showing a heating profile of a susceptor, for example, the susceptor element 214 of Figures 3A and 3B, during operation of the aerosolgenerating device 100. The graph illustrates an initial start-up process 710 comprising the preheating process 710A and the calibration process 710B described above, followed by a consumer usage session heating profile 720, during which aerosol is being produced and a consumer is able to take a puff on the aerosol-generating system 100, 170. The consumer usage session heating profile 720 excludes the pre-heating 710A and calibration 710B processes of operation, which occur prior to the heating profile 720 for the consumer usage session. Since the pre-heating process is relatively short and the aerosol-generating substrate takes time to warm up to form an aerosol, very little or substantially no aerosol is formed during the pre-heating process 710A or the calibration process 710B. Therefore, a consumer has not begun puffing on the aerosol-generating system 100, 170 during the start-up process 710 and the system 100, 170 may provide an indication to a consumer that the system is not ready during the start-up process 710. The consumer usage session heating profile 720 commences once the start-up process 710 has completed and may comprise any of the heating profiles described below, which may also include a heating profile for the external heater (not shown in Figure 7).

[0270] Although Figure 7 is illustrated as a graph of conductance against time, it is to be understood that the controller 330 may be configured to control the heating of the susceptor during the start-up process 710 and the consumer usage session heating profile 720 based on measured resistance or current as described above. Furthermore, although the techniques to control of the heating of the susceptor during the start-up process 710 and the consumer usage session heating profile 720 have been described above based on a determined conductance value or a determined resistance value associated with the susceptor, it is to be understood that the techniques described above could be performed based on a value of current measured at the input of the DC / AC converter 340.

[0271] Figures 8 to 10 show three different example heating profiles for the internal and external heaters of an aerosol-generating system a consumer usage session when controlled bydifferent example methods of controlling aerosol production. In each of Figures 8 to 10, the heating profile of each method is illustrated on a graph in which time is shown on the x-axis, the temperature of the inductor coil or external heater is shown on a first (lefthand) y-axis and conductance of the susceptor or internal heater is shown on a second (righthand) y-axis. The conductance of the susceptor can be directly correlated to a corresponding temperature of the internal heater due to the monotonic relationship between conductance and temperature described above with reference to Figure 6. In the example heating profiles of Figures 8 to 10, the relationship between the temperature of the internal heater and the percentages of the conductance span AG of the internal heater, is shown in Table 1 below.

[0272] Conductance percentage Temperature

[0273] 9% 330°C

[0274] 25% 340°C

[0275] 40% 345°C

[0276] 56% 355°C

[0277] 75% 380°C

[0278]

[0279] Table 1

[0280] The heating profiles of the different methods are controlled using the control circuitry of the aerosol-generating device, for example, the control circuitry 102 of Figures 3A and 3B. The control circuitry 102 is configured to control a supply of power from the power supply 103 of Figures 3A and 3B to provide DC power to the external heater or resistive heating element to generate heat in the resistive heating element by Joule, or resistive, heating. The control circuitry 102 is also configured to control a supply of power from the power supply 103 to heater the internal heater or susceptor, for example, by converting a direct electric current from the power supply 103 to an alternating electric current using the circuit of Figure 5A and provide the alternating electric current to the inductor coil 16 to generate an alternating magnetic field which can be used to heat the internal heater or susceptor.

[0281] Referring to Figure 8, this shows an improved or extended duration heating profile for a consumer usage session, which may provide a consumer with a consumer usage session of longer duration, that is, a consumer usage session of greater than 400 seconds or more than 20 puffs.

[0282] The consumer usage session starts at time to and ends at time to. In this example, to corresponds to a time of 490 seconds or around 8 minutes. During the consumer usage session, it is estimated that an average consumer could take as many as 24 puffs. For the fullduration of the consumer usage session, that is, between times to and t3, the conductance of the susceptor or internal heater is maintained at a constant temperature corresponding to a target conductance GTI, in which the induction load is equal to 9 percent of the full conductance span AG. GTI can be determined by Equation 1 above as follows: GTI = Glower + (0.09 x AG). At time to, the conductance of the susceptor may already be near this value following a previous calibration process or, due to the relatively small volume of the susceptor, it can be considered to be heated instantaneously to this conductance value when the consumer usage session starts. Due to the monotonic relationship between conductance and temperature discussed above, the target conductance GTI corresponds to a specific temperature, which in this case is a temperature of 330 degrees Celsius. As mentioned above, this temperature is maintained for the duration of the consumer usage session. The controller of the aerosol-generating device controls the provision of power to the heating arrangement such that the conductance of the susceptor or internal heater is maintained at a value corresponding to the target operating temperature. The target conductance value may be stored in the memory of the controller.

[0283] The conductance value GTI is a relatively low conductance value, that is, it corresponds to an induction load that is equal to only 9 percent of the full conductance span of AG. This conductance value corresponds to a temperature at which the aerosol-generating substrate will still form an aerosol in a sufficient volume and quantity for a satisfactory experience when inhaled by a consumer. However, the relatively low conductance value means that aerosol will be produced at a corresponding lower rate allowing the duration of the consumer usage session to be extended.

[0284] At time to, that is, the start of the consumer usage session, resistive heating of the resistive heating element or external heater is not activated. There is a delay between supplying AC power to the susceptor or internal heater at time to and subsequently supplying DC power to the resistive heating element or external heater at time h to resistively heat the resistive heating element. In this example, the delay is approximately 60 seconds. Therefore, during this delay period, aerosol is being produced solely by the susceptor or internal heater. The internal heater heats the aerosol-generating substrate, predominantly an inner region or portion of the aerosol-generating substrate, to form an aerosol, or a vapour which cools and condenses to form an aerosol. During the consumer usage session, a consumer may puff on the article of the system, resulting in an airflow as described above with reference to Figure 3B and inhale the aerosol formed.

[0285] Resistive heating of the resistive heating element or external heater is activated at time h. During a first external heating phase between times h and t2, the controller of the aerosolgenerating device controls the supply of DC power to the external heater such that thetemperature of the external heater increases to a first temperature Ti. In this example, the first temperature Ti is about 65 degrees Celsius and the first external heating phase h to t2 is approximately 40 seconds. The temperature of the external heater increases from the first temperature Ti to a second temperature T2 during a second external heating phase between times t2 and the conclusion of the consumer usage session at time t3. The second temperature T2 is greater than the first temperature Ti. Indeed, in this example, the second temperature T2 corresponds to the maximum temperature reached by the external heater over the duration of the consumer usage session. In this example, the second external heating phase t2 to t3is approximately 390 seconds and the second temperature T2 is approximately 190 degrees Celsius.

[0286] Therefore, during the first external heating phase, the temperature of the external heater increases at a first rate of change, and during the second external heating phase, the temperature of the external heater increases at a second rate of change. The first rate of change is greater than the second rate of change to bring the external heater to its desired heating temperature more quickly. External heating helps to generate an aerosol from the outer portion of the aerosol-generating substrate and to compensate for depletion of the aerosol forming constituents of the inner portion of the aerosol-generating substrate. This helps to maintain consistent aerosol generation over the duration of the consumer usage session. Increasing the temperature of the external heater during the firstand second external heating phases to the maximum temperature of 190 degrees Celsius helps to consume more of the aerosol-generating substrate.

[0287] It will appreciated that the first and second rates of change are not necessarily constant and that there may be some variation in the rate at which the temperature of the external heater increases and possibly a sub-period in which the temperature does not increase but is held constant. Therefore, the first and second rates of change may be average rates of change over the first and second external heating phases.

[0288] The temperature of the external heater does not exceed the maximum temperature of 190 degrees Celsius for the duration of the consumer usage session. Furthermore, the temperature of the external heater is significantly below the temperature of the internal heater of 330 degrees Celsius for the duration of the consumer usage session. This reduces the risk of combustion or pyrolysis of the aerosol-generating substrate and is significantly below the maximum external heater temperature used in conventional aerosol-generating systems. However, despite this lower maximum external heating temperature, the inventors have found that the method provides consistent delivery of aerosol over the duration of the consumer usage session, even over an extended consumer usage session of greater than 400 seconds as in the current example. In particular, where the aerosol-generating substrate is tobacco-based, the inventors have found that deliveries of nicotine and aerosol former are satisfactory and consistent over the duration of the consumer usage session without any reduction in the consumer experience.

[0289] Figure 9 shows an uplift heating profile for a consumer usage session, in which the level of heating of the aerosol-generating substrate is increased over the duration of the consumer usage session.

[0290] In the heating profile of Figure 9, the consumer usage session starts at time to. During a first internal heating phase between times to and to, the susceptor or internal heater is heated to a first temperature corresponding to a target conductance GTI, in which the induction load is equal to 9 percent of the full conductance span. GTI can be determined by Equation 1 above as follows: GTI = Glower + (0.09 x AG). At time to, the conductance of the susceptor may already be near this value following a previous calibration process or, due to the relatively small volume of the susceptor, it can be considered to be heated instantaneously to this conductance value when the consumer usage session starts. In this example, the first temperature is 330 degrees Celsius and the first internal heating phase to to to has a duration of approximately 160 seconds. The internal heater is constantly maintained at the first temperature for the duration of the first internal heating phase to to to.

[0291] During a second internal heating phase between times ts and to, the susceptor or internal heater is heated to a second temperature corresponding to a target conductance GT2, in which the induction load is equal to 40 percent of the full conductance span. GT2 can be determined by Equation 1 above as follows: GT2 = Glower + (0.40 x AG). The second temperature is greater than the first temperature. In this example, the second temperature is approximately 345 degrees Celsius and the second internal heating phase ts to ts has a duration of approximately 135 seconds. The internal heater is constantly maintained at the second temperature for the duration of the second internal heating phase ts to ts.

[0292] Between the first internal heating phase to to ts and second internal heating phase ts to ts, the example heating profile of Figure 9 has a third internal heating phase ts to ts in which the temperature of the internal heater increases from the first temperature to a third temperature that is intermediate the first and second temperatures. The third temperature corresponds to a target conductance GT3, in which the induction load is equal to 25 percent of the full conductance span. GT3 can be determined by Equation 1 above as follows: GT3 = Glower + (0.25 x AG). The temperature of the internal heater increases to the third temperature over a first portion of the third internal heating phase between times ts and t4. The temperature of the internal heater is then maintained at the third temperature for a second portion of the third internal heating phase between times t4 and ts. In this example, the third temperature is approximately 340 degrees Celsius and the first portion ts to t4 of the third internal heatingphase ta to ts has a duration of approximately 40 seconds and the second portion t4 to ts of the third internal heating phase ta to ts has a duration of approximately 40 seconds.

[0293] The control circuitry of the aerosol-generating device controls the provision of power to the heating arrangement such that the conductance of the susceptor or internal heater is driven to the target operating temperatures. The target conductance values may be stored in a memory of the control circuitry.

[0294] In the example heating profile of Figure 9, resistive heating of the resistive heating element or external heater is activated during the first internal heating phase to to ta at time ti. Resistive heating of the resistive heating element or external heater starts within a predetermined time period to to h of the internal heater being activated at time to. The predetermined time period to to h is less than 60 seconds. In this example, the predetermined time period to to h is approximately 11 seconds. By keeping the predetermined time period to to h relatively short, the external heater is able to contribute to providing a higher level of heating to the aerosol-generating substrate during the initial phases of the consumer usage session to release more aerosol, in particular, from an outer region of the aerosol-generating substrate. During the consumer usage session, a consumer may puff on the article of the system, resulting in an airflow as described above with reference to Figure 3B and inhale the aerosol formed.

[0295] It will be appreciated that the predetermined time period to to h between starting internal heating at time to and starting external heating at time h is optional and in some heating profiles resistive heating of the resistive heating element or external heater may commence at the same time as heating of the susceptor or internal heater, that is, at time to.

[0296] During a first external heating phase between times h and t2, the controller of the aerosol-generating device controls the supply of DC power to the external heater such that the temperature of the external heater increases to a first temperature Ti. In this example, the first temperature Ti is about 87 degrees Celsius and the first external heating phase ti to t2 is approximately 19 seconds. The temperature of the external heater increases from the first temperature Ti to a second temperature T2 during a second external heating phase between times t2 and the conclusion of the consumer usage session at time te. The second temperature T2 is greater than the first temperature Ti. Indeed, in this example, the second temperature corresponds to the maximum temperature reached by the external heater over the duration of the consumer usage session. In this example, the second external heating phase t2 to te is approximately 345 seconds and the second temperature T2 is approximately 180 degrees Celsius. The conclusion of the consumer usage session at time te corresponds to a time of approximately 375 seconds or around 6 minutes.

[0297] Therefore, during the first external heating phase, the temperature of the external heaterincreases at a first rate of change, and during the second external heating phase, the temperature of the external heater increases at a second rate of change. The first rate of change is greater than the second rate of change to bring the external heater to its desired heating temperature more quickly. External heating helps to generate an aerosol from the outer portion of the aerosol-generating substrate and to compensate for depletion of the aerosol forming constituents of the inner portion of the aerosol-generating substrate. This helps to maintain consistent aerosol generation over the duration of the consumer usage session. Increasing the temperature of the external heater during the firstand second external heating phases up to the maximum temperature of 180 degrees Celsius helps to consume more of the aerosol-generating substrate.

[0298] It will appreciated that the first and second rates of change are not necessarily constant and that there may be some variation in the rate at which the temperature of the external heater increases and possibly a sub-period in which the temperature does not increase but is held constant. Therefore, the first and second rates of change may be average rates of change over the first and second external heating phases.

[0299] The temperature of the external heater does not exceed the maximum temperature of 180 degrees Celsius for the duration of the consumer usage session. Furthermore, the temperature of the external heater is significantly below the temperatures reached by the internal heater for the duration of the consumer usage session. This reduces the risk of combustion or pyrolysis of the aerosol-generating substrate and is significantly below the maximum external heater temperature used in conventional aerosol-generating systems. However, despite this lower maximum external heating temperature, the inventors have found that the method provides consistent delivery of aerosol over the duration of the consumer usage session. In particular, where the aerosol-generating substrate is tobacco-based, the inventors have found that deliveries of nicotine and aerosol former are satisfactory and consistent over the duration of the consumer usage session without any reduction in the consumer experience.

[0300] Figure 10 shows a boost heating profile for a consumer usage session, in which the level of heating of the aerosol-generating substrate is increased during an initial phase of the consumer usage session to release more aerosol over a shorter period of time in order to provide a consumer with a more intense consumer experience.

[0301] In the heating profile of Figure 10, the consumer usage session starts at time to. During a first internal heating phase between times to and to, the susceptor or internal heater is heated to a first temperature corresponding to a first target conductance GTI, in which the induction load is equal to 75 percent of the full conductance span AG. GTI can be determined by Equation 1 above as follows: GTI = Glower + (0.75 x AG). Due to the relatively small volume ofthe susceptor, the susceptor can be considered to be heated instantaneously to this conductance value when the consumer usage session starts. The first internal heating phase to to t3preferably has a duration of greater than 20 seconds. In this example, the first temperature is 380 degrees Celsius and the first internal heating phase to to t3has a duration of approximately 60 seconds. The internal heater is constantly maintained at the first temperature for the duration of the first internal heating phase to to t3. The relatively high first temperature of 380 degrees Celsius provides a heating boost to rapidly start heating the aerosol-generating substrate to produce an increased amount of aerosol deliveries early in the consumer usage session.

[0302] The first temperature in the example heating profile of Figure 10 corresponds to a maximum temperature for the consumer usage session. However, it will be appreciated that the first temperature does not need to be a maximum temperature, providing it is sufficiently high to provide an initial boost to the heating of the aerosol-generating substrate, for example, it may be at least 60 percent of the full conductance span AG, and preferably at least 80 percent of the full conductance span AG.

[0303] Following the first internal heating phase to to ts, the internal heater is heated to a second temperature during a second internal heating phase between times t3and t4. The second temperature corresponds to a second target conductance GT2, in which the induction load is equal to 25 percent of the full conductance span AG. GT2 can be determined by Equation 1 above as follows: GT2 = Glower + (0.25 x AG). The second temperature is less than the first temperature. In this example, the second temperature is 340 degrees Celsius and the second internal heating phase t3to t4 has a duration of approximately 50 seconds. The internal heater is constantly maintained at the second temperature for the duration of the second internal heating phase t3to t4.

[0304] Following the second internal heating phase t3to t4, the internal heater is heated such that its temperature increases back to the first temperature during a third internal heating phase between times t4 and te. In the example of Figure 10, the temperature is increased back to the first temperature from the second temperature during the third internal heating phase t4 to te in a series of temperature steps. In a first temperature step occurring at time t4, the temperature of the internal heater is increased to a third temperature corresponding to a third target conductance GT3, in which the induction load is equal to 40 percent of the full conductance span AG. GT3 can be determined by Equation 1 above as follows: GT3 = Glower + (0.40 x AG). In this example, the third temperature is 345 degrees Celsius and the first temperature step has a duration of approximately 50 seconds. In a second temperature step occurring at time ts, the temperature of the internal heater is increased to a fourth temperature corresponding to a fourth target conductance GT4, in which the induction load is equal to 56percent of the full conductance span AG. GT4 can be determined by Equation 1 above as follows: GT4 = Glower + (0.56 x AG). In this example, the fourth temperature is 355 degrees Celsius and the second temperature step has a duration of approximately 50 seconds. In a third temperature step occurring at time to, the temperature of the internal heater is increased to back to the first temperature corresponding to the first target conductance GTI. The internal heater is constantly maintained at the first temperature for the remainder of the consumer usage session, that is, from times te to t?.

[0305] Alternatively, during the third internal heating phase t4 and te, the internal heater may be heated such that its temperature increases back to a temperature at least 80 percent of the first temperature. The internal heater may then be constantly maintained at this reduced temperature for the remainder of the consumer usage session, that is, from times te to t?.

[0306] The control circuitry of the aerosol-generating device controls the provision of power to the heating arrangement such that the conductance of the susceptor or internal heater is driven to the target operating temperatures. The target conductance values may be stored in a memory of the control circuitry.

[0307] In the example heating profile of Figure 10, resistive heating of the resistive heating element or external heater is activated during the first internal heating phase to to to at time ti. Resistive heating of the resistive heating element or external heater starts within a predetermined time period to to h of the internal heater being activated at time to. The predetermined time period to to h is less than 60 seconds. In this example, the predetermined time period to to h is approximately 11 seconds. By keeping the predetermined time period to to h relatively short, the external heater is able to contribute to providing a higher level of heating to the aerosol-generating substrate during the initial phases of the consumer usage session to release more aerosol, in particular, from an outer region of the aerosol-generating substrate. During the consumer usage session, a consumer may puff on the article of the system, resulting in an airflow as described above with reference to Figure 3B and inhale the aerosol formed.

[0308] It will be appreciated that the predetermined time period to to h between starting internal heating at time to and starting external heating at time h is optional and in some heating profiles resistive heating of the resistive heating element or external heater may commence at the same time as heating of the susceptor or internal heater, that is, at time to.

[0309] During a first external heating phase between times h and t2, the controller of the aerosol-generating device controls the supply of DC power to the external heater such that the temperature of the external heater increases to a first temperature Ti. In this example, the first temperature Ti is about 85 degrees Celsius and the first external heating phase ti to t2 is approximately 19 seconds. The temperature of the external heater increases from the firsttemperature Ti to a second temperature T2 during a second external heating phase between times t2 and the conclusion of the consumer usage session at time t?. The second temperature T2 is greater than the first temperature T1. Indeed, in this example, the second temperature corresponds to the maximum temperature reached by the external heater over the duration of the consumer usage session. In this example, the second external heating phase t2 to t3is approximately 285 seconds and the second temperature T2 is approximately 198 degrees Celsius. The conclusion of the consumer usage session at time t? corresponds to a time of approximately 315 seconds or around 5 minutes.

[0310] Therefore, during the first external heating phase, the temperature of the external heater increases at a first rate of change, and during the second external heating phase, the temperature of the external heater increases at a second rate of change. The first rate of change is greater than the second rate of change to bring the external heater to its desired heating temperature more quickly. External heating helps to generate an aerosol from the outer portion of the aerosol-generating substrate and to compensate for depletion of the aerosol forming constituents of the inner portion of the aerosol-generating substrate. This helps to maintain consistent aerosol generation over the duration of the consumer usage session. Increasing the temperature of the external heater during the firstand second external heating phases up to the maximum temperature of 198 degrees Celsius helps to consume more of the aerosol-generating substrate.

[0311] It will appreciated that the first and second rates of change are not necessarily constant and that there may be some variation in the rate at which the temperature of the external heater increases and possibly a sub-period in which the temperature does not increase but is held constant. Therefore, the first and second rates of change may be average rates of change over the first and second external heating phases.

[0312] The temperature of the external heater does not exceed the maximum temperature of 198 degrees Celsius for the duration of the consumer usage session. Furthermore, the temperature of the external heater is significantly below the temperatures reached by the internal heater for the duration of the consumer usage session. This reduces the risk of combustion or pyrolysis of the aerosol-generating substrate and is significantly below the maximum external heater temperature used in conventional aerosol-generating systems. However, despite this lower maximum external heating temperature, the inventors have found that the method provides consistent delivery of aerosol over the duration of the consumer usage session. In particular, where the aerosol-generating substrate is tobacco-based, the inventors have found that deliveries of nicotine and aerosol former are satisfactory and consistent over the duration of the consumer usage session without any reduction in the consumer experience.Figure 11 A shows an aerosol-generating article 800 having an article identifier 802. The article 800 comprises a number of substantially cylindrical elements (not visible) that are sequentially arranged in coaxial alignment and wrapped in an outer wrapper 804, similar to the aerosol-generating article 200 of Figure 3B. The article identifier 802 encodes an identity of the article 800 such that the article identifier 802 can be used to provide an identity of the article 800 during use. The article identifier 802 comprises a plurality of coloured bands 806a, 806b circumscribing the outer surface of the wrapper 804. The coloured bands 806a, 806b have been printed on an outer surface of the wrapper 804 using a visible ink. The coloured bands 806a, 806b encode the identity of the article 800. In this example, there are two coloured bands 806a, 806b. However, it will be appreciated that any suitable number of coloured bands may be used and the number will depend to some extent on the number of articles that need to be identified.

[0313] Each of the coloured bands 806a, 806b may have a different colour or they may have the same colour. In the example of Figure 11 A, the coloured bands 806a, 806b have different colours. The coloured bands 806a and 806b are spaced apart along the longitudinal length of the article 800 such that there is a space 808 (or spaces in the case of there being more than two coloured bands) between neighbouring colour bands 806a, 806b. The space 808 is not coloured and is the colour of the outer surface of the wrapper 804, which is generally white, although other coloured wrappers may be used providing they are distinct from the colour of the colour bands 806a, 806b.

[0314] In addition to the colour bands 806a, 806b, the article identifier 802 may comprise further identifying elements (not shown) for providing further identity information about the article 800. For example, the article identifier 802 may comprise bands of invisible ink, ultra violet (UV) ink, infra red (IR) ink, phosphorescent ink, fluorescent ink, or a taggant that can be used to authenticate the article as being genuine. The further identifying elements may also comprise a metallic ink or magnetic ink and may not be printed on the outer surface of the wrapper 804 but on an inner surface of the wrapper 804 or embedded elsewhere in the article 800.

[0315] Figure 11 B shows a schematic side cross-sectional view of an example aerosolgenerating system 850 comprising the aerosol-generating article 800 of Figure 11A and an example aerosol-generating device 860. The aerosol-generating device 860 is similar to the aerosol-generating device 100 described with reference to Figure 3A and like reference numerals are used to designate like parts.

[0316] The aerosol-generating device 860 differs from the aerosol-generating device 100 in that the aerosol-generating device 860 further comprises a sensor assembly 862 arranged to detect the article identifier 802 on the article 800. The sensor assembly 862 is embedded or arranged in a recess of a wall of the proximal portion 62 of the jacket 60 facing the chamber68 of the aerosol-generating device 860 such that the sensor assembly 862 can read or detect the article identifier 802 as the article 800 is inserted into the chamber 68. The sensor assembly 862 is arranged near a proximal end of the chamber 68. Figure 11 B shows the article 800 received within the chamber 68 of the device 860. The article identifier 802 is arranged at a point along the length of the article 800 such that the article identifier 802 is within the chamber 68 once the article 800 has been inserted. Furthermore, the article identifier 802 is arranged at a point along the length of the article 800 such that the coloured bands 806a, 806b move past the sensor assembly 802 as the article 800 is inserted into the chamber 68.

[0317] The sensor assembly 862 is configured to output a signal corresponding to the article identifier 802 based on the information encoded in the coloured bands 806a, 806b. The sensor assembly is communicatively connected to the control circuitry 40, which is configured to identify the aerosol-generating article 800 based on the signal received from the sensor assembly 862.

[0318] The sensor assembly 862 comprises optoelectronic emitter and an optoelectronic sensor. The type of optoelectronic emitter and optoelectronic sensor will depend on the article identifier 802 and the identifier elements being detected. In the example of Figure 11 B, the article identifier 802 uses coloured bands 806a, 806b. Therefore, the optoelectronic emitter comprises a white light emitter such as a white light emitting diode (LED) and the optoelectronic sensor comprises a colour sensor. The white light emitter emits white light containing all visible light colour components including red, green and blue. The white light emitter is arranged to irradiate the article identifier 802 on the article 800. The colour sensor is arranged to receive the light reflected from the article identifier 802. Depending on the colours of the coloured bands 806a, 806b of the article identifier 802, light will be reflected with different component amounts of red, green and blue light. The colour sensor is configured to detect the respective amounts of red, green and blue light components in the reflected light and, based on these amounts, determine the colour of a particular coloured band 806a, 806b as it passes the sensor assembly 862.

[0319] The sensor assembly 862 is configured to detect the colour of the coloured band 806b furthest from the proximal end of the article 800 first, the coloured band 806a second furthest from the proximal end of the article 800 second, and then sequentially any further coloured bands that may be provided as the article 800 moves towards the distal end of the chamber 68. The sensor assembly 862 is able to distinguish between different coloured bands 806a, 806b due to the space 808 between the coloured bands 806a, 806b. Based on an analysis of the colour of the coloured bands 806a, 806b detected and the order in which the colours are detected, the control circuitry 40 can determine which specific type of article 800 isinserted. The sensor assembly 862 can also be used to determine whether or not an aerosolgenerating article has been inserted into the chamber 68 by monitoring whether a signal is being received from the sensor assembly.

[0320] The sensor assembly 862 may also be multi-spectral such that it is able to emit and detect other types of radiation in addition to visible light, for example, radiation in the UV or IR spectrum. The sensor assembly 862 may comprise multiple optoelectronic emitters for emitting different spectrums of radiation. The sensor assembly 862 may comprise multiple optoelectronic sensors or a multi-spectral optoelectronic sensor for detecting different spectrums of radiation.

[0321] Figure 12 shows three scenarios A, B and C in which the identity of an aerosolgenerating article 900, 902, 904 determines a selection of heating profiles a, b, c that are available to heat the aerosol-generating article 900, 902, 904. The heating profile a in Figure 12 corresponds to the improved or extended duration heating profile described above with respect to Figure 8. The heating profile b in Figure 12 corresponds to the uplift heating profile described above with respect to Figure 9. The heating profile c in Figure 12 corresponds to the boost heating profile described above with respect to Figure 10. However, any suitable heating profile may be used and the selection of heating profiles may be determined from any suitable number of heating profiles. For example, the heating profiles of Figures 13 and 14 described below could also be included in the plurality of heating profiles from which the selection of heating profiles is determined.

[0322] The selection of heating profiles a, b, c of Figure 12 may be determined by the control circuitry 102 of the aerosol-generating device 860 of Figure 11 B. The control circuitry 102 comprises a memory (not shown in Figure 11 B) for storing the plurality of heating profiles a, b, c. The control circuitry 102 is configured to identify the aerosol-generating article 900, 902, 904 based on the article identifier 906, 908, 910 on the aerosol-generating article 900, 902, 904. Based on the identity of the aerosol-generating article 900, 902, 904, the control circuitry 102 is further configured to determine a selection from the plurality of heating profiles a, b, c that is available to heat the aerosol-generating substrate in the aerosol-generating article 900, 902, 904. The control circuitry 102 may also comprise a user interface (not shown in Figure 11 B) such as an LCD screen or a plurality of LEDs to display the determined selection of heating profiles to a consumer and allow the consumer to select a heating profile from the determined selection of heating profiles. The user interface may further comprise one or more buttons or dials to allow the consumer to input their choice of heating profile.

[0323] In scenario A of Figure 12, the aerosol-generating article 900 comprises an article identifier 906 comprising coloured bands 912a, 912b having different colours, for example, red and yellow. The sensor assembly 862 of the aerosol-generating device 860 of Figure 11 Breads the article identifier 906 and the control circuitry 102 identifies the aerosol-generating article 900. Based on the identity of the aerosol-generating article 900, the control circuitry 102 determines that a selection of three heating profiles are available to heat the aerosolgenerating substrate, that is, the improved or extend duration heating profile a, the uplift profile b and the boost profile c. The consumer can then select a heating profile of their choice from the determined selection of three heating profiles via a user interface. Scenario A may correspond to a premium type aerosol-generating article 900 that allows a consumer maximum choice over the heating profile used.

[0324] In scenario B of Figure 12, the aerosol-generating article 902 comprises an article identifier 908 comprising coloured bands 914a, 914b having different colours, for example, blue and green. The sensor assembly 862 of the aerosol-generating device 860 of Figure 11 B reads the article identifier 908 and the control circuitry 102 identifies the aerosol-generating article 902. Based on the identity of the aerosol-generating article 902, the control circuitry 102 determines that a selection of two heating profiles are available to heat the aerosolgenerating substrate, that is, the improved or extend duration heating profile a and the uplift profile b. The consumer can then choose one or other of the heating profiles from the determined selection of three heating profiles via a user interface. Scenario B may correspond to a less premium type aerosol-generating article 902 compared to Scenario A but one that still allows a consumer a choice over the heating profile used.

[0325] In scenario C of Figure 12, the aerosol-generating article 904 comprises an article identifier 910 comprising coloured bands 916a, 916b having different colours, for example, blue and purple. The sensor assembly 862 of the aerosol-generating device 860 of Figure 11 B reads the article identifier 910 and the control circuitry 102 identifies the aerosolgenerating article 904. Based on the identity of the aerosol-generating article 904, the control circuitry 102 determines that only one heating profile is available to heat the aerosolgenerating substrate, that is, the boost heating profile c. Given that only one heating profile is available, the control circuitry 102 will simply run that heating profile and the consumer does not get a choice of heating profile. Scenario C may correspond to a more budget or economy type aerosol-generating article 904 compared to Scenarios A and B.

[0326] Figure 13 shows another example heating profile for a consumer usage session, in which the external heater is not used to externally heat the aerosol-generating substrate to a significant extent but is instead merely heated to reduce heat loss from the aerosol-generating substrate to the external heater during internal heating of the aerosol-generating substrate.

[0327] In the heating profile of Figure 13, the consumer usage session starts at time to. During a first internal heating phase between times to and t2, the susceptor or internal heater is heated to a first temperature corresponding to a first target conductance GTI, in which the inductionload is equal to 9 percent of the full conductance span AG. GTI can be determined by Equation 1 above as follows: GTI = Glower + (0.09 x AG). Due to the relatively small volume of the susceptor, the susceptor can be considered to be heated instantaneously to this conductance value when the consumer usage session starts. In this example, the first temperature is 330 degrees Celsius and the first internal heating phase to to t2 has a duration of approximately 160 seconds. The internal heater is constantly maintained at the first temperature for the duration of the first internal heating phase to to t2.

[0328] The constant conductance value GTI maintained during the first internal heating phase is a relatively low conductance value, that is, it corresponds to an induction load that is equal to only 9 percent of the full conductance span of AG. This conductance value corresponds to a temperature at which the aerosol-generating substrate will still form an aerosol in a sufficient volume and quantity for a satisfactory experience when inhaled by a consumer, particularly in the early stages of a consumer usage session when the aerosol-generating substrate has not been significantly depleted.

[0329] Following the first internal heating phase to to t2, the internal heater is heated such that its temperature increases during a second internal heating phase between times t2 and t?. In the example of Figure 13, the temperature is increased during the second internal heating phase t2 to t? in a series of temperature steps. In a first temperature step occurring at time t2 (at 160 seconds), the temperature of the internal heater is increased to a second temperature corresponding to a second target conductance GT2, in which the induction load is equal to 25 percent of the full conductance span AG. GT2 can be determined by Equation 1 above as follows: GT2 = Glower + (0.25 x AG). In this example, the second temperature is 340 degrees Celsius and the first temperature step has a duration of approximately 40 seconds. In a second temperature step occurring at time t3(at 200 seconds), the temperature of the internal heater is increased to a third temperature corresponding to a third target conductance GT3, in which the induction load is equal to 40 percent of the full conductance span AG. GT3 can be determined by Equation 1 above as follows: GT3 = Glower + (0.40 x AG). In this example, the third temperature is 345 degrees Celsius and the second temperature step has a duration of approximately 40 seconds. In a third temperature step occurring at time ts (at 240 seconds), the temperature of the internal heater is increased to a fourth temperature corresponding to a fourth target conductance GT4, in which the induction load is equal to 56 percent of the full conductance span AG. GT4 can be determined by Equation 1 above as follows: GT4 = Glower + (0.56 x AG). In this example, the fourth temperature is 355 degrees Celsius and the third temperature step has a duration of approximately 40 seconds. In a fourth temperature step occurring at time te (at 280 seconds), the temperature of the internal heater is increased to a fifth temperature corresponding to a fifth target conductance GTS, in which the induction loadis equal to 75 percent of the full conductance span AG. GTS can be determined by Equation 1 above as follows: GTS = Glower + (0.75 x AG). In this example, the fifth temperature is 380 degrees Celsius and the fourth temperature step has a duration of approximately 85 seconds. The internal heater is constantly maintained at the fifth temperature for the remainder of the consumer usage session, that is, from times to to ty.

[0330] The control circuitry of the aerosol-generating device controls the provision of power to the heating arrangement such that the conductance of the susceptor or internal heater is driven to the target operating temperatures. The target conductance values may be stored in a memory of the control circuitry.

[0331] In the example heating profile of Figure 13, resistive heating of the resistive heating element or external heater is activated at time to. During a first external heating phase between times to and ti , the controller of the aerosol-generating device controls the supply of DC power to the external heater such that the temperature of the external heater increases to a first temperature Ti. In this example, the first temperature Ti is about 85 degrees Celsius and the first external heating phase to to ti is approximately 30 seconds.

[0332] The temperature of the external heater increases from the first temperature Ti to a second temperature T2 during a second external heating phase between times ti and the conclusion of the consumer usage session at time ty. However, the temperature of the external heater is held constant at the first temperature Ti during a first portion ti to t4 of the second external heating phase ti to ty. The first portion ti to t4 of the second external heating phase ti to ty has a duration of approximately 175 seconds, such that time t4 occurs at 205 seconds into the consumer usage session.

[0333] The temperature of the external heater increases to a second temperature T2 during a second portion t4 to ty of the second external heating phase ti to ty. The second temperature T2 is greater than the first temperature Ti. Indeed, in this example, the second temperature T2 corresponds to the maximum temperature reached by the external heater over the duration of the consumer usage session. In this example, the second temperature T2 is approximately 95 degrees Celsius and the second portion t4 to ty of the second external heating phase ti to ty has a duration of approximately 160 seconds. The conclusion of the consumer usage session at time ty corresponds to a time of approximately 365 seconds or around 6 minutes.

[0334] As can be seen in Figure 13, during the first external heating phase to to ti, the temperature of the external heater increases at a first rate of change, and during the second external heating phase ti to ty, the temperature of the external heater increases at a second rate of change. The first rate of change is greater than the second rate of change to bring the external heater to its desired temperature more quickly. Indeed, the first rate of change is initially at maximum until the temperature of the external heater reaches a temperature ofapproximately 70 degrees Celsius, after which the first rate of change reduces as the temperature of the external heater approaches the first temperature Ti of 85 degrees Celsius. Heating the external heater helps to reduce the temperature difference between the internal and external heaters and therefore helps to reduce heat loss to the external heater. This also helps to maintain consistent aerosol generation.

[0335] The second rate of change of the external heater is significantly less than the first rate of change because the first temperature Ti is sufficient to reduce heat losses to the external heater and there is no need for the temperature to raise significant above this. The temperature of the external heater increases to a second temperature T2 during a second portion t4 to ty of the second external heating phase ti to ty mainly to compensate for the increase in temperature of the internal heater during the second internal heating phase t2 to ty. However, it has been found that only a relatively small further increase in temperature is required, that is, approximately 10 degrees Celsius, in order to continue to reduce heat losses to the external heater during the second internal heating phase t2 to ty.

[0336] It will appreciated that the first and second rates of change are not constant and that there is some variation in the rate at which the temperature of the external heater increases and also a period in which the temperature does not increase but is held constant. Therefore, the first and second rates of change are average rates of change over the first and second external heating phases.

[0337] The temperature of the external heater does not exceed the maximum temperature of 95 degrees Celsius for the duration of the consumer usage session. Furthermore, the temperature of the external heater is significantly below the temperatures reached by the internal heater for the duration of the consumer usage session. This reduces the risk of combustion or pyrolysis of the aerosol-generating substrate and is significantly below the maximum external heater temperature used in conventional aerosol-generating systems. However, despite this lower maximum external heating temperature, the inventors have found that the method provides consistent delivery of aerosol over the duration of the consumer usage session. In particular, where the aerosol-generating substrate is tobacco-based, the inventors have found that deliveries of nicotine and aerosol former are satisfactory and consistent over the duration of the consumer usage session without any reduction in the consumer experience.

[0338] Figure 14 shows another example heating profile for an aerosol-generating system that provides a consumer with consistent aerosol production over the duration of the consumer usage session but has a shorter duration than the improved heating profile of Figure 8.

[0339] The consumer usage session starts at time to and ends at time t3. For the full duration of the consumer usage session, that is, between times to and ts, the conductance of thesusceptor or internal heater is maintained at a constant temperature corresponding to a target conductance GTI, in which the induction load is equal to 9 percent of the full conductance span AG. GTI can be determined by Equation 1 above as follows: GTI = Glower + (0.09 x AG). At time to, the conductance of the susceptor may already be near this value following a previous calibration process or, due to the relatively small volume of the susceptor, it can be considered to be heated instantaneously to this conductance value when the consumer usage session starts. Due to the monotonic relationship between conductance and temperature discussed above, the target conductance GTI corresponds to a specific temperature, which in this case is a temperature of 330 degrees Celsius. As mentioned above, this temperature is maintained for the duration of the consumer usage session. The controller of the aerosol-generating device controls the provision of power to the heating arrangement such that the conductance of the susceptor or internal heater is maintained at a value corresponding to the target operating temperature. The target conductance value may be stored in the memory of the controller.

[0340] The conductance value GT1 is a relatively low conductance value, that is, it corresponds to an induction load that is equal to only 9 percent of the full conductance span of AG. This conductance value corresponds to a temperature at which the aerosol-generating substrate will still form an aerosol in a sufficient volume and quantity for a satisfactory experience when inhaled by a consumer.

[0341] At time to, that is, the start of the consumer usage session, resistive heating of the resistive heating element or external heater is not activated. There is a delay between supplying AC power to the susceptor or internal heater at time to and subsequently supplying DC power to the resistive heating element or external heater at time h to resistively heat the resistive heating element. In this example, the delay is approximately 60 seconds. Therefore, during this delay period, aerosol is being produced solely by the susceptor or internal heater. The internal heater heats the aerosol-generating substrate, predominantly an inner region or portion of the aerosol-generating substrate, to form an aerosol, or a vapour which cools and condenses to form an aerosol. During the consumer usage session, a consumer may puff on the article of the system, resulting in an airflow as described above with reference to Figure 3B and inhale the aerosol formed.

[0342] Resistive heating of the resistive heating element or external heater is activated at time h. During a first external heating phase between times h and t2, the controller of the aerosolgenerating device controls the supply of DC power to the external heater such that the temperature of the external heater increases to a first temperature Ti. In this example, the first temperature Ti is about 70 degrees Celsius and the first external heating phase h to t2 is approximately 45 seconds. The temperature of the external heater increases from the firsttemperature Ti to a second temperature T2 during a second external heating phase between times t2 and the conclusion of the consumer usage session at time t3. The second temperature T2 is greater than the first temperature T1. Indeed, in this example, the second temperature T2 corresponds to the maximum temperature reached by the external heater over the duration of the consumer usage session. In this example, the second external heating phase t2 to t3is approximately 260 seconds and the second temperature T2 is approximately 158 degrees Celsius.

[0343] Therefore, during the first external heating phase, the temperature of the external heater increases at a first rate of change, and during the second external heating phase, the temperature of the external heater increases at a second rate of change. The first rate of change is greater than the second rate of change to bring the external heater to its desired heating temperature more quickly. External heating helps to generate an aerosol from the outer portion of the aerosol-generating substrate and to compensate for depletion of the aerosol forming constituents of the inner portion of the aerosol-generating substrate. This helps to maintain consistent aerosol generation over the duration of the consumer usage session. Increasing the temperature of the external heater during the firstand second external heating phases to the maximum temperature of 158 degrees Celsius helps to consume more of the aerosol-generating substrate.

[0344] It will appreciated that the first and second rates of change are not necessarily constant and that there may be some variation in the rate at which the temperature of the external heater increases and possibly a sub-period in which the temperature does not increase but is held constant. Therefore, the first and second rates of change may be average rates of change over the first and second external heating phases.

[0345] The duration of the consumer usage session in the heating profile of Figure 14 is approximately 365 seconds. Therefore, this heating profile is shorter in duration than the heating profile of Figure 8 and may be configured for use with a particular type of aerosolgenerating article.

[0346] The temperature of the external heater does not exceed the maximum temperature of 158 degrees Celsius for the duration of the consumer usage session. Furthermore, the temperature of the external heater is significantly below the temperature of the internal heater of 330 degrees Celsius for the duration of the consumer usage session. This reduces the risk of combustion or pyrolysis of the aerosol-generating substrate and is significantly below the maximum external heater temperature used in conventional aerosol-generating systems. However, despite this lower maximum external heating temperature, the inventors have found that the method provides consistent delivery of aerosol over the duration of the consumer usage session. In particular, where the aerosol-generating substrate is tobacco-based, theinventors have found that deliveries of nicotine and aerosol former are satisfactory and consistent over the duration of the consumer usage session without any reduction in the consumer experience.

[0347] For the purpose of the present description and of the appended claims, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term "about". Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein. In this context, therefore, a number A is understood as A ± 5 percent (5%) of A. Within this context, a number A may be considered to include numerical values that are within general standard error for the measurement of the property that the number A modifies. The number A, in some instances as used in the appended claims, may deviate by the percentages enumerated above provided that the amount by which A deviates does not materially affect the basic and novel characteristic(s) of the claimed invention. Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein.

Claims

Claims1. A method of controlling aerosol production in an aerosol-generating system, the aerosol-generating system comprising:an internal heater configured to heat an aerosol-generating substrate from inside the aerosol-generating substrate; andan external heater configured to heat the aerosol-generating substrate from outside the aerosol-generating substrate;the method comprising, during a consumer usage session:controlling a supply of power to the internal heater to heat the internal heater; and controlling a supply of power to the external heater such that the temperature of the external heater does not exceed a maximum temperature of 120 degrees Celsius.

2. A method according to claim 1, wherein the maximum temperature of the external heater is less than 100 degrees Celsius.

3. A method according to claim 1 or 2, wherein the supply of power to the external heater is controlled such that, during a first external heating phase, the temperature of the external heater increases at a first rate of change, and during a second external heating phase, the temperature of the external heater increases at a second rate of change, the first rate of change being greater than the second rate of change.

4. A method according to claim 4, wherein the external heater is heated to at least 80 percent of the maximum temperature during the first external heating phase, the first external heating phase being less than 15 percent of the duration of the consumer usage session.

5. A method according to claim 3 or 4, wherein the temperature of the external heater is held constant during a first portion of the second external heating phase.

6. A method according to claim 5, wherein the temperature of the external heater increases during a second portion of the second external heating phase.

7. A method according to any preceding claim, wherein the supply of power to the internal heater is controlled such that the temperature of the internal heater is maintained at a constant temperature during a first internal heating phase.

8. A method according to claim 7, wherein the supply of power to the internal heater is controlled such that the temperature of the internal heater increases during a second internal heating phase.

9. A method according to claim 8, when dependent on claims 6 or 7, wherein the second portion of the second external heating phase corresponds to at least a portion of the second internal heating phase when the temperature of the internal heater is increasing.

10. A method according to claim 9, wherein the temperature of the internal heater is increased during the second internal heating phase in a series of temperature steps.

11. A method according to claim 10, wherein the series of temperature steps comprises at least three consecutive temperature steps.

12. A method according to claim 10 or 11, wherein each temperature step provides a temperature increase of at least 5 degrees Celsius and has a duration of at least 30 seconds.

13. An aerosol-generating system comprising:an internal heater configured to heat an aerosol-generating substrate from inside the aerosol-generating substrate;an external heater configured to heat the aerosol-generating substrate from outside the aerosol-generating substrate; andcontrol circuitry,wherein the control circuitry is configured to carry out a method according to any of claims 1 to 12.

14. An aerosol-generating system according to claim 13, wherein the internal heater comprises a susceptor.

15. An aerosol-generating system according to claim 13 or 14, wherein the external heater comprises a resistive heating element.

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