Method for controlling overheating in an aerosol generating system

Abstract

A method (300) for controlling heating in an aerosol-generating system including a heating element for heating a liquid aerosol-forming substrate supplied to the heating element, the method comprising: providing a power supply to the heating element (302); monitoring an electrical parameter indicative of the temperature of the heating element; determining whether the electrical parameter is greater than a maximum threshold or less than a minimum threshold indicating that a threshold temperature of the heating element has been exceeded (304); interrupting the power supply to the heating element when the threshold temperature is exceeded (306) to allow the heating element to cool to a temperature at which the electrical parameter falls below the maximum threshold or exceeds the minimum threshold; determining, after cooling, whether a liquid aerosol-forming substrate is supplied to the heating element (312); and disabling the power supply if no liquid aerosol-forming substrate is supplied to the heating element (314).

Description

[Technical Field]

[0001] The present disclosure relates to a method for controlling the heating of an aerosol generation system. In particular, but not exclusively, the present disclosure relates to a method for controlling the heating of a handheld, electrically operated aerosol generation system for heating an aerosol-forming substrate to generate an aerosol and deliver the aerosol into a user's mouth. The present disclosure further relates to an aerosol generation system having a control circuit configured to implement the method for controlling the heating. [Background technology]

[0002] Aerosol generation systems that heat a liquid aerosol-forming substrate to generate an aerosol for delivery to a user are generally known in the prior art. These systems typically include an aerosol generator and a cartridge configured to be removably coupled to the aerosol generator. The cartridge contains a liquid aerosol-forming substrate capable of releasing a volatile compound when heated. The cartridge also typically includes a heater for heating the liquid aerosol-forming substrate. In known aerosol generation systems, the heater includes a resistive heating element to which the liquid aerosol-forming substrate is supplied by some form of wick. The aerosol generator or cartridge also includes a mouthpiece. When a user draws on the mouthpiece, an electric current passes through the heating element, causing it to heat by resistive or Joule heating, which in turn heats the liquid aerosol-forming substrate supplied by the wick. This releases the volatile compound from the liquid aerosol-forming substrate, which cools to form an aerosol. The aerosol is then drawn through the mouthpiece into the user's mouth.

[0003] Typically, aerosol generating devices are reusable, with the liquid aerosol-forming substrate contained in a disposable cartridge. After a period of use, e.g., after a predetermined number of inhalations by a user, the liquid aerosol-forming substrate becomes depleted. Once the liquid aerosol-forming substrate is depleted, the cartridge should be replaced before the next use of the aerosol generating device.

[0004] During operation, it is preferable to maintain a supply of liquid aerosol-forming substrate to the heating element so that it remains wet, helping to ensure that satisfactory aerosol is generated when the user takes a puff. A wet heating element also helps regulate the temperature of the heating element as heat generated within the heating element is transferred to the liquid aerosol-forming substrate and dissipated into the generated aerosol, which helps prevent the heating element from overheating and maintain the heating element at a predetermined threshold temperature. If the heating element rises above a predetermined threshold temperature, this may indicate a "dry heat" or "dry puff" condition, i.e., a condition in which the heating element is heated with insufficient liquid aerosol-forming substrate present, reducing the amount of heat dissipated into the aerosol. This can lead to overheating and potentially thermal decomposition of the liquid aerosol-forming substrate, which can produce undesirable by-products and an unsatisfactory aerosol. This can result in a poor user experience.

[0005] However, a dry overheating condition can result from two different causes. The first cause is that the liquid aerosol-forming substrate in the cartridge is completely depleted, and therefore no liquid aerosol-forming substrate can be supplied to the heating element. In this case, the cartridge needs to be replaced. The second cause is that the user temporarily dries out the heating element by taking a particularly strong or long puff. In this case, the cartridge is not completely depleted, and the user still has puffs to consume. Therefore, the cartridge does not need to be replaced, but it takes time for the liquid aerosol-forming substrate to re-moisten the heating element. Prior to the examples described in this disclosure, it was difficult for aerosol generating systems to distinguish between the above two causes of a dry overheating condition.

[0006] It would be desirable to provide a method for detecting and controlling dry heat conditions and reducing the production of undesirable by-products. It would be desirable to provide a method that can distinguish between a dry heat condition that results from the complete depletion of the supply of cartridges or other liquid aerosol-forming substrate and a dry heat condition that results from the user taking a particularly strong or long puff that only temporarily dries out the heating element. Summary of the Invention

[0007] According to an embodiment of the present disclosure, there is provided a method for controlling heating of an aerosol-generating system. The aerosol-generating system may include a heating element for heating a liquid aerosol-forming substrate supplied to the heating element. The method may include providing a power supply to the heating element. The method may include monitoring an electrical parameter. The electrical parameter may be indicative of a temperature of the heating element. The method may include determining whether the electrical parameter is greater than a maximum threshold or less than a minimum threshold, indicating that a threshold temperature of the heating element has been exceeded. The method may include interrupting the power supply to the heating element when the threshold temperature is exceeded. The method may include allowing the heating element to cool to a temperature below the maximum threshold or above the minimum threshold. The method may include determining whether a liquid aerosol-forming substrate is supplied to the heating element after cooling. The method may include disabling the power supply when no liquid aerosol-forming substrate is supplied to the heating element.

[0008] According to an embodiment of the present disclosure, there is provided a method for controlling heating in an aerosol-generating system including a heating element for heating a liquid aerosol-forming substrate supplied to the heating element. The method includes providing a power supply to the heating element. The method includes monitoring an electrical parameter indicative of the temperature of the heating element. The method includes determining whether the electrical parameter is greater than a maximum threshold or less than a minimum threshold, indicating that a threshold temperature of the heating element has been exceeded. The method includes interrupting the power supply to the heating element when the threshold temperature is exceeded, allowing the heating element to cool to a temperature at which the electrical parameter falls below the maximum threshold or exceeds the minimum threshold. The method includes determining whether a liquid aerosol-forming substrate is supplied to the heating element after cooling. The method includes disabling the power supply if no liquid aerosol-forming substrate is supplied to the heating element.

[0009] Advantageously, the above-described method enables an aerosol-generating system to detect and control the occurrence of an overheating or dry heat condition. By interrupting power supply when an overheating or dry heat condition is detected, the method reduces the likelihood of undesirable by-products being generated and a poor user experience. Furthermore, by allowing the heating element to cool below a threshold temperature, the method can more accurately determine whether a liquid aerosol-forming substrate is being supplied to the heating element. At temperatures above the threshold temperature, a liquid aerosol-forming substrate resupplied to the heating element after a dry heat condition may be quickly aerosolized, making it more difficult to determine whether a liquid aerosol-forming substrate remains. However, at temperatures below the threshold temperature, the liquid aerosol-forming substrate does not quickly aerosolize, allowing the heating element to re-wet, allowing for more accurate detection of the presence of a liquid aerosol-forming substrate. Furthermore, by determining whether a liquid aerosol-forming substrate is being supplied to the heating element after cooling, the method enables the aerosol-generating system to accurately distinguish between a dry heat condition that occurs as a result of complete depletion of the liquid aerosol-forming substrate or as a result of a particularly strong or long puff by the user.

[0010] As used herein, the term "threshold temperature" refers to a temperature above the normal operating temperature or aerosolization temperature of a heating element. When a heating element is operating above the threshold temperature, it may indicate that an overheating or dry heating condition is occurring. As used herein, when referring to an electrical parameter, the term "threshold" refers to the value of the electrical parameter that corresponds to the threshold temperature.

[0011] As used herein, the term "electrical parameter" refers to an electrical property or characteristic, including, but not limited to, voltage or potential difference, current or electrical resistance. An electrical parameter can be monitored by directly measuring the parameter, such as voltage, or can be determined indirectly from another electrical parameter; for example, electrical resistance can be determined using Ohm's Law by first determining the voltage across and current through a component and then dividing the voltage by the current.

[0012] The electrical parameter is indicative of the temperature of the heating element. In the above method, an electrical parameter is selected that has a relationship with temperature. This can be either a known relationship with temperature or a relationship that can be determined. For example, it is known that electrical resistance changes with temperature and can be determined by the temperature coefficient of resistance, which describes how the electrical resistance of a component changes with temperature. Over a certain temperature range, the change in resistance may vary approximately linearly with temperature, which can make determining the temperature at a particular measured resistance relatively simple. Alternatively, the relationship between the electrical parameter and temperature can be determined, for example, by experiment, and temperatures corresponding to particular values of the parameter can be stored in memory, such as a look-up table.

[0013] The monitored electrical parameter may be an electrical parameter of the heating element itself. For example, the method may determine the electrical resistance of the heating element itself. Alternatively, the method may determine an electrical parameter of a component connected to the heating element. For example, the method may determine the current through a resistor connected in series with the heating element. The current passing through two components connected in series is the same. Because current is related to electrical resistance, which in turn is related to temperature, the current through the resistor provides an indication of the temperature of the heating element.

[0014] Some electrical parameters exhibit a positive relationship with changes in temperature, i.e., as the temperature increases, the electrical parameter also increases. This is generally the case, particularly with electrical resistance across the operating temperature range of the aerosol generation system. Thus, as the temperature of a heating element in an aerosol generation system increases, the resistance of the heating element also increases. Therefore, when determining whether a heating element's temperature threshold has been exceeded, it is determined whether the resistance of the heating element is greater than a maximum threshold.

[0015] Conversely, some electrical parameters exhibit a negative relationship with changes in temperature, i.e., as temperature increases, the electrical parameter decreases. This is generally the case with electrical conductance, particularly over the operating temperature range of the aerosol-generating system. Electrical conductance is the reciprocal of electrical resistance. Thus, as the temperature of a heating element in an aerosol-generating system increases, the conductance of the heating element decreases. Therefore, when determining whether a heating element's temperature threshold has been exceeded, the heating element's conductance is determined to be below a minimum threshold.

[0016] The method may further include determining an initial value of the electrical parameter. The step of determining whether the electrical parameter is greater than a maximum threshold or less than a minimum threshold may include determining whether the ratio between the initial value and the change in the value of the monitored electrical parameter is greater than a maximum threshold or less than a minimum threshold. Advantageously, determining the initial value of the electrical parameter can be useful for taking into account different initial temperatures of the heating element, for example, when the aerosol generating system is used in environments with different ambient temperatures. It has been found that determining the ratio between the initial value of the electrical parameter and the change in the value of the electrical parameter is another effective method for determining whether a threshold temperature of the heating element has been exceeded. Furthermore, the ratio may provide an indication of the significance of the change, which can be used to more effectively control the heating element. The ratio may be a percentage.

[0017] The method may further comprise resuming the power supply when the heating element is supplied with the liquid aerosol-forming substrate. Advantageously, resuming the power supply when the heating element is supplied with the liquid aerosol-forming substrate reduces interruptions to the operation of the aerosol generation system to a minimum, allowing the user to safely continue with their user experience.

[0018] The method may further include detecting a user puff before providing a supply of power to the heating element. This means that power is only provided to the heating element when the user is actively using the aerosol generating system, which helps to improve the energy efficiency of the system. Furthermore, avoiding unnecessary heating of the heating element may help to reduce the chance of overheating.

[0019] Monitoring the electrical parameter may include monitoring the electrical resistance of the heating element. The method may include determining whether the electrical resistance is greater than a maximum threshold value, indicating that a threshold temperature of the heating element has been exceeded. As noted above, electrical resistance has a positive relationship with temperature, i.e., as the temperature of the heating element increases, the resistance of the heating element also increases. Therefore, determining whether the temperature threshold of the heating element has been exceeded involves determining whether the resistance of the heating element is greater than a maximum threshold value.

[0020] The aerosol generation system in which the method is performed may be an induction aerosol generation system. The aerosol generation system may include an inductor. The heating element may include a susceptor arranged to be heated by the inductor. Monitoring the electrical resistance of the heating element may include monitoring the equivalent resistance of the inductor. The term equivalent resistance is defined below when discussing the aerosol generation system.

[0021] The method may further include the step of monitoring the cooling of the heating element. Advantageously, by monitoring the cooling of the heating element, the method can determine as soon as this occurs when the temperature of the heating element has cooled below a threshold temperature, which allows the next step of the method, i.e., determining whether the heating element is being supplied with a liquid aerosol-forming substrate, to be carried out quickly. This helps to improve the responsiveness of the method. Furthermore, the rate at which the heating element cools can provide an indication of whether the heating element is being supplied with a liquid aerosol-forming substrate, as discussed below.

[0022] Monitoring the cooling of a heating element may include providing a probe pulse to the heating element and determining the electrical resistance of the heating element during the probe pulse. As used herein, the term "probe pulse" refers to a test pulse having significantly less power than full-power operation when the heating element is being heated. The probe pulse may last for a significantly shorter period than a pulse provided during full-power operation. The probe pulse may typically constitute less than 10 percent of full-power operation, preferably less than 7 percent of full-power operation, and more preferably 5 percent or less of full-power operation. Such a low amount of power is incapable of heating the heating element. However, the probe pulse still provides sufficient power for electrical parameters such as the resistance of the heating element to be determined, providing an indication of the temperature of the heating element. Using pulses has been found to be a particularly efficient method of monitoring the cooling of a heating element because the heating element does not consume much power.

[0023] Monitoring the cooling of the heating element can include providing multiple probe pulses to the heating element and monitoring the electrical resistance of the heating element over successive probe pulses. Each probe pulse typically constitutes less than 10 percent of the total power operation, preferably less than 7 percent of the total power operation, and more preferably 5 percent or less of the total power operation. The combined power of the multiple probe pulses does not have the ability to heat the heating element, but allows the temperature of the heating element to be tracked as it cools, and the point at which the temperature of the heating element drops below a threshold temperature can be identified more quickly than using a single pulse.

[0024] The probe pulse may have any suitable duration. When two or more probe pulses are supplied to the heating element, each probe pulse may have a substantially similar duration. The duration of each probe pulse may be substantially equal to the probe pulse duration. The probe pulse duration may be stored in memory. The probe pulse duration may be about 2 milliseconds to about 20 milliseconds, or about 5 milliseconds to about 15 milliseconds. The probe pulse duration may be about 10 milliseconds.

[0025] When two or more probe pulses are delivered to the heating element, consecutive probe pulses may be separated by a probe pulse time interval. The probe pulse time interval may be a predetermined value. The probe pulse time interval may be stored in memory. Typically, the duration of the probe pulse time interval is longer than the duration of the probe pulse to reduce the possibility of a cumulative effect of consecutive probe pulses heating the heating element. The probe pulse time interval may be substantially constant or fixed. The probe pulse time interval may be about 50 milliseconds to about 50 milliseconds, or about 70 milliseconds to about 120 milliseconds. The duration of the probe pulse time interval may be about 90 milliseconds.

[0026] The step of determining whether a liquid aerosol-forming substrate is supplied to the heating element may include monitoring the cooling rate of the heating element. When a liquid aerosol-forming substrate is supplied to the heating element, a cooling effect occurs on the heating element. Therefore, the cooling rate of the heating element may be faster when a liquid aerosol-forming substrate is supplied to the heating element than when, for example, the cartridge is not depleted. Therefore, the cooling rate of the heating element may provide an indication of whether a liquid aerosol-forming substrate is supplied to the heating element.

[0027] Alternatively, determining whether the heating element is supplied with a liquid aerosol-forming substrate can include providing a power pulse to the heating element and determining the electrical characteristics of the heating element. As used herein, the term "power pulse" refers to a total power pulse that is sufficient to initiate heating of the heating element so that the electrical characteristics of the heating element can be determined as the heating element begins to heat. As the name suggests, the power pulse is applied to the heating element as a pulse of a predetermined length, which will be significantly shorter than the period during which power is applied to the heating element to heat it during normal operation.

[0028] The power pulse may have any suitable duration. When two or more power pulses are supplied to the heating element, each power pulse may have a substantially similar duration. The duration of each power pulse may be substantially equal to the power pulse duration. The power pulse duration may be stored in memory. The power pulse duration may be from about 100 milliseconds to about 1 second, or from 200 milliseconds to about 500 milliseconds. The probe pulse duration may be about 300 milliseconds.

[0029] The electrical property determined during application of the power pulse may be the resistance of the heating element after a predetermined time. When the heating element is not provided with a liquid aerosol-forming substrate, its cooling rate is slower than when a liquid aerosol-forming substrate is provided. Thus, the resistance of the heating element will be higher after a predetermined time when the heating element is dry compared to when the heating element is wet.

[0030] The electrical property determined during application of the power pulse may be the rate of change of the resistance of the heating element over a given time. As noted above, when a heating element is not provided with a liquid aerosol-forming substrate, its cooling rate will be slower than when a liquid aerosol-forming substrate is provided. Thus, the rate of change of the resistance of the heating element over a given time may provide an indication of whether the heating element is wet or dry.

[0031] The electrical characteristic determined during the application of the power pulse may be the resistance of the heating element after a predetermined rate of change of resistance is reached. If the duration of the power pulse is long enough, the temperature of the heating element will stabilize at a certain temperature due to heat loss, either to the surroundings in the case of a dry mesh or to the aerosol in the case of a wet mesh. Once the temperature stabilizes, the rate of change of resistance approaches zero. This occurs at a higher temperature, and therefore a higher resistance, in the case of a dry mesh; therefore, this characteristic may provide an indication of whether the heating element is wet or dry.

[0032] The electrical characteristic used to determine whether the heating element is supplied with a liquid aerosol-forming substrate may be selected from one or more of the above. Values for one or more of the above electrical characteristics may be stored in a memory of the aerosol-generating system. By comparing the electrical characteristic with one or more values stored in the memory, the aerosol-generating system can determine whether the heating element is supplied with a liquid aerosol-forming substrate.

[0033] According to one embodiment of the present disclosure, an aerosol generation system is provided. The aerosol generation system may include an aerosol generation device. The aerosol generation system may include a cartridge. The cartridge may include a liquid storage portion for holding a liquid aerosol-forming substrate. The cartridge may include a heating element for heating the liquid aerosol-forming substrate. The cartridge may be configured to supply the liquid aerosol-forming substrate to the heating element. The cartridge may be configured to be removably coupled to the aerosol generation device. The aerosol generation device may include a power source for supplying power to the heating element. The aerosol generation device may include control circuitry for controlling the supply of power to the heating element. The control circuitry may be configured to provide the power supply to the heating element. The control circuitry may be configured to monitor an electrical parameter indicative of the temperature of the heating element. The control circuitry may be configured to determine whether the electrical parameter is greater than a maximum threshold, indicating a threshold temperature of the heating element has been exceeded. The control circuitry may be configured to determine whether the electrical parameter is less than a minimum threshold, indicating a threshold temperature of the heating element has been exceeded. The control circuitry may be configured to interrupt the supply of power to the heating element when the threshold temperature is exceeded. The control circuitry may be configured to allow the heating element to cool to a temperature where the electrical parameter is below the maximum threshold. The control circuit may be configured to allow the heating element to cool to a temperature where the electrical parameter is above a minimum threshold. After cooling, the control circuit may be configured to determine whether the heating element is supplied with a liquid aerosol-forming substrate. The control circuit may be configured to disable the power source if the heating element is not supplied with a liquid aerosol-forming substrate.

[0034] According to an embodiment of the present disclosure, there is provided an aerosol generation system including an aerosol generating device and a cartridge including a liquid storage portion for holding a liquid aerosol-forming substrate and a heating element for heating the liquid aerosol-forming substrate. The cartridge is configured to supply the liquid aerosol-forming substrate to the heating element and be removably connectable to the aerosol generating device. The aerosol generating device includes a power supply for supplying power to the heating element and a control circuit for controlling the supply of power to the heating element. The control circuit is configured to provide power to the heating element, monitor an electrical parameter indicative of the temperature of the heating element, determine whether the electrical parameter is greater than a maximum threshold or less than a minimum threshold indicating that a threshold temperature of the heating element has been exceeded, interrupt the supply of power to the heating element when the threshold temperature is exceeded, allow the heating element to cool to a temperature where the electrical parameter falls below the maximum threshold or exceeds the minimum threshold, determine whether a liquid aerosol-forming substrate is being supplied to the heating element after cooling, and disable the power supply if a liquid aerosol-forming substrate is not being supplied to the heating element.

[0035] The aerosol generating device can be configured to disable power until the cartridge is replaced or the liquid aerosol-forming substrate in the liquid reservoir is replenished, preventing use of the device when there is insufficient liquid aerosol-forming substrate and reducing the possibility of undesirable by-products.

[0036] The aerosol generating system may be a resistively heated aerosol generating system. The control circuit may be configured to monitor the electrical resistance of the heating element. The control circuit may be configured to determine whether the electrical resistance is greater than a maximum threshold, indicating that a threshold temperature of the heating element has been exceeded.

[0037] Monitoring the electrical parameters of the heating element may include monitoring the electrical conductance of the heating element, and the control circuit may be configured to determine whether the electrical conductance is less than a minimum threshold value indicating that a threshold temperature of the heating element has been exceeded.

[0038] The heating element may include an electrically resistive heating element. The heating element may be made from any suitable conductive material. Suitable materials include, but are not limited to, semiconductors such as doped ceramics, "conductive" ceramics (e.g., molybdenum disilicide), carbon, graphite, metals, alloys, and composites made of ceramic and metallic materials. Such composites may include doped or undoped ceramics. An example of a suitable doped ceramic includes doped silicon carbide. Examples of suitable metals include titanium, zirconium, tantalum, and platinum group metals. Examples of suitable alloys include stainless steel, constantan, nickel-containing, cobalt-containing, chromium-containing, aluminum-containing, titanium-containing, zirconium-containing, hafnium-containing, niobium-containing, molybdenum-containing, tantalum-containing, tungsten-containing, tin-containing, gallium-containing, manganese-containing, and iron-containing alloys, as well as nickel-, iron-, cobalt-, and stainless steel-based superalloys, Timetal®, iron-aluminum-based alloys, and iron-manganese-aluminum-based alloys. Timetal® is a registered trademark of Titanium Metals Corporation. The heating element may be made from stainless steel, for example, 300 series stainless steels such as AISI 304, 316, 304L, and 316L.

[0039] Additionally, the heating element may comprise a combination of the above materials. A combination of materials may be used to improve control of the resistance of the heating element. For example, a material with a high resistivity may be combined with a material with a low resistivity. This may be advantageous if one of the materials is more advantageous from another perspective, such as price, machinability, or other physical and chemical parameters. Advantageously, high resistance heating allows for more efficient use of battery energy.

[0040] The aerosol generating system may be an induction heating aerosol generating system. The induction aerosol generating system may include an inductor. The heating element may include a susceptor. The inductor may be configured to generate an alternating magnetic field for heating the susceptor and generating an aerosol from a liquid aerosol-forming substrate supplied to the susceptor. The susceptor may be arranged to be heated by the inductor.

[0041] As used herein, "susceptor" means an element that can be heated by penetration by an alternating magnetic field. The susceptor is typically heatable by at least one of Joule heating through the induction of eddy currents in the susceptor and hysteresis losses.

[0042] In an induction aerosol generation system, monitoring the electrical resistance of a heating element can include monitoring the equivalent resistance of an inductor. When referring to an inductor, the term "equivalent resistance" refers to the resistance of the inductor as seen by an electrical circuit during operation. The equivalent resistance includes resistive losses in the inductor's windings in series with the apparent resistance of the susceptor. Therefore, the equivalent series resistance of an inductor is equal to the sum of the resistive losses in the inductor's windings and the apparent resistance of the susceptor. Resistive losses in the coil's windings, especially at the inductor's operating frequency, are primarily due to skin-effect losses in the inductor's windings. The apparent resistance of the susceptor is the additional resistance seen by an electrical circuit when the susceptor is inductively coupled to the inductor and is primarily due to eddy currents and hysteresis losses within the susceptor. In circuit diagrams, the equivalent resistance is depicted as a resistance in series with the inductor. The equivalent resistance of an inductor also has a positive relationship with temperature; i.e., as the temperature of the susceptor increases, the equivalent resistance of the susceptor also increases.

[0043] Monitoring the electrical parameters of the heating element may include monitoring the equivalent conductance of the inductor, which is simply the reciprocal of the equivalent resistance. The control circuit may be configured to determine whether the equivalent conductance is less than a minimum threshold value that indicates that a threshold temperature of the heating element has been exceeded.

[0044] The susceptor may be made of any suitable electrically conductive material. Suitable materials include, but are not limited to, graphite, molybdenum, silicon carbide, stainless steel, niobium, and aluminum. The susceptor may also be a ferrite element. The material and geometry of the susceptor may be selected to provide the desired electrical resistance and heat generation.

[0045] The susceptor may comprise a magnetic material that can be heated by penetration by an alternating magnetic field. As used herein, the term "magnetic material" is used to describe a material that can interact with a magnetic field, including both paramagnetic and ferromagnetic materials. The magnetic material may be any suitable magnetic material that can be heated by penetration by an alternating magnetic field. In some preferred embodiments, the magnetic material comprises a ferritic stainless steel. Suitable ferritic stainless steels include SAE 400 series stainless steels, such as SAE types 409, 410, 420, and 430 stainless steel.

[0046] The heating element may have any suitable form. For example, the heating element may include a mesh, a flat spiral coil, a fiber, or a fabric. The heating element may be fluid permeable.

[0047] In some preferred embodiments, the heating element is planar. A planar heating element may extend in a substantially plane.

[0048] In some preferred embodiments, the heating element comprises a mesh. The heating element may include an array of filaments forming a mesh. As used herein, the term "mesh" encompasses grids and arrays of filaments having spaces therebetween. The term mesh also includes woven and nonwoven fabrics.

[0049] The filaments may define gaps between them, and the gaps may have a width of 10 micrometers to 100 micrometers. Preferably, the filaments create capillary action within the gaps so that, in use, source liquid is drawn into the gaps, increasing the contact area between the heating element and the liquid.

[0050] The filaments may form a mesh with a size of 160 to 600 mesh US (+ / - 10%) (i.e., 160 to 600 filaments per inch (+ / - 10%)). The gap width may be 35 micrometers to 140 micrometers, or 25 micrometers to 75 micrometers. For example, the gap width may be 40 micrometers or 63 micrometers. The percentage open area of the mesh, which is the ratio of the gap area to the total area of the mesh, is preferably 25 to 56%. The mesh may be formed using different types of weave or lattice structures. Alternatively, the filaments may be composed of a circular array of filaments arranged parallel to one another.

[0051] The filaments may be formed by etching a sheet material such as foil. This may be particularly advantageous when the heater assembly comprises an array of parallel filaments. Where the heating element comprises a mesh or fabric of filaments, the filaments may be individually formed or woven together.

[0052] Preferably, the mesh is sintered. The filaments of the mesh may be sintered together. Advantageously, sintering the mesh creates an electrical bond between the filaments extending in different directions. In particular, when the mesh comprises one or more woven and nonwoven fabrics, it is advantageous to sinter the mesh so that an electrical bond is created between overlapping filaments.

[0053] A mesh may also be characterized by its ability to retain liquid, as is well known in the art.

[0054] The filaments of the mesh may have a diameter of 8 micrometers to 100 micrometers, 30 micrometers to 100 micrometers, 8 micrometers to 50 micrometers, or 8 micrometers to 39 micrometers. The filaments of the mesh may have a diameter of 50 micrometers. The filaments of the mesh may have any suitable cross-section. For example, the filaments may have a round cross-section or a flat cross-section.

[0055] Advantageously, the mesh heating element may have a relative permeability of 1 to 40,000. In induction heating systems, it is desirable to be able to use materials with lower permeability when it is desired to rely mostly on eddy currents for heating, and materials with higher permeability when hysteresis effects are desired. Preferably, the material has a relative permeability of 500 to 40,000. This will provide efficient heating of the mesh susceptor.

[0056] In some embodiments, the cartridge comprises a heater assembly. The heater assembly comprises a heating element. The heater assembly may further comprise a liquid transfer element. The liquid transfer element may be in fluid communication with the heating element. The liquid transfer element may be in fluid communication with the liquid storage portion. The liquid transfer element may be arranged to transfer the liquid aerosol-forming substrate from the liquid storage portion to the heating element. In particular, the liquid transfer element may be arranged to transfer the liquid aerosol-forming substrate from the liquid storage portion across a major surface of the heating element. The heating element may be fixed to the liquid transfer element. The heating element may be integral with the liquid transfer element. The provision of the liquid transfer element improves wetting of the heating element, thereby increasing aerosol generation by the system.

[0057] In some preferred embodiments, the liquid transfer element is a wicking element, which may allow the heating element to be made from materials that do not themselves provide good wicking or wetting performance.

[0058] The heater assembly may include multiple heating elements. When the heater assembly includes multiple heating elements and liquid transfer elements, each heating element may be disposed in fluid communication with a liquid transfer element. The heater assembly may include multiple heating elements and multiple wicking elements.

[0059] In some preferred embodiments, the heater assembly includes a first heating element and a second heating element, the second heating element being spaced apart from the first heating element. A wicking element may be disposed within the space between the first and second heating elements. In some particularly preferred embodiments, the first heating element, the second heating element, and the wicking element are substantially planar, the first heating element being disposed on a first side of the planar wicking element, and the second heating element being disposed on a second side of the planar wicking element opposite the first side.

[0060] The heater assembly may comprise a heating region and at least one mounting region. The heating region is a region of the heater assembly configured to be heated to a temperature required to vaporize the aerosol-forming substrate upon penetration by a suitable alternating magnetic field. The at least one mounting region of the heater assembly is a region configured to contact the cartridge housing or heating element holder. In some preferred embodiments, the at least one mounting region extends into the liquid reservoir.

[0061] In an inductively heated aerosol generating system, the heater assembly may comprise a susceptor assembly, or the heating element may replace the susceptor.

[0062] When the liquid transfer assembly includes a wicking element, the wicking element may include a capillary material. A capillary material is a material capable of transferring liquid from one end of the material to another by capillary action. The capillary material may have a fibrous or spongy structure. Preferably, the capillary material includes a bundle of capillaries. For example, the capillary material may include multiple fibers or threads or other fine tubes. The fibers or threads may be generally aligned to transport the liquid aerosol-forming substrate toward the heating element. In some embodiments, the capillary material may include a spongy or foam-like material. The structure of the capillary material may form multiple small holes or tubes through which the liquid aerosol-forming substrate can be transferred by capillary action. When the susceptor element includes gaps or openings, the capillary material may extend into the gaps or openings in the susceptor element. The susceptor element may draw the liquid aerosol-forming substrate into the gaps or openings by capillary action.

[0063] The wicking element may comprise an electrically insulating material. The wicking element may comprise a thermally insulating material. The wicking element may comprise a hydrophilic material. The wicking element may comprise an oleophilic material. Advantageously, forming the wicking element from a hydrophilic or oleophilic material may facilitate transport of the aerosol-forming substrate through the wicking element.

[0064] The wicking element may comprise a non-metallic material. Examples of suitable materials for the wicking element include sponge or foam materials, ceramic or graphite-based materials in the form of fibers or sintered powders, expanded metal or plastic materials, and fibrous materials, such as spun or extruded fibers (such as cellulose acetate, polyester, or bonded polyolefin, polyethylene, terylene, or polypropylene fibers, nylon fibers, or ceramics). Suitable materials for the wicking element may include cellulose materials such as cotton or rayon. Preferably, the wicking element may comprise rayon. The wicking element may consist of rayon. Wicking elements comprising porous ceramic materials may be particularly advantageous when one or both of the heating elements comprise a conductive material deposited on the wicking element. Wicking elements comprising porous ceramic materials may advantageously be the substrate for manufacturing processes involving the deposition of conductive materials.

[0065] In some embodiments, the heating element may be part of the aerosol-generating device rather than the cartridge, and in such embodiments, the cartridge may be configured to convey the aerosol-forming substrate to the heating element within the device, for example, using a liquid transfer element.

[0066] The cartridge may include a liquid storage portion or reservoir for holding a liquid aerosol-forming substrate. As used herein, the term "aerosol-forming substrate" refers to a substrate capable of releasing a volatile compound that can form an aerosol. The volatile compound may be released by heating the liquid aerosol-forming substrate.

[0067] The aerosol-forming substrate may be liquid at room temperature. The aerosol-forming substrate may contain both liquid and solid components. The liquid aerosol-forming substrate may contain nicotine. The nicotine-containing liquid aerosol-forming substrate may be a nicotine salt matrix. The liquid aerosol-forming substrate may contain plant-derived material. The liquid aerosol-forming substrate may contain tobacco. The liquid aerosol-forming substrate may contain tobacco-containing material containing volatile tobacco flavour compounds that are released from the aerosol-forming substrate on heating. The liquid aerosol-forming substrate may contain homogenised tobacco material. The liquid aerosol-forming substrate may contain non-tobacco-containing material. The liquid aerosol-forming substrate may contain homogenised plant-derived material.

[0068] The liquid aerosol-forming substrate may include one or more aerosol formers. The aerosol former is any suitable known compound or mixture of compounds that facilitates the formation of a dense, stable aerosol during use and is substantially resistant to thermal decomposition at the operating temperature of the system. Examples of suitable aerosol formers include glycerin and propylene glycol. Suitable aerosol formers are well known in the art and include, but are not limited to, polyhydric alcohols (e.g., triethylene glycol, 1,3-butanediol, glycerin), esters of polyhydric alcohols (e.g., glycerol monoacetate, diacetate, or triacetate), and aliphatic esters of monocarboxylic, dicarboxylic, or polycarboxylic acids (e.g., dimethyl dodecanedioate, dimethyl tetradecanedioate). The liquid aerosol-forming substrate may include water, solvents, ethanol, plant extracts, and natural or artificial flavors.

[0069] The liquid aerosol-forming substrate may comprise nicotine and at least one aerosol former. The aerosol former may be glycerin or propylene glycol. The aerosol former may comprise both glycerin and propylene glycol. The liquid aerosol-forming substrate may have a nicotine concentration of about 0.5% to about 10%, for example about 2%.

[0070] The cartridge may have a mouth end through which the generated aerosol may be drawn by a user. The cartridge may have a connecting end configured to couple the cartridge to an aerosol generating device.

[0071] The cartridge may define an air inlet. The air inlet may be located at or around the connecting end of the cartridge. The cartridge may define a mouth-end opening. A user may be able to draw aerosol generated from the cartridge through the mouth-end opening. The cartridge may define an air flow path extending from the air inlet to the air outlet. The enclosed air flow path may extend from the air inlet, through the susceptor element, to the mouth-end opening.

[0072] The enclosed air flow path may pass through the liquid reservoir. For example, the liquid reservoir may have an annular cross-section defining an interior passage, and the air flow path may extend through the interior passage of the liquid reservoir.

[0073] The cartridge may include an outer housing. The outer housing may be formed from a durable material. The outer housing may be formed from a liquid-impermeable material. The outer housing may be formed from a moldable plastic material, such as polypropylene (PP) or polyethylene terephthalate (PET). The outer housing of the cartridge may define a liquid storage portion or a portion of a reservoir. The outer housing may define the liquid storage portion. The outer housing and the liquid storage portion may be integrally formed. Alternatively, the liquid storage portion may be formed separately from the outer housing and disposed within the outer housing.

[0074] The aerosol generating device may include a housing. The housing may be elongated. The housing may comprise any suitable material or combination of materials. Examples of suitable materials include metals, alloys, plastics, or composites containing one or more of these materials, or thermoplastics suitable for food or pharmaceutical applications, such as polypropylene, polyetheretherketone (PEEK), and polyethylene. Preferably, the material is lightweight and not brittle.

[0075] The aerosol generator housing may define a cavity for receiving portions of the cartridge. The aerosol generator may include one or more air inlets. The one or more air inlets may allow ambient air to be drawn into the cavity.

[0076] The aerosol generating device may have a connecting end configured to connect the aerosol generating device to the cartridge. The connecting end may include a cavity for receiving the cartridge.

[0077] The aerosol generating device may have a distal end opposite the connecting end, which may include an electrical connector configured to connect the aerosol generating device to an electrical connector of an external power source for charging the power source of the aerosol generating device.

[0078] In an induction-heated aerosol generation system, the inductor may have any suitable form. The inductor may be an inductor coil. The inductor coil may be a tubular coil, a helical coil, or a planar or flat coil. The aerosol generation system may further comprise at least one magnetic flux concentrator arranged to contain the alternating magnetic field generated by the inductor.

[0079] The aerosol generation system may include any suitable number of inductors. The aerosol generation system may include one inductor. The aerosol generation system may include multiple inductors. The aerosol generation system may include one, two, three, four, five, six, seven, or eight inductors.

[0080] An inductor coil may be disposed in or around a cavity for receiving the cartridge, the inductor coil preferably being disposed to generate an alternating magnetic field within the cavity, and the inductor coil may at least partially surround the cavity.

[0081] The power source may be any suitable power source. Preferably, the power source is a DC power source. The power source may be a battery. The battery may be a lithium-based battery, such as a lithium cobalt battery, a lithium iron phosphate battery, a lithium titanate battery, or a lithium polymer battery. The battery may be a nickel-metal hydride battery or a nickel-cadmium battery. The power source may be another form of charge storage device, such as a capacitor. The power source may be rechargeable and configured for numerous charge-discharge cycles. The power source may have a capacity that allows for the storage of energy sufficient for one or more user experiences with the aerosol generation system; for example, the power source may have a capacity sufficient to allow continuous generation of aerosol for approximately six minutes, or a multiple of six minutes, corresponding to the typical time it takes to smoke one conventional cigarette. In another embodiment, the power source may have a capacity sufficient to allow for a predetermined number of puffs or for discontinuous activation of the aerosol generation system.

[0082] The control circuitry may include any suitable controller or electrical component. The controller may include a memory. Information for implementing the above-described methods 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 circuit capable of providing control. The control circuitry may be configured to provide power to the heating element continuously after activation of the device, or may be configured to provide power intermittently, such as between puffs. Power may be supplied to the heating element in the form of current pulses, for example, by pulse-width modulation (PWM).

[0083] In an induction-heated aerosol generating system, the control circuit can be configured to supply an alternating current to the inductor. As used herein, "alternating current" means a current that periodically reverses direction. The alternating current can have any suitable frequency. A suitable frequency for the alternating current can be 100 kilohertz (kHz) to 30 megahertz (MHz). If the inductor is a helical inductor coil or a tubular inductor coil, the alternating current can have a frequency of 500 kilohertz (kHz) to 30 megahertz (MHz). If the inductor is a planar inductor coil, the alternating current may have a frequency of 100 kilohertz (kHz) to 1 megahertz (MHz).

[0084] Driving an alternating current through the inductor causes the inductor to generate an alternating magnetic field. The alternating magnetic field can have any suitable frequency for heating the heating region of the susceptor element located within the alternating magnetic field. A suitable frequency for the alternating magnetic field can be between 100 kilohertz (kHz) and 30 megahertz (MHz).

[0085] The control circuit may include additional electronic components, for example, in some embodiments, the control circuit may include a sensor element, a switch element, or a display element.

[0086] In an induction heated aerosol generating system having a DC power source, the control circuit may further include a DC / AC converter. The DC / AC converter may be disposed between the DC power source and the inductor. The DC / AC converter may include a capacitor. The DC / AC converter may include an LC (inductor-capacitor) load network. In a preferred embodiment, the LC load network includes an inductor used to heat the susceptor and a capacitor. The inductor may be connected in series with the capacitor. In some embodiments, the inductor may be powered by a class E power amplifier or a class D power amplifier.

[0087] The aerosol generation system may include a puff detector. The puff detector may be configured to detect when a user inhales on the aerosol generation system. The puff detector may be any suitable sensor capable of detecting when a user inhales on the aerosol generation device. For example, the puff detector may be an airflow sensor. The control circuit may be configured to provide power to the heating element when the puff detector detects a user inhaling on the aerosol generation system.

[0088] Features described with respect to one of the above embodiments may equally be applied to other embodiments of the present disclosure. [Example]

[0089] The present invention is defined in the claims. However, below 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 any other example, embodiment, or aspect described herein.

[0090] Example 1: A method for controlling heating in an aerosol-generating system comprising a heating element for heating a liquid aerosol-forming substrate supplied to the heating element, the method comprising: providing a power supply to the heating element; monitoring an electrical parameter indicative of the temperature of the heating element; determining whether the electrical parameter is greater than a maximum threshold value or less than a minimum threshold value indicative of a threshold temperature of the heating element being exceeded; determining whether a liquid aerosol-forming substrate is being supplied to the heating element if the temperature of the heating element does not exceed the threshold temperature; and disabling the power supply if a liquid aerosol-forming substrate is not being supplied to the heating element. Example 2: 2. The method of example 1, further comprising interrupting power to the heating element when the threshold temperature is exceeded to allow the heating element to cool to a temperature where the electrical parameter is below a maximum threshold or above a minimum threshold. Example 3: The method of example 2, wherein the step of determining whether the heating element is supplied with a liquid aerosol-forming substrate is performed after cooling. Example 4: 4. The method of any one of claims 2 to 3, wherein the heating element is allowed to cool to a predetermined temperature below the threshold temperature. Example 5: 5. The method of any of examples 2-4, wherein allowing the heating element to cool comprises interrupting the power supply for a predetermined period of time. Example 6: The method of example 5, wherein the power supply is interrupted for 1 to 20 seconds, preferably 1 to 10 seconds, more preferably 1 to 5 seconds. Example 7: 7. The method of any of Examples 1-6, further comprising determining an initial value for the electrical parameter, wherein determining whether the electrical parameter is greater than a maximum threshold or less than a minimum threshold comprises determining whether a ratio between the initial value and a change in the value of the monitored electrical parameter is greater than a maximum threshold or less than a minimum threshold. Example 8: The method according to any one of Examples 1 to 7, further comprising reactivating the power supply when the heating element is supplied with a liquid aerosol-forming substrate. Example 9: The method of any of Examples 1-8, further comprising detecting a user puff before providing a supply of power to the heating element. Example 10: 10. The method of any of Examples 1-9, wherein monitoring the electrical parameter comprises monitoring the electrical resistance of the heating element, and the method comprises determining whether the electrical resistance is greater than a maximum threshold value, indicating that a threshold temperature of the heating element has been exceeded. Example 11: The method of example 10, wherein the aerosol generation system is an induction aerosol generation system including an inductor, the heating element is a susceptor arranged to be heated by the inductor, and monitoring the electrical resistance of the heating element includes monitoring the equivalent resistance of the inductor. Example 12: The method of any one of Examples 1 to 11, further comprising monitoring the cooling of the heating element. Example 13: 13. The method of example 12, wherein monitoring the cooling of the heating element comprises providing a probe pulse to the heating element and determining the electrical resistance of the heating element during the probe pulse. Example 14: 14. The method of example 12 or 13, wherein monitoring the cooling of the heating element comprises providing a plurality of probe pulses to the heating element and monitoring the electrical resistance of the heating element over the successive probe pulses. Example 15: The method according to any one of Examples 1 to 14, wherein the step of determining whether the heating element is supplied with a liquid aerosol-forming substrate comprises monitoring the cooling rate of the heating element. Example 16: 15. The method of any one of Examples 1 to 14, wherein the step of determining whether the heating element is supplied with a liquid aerosol-forming substrate comprises providing a power pulse to the heating element and determining an electrical characteristic of the heating element, the electrical characteristic being selected from one or more of: the resistance of the heating element after a predetermined elapsed time; the rate of change of the resistance of the heating element over a predetermined time; and the resistance of the heating element after reaching a predetermined rate of change of resistance. Example 17: 1. An aerosol generation system comprising: an aerosol generating device; and a cartridge having a liquid storage portion for holding a liquid aerosol-forming substrate and a heating element for heating the liquid aerosol-forming substrate, the cartridge being configured to supply the liquid aerosol-forming substrate to the heating element and be removably connectable to the aerosol generating device; the aerosol generating device comprising: a power supply for supplying power to the heating element; and a control circuit for controlling the supply of power to the heating element, the control circuit being configured to: provide a power supply to the heating element; monitor an electrical parameter indicative of the temperature of the heating element; determine whether the electrical parameter is greater than a maximum threshold or less than a minimum threshold indicating that a threshold temperature of the heating element has been exceeded; determine whether a liquid aerosol-forming substrate is being supplied to the heating element if the temperature of the heating element does not exceed the threshold temperature; and disable the power supply if a liquid aerosol-forming substrate is not being supplied to the heating element. Example 18: An aerosol generation system as described in Example 17, wherein the control circuit is further configured to interrupt the supply of power to the heating element when a threshold temperature is exceeded, allowing the heating element to cool to a temperature where the electrical parameter falls below a maximum threshold or exceeds a minimum threshold. Example 19: 19. The aerosol-generating system of example 18, wherein the control circuit is configured to determine whether a liquid aerosol-forming substrate is supplied to the heating element after cooling. Example 20: An aerosol generation system as described in Example 18 or 19, wherein the control circuit is configured to allow the heating element to be cooled to a predetermined temperature below the threshold temperature. Example 21: 21. The method of any of examples 18-20, wherein allowing the heating element to cool comprises interrupting the power supply for a predetermined period of time. Example 22: 22. The method of example 21, wherein the power supply is interrupted for 1 to 20 seconds, preferably 1 to 10 seconds, more preferably 1 to 5 seconds. Example 23: An aerosol generation system described in any of Examples 17 to 22, wherein monitoring the electrical parameters includes monitoring the electrical resistance of the heating element, and the control circuit is configured to determine whether the electrical resistance is greater than a maximum threshold value indicating that the threshold temperature of the heating element has been exceeded. Example 24: An aerosol generation system as described in Example 23, wherein the aerosol generating device is an induction aerosol generating device having an inductor, the heating element is a susceptor disposed in a cartridge heated by the inductor, and monitoring the electrical resistance includes monitoring the equivalent resistance of the inductor. Example 25: An aerosol generation system described in any of Examples 17 to 24, wherein the aerosol generation device is configured to disable power until the cartridge is replaced or the liquid aerosol-forming substrate in the liquid storage portion is replenished. Example 26: An aerosol generating system described in any of Examples 14 to 25, further comprising an indicator for indicating to a user that the cartridge needs to be replaced or the liquid aerosol-forming substrate in the liquid storage portion needs to be replenished. Example 27: 27. An aerosol generation system according to any one of Examples 14 to 26, wherein the electrical parameter is resistance and the maximum threshold resistance is at least 1.05 ohms, optionally between 1.05 ohms and 2.20 ohms. Example 28: An aerosol generation system described in any of Examples 14 to 26, wherein the electrical parameter is equivalent resistance and the maximum threshold equivalent resistance is at least 0.3 ohms, optionally between about 0.3 ohms and 2.5 ohms. Example 29: An aerosol generation system described in any of Examples 14 to 26, wherein the electrical parameter is electrical conductance and the control circuit is further configured to determine whether the electrical conductance is less than a minimum threshold value indicating that the threshold temperature of the heating element has been exceeded. Example 30: An aerosol generation system described in any of Examples 14 to 26, wherein the electrical parameter is equivalent conductance and the control circuit is further configured to determine whether the equivalent conductance is less than a minimum threshold value indicating that the threshold temperature of the heating element has been exceeded. Example 31: The aerosol generating system according to any one of Examples 14 to 30, wherein the heating element is a mesh.

[0091] The embodiments will now be further described with reference to the figures. [Brief explanation of the drawings]

[0092] [Figure 1A] FIG. 1A is a schematic cross-sectional view of an inductively heated aerosol generation system according to an embodiment of the present disclosure, the aerosol generation system comprising an aerosol generator and a cartridge, the cartridge being shown detached from the aerosol generator. [Figure 1B] FIG. 1B is a schematic cross-sectional view of the aerosol generation system of FIG. 1A, showing the cartridge attached to the device. [Figure 2A] FIG. 2A is a schematic cross-sectional view of the cartridge of FIGS. 1A and 1B. [Figure 2B] FIG. 2BA is a schematic cross-sectional view of the cartridge of FIG. 2A rotated 90 degrees about the central longitudinal axis of the cartridge. [Figure 3] FIG. 3 is a schematic circuit diagram of a portion of a control circuit for an inductively heated aerosol generating system according to an embodiment of the present disclosure. [Figure 4A]FIG. 4A is a schematic cross-sectional view of a resistively heated aerosol generation system according to an embodiment of the present disclosure, the aerosol generation system comprising an aerosol generator and a cartridge, the cartridge being shown removed from the aerosol generator. [Figure 4B] FIG. 4B is a schematic cross-sectional view of the aerosol generation system of FIG. 4A showing the cartridge attached to the device. [Figure 5] FIG. 5 is a schematic circuit diagram of a portion of a control circuit for a resistively heated aerosol generating system according to an embodiment of the present disclosure. [Figure 6] FIG. 6 is a flow diagram of a method for controlling an overheating or dry heat condition in an aerosol generating system according to an embodiment of the present disclosure. [Figure 7] FIG. 7 shows three graphs a), b), and c), where graph a) is a plot of resistance against time, showing the resistance profile for a normal heating cycle in which a liquid aerosol-forming substrate is supplied to the heating element, and the resistance profile for a dry heating condition; graph b) is a plot of power against time for a normal heating cycle; and graph c) is a plot of power against time for a dry heating condition. [Figure 8] FIG. 8 is a graph of resistance against time showing the resistance profiles for wet and dry heating conditions during a power pulse used to determine whether a heating element is supplied with a liquid aerosol-forming substrate. DETAILED DESCRIPTION OF THE INVENTION

[0093] 1A and 1B, schematic diagrams of an inductively heated aerosol generation system according to an embodiment of the present disclosure are shown. The aerosol generation system includes a cartridge 10 and an aerosol generation device 60. The cartridge 10 is configured to be received by the aerosol generation device 60. In FIG. 1A, the cartridge 10 is shown removed or separate from the aerosol generation device 60. In FIG. 1B, the cartridge 10 is shown received within and attached to the aerosol generation device 60. The aerosol generation system is portable and has a size comparable to a conventional cigar or cigarette.

[0094] 2A and 2B show schematic diagrams of the cartridge 10 of FIGS. 1A and 1B. The cartridge 10 has a mouth end and a connecting end opposite the mouth end. The connecting end is configured to connect the cartridge 10 to an aerosol generation device 60, as described in detail below.

[0095] The cartridge 10 includes an outer housing 36 formed from a moldable plastic material, such as polypropylene. The outer housing 36 defines a mouth-end opening 38 at the mouth end of the cartridge 10. The outer width of the outer housing 36 is greater at the mouth end of the cartridge 10 than at the connecting end. This forms a shoulder 37 between the mouth end and the connecting end. This allows the connecting end of the cartridge 10 to be received within a cavity 64 of the aerosol generation device 60, with the shoulder 37 positioning the cartridge 10 in the correct position within the device. This also allows the mouth end of the cartridge 10 to remain outside the aerosol generation device 60, allowing the mouth end to conform to the external shape of the aerosol generation device 60.

[0096] The cartridge 10 further includes a susceptor assembly 12 mounted on a susceptor holder 14. The susceptor assembly 12 is described in more detail below. The susceptor holder 14 includes a tubular body formed from a moldable plastic material, such as polypropylene. The tubular body of the susceptor holder 14 includes a sidewall defining an internal passage 26 having an open end and a central longitudinal axis. A pair of openings 28 extend through the sidewall on opposite sides of the tubular susceptor holder 14. The openings 28 are centrally disposed along the length of the susceptor holder 14. The susceptor holder 14 further includes a base 30 partially closing one end of the internal passage 26. The base 30 includes a plurality of air inlets 32 that allow air to be drawn into the internal passage 26 through the partially closed end.

[0097] The cartridge 10 further includes a liquid storage portion or liquid reservoir 44 for storing the liquid aerosol-forming substrate 42. The liquid reservoir 44 includes an annular space defined by the outer housing 36 and an internal passageway 48 extending between the mouth-end air outlet 38 and the open end of the internal passageway 26 of the susceptor holder 14.

[0098] The cartridge 10 further includes two channels 45 defined between the inner surface of the outer housing 36 and the outer surface of the susceptor holder 14. The two channels 45 extend from a liquid reservoir 44 at the mouth end of the cartridge 10 to the connecting end of the cartridge 10.

[0099] The cartridge 10 includes a susceptor assembly 12 mounted on a susceptor holder 14. The susceptor assembly 12 and susceptor holder 14 are located toward the connecting end of the cartridge 10. The susceptor assembly 12 is planar and thin, having a thickness dimension that is substantially less than its length and width dimensions. The susceptor assembly 12 is shaped in a rectangular configuration.

[0100] The susceptor assembly 12 comprises a susceptor including a first susceptor element 16 and a second susceptor element 18 (see FIG. 2B). The first susceptor element 16 and the second susceptor element 18 act as heating elements for heating the liquid aerosol-forming substrate, as described further below. The susceptor assembly 12 also comprises a wicking element for transporting the liquid aerosol-forming substrate 42 from a liquid reservoir 44 to the susceptor. The wicking element comprises a first wicking layer 20 and a second wicking layer 22 (see FIG. 2B). The susceptor assembly 12 further comprises a spacer element 24 (see FIG. 2B) between the first wicking layer 20 and the second wicking layer 22.

[0101] The first susceptor element 16, the second susceptor element 18, the first wicking layer 20, and the second wicking layer 22 each form a generally rectangular shape. Each susceptor layer has the same length and width dimensions. The width of the susceptor elements 16, 18 is smaller than the width of the first wicking layer 20 and the second wicking layer 22. Therefore, the first wicking layer 20 and the second wicking layer 22 each include an exposed outer portion of the wicking element that protrudes into two channels 45 through openings 28 in the sidewall of the susceptor holder 14. The first susceptor element 16 and the second susceptor element 18 are substantially identical and include a sintered mesh formed from stainless steel filaments suitable for heating by an alternating magnetic field. The first wicking layer 20 and the second wicking layer 22 include a porous body of cotton filaments. The first wicking layer 20 and the second wicking layer 22 are configured to supply the liquid aerosol-forming substrate 42 from the outer exposed surfaces of the first wicking layer 20 and the second wicking layer 22 to the first susceptor element 16 and the second susceptor element 18.

[0102] The first susceptor element 16 and the second susceptor element 18 are configured to be heated by the penetration of an alternating magnetic field to vaporize the liquid aerosol-forming substrate 42. The first wicking layer 20 and the second wicking layer 22 contact the susceptor holder 14 within the opening 28 such that the susceptor holder 14 supports the susceptor assembly 12 in place within the cartridge 10.

[0103] The susceptor assembly 12 is disposed within an interior passage 26 of the tubular susceptor holder 14 and extends in a plane parallel to the central longitudinal axis of the susceptor holder 14. The first susceptor element 16 and the second susceptor element 18 are disposed entirely within the interior passage 26 of the susceptor holder 14.

[0104] The aerosol generating device 60 includes a generally cylindrical housing 62 having a connecting end and a distal end opposite the connecting end. A cavity 64 for receiving the connecting end of the cartridge 10 is located at the connecting end of the device 60. An air inlet 65 is provided through the outer housing 62 at the base of the cavity 64 to allow ambient air to be drawn into the cavity 64 at the base. A smoke puff detector in the form of an airflow sensor 63 is disposed within the base of the cavity 64 to detect when air is being drawn into the cavity 64.

[0105] The aerosol generating device 60 comprises an induction heating arrangement disposed within the device outer housing 62. The induction heating arrangement includes an inductor coil 90, a control circuit 70, and a power source 72. The power source 72 comprises a rechargeable lithium iron phosphate battery that is rechargeable via an electrical connector (not shown) at the distal end of the device 60. The control circuit 70 is connected to the power source 72 and the inductor coil 90 such that the control circuit 70 controls the supply of power to the inductor coil 90. The control circuit 70 is configured to supply an alternating current to the inductor coil 90. The control circuit 70 is also connected to the airflow sensor 63.

[0106] 1B, the inductor coil 90 is positioned around the susceptor assembly 12 when the cartridge 10 is received in the cavity 64. The inductor coil 90 has a size and shape that matches the size and shape of the heating area of the susceptor element. The inductor coil 90 is made of copper wire having a circular cross-section and is disposed on a coil former element (not shown). The inductor coil 90 is a helical coil and has a circular cross-section when viewed parallel to the longitudinal axis of the aerosol generation device 60.

[0107] The inductor coil 90 is configured such that when an alternating current is supplied to the inductor coil, the inductor coil generates an alternating magnetic field in the region of the susceptor assembly 12 when the cartridge 10 is received within the cavity 64 .

[0108] The induction heating arrangement further includes a flux concentrator element 91. The flux concentrator element 91 has a larger radius than the inductor coil 90, and therefore partially surrounds the inductor coil 90. The flux concentrator element 91 is configured to reduce stray power losses from the generated magnetic field.

[0109] 1A and 1B is that it allows for wireless coupling between the induction coil 90 of the aerosol generator 160 and the susceptor assembly 12 disposed within the cartridge 10. The wireless coupling means that when the cartridge 10 is received within the aerosol generator 160, the liquid aerosol-forming substrate contained within the reservoir 44 can remain completely sealed during storage and operation.

[0110] In operation, when a user draws on the mouth end air outlet 38 of the cartridge 10, ambient air is drawn through the system air inlet 65 into the base of the cavity 64 and into the cartridge 10 through the air inlet 32 in the base 30 of the cartridge 10. The ambient air flows through the cartridge 10 from the base 30 to the mouth end air outlet 38, through the air passageway, through the susceptor assembly 12, and particularly through and across the first susceptor element 16 and the second susceptor element 18.

[0111] Airflow sensor 63 detects air being drawn through the system by a user puffing on mouth-end air outlet 38. Airflow sensor 63 sends a signal to control circuit 70 to activate the system. Control circuit 70 controls the supply of power from power supply 72 to inductor coil 90 when the system is activated.

[0112] When the system is activated, an alternating current is established in the inductor coil 90, which generates an alternating magnetic field in the cavity 64 that penetrates the susceptor assembly 12, heating the first susceptor element 16 and the second susceptor element 18. The liquid aerosol-forming substrate 42 in the second channel 45 is drawn into the susceptor assembly 12 through the first wicking layer 20 and the second wicking layer 22 to the first susceptor element 16 and the second susceptor element 18, respectively. The liquid aerosol-forming substrate 42 may also be transferred between the first wicking layer 20 and the second wicking layer 22 through the spacer element 24 (see FIG. 2B ). The liquid aerosol-forming substrate 42 of the first susceptor element 16 and the second susceptor element 18 are heated, and volatile compounds from the heated liquid aerosol-forming substrate are released into the air passage of the cartridge 10, which cools and forms an aerosol. The aerosol is entrained in air drawn through the air passageway of the cartridge 10 and is drawn out of the cartridge 10 at the mouth-end air outlet 38 for inhalation by the user.

[0113] FIG. 2A shows a schematic diagram of the cartridge 10 separate from the aerosol generating device 60 .

[0114] 2B shows a schematic view of the cartridge of FIG. 2A rotated 90 degrees about the central longitudinal axis of the cartridge. The layered structure of the susceptor assembly 12 can be seen in FIG. 2B, particularly the spacer element 24 positioned between and in contact with the first wicking layer 20 and the second wicking layer 22. The spacer element 24 is fluid-permeable and configured to allow movement of the liquid aerosol-forming substrate 42 between the first wicking layer 20 and the second wicking layer 22. The spacer element 24 forms a generally rectangular shape and has the same length and width dimensions as the first wicking layer 20 and the second wicking layer 22. The spacer element 24 comprises a porous body of cotton. The first susceptor element 16 and the second susceptor element 18 are disposed on the outer major surface of the susceptor assembly 12.

[0115] FIG. 3 shows a more detailed schematic circuit diagram of a portion of the control circuit 70 of the inductively heated aerosol generation system of FIGS. 1A and 1B. Circuit 74 of FIG. 3 is used to drive the induction coil 90 of the aerosol generation device 60 of FIGS. 1A and 1B and to determine one or more electrical parameters of the susceptors, i.e., the first susceptor element 16 and the second susceptor element 18, shown in the cartridge 10 of FIG. 2B. Circuit 74 has an input voltage Vin received at point X in FIG. 3. Circuit 74 includes a transistor switch Q1 and a first inductor L1, which function as a drive circuit for driving the induction coil 90 and the DC / AC voltage converter. Transistor switch Q1 includes a field-effect transistor (FET), e.g., a metal-oxide semiconductor field-effect transistor (MOSFET), and the first inductor L1 includes a radio frequency choke. The input voltage Vin is supplied to transistor switch Q1 via resistor R3 (described in more detail below) and the first inductor L1. The first inductor L1 serves to reduce radio frequencies that may be present at the input X if they enter the circuit. The gate G of the transistor switch Q1 receives a switching signal generated by another component of the control circuit (not shown) to turn the transistor switch Q1 on and off. The switching signal is a square wave with a substantially 50% duty cycle.

[0116] Circuit 74 further includes a first capacitor C1 connected in series with a second inductor L2, corresponding to the induction coil 90 of the aerosol generating device 60 of FIGS. 1A and 1B. The second capacitor C2 is connected between the drain D of transistor switch Q1 and electrical ground and functions as a shunt capacitor. The first capacitor C1, second inductor L2, and second capacitor C2 define a DC / AC voltage converter for converting the switching signal passed to transistor switch Q1 into an AC voltage across an equivalent resistance R4. The equivalent resistance R4 is equivalent to the ohmic resistance R of the second inductor L2 connected in series with the apparent ohmic resistance Ra of the susceptor elements 16 and 18. Resistor R4 is shown as a dotted line in FIG. 5 to indicate that it is not an actual resistor in the circuit, but rather is the equivalent resistance of the second inductor L2 and the susceptor elements 16 and 18.

[0117] Together, the first inductor L1, the transistor switch Q1, the first capacitor C1, the second inductor L2, and the second capacitor C2 form a Class E power amplifier. The general operating principles of Class E power amplifiers are well known and are described in detail in the article "Class-E RF Power Amplifiers" by Nathan O. Sokal, appearing in the January / February 1991 issue of QEX, a bimonthly magazine of the American Radio Relay League (ARRL), Newington, Connecticut, USA, pages 9-20, and therefore will not be further described here.

[0118] Using a Class E amplifier to power the second inductor L2 has proven to be highly efficient. This is because the circuit configuration prevents current from flowing through the transistor switch Q1 at the same time that voltage is applied to the transistor switch Q1. Therefore, virtually no energy is dissipated in the transistor switch Q1; instead, virtually all of the power is delivered to the load-equivalent resistor R4. Furthermore, the first capacitor C1 and the second inductor L2 form a series resonant circuit tuned to the switching frequency of the switching signal. The first capacitor C1 and the second inductor L2 function as a bandpass filter, allowing AC voltage signals to be transmitted to the load-equivalent resistor R4 only at the desired operating frequency of the second inductor L2. This means that power is transmitted to the load-equivalent resistor R4 only at the switching frequency of the switching signal, significantly suppressing harmonic frequencies, further improving efficiency.

[0119] Additionally, second inductor L2 and capacitors C1 and C2 form an LC load or matching network configured to operate with a low ohmic load and serve to match the output impedance of the DC / AC converter to the load equivalent resistance R4. In particular, capacitors C1 and C2 are tuned to reduce the ohmic loading of second inductor L2 to susceptor elements 16, 18, thereby dissipating more heat in susceptor elements 16, 18 compared to inductor L2, which is desirable for heating the aerosol-forming substrate.

[0120] Circuit 74 includes relatively few components compared to other drive and sensing circuits for aerosol generating devices, thus keeping the printed circuit board area required to mount these components small and helping to reduce the overall size of aerosol generating device 60. Furthermore, the use of a second inductor L2 for DC / AC conversion further reduces the number of components.

[0121] During operation, the second inductor L2 generates an alternating magnetic field that induces eddy currents in the susceptor elements 16, 18 of the cartridge 10, heating the susceptor elements 16, 18. As the susceptor elements 16, 18 heat during operation, a liquid aerosol-forming substrate supplied from the liquid reservoir 44 to the susceptor elements 16, 18 is vaporized through the first wicking layer 20 and the second wicking layer 22.

[0122] The inventors have recognized that while the liquid aerosol-forming substrate is supplied to the susceptor elements 16, 18 and the liquid aerosol-forming substrate is vaporized, the temperature and apparent resistance Ra of the susceptor elements 16, 18 remain substantially constant. However, if the supply of liquid aerosol-forming substrate to the susceptor elements 16, 18 is reduced or stopped, the temperature and apparent resistance Ra of the susceptor elements 16, 18 increase as the liquid reservoir 44 is depleted, increasing the equivalent resistance R4 and the DC current drawn by the heater module 74 at a constant voltage. ICD decreases.

[0123] The circuit of FIG. 3 further includes two sensor circuits, a current sensor circuit 80 and a voltage sensor circuit 82, for determining the equivalent resistance R4 (or the corresponding equivalent conductance G4).

[0124] The current sensor circuit 80 includes a current sensor in the form of a resistor R3 having a known value. Resistor R3 is connected in series between point X (which receives the input voltage Vin) and a first inductor L1. Thus, during operation, a DC current I passes through resistor R3. DC is substantially the same as the current drawn by circuit 74. Resistor R3 has a suitably low resistance value to help reduce resistive losses.

[0125] The current sensor circuit 80 further comprises a differential amplifier 84 having two inputs 84a and 84b connected to either side of the resistor R3 and therefore receiving a voltage signal from either side of the resistor R3. The differential amplifier 84 calculates the voltage received at its inputs 84a and 84b, i.e., the voltage drop V across the resistor R3. R3The differential amplifier 84 has an output 84c that outputs a voltage proportional to the difference between the voltage drop V across resistor R3. The output 84c of the differential amplifier 84 is connected to an analog-to-digital converter (ADC) input of the microcontroller MCU, which is also part of the control circuit 70 of the aerosol generating device 60 of FIGS. 1A and 1B. Thus, based on the signal received from the output 84c of the differential amplifier 84, the microcontroller MCU calculates the voltage drop V across resistor R3. R3 Because resistor R3 has a known value, the DC current IDC through resistor R3 that is supplied to circuit 74 can be determined by the microcontroller MCU by applying Ohm's law, as shown in equation (1). I DC =V R3 / R3 (1)

[0126] The voltage sensor circuit 82 includes a first resistor R1 and a second resistor R2 connected in series between point X in FIG. 3, where the input voltage Vin is received and electrically grounded. Resistors R1 and R2 form a voltage divider or divider and have equal resistance values so that the voltage at point Y between resistors R1 and R2 is equal to half the input voltage Vin. Point Y is connected to an analog-to-digital converter (ADC) input of the microcontroller MCU, providing the microcontroller MCU with a voltage signal corresponding to the voltage at point Y. This allows the microcontroller MCU to determine the input voltage Vin by doubling the voltage signal received from point Y. The voltage sensor circuit 82 allows the input voltage Vin to determine where the input voltage may change, for example, due to the use of a different battery voltage. Naturally, other resistance values can be used for resistors R1 and R2, with corresponding adjustments to the voltage calculations performed by the microcontroller. Resistors R1 and R2 have relatively high resistance values to reduce the current flowing through the voltage divider.

[0127] As mentioned above, a Class E power amplifier has been found to be a very efficient means of transferring power to a load equivalent resistor R4. As a result, the DC current I flows through resistor R3. DCdenotes the current supplied to the load equivalent resistor R4. Furthermore, since the resistance value of resistor R3 is relatively small, the voltage drop across resistor R3 is practically negligible. Therefore, the value of load equivalent resistor R4 can be determined by the microcontroller MCU by applying Ohm's law, as shown in equation (2). R4=Vin / I DC (2)

[0128] Equation (2) above can be rewritten to give the equivalent conductance G4 of the load equivalent resistance R4 as shown in equation (3) below: G4=I DC / Vin (3)

[0129] The equivalent conductance G4 is the reciprocal of the equivalent resistance R4. The advantage of determining the equivalent conductance G4 according to equation (3) is that when the voltage Vin is constant, the conductance is proportional to the DC current I DC is indicative of or directly related to the load resistance R4, which is generally the case for the majority of the battery's discharge cycle, or when a DC voltage regulator or converter is used to provide a constant voltage to circuit 74. Thus, the current supplied to circuit 74 and measured by current sensor circuit 80 provides a direct indication of the equivalent conductance G4 of the load equivalent resistance R4. Thus, the DC current I DC The measurement of can be used by the microcontroller 70 as a proxy for the value of the equivalent conductance G4 without determining the equivalent conductance G4 or the equivalent resistance R4, thereby reducing and simplifying the calculations that need to be performed.

[0130] 4A and 4B show schematic diagrams of a resistively heated aerosol generation system according to an embodiment of the present disclosure. The aerosol generation system includes a cartridge 110 and an aerosol generation device 160. The cartridge 110 is configured to be received by the aerosol generation device 160. In FIG. 4A, the cartridge 110 is shown removed or separated from the aerosol generation device 160. In FIG. 1B, the cartridge 110 is shown received within and attached to the aerosol generation device 160.

[0131] The resistively heated aerosol generating system of Figures 4A and 4B is similar to the inductively heated aerosol generating system of Figures 1A and 1B, and like reference numerals are used in Figures 4A and 4B to label like components. The primary difference between the aerosol generating system of Figures 4A and 4B is that it is configured to resistively heat a heating element within cartridge 110, and thus aerosol generating device 160 of Figures 4A and 4B does not have an inductive coil.

[0132] Instead of a susceptor assembly, the cartridge 110 of FIGS. 4A and 4B includes a heater assembly 112. However, the heater assembly 112 has substantially the same structure as the susceptor assembly 12 of FIGS. 1A and 1B. The heater assembly 112 includes a first heating element 116 and a second heating element 118. The first heating element 116 and the second heating element 118 are configured to heat the liquid aerosol-forming substrate. The heater assembly 112 also includes a wicking element for transporting the liquid aerosol-forming substrate 42 from the liquid reservoir 44 to the first heating element 116 and the second heating element 118. The wicking element includes a first wicking layer 120 and a second wicking layer 122. The heater assembly 112 further includes a spacer element (not shown) between the first wicking layer 120 and the second wicking layer 122.

[0133] The first heating element 116, first wicking layer 120, spacer elements, second wicking layer 122, and second heating element 118 of the heater assembly 112 of Figures 4A and 4B have the same shape, size, and layered structure as the first susceptor element 16, first wicking layer 20, spacer elements 24, second wicking layer 22, and second susceptor element 18 of the susceptor assembly 12 of Figures 1A, 1B, 2A, and 2B. The only difference is that the first heating element 116 and second heating element 118 include a sintered mesh formed from stainless steel filaments suitable for being resistively heated.

[0134] The first heating element 116 and the second heating element 118 are connected to cartridge electrical contacts 33 located within the base 30 of the cartridge 110. The cartridge electrical contacts protrude distally from the base 30 and are configured to correspond and contact device electrical contacts 35 located within the base of the cavity 64 when the cartridge 110 is received within the cavity 64, as shown in FIG. 4B . Thus, electrical contact between the aerosol generation device 160 and the cartridge 110 is established via contact between the cartridge electrical contacts 33 and the device electrical contacts 35 so that power can be supplied from the power source 72 to the first heating element 116 and the second heating element 118.

[0135] In operation, the airflow sensor 63 detects a user puff at the mouth-end opening 38, and the control circuit 70 of the aerosol generating device 160 activates the device, passing current from the power supply 72 to the first heating element 116 and the second heating element 118 to resistively heat the liquid aerosol-forming substrate and form an aerosol.

[0136] Figure 5 shows a more detailed schematic circuit diagram of a portion of the control circuit 70 of the resistively heated aerosol generation system of Figures 4A and 4B. The circuit 74 of Figure 5 is used to drive the heater assembly 112 of the aerosol generation device 160 of Figures 4A and 4B and to determine one or more electrical parameters of the resistive heaters, i.e., the first heating element 116 and the second heating element 118 of the aerosol generation device 160 of Figures 4A and 4B.

[0137] The circuit 200 includes a resistive heater R 1 , which includes a first heating element 116 and a second heating element 118 , connected to a power source via a connection 202 . H The power supply provides a voltage Vin. An additional resistor R5 having a known value connects the heater R H Heater R is inserted in series. H There is a voltage Vz at point Z of circuit 200 between R1 and additional resistor R5. Voltage Vz is midway between ground and voltage Vin.

[0138] The circuit 200 includes a heater R H In this example, the electrical parameters of the heater R H An analog input 204 on the microcontroller MCU is used to monitor the voltage Vin provided by connection 202. An analog input 206 on the microcontroller MCU is used to measure the voltage V at point Z. Z The microprocessor MCU monitors the heater R H To measure the resistance of the heater R H and the current through the heater R H The voltage across the resistor R is then determined using Ohm's law. H Determine.

[0139] Heater R H The voltage across the Z and heater R H The current through the heater R is I. H The resistance can be determined by Equation 4: R H =(Vin-V Z ) / I (4)

[0140] The current through resistor R5 is connected in series with heater R H That is, the current through resistor R5 and the current through heater R H The current through is current I. As mentioned above, resistor R5 has a known value. Current I can also be approximated by Equation 5: I=V Z / R5 (5)

[0141] Therefore, combining (4) and (5), R H =((Vin-V Z ) / V Z )×R5 (6)

[0142] Therefore, when the aerosol generating system is in use, the microprocessor MCU can measure Vin and Vz, and knowing the value of resistor R5, calculate the value of heater R at a particular temperature. H The resistance of the resistor can be determined.

[0143] As mentioned above, Heater R H The resistance of is related to temperature. If necessary, a linear approximation can be used to calculate the measured resistance R according to the following equation: H The temperature T corresponding to T=(R H / (AR0))+T0-1 / A (7) where A is the thermal conductivity resistance coefficient of the heater material and R0 is the resistance of the heater at ambient temperature T0.

[0144] 6 is a flow diagram of a method 300 for controlling an overheating or dry heat condition in an aerosol generating system according to an embodiment of the present disclosure. The method begins at step 302 when the device is activated, i.e., by a user puffing on the aerosol generating system. The user puff may be detected, for example, by the airflow sensor 63 of the aerosol generating device 60, 160 of FIGS. 1A, 1B, 4A, and 4B. Upon detection of the user puff, the control circuitry of the aerosol generating system provides power to the heating elements, i.e., the susceptor elements 16, 18 of the inductively heated aerosol generating device 60 of FIGS. 1A and 1B and the heating elements 116, 118 of the resistively heated aerosol generating device 160 of FIGS. 4A and 4B.

[0145] In step 304, method 300 monitors an electrical parameter of the heating element indicative of the temperature of the heating element to detect whether an overheating or dry heat condition has occurred. The electrical parameter can be monitored using the circuits of FIGS. 3 and 5. In an inductively heated aerosol generating system, the electrical parameter can be the equivalent resistance of the induction coil, as described above with respect to the circuit of FIG. 3. In a resistively heated aerosol generating system, the electrical parameter can be the resistance of the heating element, as described above with respect to the circuit of FIG. 5. In detecting whether dry heat has occurred, method 300 determines whether a threshold temperature of the heating element has been exceeded. To do this, the method determines whether the resistance or equivalent resistance of the heating element is greater than a maximum threshold value corresponding to the threshold temperature.

[0146] If a dry heat condition is not detected, method 300 simply remains at step 304, constantly monitoring for the occurrence of a dry heat condition during normal operation. If a dry heat condition is detected, step 306 of method 300 interrupts the power supply to the heating element from the power source so that the heating element no longer heats. The interruption of power means that even if a user attempts to take a puff on the aerosol generating system, the airflow sensor detecting airflow will not trigger the control circuit to send power to the heating element.

[0147] The power interruption should be maintained until the heating element has cooled below the threshold temperature. Thus, in step 308, method 300 monitors the cooling of the heating element. Monitoring the cooling of the heating element can be performed by providing multiple probe pulses to the heating element and monitoring the electrical resistance or equivalent resistance of the heating element over successive probe pulses. The probe pulses are significantly less power than full-power operation when the heating element is heated, typically comprising about 5 percent of the power provided during full-power operation. This low amount of power is incapable of heating the heating element, but still provides enough power to determine the resistance or equivalent resistance of the heating element to provide an indication of the heating element's temperature. Probe pulses can be applied periodically during times when power is interrupted to monitor the cooling of the heating element.

[0148] While the heating element is cooling, method 300 checks whether the temperature of the heating element has cooled below a maximum threshold temperature at step 310. If the temperature of the heating element has not cooled below the threshold temperature, method 300 returns to monitoring cooling at step 308. If the temperature of the heating element has cooled below the threshold temperature, method 300 moves to step 312, where it is determined whether a liquid aerosol-forming substrate is being supplied to the heating element.

[0149] As mentioned above, a dry heat condition can result from two different causes. The first cause is that the liquid aerosol-forming substrate in the cartridge is completely depleted, and therefore no liquid aerosol-forming substrate can be supplied to the heating element. In this case, the cartridge must be replaced. The second cause is that the user temporarily dries out the heating element by taking a particularly strong or long puff, causing the liquid aerosol-forming substrate present on the heating element to be expelled when the puff is initiated. In this case, the cartridge is not completely depleted, and the user still has puffs to consume. Therefore, the cartridge does not need to be replaced, but it takes time for the liquid aerosol-forming substrate to re-wet the heating element.

[0150] If the liquid aerosol-forming substrate still remains, the time it takes for the heating element to cool below the maximum threshold temperature should provide sufficient time for the heating element to re-wet. Determining whether a liquid aerosol-forming substrate is supplied to the heating element may be performed by monitoring the cooling rate of the heating element. A heating element that is wetted by a liquid aerosol-forming substrate will cool faster than a dry heating element.

[0151] Alternatively, determining whether a liquid aerosol-forming substrate is supplied to the heating element may be performed by providing a power pulse to the heating element and determining the electrical characteristics of the heating element. The power pulse is a full power pulse sufficient to cause the heating element to begin heating, and the electrical characteristics of the heating element can be determined when the heating element begins to heat. The power pulse is significantly shorter in duration than the period during which power is applied to the heating element to heat it during normal operation, but is long enough to determine the electrical characteristics of the heating element. The electrical characteristics of a wet heating element differ from the electrical characteristics of a dry heating element, as discussed in more detail below with respect to FIG. 8. The different electrical characteristics allow the method to determine whether a liquid aerosol-forming substrate is supplied to the heating element.

[0152] If a liquid aerosol-forming substrate is being supplied to the heating element, power to the heating element is resumed (not shown) and method 300 returns to step 304 to continue monitoring the dry heat condition. If the user finishes puffing while power is interrupted, the method returns before step 302 and waits for the device to start again with the next puff, which is not shown in Figure 6. If a liquid aerosol-forming substrate is not being supplied to the heating element, method 300 moves to step 314, where power is disabled and the aerosol generation system is prevented from being used until the cartridge is replaced.

[0153] 7 shows three graphs a), b), and c) relating to the operation of the aerosol-generating system during dry heating conditions and normal operation. Graph a) is a plot of resistance versus time, showing a first resistance profile or curve 401 for a normal heating cycle in which the heating element is supplied with a liquid aerosol-forming substrate, and a second resistance profile or curve 402 for a dry heating condition. In graph a), the resistance may be the electrical resistance of the resistive heating element or the equivalent resistance of an inductor heating the susceptor, and indicates the temperature of the heating element.

[0154] Referring to the first resistance curve 401 of the moistened heating element in graph a) of Figure 7, the user takes a puff at time t0, which causes the control circuit of the aerosol generating system to provide a supply of power to the heating element, causing the heating element to heat up. As can be seen in graph a) of Figure 7, the resistance of the heating element is a threshold resistance R TH The resistance of the first resistance curve 401 increases steadily as the temperature rises until it stabilizes at a normal operating or aerosolization temperature below 100°C. The user ends a puff at time t3, at which point power to the heating element is removed and the heating element begins to cool, as indicated by the steady decrease in resistance of the first resistance curve 401 after time t3.

[0155] Graph b) of Figure 7 is a plot of power versus time for a typical heating cycle illustrated in first resistance curve 401 of graph a) of Figure 7. When a user takes a puff at time t0, the control circuitry of the aerosol generation system provides a constant power supply to heat the heating element, as illustrated by first power curve 403 of graph b). The power supply to the heating element is stopped at time t3 when the user finishes their puff.

[0156] Referring to the second resistance curve 402 of the dry heating element in graph a) of Figure 7, the user takes a puff at time t0, which causes the control circuit of the aerosol-generating system to provide power to the heating element, causing the heating element to heat up. As can be seen in graph a) of Figure 7, the resistance of the heating element in second resistance curve 402 increases more rapidly than in first resistance curve 401 because the heating element is dry and no heat is being transferred to the liquid aerosol-forming substrate. The second resistance curve 402 reaches a threshold resistance R TH , indicating that the heating element has exceeded the threshold temperature and a dry heat condition has occurred.

[0157] According to the disclosed method, power to the heating element is interrupted at time t1 to allow the heating element to cool. However, the temperature and resistance of the heating element continue to increase for a short period of time before the heating element begins to cool due to a time lag in the heating element's response. The heating element then cools down at time t2 until its resistance reaches a threshold resistance R TH7, the resistance of the heating element decreases at a slower rate for a dry heating element, as shown by the second resistance curve 402, than for a wet heating element, as shown by the first resistance curve 401, indicating that the cooling rate in the dry heated state is slower than for a heating element supplied with a liquid aerosol-forming substrate. This characteristic can be used to determine whether a liquid aerosol-forming substrate is supplied to the heating element.

[0158] Graph c) of Figure 7 is a plot of power versus time for the dry heat condition illustrated by the second resistance curve 402 of graph a) of Figure 7. When the user takes a puff at time t0, the control circuit of the aerosol generation system provides a constant power supply to heat the heating element, as illustrated by the second power curve 404 of graph b). As can be seen in graph c), the power supply to the heating element increases until the resistance of the heating element reaches the threshold resistance R of graph a) of Figure 7. TH , is interrupted at time t1 to allow the heating element to cool. While power is interrupted, multiple probe pulses 405 are provided to the heating element to periodically determine its resistance, and therefore its temperature, so that the cooling of the heating element can be monitored, as described above with respect to FIG. 6. The resistance of the heating element is determined during the probe pulses 405 while monitoring the dry heating condition, i.e., in the same manner as determined using the method described with respect to the circuits of FIGS. 3 and 5. The probe pulses are of duration Δt p and has a period Δt between each probe pulse. i The duration of the probe pulses 405 and the interval between probe pulses can be varied to change the resolution at which the temperature is monitored.

[0159] The probe pulse 405 occurring at time t2 detects a threshold resistance R 2 indicating that the temperature of the heating element falls below the threshold temperature, as shown by the second resistance curve 402 in graph a) of FIG. THThe aerosol-generating system then determines that the resistance of the heating element has fallen below a certain value. The aerosol-generating system then attempts to determine whether a liquid aerosol-forming substrate is being supplied to the heating element. This can be done by monitoring the cooling rate of the heating element. As noted above, the cooling rate in a dry-heated state is slower than the cooling rate of a heating element supplied with a liquid aerosol-forming substrate, as shown in graph a) of FIG. 7. Note that in graph a) of FIG. 7, the resistance of the second resistance profile 402 continues to gradually decrease, i.e., at no point does the cooling rate increase, indicating that the liquid aerosol-forming substrate has been completely depleted and that the cartridge needs to be replaced.

[0160] Instead of monitoring the cooling rate of the heating element, the embodiment of FIG. 7 uses a power pulse 406 to determine whether a liquid aerosol-forming substrate is supplied to the heating element. As described above with reference to FIG. 6, the power pulse is a full power pulse sufficient to cause the heating element to begin heating, allowing the electrical characteristics of the heating element to be determined when the heating element begins to heat. The heating effect of the power pulse is not significant and is therefore not shown in graph a) of FIG. 7. The power pulse 406 is supplied to the heating element during the period between times t2 and t3, i.e., when the temperature of the heating element decreases below the threshold temperature. The electrical characteristics of the heating element during the power pulse, which are used to distinguish between heating elements that are supplied with a liquid aerosol-forming substrate and those that are not, are described below with reference to FIG. 8.

[0161] FIG. 8 is a graph of resistance versus time showing the resistance of a heating element during a power pulse, which can be used to determine whether a liquid aerosol-forming substrate is being supplied to the heating element. The resistance may be the electrical resistance of the resistive heating element or the equivalent resistance of an inductor heating a susceptor, and indicates the temperature of the heating element. The graph in FIG. 8 shows a first resistance profile or curve 501 for a dry heating element and a second resistance profile or curve 502 for a wet heating element. If the heating element is dry, when the control circuit of the aerosol-generating system delivers a power pulse to the heating element, the power pulse contains a constant amount of energy, but the temperature and resistance of the heating element increase rapidly, as shown in the first resistance curve 501. If the heating element is wet, the same power pulse causes the temperature and resistance to increase much more slowly, as shown in the second resistance curve 502. As a result, it is possible to distinguish between a wet and dry heating element and whether a liquid aerosol-forming substrate is being supplied to the heating element based on the rate of change of resistance. This approach monitors the thermal mass of the heating element. A wet heating element has a larger thermal mass than a dry heating element, and therefore its temperature will increase more slowly in response to energy applied to the element. By monitoring the thermal mass of the heating element during operation, it is possible to determine whether the heating element has only temporarily dried out or whether the supply of liquid aerosol-forming substrate has been depleted.

[0162] Electrical characteristics of the heating element that may be used to determine if liquid is being applied to the heating element include, but are not limited to, monitoring the resistance of the heating element after a predetermined elapsed time, monitoring the rate of change of the resistance of the heating element over a predetermined time, and monitoring the resistance of the heating element after a predetermined rate of change in resistance is reached. Additionally, the general shape of the resistance curves 501 and 502 can be used to determine if liquid is being applied to the heating element, for example, by storing data values in memory and determining which curve the measured resistance best fits.

[0163] For purposes of this specification and the appended claims, unless otherwise indicated, all numbers expressing amounts, quantities, percentages, and the like should be understood in all instances to be modified by the term "about." Also, all ranges include the disclosed maximum and minimum points, and include any intermediate ranges therein, which may or may not be specifically recited herein. Thus, in this context, the number A is understood as A ± five percent (5%) A. Within this context, the number A may be considered to include values that are within the typical standard error for measurement of the property it modifies. In some cases, such as when used in the appended claims, the number A may deviate by the percentages recited above, provided that the amount by which A deviates does not materially affect the basic and novel characteristics of the claimed invention. Also, all ranges include the disclosed maximum and minimum points, and include any intermediate ranges therein, which may or may not be specifically recited herein.

Claims

1. 1. A method for controlling heating in an aerosol-generating system comprising a heating element for heating a liquid aerosol-forming substrate supplied to the heating element, the method comprising: providing a power supply to the heating element; monitoring an electrical parameter indicative of the temperature of the heating element; determining whether the electrical parameter is greater than a maximum threshold or less than a minimum threshold, indicating that a threshold temperature of the heating element has been exceeded; interrupting the power supply to the heating element when the threshold temperature is exceeded to allow the heating element to cool to a temperature where the electrical parameter falls below the maximum threshold or exceeds the minimum threshold; After cooling, determining whether the liquid aerosol-forming substrate is supplied to the heating element; disabling the power supply when the liquid aerosol-forming substrate is not being supplied to the heating element.

2. 2. The method of claim 1, further comprising determining an initial value of the electrical parameter, wherein determining whether the electrical parameter is greater than a maximum threshold or less than a minimum threshold comprises determining whether a ratio of the initial value to a change in the value of the monitored electrical parameter is greater than a maximum threshold or less than a minimum threshold.

3. 3. The method of claim 1, further comprising reactivating the power supply when the heating element is supplied with the liquid aerosol-forming substrate.

4. The method of any one of claims 1 to 3, further comprising the step of detecting a user puff before providing power to the heating element.

5. 5. The method of claim 1, wherein monitoring the electrical parameter comprises monitoring an electrical resistance of the heating element, the method comprising determining whether the electrical resistance is greater than a maximum threshold value indicating that a threshold temperature of the heating element has been exceeded.

6. 6. The method of claim 5, wherein the aerosol generation system is an induction aerosol generation system including an inductor, the heating element is a susceptor arranged to be heated by the inductor, and monitoring the electrical resistance of the heating element includes monitoring the equivalent resistance of the inductor.

7. The method of any preceding claim, further comprising monitoring the cooling of the heating element.

8. The method of claim 7 , wherein monitoring the cooling of the heating element comprises providing a probe pulse to the heating element and determining an electrical resistance of the heating element during the probe pulse.

9. 9. The method of claim 7 or 8, wherein monitoring the cooling of the heating element comprises providing a plurality of probe pulses to the heating element and monitoring the electrical resistance of the heating element over successive probe pulses.

10. 10. The method according to claim 1, wherein the step of determining whether the heating element is supplied with a liquid aerosol-forming substrate comprises monitoring a cooling rate of the heating element.

11. The step of determining whether a liquid aerosol-forming substrate is supplied to the heating element comprises providing a power pulse to the heating element and determining an electrical characteristic of the heating element, the electrical characteristic comprising: - the resistance of the heating element after a predetermined time has elapsed; the rate of change of the resistance of the heating element over a given time; and - the resistance of the heating element after a predetermined rate of change of the resistance has been reached.

12. 1. An aerosol generating system comprising: an aerosol generator; a cartridge having a liquid storage portion for holding a liquid aerosol-forming substrate and a heating element for heating the liquid aerosol-forming substrate; the cartridge is configured to supply a liquid aerosol-forming substrate to the heating element and to be removably connectable to the aerosol generating device; the aerosol generating device comprises a power source for supplying power to the heating element, and a control circuit for controlling the power supply to the heating element; The control circuit providing a power source to the heating element; monitoring an electrical parameter indicative of the temperature of the heating element; determining whether the electrical parameter is greater than a maximum threshold or less than a minimum threshold, indicating that a threshold temperature of the heating element has been exceeded; interrupting the supply of power to the heating element when the threshold temperature is exceeded to allow the heating element to cool to a temperature where the electrical parameter falls below the maximum threshold or exceeds the minimum threshold; After cooling, it is determined whether the liquid aerosol-forming substrate is supplied to the heating element; An aerosol generating system configured to disable the power supply when the heating element is not supplied with the liquid aerosol-forming substrate.

13. 13. The aerosol generating system of claim 12, wherein monitoring the electrical parameters includes monitoring the electrical resistance of the heating element, and the control circuit is configured to determine whether the electrical resistance is greater than a maximum threshold value indicating that a threshold temperature of the heating element has been exceeded.

14. 14. The aerosol generation system of claim 13, wherein the aerosol generation device is an induction aerosol generation device having an inductor, the heating element is a susceptor disposed within the cartridge that is heated by the inductor, and monitoring the electrical resistance includes monitoring the equivalent resistance of the inductor.

15. 15. The aerosol generation system of claim 12, wherein the aerosol generation device is configured to disable the power supply until the cartridge is replaced or the liquid aerosol-forming substrate in the liquid storage portion is replenished.

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