Smoking device equipped with temperature sensing means

Abstract

An aerosol generating device (100) for generating an aerosol from an aerosol-generating article (200) is provided. The aerosol generating device comprises a cavity (10) for receiving the aerosol-generating article (200), a heater assembly for heating the aerosol-generating article received in the cavity, and a power source (142). The power source (142) is configured to provide power to the heater assembly and is controlled by a controller (140) to be operable in at least a low power mode in which no aerosol is generated, and a high power mode in which aerosol may be generated. The controller (140) is configured to initially control the power source to operate in the low power mode. In the low power mode, the controller (140) is configured to measure a parameter related to a rate of change of temperature of the heater assembly or a rate of change of temperature of the aerosol-generating article received in the cavity. The controller (140) is configured to switch from the low power mode to the high power mode only if the measured parameter meets a predetermined criterion. A method for detecting a fault in an aerosol generating system is provided.

Description

[Technical field]

[0001] The present disclosure relates to an aerosol generating device for generating an aerosol from an aerosol-generating article. The present disclosure also relates to a method of controlling a heater assembly of an aerosol generating device. [Background technology]

[0002] Aerosol-generating devices configured to generate an aerosol from an aerosol-forming substrate, such as a tobacco-containing substrate, are known in the art. Such devices typically generate an aerosol from a substrate through application of heat to the substrate, rather than combustion of the substrate. In use, the aerosol-generating device may receive the aerosol-forming substrate, for example, in a cavity or cavity of the device. The device may provide power to a heater assembly to generate heat, which is transferred to the aerosol-forming substrate to release volatile compounds that condense to form an aerosol. The heating may be the result of resistive heating of a heater element of the aerosol-generating device in thermal contact with the aerosol-forming substrate, or inductive heating of a susceptor element of the aerosol-generating device or aerosol-generating article, which is in thermal contact with the aerosol-forming substrate.

[0003] Typically, the aerosol generating device is reusable and the aerosol-forming substrate is contained within a disposable aerosol-generating article. During use, the aerosol-generating article is heated by the aerosol generating device to generate an aerosol. After a period of use, e.g. a certain number of puffs on the aerosol-generating article, the aerosol-forming substrate may become depleted. After the aerosol-forming substrate becomes depleted, the aerosol-generating article needs to be replaced with an unused aerosol-generating article before further use of the aerosol generating device.

[0004] There is a risk that a user may attempt, either intentionally or accidentally, to use an exhausted aerosol-forming substrate in an aerosol generating device, which is undesirable: for example, if an exhausted aerosol-forming substrate is heated, an insufficient aerosol may be generated, either in terms of the amount and / or chemistry of the aerosol.

[0005] Some aerosol generating devices are configured to perform two successive use sessions. Such aerosol generating devices may be configured to perform the second use session immediately after the end of the first use session. The aerosol-forming substrate may become depleted after a single use session. In such cases, the aerosol-generating article needs to be replaced between the first use session and the successive second use session. The risk that a user may try to reuse a depleted aerosol-forming substrate may be a particular problem in the context of such devices.

[0006] It is desirable to provide an aerosol generating device that can detect when a depleted aerosol-generating article has been used with the aerosol generating device, and it is particularly desirable to provide an aerosol generating device that can detect when a depleted aerosol-generating article has been used with the aerosol generating device immediately following a previous use session involving one or both of the aerosol generating device and the aerosol-generating article. Summary of the Invention

[0007] According to a first aspect, there is provided an aerosol generating device for generating an aerosol from an aerosol-generating article.

[0008] The aerosol generating device may comprise a cavity. The cavity may be for receiving an aerosol generating article.

[0009] The aerosol generating device may include a heater assembly for heating an aerosol-generating article received within the cavity.

[0010] The aerosol generating device may include a power source. The power source may be configured to provide power to the heater assembly. The power source may be controlled by a controller. The power source may be controlled by the controller to be operable at least in a low power mode in which no aerosol is generated. The power source may be controlled by the controller to be operable in a high power mode in which aerosol can be generated. The power source may be controlled by the controller to be operable at least in a low power mode and a high power mode.

[0011] The controller may be configured to control the power supply to initially operate in a low power mode.

[0012] In the low power mode, the controller may be configured to measure a parameter related to the rate of change of temperature of the heater assembly. In the low power mode, the controller may alternatively or additionally be configured to measure the rate of change of temperature of an aerosol-generating article received within the cavity.

[0013] The controller may be configured to switch from the low power mode to the high power mode only if a measured parameter meets a predetermined criteria.

[0014] The high power mode capable of generating aerosol may advantageously be the mode in which the controller is configured to operate the power supply during the main phase of use of the aerosol generating device in which aerosol is generated which is inhaled by a user of the device.

[0015] During the high power mode, the controller may be configured to control the power source to supply power to the heater assembly according to a predetermined heating profile. The predetermined heating profile may include heating the heater assembly or the aerosol-generating article to one or more target temperatures throughout the course of a use session. Throughout the predetermined heating profile, the heater assembly may be configured to generate an appropriate amount of aerosol from the aerosol-generating article for inhalation by a user during the use session.

[0016] The predetermined criterion may advantageously relate to an expected rate of change of temperature of the heater assembly or the aerosol-generating article when an unused aerosol-generating article is received within the cavity of the aerosol generating device. The controller may be configured to determine that an unused aerosol-generating article is received within the cavity if the predetermined criterion is met. The controller may be configured to determine that a depleted aerosol-generating article is received within the cavity if the predetermined criterion is not met.

[0017] By switching from a low power mode to a higher power mode only if a measured parameter (related to the rate of change of temperature) meets a predetermined criterion, the probability that the aerosol generating device is used with a depleted aerosol generating article in the high power mode may be reduced. The controller may advantageously not switch to the high power mode if a depleted aerosol generating article is received within the cavity. Hence, the controller may advantageously prevent a major phase of use of the aerosol generating device if a depleted aerosol generating article is detected. This may advantageously prevent a user from reusing a depleted aerosol generating article, thereby minimizing the risk of unsatisfactory aerosol generation during a usage session.

[0018] Having the controller configured to determine the presence of a depleted aerosol-generating article while the power source is configured to operate in a low power mode may advantageously mean that unused or depleted aerosol-generating articles can be detected by the controller with minimal power usage, which is particularly advantageous where the power source includes, for example, a battery.

[0019] Furthermore, as described below, detection of unused or depleted aerosol-generating articles using predetermined criteria may depend on deviations in the initial temperature of the heater assembly or aerosol-generating article from expected values, and the subsequent heat transfer between the two components. As such, parameters related to the rate of change of temperature may be advantageously measured in a low power mode in which the aerosol-generating article and heater assembly are not substantially heated. The control routine may not function effectively if implemented while the power supply is configured to operate in a high power mode.

[0020] The controller may be configured to switch from the low power mode to the error mode if the measured parameter does not meet a predetermined criterion. As described above, if the measured parameter does not meet a predetermined criterion, it may be determined that a depleted aerosol-generating article is received within the cavity.

[0021] In the error mode, the controller may be configured to indicate to a user of the aerosol generating device that a depleted aerosol-generating article has been received within the cavity. For example, the aerosol generating device may include a user interface or an indicator, such as a light. The controller may be configured to control the user interface or indicator to indicate that a depleted aerosol-generating article has been received within the cavity.

[0022] In the error mode, the controller may be configured to prevent the supply of power to the heater assembly.

[0023] As used herein, an aerosol-generating article that has not been previously heated and has not been depleted of the aerosol-generating substrate may be referred to as a "virgin" aerosol-generating article.

[0024] As used herein, a previously used aerosol-generating article may be referred to as an "exhausted" aerosol-generating article. The aerosol-generating article may be configured to be used for a predetermined number of puffs, for example, 4, 5, 6, 7, 8, 9, or 10 puffs, before being exhausted. An aerosol-generating article may be referred to as exhausted when the aerosol-generating article has been used with an aerosol generating device for a predetermined number of puffs.

[0025] During use of the aerosol-generating article, the article may be heated by the aerosol generating device, which may be configured to heat the aerosol-generating article when the controller is configured to operate the power supply in the high power mode.

[0026] An exhausted aerosol-generating article may have a temperature that is substantially above ambient temperature because, unlike an unused aerosol-generating article, it may have been previously heated The shorter the time since the aerosol-generating article was last used, the higher the temperature of the aerosol-generating article may be above ambient temperature.

[0027] An unused aerosol-generating article may have a temperature substantially equal to the ambient temperature when the aerosol-generating article is initially received within the cavity of the aerosol generating device. The temperature of an unused aerosol-generating article may be slightly above the ambient temperature, for example as a result of a user handling the aerosol-generating article before the aerosol-generating article is initially received within the cavity. However, the temperature of the aerosol-generating article, particularly the aerosol-forming substrate of the aerosol-generating article, may be equal to or lower than the first temperature, or may be equal to or lower than the ambient temperature, when the ambient temperature is higher than the first temperature. The first temperature may be between 25 and 40 degrees Celsius. The first temperature may be between 30 and 35 degrees Celsius. The first temperature may be equal to or lower than 40 degrees Celsius.

[0028] An unused aerosol-generating article may have a lower temperature than an exhausted aerosol-generating article immediately after use of the exhausted aerosol-generating article.

[0029] In some embodiments, the aerosol-generating article may comprise a susceptor element, in which case references to the temperature of the aerosol-generating article may correspond to the temperature of the susceptor element.

[0030] The heater assembly of the aerosol generating device may include a heater element, such as a resistive heater element or a susceptor element. The heater element may be configured to heat an aerosol-generating article received within the cavity when the controller is configured to control the power supply in the high power mode. The temperature of the heater assembly, and in particular the heater element of the heater assembly, after power is applied in the high power mode may be substantially above ambient temperature. The shorter the time since the aerosol generating device was last used in the high power mode, the higher the temperature of the heater assembly may be above ambient temperature.

[0031] If the heater assembly has not been used recently in the high power mode, the temperature of the heater assembly may be substantially equal to the ambient temperature.

[0032] Considering the temperature difference between unused and depleted aerosol-generating articles and recently used and recently unused heater assemblies, the rate of change of temperature of the aerosol-generating article or heater assembly may differ from the expected rate of change of temperature if a depleted aerosol-generating article is received in the cavity instead of an unused aerosol-generating article. Thus, whether a measured parameter (which may be related to the rate of change of temperature of the heater assembly or the rate of change of temperature of the aerosol-generating article) meets a predetermined criterion may be advantageously used to detect whether an unused aerosol-generating article has been received in the cavity.

[0033] The predetermined criteria may include a comparison of the magnitude of the measured parameter to a predetermined threshold.

[0034] In one embodiment, the predetermined criterion may relate to an expected rate of change of temperature of the heater assembly or aerosol-generating article when an unused aerosol-generating article is received within a cavity of the aerosol generating device.

[0035] Where the heater assembly includes a heater element, the predetermined criterion may relate to an expected rate of change of temperature of the heater assembly or aerosol-generating article when an unused aerosol-generating article is received within the cavity of the aerosol generating device if the heater assembly has not been used recently in a high power mode.

[0036] The predetermined criteria may include the magnitude of the measured parameter being less than a first predetermined threshold, preferably substantially equal to zero.

[0037] The first predetermined threshold may be a value of the measured parameter corresponding to a rate of change of temperature of the aerosol-generating article or heater assembly of less than 1 degree Celsius / second, preferably less than 0.5 degrees Celsius / second, and even more preferably less than 0.25 degrees Celsius / second. Preferably, the first predetermined threshold may be a magnitude of the measured parameter.

[0038] In this example, the first predetermined threshold may correspond to the maximum rate of change of temperature at which a depleted aerosol-generating article can be detected. In this example, the first predetermined threshold may be advantageously low because the expected rate of change of temperature of the aerosol-generating article or heater assembly is close to zero. This may be because an unused aerosol-generating article has a temperature that is substantially equal to the ambient temperature. This may also be because the heater assembly may have substantially the same temperature as the aerosol-generating article.

[0039] However, selecting a predetermined threshold value slightly above zero may advantageously take into account unintentional heating of the aerosol-generating article prior to insertion of the aerosol-generating article into the cavity, for example as a result of handling the aerosol-generating article.

[0040] If the magnitude of the measured parameter is greater than a predetermined threshold, the predetermined criteria may not be met. A magnitude of the measured parameter greater than a predetermined threshold may advantageously indicate that a depleted aerosol-generating article has been inserted into the heater assembly instead of an unused aerosol-generating article.

[0041] The depleted aerosol-generating article may have a temperature that is higher than the ambient temperature. Therefore, the rate of change of temperature of the depleted aerosol-generating article may be greater than the rate of change of temperature of an unused aerosol-generating article in this embodiment. Furthermore, the depleted aerosol-generating article may have a heating effect on the heater assembly. Therefore, the rate of change of temperature of the heater assembly may be positive.

[0042] The heater assembly may have a cooling effect on the aerosol-generating article. The air surrounding the article at ambient temperature may also have a cooling effect on the aerosol-generating article. Therefore, the rate of change of temperature of the aerosol-generating article may be negative.

[0043] Thus, the magnitude of the rate of change of temperature of the aerosol-generating article or heater assembly may be greater than a predetermined threshold, and thus the predetermined criteria may not be met and the presence of a depleted aerosol-generating article may be detected.

[0044] If the magnitude of the measured parameter is greater than a predetermined threshold, the predetermined criterion may not be met, and at least The measured parameter indicates that the rate of change of the heater assembly temperature is positive, or the measured parameter indicates that the rate of change of temperature of the aerosol-generating article is negative.

[0045] In another example, the predetermined criterion may relate to an expected rate of change of temperature of the heater assembly or aerosol-generating article when an unused aerosol-generating article is received within the cavity of an aerosol generating device that has recently been used in a high power mode, which may only be the case if the heater assembly itself includes a heater element.

[0046] The predetermined criteria may include a magnitude of the measured parameter being greater than a second predetermined threshold, which may be a value of the measured parameter corresponding to a rate of change of temperature of the aerosol-generating article or assembly of greater than 3 degrees Celsius / second, preferably greater than 5 degrees Celsius / second, preferably greater than 7 degrees Celsius / second, and even more preferably greater than 9 degrees Celsius / second.

[0047] An unused aerosol-generating article may have a substantially different temperature than a heater assembly that has recently been used in a high power mode, so there may be a temperature difference between the two components.

[0048] The heater assembly may be above ambient temperature. The heater assembly may have a temperature substantially higher than the temperature of an unused aerosol-generating article. Thus, an unused aerosol-generating article received within the cavity of the aerosol generating device may have a cooling effect on the heater assembly. The heater assembly may have a heating effect on an unused aerosol-generating article.

[0049] If the magnitude of the measured parameter is less than a second predetermined threshold, the predetermined criterion may not be met. If a depleted aerosol-generating article is instead inserted into the heater assembly, the predetermined criterion may not be met.

[0050] When a depleted aerosol-generating article is received in the cavity instead of an unused aerosol-generating article, the initial temperature of the aerosol-generating article may be closer to the temperature of the heater assembly than if an unused aerosol-generating article were received in the cavity. The cooling effect of the depleted aerosol-generating article on the heater assembly may be less than that on an unused aerosol-generating article. The heating effect of the heater assembly on the aerosol-generating article may be less than that on an unused aerosol-generating article. Hence, the rate of change of temperature of the aerosol-generating article may not exceed the second predetermined threshold. Thus, the predetermined criterion may not be met and the presence of a depleted aerosol-generating article may be detected.

[0051] If the magnitude of the measured parameter is less than a second predetermined threshold, the predetermined criteria may not be met and the measured parameter indicates that the rate of change of temperature of the heater assembly is negative.

[0052] If the aerosol generating device comprises a heater element, the controller may be configured to select the predetermined criteria based on an initial temperature of the heater element. Preferably, the controller may be configured to select a predetermined threshold to be used in the predetermined criteria based on the initial temperature of the heater element. Preferably, the controller may be configured to select whether the predetermined criteria includes whether the magnitude of the measured parameter is greater than, less than or equal to a predetermined threshold based on the initial temperature of the heater element.

[0053] For example, both the first and second predetermined thresholds described above may be stored in a memory of the controller, and the controller may be configured to select either the first predetermined threshold or the second predetermined threshold based on an initial temperature of the heater element.

[0054] Having the predetermined criterion be based on the initial temperature of the heater element advantageously allows the controller to select the predetermined criterion based on whether the heater assembly has been used recently, since the initial temperature of the heater element will be higher if the heater element has been used recently than if it has not been used recently. The controller may advantageously select the appropriate predetermined criterion depending on whether the heater assembly has been used recently. Preferably, the controller may be able to select to operate according to any of the previously described embodiments, one embodiment described with respect to a first predetermined threshold and the other embodiment described with respect to a second predetermined threshold.

[0055] The controller may be configured to select a first predetermined threshold if the determined initial temperature of the heater element is equal to or less than the threshold temperature.The controller may be configured to select predetermined criteria including a magnitude of the measured parameter being less than the first predetermined threshold, and preferably substantially zero, if the determined initial temperature of the heater element is equal to or less than the threshold temperature.

[0056] The controller may be configured to select a second predetermined threshold if the determined initial temperature of the heater element is greater than the threshold temperature.The controller may be configured to select the predetermined criteria including a magnitude of the measured parameter greater than a second predetermined threshold if the determined initial temperature of the heater element is greater than the threshold temperature.

[0057] The controller may be configured to determine an initial temperature of the heater element, or a parameter related to the initial temperature of the heater element. The controller may be configured to determine an initial temperature of the heater element, or a parameter related to the initial temperature of the heater element, when the power supply is configured to operate in the low power mode. The controller may be configured to determine an initial temperature of the heater element, or a parameter related to the initial temperature of the heater element, upon initiation of operation of the power supply in the low power mode.

[0058] The parameter related to the initial temperature of the heater element determined by the controller may be the resistance or conductance of the heater element.

[0059] The threshold temperature may be between about 15 degrees Celsius and about 60 degrees Celsius, and is preferably between about 20 degrees Celsius and about 50 degrees Celsius.

[0060] The threshold temperature may be a predetermined value stored in the memory of the controller, or alternatively, the threshold temperature may be derived from a measurement of the ambient temperature made using a temperature sensor in the aerosol generating device.

[0061] If the controller is configured to determine a parameter related to the initial temperature of the heater element rather than the initial temperature itself, the controller may be configured to select the predetermined criterion based on a threshold for the parameter equal to the threshold temperature. The controller may be configured to select the predetermined criterion based on a comparison of the initial value of the parameter related to the temperature of the heater element to a threshold for that parameter.

[0062] For example, the threshold value may be a resistance threshold value. The resistance threshold value may correspond to a temperature of the heater element between about 15 degrees Celsius and about 60 degrees Celsius, preferably between about 20 degrees Celsius and about 50 degrees Celsius. The resistance threshold value may be stored in a memory of the controller.

[0063] The controller may be configured to control the power supply to operate the heater assembly in a low power mode for a predetermined time following start-up of the device or detection of an aerosol-generating article received within the device. The longer the power supply operates in a low power mode before operating in a high power mode, the longer the delay between the start of a use session of the device and aerosol generation. It may be advantageous for this delay to be short.

[0064] The predetermined time period is advantageously relatively short so that the rate of change of the temperature of the aerosol-generating article or heater assembly can still be accurately determined. Preferably, the predetermined time period may be less than 3 seconds, preferably less than 2 seconds, and most preferably about 1 second.

[0065] The predetermined time may begin at the start of a usage session of the device. The predetermined criteria may include a time elapsed while operating in the low power mode being equal to or greater than a predetermined time. Thus, the controller may be configured to switch out of the low power mode only after the predetermined time has elapsed.

[0066] In the low power mode, the controller may be configured to measure a parameter related to the rate of change of temperature of the heater assembly or the rate of change of temperature of an aerosol-generating article received within the cavity by passing an electrical current through the heater assembly and measuring a corresponding electrical parameter that is indirectly related to the temperature of the heater assembly or the aerosol-generating article. By measuring the electrical parameter, the controller may advantageously be configured to indirectly determine the rate of change of temperature of the heater assembly or the aerosol-generating article, as will be described in more detail below.

[0067] Rather than measuring the temperature directly, it can be advantageous to measure an electrical parameter that is indirectly related to the temperature of the heater assembly or aerosol-generating article, as this eliminates the need for a dedicated temperature sensor.

[0068] The controller may be configured to control the power supply to flow current to the heater assembly in the low power mode, although the actual power supplied to the heater assembly may advantageously be relatively low. The controller may be configured to supply sufficient power to the heater assembly to measure the electrical parameter without causing substantial heating of the heater assembly.

[0069] The controller may be configured to repeatedly measure the electrical parameter. The rate of change of the electrical parameter may be related to the rate of change of the temperature of the heater assembly or the aerosol-generating article. The controller may be configured to determine the rate of change of the electrical parameter by repeatedly measuring the electrical parameter at different time intervals and then calculating the rate of change of the electrical parameter between those time intervals. The time interval between successive measurements may be between 50 ms and 1 s, preferably between 100 ms and 500 ms, even more preferably between 200 ms and 300 ms, and most preferably about 250 ms.

[0070] In the low power mode, the controller may be configured to control the power supply to provide current with a duty cycle of less than 2%, preferably less than 1%, preferably less than 0.5%, preferably less than 0.4%, preferably less than 0.2%, preferably less than 0.15%, and even more preferably less than 0.1%. Such duty cycle values ​​may advantageously allow for measuring electrical parameters associated with the heater assembly without causing substantial heating of the heater assembly.

[0071] In the low power mode, the controller may be configured to provide power to the heater assembly in multiple pulses. Successive pulses may be separated by a time interval. The length of each pulse may be shorter than the length of the time interval between successive pulses. The length of each pulse may be significantly shorter than the length of the time interval between successive pulses. Between the pulses, the power may be interrupted. By using relatively short power pulses with relatively large intervals between pulses, significant heating of the heater assembly and the aerosol-generating article received within the cavity in the low power mode may be avoided. The temperature of the heater assembly or the aerosol-generating article may be indirectly determined during each pulse.

[0072] The length of each pulse may be between 0.1 ms and 50 ms, preferably between about 0.5 ms and 10 ms, and even more preferably about 1 ms.

[0073] The length of the interval between successive pulses may be between 25 ms and 500 ms, preferably between 50 ms and 300 ms, and even more preferably about 250 ms.

[0074] As used herein, the term "discontinued" is used to encompass embodiments in which power supply from a power source is stopped or reduced so that effectively no power is supplied to the heater assembly.

[0075] The term "contiguous" as used herein refers to a series or sequence of consecutive, adjacent or proximate values.

[0076] The controller may be configured to measure a parameter related to the rate of change of temperature of the heater assembly or the rate of change of temperature of the aerosol-generating article received within the cavity during at least a portion of the multiple pulses. During the multiple pulses, the controller may be configured to measure an electrical parameter by measuring the current provided by the power source during each pulse. The electrical parameter may be conductance or resistance.

[0077] The heater assembly may be an induction heater assembly.

[0078] The heater assembly may include an inductor coil, which may be positioned around or adjacent to the cavity of the aerosol generating device.

[0079] The inductor coil may have the form of a helical coil. The helical inductor coil may surround the cavity.

[0080] The inductor coil may have the form of a flat spiral coil, which may be positioned adjacent to the cavity.

[0081] The heater assembly may include a plurality of inductor coils, a first inductor coil may be positioned on a first side of the cavity, and a second inductor coil may be positioned on a second side of the cavity opposite the first side.

[0082] The aerosol generating device may be for use with an aerosol-generating article that includes a susceptor element.

[0083] Alternatively, the aerosol-generating device may comprise a susceptor element. The susceptor element of the device may enclose a cavity for receiving the aerosol-generating article. Alternatively, the susceptor element may be positioned within the cavity.

[0084] The susceptor element positioned within the cavity may be elongated. The susceptor element may extend along a longitudinal axis parallel to the longitudinal axis of the cavity. The susceptor element may be configured to penetrate an aerosol-forming substrate of an aerosol-generating article received within the cavity. The susceptor element may have the form of a blade, a pin, or a rod.

[0085] Whether or not the aerosol generating device or aerosol generating article comprises a susceptor element, the power source may be configured to provide an oscillating current to the inductor coil. The oscillating current may be a high frequency oscillating current. As used herein, the term "high frequency" is used to describe frequencies in the ranges of about 1 megahertz (MHz) to about 30 megahertz (MHz), about 1 megahertz (MHz) to about 10 MHz (including the range of about 1 MHz to about 10 MHz), and about 5 megahertz (MHz) to about 7 megahertz (MHz) (including the range of about 5 MHz to about 7 MHz). This may generate a changing magnetic field. The susceptor element of the aerosol generating article received in the cavity may interact with the changing magnetic field such that a changing current is induced in the susceptor element. This may generate heat.

[0086] In the low power mode, the controller may be configured to provide an oscillating current such that a relatively low power is provided to the susceptor element In this manner, minimal heat may be generated by the susceptor element of the aerosol-generating article and no aerosol may be generated.

[0087] In the high power mode, the controller may be configured to provide an oscillating current such that a relatively high power is provided to the susceptor element. In this manner, sufficient heat to generate an aerosol may be generated by the susceptor element of the aerosol-generating article. In particular, the heat generated within the susceptor element may be transferred, for example by conduction, to the aerosol-forming substrate of the aerosol-generating article to generate an aerosol.

[0088] If the controller is configured to power the heater assembly in multiple pulses, the oscillating current may only be supplied during each pulse.

[0089] The power source may include a DC power source, such as a battery. If the heater assembly is an induction heater assembly, the aerosol generating device may further include a DC / AC converter connected to the DC power source. The DC / AC converter may include a power amplifier. In particular, the DC / AC converter may include a class-E power amplifier including a transistor switch and a transistor switch driver circuit. Class-E power amplifiers are generally well known and are described in detail, for example, in the article "Class-E RF Power Amplifiers" by Nathan O. Sokal, published in the bimonthly magazine "QEX" of The American Radio Relay League (ARRL), Newington, Connecticut, USA, January / February 2001, pp. 9-20. Class E power amplifiers can be advantageous because they operate at high frequencies, but at the same time have a relatively simple circuit structure with a minimum number of components (e.g., Class E power amplifiers require only one transistor switch, which is advantageous compared to Class D power amplifiers, which require two transistor switches controlled at high frequency to ensure that one of the two transistors is on when the other one is off). Additionally, Class E power amplifiers are known to have low power consumption across the switching transistors during switching transitions. The Class E power amplifier can be a single-ended, primary Class E power amplifier with only a single transistor switch.

[0090] As mentioned above, the aerosol-generating device may be for receiving an aerosol-generating article that includes a susceptor element, or the aerosol-generating device may itself comprise a susceptor element. The measured parameter may be the rate of change of conductance of the susceptor element, or the rate of change of resistance of the susceptor element.

[0091] The susceptor element preferably comprises or consists of a material having a conductance that is temperature dependent. Thus, the rate of change of the conductance or resistance of the susceptor element may advantageously be related to the rate of change of the temperature of the susceptor element. Preferably, the measured parameter may be the rate of change of the conductance of the susceptor element. Since conductance is the reciprocal of resistance, references to conductance below may be replaced with a corresponding statement of resistance.

[0092] The temperature dependence of the susceptor element may depend on the material forming the susceptor element. Some susceptor elements have an S-shaped dependence between conductance and temperature, where the conductance initially drops with increasing temperature. As the temperature continues to increase, the conductance may begin to increase. If the temperature increases further, the conductance may then drop again.

[0093] Where the measured parameter is conductance, the predetermined criteria may relate to the expected behaviour of the conductance when an unused aerosol-generating article is received within the cavity.

[0094] The first predetermined threshold may be a maximum rate of change of conductance of the susceptor element when an unused aerosol-generating article is received in the cavity. The first predetermined threshold may represent a magnitude of a maximum rate of change of conductance of the susceptor element when an unused aerosol-generating article is received in the cavity.

[0095] The predetermined criteria may include a rate of change of conductance of the susceptor element being less than a first predetermined threshold, for example, where the predetermined criteria may relate to an expected rate of change of temperature of the susceptor element when an unused aerosol-generating article is received in a cavity of an aerosol-generating device that has not been recently used, such that there is negligible heating or cooling of the unused aerosol-generating article because the temperature of the unused aerosol-generating article is similar to the temperature of the heater assembly.

[0096] If the rate of change of the measured susceptor element conductance is greater than a first predetermined threshold, the predetermined criterion may not be met.

[0097] If the rate of change of conductance of the susceptor element is positive, the predetermined criteria may not be met. It may be advantageous if the susceptor element has an inverse temperature and inverse conductance relationship, at least in the temperature region between the ambient temperature and the expected temperature of the recently depleted aerosol-generating article, since a positive rate of change of conductance may indicate that such a susceptor element is cooling.

[0098] Preferably, if the magnitude of the rate of change of conductance of the susceptor is greater than a first predetermined threshold and the rate of change of conductance is positive, the predetermined criterion may not be met.

[0099] When the aerosol-generating article comprises a susceptor element, the controller configured to measure the rate of change of conductance of the susceptor element includes a controller that measures a parameter related to the rate of change of temperature of the aerosol-generating article received in the cavity.

[0100] Where the aerosol generating device comprises a susceptor element, the controller configured to measure the rate of change of conductance of the susceptor element includes a controller that measures a parameter related to the rate of change of temperature of the heater assembly.

[0101] If the aerosol generating device comprises a susceptor element, the second predetermined threshold may be a minimum rate of change of conductance of the susceptor element when an unused aerosol generating article is received in the cavity. This may be, for example, where the predetermined criterion relates to an expected rate of change of temperature of the heater assembly when an unused aerosol generating article is received in the cavity of a recently used aerosol generating device. This may be because the temperature of an unused aerosol generating article may be lower, and preferably significantly lower, than the temperature of the heater assembly, so that there is a significant cooling effect of the unused aerosol generating article on the heater element.

[0102] If the rate of change of the measured susceptor element conductance is less than a second predetermined threshold, the predetermined criterion may not be met.

[0103] The controller may be configured to determine the rate of change of conductance by repeatedly measuring the conductance value at different time intervals and then calculating the rate of change between those time intervals. The time interval between successive conductance values ​​may be between 50 ms and 1 s, preferably between 100 ms and 500 ms, even more preferably between 200 ms and 300 ms, and most preferably about 250 ms.

[0104] The controller may preferably be configured to determine a conductance value of the susceptor element based on one or more measurements of current provided by the power supply and the voltage across the power supply. When the controller is configured to provide power to the heater assembly in multiple pulses, the controller may determine the conductance value during at least a portion of the multiple pulses.

[0105] The conductance value may be determined from a quotient or ratio of a current measurement and a voltage measurement. The controller may be configured to determine a quotient of one or more current measurements and one or more voltage measurements. In other words, the controller may be configured to determine the conductance value by dividing one or more current measurements by one or more voltage measurements.

[0106] In one embodiment, the voltage supplied from the power supply to the induction heating assembly is constant. When the controller is configured to supply power to the heater assembly in multiple pulses, a constant supplied voltage may mean that the voltage is constant throughout the duration of the pulse. The electrical conductance of the susceptor arrangement may be directly proportional to the supply current drawn by the induction heating assembly. Thus, by determining a value indicative of the supply current drawn by the induction heating arrangement in heating the susceptor arrangement, the controller may also determine a value indicative of the electrical conductance of the susceptor element. The same is true for the apparent electrical resistance of the susceptor element, which is inversely proportional to the supply current drawn by the induction heating assembly in heating the susceptor arrangement.

[0107] It will be understood that all references to current measurements referred to herein may additionally include voltage measurements. It will be understood that all references to current measurements referred to herein may additionally include voltage measurements and conductance determinations.

[0108] The heater assembly may be a resistive heater assembly, which may include a resistive heater element configured, in use, to heat an aerosol-generating article received within the cavity.

[0109] The resistive heater element may surround a cavity for receiving an aerosol-generating article.

[0110] Alternatively, a resistive heater element may be positioned within the cavity. The resistive heater element may be elongated. The resistive heater element may extend along a longitudinal axis parallel to the longitudinal axis of the cavity. The resistive heater element may be configured to penetrate an aerosol-forming substrate of an aerosol-generating article received within the cavity. The resistive heater element may be in the form of a blade, pin, or rod.

[0111] The power source may include a DC power source, such as a battery.

[0112] In the low power mode, the controller may be configured to supply current to the resistive heater element such that a relatively low power is supplied to the resistive heater element, in this manner, minimal heat is generated by the resistive heater element and no aerosol may be generated.

[0113] In the high power mode, the controller may be configured to provide a current such that a relatively high power is supplied to the resistive heater element. In this manner, sufficient heat may be generated by the resistive heater element to generate an aerosol. In particular, the heat generated in the resistive heater element may be transferred, for example by conduction, to an aerosol-forming substrate of the aerosol-generating article to generate an aerosol.

[0114] If the controller is configured to power the heater assembly in multiple pulses, current may only be supplied during each pulse.

[0115] During the low power mode, the controller may be configured to measure a parameter related to the rate of change of temperature of a heater assembly that includes a resistive heater element.

[0116] The measured parameter may be the resistance or conductance of the heater element, preferably the resistance.

[0117] The resistive heater element preferably comprises or consists of a material having a resistance that is temperature dependent, such that the rate of change of the resistance of the resistive heater element is advantageously related to the rate of change of the temperature of the resistive heater element.

[0118] Where the measured parameter is the resistance of the heater element, the predetermined criteria may relate to the expected behavior of the resistance when an unused aerosol-generating article is received within the cavity.

[0119] In one embodiment, the first predetermined threshold may be a maximum value of the rate of change of resistance of the resistive heater element when an unused aerosol-generating article is received within the cavity. The predetermined criterion may include a magnitude of the rate of change of resistance of the heater element being less than the first predetermined threshold. This may be, for example, where the predetermined criterion relates to an expected rate of change of temperature of the heater assembly when an unused aerosol-generating article is received within a cavity of an aerosol generating device that has not been used recently. This may be because the temperature of an unused aerosol-generating article will be similar to the temperature of the heater assembly, and therefore the heating or cooling effect of an unused aerosol-generating article on the heater element will be minimal.

[0120] In one embodiment, the second predetermined threshold may be a minimum rate of change of resistance of the resistive heater element when an unused aerosol-generating article is received within the cavity. The predetermined criterion may include a magnitude of the rate of change of resistance of the heater element being greater than the second predetermined threshold. This may be, for example, where the predetermined criterion relates to an expected rate of change of temperature of the heater assembly when an unused aerosol-generating article is received within the cavity of a recently used aerosol generating device. This may be because the temperature of an unused aerosol-generating article is lower, and preferably significantly lower, than the temperature of the heater assembly, such that there is a significant cooling effect of the unused aerosol-generating article on the heater element.

[0121] The resistive heating element preferably comprises an electrically resistive material. Suitable electrically resistive materials include, but are not limited to, semiconductors such as doped ceramics, "conductive" ceramics (such as, for example, molybdenum disilicide), carbon, graphite, metals, alloys, and composites made of ceramic and metallic materials. Such composites may include doped or undoped ceramics. Examples of suitable doped ceramics include doped silicon carbide. Examples of suitable metals include titanium, zirconium, tantalum, and platinum group metals. Examples of suitable metal 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-, stainless steel-based superalloys, Timetal®, iron-aluminum-based alloys, and iron-manganese-aluminum-based alloys. Timetal® is a registered trademark of Titanium Metals Corporation. In composites, the electrically resistive material may be optionally embedded in, encapsulated in, or coated with an insulating material, or vice versa, depending on the required energy transfer kinetics and external physicochemical properties. The heating element may include a metallic etched foil insulated between two layers of inert material. In that case, the inert material may include Kapton®, an all-layer polyimide, or a mica foil. Kapton® is a registered trademark of EI du Pont de Nemours and Company.

[0122] The controller may be a microprocessor, which may be a programmable microprocessor, a microcontroller, or an application specific integrated circuit chip (ASIC) or other electronic control circuit.

[0123] According to a second aspect, there is provided an aerosol generation system comprising an aerosol generating device according to the first aspect. The aerosol generation system may comprise an aerosol-forming substrate.

[0124] The term "aerosol-forming substrate" as used herein refers to a substrate capable of releasing volatile compounds capable of forming an aerosol. Such volatile compounds may be released by heating the aerosol-forming substrate. The aerosol-forming substrate may conveniently be part of an aerosol-generating article or a smoking article.

[0125] The aerosol-forming substrate may be a solid aerosol-forming substrate. Alternatively, the aerosol-forming substrate may comprise both solid and liquid components. The aerosol-forming substrate may comprise a tobacco-containing material that contains volatile tobacco flavour compounds that are released from the substrate upon heating. Alternatively, the aerosol-forming substrate may comprise a non-tobacco material. The aerosol-forming substrate may further comprise an aerosol former that facilitates the formation of a dense and stable aerosol. Examples of suitable aerosol formers are glycerin and propylene glycol.

[0126] In a particularly preferred embodiment, the aerosol-forming substrate comprises an assemblage of a crimped sheet of homogenized tobacco material. As used herein, the term "crimped sheet" means a sheet having a plurality of substantially parallel ridges or corrugations.

[0127] The aerosol generating system may comprise a cartridge containing the aerosol-forming substrate. The cartridge may be receivable within a cavity of an aerosol generating device. The aerosol-forming substrate may be solid or liquid, or may contain both solid and liquid components. Preferably, the aerosol-forming substrate is a liquid.

[0128] The aerosol-forming substrate may comprise a plant-derived material. The aerosol-forming substrate may comprise tobacco. The aerosol-forming substrate may comprise a tobacco-containing material that contains volatile tobacco flavour compounds that are released from the aerosol-forming substrate upon heating. Preferably, the aerosol-forming substrate may alternatively comprise a non-tobacco-containing material.

[0129] The aerosol-generating article may comprise a susceptor element, or alternatively, a heater assembly of an aerosol-generating device may include a susceptor element, as described above with reference to the first aspect.

[0130] As used herein, "susceptor" or "susceptor element" refers to an electrically conductive element that heats up when subjected to a fluctuating magnetic field. This may be the result of eddy currents induced in the susceptor element, or hysteresis losses (or both eddy currents and hysteresis losses). Possible materials for the susceptor include graphite, molybdenum, silicon carbide, stainless steel, niobium, aluminum, and virtually any other electrically conductive element. Advantageously, the susceptor element is a ferrite element. The material and geometry for the susceptor element can be chosen to provide the desired electrical resistance and heat generation. The susceptor element may include, for example, a mesh, a flat spiral coil, a fiber, or a fabric. Advantageously, the susceptor is in contact with the first aerosol-forming substrate. The susceptor element may advantageously be fluid-permeable.

[0131] The susceptor element may include a first susceptor material.The susceptor element may include a second susceptor material.

[0132] The first susceptor material may have a first Curie temperature. The second susceptor material may have a second Curie temperature. The second Curie temperature may be lower than the first Curie temperature.

[0133] Above its Curie temperature, a material is no longer ferromagnetic, so heating due to hysteresis losses no longer occurs. If the susceptor element is made of a single material, the Curie temperature may correspond to the maximum temperature the susceptor element should have (i.e., the Curie temperature is equal to the maximum temperature to which the susceptor element should be heated, or deviates from this maximum temperature by about 1-3%). This reduces the possibility of sudden overheating.

[0134] If the susceptor element is made of more than one material, the material of the susceptor element can be optimized for further aspects. For example, a material can be selected such that a first material of the susceptor element may have a Curie temperature above the maximum temperature to which the susceptor element should be heated. This first material of the susceptor element may then be optimized for example for maximum heat generation, while being optimized for maximum heat transfer to the aerosol-forming substrate to provide efficient heating of the susceptor. However, the susceptor element may then additionally comprise a second material with a Curie temperature corresponding to the maximum temperature to which the susceptor should be heated, and when the susceptor element reaches this Curie temperature, the magnetism of the entire susceptor element changes. This change can be detected and communicated to the controller, and then the supply of power to the heater assembly is interrupted until the temperature of the susceptor element cools down again below the Curie temperature, and the supply of power can be resumed as soon as it cools down.

[0135] The parameter measured by the controller may be the rate of change of the conductance of the susceptor element or the rate of change of the resistance of the susceptor element.

[0136] The heater assembly of the aerosol generating device may include an inductor coil. The power source may be configured to provide an oscillating current to the inductor coil. The inductor coil may be positioned within or adjacent to the cavity. When the aerosol-generating article is received within the cavity, the inductor coil may surround the aerosol-generating article.

[0137] The aerosol-generating article may be rod-shaped. The aerosol-forming substrate may be at or towards the distal end of the rod. The proximal end of the rod may form or be provided with a mouthpiece.

[0138] In a third aspect, there is provided a method of controlling a heater assembly of an aerosol generating device. The heater assembly of the aerosol generating device may be for heating an aerosol-generating article received within a cavity of the aerosol generating device. The heater assembly may be operable in at least a low power mode in which no aerosol is generated, and a high power mode in which aerosol may be generated. The aerosol generating device may be an aerosol generating device according to the first aspect.

[0139] The method may include controlling power supplied to the heater assembly such that the heater assembly initially operates in a low power mode.

[0140] While operating the heater assembly in the low power mode, the method may include measuring a parameter related to the rate of change of temperature of the heater assembly or the rate of change of temperature of an aerosol-generating article received within the cavity of the aerosol generating device.

[0141] The method may be configured to switch from the low power mode to the high power mode only if the measured parameter meets a predetermined criterion.

[0142] The method may further be configured to switch from the low power mode to an error mode if the measured parameter does not meet a predetermined criterion.

[0143] The predetermined criteria may include a comparison of the magnitude of the measured parameter to a predetermined threshold.

[0144] The predetermined criteria may include the magnitude of the measured parameter being less than a first predetermined threshold, preferably substantially equal to zero.

[0145] If the magnitude of the measured parameter is greater than a first predetermined threshold, the measured parameter may not meet the predetermined criteria.

[0146] The first predetermined threshold may be a value of the measured parameter corresponding to a rate of change of temperature of the aerosol-generating article or heater assembly of less than 1 degree Celsius / second, preferably less than 0.5 degrees Celsius / second, and even more preferably less than 0.25 degrees Celsius / second. Preferably, the first predetermined threshold may be a magnitude of the measured parameter.

[0147] The measured parameter may not meet the predetermined criteria if the magnitude of the measured parameter is greater than a first predetermined threshold, the measured parameter indicates that the rate of change of temperature of the heater assembly is positive, or the measured parameter indicates that the rate of change of temperature of the heater assembly is negative.

[0148] The predetermined criteria may include a magnitude of the measured parameter being greater than a second predetermined threshold, which may be a value of the measured parameter corresponding to a rate of change of temperature of the aerosol-generating article or assembly of greater than 3 degrees Celsius / second, preferably greater than 5 degrees Celsius / second, preferably greater than 7 degrees Celsius / second, and even more preferably greater than 9 degrees Celsius / second.

[0149] If the magnitude of the measured parameter is less than a second predetermined threshold, the predetermined criterion may not be met.

[0150] If the magnitude of the measured parameter is less than a second predetermined threshold, the predetermined criterion may not be met. The measured parameter may indicate that the rate of change of temperature of the heater assembly is negative.

[0151] The method may further include activating the device or detecting that an aerosol-generating article is received within the device.

[0152] The step of operating the heater assembly in the low power mode may occur immediately after activating the device or detecting that an aerosol-generating article is received within the device.

[0153] The heater assembly may be operated in a low power mode for a predetermined period of time.

[0154] The predetermined time period may be less than 3 seconds, preferably less than 2 seconds, and even more preferably about 1 second.

[0155] The method may further include switching out of the low power mode only after a predetermined amount of time has elapsed.

[0156] The method may further include controlling the power supply to supply current with a duty cycle of less than 2%, preferably less than 1%, preferably less than 0.5%, preferably less than 0.4%, preferably less than 0.2%, preferably less than 0.15%, and even more preferably less than 0.1%, while operating the heater assembly in the low power mode.

[0157] The method may further include powering the heater assembly in a plurality of pulses, the plurality of pulses may be separated by a time interval, and a length of each pulse may be less than a length of the time interval between successive pulses while operating the heater assembly in the low power mode.

[0158] The length of each pulse may be between 0.1 ms and 50 ms, preferably between about 0.5 ms and 10 ms, and even more preferably about 1 ms.

[0159] The length of the interval between successive pulses may be between 25 ms and 500 ms, preferably between 50 ms and 300 ms, and even more preferably about 250 ms.

[0160] The method may further include measuring a parameter related to the rate of change of temperature of the heater assembly or the rate of change of temperature of an aerosol-generating article received within the cavity during at least a portion of the multiple pulses.

[0161] Measuring the parameter during at least a portion of the plurality of pulses may include measuring a current supplied from the power source during each pulse.

[0162] The heater assembly may include an inductor coil. The method may include supplying power to the inductor coil as an oscillating current.

[0163] The power may be provided by a DC power source, such as a battery. The method may further include converting the power provided by the DC power source into alternating current using a DC / AC converter connected to the DC power source.

[0164] The aerosol-generating device may be for receiving an aerosol-generating article comprising a susceptor element. Alternatively, the aerosol-generating device may comprise a susceptor element. The measured parameter may be the rate of change of conductance of the susceptor element or the rate of change of resistance of the susceptor element.

[0165] The measured parameter may be the rate of change of conductance of the susceptor element.

[0166] Features described with respect to one aspect, example or embodiment may also be applicable to other example aspects and embodiments. In particular, features of the test setup of the first aspect may be applied to the test setup used in the methods of the second and third aspects. Similarly, features described with respect to the method of the second aspect may also be applied to the method of the third aspect and vice versa. EXAMPLES

[0167] 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 another example, embodiment, or aspect described herein.

[0168] Example 1. 1. An aerosol generating device for generating an aerosol from an aerosol-generating article, comprising: a cavity for receiving an aerosol-generating article; a heater assembly for heating an aerosol-generating article received within the cavity; a power supply configured to supply power to the heater assembly and controlled by the controller to be operable in at least a low power mode in which no aerosol is generated, and a high power mode in which aerosol may be generated; a controller configured to control the power source to initially operate in a low power mode, wherein in the low power mode the controller is configured to measure a parameter related to a rate of change of temperature of the heater assembly or a rate of change of temperature of an aerosol-generating article received within the cavity; An aerosol generating device, wherein the controller is configured to switch from the low power mode to the high power mode only if a measured parameter meets a predetermined criterion. Example 2. An aerosol generating device according to Example 1, wherein the controller is configured to switch from the low power mode to an error mode if the measured parameter does not meet a predetermined criterion. Example 3. 3. An aerosol generating device according to embodiment 1 or 2, wherein the predetermined criteria comprises a comparison of the magnitude of the measured parameter with a predetermined threshold value. Example 4. 4. An aerosol generating device according to example 3, wherein the predetermined criteria includes the magnitude of the measured parameter being below a predetermined threshold. Example 5. An aerosol generating device according to embodiment 3 or 4, wherein if the magnitude of the measured parameter is greater than a predetermined threshold value, the predetermined criterion is not met. Example 6. if the magnitude of the measured parameter is greater than a predetermined threshold, the predetermined criterion is not met; The measured parameter indicates that the rate of change of the heater assembly temperature is positive, or An aerosol generating apparatus according to any one of Examples 3 to 5, wherein the measured parameter indicates that the rate of change of temperature of the aerosol-generating article is negative. Example 7. An aerosol generating device according to example 3, wherein the predetermined criterion is met if the magnitude of the measured parameter is greater than a predetermined threshold. Example 8. An aerosol generating device according to example 3 or 7, wherein if the magnitude of the measured parameter is below a predetermined threshold, the predetermined criterion is not met. Example 9. if the magnitude of the measured parameter is less than a predetermined threshold, the predetermined criterion is not met; An aerosol generating device according to Examples 3, 7 or 8, wherein the measured parameter is indicative of the rate of change of temperature of the heater assembly and is positive. Example 10. An aerosol generating device according to any one of Examples 7 to 9, wherein the measured parameter is related to the rate of change of temperature of the heater assembly. Example 11. An aerosol generating device according to any one of Examples 1 to 10, wherein the controller is configured to control the power supply to operate the heater assembly in a low power mode for a predetermined time after startup of the device or after detection of an aerosol generating article received within the device. Example 12. An aerosol generating device according to example 11, wherein the predetermined time is less than 3 seconds, preferably less than 2 seconds, and even more preferably about 1 second. Example 13. An aerosol generating device according to Example 11 or 12, wherein the predetermined time period begins with the start of a session of use of the device. Example 14. An aerosol generating device according to any one of Examples 11 to 13, wherein the predetermined criteria comprises the time elapsed while operating in the low power mode being equal to or greater than a predetermined time. Example 15. In the low power mode, the controller is configured to control the power supply to supply current with a duty cycle of less than 2%, preferably less than 1%, preferably less than 0.4%, preferably less than 0.2%, preferably less than 0.15%, and even more preferably less than 0.1%. An aerosol generating device according to any one of Examples 1 to 14. Example 16. An aerosol generating device according to any one of Examples 1 to 15, wherein in a low power mode, the controller is configured to power the heater assembly in multiple pulses separated by time intervals, such that the length of each pulse is less than the length of the time interval between successive pulses. Example 17. 17. The aerosol generating apparatus according to embodiment 16, wherein the length of each pulse is between 0.1 ms and 50 ms, preferably between about 0.5 ms and 10 ms, and even more preferably about 1 ms. Example 18. An aerosol generating device according to embodiment 16 or 17, wherein the length of the interval between successive pulses is between 25 ms and 500 ms, preferably between 50 ms and 300 ms, and even more preferably about 250 ms. Example 19. An aerosol generating device according to any one of Examples 16 to 18, wherein the controller is configured to measure a parameter related to the rate of change of temperature of the heater assembly or the rate of change of temperature of an aerosol generating article received within the cavity during at least a portion of the multiple pulses. Example 20. An aerosol generating device according to Example 19, wherein the controller is configured to measure the parameter by measuring the current provided by the power supply during the pulse. Example 21. An aerosol generating apparatus according to any one of Examples 1 to 20, wherein the aerosol generating apparatus is for use with an aerosol generating article including a susceptor element, the heater assembly includes an inductor coil, and the power supply is configured to provide an oscillating current to the inductor coil. Example 22. 22. An aerosol generating device according to Example 21, wherein the power source comprises a DC power source, such as a battery, and the aerosol generating device further comprises a DC / AC converter connected to the DC power source. Example 23. 23. An aerosol generating apparatus according to embodiment 21 or 22, wherein the measured parameter is the rate of change of the conductance of the susceptor element or the rate of change of the resistance of the susceptor element. Example 24. 24. An aerosol generating apparatus according to example 23, wherein the measured parameter is the rate of change of conductance of the susceptor element. Example 25. 25. An aerosol generating apparatus according to example 24, wherein the predetermined criteria includes a rate of change in conductance of the susceptor element being less than a predetermined threshold. Example 26. An aerosol generating apparatus according to any one of Examples 24 to 25, wherein the predetermined criterion is not met if the measured rate of change in conductance of the susceptor element is positive and greater than the predetermined threshold. Example 27. An aerosol generating device according to any one of Examples 1 to 26, wherein the heater assembly includes a heater element configured to heat an aerosol generating article received in the cavity during use, and during the low power mode, the controller is configured to measure a parameter related to the rate of change of temperature of the heater element. Example 28. 28. The aerosol generating device according to Example 27, wherein the heater element is a resistive heater element. Example 29. 29. An aerosol generating device according to embodiment 27 or 28, wherein the heater element is configured to penetrate the aerosol-forming substrate of the aerosol-generating article when the aerosol-generating article is received within the cavity. Example 30. 30. An aerosol generating device according to any one of Examples 27 to 29, wherein the heater element is in the form of a blade. Example 31. An aerosol-generating system comprising the aerosol-generating device according to any one of Examples 1 to 30, and an aerosol-generating article including an aerosol-forming substrate. Example 32. 32. An aerosol-generating system according to example 31, wherein the aerosol-generating article comprises a susceptor element. Example 33. 33. The aerosol generating system according to Example 32, wherein the susceptor comprises a first susceptor material having a first Curie temperature and a second susceptor material and a second Curie temperature, the second Curie temperature being less than the first Curie temperature. Example 34. The aerosol generating system according to Example 33, wherein the first and second susceptor materials are two separate materials bonded together and in intimate physical contact with each other. Example 35. The aerosol generation system according to any one of Examples 32 to 34, wherein the parameter measured by the controller is the rate of change of the conductance of the susceptor element or the rate of change of the resistance of the susceptor element. Example 36. An aerosol generation system according to any one of Examples 36 to 39, wherein the heater assembly of the aerosol generation device includes an inductor coil, and the power supply is configured to provide an oscillating current to the inductor coil. Example 37. 37. An aerosol generation system according to example 36, wherein the inductor coil is positioned within, around, or adjacent to the cavity. Example 38. 38. An aerosol generating system according to example 37, wherein the inductor coil surrounds the aerosol generating article when the aerosol generating article is received within the cavity. Example 39. An aerosol-generating system according to any one of Examples 31 to 38, wherein the aerosol-generating article is in the shape of a rod and the aerosol-forming substrate is at or towards the distal end of the rod. Example 40. 40. An aerosol generating system according to Example 39, wherein the proximal end of the rod forms or includes a mouthpiece. Example 41. 1. A method of controlling a heater assembly of an aerosol generating device, the heater assembly for heating an aerosol generating article received within a cavity of the aerosol generating device, the heater assembly being operable in at least a low power mode in which no aerosol is generated, and a high power mode in which aerosol may be generated, the method comprising: controlling power supplied to the heater assembly such that the heater assembly initially operates in a low power mode; measuring a parameter related to a rate of change of temperature of the heater assembly or a rate of change of temperature of an aerosol-generating article received within the cavity of the aerosol-generating device while operating the heater assembly in the low power mode; and switching from the low power mode to the high power mode only if a measured parameter meets a predetermined criterion. Example 42. 42. The method according to example 41, further comprising switching from the low power mode to an error mode if the measured parameter does not meet a predetermined criterion. Example 43. 43. The method according to example 41 or 42, wherein the predetermined criteria comprises a comparison of the magnitude of the measured parameter with a predetermined threshold value. Example 44. 44. The method according to example 43, wherein the predetermined criteria includes the magnitude of the measured parameter being less than a predetermined threshold. Example 45. 45. The method according to example 43 or 44, wherein the measured parameter does not meet the predetermined criterion if the magnitude of the measured parameter is greater than the predetermined threshold. Example 46. if the magnitude of the measured parameter is greater than a predetermined threshold, the measured parameter does not meet the predetermined criterion; The measured parameter indicates that the rate of change of the heater assembly temperature is positive, or The method according to any of examples 43-45, wherein the measured parameter indicates that the rate of change of temperature of the heater assembly is negative. Example 47. 44. The method according to example 43, wherein the predetermined criteria includes the magnitude of the measured parameter being greater than a predetermined threshold. Example 48. The method according to example 43 or 47, wherein the predetermined criterion is not met if the magnitude of the measured parameter is below a predetermined threshold. Example 49. if the magnitude of the measured parameter is less than a predetermined threshold, the predetermined criterion is not met; The method according to example 43, 47 or 48, wherein the measured parameter indicates that the rate of change of temperature of the heater assembly is negative. Example 50. The method according to any one of Examples 41-49, further comprising activating the device or detecting that an aerosol-generating article is received within the device. Example 51. The method according to example 50, wherein the step of operating the heater assembly in the low power mode occurs immediately after the step of activating the device or detecting that an aerosol-generating article is received within the device. Example 52. The method according to any one of embodiments 41-51, wherein the heater assembly operates in a low power mode for a predetermined period of time. Example 53. The method according to example 52, wherein the predetermined time is less than 3 seconds, preferably less than 2 seconds, and even more preferably about 1 second. Example 54. 54. The method according to example 52 or 53, further comprising switching out of the low power mode only after a predetermined time has elapsed. Example 55. The method according to any one of Examples 41-54, further comprising controlling the power supply to supply current with a duty cycle of less than 2%, preferably less than 1%, preferably less than 0.5%, preferably less than 0.4%, preferably less than 0.2%, preferably less than 0.15%, and even more preferably less than 0.1%, while operating the heater assembly in the low power mode. Example 56. The method according to any one of Examples 41-55, further comprising, while operating the heater assembly in the low power mode, powering the heater assembly in multiple pulses separated by time intervals, such that a length of each pulse is less than a length of the time interval between successive pulses. Example 57. The method according to example 56, wherein the length of each pulse is between 0.1 ms and 50 ms, preferably between about 0.5 ms and 10 ms, and even more preferably about 1 ms. Example 58. The method according to example 56 or 57, wherein the length of the interval between successive pulses is between 25 ms and 500 ms, preferably between 50 ms and 300 ms, and even more preferably about 250 ms. Example 59. The method according to any one of Examples 56-58, further comprising measuring a parameter related to the rate of change of temperature of the heater assembly or the rate of change of temperature of an aerosol-generating article received within the cavity during at least a portion of the multiple pulses. Example 60. 60. The method according to example 59, wherein the step of measuring the parameter during at least a portion of the plurality of pulses comprises measuring a current provided by the power source during each pulse. Example 61. The method according to any one of Examples 41-60, wherein the heater assembly includes an inductor coil, and the method includes supplying power to the inductor coil as an oscillating current. Example 62. The method according to example 61, wherein the power is supplied by a DC power source, such as a battery, and the method further includes converting the power supplied by the DC power source to alternating current using a DC / AC converter connected to the DC power source. Example 63. A method according to embodiment 61 or 62, wherein the aerosol generating device is for receiving an aerosol-generating article including a susceptor element, and the measured parameter is the rate of change of conductance of the susceptor element or the rate of change of resistance of the susceptor element. Example 64. 64. The method according to example 63, wherein the measured parameter is the rate of change of conductance of the susceptor element. Example 65. 65. The method according to example 64, wherein the predetermined criteria includes a rate of change of conductance of the susceptor element being less than a predetermined threshold. Example 66. The method according to example 64 or 65, wherein the predetermined criterion is not met if the rate of change of conductance of the susceptor element is positive and greater than the predetermined threshold.

[0169] The embodiments will now be further described with reference to the figures. [Brief description of the drawings]

[0170] [Figure 1] FIG. 1 is a schematic cross-sectional view of a first aerosol generating device. [Diagram 2] FIG. 2 is a flow diagram of a method implemented by the controller of the aerosol generating device of FIG. [Diagram 3] FIG. 3 is a graph showing how the conductance of a susceptor element of an aerosol-generating article received in the aerosol generating device of FIG. 1 changes over time when the aerosol-generating article is an unused aerosol-generating article. [Figure 4] FIG. 4 is a graph showing how the conductance of a susceptor element varies with time when the aerosol-generating article is a depleted aerosol-generating article. [Diagram 5]FIG. 5 is a schematic cross-sectional view of a second aerosol generating device. [Figure 6] FIG. 6 is a flow diagram of a method implemented by the controller of the aerosol generating device of FIG. [Figure 7] FIG. 7 is a graph showing how the resistance of the heater blade of the aerosol generating device of FIG. 5 changes over time when an unused aerosol generating article is received in the cavity of the aerosol generating device and when the heater blade has not been used recently. [Figure 8] FIG. 8 is a graph showing how the resistance of a heater blade changes over time when a depleted aerosol-generating article is received in the cavity of the aerosol generating device of FIG. 5 and when the heater blade has not been used recently. [Figure 9] FIG. 9 is a graph showing how the resistance of the heater blade of the aerosol generating device of FIG. 5 changes over time when an unused aerosol generating article is received in the cavity of the aerosol generating device and when the heater blade has been recently used. [Figure 10] FIG. 10 is a graph showing how the resistance of a heater blade changes over time when a depleted aerosol-generating article is received in the cavity of the aerosol generating device of FIG. 5 and when the heater blade has been recently used. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0171] 1 is a schematic cross-sectional view of a first aerosol generating device 100. The aerosol generating device 100 comprises a cavity 10 defined by a device housing. The cavity 10 is tubular, made of stainless steel, and has a base 12 at an upstream end. The cavity 10 is configured to receive an aerosol-generating article 200.

[0172] The aerosol-generating article 200 is received within the cavity 10. The aerosol-generating article 200 contains an aerosol-forming substrate 202. The aerosol-forming substrate is a solid tobacco-containing substrate. In particular, the aerosol-forming substrate is an assembly of homogenized tobacco sheets. As shown in Figure 1, the aerosol-generating article and the cavity are configured such that when the aerosol-generating article is received within the cavity 10, a mouth end of the aerosol-generating article 200 protrudes from the cavity 10 and from the aerosol generating device. This mouth end forms a mouthpiece 204 through which a user of the aerosol generating device may draw smoke in use.

[0173] The aerosol-generating article further comprises a susceptor element 206. The susceptor element 206 is formed of a sheet of conductive material embedded within the aerosol-forming substrate 202. The susceptor element 206 is radially centrally located within the aerosol-forming substrate 202.

[0174] The aerosol-generating device 100 further comprises a heater assembly including an inductor coil 110. The inductor coil 110 is a helical coil that surrounds the cavity 10. When the aerosol-generating article 200 is received within the cavity 10, the susceptor element 206 is positioned such that it is surrounded by the inductor coil 110.

[0175] The aerosol generating device 100 together with the aerosol generating article 200 may be referred to as an aerosol generating system.

[0176] The airflow channel 120 extends from an air inlet 122 of the aerosol generating device 100. Upstream of the cavity, the airflow channel 120 is defined primarily by airflow channel walls 124. Downstream of the airflow channel walls 124, the airflow channel 120 passes through an air inlet defined in the base 12 of the cavity. The airflow channel 120 then extends through the cavity 10.

[0177] The aerosol generating device 100 further comprises a power source 142 in the form of a rechargeable battery. The power source 142 is a DC power source. The power source is connected to the inductor coil 110 of the heater assembly through a DC / AC converter (not shown in the drawings) that converts the direct current of the power source to high frequency alternating current. This causes the inductor 110 to generate a varying electromagnetic field in the distal portion of the cavity 10 of the device. When the aerosol generating article 200 is correctly positioned in the cavity 10, the susceptor element 206 of the article 10 is located in this varying electromagnetic field. The varying field generates eddy currents in the susceptor element 206, which results in the generation of heat in the susceptor element 206. Heat may also be generated by magnetic hysteresis losses in the susceptor 14.

[0178] The power source is controllable by the controller 140. The power source is connected to the controller and the inductor coil 110 via electrical wires and connections not shown in the figure. The aerosol generating device may include further elements not shown in the figures, such as a button for activating the aerosol generating device.

[0179] When using the aerosol generating device 100, a user first activates the device by pressing a button. Immediately after activation, the controller 140 is configured to implement the method illustrated in FIG.

[0180] At method step 302, the controller is configured to initiate power supply to the inductor coil 110 of the heater assembly.

[0181] As described above, the power is provided as a high frequency alternating current. In step 302, the controller is configured to only provide power to the heater assembly such that the heater assembly operates in a low power mode. In the low power mode, substantial heating of the susceptor element 206 of the aerosol-generating article 200 is avoided. This is achieved by providing power to the inductor coil 110 as a series of consecutive pulses separated by time intervals. The pulses have a length of about 1 millisecond and are separated by a time interval of about 250 milliseconds. During the time intervals, the power provided to the inductor coil 110 is interrupted. Thus, a fluctuating field is generated by the inductor coil 110 only during the pulses, and therefore heat is generated in the susceptor element 206 only during the pulses. Because the pulses are much shorter than the intervals between the pulses, the temperature of the susceptor element 206 does not increase substantially in the low power mode.

[0182] Step 304 is performed during step 302. Step 304 of the method includes determining a rate of change of the conductance of the susceptor element 206. The susceptor element 206 is made of a material having a conductance that is temperature dependent. Thus, determining the rate of change of the conductance of the susceptor element 206 provides a proxy for the rate of change of the temperature of the susceptor element 206.

[0183] During the pulse in the low power mode, the controller is configured to probe and measure the conductance of the susceptor elements 206. The controller is configured to measure the conductance of the susceptor elements 206 by measuring the voltage and current of the power supplied to the inductor coil 110. The electrical conductance of the susceptor elements 206 is directly proportional to the supply of electrical current drawn by the induction heating assembly. Thus, by measuring the current drawn by the induction heating arrangement, the controller can also determine a value indicative of the electrical conductance of the susceptor elements.

[0184] The controller can determine the rate of change of conductance by comparing the difference in conductance values ​​during successive pulses and dividing by the time separation between those measurements. In this embodiment, the controller is configured to determine the rate of change of conductance over a 2 second period.

[0185] In method step 306, the controller is configured to compare the determined rate of change of conductance of the susceptor element 206 to a predetermined threshold stored in the memory of the controller, the predetermined threshold corresponding to a maximum expected rate of change of conductance of the susceptor element 206 when an unused aerosol-generating article 200 is received within the cavity 10.

[0186] The expected rate of change of conductance of the susceptor element 206 of an unused aerosol-generating article is relatively low because the expected rate of change of temperature of the susceptor element 206 is low, since the initial temperature of the susceptor element 206 is expected to be at or near ambient temperature. Thus, the predetermined threshold corresponds to a rate of change of temperature of less than 0.25 degrees Celsius.

[0187] The rate of change of conductance of the susceptor element 206 may deviate from the expected rate if the susceptor element 206 has been recently heated. This is indicative of a depleted aerosol-generating article. The deviation is because the starting temperature of the susceptor element 206 of a depleted aerosol-generating article is higher than the ambient temperature, so cooling of the susceptor element 206 can be measured as the aerosol-generating article cools at ambient conditions.

[0188] Figure 3 is a graph showing how the conductance of the susceptor element 206 of an unused aerosol-generating article changes over time. Figure 4 shows a graph representing how the conductance of the susceptor element of a depleted aerosol-generating article changes over time. Both Figures 3 and 4 show time on the x-axis and conductance on the y-axis. The time spans a relatively short 2 second period. Over this period, the rate of change of conductance can be approximated as linear, even though over longer periods the rate of change of conductance is actually non-linear.

[0189] Comparing the graphs of FIGS. 3-4, it is apparent that the slope of the graph is steeper when a depleted aerosol-generating article is received within cavity 10.

[0190] 3 only has a non-zero slope because the temperature of the susceptor element 206 had a starting temperature slightly above ambient temperature as a result of the user's handling of the aerosol-generating article 200. The non-zero slope corresponds to a slight cooling of the susceptor element 206 back toward ambient temperature. However, the non-zero slope is below a predetermined threshold.

[0191] If the controller determines that the magnitude of the rate of change of conductance of the susceptor element 206 is less than or equal to the predetermined threshold, the controller is configured to perform method step 308 .

[0192] Step 308 of the method includes switching from a low power mode to a high power mode. In the high power mode, power is supplied to the inductor coil 110 such that significant heating of the susceptor element 206 occurs. Power can be supplied either continuously or, if power is supplied in pulses, the length of the pulses is substantially longer than the interval between pulses. In the high power mode, a user can puff on the aerosol generating device to inhale the aerosol. The high power mode can be considered a normal use phase of the device. In some embodiments, the aerosol generating device includes a user interface that indicates to the user that the device is ready for puffing.

[0193] During the high power mode, the user puffs on the mouthpiece 204 of the received aerosol-generating article 200, which results in air being drawn through the airflow channel 120 towards the user's mouth. During puffing, air enters the airflow channel 120 from the exterior of the aerosol-generating device through the air inlet 122. The air is drawn through a portion of the airflow channel defined by the airflow channel walls 124 and into the cavity through the air inlet defined in the base 12 of the cavity 10. Because the aerosol-generating article 200 is received within the cavity, the air drawn into the cavity enters the aerosol-generating article 200 at its distal end. Thus, the air passes through the aerosol-forming substrate 202. In doing so, volatile compounds generated by heating of the substrate 202 may become entrained in the air. As the air travels towards the mouth end of the aerosol-generating article 200, the volatile compounds cool and form an aerosol. The direction of airflow through the aerosol-generating device and the aerosol-generating article is represented by dashed arrows in FIG.

[0194] If the controller determines that the magnitude of the rate of change of conductance of the susceptor element 206 exceeds a predetermined threshold, the controller is configured to perform method step 310 instead of step 308 .

[0195] Step 310 involves switching from the low power mode to an error mode. In the error mode, the controller is configured to prevent power from being supplied to the heater assembly, thereby preventing a user from continuing to use the aerosol generating device. By switching to the error mode, the controller prevents the depleted aerosol-generating article 200 from being reheated and reused.

[0196] 5 is a schematic cross-sectional view of a second aerosol generation device 400. The aerosol generation device 400 has many features in common with the first aerosol generation device, and like features are numbered accordingly.

[0197] Unlike the first aerosol generating device 100, which includes an induction heater assembly, the heater assembly of the second aerosol generating device 400 is a resistive heater assembly. The heater assembly includes a resistive heater blade 402 extending from the base 12 into the cavity 10. The resistive heater blade 402 includes a heater element electrically connected to the power supply 142. The second aerosol generating device 400 does not require a DC / AC converter. When power is supplied to the heater blade 402 from the power supply 142, the temperature of the heater blade 402 may increase.

[0198] The aerosol-generating article 500 is received within the cavity 10. The aerosol-generating article 500 includes an aerosol-forming substrate 502, which is a solid tobacco-containing substrate. In particular, the aerosol-forming substrate is an assembly of homogenized tobacco sheets. When the aerosol-generating article 500 is received within the cavity 10, the heater blade 402 penetrates the aerosol-forming substrate 502. The mouth end of the aerosol-generating article 400 protrudes from the cavity 10 and from the aerosol generating device when the aerosol-generating article is received within the cavity. This mouth end forms a mouthpiece 504 through which a user of the aerosol generating device may draw smoke in use.

[0199] In using the aerosol generating device 400, a user first activates the device by pressing a button. Immediately after activation, the controller 140 is configured to implement the method illustrated in FIG.

[0200] At method step 602, the controller is configured to initiate power supply to the heater blades 402 of the heater assembly.

[0201] Power is provided as direct current. In step 602, the controller is configured to provide power to the heater assembly such that the heater assembly operates in a low power mode. In the low power mode, substantial heating of the heater blades 402 is avoided. This is accomplished by providing power to the heater blades 402 as a series of consecutive pulses separated by time intervals. The pulses have a length of about 1 millisecond and are separated by time intervals of about 250 milliseconds. During the time intervals, power provided to the heater blades 402 is interrupted. Because the pulses are much shorter than the intervals between the pulses, the temperature of the heater blades 402 does not increase substantially in the low power mode, thereby avoiding substantial generation of aerosols in the low power mode.

[0202] Step 604 is performed during step 602. Method step 604 includes determining a rate of change of resistance of the heater blade 402. The heater blade 402 is made of a material that has a resistance that is temperature dependent. In this manner, determining the rate of change of resistance of the heater blade 402 provides a proxy for the rate of change of temperature of the heater blade 402.

[0203] During the pulse in the low power mode, the controller is configured to probe and measure the resistance of the heater blades 402. The controller is configured to measure the resistance of the heater blades 402 by measuring the voltage and current of the power supplied to the heater blades 402 and dividing the voltage by the current.

[0204] The controller can determine the rate of change of resistance by comparing the difference in resistance values ​​during successive pulses and dividing by the time separation between those measurements. In this embodiment, the controller is configured to determine the rate of change of resistance over a 2 second period.

[0205] In method step 606, the controller is configured to compare the determined rate of change of the resistance of the heater blade 402 to a predetermined threshold stored in the memory of the controller, the predetermined threshold corresponding to a maximum expected rate of change of the resistance of the heater blade when an unused aerosol-generating article 200 is received within the cavity 10 and the heater blade 402 has not been recently heated.

[0206] The expected rate of change of resistance of the heater blade 402 is relatively low because the expected rate of change of the heater blade temperature is low, since the initial temperature of the heater blade 402 and the aerosol-generating article is expected to be at or near ambient temperature. Thus, the predetermined threshold corresponds to a rate of change of temperature of less than 0.25 degrees Celsius.

[0207] If the aerosol-generating article has a temperature above ambient temperature, the aerosol-generating article may have a heating effect on the heater blade 402, such that the rate of change of resistance of the heater blade 4023 may deviate from the expected rate, which is indicative of a depleted aerosol-generating article.

[0208] Figure 7 is a graph showing how the resistance of the heater blade 402 changes over time when an unused aerosol-generating article is received within the cavity. Figure 8 is a graph showing how the resistance of the heater blade 402 changes over time when a depleted aerosol-generating article having a temperature above ambient temperature is received within the cavity. Both Figures 7 and 8 show time on the x-axis and resistance on the y-axis. The time spans a relatively short period of 2 seconds.

[0209] 7-8, it is apparent that the slope of the graph is steeper when a depleted aerosol-generating article is received within cavity 10. This is because the heating effect of the depleted aerosol-generating article on heater blade 402 causes the heater blade to increase in temperature, which in turn increases its resistance.

[0210] If the controller determines that the magnitude of the rate of change of resistance of the heater blade 402 is less than or equal to the predetermined threshold, the controller is configured to perform method step 608.

[0211] Method step 608 includes switching from a low power mode to a high power mode. In the high power mode, power is supplied to the heater blades 402 such that significant heating of the heater blades 402 occurs. Power can be supplied either continuously or, if power is supplied in pulses, the length of the pulses is substantially longer than the interval between pulses. In the high power mode, a user can puff on the aerosol generating device to inhale the aerosol. The high power mode can be considered a normal use phase of the device. In some embodiments, the aerosol generating device includes a user interface that indicates to the user that the device is ready for puffing.

[0212] During the high power mode, the user puffs on the mouthpiece 504 of the received aerosol-generating article 500, which results in air being drawn through the airflow channel 120 towards the user's mouth. During puffing, air flows from the exterior of the aerosol-generating device into the airflow channel 120 through the air inlet 122. The air is drawn through a portion of the airflow channel defined by the airflow channel walls 124 and into the cavity through the air inlet defined in the base 12 of the cavity 10. Because the aerosol-generating article 500 is received within the cavity, the air drawn into the cavity enters the aerosol-generating article 500 at its distal end. The air therefore passes through the aerosol-forming substrate 502. In doing so, volatile compounds generated by the heating of the substrate 502 may become entrained in the air. As the air continues towards the mouth end of the aerosol-generating article 500, the volatile compounds cool and form an aerosol.

[0213] If the controller determines that the magnitude of the rate of change of the resistance of the heater blade exceeds a predetermined threshold, the controller is configured to execute method step 610.

[0214] Step 610 involves switching from the low power mode to an error mode. In the error mode, the controller is configured to prevent power from being supplied to the heater assembly, thereby preventing a user from continuing to use the aerosol generating device. By switching to the error mode, the controller prevents the depleted aerosol generating article from being reheated and reused.

[0215] In an alternative embodiment of the second aerosol generating apparatus, the predetermined threshold used in method step 606 corresponds to a minimum expected rate of change in heater blade resistance when an unused aerosol generating article 200 is received in the cavity 10 and the heater blade 402 has not been recently heated. In this case, the expected rate of change in heater blade 402 resistance will be relatively high because the starting heater temperature of the recently heated heater blade 402 is significantly higher than the ambient temperature. The heater blade 402 cools down over time. The cooling effect is particularly noticeable when an unused aerosol generating article is received in a cavity 10 that has a temperature significantly below that of the heater blade 402.

[0216] If the aerosol-generating article has a temperature above ambient temperature, the rate of change of conductance of the susceptor element 206 may deviate from the expected rate because the aerosol-generating article has a small cooling effect on the heater blade 402. This is indicative of a depleted aerosol-generating article.

[0217] Figure 9 is a graph showing how the resistance of the heater blade 402 changes over time when an unused aerosol-generating article is received in the cavity if the heater blade 402 has recently been heated. Figure 10 is a graph showing how the resistance of the heater blade 402 changes over time when a depleted aerosol-generating article having a temperature above ambient temperature is received in the cavity. Both Figures 9 and 10 show time on the x-axis and resistance on the y-axis. The time spans a relatively short period of 2 seconds.

[0218] 9-10, it is apparent that the slope of the graph is steeper when an unused aerosol-generating article is received within cavity 10. This is because the cooling effect of the unused aerosol-generating article on heater blade 402 reduces the temperature of the heater blade, which in turn reduces its resistance. In Figure 10, the aerosol-generating article has a higher starting temperature and therefore has less cooling effect on heater blade 402.

[0219] If the controller determines that the magnitude of the rate of change of resistance of the heater blade 402 is greater than or equal to the predetermined threshold, the controller is configured to perform method step 608.

[0220] If the controller determines that the magnitude of the rate of change of resistance of the heater blade 402 is less than the predetermined threshold, the controller is configured to execute method step 610.

[0221] In a further embodiment of the second aerosol-generating article, method step 604 additionally includes determining a resistance of the heater blade 402 and comparing the resistance to a threshold resistance value stored in a memory of the controller. The controller is configured to determine the resistance of the heater blade 402 immediately after power is supplied to the heater blade 402 in step 602.

[0222] The threshold resistance is the resistance of the heater blade when it is at or near ambient temperature. For example, the threshold resistance is the resistance of the heater blade 402 at 35 degrees Celsius. The purpose of comparing the determined resistance to the threshold resistance is to determine whether the heater blade 402 is initially near or hotter than ambient temperature. This indicates whether the second device 400 has been used recently.

[0223] If the determined resistance is equal to or less than the threshold resistance, the controller may determine that the second aerosol generating device 400 has not been used recently. In that case, the predetermined threshold for the rate of change of resistance that the controller is configured to use in method step 606 corresponds to the maximum expected rate of change of resistance of the heater blade when an unused aerosol generating article 200 is received within the cavity 10 and the heater blade 402 has not been heated recently.

[0224] If the determined resistance is greater than the threshold resistance, the controller may determine that the second aerosol generating device 400 has been used recently. In that case, the predetermined threshold for the rate of change of resistance that the controller is configured to use in method step 606 corresponds to the minimum expected rate of change in resistance of the heater blades 402 when an unused aerosol generating article 200 is received within the cavity 10 and when the heater blades 402 have been recently heated.

[0225] By selecting the predefined threshold used in method step 606 based on the detected resistance of the heater blades 402, the controller can adapt the method of Fig. 6 depending on the starting condition of the heater blades 402. In effect, the previous two embodiments of the second aerosol generating device 400 described above are combined.

Claims

1. 1. An aerosol generating apparatus for generating an aerosol from an aerosol-generating article, the aerosol generating apparatus comprising: a cavity for receiving an aerosol-generating article; a heater assembly for heating the aerosol-generating article received within the cavity; and a power supply configured to supply power to the heater assembly and controlled by a controller to be operable in at least a low power mode in which no aerosol is generated, and a high power mode in which aerosol may be generated; the controller is configured to control the power source to initially operate in the low power mode, and in the low power mode, the controller is configured to measure a parameter related to a rate of change of temperature of the heater assembly or a rate of change of temperature of the aerosol-generating article received within the cavity; An aerosol generating device, wherein the controller is configured to switch from the low power mode to the high power mode only if the measured parameter meets a predetermined criterion.

2. 2. The aerosol generating device of claim 1, wherein the controller is configured to switch from the low power mode to an error mode if the measured parameter does not meet the predetermined criterion.

3. 3. The aerosol generating device of claim 1, wherein the predetermined criteria comprises a comparison of the magnitude of the measured parameter with a predetermined threshold value.

4. 4. The aerosol generating device of claim 3, wherein the predetermined criterion is met if the magnitude of the measured parameter is less than the predetermined threshold.

5. 4. The aerosol generating device of claim 3, wherein the predetermined criterion is met if the magnitude of the measured parameter is greater than the predetermined threshold.

6. An aerosol generating device as described in any one of claims 1 to 5, wherein the controller is configured to control the power source to operate the heater assembly in the low power mode for a predetermined time after startup of the device or after detection of an aerosol generating article received within the device.

7. 7. The aerosol generating device of claim 6, wherein the predetermined time is less than 3 seconds.

8. 8. An aerosol generating apparatus according to any one of claims 1 to 7, wherein the aerosol generating apparatus is for use with an aerosol generating article including a susceptor element, the heater assembly includes an inductor coil, and the power supply is configured to provide an oscillating current to the inductor coil.

9. 9. The aerosol generating apparatus of claim 8, wherein the measured parameter is the rate of change of conductance of the susceptor element of a received aerosol-generating article.

10. 10. The aerosol generating device of claim 9, wherein the predetermined criterion is met if the rate of change of the conductance of the susceptor element is less than a predetermined threshold.

11. An aerosol generating device according to any one of claims 1 to 10, wherein in the low power mode, the controller is configured to control the power source to supply current with a duty cycle of less than 2%.

12. An aerosol generating device as described in any one of claims 1 to 7, wherein the heater assembly includes a heater element configured to heat the aerosol generating article received in the cavity in use, and during the low power mode, the controller is configured to measure a parameter related to the rate of change of temperature of the heater element.

13. An aerosol generating system comprising an aerosol generating device according to any one of claims 1 to 12 and an aerosol-generating article comprising an aerosol-forming substrate.

14. 14. The aerosol generating system of claim 13, wherein the aerosol generating article comprises a susceptor element.

15. 1. A method of controlling a heater assembly of an aerosol generating device, the heater assembly being for heating an aerosol-generating article received within a cavity of the aerosol generating device and operable in at least a low power mode in which aerosols are not generated and a high power mode in which aerosols may be generated, the method comprising: controlling power supplied to the heater assembly such that the heater assembly initially operates in a low power mode; measuring a parameter related to a rate of change of temperature of the heater assembly or a rate of change of temperature of an aerosol-generating article received within the cavity of the aerosol generating device while operating the heater assembly in the low power mode; and switching from the low power mode to the high power mode only if the measured parameter meets a predetermined criterion.

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