The present disclosure relates to an inductive heating device for heating an aerosol-forming substrate. The present invention further relates to an aerosol-generating device comprising such an inductive heating device and a method for controlling aerosol production in the aerosolgenerating device.

Aerosol-generating devices may comprise an electrically-operated heat source that is configured to heat an aerosol-forming substrate to produce an aerosol. It is important for aerosolgenerating devices to accurately monitor and control the temperature of the electrically operated heat source to ensure optimum generation and delivery of an aerosol to a user. In particular, it is important to ensure that the electrically-operated heat source evenly heats the aerosol-forming substrate to provide optimum taste and aroma for the user as well as preventing the generation of undesirable compounds if a portion of the aerosol-forming substrate were to overheat.

It would be desirable to provide temperature monitoring and control of an inductive heating device that provides for reliable temperature regulation in order to provide for even heat distribution within the heat source and therefore optimal heating of the energy-forming substrate by the aerosol-generating device.

According to an embodiment of the present invention, there is provided a method for controlling aerosol production in an aerosol-generating device, the aerosol-generating device comprising an inductive heating arrangement and a power source for providing power to the inductive heating arrangement. The method comprises: performing, during a first heating phase during user operation of the aerosol-generating device for producing an aerosol, a calibration process for measuring one or more calibration values associated with a susceptor inductively coupled to the inductive heating arrangement, wherein the susceptor is configured to heat an aerosol-forming substrate; and during a second heating phase during user operation of the aerosol-generating device for producing an aerosol, controlling power provided to the inductive heating arrangement such that the temperature of the susceptor is adjusted based on the one or more calibration values. The method further comprises, during the first heating phase, performing a pre-heating process, wherein the pre-heating process is performed before the calibration process. The pre-heating process comprises the steps of: i) controlling the power provided to the inductive heating arrangement to cause an increase of the temperature of the susceptor; ii) monitoring a power source parameter, wherein the power source parameter is based at least in part on current; and iii) interrupting provision of power to the inductive heating arrangement at a first predetermined value of the monitored power source parameter, wherein the first predetermined value of the monitored power source parameter is associated with a current value that is greater than a minimum operating current.

The pre-heating process allows for heat to spread within the aerosol-forming substrate so that there is an even heat distribution within the susceptor before launching the calibration process, thereby improving the reliability of the calibration values. Further, the pre-heating process provides enough heating to the susceptor to reduce temperature gradients within the aerosol-forming substrate without the need to increase the length of time required for pre-heating. The pre-heating process therefore provides improved heating of the aerosol-forming substrate during the user operation of the aerosol-generating device for producing an aerosol without affecting the user experience.

The first predetermined value of the monitored power source parameter may be between 101 percent and 150 percent of a power source parameter value at the minimum current.

The first predetermined value of the monitored power source parameter may correspond to a susceptor temperature between 170 and 270 degrees Celsius, preferably between 170 and 240 degrees Celsius or between 240 and 270 degrees Celsius.

The monitored power source parameter may be conductance or resistance.

The method may further comprise storing at least the first predetermined value of the monitored power source parameter in a memory of the aerosol-generating device.

Heating to a predefined value reduces the time required for the pre-heating process and ensures that an even heating of the aerosol-forming substrate is reliably enabled.

Monitoring the power source parameter may comprise measuring a plurality of values of the power source parameter. Interrupting provision of power to the inductive heating arrangement at a first predetermined value of the monitored power source parameter may comprise determining that a difference between consecutive values of the plurality of values is below a threshold difference.

Subsequent to interrupting the provision of power to the inductive heating arrangement, the pre-heating process may further comprise the steps of: iv) at a second predetermined value of the monitored power source parameter, controlling the power provided to the inductive heating arrangement to cause an increase of the temperature of the susceptor, wherein the second predetermined value of the monitored power source parameter is associated with a current value that is less than the minimum operating current; and vi) repeating steps i) to iv) fora predetermined duration of the pre-heating process.

This provides for more even heat distribution in the susceptor and the aerosol-forming substrate during the pre-heating process. The predetermined duration of the heating process may be between 10 seconds and 15 seconds.

The method may further comprise, if the monitored power source parameter does not reach a value corresponding to the minimum operating current of the susceptor during the predetermined duration of the pre-heating process, ceasing operation of the aerosol-generating device.

The susceptor is preferably comprised in an aerosol-generating article that is configured to be inserted into the aerosol-generating device. Aerosol-generating articles that are not configured to be used with the aerosol-generating device will not exhibit the same behavior as authorized aerosol-generating articles. Specifically, for aerosol-generating articles that are not configured to be used with the aerosol-generating device, the minimum current/conductance value or the maximum resistance value will not be observed during the pre-determined duration of the preheating process. Accordingly, this prevents the use of non-authorized aerosol-generating articles.

The second predetermined value of the power source parameter may correspond to a susceptor temperature between 110 and 220 degrees Celsius.

The pre-heating process may be performed in response to detecting a user input. The user input may correspond to a user activation of the aerosol-generating device. The aerosolgenerating device may comprise a cavity configured to receive an aerosol-generating article, wherein the aerosol-generating article comprises the susceptor, and wherein the pre-heating process is performed in response to detecting the aerosol-generating article.

Detecting the aerosol-generating article may comprise detecting the susceptor.

The one or more calibration values may comprise a power source parameter value corresponding to the minimum operating temperature of the susceptor.

The one or more calibration values may further comprise a power source parameter value corresponding to a maximum operating temperature of the susceptor.

Controlling power provided to the inductive heating arrangement such that the temperature of the susceptor is adjusted based on the one or more calibration values may comprise maintaining the temperature of the susceptor between the minimum operating temperature of the susceptor and the maximum operating temperature of the susceptor.

According to an aspect, there is provided an aerosol-generating device comprising: a power source for providing a DC supply voltage and a DC current; and power supply electronics connected to the power source. The power supply electronics comprise: a DC/AC converter; an inductor connected to the DC/AC converter for the generation of an alternating magnetic field; and a controller. When energized by an alternating current from the DC/AC converter, the inductor is couplable to a susceptor, wherein the susceptor is configured to heat an aerosol-forming substrate. The controller is configured to: perform, during a first heating phase during user operation of the aerosol-generating device for producing an aerosol, a calibration process for measuring one or more calibration values associated with the susceptor; and during a second heating phase during user operation of the aerosol-generating device for producing an aerosol, control power provided to the inductor such that the temperature of the susceptor is adjusted based on the one or more calibration values. During the first heating phase, the controller is further configured to perform a pre-heating process, wherein the pre-heating process is performed before the calibration process. The pre-heating process comprises the steps of: i) controlling the power provided to the inductor to cause an increase of the temperature of the susceptor; ii) monitoring a power source parameter wherein the power source parameter is based at least in part on current; and iii) interrupting provision of power to the inductor at a first predetermined value of the monitored power source parameter, wherein the first predetermined value of the monitored power source parameter is associated with a current value that is greater than a minimum operating current.

The first predetermined value of the monitored power source parameter may be between 101 percent and 150 percent of a power source parameter value that corresponds to the minimum operating current.

The first predetermined value of the monitored power source parameter may correspond to a susceptor temperature between 170 and 270 degrees Celsius, preferably between 170 and 240 degrees Celsius or between 240 and 270 degrees Celsius.

The monitored power source parameter may be conductance or resistance.

The aerosol-generating device may further comprise a memory. The memory may be configured to store at least the first predetermined value of the monitored power source parameter.

Monitoring the power source parameter may comprise measuring a plurality of values of the power source parameter. Interrupting provision of power to the inductor at a first predetermined value of the monitored power source parameter may comprise determining that a difference between consecutive values of the plurality of values is below a threshold difference.

Subsequent to interrupting the provision of power to the power supply electronics, the preheating process may further comprise the steps of: iv) at a second predetermined value of the monitored power source parameter, controlling the power provided to the inductor to cause an increase of the temperature of the susceptor, wherein the second predetermined value of the monitored power source parameter corresponds to a susceptor temperature that is less than the minimum operating current; and vi) repeating steps i) to iv) for a predetermined duration of the pre-heating process.

The predetermined duration of the heating process may be between 10 seconds and 15 seconds. If the monitored power source parameter does not reach a value corresponding to the minimum operating current of the susceptor during the predetermined duration of the pre-heating process, the controller may be further configured to cease operation of the aerosol-generating device.

The second predetermined value of the monitored power source parameter may correspond to a susceptor temperature between 110 and 220 degrees Celsius.

The controller may be configured to perform the pre-heating process in response to detecting a user input.

The user input may correspond to a user activation of the aerosol-generating device.

The aerosol-generating device may comprise a cavity configured to receive an aerosolgenerating article. The aerosol-generating article may comprise the susceptor. The controller may be configured to perform the pre-heating process in response to detecting the aerosol-generating article. Detecting the aerosol-generating article may comprise detecting the susceptor.

The one or more calibration values may comprise a power source parameter value corresponding to a minimum operating temperature of the susceptor.

The one or more calibration values may further comprise a power source parameter value corresponding to a maximum operating temperature of the susceptor.

Controlling power provided to the inductive heating arrangement such that the temperature of the susceptor is adjusted based on the one or more calibration values may comprise maintaining the temperature of the susceptor between the minimum operating temperature of the susceptor and the maximum operating temperature of the susceptor.

According to a further aspect there is provided an aerosol-generating system, comprising: the aerosol-generating device described above; and an aerosol-generating article, wherein the aerosol-generating article comprises the aerosol-generating substrate and the susceptor.

As used herein, the term “aerosol-generating device” refers to a device that interacts with an aerosol-forming substrate to generate an aerosol. An aerosol-generating device may interact with one or both of an aerosol-generating article comprising an aerosol-forming substrate, and a cartridge comprising an aerosol-forming substrate. In some examples, the aerosol-generating device may heat the aerosol-forming substrate to facilitate release of volatile compounds from the substrate. An electrically operated aerosol-generating device may comprise an atomizer, such as an electric heater, to heat the aerosol-forming substrate to form an aerosol.

As used herein, the term "aerosol-generating system" refers to the combination of an aerosol-generating device with an aerosol-forming substrate. When the aerosol-forming substrate forms part of an aerosol-generating article, the aerosol-generating system refers to the combination of the aerosol-generating device with the aerosol-generating article. In the aerosol- generating system, the aerosol-forming substrate and the aerosol-generating device cooperate to generate an aerosol.

As used herein, the term “aerosol-forming substrate” refers to a substrate capable of releasing volatile compounds that can form an aerosol. The volatile compounds may be released by heating or combusting the aerosol-forming substrate. As an alternative to heating or combustion, in some cases, volatile compounds may be released by a chemical reaction or by a mechanical stimulus, such as ultrasound. The aerosol-forming substrate may be solid or may comprise both solid and liquid components. An aerosol-forming substrate may be part of an aerosol-generating article.

As used herein, the term “aerosol-generating article” refers to an article comprising an aerosol-forming substrate that is capable of releasing volatile compounds that can form an aerosol. An aerosol-generating article may be disposable. An aerosol-generating article comprising an aerosol-forming substrate comprising tobacco may be referred to herein as a tobacco stick.

An aerosol-forming substrate may comprise nicotine. An aerosol-forming substrate may comprise tobacco, for example the aerosol-forming substrate may comprise a tobacco-containing material containing volatile tobacco flavor compounds, which are released from the aerosolforming substrate upon heating. In preferred embodiments an aerosol-forming substrate may comprise homogenized tobacco material, for example cast leaf tobacco. The aerosol-forming substrate may comprise both solid and liquid components. The aerosol-forming substrate may comprise a tobacco-containing material containing volatile tobacco flavor compounds, which are released from the substrate upon heating. The aerosol-forming substrate may comprise a nontobacco material. The aerosol-forming substrate may further comprise an aerosol former. Examples of suitable aerosol formers are glycerin and propylene glycol.

As used herein, “aerosol-cooling element” refers to a component of an aerosol-generating article located downstream of the aerosol-forming substrate such that, in use, an aerosol formed by volatile compounds released from the aerosol-forming substrate passes through and is cooled by the aerosol cooling element before being inhaled by a user. An aerosol cooling element has a large surface area, but causes a low pressure drop. Filters and other mouthpieces that produce a high pressure drop, for example filters formed from bundles of fibers, are not considered to be aerosol-cooling elements. Chambers and cavities within an aerosol-generating article are not considered to be aerosol cooling elements.

As used herein, the term "mouthpiece" refers to a portion of an aerosol-generating article, an aerosol-generating device or an aerosol-generating system that is placed into a user's mouth in order to directly inhale an aerosol. As used herein, the term “susceptor” refers to an element comprising a material that is capable of converting the energy of a magnetic field into heat. When a susceptor is located in an alternating magnetic field, the susceptor is heated. Heating of the susceptor may be the result of at least one of hysteresis losses and eddy currents induced in the susceptor, depending on the electrical and magnetic properties of the susceptor material.

As used herein when referring to an aerosol-generating device, the terms “upstream” and “front”, and “downstream” and “rear”, are used to describe the relative positions of components, or portions of components, of the aerosol-generating device in relation to the direction in which air flows through the aerosol-generating device during use thereof. Aerosol-generating devices according to the invention comprise a proximal end through which, in use, an aerosol exits the device. The proximal end of the aerosol-generating device may also be referred to as the mouth end or the downstream end. The mouth end is downstream of the distal end. The distal end of the aerosol-generating article may also be referred to as the upstream end. Components, or portions of components, of the aerosol-generating device may be described as being upstream or downstream of one another based on their relative positions with respect to the airflow path of the aerosol-generating device.

As used herein when referring to an aerosol-generating article, the terms “upstream” and “front”, and “downstream” and “rear”, are used to describe the relative positions of components, or portions of components, of the aerosol-generating article in relation to the direction in which air flows through the aerosol-generating article during use thereof. Aerosol-generating articles according to the invention comprise a proximal end through which, in use, an aerosol exits the article. The proximal end of the aerosol-generating article may also be referred to as the mouth end or the downstream end. The mouth end is downstream of the distal end. The distal end of the aerosol-generating article may also be referred to as the upstream end. Components, or portions of components, of the aerosol-generating article may be described as being upstream or downstream of one another based on their relative positions between the proximal end of the aerosol-generating article and the distal end of the aerosol-generating article. The front of a component, or portion of a component, of the aerosol-generating article is the portion at the end closest to the upstream end of the aerosol-generating article. The rear of a component, or portion of a component, of the aerosol-generating article is the portion at the end closest to the downstream end of the aerosol-generating article.

As used herein, the term “inductively couple” refers to the heating of a susceptor when penetrated by an alternating magnetic field. The heating may be caused by the generation of eddy currents in the susceptor. The heating may be caused by magnetic hysteresis losses. As used herein, the term “puff” means the action of a user drawing an aerosol into their body through their mouth or nose.

As used herein, the term “temperature detector” refers to a thermocouple, a negative temperature coefficient resistive temperature sensor or a positive temperature coefficient resistive temperature sensor.

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

Example Ex1 : A method for controlling aerosol production in an aerosol-generating device, the aerosol-generating device comprising an inductive heating arrangement and a power source for providing power to the inductive heating arrangement, and the method comprising: performing, during a first heating phase during user operation of the aerosol-generating device for producing an aerosol, a calibration process for measuring one or more calibration values associated with a susceptor inductively coupled to the inductive heating arrangement, wherein the susceptor is configured to heat an aerosol-forming substrate; and during a second heating phase during user operation of the aerosol-generating device for producing an aerosol, controlling power provided to the inductive heating arrangement such that the temperature of the susceptor is adjusted based on the one or more calibration values; wherein the method further comprises, during the first heating phase, performing a pre-heating process, wherein the pre-heating process is performed before the calibration process, and wherein the pre-heating process comprises the steps of: i) controlling the power provided to the inductive heating arrangement to cause an increase of the temperature of the susceptor; ii) monitoring a power source parameter, wherein the power source parameter is based at least in part on current; and iii) interrupting provision of power to the inductive heating arrangement at a first predetermined value of the monitored power source parameter, wherein the first predetermined value of the monitored power source parameter is associated with a current value that is greater than a minimum operating current.

Example Ex2: The method according to example Ex1 , wherein the first predetermined value of the monitored power source parameter is between 101 percent and 150 percent of a power source parameter value at the minimum current.

Example Ex3: The method according to example Ex1 or Ex2, wherein the first predetermined value of the monitored power source parameter corresponds to a susceptor temperature between 170 and 270 degrees Celsius.

Example Ex4: The method according to one of the preceding examples, wherein the monitored power source parameter is conductance or resistance. Example Ex5: The method according to one of the preceding examples, further comprising storing at least the first predetermined value of the monitored power source parameter in a memory of the aerosol-generating device.

Example Ex6: The method according to one of examples Ex1 to Ex4, wherein monitoring the power source parameter comprises measuring a plurality of values of the power source parameter, and wherein interrupting provision of power to the inductive heating arrangement at a first predetermined value of the monitored power source parameter comprises determining that a difference between consecutive values of the plurality of values is below a threshold difference.

Example Ex7: The method according to one of the preceding examples, wherein, subsequent to interrupting the provision of power to the inductive heating arrangement, the preheating process further comprises the steps of: iv) at a second predetermined value of the monitored power source parameter, controlling the power provided to the inductive heating arrangement to cause an increase of the temperature of the susceptor, wherein the second predetermined value of the monitored power source parameter is associated with a current value that is less than the minimum operating current; and vi) repeating steps i) to iv) fora predetermined duration of the pre-heating process.

Example Ex8: The method according to example Ex7, wherein the predetermined duration of the heating process is between 10 seconds and 15 seconds.

Example Ex9: The method according to example Ex7 or Ex8, further comprising: if the monitored power source parameter does not reach a value corresponding to the minimum operating current of the susceptor during the predetermined duration of the pre-heating process, ceasing operation of the aerosol-generating device.

Example Ex10: The method according to one of examples Ex7 to Ex9, wherein the second predetermined value of the power source parameter corresponds to a susceptor temperature between 110 and 220 degrees Celsius.

Example Ex11 : The method according to one of the preceding examples, wherein the preheating process is performed in response to detecting a user input.

Example Ex12: The method according to example Ex11 , wherein the user input corresponds to a user activation of the aerosol-generating device.

Example Ex13: The method according to one of examples Ex1 to Ex10, wherein the aerosol-generating device comprises a cavity configured to receive an aerosol-generating article, wherein the aerosol-generating article comprises the susceptor, and wherein the pre-heating process is performed in response to detecting the aerosol-generating article.

Example Ex14: The method according to example Ex13, wherein detecting the aerosolgenerating article comprises detecting the susceptor. Example Ex15: The method according to one of the preceding examples, wherein the one or more calibration values comprise a power source parameter value corresponding to the minimum operating temperature of the susceptor.

Example Ex16: The method according to example Ex15, wherein the one or more calibration values further comprise a power source parameter value corresponding to a maximum operating temperature of the susceptor.

Example Ex17: The method according to example Ex16, wherein controlling power provided to the inductive heating arrangement such that the temperature of the susceptor is adjusted based on the one or more calibration values comprises maintaining the temperature of the susceptor between the minimum operating temperature of the susceptor and the maximum operating temperature of the susceptor.

Example Ex18: An aerosol-generating device comprising: a power source for providing a DC supply voltage and a DC current; power supply electronics connected to the power source, the power supply electronics comprising: a DC/AC converter; an inductor connected to the DC/AC converter for the generation of an alternating magnetic field, when energized by an alternating current from the DC/AC converter, the inductor being couplable to a susceptor, wherein the susceptor is configured to heat an aerosol-forming substrate; and a controller configured to: perform, during a first heating phase during user operation of the aerosol-generating device for producing an aerosol, a calibration process for measuring one or more calibration values associated with the susceptor; and during a second heating phase during user operation of the aerosol-generating device for producing an aerosol, control power provided to the inductor such that the temperature of the susceptor is adjusted based on the one or more calibration values, wherein, during the first heating phase, the controller is further configured to perform a pre-heating process, wherein the pre-heating process is performed before the calibration process, and wherein the pre-heating process comprises the steps of: i) controlling the power provided to the inductor to cause an increase of the temperature of the susceptor; ii) monitoring a power source parameter wherein the power source parameter is based at least in part on current; and iii) interrupting provision of power to the inductor at a first predetermined value of the monitored power source parameter, wherein the first predetermined value of the monitored power source parameter is associated with a current value that is greater than a minimum operating current.

Example Ex19: The aerosol-generating device according to example Ex18, wherein the first predetermined value of the monitored power source parameter is between 101 percent and 150 percent of a power source parameter value that corresponds to the minimum operating current. Example Ex20: The aerosol-generating device according to example Ex18 or Ex19, wherein the first predetermined value of the monitored power source parameter corresponds to a susceptor temperature between 170 and 270 degrees Celsius.

Example Ex21 : The aerosol-generating device according to one of examples Ex18 to Ex20, wherein the monitored power source parameter is conductance or resistance.

Example Ex22: The aerosol-generating device according to one of examples Ex18 to Ex21 , wherein the aerosol-generating device further comprises a memory, wherein the memory is configured to store at least the first predetermined value of the monitored power source parameter.

Example Ex23: The aerosol-generating device according to one of examples Ex18 to Ex20, wherein monitoring the power source parameter comprises measuring a plurality of values of the power source parameter, and wherein interrupting provision of power to the inductor at a first predetermined value of the monitored power source parameter comprises determining that a difference between consecutive values of the plurality of values is below a threshold difference.

Example Ex24: The aerosol-generating device according to one of examples Ex18 to Ex23, wherein, subsequent to interrupting the provision of power to the power supply electronics, the pre-heating process further comprises the steps of: iv) at a second predetermined value of the monitored power source parameter, controlling the power provided to the inductor to cause an increase of the temperature of the susceptor, wherein the second predetermined value of the monitored power source parameter corresponds to a susceptor temperature that is less than the minimum operating current; and vi) repeating steps i) to iv) for a predetermined duration of the pre-heating process.

Example Ex25: The aerosol-generating device according to example Ex24, wherein the predetermined duration of the heating process is between 10 seconds and 15 seconds.

Example Ex26: The aerosol-generating device according to example Ex24 or Ex25, wherein if the monitored power source parameter does not reach a value corresponding to the minimum operating current of the susceptor during the predetermined duration of the pre-heating process, the controller is further configured to cease operation of the aerosol-generating device.

Example Ex27: The aerosol-generating device according to one of examples Ex24 to Ex26, wherein the second predetermined value of the monitored power source parameter corresponds to a susceptor temperature between 110 and 220 degrees Celsius.

Example Ex28: The aerosol-generating device according to one of examples Ex18 to Ex27, wherein the controller is configured to perform the pre-heating process in response to detecting a user input.

Example Ex29: The aerosol-generating device according to example Ex28, wherein the user input corresponds to a user activation of the aerosol-generating device. Example Ex30: The aerosol-generating device according to one of examples Ex18 to Ex27, wherein the aerosol-generating device comprises a cavity configured to receive an aerosolgenerating article, wherein the aerosol-generating article comprises the susceptor, and wherein the controller is configured to perform the pre-heating process in response to detecting the aerosol-generating article.

Example Ex31 : The aerosol-generating device according to example Ex30, wherein detecting the aerosol-generating article comprises detecting the susceptor.

Example Ex32: The aerosol-generating device according to one of examples Ex18 to Ex31 , wherein the one or more calibration values comprise a power source parameter value corresponding to a minimum operating temperature of the susceptor.

Example Ex33: The aerosol-generating device according to example Ex32, wherein the one or more calibration values further comprise a power source parameter value corresponding to a maximum operating temperature of the susceptor.

Example Ex34: The aerosol-generating device according to example Ex33, wherein controlling power provided to the inductive heating arrangement such that the temperature of the susceptor is adjusted based on the one or more calibration values comprises maintaining the temperature of the susceptor between the minimum operating temperature of the susceptor and the maximum operating temperature of the susceptor.

Example Ex35: An aerosol-generating system, comprising: the aerosol-generating device according to any of examples Ex18 to Ex34; and an aerosol-generating article, wherein the aerosol-generating article comprises the aerosol-generating substrate and the susceptor.

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

Figure 1 shows a schematic cross-sectional illustration of an aerosol-generating article;

Figure 2A shows a schematic cross-sectional illustration of an aerosol-generating device for use with the aerosol-generating article illustrated in Figure 1 ;

Figure 2B shows a schematic cross-sectional illustration of the aerosol-generating device in engagement with the aerosol-generating article illustrated in Figure 1 ;

Figure 3 is a block diagram showing an inductive heating device of the aerosol-generating device described in relation to Figure 2;

Figure 4 is a schematic diagram showing electronic components of the inductive heating device described in relation to Figure 3;

Figure 5 is a schematic diagram on an inductor of an LC load network of the inductive heating device described in relation to Figure 4;

Figure 6 is a graph of DC current vs. time illustrating the remotely detectable current changes that occur when a susceptor material undergoes a phase transition associated with its Curie point; Figure 7 illustrates a conductance profile of the susceptor during operation of the aerosolgenerating device;

Figure 8 is a flow diagram showing a method for controlling aerosol-production in the aerosol-generating device of Figure 2.

It will be appreciated that the figures are for illustration purposes and are not to scale.

Figure 1 illustrates a schematic side sectional view of an aerosol-generating article 100. The aerosol-generating article 100 comprises a rod of aerosol-forming substrate 110 and a downstream section 115 at a location downstream of the rod of aerosol-forming substrate 110. The aerosol-generating article 100 comprises an upstream section 150 at a location upstream of the rod of aerosol-forming substrate 110. Thus, the aerosol-generating article 100 extends from an upstream or distal end 180 to a downstream or mouth end 170. In use, air is drawn through the aerosol-generating article 100 by a user from the distal end 180 to the mouth end 170.

The downstream section 115 comprises a support element 120 located immediately downstream of the rod of aerosol-forming substrate 110, the support element 120 being in longitudinal alignment with the rod 110. The upstream end of the support element 120 abuts the downstream end of the rod of aerosol-forming substrate 110. In addition, the downstream section 115 comprises an aerosol-cooling element 130 located immediately downstream of the support element 120, the aerosol-cooling element 130 being in longitudinal alignment with the rod 110 and the support element 120. The upstream end of the aerosol-cooling element 130 abuts the downstream end of the support element 120. In use, volatile substances released from the aerosol-forming substrate 110 pass along the aerosol-cooling element 130 towards the mouth end 170 of the aerosol-generating article 100. The volatile substances may cool within the aerosolcooling element 130 to form an aerosol that is inhaled by the user.

The support element 120 comprises a first hollow tubular segment 125. The first hollow tubular segment 125 is provided in the form of a hollow cylindrical tube made of cellulose acetate. The first hollow tubular segment 125 defines an internal cavity 145 that extends all the way from an upstream end 165 of the first hollow tubular segment 125 to a downstream end 175 of the first hollow tubular segment 125.

The aerosol-cooling element 130 comprises a second hollow tubular segment 135. The second hollow tubular segment 135 is provided in the form of a hollow cylindrical tube made of cellulose acetate. The second hollow tubular segment 135 defines an internal cavity 155 that extends all the way from an upstream end 185 of the second hollow tubular segment 135 to a downstream end 195 of the second hollow tubular segment 135. In addition, a ventilation zone (not shown) is provided at a location along the second hollow tubular segment 135. A ventilation level of the aerosol-generating article 100 is about 25 percent. The downstream section 115 further comprises a mouthpiece 140 positioned immediately downstream of the aerosol-cooling element 130. As shown in the drawing of Figure 1 , an upstream end of the mouthpiece 140 abuts the downstream end 195 of the aerosol-cooling element 130. The mouthpiece 140 is provided in the form of a cylindrical plug of low-density cellulose acetate.

The aerosol-generating article 100 further comprises an elongate susceptor 160 within the rod of aerosol-generating substrate 110. In more detail, the susceptor 160 is arranged substantially longitudinally within the aerosol-forming substrate 110, such as to be approximately parallel to the longitudinal direction of the rod 110. As shown in the drawing of Figure 1 , the susceptor 160 is positioned in a radially central position within the rod and extends effectively along the longitudinal axis of the rod 110.

The susceptor 160 extends all the way from an upstream end to a downstream end of the rod of aerosol-forming substrate 110. In effect, the susceptor 160 has substantially the same length as the rod of aerosol-forming substrate 110. The susceptor 160 is located in thermal contact with the aerosol-forming substrate 110, such that the aerosol-forming substrate 110 is heated by the susceptor 160 when the susceptor 160 is heated.

The upstream section 150 comprises an upstream element 190 located immediately upstream of the rod of aerosol-forming substrate 110, the upstream element 190 being in longitudinal alignment with the rod 110. The downstream end of the upstream element 190 abuts the upstream end of the rod of aerosol-forming substrate. This advantageously prevents the susceptor 160 from being dislodged. Further, this ensures that the consumer cannot accidentally contact the heated susceptor 160 after use. The upstream element 190 is provided in the form of a cylindrical plug of cellulose acetate circumscribed by a stiff wrapper.

The susceptor 160 comprises at least two different materials. The susceptor 160 comprises at least two layers: a first layer of a first susceptor material disposed in physical contact with a second layer of a second susceptor material. The first susceptor material and the second susceptor material may each have a Curie temperature. In this case, the Curie temperature of the second susceptor material is lower than the Curie temperature of the first susceptor material. The first material may not have a Curie temperature. The first susceptor material may be aluminum, iron, or stainless steel. The second susceptor material may be nickel or a nickel alloy.

The susceptor 160 may be formed by electroplating at least one patch of the second susceptor material onto a strip of the first susceptor material. The susceptor may be formed by cladding a strip of the second susceptor material to a strip of the first susceptor material.

The aerosol-generating article 100 illustrated in Figure 1 is designed to engage with an aerosol-generating device, such as the aerosol-generating device 200 illustrated in Figure 2A, for producing an aerosol. The aerosol-generating device 200 comprises a housing 210 having a cavity 220 configured to receive the aerosol-generating article 100 and an inductive heating device 230 configured to heat an aerosol-generating article 100 for producing an aerosol. Figure 2B illustrates the aerosol-generating device 200 when the aerosol-generating article 100 is inserted into the cavity 220.

The inductive heating device 230 is illustrated as a block diagram in Figure 3. The inductive heating device 230 comprises a DC power source 310 and a heating arrangement 320 (also referred to as power supply electronics). The heating arrangement 320 comprises a controller 330, a DC/AC converter 340, a matching network 350 and an inductor 240.

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

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

Figure 4 schematically illustrates the electrical components of the inductive heating device 230, in particular the DC/AC converter 340. The DC/AC converter 340 preferably comprises a Class-E power amplifier. The Class-E power amplifier comprises a transistor switch 410 comprising a Field Effect Transistor 420, for example a Metal-Oxide-Semiconductor Field Effect Transistor, a transistor switch supply circuit indicated by the arrow 430 for supplying a switching signal (gate-source voltage) to the Field Effect Transistor 420, and an LC load network 440 comprising a shunt capacitor C1 and a series connection of a capacitor C2 and inductor L2, corresponding to inductor 240. In addition, the DC power source 310, comprising a choke L1 , is shown for supplying the DC supply voltage VDC, with a DC current IDC being drawn from the DC power source 310 during operation. The ohmic resistance R representing the total ohmic load 450, which is the sum of the ohmic resistance R _CO ii of the inductor L2 and the ohmic resistance Ri _oa d of the susceptor 160, is shown in more detail in Figure 5.

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

Turning back to Figure 3, the inductor 240 may receive the alternating current from the DC/AC converter 340 via a matching network 350 for optimum adaptation to the load, but the matching network 350 is not essential. The matching network 350 may comprise a small matching transformer. The matching network 350 may improve power transfer efficiency between the DC/AC converter 340 and the inductor 240.

As illustrated in Figure 2A, the inductor 240 is located adjacent to the distal portion 225 of the cavity 220 of the aerosol-generating device 200. Accordingly, the high frequency alternating current supplied to the inductor 240 during operation of the aerosol-generating device 200 causes the inductor 240 to generate a high frequency alternating magnetic field within the distal portion 225 of the aerosol-generating device 200. The alternating magnetic field preferably has a frequency of between 1 and 30 megahertz, preferably between 2 and 10 megahertz, for example between 5 and 7 megahertz. As can be seen from Figure 2B, when an aerosol-generating article 100 is inserted into the cavity 200, the aerosol-forming substrate 110 of the aerosol-generating article 100 is located adjacent to the inductor 240 so that the susceptor 160 of the aerosolgenerating article 100 is located within this alternating magnetic field. When the alternating magnetic field penetrates the susceptor 160, the alternating magnetic field causes heating of the susceptor 160. For example, eddy currents are generated in the susceptor 160 which is heated as a result. Further heating is provided by magnetic hysteresis losses within the susceptor 160. The heated susceptor 160 heats the aerosol-forming substrate 110 of the aerosol-generating article 100 to a sufficient temperature to form an aerosol. The aerosol is drawn downstream through the aerosol-generating article 100 and inhaled by the user.

The controller 330 may be a microcontroller, preferably a programmable microcontroller. The controller 330 is programmed to regulate the supply of power from the DC power source 310 to the inductive heating arrangement 320 in order to control the temperature of the susceptor 160.

Figure 6 illustrates the relationship between the DC current l _D c drawn from the power source 310 over time as the temperature of the susceptor 160 (indicated by the dashed line) increases. More specifically, the solid line 600 in Figure 6 illustrates the remotely-detectable DC current changes that occur when a susceptor material undergoes a phase transition associated with its Curie point. The DC current IDC drawn from the power source 310 is measured at an input side of the DC/AC converter 340. For the purpose of this illustration, it may be assumed that the voltage VDC of the power source 310 remains approximately constant.

As the susceptor 160 is inductively heated, the apparent resistance of the susceptor 160 increases. This increase in resistance is observed as a decrease in the DC current IDC drawn from the power source 310, which at constant voltage decreases as the temperature of the susceptor 160 increases. The high frequency alternating magnetic field provided by the inductor 240 induces eddy currents in close proximity to the susceptor surface, an effect that is known as the skin effect. The resistance in the susceptor 160 depends in part on the electrical resistivity of the first susceptor material, the resistivity of the second susceptor material, and in part on the depth of the skin layer in each material available for induced eddy currents, and the resistivity is in turn temperature dependent.

As the second susceptor material reaches its Curie temperature, it loses its magnetic properties. This causes an increase in the skin layer available for eddy currents in the second susceptor material, which causes a decrease in the apparent resistance of the susceptor 160. The result is a temporary increase in the detected DC current IDC. Then, when the skin depth of the second susceptor material begins to increase, the resistance begins to fall. This is seen as the valley (the local minimum 610) in Figure 6.

As heating continues, the current continues to increase until the maximum skin depth is reached, which coincides with the point where the second susceptor material has lost its spontaneous magnetic properties. This point is called the Curie temperature and is seen as the hill (the local maximum 620) in Figure 6. At this point the second susceptor material has undergone a phase change from a ferro-magnetic or ferri-magnetic state to a paramagnetic state. At this point, the susceptor 160 is at a known temperature (the Curie temperature, which is an intrinsic material-specific temperature).

If the inductor 240 continues to generate an alternating magnetic field (i.e. power to the DC/AC converter 340 is not interrupted) after the Curie temperature has been reached, the eddy currents generated in the susceptor 160 will run against the resistance of the susceptor 160, whereby Joule heating in the susceptor 160 will continue, and thereby the resistance will increase again (the resistance will have a polynomial dependence of the temperature, which for most metallic susceptor materials can be approximated to a third degree polynomial dependence for our purposes) and current will start falling again as long as the inductor 240 continues to provide power to the susceptor 160.

Therefore, the second susceptor material undergoes a reversible phase transition when heated through the (known) temperature range between the valley 610 and the hill 620 shown in Figure 6. The first turning point 610 (corresponding to a local minimum for current and a local maximum for resistance) corresponds to the start of the phase transition. The second turning point 620 (corresponding to a local maximum for current and a local minimum for resistance) corresponds to the end of the phase transition.

As can be seen from Figure 6, the apparent resistance of the susceptor 160, and hence the start and end of the phase transition, can be remotely detected by monitoring the DC current IDC drawn from the power source 310. Alternatively, the apparent resistance of the susceptor 160, and hence the start and end of the phase transition, can be remotely detected by monitoring a conductance value (where conductance is defined as the ratio of the DC current IDC to the DC supply voltage VDC) or a resistance value (where resistance is defined as the ratio of the DC supply voltage VDC to the DC current IDC). At least the DC current IDC drawn from the power source 310 is monitored by the controller 330. Although the DC supply voltage DC is known, preferably both the DC current IDC drawn from the power source 310 and the DC supply voltage VDC are monitored. The DC current IDC, the conductance value and the resistance value may be referred to as power source parameters.

As can be seen from Figure 6, the apparent resistance of the susceptor 160 (and correspondingly the current l _D c drawn from the power source 310) may vary with the temperature of the susceptor 160 in a strictly monotonic relationship over certain ranges of temperature of the susceptor 160, such as between the valley 610 and the hill 620. The strictly monotonic relationship allows for an unambiguous determination of the temperature of the susceptor 160 from a determination of the apparent resistance (R) or apparent conductance (1/R). This is because each determined value of the apparent resistance is representative of only one single value of the temperature, so that there is no ambiguity in the relationship. The monotonic relationship of the temperature of the susceptor 160 and the apparent resistance in the temperature range in which the second susceptor material undergoes the reversible phase transition allows for the determination and control of the temperature of the susceptor 160 and thus for the determination and control of the temperature of the aerosol-forming substrate 110.

The controller 330 regulates the supply of power provided to the heating arrangement 320 based on a power source parameter. Specifically, the heating arrangement 320 may comprise a current sensor (not shown) to measure the DC current IDC. The heating arrangement may optionally comprise a voltage sensor (not shown) to measure the DC supply voltage VDC. The current sensor and the voltage sensor are located at an input side of the DC/AC converter 340. The DC current IDC and optionally the DC supply voltage VDC are provided by feedback channels to the controller 330 to control the further supply of AC power PAC to the inductor 240. The controller 330 may control the temperature of the susceptor 160 by maintaining the measured power source parameter value at a target value corresponding to a target operating temperature of the susceptor 160. The controller 330 may use any suitable control loop to maintain the measured power source parameter at the target value, for example by using a proportional- integral-derivative control loop.

In order to take advantage of the strictly monotonic relationship between the apparent resistance (or apparent conductance) of the susceptor 160 and the temperature of the susceptor 160, during user operation for producing an aerosol, the power source parameter measured at the input side of the DC/AC converter 340 is maintained between a first calibration value corresponding to a first calibration temperature and a second calibration value corresponding to a second calibration temperature. The second calibration temperature is the Curie temperature of the second susceptor material (the hill 620 in the current plot in Fig. 6). The first calibration temperature is a temperature greater than or equal to the temperature of the susceptor at which the skin depth of the second susceptor material begins to increase, leading to a temporary lowering of the resistance (the valley 610 in the current plot in Figure 6). Thus, the first calibration temperature is a temperature greater than or equal to the temperature at maximum permeability of the second susceptor material. The first calibration temperature is at least 50 degrees Celsius lower than the second calibration temperature. At least the second calibration value may be determined by calibration of the susceptor 160, as will be described in more detail below. The first calibration value and the second calibration value may be stored as calibration values in a memory of the controller 330. Since the power source parameter will have a polynomial dependence on the temperature, the power source parameter will behave in a nonlinear manner as a function of temperature. However, the first and the second calibration values are chosen so that this dependence may be approximated as being linear between the first calibration value and the second calibration value because the difference between the first and the second calibration values is small, and the first and the second calibration values are in the upper part of the operational temperature range. Therefore, to adjust the temperature to a target operating temperature, the power source parameter is regulated according to the first calibration value and the second calibration value, through linear equations.

For example, if the first and the second calibration values are conductance values, the target conductance value corresponding to the target operating temperature may be given by:

^Target ^Lower T (^ X AG) where AG is the difference between the first conductance value and the second conductance value and x is a percentage of AG. The controller 330 may control the provision of power to the heating arrangement 320 by adjusting the duty cycle of the switching transistor 410 of the DC/AC converter 340. For example, during heating, the DC/AC converter 340 continuously generates alternating current that heats the susceptor 160, and simultaneously the DC current IDC and optionally the DC supply voltage VDC may be measured, preferably every millisecond for a period of 100 milliseconds.

For example, if the conductance or current is monitored by the controller 330 for adjusting the susceptor temperature, when the conductance or current reaches or exceeds a value corresponding to the target operating temperature for adjusting the susceptor temperature, the duty cycle of the switching transistor 410 is reduced. If the resistance is monitored by the controller 330 for adjusting the susceptor temperature, when the resistance reaches or goes below a value corresponding to the target operating temperature, the duty cycle of the switching transistor 410 is reduced. For example, the duty cycle of the switching transistor 410 may be reduced to about 10%. In other words, the switching transistor410 may be switched to a mode in which it generates pulses only every 10 milliseconds fora duration of 1 millisecond. During this 1 millisecond on-state (conductive state) of the switching transistor 410, the values of the DC supply voltage VDC and of the DC current IDC are measured and the conductance is determined. As the conductance decreases (or the resistance increases) to indicate that the temperature of the susceptor 160 is below the target operating temperature, the gate of the transistor 410 is again supplied with the train of pulses at the chosen drive frequency for the system.

The power may be supplied by the controller 330 to the inductor 240 in the form of a series of successive pulses of electrical current. In particular, power may be supplied to the inductor 240 in a series of pulses, each separated by a time interval. The series of successive pulses may comprise two or more heating pulses and one or more probing pulses between successive heating pulses. The heating pulses have an intensity such as to heat the susceptor 160. The probing pulses are isolated power pulses having an intensity such as not to heat the susceptor 160, but rather to obtain a feedback on the power source parameter and then on the evolution (decreasing) of the susceptor temperature. The controller 330 may control the power by controlling the duration of the time interval between successive heating pulses of power supplied by the DC power supply to the inductor 240. Additionally or alternatively, the controller 330 may control the power by controlling the length (in other words, the duration) of each of the successive heating pulses of power supplied by the DC power supply to the inductor 240.

The controller 330 is programmed to perform a calibration process in order to obtain the calibration values at which the power source parameter is measured at known temperatures of the susceptor 160. The known temperatures of the susceptor may be the first calibration temperature corresponding to the first calibration value and the second calibration temperature corresponding to the second calibration value. The calibration process is performed each time the user operates the aerosol-generating device 200. For example, the calibration process is performed during a first heating phase of the aerosol-generating device, before user operation of the aerosol-generating device 200 for generating an aerosol. The calibration process may be repeated during user operation of the aerosol-generating device 200 for generating an aerosol.

Figure 7 is a graph of conductance against time showing a heating profile of the susceptor 160, including a first heating phase 710 comprising the calibration process 710B described above. The first heating phase 710 is followed by a second heating phase 720 for heating the aerosolforming substrate to generate an aerosol for inhalation by a user of the aerosol-generating device.

Although Figure 7 is illustrated as a graph of conductance against time, it is to be understood that the controller 330 may be configured to control the heating of the susceptor 160 during the first heating phase 710 and the second heating phase 720 based on measured resistance or current as described above.

During the calibration process, the controller 330 controls the DC/AC converter 340 to continuously or continually supply power to the inductor 240 in order to heat the susceptor 160. The controller 330 monitors the power source parameter by measuring the current IDC drawn by the power supply and, optionally the power supply voltage V _D c- As discussed above in relation to Figure 6, as the susceptor 160 is heated, the measured current decreases until a first turning point E (corresponding to 610 in Figure 6) is reached and the current begins to increase. This first turning point E corresponds to a local minimum conductance or current value (a local maximum resistance value). The controller 330 may record the power source parameter at the first turning point as the first calibration value.

When the power source parameter is conductance or resistance, the power source parameter values may be determined based on the measured current IDC and the measured voltage VDC. Alternatively, it may be assumed that the power supply voltage VDC, which is a known property of the power source 310, is approximately constant. The temperature of the susceptor 160 at the first calibration value is referred to as the first calibration temperature. Preferably, the first calibration temperature is between 150 degrees Celsius and 350 degrees Celsius. More preferably, when the aerosol-forming substrate 110 comprises tobacco, the first calibration temperature is 320 degrees Celsius. The first calibration temperature is at least 50 degrees Celsius lower than the second calibration temperature.

As the controller 330 continues to control the power provided by the DC/AC converter 340 to the inductor 240, the controller 330 continues to monitor the power source parameter until a second turning point F (corresponding to 620 in Figure 6) is reached. The second turning point corresponds to a maximum current (corresponding to the Curie temperature of the second susceptor material) before the measured current begins to decrease. This turning point F corresponds to a local maximum conductance or current value (a local minimum resistance value). The controller 330 records the power source parameter value at the second turning point F as the second calibration value. The temperature of the susceptor 160 at the second calibration value is referred to as the second calibration temperature. Preferably, the second calibration temperature is between 200 degrees Celsius and 400 degrees Celsius. When the maximum is detected, the controller 330 controls the DC/AC converter 340 to interrupt provision of power to the inductor 240, resulting in a decrease in susceptor 160 temperature and a corresponding decrease in measured current.

Due to the shape of the graph, this process of continuously heating the susceptor 160 to obtain the first calibration value and the second calibration value may be repeated at least once during the calibration process 710B. After interrupting provision of power to the inductor 240, the controller 330 continues to monitor the power source parameter until a third turning point is observed. The third turning point corresponds to a second minimum conductance or current value (a second maximum resistance value). When the third turning point is detected, the controller 330 controls the DC/AC converter 340 to continuously provide power to the inductor 240 until a fourth turning point in the monitored power source parameter is observed. The fourth turning point corresponds to a second maximum conductance or current value (a second minimum resistance value). The controller 330 stores the power source parameter value that is measured at the third turning point as the first calibration value and the power source parameter value measured the fourth turning point as the second calibration value. The repetition of the measurement of the turning points corresponding to minimum and maximum measured current significantly improves the subsequent temperature regulation during user operation of the device for producing an aerosol. Preferably, controller 330 regulates the power based on the power source parameter values obtained from the second maximum and the second minimum, this being more reliable because the heat will have had more time to distribute within the aerosol-forming substrate 110 and the susceptor 160.

The controller 330 is configured to detect the turning points by measuring a sequence of power source parameter values. With reference to Figures 6 and 7, the sequence of measured power source parameter values will form a curve, with each value being greater than or less than the previous value. The controller 330 is configured to measure the calibration value at the point where the curve begins to flatten. In other words, the controller 330 records the calibration values when the difference between consecutive power source parameter values is below a predetermined threshold value. Further, during the first heating phase 710, the controller 330 is programmed to perform a pre-heating process 71 OA before the calibration process 71 OB.

To perform the pre-heating process 710A, the controller 330 is configured to continuously provide power to the inductor 240 to cause an increase of temperature of the susceptor 160. As described above, the measured current IDC starts decreasing with increasing susceptor 160 temperature until a turning point A, corresponding to minimum measured current, is reached. At this stage, the controller 330 continues to provide power to the inductor 240 and the measured current IDC starts increasing with increasing susceptor 110 temperature. The controller 330 is configured to interrupt provision of power to the inductor 240 when the measured power source parameter reaches a predetermined value B.

The predetermined power source parameter value at which the controller 330 interrupts provision of power to the inductor may be regulated according to the power source parameter value measured at turning point A. For example, if the power source parameter value is conductance, the conductance value at which the controller 330 interrupts provision of power to the inductor 240 may be given by:

Gg = G _A + (x X AG) where x may be between 1.01 and 1.5.

Alternatively, the controller 330 may configured to interrupt provision of power to the inductor 240 when an inflection point is reached, in other words just before the local maximum 620. In this example, the controller 330 is configured to determine a difference between consecutive measured current values. The controller 330 interrupts provision of power to the inductor 240 when the determined difference between the consecutive measured current values is lower than a predetermined threshold difference, where the predetermined threshold difference is the power source parameter value.

When the provision of power to the inductor 240 is interrupted, the susceptor 160 begins to cool and the value of the monitored current begins to decrease until a local minimum C is reached. The controller 330 may be configured to provide power to the inductor 240 when the measured power source parameter value reaches another predetermined power source value that corresponds to a minimum value of current at C. Alternatively, the controller 330 may be configured to provide power to the inductor when the measured current reaches another predetermined power source value that corresponds a predetermined value of current D. Alternatively, the controller 330 is configured to wait for a predetermined period of time to allow the susceptor 160 to cool before continuing heating.

The predetermined power source parameter values are predefined and stored on a memory of the aerosol-generating device. The predetermined power source parameter values are determined prior to use of the aerosol-generating device for generating an aerosol for inhalation by a user. For example, the predetermined power source parameter values may be determined during manufacture of the aerosol-generating device.

As illustrated in Figure 7, heating and cooling of the susceptor 160 is repeated for the predetermined duration of time of the pre-heating process 710A.The predetermined duration of the pre-heating process 710A is preferably 11 seconds. The predetermined combined durations of the pre-heating process 710A followed by the calibration process 710B is preferably 20 seconds.

The pre-heating process 710A improves the reliability of the calibration process 71 OB by enabling heat to spread evenly within the susceptor 160 and aerosol-forming substrate 110 before performing the calibration. More specifically when energy is provided to the susceptor 160, heating is greatest at the center of the susceptor 160 along the longitudinal axis. In other words, heat generation in the susceptor 160 decreases when moving away from the susceptor center in an axial direction. The heat then diffuses along the susceptor 160 and into the aerosol-generating substrate 110. There is therefore a temperature gradient within the susceptor 160 and, as the susceptor 160 is heated, the temperature increase within the susceptor 160 and the aerosolforming substrate 110 depends on the axial position along the susceptor 160. However, the measured change of the power source parameter that is associated with the temperature of the susceptor as a whole. With time and at elevated temperature, the temperature gradient reduces as heat spreads in the susceptor 160 and in the aerosol-forming substrate 110.

The preheating phase 710A therefore brings additional energy into the aerosol-generating article to elevate the average temperature of the aerosol-generating article, in particular by heating to a temperature above the temperature at turning point A and by allowing time for the generated heat to diffuse along the susceptor and into the aerosol-forming substrate.

During the calibration process 710B, to reach the hill point F, additional energy is provided to the susceptor in a short period of time. Heat generation is mostly occurring at the susceptor center, as before. However, since more heat has been provided during the preheating phase 710A, the extremities of the susceptor are at a higher temperature compared to the one achieved if the susceptor was heated only to reach the valley point A during phase 710A. Therefore the temperature gradient to achieve the hill point F is lower. Further, to maintain the same average susceptor temperature, the maximum temperature reached in the susceptor center is lower (since the temperature at the extremities is higher). This mitigates the risk of overheating the aerosolforming substrate located in the vicinity of (or in contact with) the susceptor center as a lower maximum temperature is reached. For example, if the aerosol-forming substrate 110 is particularly dry or in similar conditions, the calibration may be performed before heat has spread within the aerosol-forming substrate 110, reducing the reliability of the calibration values. If the aerosol-forming substrate 110 were humid, the susceptor 160 takes more time to reach the valley temperature (due to water content in the substrate 110). Therefore, performing the pre-heating process 710A for a predetermined duration ensures that, whatever the physical condition of the substrate 110, the time is sufficient for the whole of the aerosol-forming substrate 110 to reach the minimum operating temperature, in order to be ready to feed continuous power and reach the first maximum F. This allows a calibration as early as possible, but still without risking that the substrate 110 would not have reached the valley beforehand.

Further, the aerosol-generating article 100 may be configured such that the current minimum A is always reached within the predetermined duration of the pre-heating process 710A. If the current minimum A is not reached within the pre-determined duration of the pre-heating process 710A, this may indicate that the aerosol-generating article 100 comprising the aerosol-forming substrate 110 is not suitable for use with the aerosol-generating device 200. For example, the aerosol-generating article 100 may comprise a different or lower-quality aerosol-forming substrate 110 than the aerosol-forming substrate 100 intended for use with the aerosol-generating device 200. As another example, the aerosol-generating article 100 may not be configured for use with the heating arrangement 320, for example if the aerosol-generating article 100 and the aerosolgenerating device 200 are manufactured by different manufacturers. Thus, the controller 330 may be configured to generate a control signal to cease operation of the aerosol-generating device 200 if the controller 330 detects that the current minimum A has not been reached within the predetermined duration of the pre-heating process.

The pre-heating process 710A may be performed in response to receiving a user input, for example user activation of the aerosol-generating device 200. Additionally or alternatively, the controller 330 may be configured to detect the presence of an aerosol-generating article 100 in the aerosol-generating device 200 and the pre-heating process may be performed in response to detecting the presence of the aerosol-generating article 100 within the cavity 220 of the aerosolgenerating device 200. The controller 330 may be configured to automatically perform the calibration process 710B in response to detection of the end of the pre-heating process 710A. The first heating phase 710 may have a duration of between 5 seconds and 30 seconds, preferably between 10 and 20 seconds.

During the second heating phase 720, the controller 330 is configured to control the operating temperature of the susceptor 160 for generating an aerosol based on at least the first calibration value measured during the calibration process 710B. The second heating phase 720 may have a duration of up to 340 seconds. The controller 330 may stop heating during the second heating phase 720 before the end of the second heating phase 720 in response to receiving a user input. Further, the controller 330 may be configured to stop the power supply to the inductive heating arrangement during the second heating phase 720 before the end of the second heating phase 720 if a temperature above a predetermined temperature is detected, in order to prevent overheating of the aerosol-forming substrate.

Figure 7 illustrates that the second heating phase 720 comprises a plurality of conductance steps, corresponding to a plurality of temperature steps from a first operating temperature of the susceptor 160 to a second operating temperature of the susceptor 160. The first operating temperature of the susceptor 160 is a temperature at which the aerosol-forming substrate 110 forms an aerosol so that an aerosol is formed during each temperature step. Preferably, the first operating temperature of the susceptor is a minimum temperature at which the aerosol-forming substrate will form an aerosol in a sufficient volume and quantity for a satisfactory experience when inhaled a user. The second operating temperature of the susceptor is the maximum temperature at which it is desirable for the aerosol-forming substrate to be heated for the user to inhale the aerosol.

The first operating temperature of the susceptor 160 is greater than or equal to the first calibration temperature of the susceptor 160, corresponding to the first calibration value (the valley of the current plot shown in Figure 6). The first operating temperature may be between 150 degrees Celsius and 330 degrees Celsius. The second operating temperature of the susceptor 160 is less than or equal to the second calibration temperature of the susceptor 160, corresponding to the second calibration value at the Curie temperature of the second susceptor material (the hill of the current plot shown in Figure 6). The second operating temperature may be between 200 degrees Celsius and 400 degrees Celsius. The difference between the first operating temperature and the second operating temperature is at least 50 degree Celsius.

It is to be understood that the number of temperature steps illustrated in Figure 7 is exemplary. The second heating phase 720 may comprise at least three consecutive temperature steps, preferably between two and fourteen temperature steps, most preferably between three and eight temperature steps. Each temperature step may have a predetermined duration. Preferably the duration of the first temperature step is longer than the duration of subsequent temperature steps. The duration of each temperature step is preferably longer than 10 seconds, preferably between 30 seconds and 200 seconds, more preferably between 40 seconds and 160 seconds. The duration of each temperature step may correspond to a predetermined number of user puffs. Preferably, the first temperature step corresponds to four user puffs and each subsequent temperature step corresponds to one user puff. Alternatively, the controller 330 may be configured to initiate each temperature step in response to receipt of a control signal, such as a user input.

For the duration of each temperature step, the temperature of the susceptor 160 is maintained at a target operating temperature corresponding to the respective temperature step. Thus, for the duration of each temperature step, the controller 330 controls the provision of power to the heating arrangement 320 such that the measured power source parameter is maintained at a target value corresponding to the target operating temperature of the respective temperature step, where the target value is determined with reference to the first calibration value and the second calibration value as described above.

Alternatively, the controller 330 may be configured to control the provision of power to the inductor 240 to maintain the temperature of the susceptor 160 at a constant temperature for the duration of the second heating phase 720. The constant temperature may be between 150 and 400 degrees Celsius.

Figure 8 is a flow diagram of a method 800 for controlling aerosol-production in an aerosolgenerating device 200. As described above, the controller 330 may be programmed to perform the method 800.

The method begins at step 810, where the controller 330 detects user operation of the aerosol-generating device 200 for producing an aerosol. Detecting user operation of the aerosolgenerating device 200 may comprise detecting a user input, for example user activation of the aerosol-generating device 200. Additionally or alternatively, detecting user operation of the aerosol-generating device 200 may comprise detecting that an aerosol-generating article 100 has been inserted into the aerosol-generating device 200.

In response to detecting the user operation at step 810, the controller 330 performs the preheating process 710A, at step 820. At the end of the predetermined duration of the pre-heating process, the controller 330 is configured to perform the calibration process 710B (step 830) as described above. Following completion of the calibration process 710B, the controller 330 enters the second heating phase in which the aerosol is produced at step 840.

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