WO2025093684A1

WO2025093684A1 - Inductive heaters for an aerosol provision device

Info

Publication number: WO2025093684A1
Application number: PCT/EP2024/080833
Authority: WO
Inventors: Juan Esteban Paz JAUREGUI
Original assignee: Nicoventures Trading Ltd
Current assignee: Nicoventures Trading Ltd
Priority date: 2023-10-31
Filing date: 2024-10-31
Publication date: 2025-05-08
Anticipated expiration: 2026-04-30
Also published as: GB202316694D0

Abstract

A method including the step (101) of driving a resonant circuit (14) of an inductive heater (12) for an aerosol provision device at a determined resonant frequency of the resonant circuit (14) in a heating mode. The inductive heater (12) comprises a switching circuit (13) and a resonant circuit (14). The inductive heater (12) is for heating a susceptor (16). The method further includes the steps (102, 103) of measuring the resonant frequency of the inductive heater (12) during a sampling mode and estimating the temperature of the susceptor (13) based at least in part on the resonant frequency of the inductive heater (12).

Description

Inductive heaters for an aerosol provision device

Technical Field

The present invention relates to a method for operating inductive heaters for an aerosol provision device and an apparatus for an aerosol provision device. The present invention also relates to an aerosol provision device, an aerosol provision system, and a method of forming an aerosol generator of an article for an aerosol provision device.

Background

Smoking articles such as cigarettes, cigars and the like burn tobacco during use to create tobacco smoke. Attempts have been made to provide alternatives to these articles by creating products that release compounds without combusting.

Examples of such products are so-called “heat not burn” products or tobacco heating devices or products, which release compounds by heating, but not burning, material. The material may be, for example, tobacco or other non-tobacco products, which may or may not contain nicotine.

Aerosol provision systems, which cover the aforementioned devices or products, are known. Common systems use heaters to create an aerosol from a suitable medium which is then inhaled by a user. Often the medium used needs to be replaced or changed to provide a different aerosol for inhalation. It is known to use inductive heating systems as heaters to create an aerosol from a suitable medium. Induction heating systems generally comprise a magnetic field generating device for generating a varying magnetic field, and a susceptor or heating material which is heatable by penetration with the varying magnetic field to heat the suitable medium.

Summary

According to a first aspect, there is provide a method comprising: driving a resonant circuit of an inductive heater for an aerosol provision device at a determined resonant frequency of the resonant circuit in a heating mode, wherein the inductive heater comprises a switching circuit and a resonant circuit and wherein the inductive heater is for heating a susceptor; measuring the resonant frequency of the inductive heater during a sampling mode; estimating the temperature of the susceptor based at least in part on the resonant frequency of the inductive heater.

The method may comprise driving the resonant circuit at a resonant frequency of the resonant circuit (e.g. at a determined or estimated resonant frequency) in a heating mode of operation. The method may further comprise determining or estimating said resonant frequency.

The method may further comprise measuring an ambient temperature proximal to the inductive heater; and estimating the temperature of the susceptor based at least in part on the ambient temperature proximal to the inductive heater.

Estimating the temperature of the susceptor may comprise determining the difference between a first measured frequency and a second measured frequency. Estimating the temperature of the susceptor may comprise multiplying the difference between the first measured frequency and a second measured frequency by a constant factor.

The first measured frequency and the second measured frequency may be measurements that are taken at different times. The first measured frequency and the second measured frequency may be two consecutive measurements of the frequency.

The constant factor may be proportional to the capacitance of the resonant circuit of the device.

The ambient temperature may be the temperature of the air surrounding the resonant circuit.

The method may further comprise applying a pulse to the resonant circuit in the sampling mode of operation to generate a pulse response for use in estimating temperature. The method may comprise applying a pulse to the resonant circuit in the sampling mode of operation to generate a pulse response for use in estimating temperature (which temperature estimation may then be used in setting the sampling period or frequency).

The method may further comprise determining or estimating a difference between the estimated temperature of the susceptor and a target temperature of said susceptor, wherein said susceptor is heated by an inductive heater circuit comprising a switching circuit and a resonant circuit. The method may further comprise setting a sampling period or frequency based, at least in part, on said difference, wherein the sampling period or frequency defines an interval between successive sampling modes of operation of the inductive heater circuit.

The method may further comprise decreasing the sampling period if the difference between the estimated temperature and the target temperature is reduced. The method may further comprise increasing the sampling period if the difference between the estimated temperature and the target temperature is increased.

According to another aspect there is provided an apparatus for an aerosol provision device comprising: a resonant circuit comprising an inductive element and a capacitor, wherein the inductive element is for inductively heating a susceptor; a driving circuit for applying a pulse to said resonant circuit, wherein an edge of applied pulse induces a pulse response between the capacitor and the inductive element of the resonant circuit, wherein the pulse response has a resonant frequency; and a processor. The processor is configured for: measuring the resonant frequency of the inductive heater during a sampling mode of operation; and estimating the temperature of the susceptor based at least in part on the resonant frequency of the inductive heater.

The processor may be further configured to determine or estimate a difference between the estimated temperature of the susceptor and a target temperature of said susceptor, wherein said susceptor is heated by an inductive heater circuit comprising a switching circuit and a resonant circuit. The processor may be further configured to set a sampling period or frequency based, at least in part, on said difference, wherein the sampling period or frequency defines an interval between successive sampling modes of operation of the inductive heater circuit.

The processor may be further configured to decrease a sampling period if the difference between the estimated temperature and the target temperature is reduced. The processor may be further configured to increase the sampling period if the difference between the estimated temperature and the target temperature is increased.

The driving circuit may be configured to drive the resonant circuit at a determined resonant frequency of the resonant circuit in the heating mode of operation. The driving circuit may be an H-bridge circuit.

According to another aspect there is provided an aerosol provision device comprising the apparatus as described above.

The aerosol provision device may comprise a heating chamber for removably receiving an article comprising an aerosol generating material.

The inductive elements of the plurality of resonant circuits may be arranged along a side wall of the heating chamber. The aerosol provision device may comprise at least four inductive elements arranged along a side wall of the heating chamber. The aerosol provision device may comprise at least five inductive elements arranged along a side wall of the heating chamber. The aerosol provision device may comprise at a grid arrangement of inductive elements arranged along a side wall of the heating chamber, for example a 2x4 grid or a 2x5 grid.

The inductive elements of the plurality of resonant circuits may be arranged along two side walls of the chamber. The inductive elements of the plurality of resonant circuits may be arranged along two opposite side walls of the chamber. The inductive elements may be arranged in two arrays, each array comprising at least four inductive elements. The inductive elements may be arranged in two arrays, each array comprising at five inductive elements. The inductive elements may be planar coils. The inductive elements may be planar spiral inductor coils. The inductive elements may be planar non-spiral inductor coils. The inductor coil may be substantially square. The inductor coil may be substantially rectangular. The inductor coil may be trapezoidal.

The inductive elements may be disposed on a printable circuit board (PCB).

The aerosol provision device may comprise a susceptor provided within the heating chamber. The aerosol provision device may comprise two or more susceptor elements. The aerosol provision device may comprise a plurality of susceptors, each susceptor associated with a respective inductive element.

The inductive elements may be helical inductor coils, which surround the heating chamber

The aerosol provision device may comprise a power source. The power source may be aligned along a longitudinal axis of the heating chamber. The power source may be aligned along a second longitudinal axis, parallel to the longitudinal axis of the heating chamber.

The aerosol provision device may comprise a hinged door or removable part of an outer housing to permit access to the chamber such that a user may insert and/or remove an aerosol generating article.

The aerosol provision device may be configured for wireless charging.

According to another aspect there is provided an aerosol provision system comprising the aerosol provision device as described above, and an article comprising an aerosol generating material.

The aerosol provision device may comprise a susceptor provided within the chamber. The aerosol provision device may comprise two or more susceptors.

The article may be a cylindrical or rod shape. The article may be substantially flat. The article may comprise a carrier component. The carrier component may comprise aerosol generating material provided on the carrier component. The aerosol generating material may be provided as a continuous layer of aerosol generating material. The aerosol generating material may be provided as a plurality of discrete portions of aerosol generating material.

The carrier component may comprise a heating layer. The carrier component may comprise a heating layer and a support layer.

The article may comprise one or more susceptor elements.

The article may comprise a single susceptor element. The single susceptor element may comprise a plurality of susceptor portions. The plurality of susceptor portions may align with a plurality of inductive heating elements provided in the aerosol provision device, when the article is inserted into the device.

The article may provide a plurality of susceptors. The plurality of susceptors may align with a plurality of inductive heating elements provided in the aerosol provision device, when the article is inserted into the device.

The aerosol provision system may further comprise a charging unit having a cavity for removably receiving the aerosol provision device.

According to another aspect there is provided a method of generating aerosol comprising: providing an aerosol provision system as described above, and at least partially inserting the aerosol generating article into the chamber.

According to a further aspect, there is provided computer program_comprising instructions for causing an apparatus for an aerosol provision device to perform at least the following: driving a resonant circuit of an inductive heater at a determined resonant frequency of the resonant circuit in a heating mode of operation, wherein the inductive heater comprises a switching circuit and a resonant circuit and wherein the inductive heater is for heating a susceptor; measuring the resonant frequency of the inductive heater during a sampling mode of operation; and estimating the temperature of the susceptor based at least in part on the resonant frequency of the inductive heater. Brief Description of the Drawings

Various embodiments will now be described, by way of example only, and with reference to the accompanying drawings, in which:

Figure 1a is a schematic representation of an apparatus for an aerosol provision device;

Figure 1 b is a block diagram of a circuit which is an example implementation of the circuit of Figure 1a;

Figure 2 shows a temperature estimation according to an example embodiment;

Figure 3 shows a temperature estimation according to another example embodiment;

Figure 4 shows a flow chart of a method according to an example embodiment;

Figure 5 is a method which may be implemented using the apparatus of Figure 1a ; Figures 6a-c are schematic representations of systems, indicated generally by the reference numeral 70, in accordance with example embodiments.

Figures 7a and 7b are plots showing a pulse and a pulse response in accordance with example embodiments;

Figures 8a and 8b are schematic views of a non-combustible aerosol provision system;

Figure 8c is a cross-sectional view of an article comprising aerosol generating material of the aerosol provision system of Figure 8a;

Figure 9a shows a schematic view of another non-combustible aerosol provision system;

Figure 9b shows a schematic view of an article comprising aerosol generating material of the aerosol provision system of Figure 9a;

Figure 10a shows an isometric exploded view of another aerosol provision device;

Figure 10b shows a schematic view of an articles comprising aerosol generating material for use in the aerosol provision system of Figure 10a;

Figure 11a shows a schematic view of another non-combustible aerosol provision system; and

Figures 11b to 11e show cross-sectional views articles comprising aerosol generating material for use in the aerosol provision system of Figure 9a. Detailed Description

As used herein, the term “delivery mechanism” is intended to encompass systems that deliver a substance to a user, and includes: non-combustible aerosol provision systems that release compounds from an aerosolisable material without combusting the aerosolisable material, such as electronic cigarettes, tobacco heating products, and hybrid systems to generate aerosol using a combination of aerosolisable materials; and articles comprising aerosolisable material and configured to be used in one of these non-combustible aerosol provision systems.

According to the present disclosure, a “non-combustible” aerosol provision system is one where a constituent aerosol-generating material of the aerosol provision system (or component thereof) is not combusted or burned in order to facilitate delivery of at least one substance to a user.

In some embodiments, the delivery system is a non-combustible aerosol provision system, such as a powered non-combustible aerosol provision system.

In some embodiments, the non-combustible aerosol provision system is an electronic cigarette, also known as a vaping device or electronic nicotine delivery system (END), although it is noted that the presence of nicotine in the aerosolgenerating material is not a requirement.

In some embodiments, the non-combustible aerosol provision system is an aerosolgenerating material heating system, also known as a heat-not-burn system. An example of such a system is a tobacco heating system.

In some embodiments, the non-combustible aerosol provision system is a hybrid system to generate aerosol using a combination of aerosol-generating materials, one or a plurality of which may be heated. Each of the aerosol-generating materials may be, for example, in the form of a solid, liquid or gel and may or may not contain nicotine. In some embodiments, the hybrid system comprises a liquid or gel aerosol-generating material and a solid aerosol-generating material. The solid aerosol-generating material may comprise, for example, tobacco or a non-tobacco product. Typically, the non-combustible aerosol provision system may comprise a noncombustible aerosol provision device and a consumable for use with the noncombustible aerosol provision device.

In some embodiments, the disclosure relates to consumables comprising aerosolgenerating material and configured to be used with non-combustible aerosol provision devices. These consumables are sometimes referred to as articles throughout the disclosure.

In some embodiments, the non-combustible aerosol provision system, such as a non-combustible aerosol provision device thereof, may comprise a power source and a controller. The power source may, for example, be an electric power source.

In some embodiments, the non-combustible aerosol provision system may comprise an area for receiving the consumable, an aerosol generator, an aerosol generation area, a housing, a mouthpiece, a filter and/or an aerosol-modifying agent.

In some embodiments, the consumable for use with the non-combustible aerosol provision device may comprise aerosol-generating material, an aerosol-generating material storage area, an aerosol-generating material transfer component, an aerosol generator, an aerosol generation area, a housing, a wrapper, a filter, a mouthpiece, and/or an aerosol-modifying agent.

As used herein, the term “aerosol-generating material” (which is sometimes referred to herein as an aerosolisable material) is a material that is capable of generating aerosol, for example when heated, irradiated or energized in any other way. Aerosol-generating material may, for example, be in the form of a solid, liquid or semi-solid (such as a gel) which may or may not contain an active substance and/or flavourants.

In some embodiments, the substance to be delivered comprises an active substance (sometimes referred to herein as an active compound). The aerosol-generating material may comprise one or more active substances and/or flavours, one or more aerosol-former materials, and optionally one or more other functional material.

The aerosol-generating material may comprise a binder, such as a gelling agent, and an aerosol former. Optionally, a substance to be delivered and/or filler may also be present. Optionally, a solvent, such as water, is also present and one or more other components of the aerosol-generating material may or may not be soluble in the solvent. In some embodiments, the aerosol-generating material is substantially free from botanical material. In particular, in some embodiments, the aerosol-generating material is substantially tobacco free.

The aerosol-generating material may comprise or be in the form of an aerosolgenerating film. The aerosol-generating film may comprise a binder, such as a gelling agent, and an aerosol former. Optionally, a substance to be delivered and/or filler may also be present. The aerosol-generating film may be substantially free from botanical material. In particular, in some embodiments, the aerosolgenerating material is substantially tobacco free.

The aerosol-generating film may have a thickness of about 0.015 mm to about 1 mm. For example, the thickness may be in the range of about 0.05 mm, 0.1 mm or 0.15 mm to about 0.5 mm or 0.3 mm.

The aerosol-generating film may be continuous. For example, the film may comprise or be a continuous sheet of material. The aerosol-generating film may be discontinuous. For example, the aerosol-generating film may comprise one or more discrete portions or regions of aerosol-generating material, such as dots, stripes or lines, which may be supported on a support. In such embodiments, the support may be planar or non-planar.

The aerosol-generating film may be formed by combining a binder, such as a gelling agent, with a solvent, such as water, an aerosol-former and one or more other components, such as one or more substances to be delivered, to form a slurry and then heating the slurry to volatilise at least some of the solvent to form the aerosol-generating film. The slurry may be heated to remove at least about 60 wt%, 70 wt%, 80 wt%, 85 wt% or 90 wt% of the solvent.

The aerosol-generating material may be an “amorphous solid”. In some embodiments, the amorphous solid is a “monolithic solid”. The aerosol-generating material may be non-fibrous or fibrous. In some embodiments, the aerosolgenerating material may be a dried gel. The aerosol-generating material may be a solid material that may retain some fluid, such as liquid, within it. In some embodiments the retained fluid may be water (such as water absorbed from the surroundings of the aerosol-generating material) or the retained fluid may be solvent (such as when the aerosol-generating material is formed from a slurry). In some embodiments, the solvent may be water.

The aerosol-former material may comprise one or more constituents capable of forming an aerosol. In some embodiments, the aerosol-former material may comprise one or more of glycerine, glycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1 ,3-butylene glycol, erythritol, meso- Erythritol, ethyl vanillate, ethyl laurate, a diethyl suberate, triethyl citrate, triacetin, a diacetin mixture, benzyl benzoate, benzyl phenyl acetate, tributyrin, lauryl acetate, lauric acid, myristic acid, and propylene carbonate.

The one or more other functional materials may comprise one or more of pH regulators, colouring agents, preservatives, binders, fillers, stabilizers, and/or antioxidants.

The material may be present on or in a support, to form a substrate. The support may, for example, be or comprise paper, card, paperboard, cardboard, reconstituted material, a plastics material, a ceramic material, a composite material, glass, a metal, or a metal alloy.

An aerosol provision device can receive an article comprising aerosol generating material for heating. An “article” in this context is a component that includes or contains in use the aerosol generating material, which is heated to volatilise the aerosol generating material, and optionally other components in use. A user may insert the article into or onto the aerosol provision device before it is heated to produce an aerosol, which the user subsequently inhales.

An aerosol generator is an apparatus configured to cause aerosol to be generated from the aerosol-generating material. In some embodiments, the aerosol generator is a heater configured to subject the aerosol-generating material to heat energy, so as to release one or more volatiles from the aerosol-generating material to form an aerosol. In inductive heating systems, the aerosol generator comprises a magnetic field generator, such as an inductive element and a susceptor.

A susceptor is material that is heatable by penetration with a varying magnetic field, such as an alternating magnetic field. The heating material may be an electrically- conductive material, so that penetration thereof with a varying magnetic field causes induction heating of the heating material. The heating material may be magnetic material, so that penetration thereof with a varying magnetic field causes magnetic hysteresis heating of the heating material. The heating material may be both electrically-conductive and magnetic, so that the heating material is heatable by both heating mechanisms.

A consumable is an article comprising or consisting of aerosol-generating material, part or all of which is intended to be consumed during use by a user. A consumable may comprise one or more other components, such as an aerosolgenerating material storage area, an aerosol-generating material transfer component, an aerosol generation area, a housing, a wrapper, a mouthpiece, a filter and/or an aerosol-modifying agent. A consumable may also comprise an aerosol generator, such as a heater, that emits heat to cause the aerosolgenerating material to generate aerosol in use. The heater may, for example, comprise a material heatable by electrical conduction.

Non-combustible aerosol provision systems may comprise a modular assembly including both a reusable aerosol provision device and a replaceable aerosol generating article. In some implementations, the non-combustible aerosol provision device may comprise a power source and a controller (or control circuitry). The power source may, for example, comprise an electric power source, such as a battery or rechargeable battery. In some implementations, the non-combustible aerosol provision device may also comprise an aerosol generating component. However, in other implementations the aerosol generating article may comprise partially, or entirely, the aerosol generating component.

Figure 1a is a schematic representation of an apparatus, indicated generally by the reference numeral 10, in accordance with an example embodiment. The system 10 comprises a power source in the form of a direct current (DC) voltage supply 11 , a switching arrangement 13, a resonant circuit 14, a susceptor arrangement 16, and a control circuit 18. The switching arrangement 13 and the resonant circuit 14 may be coupled together in an inductive heating arrangement 12 that can be used to heat the susceptor 16.

The resonant circuit 14 may comprise one or more capacitors and one or more inductive elements for inductively heating the susceptor arrangement 16 to heat an aerosol generating material. Heating the aerosol generating material may thereby generate an aerosol.

The switching arrangement 13 may enable an alternating current to be generated from the DC voltage supply 11 (under the control of the control circuit 18). The alternating current may flow through the one or more inductive elements and may cause the heating of the susceptor arrangement 16. The switching arrangement may comprise a plurality of transistors. Example DC-AC converters include H- bridge or inverter circuits, examples of which are discussed below

Temperature estimation of the susceptor 16 can be used as an input to control various aspects of the operation of the apparatus 10.

Figure 1b is a block diagram of a circuit, indicated generally by the reference numeral 60, in accordance with an example embodiment. The circuit 60 is an example implementation of the circuit 10 described above.

The circuit 60 comprises a positive terminal 67 and a negative (ground) terminal 68 (that are an example implementation of the DC voltage supply 11 of the system 10 described above). The circuit 60 comprises a switching arrangement 64a, 64b (implementing the switching arrangement 13 described above), where the switching arrangement 64a, 64b comprises a bridge circuit (e.g. an H-bridge circuit, such as an FET H-bridge circuit). The switching arrangement 64a, 64b comprises a first limb 64a and a second limb 64b, where the first limb 64a and the second limb 64b are coupled by a resonant circuit 69 (which resonant circuit implements the resonant circuits 14 described above). The first limb 64a comprises switches 65a and 65b and the second limb 64b comprises switches 65c and 65d. The switches 65a, 65b, 65c, and 65d may be transistors, such as field-effect transistors (FETs), and may receive inputs from a controller, such as the control circuit 18 of the system 10.

The resonant circuit 69 comprises a capacitor 66 and an inductive element 63 such that the resonant circuit 69 may be an LC resonant circuit (but may, in practice, be an RLC resonant circuit). The circuit 60 further shows a susceptor equivalent circuit 62 (e.g. representing the susceptor arrangement 16 of the system 10 described above). The susceptor equivalent circuit 62 comprises a resistance and an inductive element that indicate the electrical effect of an example susceptor arrangement (such as the susceptor 16). When a susceptor is present, the susceptor arrangement 62 and the inductive element 63 may act as a transformer 61. Transformer 61 may produce a varying magnetic field such that the susceptor is heated when the circuit 60 receives power. During a heating mode of operation (e.g. during the operation 22 of the algorithm 20), in which the susceptor arrangement 16 is heated by the inductive arrangement, the switching arrangement 64a, 64b is driven (e.g., by control circuit 18) such that each of the first and second branches are coupled in turn such that an alternating current is passed through the resonant circuit 69. The resonant circuit 69 will have a resonant frequency, which is based in part on the susceptor arrangement 16, and the control circuit 18 may be configured to control the switching arrangement 64 to switch at the resonant frequency or a frequency close to the resonant frequency. Driving the switching circuit at or close to resonance helps improve efficiency and reduces the energy being lost to the switching elements (which causes unnecessary heating of the switching elements). In an example in which an article comprises an aluminium foil is to be heated, the switching arrangement 64 may be driven at a frequency of around 2.5 MHz. However, in other implementations, the frequency may, for example, be anywhere between 500 kHz to 4 MHz, or any other frequency range. Figure 2 shows a first example of a temperature estimation according to the present disclosure. In this example, the temperature of the susceptor is estimated using two (e.g. consecutive) measurements of the resonant frequency f. In this example, the estimated temperature of the susceptor 16 is directly proportional to the percentage change between two measurements. The first measurement, f (tl), is taken at a first time tl, and the second measurement, f (t2), is taken at a second time t2, where the second time t2 is later than the first time tl. The percentage change between the two measurements is calculated as:

The percentage change between the two measurements is multiplied by a constant factor K. In some examples, the constant factor K may be determined numerically (e.g. from existing data that has been collected on the relationship between resonant frequency and the temperature of the susceptor). In some examples, the constant factor K may be determined analytically (e.g. by performing a circuit analysis based on the values of resistance, conductance, capacitance etc of the resonant circuit 14 of the apparatus or device that is configured to heat the susceptor 16). In some examples, the constant factor K may be proportional to the capacitance of the resonant circuit 14.

In this example, the calculation also includes a measurement of the ambient temperature T_ambient. The ambient temperature may be a temperature outside the device or apparatus (e.g. the temperature of the room in which the device/ apparatus is located) or the ambient temperature may be a temperature in an unheated region of the apparatus/device (e.g. the temperature of a region that is insulated from the heating zone of the device).

Figure 2 shows an example of a temperature estimation for a device in accordance with the first example of the present disclosure. Line A and line B represent the resonant frequency ( ) and the estimated temperature (T_susceptor) of the susceptors 16 for two devices or apparatus with different capacitances. It can be seen that the estimated temperature of the susceptors diverges as the frequency increases. The actual measured temperatures of the two susceptors does not show such a large divergence. Therefore, a limitation of the calculation shown in Figure 1 is that the calculation has limited accuracy across devices or apparatus with different capacitance.

Figure 3 shows a second example of a temperature estimation according to the present disclosure. In this example, the temperature of the susceptor 16 is estimated using two (e.g. consecutive) measurements of the resonant frequency f . In this example, the estimated temperature of the susceptor 16 is directly proportional to the difference between two measurements. The first measurement, f (tl), is taken at a first time tl, and the second measurement, f (t2), is taken at a second time t2, where the second time t2 is later than the first time tl. The difference between the two measurements is calculated as f (tl) - f(t2).

The difference between the two measurements is multiplied by a constant factor K. In some examples, the constant factor K may be determined numerically (e.g. from existing data that has been collected on the relationship between resonant frequency and the temperature of the susceptor 16). In some examples, the constant factor K may be determined analytically (e.g. by performing a circuit analysis based on the values of resistance, conductance, capacitance etc of the resonant circuit 14 of the device/apparatus that is configured to heat the susceptor 16). In some examples, the constant factor K may be proportional to the capacitance of the resonant circuit of the device or apparatus.

In this example, the calculation also includes a measurement of the ambient temperature T_ambient. The ambient temperature may be a temperature outside the device or apparatus (e.g. the temperature of the room in which the device is located) or the ambient temperature may be a temperature in an unheated region of the device/apparatus (e.g. the temperature of a region that is insulated from the heating zone of the device/apparatus).

Figure 3 shows an example of a temperature estimation for a device in accordance with the second example of the present disclosure. Line A and line B represent the resonant frequency ( ) and the estimated temperature (T_susceptor) of the susceptors 16 for two devices or apparatus with different capacitances. It can be seen that the estimated temperature of the susceptors does not diverge to the same extent as the example shown in Figure 2.

When the percentage change is used to estimate the temperature, as shown in Figure 2, the calculation includes the value of the resonant frequency f (tl) on the denominator of the fraction. Therefore, the estimated temperature is dependent on the absolute value of the resonant frequency.

The absolute value of the resonant frequency may change depending on the capacitance of the resonant circuit 14. Therefore, the constant factor K may also change depending on the capacitance of the circuit 14. When the correct value of the constant factor K is used, the first example of the present disclosure (shown in Figure 2) can accurately predict the temperature of the susceptor 16. However, if the wrong value of the constant factor K is used (e.g. a value that is associated with a resonant circuit having different capacitance), this may reduce the accuracy of the temperature estimation.

Measuring the difference between the measurements, as shown in Figure 3, instead of the percentage change, as shown in Figure 2, removes the dependence on any absolute values of resonant frequency in the estimation of temperature. Therefore, the same constant factor K may be used for estimating the temperature of a susceptor 16 in resonant circuits 14 having different capacitances. Therefore, an advantage of this calculation is that the same constant K can be applied across devices/apparatus with different capacitance.

Figure 4 shows a method of operating a resonant circuit, such as those described above and below. Step 101 of the method includes driving a resonant circuit of an inductive heater at a determined resonant frequency of the resonant circuit in a heating mode, wherein the inductive heater comprises a switching circuit and a resonant circuit and wherein the inductive heater is for heating a susceptor. Step 102 of the method includes measuring the resonant frequency of the inductive heater during a sampling mode. Step 103 of the method includes estimating the temperature of the susceptor based at least in part on the resonant frequency of the inductive heater. It will be appreciated that the temperature estimation methods outlined above may be used to control various applications.

Figure 5 is a flow chart showing an algorithm 20 which may be implemented using the system of Figure 1.

The algorithm 20 starts in operation 22, where a resonant circuit (e.g. the resonant circuit 14) is driven at a resonant frequency of the resonant circuit in a heating mode of operation. In this embodiment, the resonant circuit is driven at a predetermined starting resonant frequency.

In an alternative embodiment, the algorithm may start at operation 24, where the sampling mode is triggered prior to heating for the first time, in other words the sampling mode pings the susceptor prior to heating. The sampling mode determines frequency to start heating at.

At operation 24, a sampling mode of operation is entered. The sampling mode may seek to determine the resonant frequency for use in the heating mode (e.g. during the next iteration of the algorithm 20). As discussed below, the sampling mode may include applying a pulse to the resonant circuit at a specified time interval and processing the resonant response to determine/estimate the resonant frequency. The determined resonant frequency can then be used to estimate the temperature of the susceptor using a method as described above.

At operation 26, the driving frequency for the resonant circuit is set based on the estimated temperature of the susceptor.

The parameters of the heating mode (including the driving frequency and the sampling interval) are set in the operation 26. The heating of the susceptor occurs in the next iteration of the heating mode 22 until the time interval dictated by the sampling mode occurs. The algorithm 20 then re-enters the sampling mode 24 where the resonant frequency of the resonant circuit is again determined and the parameters of the heating and sampling modes are updated (in the operation 26). A controller (which may be part of the control circuit 18) may be used to determine how often to initiate the sampling mode 24. The controller may seek to strike a balance between sampling sufficiently often to ensure that the resonant circuit is being driven at (or close to) its resonant frequency in the heating mode 22 (thereby tending to increase heating efficiency) and having a low sampling rate (i.e. a high sampling period) so that the susceptor spends a large proportion of its time being heated (again, tending to increase heating efficiency).

The sampling period (i.e. how often the sampling mode 24 is entered) may be a controllable variable. As discussed in detail below, there are a number of mechanisms that could be used for setting the sampling period.

Figure 6a is a schematic representation of a system, indicated generally by the reference numeral 70, in accordance with an example embodiment.

The system 70 comprises a pulse generation circuit 72, a resonant circuit 74 (such as the resonant circuits 14), a susceptor 76 (such as the susceptor arrangement 16) and a pulse response processor 78. The pulse generation circuit 72 and the pulse response processor 74 may be implemented as part of the control circuit 18 of the system 10 and may be used during the sampling mode 26 of the algorithm 20. Indeed, the pulse generation circuit 72 and the pulse response processor 74 may collectively form a controller for an inductive heater for heating a susceptor in accordance with the principles described herein.

The pulse generation circuit 72 may be implemented using the switching arrangements of the circuit 60 described above in order to generate a pulse (e.g. pulse edges) by switching between positive and negative voltage sources. This is not essential to all example embodiments; for example, the pulse generation circuit 72 may be implemented using a half-bridge circuit.

The pulse response processor 78 may determine one or more performance metrics (or characteristics) of the resonant circuit 74 and the susceptor 76 based on the pulse response. For example, the pulse response processor 78 may generate an estimate of the temperature of the susceptor 76 and/or a resonant frequency of the resonant circuit. Figure 6b is a schematic representation of a system, indicated generally by the reference numeral 70, in accordance with another example embodiment. In this example, a plurality of resonant circuits 74 and a plurality of susceptors 76. Three resonant circuits and three susceptors are shown. However, it will be appreciated that any number of resonant circuits and susceptors may be provided. For example, at least eight resonant circuits and eight susceptors may be provided. In one embodiment, ten resonant circuits and ten susceptors are provided.

It will be appreciated that the resonant circuits 74 can be controlled individually, to heat respective susceptor(s) 76 as required. For example, only one resonant circuit may be in operation at any given time. Alternative, two or more resonant circuits can be in operation simultaneously.

The resonant circuits may be operated in a predetermined order. For example, the susceptors may be aligned along an axis or path, and the resonant circuits may be operated in a predetermined order, for example to heat susceptors sequentially along the length of the axis or path.

Figure 6c is a schematic representation of a system, indicated generally by the reference numeral 70, in accordance with another example embodiment. In this example, a plurality of resonant circuits 74 and a single susceptor 76.

Three resonant circuits are shown. However, it will be appreciated that any number of resonant circuits and susceptors may be provided. For example, at least eight resonant circuits may be provided. In one embodiment, ten resonant circuits are provided.

It will be appreciated that the resonant circuits 74 can be controlled individually, to heat respective portions of the susceptor(s) 76 as required. For example, only one resonant circuit may be in operation at any given time. Alternative, two or more resonant circuits can be in operation simultaneously.

The resonant circuits may be operated in a predetermined order. For example, the one or more susceptors may be aligned along an axis or path, and the resonant circuits may be operated in a predetermined order to heat respective susceptor portions sequentially along the length of the axis or path. Figure 7a is a plot showing a pulse 140 in accordance with an example embodiment. The pulse 140 is includes a rising pulse edge 142 that is an example of a pulse edge that may be generated by the pulse generation circuit 72 (e.g. by an H-bridge or half-bridge circuit). The pulse 140 may, for example, be applied during the sampling mode 24 of the algorithm 20.

The pulse 140 may be applied to the resonant circuit 74. Alternatively, in systems having multiple inductive elements, the pulse generation circuit 72 may select one of a plurality of resonant circuits, each resonant circuit comprising an inductive element for inductively heating a susceptor and a capacitor, wherein the applied pulse induces a pulse response between the capacitor and the inductive element of the selected resonant circuit. The application of the pulse edge 142 to the resonant circuit 74 generates a pulse response.

Figure 7b is a plot, indicated generally by the reference numeral 150, showing an example pulse response that might be generated at a connection point between the capacitive element and the inductive element of the resonant circuit 14 described above in response to the pulse edge 92. This response may be received by the control circuit.

As shown in Figure 7b, the pulse response 150 may take the form of a ringing resonance. The pulse response is a result of charge bouncing between the capacitive element and the inductive element of the resonant circuit. As shown in Figure 7b a period 102 between zero-crossings can be used to determine a resonant frequency of the pulse response. Note that in some example embodiments other measurements may be taken, such as the period between successive peaks of the ringing response.

Figures 8a to 11e show non-combustible aerosol provision devices and systems which may be controlled in accordance with the principles described herein.

Figure 8a is a perspective illustration of an aerosol provision system 200 comprising an aerosol provision device 210 with an outer housing 221 and a replaceable article 250 (also known as a consumable) that may be inserted in the aerosol provision device 210. The aerosol provision device 210 may further comprise an activation switch 212 that may be used for switching on or switching off the aerosol provision device 220. In other embodiments, the device does not include an activation switch 212 and a pressure trigger or some other activation-on-demand arrangement may be provided.

Figure 8b shows the aerosol provision system 200 with a front portion of the outer housing removed. The aerosol generating device 210 comprises a plurality of inductive heaters (also referred to as inductive heater units) 8a, 8b, 8c surrounding a heating chamber 240 into which a distal end of the article 250 is inserted.

The plurality of inductive heaters 8a-c comprise a resonant circuit, such as the resonant circuit 14 described above. The or each inductive heater units 8a-c may comprise an inductive element 9 such as a helical inductor coil. In one example, the helical inductor coil is made from Litz wire/cable which is wound in a helical fashion to provide the helical inductor coil. In other embodiments, other types are inductor elements are provided, as inductors formed within a printed circuit board. The inductive heater units and inductive element provided therein may be the same or similar. The use of three inductive heater units is not essential to all example embodiments.

Thus, the aerosol generating device 210 may comprise one or more inductive heaters. In other embodiments, the device 210 may include four or more helical coil inductive elements.

The aerosol provision system 200 includes a susceptor 245 provided within the heating chamber 240, such that when the article is inserted into the heating chamber 240 and at least partially surrounded by the susceptor.

In use, the article 250 is received in the article chamber 240. The inductive elements 9a-c surrounds the susceptor 245. The inductive elements 9a-c induce a varying magnetic field in the susceptor 245, which causes heating of the susceptor 245. The susceptor 245 in turn heats aerosol generating material in the article 250. Figure 8c shows an embodiment of an article 250 for use in an aerosol provision device 210 as described above, having a susceptor provided in the device. The article 250 comprises a mouthpiece 251, and a cylindrical rod of aerosol generating material 254 connected to the mouthpiece 251. The aerosol generating material 254 is wrapped in a wrapper 252. The wrapper 252 can, for instance, be a paper or paper-backed foil wrapper. The wrapper 252 may be substantially impermeable to air. In one embodiment, the wrapper 252 comprises aluminium foil.

The mouthpiece 251, in the present example, includes a body of material 256 upstream of a hollow tubular element 255, in this example adjacent to and in an abutting relationship with the hollow tubular element 255. The body of material 256 and hollow tubular element 255 each define a substantially cylindrical overall outer shape and share a common longitudinal axis. The body of material 256 is wrapped in a first plug wrap 257. The mouthpiece 251 also includes a second hollow tubular element 258, also referred to as a cooling element, upstream of the first hollow tubular element 254. The body of material 256 and second hollow tubular element 258 each define a substantially cylindrical overall outer shape and share a common longitudinal axis. The second hollow tubular element 258 is formed from a plurality of layers of paper which are parallel wound, with butted seams, to form the tubular element 258. A second plug wrap 259 is also provided around the mouthpiece 251.

The aerosol generating material 254, also referred to herein as an aerosol generating substrate 254, comprises at least one aerosol forming material. In the present example, the aerosol forming material is glycerol. In alternative examples, the aerosol forming material can be another material as described herein or a combination thereof. The aerosol generating substrate may comprise botanical material, for example tobacco.

In alternative embodiment, the susceptor 245 may be provided in the article 250, for example embedded in the aerosol generating material 254.

Figure 9a is a cross-sectional view through a schematic representation of an aerosol provision system 200 in accordance with another embodiment. The aerosol generating system 200 comprises an aerosol provision device 210 and an aerosol generating article 250. The aerosol provision device 210 comprises an outer housing 221, a power source 222, control circuitry 223, a plurality of inductive elements 8a-8c, a chamber 240, a mouthpiece end 226, an air inlet 227, an air outlet 228, a touch-sensitive panel 229, an inhalation sensor 230, and an end of use indicator 231.

The plurality of inductive heaters 8a-c comprise a resonant circuit, such as the resonant circuit 14 described above. The inductive elements 8a-8c may comprise any suitable inductive element, such as but not limited to a substantially planar inductor coil.

The outer housing 221 may be formed from any suitable material, for example a plastics material. The outer housing 221 is arranged such that the power source 222, control circuitry 223, aerosol generating components 224, chamber 240 and inhalation sensor 230 are located within the outer housing 221. The outer housing 221 also defines the air inlet 227 and air outlet 228, described in more detail below. The touch sensitive panel 229 and end of use indicator are located on the exterior of the outer housing 221. The outer housing 221 and mouthpiece end 226 are formed as a single component (that is, the mouthpiece end 226 forms a part of the outer housing 221). In other embodiments, the mouthpiece end 226 may be a removable component that is separate from but able to be coupled to the outer housing 221 , and may be removed for cleaning and/or replacement with another mouthpiece end 226.

The chamber 240 is suitable sized to removably receive the aerosol generating article 250 therein. Although not shown, the aerosol provision device 210 may comprise a hinged door or removable part of the outer housing 221 to permit access to the chamber 240 such that a user may insert and/or remove the aerosol generating article 250. The hinged door or removable part of the outer housing 210 may also act to retain the aerosol generating article 250 within the chamber 240 when closed. Alternatively, the aerosol provision device 210 may include a permanent opening that communicates with the chamber 240 and through which the aerosol generating article 250 can be inserted into the chamber 240. In such implementations, a retaining mechanism for retaining the aerosol generating article 250 within the chamber 240 of the aerosol provision device 210 may be provided. The power source 222 is configured to provide operating power to the aerosol provision device 210. The power source 222 may be any suitable power source, such as a battery. For example, the power source 222 may comprise a rechargeable battery, such as a Lithium Ion battery. The power source 222 may be removable or form an integrated part of the aerosol provision device 210. In some implementations, the power source 222 may be recharged through connection of the aerosol provision device 210 to an external power supply (such as mains power) through an associated connection port, such as a USB port (not shown) or via a suitable wireless receiver (not shown).

The control circuitry 223 is suitably configured I programmed to control the operation of the aerosol provision device to provide certain operating functions of aerosol provision device 210. The control circuitry 223 is connected to the power supply and receives power from the power source 222 and may be configured to distribute or control the power supply to other components of the aerosol provision device 210.

The aerosol provision device 210 further comprises a chamber 240 which is arranged to receive an aerosol generating article 250. The aerosol generating article comprises a carrier component 262 and aerosol generating material 254 (for example an aerosol generating film) provided on or within a surface of the carrier 262. The article 250 further comprises a susceptor material (not shown in Figure 7a).

The inductive elements 8a-c may be referred to as heating elements. The inductive elements 8a-8c are aligned along an axis parallel to a longitudinal axis of the device 210. Each inductive element aligns with a corresponding discrete portion of aerosol generating material 254, defining a respective aerosol generating region.

In some implementations, to improve the heat-transfer efficiency, the chamber may comprise components which apply a force to the surface of the carrier component 262 so as to press the carrier component 262 onto the inductive elements 8a-c, thereby increasing the efficiency of heat transfer via conduction to the aerosol generating material 254. In other embodiments four or more inductive elements may be provided aligned along an axis parallel to the longitudinal axis of the device 210.

Figure 9b shows a schematic view of the article 250 from Figure 9a. The carrier component 262 is broadly cuboidal in shape has a length I, a width w and a thickness tc.

The aerosol generating article 250 comprises a plurality of discrete portions of aerosol generating material 254 disposed on a surface of the carrier component 262. The discrete portions of aerosol generating material 254 are separate from one another such that each of the discrete portions may be energised (e.g. heated) individually or selectively to produce an aerosol. The aerosol generating article 250 may comprise a plurality of portions of aerosol generating material all formed form the same aerosol generating material. Alternatively, the aerosol generating article 250 may comprise a plurality of portions of aerosol generating material 254 where at least two portions are formed from different aerosol generating material.

In this embodiment, the aerosol generating article 250 comprises three discrete portions of aerosol generating material 254, aligned along a central axis of the article in order to align with the inductive elements in the device 210. In other embodiments, a greater or lesser number of discrete portions may be provided, and/or the portions may be disposed in a different pattern so as to align with any arrangement of inductive elements in the aerosol provision device.

The carrier layer 262 comprises a heating layer 264 which acts as the susceptor 245 and a support layer 266. The aerosol generating material 254 is provided on a first side 264a of the heating layer 264. The aerosol generating material 254 is divided into the discrete portions which may be easily sequentially heated (e.g. one by one) during an aerosol generation session.

In the present example, the heating layer 264 is formed of an aluminium foil material. In other examples, the heating layer 264 may be formed of a different material, for example another metal or a metal alloy. The support layer 266 is provided on a second side 264b of the heating layer 264. The support layer 266 comprises a single layer of material. The support layer 266 is formed entirely of the same material. In the present example, the support layer 266 is formed of paper or cardboard. The support layer 266 provides structural support to the heating layer 264. The support layer 266 provides structural support to the article 250.

In other embodiments, the article comprises a continuous layer of aerosol generating material provided on the carrier component 262.

In other embodiments, the carrier component 262 may comprise a single layer which is a heating layer 264 which acts as the susceptor 245.

In use, the article 250 is received in the article chamber 240. The inductive elements 8a-c surround the susceptor 245. The inductive elements 8a-c induce a varying magnetic field in the susceptor 245, which causes heating of the susceptor 245. The susceptor 245 in turn heats aerosol generating material in the article 250.

Figure 10a shows an isometric exploded view of an aerosol provision device 210 in accordance with another embodiment. The aerosol provision device 210 includes components that are broadly similar to those described in relation to Figure 9a, the same reference numbers are used and they should be understood to be broadly the same as their counterparts unless otherwise stated.

The device 210 comprises a plurality of inductive elements 8, which in this example are in a 2x5 configuration. The plurality of inductive heaters 8 comprise a resonant circuit, such as the resonant circuit 14 described above. In this embodiment, the device 210 includes a plurality of air inlet holes 227 and air transmission channels 237 to direct air to the inductive elements 8.

In another embodiment (not shown), each of the plurality of inductive elements 8 enclosed by the respective aerosol transmission channels have an individual air supply hole. It will be appreciated that in other embodiments, the device can have a single air inlet (as described previously). Figure 10b shows an article 250 in accordance with another embodiment for use with the device of Figure 8a. The article 250 includes components that are broadly similar to those described in relation to Figure 9b, the same reference numbers are used and they should be understood to be broadly the same as their counterparts unless otherwise stated. In Figure 10b, the article 250 includes ten discrete portions of aerosol generating material 254 provided on a first side of a carrier component 262. The discrete portions are provided in a 2x5 grid. In this embodiment, the carrier component 262 comprises a heating layer 264.

It will be appreciated that in other embodiments, the carrier component 262 also includes a support layer.

In other embodiments, aerosol provision devices may be provided with any number of inductive elements may be provided in alternative grid configuration, for example a 2x3 grid, a 2x4 grid or a 3x3 grid.

In alternative embodiments, aerosol generating articles may be provided with the aerosol generating material 254 may be distributed in a different number of discrete portions and in different locations on the first side of the heating layer 264 as required.

Figure 11a shows an aerosol provision system 200 in accordance with another embodiment. The aerosol provision device 210 includes components that are broadly similar to those described in relation to Figure 9a, the same reference numbers are used and they should be understood to be broadly the same as their counterparts unless otherwise stated.

The device 210 comprises a plurality of inductive elements 8a-j, which in this embodiment are provided in a first array 8a to e and a second array 8f to 8j. The first array of inductive elements 8a to 8e is provided on a first side of the chamber 240 and the second array 8f to 8j is provided on a second, opposite side of the chamber 240.

In other embodiments, the aerosol provision device 210 may comprise a hinged door or removable part of the outer housing 221 to permit access to the chamber 240 such that a user may insert and/or remove the aerosol generating article 250 from the chamber 240.

Figures 11b to 11e show various articles which can be used with the device of Figure 11a. The articles are broadly cuboidal in shape so as to be received in the chamber 240 of the device 210.

Figure 11 b shows a cross-sectional view through an article 250 comprising a carrier component 262 comprising a heating layer 264. Discrete portions of aerosol generating material 254 are provided on a first side 264a and a second side 264b of the heating layer 264.

Figure 11c shows a cross-sectional view through an article 250 comprising a carrier component 262 comprising a support layer 266 and two heating layers 264, wherein the support layer is provided between the heating layers 264. Discrete portions of aerosol generating material 254 are provided on outer surfaces of the heating layers 264.

Figure 11 d shows a cross-sectional view through an article 250 comprising a substantially cuboidal carrier component 262. The article defines an inner void 263 having with open first and second ends 262a, 262b. The carrier component 262 comprises a heating layer 264 provided on opposition sides of the inner void. Discrete portions of aerosol generating material 254 are provided inner surfaces of the heating layers 264.

Figure 11e shows a cross-sectional view through an article 250 comprising a substantially cuboidal carrier component 262. The article defines an inner void 263 having with open first and second ends 262a, 262b. The carrier component 262 comprises a heating layer 264 and a support layer 266. Discrete portions of aerosol generating material 254 are provided on inner surfaces of the heating layer 264.

The various embodiments described herein are presented only to assist in understanding and teaching the claimed features. These embodiments are provided as a representative sample of embodiments only, and are not exhaustive and/or exclusive. It is to be understood that advantages, embodiments, examples, functions, features, structures, and/or other aspects described herein are not to be considered limitations on the scope of the invention as defined by the claims or limitations on equivalents to the claims, and that other embodiments may be utilised and modifications may be made without departing from the scope of the claimed invention. Various embodiments of the invention may suitably comprise, consist of, or consist essentially of, appropriate combinations of the disclosed elements, components, features, parts, steps, means, etc., other than those specifically described herein. In addition, this disclosure may include other inventions not presently claimed, but which may be claimed in future.

Claims

1. A method comprising: driving a resonant circuit of an inductive heater for an aerosol provision device at a determined resonant frequency of the resonant circuit in a heating mode, wherein the inductive heater comprises a switching circuit and a resonant circuit and wherein the inductive heater is for heating a susceptor; measuring the resonant frequency of the inductive heater during a sampling mode; estimating the temperature of the susceptor based at least in part on the resonant frequency of the inductive heater.

2. The method of claim 1, wherein the method further comprises: measuring an ambient temperature proximal to the inductive heater; and estimating the temperature of the susceptor based at least in part on the ambient temperature proximal to the inductive heater.

3. The method of claim 1 or 2, wherein estimating the temperature of the susceptor comprises: determining the difference between a first measured frequency and a second measured frequency; and multiplying the difference between the first measured frequency and a second measured frequency by a constant factor.

4. The method of claim 3, wherein the first measured frequency and the second measured frequency are measurements that are taken at different times.

5. The method of claim 4, wherein the first measured frequency and the second measured frequency are two consecutive measurements of the frequency.

6. The method of claims 3, 4 or 5, wherein the constant factor is proportional to the capacitance of the resonant circuit of the device.

7. The method of any preceding claim, wherein the ambient temperature is the temperature of the air surrounding the resonant circuit.

8. The method of any preceding claim further comprising: applying a pulse to the resonant circuit in the sampling mode of operation to generate a pulse response for use in estimating temperature.

9. The method of any preceding claim, further comprising determining or estimating a difference between the estimated temperature of the susceptor and a target temperature of said susceptor, wherein said susceptor is heated by an inductive heater circuit comprising a switching circuit and a resonant circuit; and setting a sampling period or frequency based, at least in part, on said difference, wherein the sampling period or frequency defines an interval between successive sampling modes of operation of the inductive heater circuit.

10. The method of claim 9, further comprising decreasing the sampling period if the difference between the estimated temperature and the target temperature is reduced; and/or increasing the sampling period if the difference between the estimated temperature and the target temperature is increased.

11. An apparatus for an aerosol provision device comprising: a resonant circuit comprising an inductive element and a capacitor, wherein the inductive element is for inductively heating a susceptor; a driving circuit for applying a pulse to said resonant circuit, wherein an edge of applied pulse induces a pulse response between the capacitor and the inductive element of the resonant circuit, wherein the pulse response has a resonant frequency; and a processor for: measuring the resonant frequency of the inductive heater during a sampling mode of operation; estimating the temperature of the susceptor based at least in part on the resonant frequency of the inductive heater.

12. The apparatus of claim 11 , wherein the processor is further configured to: measure an ambient temperature proximal to the inductive heater; and estimate the temperature of the susceptor based at least in part on the ambient temperature proximal to the inductive heater.

13. The apparatus of claim 11 or 12, wherein the processor is further configured to: determine the difference between a first measured frequency and a second measured frequency; and multiply the difference between the first measured frequency and a second measured frequency by a constant factor.

14 The apparatus of any of claims 11-13, wherein the processor is further configured to determine or estimate a difference between the estimated temperature of the susceptor and a target temperature of said susceptor, wherein said susceptor is heated by an inductive heater circuit comprising a switching circuit and a resonant circuit; and set a sampling period or frequency based, at least in part, on said difference, wherein the sampling period or frequency defines an interval between successive sampling modes of operation of the inductive heater circuit.

15. The apparatus of claim 14, wherein the processor is further configured to: decrease a sampling period if the difference between the estimated temperature and the target temperature is reduced; and/or increase the sampling period if the difference between the estimated temperature and the target temperature is increased.

16. An apparatus as claimed in claim 14 or claim 15, wherein the driving circuit is configured to drive the resonant circuit at a determined resonant frequency of the resonant circuit in the heating mode of operation.

17. An aerosol provision device comprising the apparatus according to any of claims 11-16.

18. The aerosol provision device of claim 17 comprising a plurality of resonant circuits.

19. The aerosol provision device of claim 20, comprising a chamber for removably receiving an article comprising an aerosol generating material, wherein the inductive elements of the plurality of resonant circuits are arranged along a side wall of the chamber.

20. The aerosol provision device of claim 19, comprising a chamber for removably receiving an article comprising an aerosol generating material, wherein the inductive elements of the plurality of resonant circuits are arranged along two side walls of the chamber.

21. An aerosol provision system comprising the aerosol provision device of any of claims 17-20, and an article comprising an aerosol generating material.

22. The aerosol provision system of claim 21 , wherein the article comprises a susceptor.

23. A method of generating aerosol comprising: providing an aerosol provision system according to claim 21 or 22, and at least partially inserting the aerosol generating article into the chamber.

24. A computer program comprising instructions for causing an apparatus for an aerosol provision device to perform at least the following: driving a resonant circuit of an inductive heater at a determined resonant frequency of the resonant circuit in a heating mode of operation, wherein the inductive heater comprises a switching circuit and a resonant circuit and wherein the inductive heater is for heating a susceptor; measuring the resonant frequency of the inductive heater during a sampling mode of operation; estimating the temperature of the susceptor based at least in part on the resonant frequency of the inductive heater.