Field

The present specification relates to inductive heating of a susceptor.

Background

Many inductive heating systems for heating susceptors are known. There remains a need for further developments in this field. Summary

In a first aspect, this specification describes an apparatus comprising: a plurality of heater modules, each heater module comprising a resonant circuit having an inductive element for inductively heating a susceptor arrangement and one or more capacitors, wherein each of the plurality of heater modules further comprises a bridge circuit for selectively coupling a first side and a second side of the respective resonant circuit to positive and negative supply voltages; a de-multiplexer arrangement for providing clock signals to a selected one of said heater modules depending on a control signal received from a control module; and a multiplexer arrangement for providing a feedback signals from the selected one of the heater modules. The apparatus may further comprise the said control module. The apparatus may be (or may form part of) an aerosol generating device.

The de-multiplexer arrangement may comprise: an input for receiving the clock signal; a control input for receiving the control signal; and a plurality of outputs for selectively providing said clock signal to said plurality of heater modules.

The multiplexer arrangement may comprise: a plurality of inputs coupled to feedback outputs of each of said plurality of heater modules; a control input for receiving the control signal; and an output for providing the feedback signals from the selected one of the heater modules.

The multiplexer arrangement may provide said feedback signals to said control module.

Some example embodiments further comprise a clock signal generator for generating said clock signals. The bridge circuit of each heater module may provide an alternating current to the respective resonant circuit under the control of said control circuit. The said bridge circuit of each heater module may, for example, comprise two half-bridge circuits. The one or more capacitors of each respective heater module may include a tuning capacitor. Each respective tuning capacitor may have a capacitance set depending, at least in part, on a location of the respective heater module within said apparatus. Each respective tuning capacitor may have a capacitance set dependent, at least in part, on one or more parameters affecting a resonant frequency of the respective heater module.

In another aspect, this specification describes an aerosol provision device comprising an apparatus as described above with respect to the first aspect. The aerosol generating device may be configured to receive a removable article comprising an aerosol generating material. The said aerosol generating material may comprise an aerosol generating substrate and an aerosol forming material. The said removable article may include a susceptor arrangement. The apparatus may comprise a tobacco heating system.

According to a further aspect, there is provided an aerosol provision system comprising an aerosol provision device comprising an apparatus as described above with reference to the third aspect, and an article comprising aerosol generating material.

The article may comprise a susceptor. According to a further 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.

In a further aspect, this specification describes a method comprising: providing clock signals to a selected one of a plurality of heater modules depending on a control signal received from a control module; and providing feedback signals from the selected one of the heater modules, wherein each heater module comprises a resonant circuit having an inductive element for inductively heating a susceptor arrangement and one or more capacitors, wherein each of the plurality of heater modules further comprises a bridge circuit for selectively coupling a first side and a second side of the respective resonant circuit to positive and negative supply voltages. The feedback signals may be provided to said control module. The method may further comprise generating said clock signals.

The method may further comprise setting a capacitance of one or more of said capacitors depending, at least in part, on a location of the respective heater module and/or dependent, at least in part, on one or more parameters affecting a resonant frequency of the respective heater module.

In a further aspect, this specification describes a method comprising: providing a control signal to a de-multiplexer arrangement, wherein the de-multiplexer arrangement is configured to provide clock signals to a selected one of a plurality of heater modules depending on said control signal, wherein each heater module comprises a resonant circuit having an inductive element for inductively heating a susceptor arrangement and one or more capacitors, wherein each of the plurality of heater modules further comprises a bridge circuit for selectively coupling a first side and a second side of the respective resonant circuit to positive and negative supply voltages; and receiving feedback signals from a multiplexer arrangement, wherein said feedback signals are provided by the selected one of the heater modules. The method may comprise providing said control signal to said multiplexer arrangement.

The method may further comprise setting a capacitance of one or more of said capacitors depending, at least in part, on a location of the respective heater module and/or dependent, at least in part, on one or more parameters affecting a resonant frequency of the respective heater module.

In a further aspect, this specification describes a computer program comprising instructions for causing an apparatus to perform (at least) any method as described herein (including the method as described above). In a further aspect, this specification describes a computer-readable medium (such as a non-transitory computer-readable medium) comprising program instructions stored thereon for performing (at least) any method as described herein (including the method as described above). In a further aspect, this specification describes computer-readable instructions which, when executed by a computing apparatus, cause the computing apparatus to perform (at least) any method as described herein (including the method as described above). In an further aspect, this specification describes an apparatus comprising: at least one processor; and at least one memory including computer program code which, when executed by the at least one processor, causes the apparatus to perform (at least) any method as described herein (including the method as described above). Brief Description of the Drawings

Example embodiments will now be described, by way of example only, with reference to the following schematic drawings, in which:

FIG. i is a block diagram of a system in accordance with an example embodiment; FIG. 2 is a block diagram of a heating arrangement in accordance with an example embodiment;

FIG. 3 is a view of a non-combustible aerosol provision system in accordance with an example embodiment;

FIG. 4 is a view of an article for use with a non-combustible aerosol provision device in accordance with an example embodiment;

FIGS. 5 and 6 are block diagrams of circuits in accordance with example embodiments;

FIG. 7 is a flow chart showing an algorithm in accordance with an example embodiment;

FIG. 8 is a block diagram of a system in accordance with an example embodiment; FIG. 9 is a plot showing a pulse in accordance with an example embodiment;

FIG. 10 is a plot showing a pulse response in accordance with an example embodiment; FIG. 11 is a block diagram of a system in accordance with an example embodiment;

FIG. 12 is a flow chart showing an algorithm in accordance with an example embodiment; FIG. 13 is a block diagram of a circuit in accordance with an example embodiment; FIG. 14 is a block diagram of a circuit in accordance with an example embodiment; FIG. 15 is a flow chart showing an algorithm in accordance with an example embodiment;

FIG. 16 is a block diagram of a system in accordance with an example embodiment; FIG. 17 is a flow chart showing an algorithm in accordance with an example embodiment; FIG. 18 is a block diagram of a circuit in accordance with an example embodiment;

FIG. 19 shows a circuit used in some example embodiments;

FIG. 20 is a flow chart showing an algorithm in accordance with an example embodiment; and FIG. 21 is a block diagram of a system in accordance with an example embodiment.

Detailed Description

As used herein, the term “aerosol delivery device” 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 “combustible” aerosol provision system is one where a constituent aerosolisable material of the aerosol provision system (or component thereof) is combusted or burned in order to facilitate delivery to a user.

According to the present disclosure, a “non-combustible” aerosol provision system is one where a constituent aerosolisable material of the aerosol provision system (or component thereof) is not combusted or burned in order to facilitate delivery to a user. In embodiments described herein, the delivery system is a non-combustible aerosol provision system, such as a powered non-combustible aerosol provision system.

In one embodiment, 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 aerosolisable material is not a requirement.

In one embodiment, the non-combustible aerosol provision system is a tobacco heating system, also known as a heat-not-burn system. In one embodiment, the non-combustible aerosol provision system is a hybrid system to generate aerosol using a combination of aerosolisable materials, one or a plurality of which may be heated. Each of the aerosolisable materials may be, for example, in the form of a solid, liquid or gel and may or may not contain nicotine. In one embodiment, the hybrid system comprises a liquid or gel aerosolisable material and a solid aerosolisable material. The solid aerosolisable 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 an article for use with the non-combustible aerosol provision system. However, it is envisaged that articles which themselves comprise a means for powering an aerosol generating component may themselves form the non-combustible aerosol provision system.

In one embodiment, the non-combustible aerosol provision device may comprise a power source and a controller. The power source may be an electric power source or an exothermic power source. In one embodiment, the exothermic power source comprises a carbon substrate which may be energised so as to distribute power in the form of heat to an aerosolisable material or heat transfer material in proximity to the exothermic power source. In one embodiment, the power source, such as an exothermic power source, is provided in the article so as to form the non-combustible aerosol provision.

In one embodiment, the article for use with the non-combustible aerosol provision device may comprise an aerosolisable material, an aerosol generating component, an aerosol generating area, a mouthpiece, and/or an area for receiving aerosolisable material.

In one embodiment, the aerosol generating component is a heater capable of interacting with the aerosolisable material so as to release one or more volatiles from the aerosolisable material to form an aerosol. In one embodiment, the aerosolisable material may comprise an active material, an aerosol forming material and optionally one or more functional materials. The active material may comprise nicotine (optionally contained in tobacco or a tobacco derivative) or one or more other non-olfactory physiologically active materials. A nonolfactory physiologically active material is a material which is included in the aerosolisable material in order to achieve a physiological response other than olfactory perception. The active substance as used herein maybe a physiologically active material, which is a material intended to achieve or enhance a physiological response. The active substance may for example be selected from nutraceuticals, nootropics, psychoactives. The active substance may be naturally occurring or synthetically obtained. The active substance may comprise for example nicotine, caffeine, taurine, theine, vitamins such as B6 or B12 or C, melatonin, cannabinoids, or constituents, derivatives, or combinations thereof. The active substance may comprise one or more constituents, derivatives or extracts of tobacco, cannabis or another botanical. In some embodiments, the active substance comprises nicotine. In some embodiments, the active substance comprises caffeine, melatonin or vitamin B12. In one embodiment, the active substance is a legally permissible recreational drug.

The aerosol forming 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 functional materials may comprise one or more of flavours, carriers, pH regulators, stabilizers, and/or antioxidants.

In one embodiment, the article for use with the non-combustible aerosol provision device may comprise aerosolisable material or an area for receiving aerosolisable material. In one embodiment, the article for use with the non-combustible aerosol provision device may comprise a mouthpiece. The area for receiving aerosolisable material maybe a storage area for storing aerosolisable material. For example, the storage area may be a reservoir. In one embodiment, the area for receiving aerosolisable material may be separate from, or combined with, an aerosol generating area. Aerosolisable material, which also may be referred to herein as aerosol generating material, is material that is capable of generating aerosol, for example when heated, irradiated or energized in any other way. Aerosolisable material may, for example, be in the form of a solid, liquid or gel which may or may not contain nicotine and/or flavourants. The aerosol-generating material maybe an “amorphous solid”. In some embodiments, the amorphous solid is a “monolithic solid”. The aerosol-generating material maybe non-fibrous or fibrous. In some embodiments, the aerosol-generating material maybe 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 maybe water. The aerosolisable material may be present on a substrate. The substrate may, for example, be or comprise paper, card, paperboard, cardboard, reconstituted aerosolisable material, a plastics material, a ceramic material, a composite material, glass, a metal, or a metal alloy. 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 aerosol-generating 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 aerosol-generating material to generate aerosol in use. The heater may, for example, comprise combustible material or a material heatable by electrical conduction. FIG. 1 is a block diagram of a system, 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.

As discussed in detail below, 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.

A susceptor is a 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, and a thermally conductive 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.

Induction heating is a process in which an electrically-conductive object is heated by penetrating the object with a varying magnetic field. The process is described by Faraday's law of induction and Ohm's law. An induction heater may comprise an electromagnet and a device for passing a varying electrical current, such as an alternating current, through the electromagnet. When the electromagnet and the object to be heated are suitably relatively positioned so that the resultant varying magnetic field produced by the electromagnet penetrates the object, one or more eddy currents are generated inside the object. The object has a resistance to the flow of electrical currents. Therefore, when such eddy currents are generated in the object, their flow against the electrical resistance of the object causes the object to be heated. This process is called Joule, ohmic, or resistive heating. An object that is capable of being inductively heated is known as a susceptor. Magnetic hysteresis heating is a process in which an object made of a magnetic material is heated by penetrating the object with a varying magnetic field. A magnetic material can be considered to comprise many atomic-scale magnets, or magnetic dipoles. When a magnetic field penetrates such material, the magnetic dipoles align with the magnetic field. Therefore, when a varying magnetic field, such as an alternating magnetic field, for example as produced by an electromagnet, penetrates the magnetic material, the orientation of the magnetic dipoles changes with the varying applied magnetic field. Such magnetic dipole reorientation causes heat to be generated in the magnetic material.

When an object is both electrically-conductive and magnetic, penetrating the object with a varying magnetic field can cause both Joule heating and magnetic hysteresis heating in the object. Moreover, the use of magnetic material can strengthen the magnetic field, which can intensify the Joule heating.

In each of the above processes, as heat is generated inside the object itself, rather than by an external heat source by heat conduction, a rapid temperature rise in the object and more uniform heat distribution can be achieved, particularly through selection of suitable object material and geometry, and suitable varying magnetic field magnitude and orientation relative to the object. Moreover, as induction heating and magnetic hysteresis heating do not require a physical connection to be provided between the source of the varying magnetic field and the object, design freedom and control over the heating profile may be greater, and cost may be lower.

FIG. 2 is a block diagram of a heating arrangement, indicated generally by the reference numeral 12a, in accordance with an example embodiment. The heating arrangement 12a is similar to the heating arrangement 12 described above. In the heating arrangement 12a, a plurality of resonant circuits are provided (first resonant circuit 14a, second resonant circuit 14b and nth resonant circuit I4n are shown) in place of the single resonant circuit 14 of the heating arrangement 12. The switching module 13 of the heating arrangement 11 is replaced with a switching arrangement 13a that is able to independent control the plurality of resonant circuits 14a to I4n.

Each of the resonant circuits 14a to I4n may comprise a capacitor and one or more inductive elements for inductively a susceptor arrangement (such as the susceptor arrangement 16). This heating can be used, for example, to heat an aerosol generating material to thereby generate an aerosol. In one example use of the heating arrangement 12a, the resonant circuits 14a to i4n can be used to heat different parts of a susceptor (such as the susceptor 16).

FIG. 3 is a view of a non-combustible aerosol provision system, indicated generally by the reference numeral 20, in accordance with an example embodiment. The aerosol provision system 20 comprises an aerosol provision device 20A which is shown with an outer cover removed. The aerosol provision device 20A is an example of an inductively heated device that may be controlled in accordance with the principles described herein. The aerosol provision system 20 comprises a replaceable article 21 that may be inserted in the aerosol provision device 20A to enable heating of a susceptor (which may be comprised within the article 21, as discussed further below). The aerosol provision device 20A may further comprise an activation switch 22 that may be used for switching on or switching off the aerosol provision device 20A.

The aerosol generating device 20A includes a plurality of inductive elements 23a, 23b, and 23c, and one or more air tube extenders 24 and 25. The one or more air tube extenders 24 and 25 maybe optional. The activation switch 22 maybe optional; for example a pressure trigger or some other activation-on-demand arrangement may be provided.

The plurality of inductive elements 23a, 23b, and 23c may each form part of a resonant circuit, such as the resonant circuits 14a, 14b and i4n described above. The inductive element 23a may comprise 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. Many alternative inductor formations are possible, such as inductors formed within a printed circuit board. The inductive elements 23b and 23c may be similar to the inductive element 23a. Of course, the use of three inductive elements 23a, 23b and 23c is an example only; the aerosol generating device 20 may more or fewer than three inductive elements.

A susceptor may be provided as part of the article 21. In an example embodiment, when the article 21 is inserted in aerosol generating device 20A, the aerosol generating device 20A may be turned on due to the insertion of the article 21. This may be due to detecting the presence of the article 21 in the aerosol generating device using an appropriate sensor (e.g., a light sensor) or, in cases where the susceptor forms a part of the article 21, by detecting the presence of the susceptor using the resonant circuit 14, for example. When the aerosol generating device 20A is turned on, the inductive elements 23a to 23c may cause the article 21 to be inductively heated through the susceptor. In an alternative embodiment, the susceptor may be provided as part of the aerosol generating device 20A (e.g. as part of a holder for receiving the article 21). FIG. 4 is a view of an article, indicated generally by the reference numeral 30, for use with a non-combustible aerosol provision device in accordance with an example embodiment. The article 30 is an example of the replaceable article 21 described above with reference to FIG. 3.

The article 30 comprises a mouthpiece 31, and a cylindrical rod of aerosol generating material 33, in the present case tobacco material, connected to the mouthpiece 31. The aerosol generating material 33 provides an aerosol when heated, for instance within a non-combustible aerosol generating device, such as the aerosol generating device 20, as described above. The aerosol generating material 33 is wrapped in a wrapper 32. The wrapper 32 can, for instance, be a paper or paper-backed foil wrapper. The wrapper 32 may be substantially impermeable to air. In one embodiment, the wrapper 32 comprises aluminium foil. Aluminium foil has been found to be particularly effective at enhancing the formation of aerosol within the aerosol generating material 33. In one example, the aluminium foil has a metal layer having a thickness of about 6 pm. The aluminium foil may have a paper backing. However, in alternative arrangements, the aluminium foil can have other thicknesses, for instance between 4 pm and 16 pm in thickness. The aluminium foil also need not have a paper backing, but could have a backing formed from other materials, for instance to help provide an appropriate tensile strength to the foil, or it could have no backing material. Metallic layers or foils other than aluminium can also be used. Moreover, it is not essential that such metallic layers are provided as part of the article 30; for example, such a metallic layer could be provided as part of the apparatus 20.

The aerosol generating material 33, also referred to herein as an aerosol generating substrate 33, 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 forming material has been found to improve the sensory performance of the article, by helping to transfer compounds such as flavour compounds from the aerosol generating material to the consumer. As shown in FIG. 4, the mouthpiece 31 of the article 30 comprises an upstream end 31a adjacent to an aerosol generating substrate 33 and a downstream end 31b distal from the aerosol generating substrate 33. The aerosol generating substrate may comprise tobacco, although alternatives are possible.

The mouthpiece 31, in the present example, includes a body of material 36 upstream of a hollow tubular element 34, in this example adjacent to and in an abutting relationship with the hollow tubular element 34. The body of material 36 and hollow tubular element 34 each define a substantially cylindrical overall outer shape and share a common longitudinal axis. The body of material 36 is wrapped in a first plug wrap 37. The first plug wrap 37 may have a basis weight of less than 50 gsm, such as between about 20 gsm and 40 gsm.

In the present example the hollow tubular element 34 is a first hollow tubular element 34 and the mouthpiece includes a second hollow tubular element 38, also referred to as a cooling element, upstream of the first hollow tubular element 34. In the present example, the second hollow tubular element 38 is upstream of, adjacent to and in an abutting relationship with the body of material 36. The body of material 36 and second hollow tubular element 38 each define a substantially cylindrical overall outer shape and share a common longitudinal axis. The second hollow tubular element 38 is formed from a plurality of layers of paper which are parallel wound, with butted seams, to form the tubular element 38. In the present example, first and second paper layers are provided in a two-ply tube, although in other examples 3, 4 or more paper layers can be used forming 3, 4 or more ply tubes. Other constructions can be used, such as spirally wound layers of paper, cardboard tubes, tubes formed using a papier-mache type process, moulded or extruded plastic tubes or similar. The second hollow tubular element 38 can also be formed using a stiff plug wrap and/ or tipping paper as the second plug wrap 39 and/or tipping paper 35 described herein, meaning that a separate tubular element is not required.

The second hollow tubular element 38 is located around and defines an air gap within the mouthpiece 31 which acts as a cooling segment. The air gap provides a chamber through which heated volatilised components generated by the aerosol generating material 33 may flow. The second hollow tubular element 38 is hollow to provide a chamber for aerosol accumulation yet rigid enough to withstand axial compressive forces and bending moments that might arise during manufacture and whilst the article 21 is in use. The second hollow tubular element 38 provides a physical displacement between the aerosol generating material 33 and the body of material 36. The physical displacement provided by the second hollow tubular element 38 will provide a thermal gradient across the length of the second hollow tubular element 38.

Of course, the article 30 is described byway of example only. The skilled person will be aware of many alternative arrangements of such an article that could be used in the systems described herein. Similarly, the skilled person will be aware of other articles that may be heated using the principles described herein.

FIG. 5 is a block diagram of a circuit, indicated generally by the reference numeral 50, in accordance with an example embodiment. The circuit 50 comprises a first switch 51, a second switch 52, a third switch 53, a fourth switch 54 and a resonant circuit 56. The first to fourth switches 51 to 54 maybe implemented using transistors, as discussed further below. The first to fourth switches 51 to 54 form an H-bridge bridge circuit that may be used to apply pulses to the resonant circuit 56, with the first and second switches 51 and 52 forming a first half-bridge, and the third and fourth switches 53 and 54 forming a second half-bridge. Thus, the first to fourth switches 51 to 54 are an example implementation of the switching arrangements 13 and 13a and the resonant circuit 56 is an example of the resonant circuits 14, 14a, 14b and i4n described above.

The first and second switches 51 and 52 form a first limb of the full H-bridge circuit and the third and fourth switches 53 and 54 form a second limb. More specifically, the first switch 51 can selectively provide a connection between a first power source (labelled VDD in FIG. 5) and a first connection point, the second switch 52 can selectively provide a connection between the first connection point and ground, the third switch 53 can selectively provide a connection between the first power source and a second connection point and the fourth switch 54 can selectively provide a connection between the second connection point and ground. The resonant circuit 56 is provided between the first and second connection points.

FIG. 6 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 50 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 64 (implementing the switching arrangements 13 and 13a described above), where the switching arrangement 64 comprises a bridge circuit (e.g. an H-bridge circuit, such as an FET H- bridge circuit). The switching arrangement 64 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, 14a, 14b, I4n and 56 described above). The first limb 64a comprises switches 65a and 65b (implementing the switches 51 and 52 described above), and the second limb 64b comprises switches 65c and 63d (implementing the switches 53 and 54 described above). The switches 65a, 65b, 65c, and 63d maybe 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. 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, in which the susceptor arrangement 16 is heated by the inductive arrangement, the switching arrangement 64 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. FIG. 7 is a flow chart showing an algorithm, indicated generally by the reference numeral 70, in accordance with an example embodiment. The algorithm 70 may be implemented using the system 10 described above.

The algorithm 70 starts in operation 72, where a resonant circuit (e.g. the resonant circuit 14, or one of the resonant circuits 14a, 14b and I4n) is driven at a resonant frequency of the resonant circuit in a heating mode of operation. For example, the switching arrangement 13 or 13a may be switched at a determined resonant frequency of the respective resonant circuit 14, 14a, 14b, I4n (e.g. under the control of the control circuit 18). The effectiveness of the heating mode 72 may be dependent on the accuracy of the determination of the resonant frequency. The effectiveness of the heating mode 72 may be dependent on the resolution of the output frequency used to drive the resonant circuit.

At operation 74, 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 70). As discussed in detail 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.

At operation 76, the driving frequency for the resonant circuit is set based on the determined resonant frequency. Thus, the parameters of the heating mode (including the driving frequency and the sampling interval) are set in the operation 76. The heating of the susceptor occurs in the next iteration of the heating mode 72 until the time interval dictated by the sampling mode occurs. The algorithm 70 then re-enters the sampling mode 74 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 76).

FIG. 8 is a block diagram of a system, indicated generally by the reference numeral 80, in accordance with an example embodiment. The system 80 comprises a pulse generation circuit 82, a resonant circuit 84 (such as the resonant circuits 14, 14a, 14b, i4n, 56 and 69), a susceptor 86 (such as the susceptor 16) and a pulse response processor 88. The pulse generation circuit 82 and the pulse response processor 84 may be implemented as part of the control circuit 18 of the system 10 and may be used during the sampling mode 76 of the algorithm 70. The pulse generation circuit 82 may be implemented using the switching arrangements of the circuits 50 and 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 82 may be implemented using a half-bridge circuit.

The pulse response processor 88 may determine one or more performance metrics (or characteristics) of the resonant circuit 84 and the susceptor 86 based on the pulse response. For example, the pulse response processor 88 may generate an estimate of the temperature of the susceptor 86 and/or a resonant frequency of the resonant circuit.

FIG. 9 is a plot showing a pulse 90 in accordance with an example embodiment. The pulse 90 is includes a rising pulse edge 92 that is an example of a pulse edge that may be applied to the resonant circuit 84. The pulse 90 may be generated by the pulse generation circuit 82 (e.g. by an H-bridge or half-bridge circuit). The pulse 90 may, for example, be applied during the sampling mode 74 of the algorithm 70 (e.g. to generate a pulse response for use in estimating temperature and/or resonant frequency).

The pulse 90 may be applied to the resonant circuit 84. Alternatively, in systems having multiple inductive elements, the pulse generation circuit 82 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 92 to the resonant circuit 84 generates a pulse response.

FIG. 10 is a plot, indicated generally by the reference numeral too, showing an example pulse response that might be generated at a connection point between the capacitor 66 and the inductor 63 of the resonant circuit 69 described above in response to the pulse edge 92. As shown in FIG. 10, the pulse response 100 may take the form of a ringing resonance. The pulse response is a result of charge bouncing between the inductor(s) and capacitor(s) of the resonant circuit. In one arrangement, no heating of the susceptor is caused as a result. That is, the temperature of the susceptor remains substantially constant (e.g., within ±1°C or ±o.i°C of the temperature prior to applying the pulse). As shown in FIG. 10, 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 maybe taken, such as the period between successive peaks of the ringing response).

FIG. 11 is a block diagram of a system, indicated generally by the reference numeral 110, in accordance with an example embodiment. The system 110 may form part of an aerosol generating device (such as the aerosol provision device 20 discussed above). The system 110 comprises a de-multiplexer arrangement 112, a plurality of heater modules 114a, 114b, H4n, a multiplexer arrangement 116, a control module 117 and a clock generator 118. Each of the heater modules comprises a resonant circuit, as discussed in detail below. Although three heater modules are shown in FIG. 11, example systems may include more or fewer than three heater modules.

The de-multiplexer arrangement 112 has an input for receiving a clock signal from the clock generator 118, a control input for receiving a control signal from the control module 117 and a plurality of outputs. The plurality of outputs selectively provide the clock signal (or a signal derived from the clock signal) to said plurality of heater modules 114a to H4n. In this way, the de-multiplexer arrangement 112 provides clock signals to a selected one of said heater modules 114a, 114b, H4n depending on a control signal.

Each of the plurality of heater modules 114a, 114b, H4n comprises a resonant circuit having an inductive element for inductively heating a susceptor arrangement and one or more capacitors (as discussed further below) such that the heater modules 114a, 114b and H4n are similar to the resonant circuits 14a, 14b and i4n described above. Each of the heater modules provides a feedback signal (e.g. a current measurement) to the multiplexer arrangement 116. The multiplexer arrangement 116 receives a control input from the control module 117. Based on the control input, the feedback signal from the selected heater module is provided to the control module 117. The control signal received at the multiplexer 116 may the same control signal that is provided to the de-multiplexer arrangement 112. In this way, the feedback signal output by the multiplexer arrangement 116 relates to the heater module that is driven by the clock signal output by the de-multiplexer arrangement 112.

FIG. 12 is a flow chart showing an algorithm, indicated generally by the reference numeral 120, in accordance with an example embodiment. The algorithm 120 maybe implemented using the system 110 described above.

The algorithm 120 starts at operation 122 where signals for driving heater modules are generated. For example, clock signals maybe provided to a selected one of a plurality of heater modules (e.g. one of the modules 114a, 114b and H4n) depending on a control signal received from a control module. For example, clock signals maybe provided to a selected one of the heater modules 114a, 114b, H4n described above based on a control signal received from the control module 117. At operation 124, feedback signals are obtained from the heater module selected in the operation 122. For example, selected feedback signals may be provided to the control module 117. As discussed above, the feedback signal may be output by the multiplexer arrangement 116 in response to a control signal received from the control module 117. At operation 126, the control of the heating system is updated based on the feedback signals. For example, the feedback signals may provide temperature information related to a heating operation and the control of the heating operation maybe updated based on said feedback signals. The skilled person will be aware of alternative feedback signals that could be used to control the system.

FIG. 13 is a block diagram of a circuit, indicated generally by the reference numeral 130, in accordance with an example embodiment. The circuit 130 may be used to implement each of the heater modules 114a, 114b and H4n. The circuit 130 comprises a first half-bridge circuit 132, a second half-bridge circuit 133 and a RLC resonance circuit 134 (comprising an inductive element for inductively heating a susceptor arrangement and one or more capacitors). The half-bridge circuits 132 and 133 receive control signals from the de-multiplexer arrangement 112 and are used for selectively coupling a first side and a second side of the resonant circuit 134 to positive and negative supply voltages. The half-bridge circuits collectively provide an alternating current to the resonant circuit under the control inputs received from the de-multiplexer arrangement 112. In this way, a selected heater module can be driven.

FIG. 14 is a block diagram of a circuit, indicated generally by the reference numeral 140, in accordance with an example embodiment. The circuit 140 is an example implementation of the circuit 130 described above and is similar to the circuit 50 described above.

The circuit 50 comprises a first switch 141, a second switch 142, a third switch 143, a fourth switch 144 and a resonant circuit 146 (e.g. a RLC resonance circuit). The first to fourth switches 141 to 144 may be implemented using transistors, as discussed further below.

The first and second switches 141 and 142 form a half-bridge circuit (such as the first half-bridge circuit 132) and he third and fourth switches 143 and 144 form a second half-bridge circuit (such as the second half-bridge circuit 133). The switches receive clock signals (CLKn and the inverse / CLKn) that may be used to apply pulses to the resonant circuit 146.

The clock signals may be received from the de-multiplexer arrangement 112. If the resonant circuit 140 is not selected for heating, then the clock signals can be disabled (e.g. the second switch 142 and the fourth switch 144 may be closed, so that both sides of the resonant circuit 146 are grounded, with the first and third switches 141 and 143 being open). If the resonant circuit is selected for heating, then the de-multiplexer arrangement 112 can provide switching signals to the first to fourth switches so that the resonant circuit 146 is driven, ideally at (or close to) the resonant frequency of the resonant circuit. Each of a plurality of heater modules (such as the heater modules 114a, 114b and H4n will be physically positioned at a different position within a circuit and at a different distance from other circuit elements (such as the de-multipl exer 112). This can have an impact on the capacitances in the circuit and hence on the resonant frequency of the resonant heater circuit. Some example embodiments seek to compensate for this variation in resonant frequency. For example, one or more capacitors of each respective heater module may include a tuning capacitor.

FIG. 15 is a flow chart showing an algorithm, indicated generally by the reference numeral 150, in accordance with an example embodiment.

The algorithm 150 starts at operation 152, where parameters that may have an effect on the resonant frequency of a respective heater module (such as one of the heater modules 114a, 114b and H4n) are determined. Such parameters may include a location of the respective heater module within a circuit (which may in particular affect the resistance of an RLC heater module, but also may affect the inductance and/or capacitance). Relevant distances are determined based on this location. Alternatively, or in addition, such parameters may include manufacturing tolerances of the resistors, inductors and/or capacitors of the respective heater modules.

At operation 154, the capacitance of a tuning capacitor of the respective heater module is set depending, at least in part, on the parameters determined in the operation 152.

FIG. 16 is a block diagram of a system in accordance with an example embodiment. The system 160 may form part of an aerosol generating device (such as the aerosol provision device 20 discussed above).

The system 160 comprises a clock signal generator 161, a first switching circuit 162, a second switching circuit 163, a plurality of heater modules 164a, 164b, i64n, and a control circuit 166. The clock signal generator 161 provides a clock signal to said first and second switching circuits 162 and 163. Each of the heater modules comprises a resonant circuit having an inductive element for inductively heating a susceptor arrangement and one or more capacitors. Although three heater modules are shown in FIG. 16, example systems may include more or fewer than three heater modules. The first switching circuit 162 has an output for providing a first positive or negative supply voltage to the heater modules. Similarly, the second switching circuit 163 has an output for providing a second positive or negative supply voltage to the heater modules. As discussed further below, each of the plurality of heater modules 164a to i64n has a first switch for selectively coupling a first side of the resonant circuit to the output of the first switching circuit 162 and a second switch for selectively coupling a second side of the resonant circuit to the output of the second switching circuit 163. The control module 166 operates as a heater selection module for selecting one of said plurality of heater modules 164a, 164b and i64n to be the selected heater module and controlling said first and second switches accordingly. All heater modules other than the active module may be unselected heater modules. Similarly, a single feedback signal may be provided by the selected heater module to the control module 166. The feedback signal may, for example, be indicative of current flowing in the selected resonant circuit.

The first and second switching circuits 162 and 163 can be used to provide an alternating current to the selected heater module (as selected by the control module 166). The first and second switching circuits maybe half-bridge circuits (such as the half-b ridge circuits described above with reference to FIG. 14).

It should be noted that the provision of switches within the heater modules 164a to i64n means that there is no need for the multiplexing arrangement of the system 110 described above. As described above with reference to the algorithm 150, each of a plurality of heater modules (such as the heater modules 164a, 164b and i64n) will be physically positioned at a different position within a circuit and at a different distance from other circuit elements (such as the switching circuits 162 and 163 and the control circuit 166). This can have an impact of the capacitances in the circuit and hence on the resonant frequency of the resonant heater circuit. Some example embodiments seek to compensate for this variation in resonant frequency. For example, one or more capacitors of each respective heater module may include a tuning capacitor. As discussed with reference to the algorithm 150, the capacitance of a tuning capacitor of the respective heater module may be set depending, at least in part, on the location of the heater module. The capacitance of the tuning capacitor of the respective heater module may also (or alternatively) be set depending on other parameters that may have an effect on the resonant frequency of a respective heater module (such as manufacturing tolerances of the resistors, inductors and/or capacitors of the respective heater modules). FIG. 17 is a flow chart showing an algorithm, indicated generally by the reference numeral 170, in accordance with an example embodiment. The algorithm 170 may be implemented using the system 160 described above.

The algorithm 170 starts at operation 172, where the first switching circuit 162 and the second switching circuit 163 are driven to provide a first positive or negative supply voltage and a second positive or negative supply voltage respectively (thereby providing an alternating current).

At operation 174 of the algorithm 174, first and second switches of each of the plurality of heater modules are controlled to couple a selected heater module to said first positive or negative supply voltage and to couple the selected heater module to said second positive or negative supply voltage. The switches of unselected heater modules can be opened so that those heater modules are decoupled from the driving voltages generated in the operation 172.

FIG. 18 is a block diagram of a circuit, indicated generally by the reference numeral 180, in accordance with an example embodiment. The circuit 180 may be used to implement each of the heater modules 164a, 164b and 164m The circuit 180 comprises a first switch 182, a second switch 183 and a RLC resonance circuit 184 (comprising an inductive element for inductively heating a susceptor arrangement and one or more capacitors).

The first and second switches 182 and 183 are turned on if the respective heater module is the selected heater module and are turned off if the respective heater module is not the selected heater module (e.g. in response to a control signal from the control module 166 described above). The first and second switches maybe bi-directional current switches. FIG. 19 shows a circuit, indicated generally by the reference numeral 190, used in some example embodiments. The circuit 190 comprises a MOSFET and a free-wheeling diode. The circuit 190 may be used as the bi-directional current switches discussed above (e.g. the first and second switches 182 and 183).

FIG. 20 is a flow chart showing an algorithm, indicated generally by the reference numeral 200, in accordance with an example embodiment. The algorithm 200 may be implemented by a control module (e.g. a processor); for example, the algorithm 200 may be implemented by the control module 117 of the system 110 described above or the control module 166 of the system 160 described above. The algorithm 200 starts at operation 202, where control signals are provided. For example, control signals may be provided by the control module 117 to the demultiplexer 112 or from the control module 166 to the first and second switching circuits 162 and 163. At operation 204, feedback signals are received. For example, feedback signals may be received by the control module 117 from the multiplexer 116 or may be received by the control module 166 from the heater modules 164.

FIG. 21 is a block diagram of a system, indicated generally by the reference numeral 210, in accordance with an example embodiment. The system 210 may be used to implement the algorithm 200 described above. The system 210 may be used to implement the control module 117 or the control module 166.

The system 210 comprises a processor 212, memory 214 (e.g. RAM or RAM) and may include inputs or outputs 216. The processor 212 may be used to implement the algorithm 200, for example based on computer program code stored in the memory 214.

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 maybe claimed in future.