Temperature estimation

Abstract

A method, apparatus and computer program is described comprising: applying a pulse edge to a resonant circuit comprising an inductive element (for inductively heating a susceptor) and a capacitor, wherein the applied pulse edge induces a pulse response between the capacitor and the inductive element of the resonant circuit, wherein the pulse response has a resonant frequency; determining a period or frequency of the resonant frequency of said pulse response; and converting the determined period or frequency into a temperature estimate based on a temperature gradient and a calibration measurement.

Description

WO 2022 / 118005 PCT / GB2021 / 053113 -1- Temperature Estimation Technical Field The present specification relates temperature estimation, for example to temperature 5 estimation for an aerosol generating 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 10 by creatjng products that release compounds ·without combusting. For example, tobacco heating devices heat an aerosol generating substrate such as tobacco to form an aerosol by heating, but not burning, the substrate. Summary 15 In a first aspect, this specification describes a method comprising: applying a pulse edge to a resonant circuit comprising an inductive element, for inductively heating a susceptor, and a capacitor, wherein the applied pulse edge induces a pulse response between the capacitor and the inductive element of the resonant circuit, wherein the pulse response has a resonant frequency; determining a period or frequency of the 20 resonant frequency of said pulse response; and converting the determined period or frequency into a temperature estimate based on a temperature gradient (e.g. a rate of change of the resonant frequency of said pulse response w1th respect to temperature) and a calibration measurement. The pulse edge may form part of an off-resonance pulse. 25 30 In some example embodiments, converting the determined period or frequency into said temperature estimate may comprise: subtracting the calibration measurement from tbe determined period or frequency of the resonant frequency of said pulse response; and dividing the result of the subtraction by said temperature gradient. The calibration measurement may define a first period or frequency of the resonant frequency of said pulse response at a first temperature (e.g. room temperature). The calibration measurement may, for example, be obtained by subtracting the product 35 of said gradient and a calibration temperature from a period of said pulse response at said calibration temperature. CA 03198563 2023-5-11 WO 2022 / 118005 PCT / GB2021 / 053113 - 2 - The method may comprise determining said calibration measurement. Alternatively, or in addition, the method may comprise determining said gradient. 5 In a second aspeet, this specification describes an apparatus comprising: a resonant circuit comprising an inductive element and a capacitor, wherein the inductive element is for inductively beating a susceptor; a driving circuit (such as an H-bridge circuit or a half bridge circuit) for applying a pulse edge to said resonant circuit, wherein the applied pulse edge induces a pulse response between the capacitor and the inductive 10 element of the resonant circuit, wherein the pulse response has a resonant frequency; and a processor for: determining a period or frequency of the resonant frequency of said pulse response and converting the determined period or frequency into a temperature estimate based on a temperature gradient and a calibration measurement. The inductive element and the capacitor may be connected in series. 15 20 The processor may convert the determined period or frequency into said temperature estimate by: subtracting the calibration measurement from the determined period or frequency of the resonant frequency of said pulse response; and dividing the result of the subtraction by said temperature gradient. The processor may be for determining said calibration measurement. Alternatively, or i n addition, the processor may be for determining said gradient. In a third aspect, this specification describes a non-combustible aerosol generating 25 device comprising an apparatus as described above vvith reference to the second aspect. 30 The aerosol generating device may be configured to receive a removable article comprising an aerosol generating material. The aerosol generating material may, for example, comprise an aerosol generating substrate and an aerosol forming material. The removable article may include a susceptor arrangement. In a fourth aspect, this specification describes a kit of parts comprising an article for use in a non-combustible aerosol generating system, wherein the non-cornbustible aerosol generating system comprises an apparatus as described above ,.,vith reference to the second aspect or an aerosol generating device as described above with reference to 35 the third aspect. The article may be a removable article comprising an aerosol generating material. CA 03198563 2023-5-11 WO 2022 / 118005 PCT / GB2021 / 053113 In a fifth aspect, this specification describes a computer program comprising instructions for causing an apparatus to perform at least the following: apply a pulse edge to a resonant circuit comprising an inductive element, for inductively heating a 5 :susceptor, anu a r:apacitor, wherein the applied pul:se edge i nduce:s a pulse re:sponse between the capacitor and the inductive element of the resonant circuit, wherein the pulse response has a resonant frequency; determine a period or frequency of the resonant frequency of said pulse response; and convert the determined period or frequency into a temperature estimate based on a temperature gradient and a 10 calibration measurement. The computer program may be further configured to perform any aspect of the method described above with reference to the first aspect. Brief Description of the Drmvings Example embodjments vvill now be described, byway of example only, with reference to 15 the following schematic drawings, in which: F IG. 1 is a block diagram of a system in accordance with an example embodiment; F IG. 2 shows a non-combustible aerosol provision device in accordance vvith an example embodiment: 20 F IG. 3 is a view of a non-combustible aerosol provision device in accordance with an example embodiment; F IG. 4 is a view of an article for use vvith a non-combustible aerosol provision device in accordance with an example embodiment; F IG. 5 and 6 are block diagrams of circuits in accordance with example ernbodiments; 25 FIG. 7 is a block diagram of a system in accordance vvith an example embodiment; F IG. 8 is a flow chart showing an algorithm in accordance with an example embodiment; F IG. 9 is a plot shovving a pulse in accordance with an example embodiment; F IGS. 10 and 11 are plots shovving pulse responses in accordance with example 30 embodiments; F IG. 12 is a plot showing a relationship between pulse response period and temperature in accordance 'v\rith an example embodiment; FIG. 13 is a flow chart showing an algorithm in accordance ,i\.rith an example embodiment; and 35 F IG. 14 is a block diagram of a circuit in accordance ,,vith an example embodiment. CA 03198563 2023-5-11 WO 2022 / 118005 PCT / GB2021 / 053113 Detailed Description As used herein, the term " aerosol delivery device" is i ntended to encompass systems that d eliver a su bstance to a u s er, and incl ud es : non-combustible aerosol provision systems that release compounds from an 5 aerosolisable material without comlmsting the aerosol isal.Jle material, such as electronic cigarettes, tobacco heating products, and hybrid systems to generate aerosol using a combi nation of aerosoli sable materials; and 10 articles comprising aerosolisable material and configured to be used i n one of these non-combustible aerosol provision systems. According to the present disclosure, a " combustible" aerosol provision syste m is one where a constituent aerosolisable material of the aerosol provision system (or component thereof) is combusted or b u rned i n order to facilitate d el i very to a u ser. 15 According to the present disclosure, a " non-combustible" aerosol provision system is one where a constituent aeroso1i sab1e mater i al of the aerosol provi sion system (or component thereof) is not combusted or burned i n 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. 20 25 In one embod iment, the non-combustible aerosol provision system is an electronic cigarette, also known as a vapi ng d evice or electroni c 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-comb ustible aerosol provision syslem is a lobacco heating system, also known as a heat-not-burn system. In one embodiment, the non-combustible aerosol provision system is a hybrid system 30 to generate aerosol using a combination of aerosolisabie 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, liqui d or gel and may or may not contain nicotine. In one ernbodiment, the hybrid system comprises a liquid or gel aerosolisable material and a solid aerosolisable material . The solid aerosolisable material may comprise, for example, 35 tobacco or a non-tobacco product. CA 03198563 2023-5-11 WO 2022 / 118005 PCT / GB2021 / 053113 - 5 - Typically, the non-combustibie aerosol p rovi sion system may comprise a noncombustible aerosol provision device and an article for use vnth the non-combustible aerosol provision system. However, it is envisaged that articles which themselves comprise a means for p owering an aerosol generating component may themselves form 5 the non-<.:ombustible aero:sol p rovision sy:stem. In one embodiment, the non -combustible aerosol provision device m ay comprise a power source and a controll er. The power source may be an electric power source or an exothermic power source. In one embodiment, the exothermic power source comprises 10 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 i n p roximity 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. 15 In one embodiment, the article for use with the non-combustible aerosol provision device may comprise an aeroso1isab l e rnateria1, an aerosol generating component, an aerosol generating area, a mouthpiece, and / or an area for receiving aerosolisable material. 20 In one embodiment, the aerosol generating component is a heater capable of interacting s'V7th the aerosolisable material so as to release one or more volatiles from the aerosolisable material to forrn an aerosol. In one embodiment, the aerosol generating component is capable of generating an aerosol fro m the aerosolisable material with o ut heating. For example, the aerosol generating component may be 25 capable of generating an aerosol from the aerosolisable material vvithout applying heat therelo, for example via one or more of vibrational, m echanical, press u risation or electrostatic means. In one embodiment, the aerosolisable material may comprise an active material, an 30 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 p hysiologically active materials. A nonolfactory p hysiologically active material is a material which is i ncluded in the aerosolisable m aterial in order to achieve a physiological response other than olfactory 35 p erception. The active substance as used herein may be a physiologically active material, which is a material intended to achieve or enhance a p hysiological response. CA 03198563 2023-5-11 WO 2022 / 118005 PCT / GB2021 / 053113 - 6 - The active substance may for example be selected from rrntraceuticals, nootropics, p sychoactives. The active substance may be naturally occurring or synthetically obtained. The active substance may cornprise for example nicotine, caffeine, taurine, theine, vitamins such as B6 or B12 or C, melatonin, cannabinoids, or constituents, 5 derivatives, or combinations thereof. The active substance m ay co1nprise one or more constituents, derivatives or extracts of tobacco, cannabis or another botanical. In some embodiments, the active s ubstance comprises n icotine. In some embodiments, the actjve substance comprises caffeine, melatonin or vitamin B12. 10 The aerosol forming material may comprise one or more of glycerine, glycerol,prnpylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,3- butylene glycol, erythritol, meso- Erythritol , ethyl vanillate, ethyl laurate, a diethyl subernte, triethyl citrate, triacetin, a diacetin mixtu re, benzyl benzoate, benzyl p henyl acetate, tribut)Tin, lamyl acetate, lauric acid, myristi c acid, and propylene carbonate. 15 The one or more functional materials may comprise one or more of fl avours, carriers, p H regulators, stabilizers, and / or antioxidants. In one embodiment, the article for use with the non-combustible aerosol provision 20 device may comprise aerosolisabl e material or an area for receivi ng aeroso1isable material. In one embodiment, the article for use vvith the non-combustible aerosol provision d evi ce may comp rise a mouthpiece. Th e area for receiving aerosolisable material may be a storage area for storing aerosolisable material. For example, the storage area may be a reservoir. In one embodiment, the area for receiving 25 aerosolisable material may be separate from , or combined vvith, an aerosol generating area. Aerosolisabl e material , which also may be referred to herein as aerosol generating material, is material that is capable of generating aerosol, for example vvhen heated, 30 irradiated or energized in any other way. Aerosolisable material may, for example, be i n the for m of a solid, l iquid or gel which may or may not contain nicotine and / or flavourants. In some embodi ments, the aerosolisable material may comp rise an " amorphous solid", which may alternatively be referred to as a " monolithic solid" (i.e. non-fibrous). In some embodiments, the amorphous solid may be a dried gel. The 35 amorphous solid is a solid material that may retain some fluid, such as liqui d, vdthin it. CA 03198563 2023-5-11 5 WO 2022 / 118005 PCT / GB2021 / 053113 The aerosolisable materiai 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 a n article comprising or consisting of aerosol-generating material, part or all of whi ch 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, a n aerosol-generating material transfer component, an aerosol generation 10 area, a housing, a '\¾Tapper, a mouthpiece, a filter and / o r an aerosol- modifying agent. A consumable may also comprise an aerosol generator, such as a heater, that emits heat 15 to cause the aerosol-generating materi al to generate aerosol in use. The heater may, for example, comprise combustible material, a material heatable by electrical conduction, or a susceptor. FIG. 1 is a b1ock diagram of a system, indicated generally by the reference n umera1 10, in accordance with an example embodiment. The system 10 comprises a power source i n the form of a direct current (DC) voltage supply 11, a sv.itching arrangement 13, a resonant circuit 14, a susceptor arrangemen t 16, and a control circuit 18 . The switching 20 arrangement 13 and the resonant circuit 14 may be coupled together i n an i nductive heating arrangement 12 that can be used to heat the susceptor 16. As d iscussed in detail below, the resonant circuit 14 may comprise a capacitor and one or more i nductive elements for i nductively heating the susceptor arrangement 16 to 25 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 30 current may fl ow through the one or more in ductive elem e nts a n d may cause the heating of the susceptor arrangement 16. The switching arrangement may comprise a plurality of transistors. Example DC-AC converters include I-I -bridge or i nverter circuits, examples of which are discussed below. 35 A susceptor is a material that is heatable by penetrati on with a varying magnetic field, such as an alternating magnetic field. The heating material may be an electrically- CA 03198563 2023-5-11 WO 2022 / 118005 PCT / GB2021 / 053113 - 8 - cond uctive material, so that penetration thereof vvith a varying magnetic field causes induction heating of the heating material. The heating material may be magnetic material, so that p enetration thereof with a varying magnetic field causes magneti c hysteresis heating o f the heating material. The heating material may be both 5 electrically-conductive and magnetic, so that the heating mate rial is heatable by both heating mechan ismso I nduction heating is a process in which an electrica1ly-conductive obj ect i s heated by penetrating the obj ect vvith a varyin g magnetic field. The process is described by 10 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, s uch as an alternating current, through the electromagnet. \Vhen the electromagnet and the obj ect to be heated are suitably relatively positioned so that the resultant varying magnetic field produced by the electromagnet penetrates the obj ect, one or more eddy 15 currents are generated inside the obj ecL The obj ect has a resistance to the flow of e1ectrica1 currents. Therefore, when such eddy currents are generated i n the obj ect, their flow against the electrical resistance of the obj ect causes the obj ect to be heated. This process is called ,Joule, ohmic, or resistive heating. An obj ect that is capable of being i nductively heated is known as a susceptor. 20 25 I n one embod i ment, the susceptor is i n the form of a closed circuit. It has been found i n some embodiments that, when the susceptor is in the form o f a closed circuit, magnetic coupling between the susceptor a n d the electromagnet in use is enhanced, which results in greater or i mproved Joule h eating. Magnelic hysteresi s heating is a process i n which an obj ect m ade of a magnetic material is heated by penetrating the obj ect vvith a varying magnetic field. A magnetic material can be considered to cornpdse many atomic-scale magnets, or magnetic dipoles. VVhen a magnetic field penetrates such material, the magnetic dipoles align vvit h the magnetic 30 fi eld. Therefore, vvhen a varying magnetic field, such as an alternating magnetic field, for example as produ ced by an electromagnet, penetrates the magnetic material, the orientation of the magnetic dipoles changes vd th the varying applied magnetic field. Such magnetic dipole reorientation causes heat to be generated in the magnetic material. 35 CA 03198563 2023-5-11 5 WO 2022 / 118005 PCT / GB2021 / 053113 ·when an object i s both electrically-conductive and magnetic, penetrating the object with a varying magnetic field can cause both ,Joule heating and magnetic hysteresis heating in the obj ect. Moreover, the use of magnetic material can strengthen the magnetic field, which can intensify the ,f oule h eating. 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 obj ect and more uniform heat distribution can be achieved, particul arly through selection of suitable obj ect material and geometry, and suitable varying magnetic field magnitude 10 and orientation relative to the object. Moreover, as induction heating and magnetic hysteresis heating do not require a physical connection to be p rovided betvveen the source of the varying magnetic field and the obj ect, design freedom and control over the heating profile may be greater, and cost may be lower. 15 F IGS. 2 and 3 show a non-combustible aerosol provision device, indicated generally by the reference numeral 20, in accordan ce with an exampl e embodiment. F1G. 2 is a perspective illustration of an aerosol provision device 20A with an outer cover. The aeroso1 provision device 20A may comprise a replaceable article 21 that may be inserted in the aerosol provision d evice 20A to enable heating of a susceptor (which may be 20 comprised vvithin the article 21, as discussed further below) . The aeroso1 provision device 20A may further comprise an activation svvitch 22 that may be used for switching on or S'-'v:itching off the aerosol provision device 20A. FIG. 3 depicts an aerosol provi sion device 20B with the outer cover removed. The 25 aerosol generating device 20B comprises the article 21, the activation sv-ritch 22, a plurality of indu c tiv e elements 23a, 23 b, and 23c, and one or more air lube extenders 24 and 25. The one or more air tube extenders 24 and 25 may be optional. The plurality of inductive elements 23a, 23b, and 23c may each form part of a resonant 30 circuit, such as the resonant circuit 14. 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 vvithin a printed circuit board. The inductive elements 23b and 23c may be similar to the inductive 35 element 23a. The use of three inductive elements 23a , 23b and 23c is not essential to all CA 03198563 2023-5-11 WO 2022 / 118005 PCT / GB2021 / 053113 - 10 - example en1bodiments. Thus, the aerosol generating device 20 may comprise one or more inductive elements. A susceptor may be p rovided as p art of the article 21. In an example embodiment, when 5 the article 21 is inserted in aerosol generating device 20, the aerosol generating device 20 may be turned on due to the insertion of the article 21. This may be due to detecting the presence of the art i cle 21 i n 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 2 1, by detecting the presence of the susceptor u sing the resonant circuit 14, for example. 10 When the aerosol genernting device 20 i s turned on, the inductive elements 23 may cause the article 21 to be inductively heated through the susceptor. In an alternative embodiment, the susceptor may be provided as p art of the aerosol generating device 20 (e.g. as part of a holder fo r receiving the article 21). 15 FIG. 4 is a view of an article, indicated generally by the reference numeral 30, for use 'vvith a non-combustible aerosol provision device in accordance vvith an exampl e embodiment. The article 30 is an example of the replaceable article 21 described above with reference to FIGS. 2 and 3 . 20 The article 30 comprises a mouthpiece 31, a n d a cylindrical rod of aerosol generating material 33, in the present case tobacco material, connected to the mouthpiece 3 1. The aerosol generating material 33 p rovides an aerosol when heated, for instance within a non-combustible aerosol generating device, such as the aerosol generating d evice 20, as described herein. The aerosol generat i ng material 33 is wrapp ed in a wrapper 32. The 25 wrapper 32 can, for instance, be a p aper or paper-backed foil wrapper. The wrapper 3 2 may be substanlial ly impermeable to air. In one embodiment, the wrapper 32 comprises aluminium fo il. Aluminium foil has been found to be particularly effective at enhancing the formation of aerosol ·within the 30 aerosol generating material 33. In one examp le, the alum ini um foil has a metal layer having a thickness of about 6 􀦋tm. The aluminiu m foil may have a pap er backing. However, in alternative arrangements, the alu mini um foi l can have other thicknesses, for instance ben,veen 4 μm and 16 􀦌tm in thickness. The aluminium foil also need not have a paper backing, but could have a backing formed from other materials, for 35 instance to help provide an appropriate tensile strength to the foil, or it could have n o backing material. Th'1etallic layers o r foils other than aluminium can also b e u sed. CA 03198563 2023-5-11 WO 2022 / 118005 PCT / GB2021 / 053113 - l1 - Moreover, it i s not essential that such metallic layers are provided as part of the article 30; for example, s uch a metallic layer could be provided as part of the apparatus 20. The aerosol generating matelial 33, also referred to herein as an aerosol generating 5 :sub:strate 3;3, compri:ses at least o ne aerosol fo rming material. In the p re:sent example, the aerosol forming material is glycerol. In alternative examples, the aerosol forming material can be another materi al 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 10 generating material to the consumer. As shovvn in FIG. 4, the mouthpiece 31 of the article 30 comprises an upstream end 31a adj acent to an aerosol generating substrate 33 and a downstream end 31b distal from the aerosol generating substrate 33. The aerosol generating substrate may comprise 15 tobacco, although alternatives are possible. The mouthpiece 3 1 , in the present example, includes a body of material 36 upstream of a hollow tubular element 34, in this example adj acent to and i n an abutting relationship with the hollow tubular element 34. The body of material 36 and hollow tubular 20 element 34 each defi ne a substantially cylindrical overall o uter shape and share a common longitud inal axis. The body of material 36 is wrapped in a first plug wrap 3 7. T he first plug \-vrap 37 may have a basis weight of less than 50 gsm, such as between about 20 gsm and 40 gsm. 25 In the present example the hollow tubular element 34 is a first hollow tubular element :34 and t he mout hpiece includes a second hollow tubular element 3 8 , also referred to as a cooling element, upstream of the first hollow tubular element 34. In the present example, t he second hollow tubular element 38 is upstream of, adj acent to and in an abutting relationship v.ith the body of material 36. The b o dy of material 36 and second 30 holl ow 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 parall el 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 35 can be used forming 3, 4 or more ply tubes. Other constructions can be used, such as spirally wound layers of paper, cardboard tubes, tu bes formed using a papier-maehe CA 03198563 2023-5-11 5 WO 2022 / 118005 PCT / GB2021 / 053113 - 12 - type process, moul d ed or extruded plastic tubes or similar. The second hollow tubuiar element 38 can also be formed using a stiff p l ug 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 whic h 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 10 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 i n use. The second ho How tubular element 38 proyj des a physical displacement between the aerosol generating material 33 and the body of material 36. The physical displacement provided by the second hollow tubular e1ernent 38 vv'iU provide a thermal 15 gradient across the length of the second hollow tubular element 38. 20 Of course, the article 30 is provided by way of example only. The skilled person will b e aware o f many alternative arrangements o f such an article that could b e used i n the systems 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 may be i mplemented using transistors , as discussed 25 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. Thus the first to fourt h S•\􀝊 tcbes 51 to 54 are a n example i mplementation o f the switching arrangement 1 3 and the resonant circuit 56 is 30 an example of the resonant circuit 14. The first and second switch es 51 and 52 form a first limb of the brid ge circuit and the third and fourth svvitches 53 and 54 form a second limb. More specifically, the first switch 51 can selectively provide a connection between a first power source (labelled 35 V DD i n FIG. 5) and a first connection point, the second switch 52 can selectively proyjde a connection between the first connection point and ground, the third switch 53 can CA 03198563 2023-5-11 5 WO 2022 / 118005 PCT / GB2021 / 053113 selectively provide a connecti on between the first power source and a second connection point and the fourth switch 54 can selectively provide a connectio n between the second connection point and groun d . 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 ,vith an exam ple embodiment . The circuit 60 is an example implementation of the circuit 50 described above. 10 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 sv.ritcbin g arrangement 64 (implementing the switching arrangement 13 described above) , where t he switching arrangement 64 comprises a bridge circuit (e.g. an H-bridge circuit, such as an FET H-bridge circuit). 15 The switching arrangement 64 comprises a first l imb 64a and a second limb 64b, where t h e first 1 i rnb 64a and the second limb 64b are coupled by a resonant circuit 69 (which resonant circuit i mplements the resonant circuits 14 and 56 described above). The first limb 64a comprises s,,,.,itches 65a and 65b (implementing the sv,ritches 51 and 52 described above). and the second limb 64b comprises switches 65c and 65d 20 (implementing the s,,,.,itches 53 and 54 described above). The sv,itches 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 ci rcuit 69 compri ses a capacitor 66 and a n inductive element 63 such t hat 25 the resonant circuit 69 may be a n LC resonant circuit. The circuit 60 further s hows a susceptor equivalent circuit 62 (thereby implementing the susceptor arrangement 16). The susceptor equivalent circuit 62 comprises a resistance and an inductive element that indicate t he electrical effect of an example susceptor arrangement 16. When a susceptor is present, the susceptor arrangement 62 and the inductive element 63 may 30 act as a transformer 6 1. Tran sformer 61 may produce a varying magnetic field such t hat the susceptor is heated when t he circuit 60 receives power . Du ring a heating operation, in which the susceptor arrangernent 16 is heated by the inductive arrangement, the switching arrangement 64 is driven (e.g., by control circuit 18) such t hat each of the first and second branches are coupled in turn such that an alternating current is passed 35 through the resonant circuit 69. The resonant circuit 69 wiU have a resonant frequency, which is based i n p art on the susceptor arrangement 16, and the control circuit 18 may CA 03198563 2023-5-11 WO 2022 / 118005 PCT / GB2021 / 053113 be configured to control the S'-'Vitching arrangement 64 to switch at the resonance frequency or a frequency close to the resonant frequency. D riving the switching circuit at or close to resonance helps i mprove efficiency and reduces the energy being lost to the s,v:itching elements (which causes unnecessary heating of the s,v:itching elements). 5 In an example in which the article 21 comprising an al uminium foil is to be heated, the switching arrangement 64 may be driven at a frequency of around 205 MHz. H owever, in other i mplementations, the frequency may, for example, be anywhere between 500 kHz to 4 MHz. 10 FIG. 7 is a bl ock diagram of a system, i ndicated generally by the reference numeral 70, i n accordance with an example embodiment. The system 70 comprises a p u lse generation circuit 72, a resonant circuit 74 (such as the resonant circuits 56 and 69), a susceptor 76 (such as the susceptor 16) an d a pulse 15 response processor 78. The p ulse generation circuit 72 and the pulse response processor 74 may be i mplemented as part of the control circuit 18 of the system 10 . The pulse generation cir cuit 72 may be i mplemented using the switching affangements of the circuits 50 and 60 described above in order to generate a pulse (e.g. p ulse edges) 20 by svvitch ing between positive and n egative voltage sources. This is n ot essential to all example embodiments; for example, the pulse generation circuit 72 may be i mplemented using a half-bridge circuit, as discussed further below. The pulse response processor 78 may determine one or more performance metrics (or 25 characteristics) of the resonant circuit 74 and the susceptor 76 based on the p ulse response. For example the p ulse response p rocessor 78 may generate an estimate of the temperature of the susceptor 76. F IG. 8 i s a flow chart shmving an algorithm, indicated generally by the reference 30 numeral 80, in accordance \,\rith an example embodiment. The algorithm 80 shows an example use of the system 70. The algorithm 80 starts at operation 82 where a pulse edge is applied to the resonant circuit 74. The pulse edge is a rising or falling edge generated by the pulse generation 35 circuit 72. CA 03198563 2023-5-11 5 WO 2022 / 118005 PCT / GB2021 / 053113 FIG. 9 is a plot showing a puise 90 in accordance with an example embodiment. The pulse 90 is includes a rising p ulse edge 92 that is an example of a pulse edge that may be applied in the operation 82. The pulse 90 may be generated by the p ulse generation circuit 72 (e.g. by an H -bridge or half-bridge circuit) . The pulse 90 may be applied to the resonant circuit 74. Alternatively, in systems having multiple inductive elements (such as non-combustjble aerosol arrangement 20 described above vvith reference to FIGS. 2 and 3), the pulse generation circuit 72 may select one of a plurality of resonant circuits, each resonant circuit comprising an 10 jnductive element for inductively hec1ting a susceptor and a cc1pacitor, wherein the applied pulse induces an pulse response between the capacitor and the inductive element of the selected resonant drcujt. 15 The application of the pulse edge 92 to the resonant circuit generates a pulse response. FIG. 10 is a plot, indicated genera11 y by the reference n umeral 100, shovving 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 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 20 pulse response is a result of charge bouncing between the inductor(s) and capacitor 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 substantial1y constant (e.g .. , within ± 1°C or ±o.1° C of the temperature prior to applying the pulse). As shown in FIG. 10, the pulse response 100 has a resonant frequency having a period 102 (that period 25 being the time between successive peaks of the ringing response) . 30 FIG. 11 is a plot, indicated generally by the reference numeral 110, showing another example p ulse response that might be generated in response to the pulse edge 92. The p ulse response 110 has a resonant frequency having a period 112. At operation 84 of the algorithm 80, a period or frequency of the resonant frequ ency of the pulse response generated in response to the applied pulse edge is determined (e.g. by the pulse response processor 78). For the example pulse response 100, the period or frequency determined in the operation 84 is the period 102. Similarly, for the example 35 pulse response 110, the period or frequency determined in the operation 84 is the period 112. CA 03198563 2023-5-11 WO 2022 / 118005 PCT / GB2021 / 053113 - 16 - At operation 86 of the algorithm 80, the period or frequency determined in the operati on 84 is converted into a temperature estimate, as d iscussed in detail below. 5 The voltage (V0 ) of the pulse responses 100 and no may be exp ressed mathematically as : Where : 10 cad is the damped resonant frequency of the system (including a s usceptor). 15 The relationship betvveen alph a d ecay and d amped frequency oscill ation may be given by: 2 L vVhere: :20 oJn is the natural resonant frequency of the system (vvithout the susceptor). rcoil is the coil resistance; a nd 30 CA 03198563 2023-5-11 rsus is the reflective snsceptor resistance. The period that is measured in the operation 84 described above is based on the damped frequency (cod ) . FIG. 12 i s a plot, indicated generally by t h e reference numeral 120, showing a relationship between pulse response period and temperature in accordance \'\iith an example embodiment. As an inductive heating system, such as the circuits 50 or 60 or the system 70, warms, the res istances in the system change. This res ults in a change in the resonant frequency (and hence the period of the pulse response determined in the operation 84 described above) . As show in the example plot 120, the pul se response period may increase as the WO 2022 / 118005 PCT / GB2021 / 053113 temperature i ncreases. In some example embodiments this change i n linear (or almost linear) and so can be used for temperature measurement estimations. If the characteristics of the plot 120 are known, then the period or frequency (e.g. the 5 damped frequern:y of the system) determined in the operation 84 can be converted i nto a temperature estimate in the operation 86. In the operation 86, the tempe rature (x) may be given by the formula: y - c x =-· -- rn 10 where: y is the period d etermined in the operation 84; c is a calibration value; and m. is the gradient of the plot 120. 15 The gradient m can be determined from two data points (x1, y1) and (x2, y2) as follows: 20 25 30 CA 03198563 2023-5-11 y2 - y1 ni = ---xZ - x1 The calibration value c may be given by: c = -ma + b where: m is the gradient discussed above; a is a calibration temperature (e.g. room temperature); b i s the pul se response period at the calibration temperature. For example, ass u me that a pulse response period of 4oons was measured at a calibration temperature of 20 degrees centigrade. if the gradient of the plot 120 has been d etermined to be 250 picoseconds per degree centigrade, then the values above are given by: m = 2 50ps / ° C = 0. 2 5ns;0 c C = - 0, 2 5 0 "' 2 0 + 400 = 3 9 5 Thus, i f a period of 42ons is determined in the operation 84, this can be converted i n the operation 8 6 into a temperature estimate using the formula: 5 WO 2022 / 118005 - 18 - y - c X=-- 111, 420 - 3 9 5 X = ---- = 1 0 0 0. 2 50 Thus, the temperature estimate x is 1000c. PCT / GB2021 / 053113 F IG . 13 is a flow chart s how-ing an algorithm, i ndicated generally by the reference numeral 130, i n accordance with an example embod iment. At operation 132, the gradient of the system in determi ned. The gradient is the rate of 10 change of the resonant frequency of said pulse resp onse vvith respect to temperature. The gradient may be generated once (as part of an initialisation process) and may t hen be stored and not changed (or only rarely changed). Alternatively, the gradient measurement m a y be u pd ated from time-to-ti me (e.g. peri o d i call y or 1n response to a determination that the gradient measurement may be unreliable). At operation 134, a calibration measurement is determined. The calibration measurement may be d etermined by determining a period or frequency of a resonant frequency at a known temp erature (e.g. a measured temperature). For example, the system may be calibrated based on a known room temperature (e.g. during a 20 calibration process). Thus room temperature may be measured (e.g. using a thermocouple) and a pulse duration measured at this known room temperature. The calibration measurement may be a one-time measurement that is stored. A1ternative1y, the calibration measurement may be taken repeatedly, such as whenever 25 the configuration of the system may have changed. There are many possible calibration a rrangements. For example, for systems having removable articl e i ncludi ng a susceptor arrangement for heating, the system may be recalibrated each time the removable article is changed. 30 At operation 1;36, a temperature estimate is generated. The operation 136 may be impl emented using the algorithm 100 described above . CA 03198563 2023· 5· 11 As described above, the p ulse edge may be generated in the operation 82 using a fullbridge circuit. This is not essential; for example, a half-bridge circuit may be used. WO 2022 / 118005 PCT / GB2021 / 053113 FIG. 14 is a block diagram of a circuit, indicated generally by the reference n umeral 140, i n accordance ,vi.th an example embodiment. The circuit 140 comprises the third switch 53, the fourth svvitch 54 and the resonant circuit 56 of the circuit 50 described 5 above. In addition, the first connect i o n point (between the first switch 5 1 and the resonant circuit 56) is connected to ground. Thus, the second switch 52 of the circuit 50 is replaced with a permanent connection to ground and the fi rst switch 51 may be omitted. 10 The circuit 50 described above provides a full-bridge circuit for dri ving the resonant circuit 56. The c ircuit 140 provides a half-bridge c ircuit for driving the resonant c ircuit 56. For example, the circuit 50 may be p articu larly suitable for provi ding pulses for driving the resonant circuit for inductively heating a susceptor and the circuit 140 may be particularly suitable for providing pulse edges for generating p ulse responses from 15 the resonant circuit for analysis (e.g. measurement). 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 20 i s to be understood that advantages, embodiments, examples, functions, features, structures, and / or other aspects described herein are not to be considered lim itations o n the scope of the invention a s defined by the claims or li mitations on equivalents t o the claims, and that other embodiments may be utilised and modifications may be made without d eparting f rom the scope of the daimed invention. Various embodiments of the 25 invention may suitably comprise, consist of, or consist essentially of, appropriate combinati ons of the disclosed elemenls, 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 clai med in future. 30 CA 03198563 2023-5-11

Claims

- 20 - CLAIMS:

1. A method comprising: applying a pulse edge to a resonant circuit comprising an inductive element, for inductively heating a susceptor, and a capacitor, wherein the applied pulse edge 5 induces a pulse response between the capacitor and the inductive element of the resonant circuit, wherein the pulse response has a resonant frequency; determining a period or frequency of the resonant frequency of said pulse response; and converting the determined period or frequency into a temperature of the 10 susceptor estimate based on a temperature gradient and a calibration measurement.

2. A method as claimed in claim 1, wherein converting the determined period or frequency into said temperature estimate comprises: subtracting the calibration measurement from the determined period or 15 frequency of the resonant frequency of said pulse response; and dividing the result of the subtraction by said temperature gradient.

3. A method as claimed in claim 1 or claim 2, wherein said calibration measurement defines a first period or frequency of the resonant frequency of said pulse 20 response at a first temperature.

4. A method as claimed in claim 3, wherein the first temperature is room temperature. 25 5. A method as claimed in any one of claims 1 to 4, wherein said calibration measurement is obtained by subtracting the product of said temperature gradient and a calibration temperature from a period of said pulse response at said calibration temperature. 30 6. A method as claimed in any one of claims 1 to 5, wherein said temperature gradient comprises a rate of change of the resonant frequency of said pulse response with respect to temperature.

7. A method as claimed in any one of claims 1 to 6, further comprising determining 35 said calibration measurement. CA 3198563 Date reçue / Received date 2025-09-02 - 21 - 8. A method as claimed in any one of claims 1 to 7, further comprising determining said temperature gradient.

9. A method as claimed in any one of claims 1 to 8, wherein the pulse edge forms 5 part of an off-resonance pulse.

10. An apparatus comprising: a resonant circuit comprising an inductive element and a capacitor, wherein the inductive element is for inductively heating a susceptor; 10 a driving circuit for applying a pulse edge to said resonant circuit, wherein the applied pulse edge 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: determining a period or frequency of the resonant frequency of 15 said pulse response and converting the determined period or frequency into a temperature of the susceptor estimate based on a temperature gradient and a calibration measurement.

11. An apparatus as claimed in claim 10, wherein said processor converts the 20 determined period or frequency into said temperature estimate by: subtracting the calibration measurement from the determined period or frequency of the resonant frequency of said pulse response; and dividing the result of the subtraction by said temperature gradient. 25 12. An apparatus as claimed in claim 10 or claim 11, wherein said processor is for determining said calibration measurement.

13. An apparatus as claimed in any one of claims 10 to 12, wherein said processor is for determining said temperature gradient. 30 14. An apparatus as claimed in any one of claims 10 to 13, wherein said inductive element and said capacitor are connected in series.

15. An apparatus as claimed in any one of claims 10 to 14, wherein said driving 35 circuit is an H-bridge circuit. CA 3198563 Date reçue / Received date 2025-09-02 - 22 - 16. An apparatus as claimed in any one of claims 10 to 14, wherein said driving circuit is a half-bridge circuit.

17. A non-combustible aerosol generating device comprising an apparatus as 5 claimed in any one of claims 10 to 16.

18. A non-combustible aerosol generating device as claimed in claim 17, wherein the aerosol generating device is configured to receive a removable article comprising an aerosol generating material. 10 19. A non-combustible aerosol generating device as claimed in claim 18, wherein said aerosol generating material comprises an aerosol generating substrate and an aerosol forming material. 15 20. A non-combustible aerosol generating device as claimed in claim 18 or claim 19, wherein said removable article includes a susceptor arrangement.

21. A kit of parts comprising an article for use in a non-combustible aerosol generating system, wherein the non-combustible aerosol generating system comprises 20 the apparatus as claimed in any one of claims 10 to 16 or the aerosol generating device as claimed in any one of claims 17 to 20.

22. A kit of parts as claimed in claim 21, wherein the article is a removable article comprising an aerosol generating material. 25 23. A computer readable storage medium having stored thereon a computer program comprising instructions for causing an apparatus to perform at least the following: apply a pulse edge to a resonant circuit comprising an inductive element, for 30 inductively heating a susceptor, and a capacitor, wherein the applied pulse edge induces a pulse response between the capacitor and the inductive element of the resonant circuit, wherein the pulse response has a resonant frequency; determine a period or frequency of the resonant frequency of said pulse response; and 35 CA 3198563 Date reçue / Received date 2025-09-02 - 23 - convert the determined period or frequency into a temperature of the susceptor estimate based on a temperature gradient and a calibration measurement. CA 3198563 Date reçue / Received date 2025-09-02