Apparatus for an aerosol generating device

A method, apparatus and computer program is described including: applying an impulse to a resonant circuit including an inductive element, for inductively heating a susceptor, and a capacitor, wherein the applied impulse induces an impulse response between the capacitor and the inductive element of the resonant circuit, wherein each impulse response has a resonant frequency; and generating an output signal dependent on one or more properties of the impulse response.

PRIORITY CLAIM

The present application is a National Phase entry of PCT Application No. PCT/GB2020/051543, filed Jun. 23, 2020, which claims priority from Great Britain Application No. 1909384.8, filed Jun. 28, 2019, each of which is hereby fully incorporated herein by reference.

TECHNICAL FIELD

The present specification relates to an apparatus 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 by creating 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

In a first aspect, this specification describes an apparatus comprising: an impulse generation circuit for applying an impulse to a resonant circuit comprising an inductive element (for inductively heating a susceptor) and a capacitor, wherein the applied impulse induces an impulse response between the capacitor and the inductive element of the resonant circuit, wherein the impulse response has a resonant frequency; and an output circuit for providing an output signal dependent (at least in part) on one or more properties of the impulse response. The susceptor may be included as part of a removable consumable.

The output signal may be dependent on a time period of oscillations of the impulse response, such that the output signal is indicative of the resonant frequency of the impulse response.

The output circuit may comprise an edge detection circuit for identifying edges of said impulse response. The edge detection circuit may, for example, be provided as part of a charge time measurement unit (CTMU). The output signal may be based on a time period from a first edge of the impulse response and a second edge that is at least one complete cycle of said impulse response later. Furthermore, the output circuit may comprise a voltage ramp that is initiated when the first edge is identified and ends when the second edge is identified, wherein the output signal is based on an output of said voltage ramp.

In the event that an edge detection circuit is provided, the edge detection circuit may be configured to determine a propagation delay between an application of the impulse to the resonant circuit and a detection of the impulse response in response to the applied impulse, wherein the output signal is dependent on said propagation delay.

In some embodiments, an impulse detection circuit may be provided, wherein: the impulse generation circuit is configured to apply a first impulse and a second impulse to the resonant circuit, wherein the first impulse induces a first impulse response and the second impulse induces a second impulse response, wherein each impulse response has a resonant frequency; the impulse detection circuit is configured to determine a first time period from the end of a first wait period following the application of the first impulse to the end of a respective impulse response period of the impulse response and a second time period from the end of a second wait period following the application of the second impulse to the end of a respective impulse period of the impulse response; and the output circuit is configured to determine an impulse response period dependent (at least in part) on a sum of the difference between the first and second wait periods and the difference between the first and second time periods.

In embodiments including an impulse detection circuit, the impulse detection circuit may comprise a current source control circuit for initiating a current source at the end of the wait period following the application of a respective impulse and terminating the current source at the end of the impulse response period of the said impulse response. An analog-to-digital converter may be provided and coupled to the current source, wherein the analog-to-digital converter provides an output for use in determining the first and/or second time periods. The said impulse response period may be used to provide a temperature measurement of said susceptor.

The output signal may be dependent on a decay rate of voltage oscillations of the impulse response.

Some embodiments further comprise a processor for determining a Q-factor measurement of the impulse response, wherein the output signal is based on said Q-factor measurement. The processor for determining the Q-factor measurement of the impulse response may determine said Q-factor measurement by determining a number of oscillation cycles for the impulse response to halve (or approximately halve) in amplitude (or meet some other predefined relative value) and multiplying the determined number of cycles by a predetermined value. The said Q-factor may be used for determining one or more performance properties (based on the determined Q-factor).

Some embodiments further comprise a counter for determining a number of oscillations in a defined time period. The output circuit may be configured to provide the output signal to indicate whether or not a removable article is fitted within the apparatus on the basis of said determined number of oscillations.

The output signal may be used to provide a temperature measurement of said susceptor. The output signal may be scaled to provide said temperature measurement.

The impulse generation circuit may comprise a first switching arrangement used to generate the impulse by switching between positive and negative voltage sources.

The susceptor may be configured to aerosolize a substance in a heating mode of operation.

Some embodiments include a signal conditioning circuit to provide an offset to the impulse response.

A current sensor may be provided for measuring a current flowing in the inductive element.

A control module may be provided for determining a performance of said apparatus based on said output signal.

In a second aspect, this specification describes a system comprising: a plurality of resonant circuits, each resonant circuit comprising an inductive element (for inductively heating a susceptor) and a capacitor; an impulse generation circuit for applying an impulse to at least one of the plurality of resonant circuits, wherein the applied impulse induces an impulse response between the capacitor and the inductive element of the selected resonant circuit, wherein the impulse response has a resonant frequency; and an output circuit for providing an output signal dependent (at least in part) on one or more properties of the impulse response. The one or more properties of the impulse response may comprise a time period of voltage oscillations of the impulse response, such that the output signal is indicative of the resonant frequency of the impulse response.

In a third aspect, this specification describes an aerosol provision system for generating aerosol from an aerosolizable material, the aerosol provision system comprising an apparatus including of any of the features of the first aspect described above or a system including any of the features of the second aspect described above, wherein the aerosol provision system is configured to perform an action in response to receiving the output signal from the output circuit.

In a fourth aspect, this specification describes a method comprising: applying an impulse to a resonant circuit comprising an inductive element (for inductively heating a susceptor) and a capacitor, wherein the applied impulse induces an impulse response between the capacitor and the inductive element of the resonant circuit, wherein each impulse response has a resonant frequency; and generating an output signal dependent (at least in part) on one or more properties of the impulse response. The method may further comprise inductively heating a susceptor using said inductive element in order to aerosolize a substance in a heating mode of operation.

The output signal may be dependent on a time period of oscillations of the impulse response, wherein the output signal is indicative of the resonant frequency of the impulse response.

The impulse may be applied to the resonant circuit in a temperature measurement mode of operation.

Some embodiments further comprise determining a Q-factor measurement of the impulse response. Determining the Q-factor measurement of the impulse response may comprise determining a number of oscillation cycles for the impulse response to halve (or approximately halve) in amplitude (or meet some other predefined relative value) and multiplying the determined number of cycles by a predetermined value. Further, one or more performance properties may be determined based on the determined Q-factor.

The method may comprise: applying a first impulse to the resonant circuit to induce a first impulse response, wherein the first impulse occurs on a rising edge of a control signal; and applying a second impulse to the resonant circuit to induce a second impulse response, wherein the second impulse occurs on a falling edge of a control signal. Further, the method may comprise: generating a first output signal dependent on one or more properties of the first impulse response; and generating a second output signal dependent on one or more properties of the second impulse response.

In a fifth aspect, this specification describes computer-readable instructions which, when executed by computing apparatus, cause the computing apparatus to perform any method as described with reference to the fourth aspect.

In a sixth aspect, this specification describes a kit of parts comprising an article for use in a non-combustible aerosol generating system, wherein the non-combustible aerosol generating system comprises an apparatus including any of the features of the first aspect described above or a system including any of the features of the second aspect described above. The article may, for example, be a removable article comprising an aerosol generating material.

In a seventh aspect, this specification describes a computer program comprising instructions for causing an apparatus to perform at least the following: apply an impulse to a resonant circuit comprising an inductive element (for inductively heating a susceptor) and a capacitor, wherein the applied impulse induces an impulse response between the capacitor and the inductive element of the resonant circuit, wherein each impulse response has a resonant frequency; and generate an output signal dependent on one or more properties of the impulse response.

DETAILED DESCRIPTION OF THE DRAWINGS

As used herein, the term “delivery system” is intended to encompass systems that deliver a substance to a user, and includes:combustible aerosol provision systems, such as cigarettes, cigarillos, cigars, and tobacco for pipes or for roll-your-own or for make-your-own cigarettes (whether based on tobacco, tobacco derivatives, expanded tobacco, reconstituted tobacco, tobacco substitutes or other smokable material);non-combustible aerosol provision systems that release compounds from an aerosolizable material without combusting the aerosolizable material, such as electronic cigarettes, tobacco heating products, and hybrid systems to generate aerosol using a combination of aerosolizable materials;articles comprising aerosolizable material and configured to be used in one of these non-combustible aerosol provision systems; andaerosol-free delivery systems, such as lozenges, gums, patches, articles comprising inhalable powders, and smokeless tobacco products such as snus and snuff, which deliver a material to a user without forming an aerosol, wherein the material may or may not comprise nicotine.

According to the present disclosure, a “combustible” aerosol provision system is one where a constituent aerosolizable 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 aerosolizable 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 aerosolizable 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 aerosolizable materials, one or a plurality of which may be heated. Each of the aerosolizable 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 aerosolizable material and a solid aerosolizable material. The solid aerosolizable material may comprise, for example, tobacco or a non-tobacco product.

Typically, the non-combustible aerosol provision system may comprise a non-combustible 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 energized so as to distribute power in the form of heat to an aerosolizable 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 aerosolizable material, an aerosol generating component, an aerosol generating area, a mouthpiece, and/or an area for receiving aerosolizable material.

In one embodiment, the aerosol generating component is a heater capable of interacting with the aerosolizable material so as to release one or more volatiles from the aerosolizable material to form an aerosol. In one embodiment, the aerosol generating component is capable of generating an aerosol from the aerosolizable material without heating. For example, the aerosol generating component may be capable of generating an aerosol from the aerosolizable material without applying heat thereto, for example via one or more of vibrational, mechanical, pressurization or electrostatic means.

In one embodiment, the aerosolizable 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 non-olfactory physiologically active material is a material which is included in the aerosolizable material in order to achieve a physiological response other than olfactory perception.

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

In one embodiment, the article for use with the non-combustible aerosol provision device may comprise aerosolizable material or an area for receiving aerosolizable material. In one embodiment, the article for use with the non-combustible aerosol provision device may comprise a mouthpiece. The area for receiving aerosolizable material may be a storage area for storing aerosolizable material. For example, the storage area may be a reservoir. In one embodiment, the area for receiving aerosolizable material may be separate from, or combined with, an aerosol generating area.

Aerosolizable 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. Aerosolizable material may, for example, be in the form of a solid, liquid or gel which may or may not contain nicotine and/or flavorants. In some embodiments, the aerosolizable material may comprise 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 amorphous solid is a solid material that may retain some fluid, such as liquid, within it.

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

FIG.1is a block diagram of a system, indicated generally by the reference numeral10, in accordance with an example embodiment. System10comprises a power source in the form of a direct current (DC) voltage supply11, a switching arrangement13, a resonant circuit14, a susceptor arrangement16, and a control circuit18. The switching arrangement13and the resonant circuit14may be coupled together in an inductive heating arrangement12.

The resonant circuit14may comprise a capacitor and one or more inductive elements for inductively heating the susceptor arrangement16to heat an aerosol generating material. Heating the aerosol generating material may thereby generate an aerosol.

The switching arrangement13may enable an alternating current to be generated from the DC voltage supply11. The alternating current may flow through the one or more inductive elements and may cause the heating of the susceptor arrangement16. 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. It should be noted that the provision of a DC voltage supply11from which a pseudo AC signal is generated is not an essential feature; for example, a controllable AC supply or an AC-AC converter may be provided. Thus, an AC input could be provided (such as from a mains supply or an inverter).

Example arrangements of the switching arrangement13and the resonant circuit14are discussed in greater detail below.

It should be noted that the DC voltage supply11of the system10is not essential to all example embodiments. For example, an AC input could be provided (such as from a mains supply or from an inverter).

FIGS.2and3show a non-combustible aerosol provision device, indicated generally by the reference numeral20, in accordance with an example embodiment.FIG.2is a perspective illustration of an aerosol provision device20A with an outer cover. The aerosol provision device20A may comprise a replaceable article21that may be inserted in the aerosol provision device20A to enable heating of a susceptor (which may be comprised within the article21, as discussed further below). The aerosol provision device20A may further comprise an activation switch22that may be used for switching on or switching off the aerosol provision device20A.

FIG.3depicts an aerosol provision device20B with the outer cover removed. The aerosol generating device20B comprises the article21, the activation switch22, a plurality of inductive elements23a,23b, and23c, and one or more air tube extenders24and25. The one or more air tube extenders24and25may be optional.

The plurality of inductive elements23a,23b, and23cmay each form part of a resonant circuit, such as the resonant circuit14. The inductive element23amay 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 elements23band23cmay be similar to the inductive element23a. The use of three inductive elements23a,23band23cis not essential to all example embodiments. Thus, the aerosol generating device20may comprise one or more inductive elements.

A susceptor may be provided as part of the article21. In an example embodiment, when the article21is inserted in aerosol generating device20, the aerosol generating device20may be turned on due to the insertion of the article21. This may be due to detecting the presence of the article21in the aerosol generating device using an appropriate sensor (e.g., a light sensor) or, in cases where the susceptor forms a part of the article21, by detecting the presence of the susceptor using the resonant circuit14, for example. When the aerosol generating device20is turned on, the inductive elements23may cause the article21to be inductively heated through the susceptor. In an alternative embodiment, the susceptor may be provided as part of the aerosol generating device20(e.g. as part of a holder for receiving the article21).

FIG.4is a view of an article, indicated generally by the reference numeral30, for use with a non-combustible aerosol provision device in accordance with an example embodiment. The article30is an example of the replaceable article21described above with reference toFIGS.2and3.

The article30comprises a mouthpiece31, and a cylindrical rod of aerosol generating material33, in the present case tobacco material, connected to the mouthpiece31. The aerosol generating material33provides an aerosol when heated, for instance within a non-combustible aerosol generating device, such as the aerosol generating device20, as described herein. The aerosol generating material33is wrapped in a wrapper32. The wrapper32can, for instance, be a paper or paper-backed foil wrapper. The wrapper32may be substantially impermeable to air.

In one embodiment, the wrapper32comprises aluminum foil. Aluminum foil has been found to be particularly effective at enhancing the formation of aerosol within the aerosol generating material33. In one example, the aluminum foil has a metal layer having a thickness of about 6 μm. The aluminum foil may have a paper backing. However, in alternative arrangements, the aluminum foil can have other thicknesses, for instance between 4 μm and 16 μm in thickness. The aluminum 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 aluminum can also be used. Moreover, it is not essential that such metallic layers are provided as part of the article30; for example, such a metallic layer could be provided as part of the apparatus20.

The aerosol generating material33, also referred to herein as an aerosol generating substrate33, 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 flavor compounds from the aerosol generating material to the consumer.

As shown inFIG.4, the mouthpiece31of the article30comprises an upstream end31aadjacent to an aerosol generating substrate33and a downstream end31bdistal from the aerosol generating substrate33. The aerosol generating substrate may comprise tobacco, although alternatives are possible.

The mouthpiece31, in the present example, includes a body of material36upstream of a hollow tubular element34, in this example adjacent to and in an abutting relationship with the hollow tubular element34. The body of material36and hollow tubular element34each define a substantially cylindrical overall outer shape and share a common longitudinal axis. The body of material36is wrapped in a first plug wrap37. The first plug wrap37may 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 element34is a first hollow tubular element34and the mouthpiece includes a second hollow tubular element38, also referred to as a cooling element, upstream of the first hollow tubular element34. In the present example, the second hollow tubular element38is upstream of, adjacent to and in an abutting relationship with the body of material36. The body of material36and second hollow tubular element38each define a substantially cylindrical overall outer shape and share a common longitudinal axis. The second hollow tubular element38is formed from a plurality of layers of paper which are parallel wound, with butted seams, to form the tubular element38. 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-mâché type process, molded or extruded plastic tubes or similar. The second hollow tubular element38can also be formed using a stiff plug wrap and/or tipping paper as the second plug wrap39and/or tipping paper35described herein, meaning that a separate tubular element is not required.

The second hollow tubular element38is located around and defines an air gap within the mouthpiece31which acts as a cooling segment. The air gap provides a chamber through which heated volatilized components generated by the aerosol generating material33may flow. The second hollow tubular element38is 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 article21is in use. The second hollow tubular element38provides a physical displacement between the aerosol generating material33and the body of material36. The physical displacement provided by the second hollow tubular element38will provide a thermal gradient across the length of the second hollow tubular element38.

Of course, the article30is provided by way 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.

FIG.5is a block diagram of a circuit, indicated generally by the reference numeral40, in accordance with an example embodiment. The circuit40comprises a positive terminal47and a negative (ground) terminal48(that are an example implementation of the DC voltage supply11of the system10described above). The circuit40comprises a switching arrangement44(implementing the switching arrangement13described above), where the switching arrangement44comprises a bridge circuit (e.g. an H-bridge circuit, such as an FET H-bridge circuit). The switching arrangement44comprises a first circuit branch44aand a second circuit branch44b, where the first circuit branch44aand the second circuit branch44bmay be coupled by a resonant circuit49(implementing the resonant circuit14described above). The first circuit branch44acomprises switches45aand45b, and the second circuit branch44bcomprises switches45cand45d. The switches45a,45b,45c, and45dmay be transistors, such as field-effect transistors (FETs), and may receive inputs from a controller, such as the control circuit18of the system10. The resonant circuit49comprises a capacitor46and an inductive element43such that the resonant circuit49may be an LC resonant circuit. The circuit40further shows a susceptor equivalent circuit42(thereby implementing the susceptor arrangement16). The susceptor equivalent circuit42comprises a resistance and an inductive element that indicate the electrical effect of an example susceptor arrangement16. When a susceptor is present, the susceptor arrangement42and the inductive element43may act as a transformer41. Transformer41may produce a varying magnetic field such that the susceptor is heated when the circuit40receives power. During a heating operation, in which the susceptor arrangement16is heated by the inductive arrangement, the switching arrangement44is driven (e.g., by control circuit18) such that each of the first and second branches are coupled in turn such that an alternating current is passed through the resonant circuit14. The resonant circuit14will have a resonant frequency, which is based in part on the susceptor arrangement16, and the control circuit18may be configured to control the switching arrangement44to switch at the resonance 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 the article21comprising an aluminum foil is to be heated, the switching arrangement44may 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.

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. 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.

In one embodiment, the susceptor is in the form of a closed circuit. It has been found in some embodiments that, when the susceptor is in the form of a closed circuit, magnetic coupling between the susceptor and the electromagnet in use is enhanced, which results in greater or improved Joule heating.

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.6is a block diagram of a system, indicated generally by the reference numeral60, in accordance with an example embodiment. The system60comprises the resonant circuit14and the susceptor16of the system10described above. The system further comprises an impulse generation circuit62and an impulse response processor64. The impulse generation circuit62and the impulse response processor64may be implemented as part of the control circuit18of the system10.

The impulse generation circuit62may be implemented using a first switching arrangement (such as an H-bridge circuit) to generate the impulse by switching between positive and negative voltage sources. For example, the switching arrangement44described above with reference toFIG.5may be used. As described further below, the impulse generation circuit62may generate an impulse by changing the switching states of the FETs of the switching arrangement44from a condition where the switches45band45dare both on (such that the switching arrangement is grounded) and the switches45aand45bare off, to a state where the switch states of one of the first and second circuit branches44aand44bare reversed. The impulse generation circuit62may alternatively be provided using a pulse width modulation (PWM) circuit. Other impulse generation arrangements are also possible.

The impulse response processor64may determine one or more performance metrics (or characteristics) of the resonant circuit14and the susceptor16based on the impulse response. Such performance metrics include properties of an article (such as the removable article21), presence or absence of such an article, type of article, temperature of operation etc.

FIG.7is a flow chart showing an algorithm, indicated generally by the reference numeral70, in accordance with an example embodiment. The algorithm70shows an example use of the system60.

The algorithm70starts at operation72where an impulse (generated by the impulse generation circuit62) is applied to the resonant circuit14.FIG.8is a plot, indicated generally by the reference numeral80, showing an example impulse that might be applied in the operation72.

The impulse may be applied to the resonant circuit14. Alternatively, in systems having multiple inductive elements (such as non-combustible aerosol arrangement20described above with reference toFIGS.2and3), the impulse generation circuit62may 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 impulse induces an impulse response between the capacitor and the inductive element of the selected resonant circuit.

At operation74, an output is generated (by the impulse response processor64) based on an impulse response that is generated in response to the impulse applied in operation72.FIG.9is a plot, indicated generally by the reference numeral90, showing an example impulse response that might be received at the impulse response processor64in response to the impulse80. As shown inFIG.9, the impulse response may take the form of a ringing resonance. The impulse response is a result of charge bouncing between the inductor(s) and capacitor of the resonant circuit14. 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 ±0.1° C. of the temperature prior to applying the impulse).

At least some of the properties of the impulse response (such as frequency and/or decay rate of the impulse response) provide information regarding the system to which the impulse is applied. Thus, as discussed further below, the system60can be used to determine one or more properties of the system to which the impulse is applied. For example one or more performance properties, such as fault conditions, properties of an inserted article21, presence or absence of such an article, whether the article21is genuine, temperature of operation etc., can be determined based on output signal derived from an impulse response. The system60may use the determined one or more properties of the system to perform further actions (or prevent further actions if so desired) using the system10, for example, to perform heating of the susceptor arrangement16. For instance, based on the determined temperature of operation, the system60can choose what level of power is to be supplied to the induction arrangement to cause further heating of the susceptor arrangement, or whether power should be supplied at all. For some performance properties, such as fault conditions or determining whether the article21is genuine, a measured property of the system (as measured using the impulse response) can be compared to an expected value or range of values for the property, and actions taken by the system60are performed on the basis of the comparison.

FIG.10is a flow chart showing an algorithm, indicated generally by the reference numeral100, in accordance with an example embodiment. At operation102of the algorithm100, an impulse is applied to the resonant circuit14by the impulse generation circuit62. At operation104, a time to a first impulse response induced in response to the applied impulse is determined by the impulse response processor64. Finally, at operation106, an output is generated (based on the time to the first impulse response).

FIG.11is a plot, indicated generally by the reference numeral110, showing an example use of the algorithm100. The plot110shows an impulse112applied to the resonant circuit14by the impulse generation circuit62. The application of the impulse112implements the operation102of the algorithm100. An impulse response114is induced in response to the applied impulse. The impulse112may be held in its final state (high in the plot110) for the duration of the measurement, but this is not essential. For example, a high-low impulse could be applied (and then held low).

The impulse response processor64generates a signal116indicating edges of the impulse response114. As discussed further below, the signal116may be generated by a comparator and there may be a delay between the occurrence of the edge and the generation of the signal. If consistent, that delay may not be significant to the processing.

At operation104of the algorithm100, a time to the first impulse response is determined. That time is the time between the impulse112and the first rise of the signal116. An example time is indicated by the arrow118inFIG.11.

At operation106of the algorithm100, an output is generated based on the determined time period118. In some embodiments, the time period118is temperature dependent. Accordingly, the output generated in operation106may be used to provide a temperature estimate.

FIG.12is a flow chart showing an algorithm, indicated generally by the reference numeral120, in accordance with an example embodiment. At operation122of the algorithm120, an impulse is applied to the resonant circuit14by the impulse generation circuit62. Thus, the operation122is the same as the operation102described above.

At operation124of the algorithm120, a period of an impulse response induced in response to the applied impulse is determined by the impulse response processor64. Finally, at operation126, an output is generated (based on the determined period of the impulse response).

FIG.13is a plot, indicated generally by the reference numeral130, showing an example use of the algorithm120. The plot130shows an impulse132applied to the resonant circuit14by the impulse generation circuit62. The application of the impulse132implements the operation122of the algorithm100. An impulse response134is induced in response to the applied impulse. The impulse132may be held in its final state (high in the plot130) for the duration of the measurement, but this is not essential. For example, a high-low impulse could be applied (and then held low).

The impulse response processor64generates a signal136indicating edges of the impulse response134. As discussed further below, the signal136may be generated by a comparator and there may be a delay between the occurrence of the edge and the generation of the signal. If consistent, that delay may not be significant to the processing.

At operation124of the algorithm120, a period of the impulse response is determined. An example period is indicated by the arrow138inFIG.13.

At operation126of the algorithm100, an output is generated based on the determined period138. Thus, the output signal is based on a time period from a first edge of the impulse and a second edge that is one complete cycle of said impulse response later. The output signal is therefore dependent on a time period of voltage oscillations of the impulse response, such that the output signal is indicative of the resonant frequency of the impulse response.

In some embodiments, the period138is temperature dependent. In one example implementation, a change in temperature of 250 degrees centigrade resulted in a change in the period138of 13 ns. Accordingly, the output generated in operation126may be used to provide a temperature estimate of the susceptor16based on the measured period. That is, the period138of the impulse response134(as determined from signal136in the present example) may be used to determine the temperature of the susceptor16, e.g. by use of a look-up table determined in advance.

FIG.14is a block diagram of a system, indicated generally by the reference numeral140, in accordance with example embodiments. The system140may be used to implement the operations106and126of the algorithms100and120described above.

The system140comprises an edge detection circuit142, a current source143and a sample-and-hold circuit144.

The edge detection circuit142can be used to determine edges of signals, such as the impulse response signals114and134described above. Accordingly, the edge detection circuit142may generate the signals116and136described above. The edge detection circuit142may, for example, be implemented using a comparator or some similar circuit.

The edge detection circuit142provides an enable signal to the current source143. Once enabled, the current source143can be used to generate an output (such as a voltage output across a capacitor). The current source143has a discharge input that acts as a reset input. The current source output can be used to indicate a time duration since an output of edge detection circuit142enabled the current source143. Thus, the current source output can be used as an indication of time duration (e.g. pulse duration).

The sample-and-hold circuit144can be used to generate an output signal based on the output of the current source143at a particular time. The sample-and-hold circuit144may have a reference input. The sample-and-hold circuit144can be used as an analog-to-digital converter (ADC) that converts a capacitor voltage into a digital output. In other systems, any other suitable electronic components, such as a voltmeter, may be used to measure the voltage.

The system140may be used in an example implementation of the algorithm100. For example, the edge detection circuit142may detect an edge of the impulse response114, thereby generating the signal116. The edge detection circuit can enable the current source143when the impulse is generated until the signal116is generated. Thus, the edge detection circuit142can be configured to determine a propagation delay between an application of an impulse to the resonant circuit14. The current source may therefore be enabled during the time period118indicated inFIG.11. The output of the sample-and-hold circuit144can therefore be dependent on the time period118.

Similarly, the system140may be used in an implementation of the algorithm120. For example, the edge detection circuit142may detect successive edges of the impulse response134, thereby generating the signal136. The edge detection circuit can enable the current source143for the period between two edges. The current source may therefore be enabled during the time period138indicated inFIG.13. The output of the sample-and-hold circuit144can therefore be dependent on the time period138.

The system140may be implemented using a charge time measurement unit (CTMU), such as an integrated CTMU.

FIG.15is a block diagram of a system, indicated generally by the reference numeral150, in accordance with example embodiments. The system150shows features of a CTMU that may be used in example embodiments.

The system150comprises a reference voltage generator151, a comparator152, an edge detection module153, a current source controller154, a constant current source155, an analog-to-digital converter156providing a data output157to a data bus, and an external capacitor158. As discussed further below, the voltage generator151, the comparator152and the edge detection module153may be used to implement the edge detection circuit142described above, the current source controller154and the constant current source155may be used to implement the current source143described above, and the analog-to-digital converter156may be used to implement the sample-and-hold circuit144described above.

The impulse responses generated in the operations104and124described above are provided to an input of the comparator152, where the impulse response is compared with the output of the reference voltage generator151. The comparator may output a logical high signal when the impulse response is greater than the reference voltage and a logical low signal when the impulse response is less than the reference voltage (or vice versa). The output of the comparator152is fed into an input (IN2) of the edge detection circuit153. The other input of the edge detection circuit153(IN1) is a firmware controlled input. The edge detection circuit153(which may simply be a selectable RS flip-flop) generates an enable signal dependent on the identification of edges at the output of the comparator152. The edge detection circuit153may be programmable such that the nature of edges that are to be detected (e.g. rising or falling edges, first edges etc.) can be indicated.

The enable signal is provided as an input to the current source controller154. When enabled, the current source controller154applies a current (from the constant current source155) that is used to charge the external capacitor158. The discharge input to the current source controller can be used to discharge the external capacitor158(and effectively reset the stored charge on the capacitor to a baseline value).

The analog-to-digital converter156is used to determine the voltage across the external capacitor158, which voltage is used to provide the data output157. In this way, the system150provides a voltage ramp that is initialized on an identified edge and ends when a second edge is identified.

FIG.16is a block diagram of a circuit, such as a signal conditioning circuit, indicated generally by the reference numeral160, in accordance with example embodiments. The circuit160may be used to provide an offset to an impulse response to enable the comparator152to correctly compare the impulse response to the output of the reference voltage generator151. The offset may, for example, be programmable such that the threshold level of the comparator circuit152is at a mid-point of the offset pulse response.

The signal conditioning circuit160has at least three purposes. The first is to provide protection from voltage spikes. This is achieved by the stacked diodes and a resistor (not shown) between the mid-points of the diodes and the output. The second is to provide signal decoupling; this is the purpose of the capacitor at the input of the circuit160. The third, as described above, is to set the offset voltage of the impulse response to match that of the input of the comparator152to ensure that the comparator triggers at the mid-point of the impulse response. This is achieved using the resistors R1and R2.

The algorithms100and120are two of many example algorithms in accordance with the principles described herein. In some embodiments, the algorithm100may be inaccurate. Moreover, in some embodiments, the algorithm120can require a lengthy time determination, which can reduce the available resolution of a digital output.FIG.17is a flow chart showing an algorithm, indicated generally by the reference numeral170, in accordance with another example use of the system60.

At operation171of the algorithm170, a first impulse is applied to the resonant circuit14by the impulse generation circuit62. At operation172, a first impulse response period of an impulse response induced in response to the first applied impulse is determined by the impulse response processor64.

At operation173, a second impulse is applied to the resonant circuit14by the impulse generation circuit62. At operation174, a second impulse response period of an impulse response induced in response to the second applied impulse is determined by the impulse response processor64.

Finally, at operation175, an output is generated based on an estimated impulse response period. The estimated impulse response period may, for example, be indicative of a temperature of operation. As discussed in detail below, the estimated impulse response period is derived from the time periods determined in operations172and174.

FIG.18shows a first plot, indicated generally by the reference numeral180, and a second plot, indicated generally by the reference numeral190, demonstrating an example use of the algorithm170.

The plot180shows a first impulse181applied to the resonant circuit14by the impulse generating circuit62. The application of the first impulse181implements the operation171of the algorithm170. A first impulse response182is induced in response to the application of the first impulse.

The impulse response processor64generates a signal183indicating edges of the first impulse response182. As discussed elsewhere herein, the signal183may be generated by a comparator (such as the comparator152).

At operation172of the algorithm170, a first impulse time period is determined. The first time response period starts at the end of a first wait period184following the application of the first impulse and ends at the end of an impulse response period of the relevant impulse response. InFIG.18, the first response time period starts at time185and ends at time186and is indicated by the arrow187. During the first time period187, the current source143is enabled and a voltage is generated at the sample-and-hold circuit144. That voltage is indicated by the reference numeral188. The voltage shown by line188corresponds to the charging of the capacitor158with time (that is, the charge on the capacitor158increases with time due to the application of the constant current). At the end of the relevant impulse response, when the constant current is no longer supplied to the capacitor156, the voltage at the sample-and-hold circuit is indicative of the first time period187. The determination of the first time period187implements the operation172of the algorithm170.

The plot190shows a second impulse191applied to the resonant circuit14by the impulse generating circuit62. The application of the second impulse191implements the operation173of the algorithm170. A second impulse response192is induced in response to the application of the first impulse.

The impulse response processor64generates a signal193indicating edges of the second impulse response192. As discussed elsewhere herein, the signal193may be generated by a comparator (such as the comparator152).

At operation174of the algorithm170, a second impulse time period is determined. The first time response period starts at the end of a second wait period194following the application of the second impulse and ends at the end of an impulse response period of the relevant impulse response. The second wait period194in some embodiments is different to, e.g., greater than, the first wait period184. In some further embodiments, the second wait period194is greater than the wait period184by an amount on the order of 1/f of the signal182or192. This may be determined in advance based on empirical testing, for example. InFIG.18, the second response time period starts at time195and ends at time196and is indicated by the arrow197. During the time period197, the current source143is enabled and a voltage is generated at the sample-and-hold circuit144. That voltage is indicated by the reference numeral198. At the end of the relevant impulse response, the voltage at the sample-and-hold circuit is indicative of the time period197. The determination of the second time period197implements the operation174of the algorithm170.

The delays184and194may be fixed and may be dependent and determined by the hardware configuration and then remain fixed for that design. For example, the delay184may be chosen such that the H bridge has had time to switch and the first half cycle of the response signal has had chance to complete (this tends to be a distorted cycle as shown in the plot). The delay194may be determined by the delay184plus the expected period of the response signal.

At operation175of the algorithm170, an output is generated based on an estimated impulse response period. The impulse response period may be determined based on the sum of the difference between the first and second wait periods and the difference between the first and second impulse time periods.

Thus, for example, if the first wait period184is denoted by w1, the second wait period194is denoted by w2, the first time period187is denoted by t1and the second time period197is denoted by t2, then the impulse response period is given by:
(w2−w1)+(t2−t1)

The impulse response period (and therefore the impulse response frequency) is temperature dependent and can therefore be used as a temperature indication (with appropriate scaling). It should be noted that although the period changes over time (with changing temperature), the temperature difference between successive pulses used to generate the estimate described above is negligible.

As noted above, in one example implementation, a change in temperature of 250 degrees centigrade resulted in a change in the impulse response period138of 13 ns. In that example, the overall period was of the order of 390 ns. Measuring a change of 13 ns in a period of 390 ns is not trivial. In at least some embodiments, the example described with reference toFIGS.17and18can be implemented with greater precision, particularly when data storage is limited.

In one embodiment, the first wait period184and the second wait period194are a predetermined number of instruction cycles of a CPU. For example, the first wait period184may be 9 instruction cycles and the second wait period194may be 14 instructions cycles. Such an arrangement is very simple to implement. In one example implementation, an instruction cycle has a period of 62.5 ns. The difference between the delays184and194for a 2.5 MHz system should be 400 ns or less. This would work out to be no more than 6 instruction cycles. In the example of 9 and 14 instructions (for the wait periods184and194respectively), we have a 5 instruction cycle difference. This has been found to work well in one example implementation and allows the system to still work if the period changes (e.g. due to heating or the insert being removed).

FIG.19is a flow chart showing an algorithm, indicated generally by the reference numeral260, in accordance with an example embodiment. The algorithm260starts at operation261where an impulse is generated and applied to the resonant circuit14. At operation262, a decay rate of the impulse response induced in response to the applied impulse is determined. The decay rate may, for example, be used to determine information regarding the circuit to which the impulse is applied. By way of example, a decay rate in the form of a Q-factor measurement may be used to estimate a temperature of operation. The operation262is an example of the operation74inFIG.7. That is, the decay rate is an example of an output based on the impulse response.

Impulse responses can be used to estimate a range of information about a circuit or system to which an impulse is applied. For example, variables of the aerosol provision device20described above can be estimated on the basis of impulse response variables. By way of example, such variables include temperature of operation, the presence or absence of a susceptor and/or a removable article; other properties of a susceptor and/or a removable article, fault conditions etc. Example fault conditions includes whether the removable article is inserted in the aerosol generating device in a correct manner (such as being inserted the right way round and/or being fully inserted) and whether the removable article is in good condition.

FIG.20is a flow chart showing an algorithm, indicated generally by the reference numeral270, in accordance with an example embodiment. The algorithm270starts at operation271where a number of oscillations in a given period of an impulse response is counted. At operation272, circuit information (such as the presence or absence of an inserted article and/or a susceptor, temperature of operation, other properties of a susceptor and/or a removable article etc.) is determined on the basis of the counted number of oscillations. By way of example, a processor (such as the impulse response processor64) may be provided for determining the number of oscillations in a given period of time of the impulse response signal. Such a measurement may, for example, be used to determine whether or not a removable article is fitted within the apparatus on the basis of said determined number of oscillations.

FIG.21is a flow chart showing an algorithm, indicated generally by the reference numeral280, in accordance with an example embodiment. The algorithm280starts at operation281where a Q-factor of an impulse response is determined. At operation282, circuit information (such as the presence or absence of an inserted article and/or a susceptor, temperature of operation, other properties of a susceptor and/or a removable article etc.) is determined on the basis of the counted number of oscillations. By way of example, a processor (such as the impulse response processor64) may be provided for determining the Q-factor measurement of the impulse response by determining a number of oscillation cycles for the impulse response to halve in amplitude and multiplying the determined number of cycles by a predetermined value. Such a measurement may, for example, be used to determine whether or not a removable article is fitted within the apparatus on the basis of said determined Q-factor. The skilled person will be aware of other arrangements for determining or estimating a Q-factor of the relevant circuit.

FIG.22is a plot, indicated generally by the reference numeral300, showing an output in accordance with an example embodiment. The plot300shows an impulse response detected by the impulse response processor64in a mode of operation of the aerosol provision device20when an article21was inserted and operating at a temperature of about 176 degrees centigrade (i.e. a ‘hot’ mode of operation). The Q-factor of the plot300is about 7.9.

FIG.23is a plot, indicated generally by the reference numeral301, showing an output in accordance with an example embodiment. The plot301shows an impulse response detected by the impulse response processor64in a mode of operation of the aerosol provision device20when an article21was inserted and operating at a temperature of about 20 degrees centigrade (i.e. a ‘cold’ mode of operation). The Q-factor of the plot302is about 11.3.

FIG.24is a plot, indicated generally by the reference numeral302, showing an output in accordance with an example embodiment. The plot302shows an impulse response detected by the impulse response processor64in a mode of operation of the aerosol provision device20when an article21was not inserted (i.e. a ‘no rod’ mode of operation). The Q-factor of the plot300is about 31.7.

It will be readily apparent that the algorithm280could be used to distinguish between the scenarios shown in plots300to302described above. That is, based on the calculated Q-factor (which is an example of the decay rate data of the impulse response signal), it is possible to distinguish between a susceptor present or absent condition (e.g., an article21inserted or not), a ‘cold’ susceptor and a ‘warm’ susceptor. Moreover, it is also possible to determine the temperature of the susceptor on the basis of the Q-value. From the above plots, it can be seen that (in these examples) the Q-factor generally decreases with increasing temperature.

Equally, it will be readily apparent that the algorithm270could be used to distinguish between the scenarios shown in plots301and302described above. In accordance with algorithm270, counting the number of oscillations in a given time period provides characteristic data, e.g., the temperature, of a susceptor. Indeed, plot301has a much lower oscillation count for a given time period than plot302. In other words, the number of oscillations for a given time period correlates with the temperature of the susceptor. From the above plots, it can be seen that (in these examples) the number of oscillations generally increases with increasing temperature.

FIG.25is a block diagram of a system, indicated generally by the reference numeral350, in accordance with an example embodiment. System350comprises the direct current (DC) voltage supply11, the switching arrangement13, the resonant circuit14, the susceptor arrangement16, and the control circuit18of the system10described above. In addition, the system350comprises a current sensor15. The switching arrangement13, the resonant circuit14, and the current sensor15may be coupled together in an inductive heating arrangement12.

FIG.26is a flow chart showing an algorithm, indicated generally by the reference numeral360, in accordance with an example embodiment. The algorithm360shows an example use of the system350.

At operation361of the algorithm360, a resonant circuit of an aerosol generating device may be controlled, where the resonant circuit may comprise one or more inductive elements. The one or more inductive elements may be used for inductively heating a susceptor arrangement to heat an aerosol generating material. Heating the aerosol generating material may thereby generate an aerosol in a heating mode of operation of the aerosol generating device. For example, the resonant circuit14of the system350may be controlled by the control module18.

At operation362, a current flowing in an inductive element is measured by a current sensor. For example, a current flowing in one or more inductive elements of the resonant circuit14may be measured by the current sensor15.

At operation363, one or more characteristics of the aerosol generating device and/or an apparatus for the aerosol generating device may be determined based, at least in part, on the measured current. The one or more characteristics may include one or more of the following: the presence or absence of a susceptor; the presence or absence of a removable article; properties of the removable article; fault conditions (such as whether the removable article is inserted in the aerosol generating device in a correct manner (such as being inserted the right way round and/or being fully inserted) and whether the removable article is in good condition); whether the current matches the current of a genuine susceptor and/or removable article; whether the current is consistent with the susceptor having a temperature above a first temperature threshold and/or below a second temperature threshold.

The use of a current measurement to determine characteristics of a circuit or system may be used in combination with any of the other methods described herein (such as Q-factor and/or resonant frequency determining arrangements and/or oscillation counting arrangements). It should be noted that the use of a current measurement to determine the presence or absence of a susceptor, for example, is not required as it is possible to determine the presence or absence of a susceptor based on the calculated Q-factor alone.

In the example embodiments described above, each of the impulse responses has been generated in response to a rising impulse signal. For example,FIG.8shows an example impulse80based on a rising edge that might be applied to a resonant circuit, withFIG.9showing an example impulse response that might be received in response to that impulse. It is not essential to all embodiments that impulses are generated on a rising edge. For example, the circuit40could be used to generate an impulse as a falling edge. Moreover, both rising and falling edges could be used. This may, for example, have the advantage of providing more impulse responses in a given time period (since impulse responses could be generated on both rising and falling edges).

By way of example,FIG.27is a plot, indicated generally by the reference numeral370, showing an example pair of impulses in accordance with an example uses of example embodiments. The plot370includes a first impulse on a rising edge and a second impulse on a falling edge. The first impulse may be referred to as a forward ping, with the second impulse being referred to as a backward ping. The use of both forward and backward pings may be useful, for example, in conjunction with the algorithm170in which two pings may be generated in a relatively short time period.

FIG.28is a block diagram of a circuit switching arrangement, indicated generally by the reference numeral380, in accordance with an example embodiment. The switching arrangement380shows switch positions of the circuit40in a first state, indicated generally by the reference numeral382, and a second state, indicated generally by the reference numeral383.

In the first state382, the switches45aand45cof the circuit40are off (i.e. open) and the switches45band45dare on (i.e. closed). In the second state383, the switches45aand45dare on (i.e. closed) and the switches45band45care off. Thus, in the first state382, both sides of the resonant circuit49are connected to ground. In the second state383, a voltage pulse (i.e. an impulse) is applied to the resonant circuit.

FIG.29is a block diagram of a circuit switching arrangement, indicated generally by the reference numeral390, in accordance with an example embodiment. The switching arrangement390shows switch positions of the circuit40in a first state, indicated generally by the reference numeral392, and a second state, indicated generally by the reference numeral393.

In the first state392, the switch45bis on (i.e. closed) and the switches45a,45cand45dare off (i.e. open). Thus, one side of the resonant circuit49is grounded. In the second state393, a voltage pulse (i.e. an impulse) is applied to the resonant circuit.

In the second state382of the switching arrangement380, a current is able to flow through the first switch45a, the resonant circuit49and the switch45d. This current flow may lead to heat generation and discharging of a power supply (such as a battery). Conversely, in the second state393of the switching arrangement390, a current will not flow through the switch45d. Accordingly, heat generation and power supply discharge may be reduced. Moreover, noise generation may be reduced on the generation of each impulse.

FIG.30is a flow chart, indicated generally by the reference numeral400, showing an algorithm in accordance with an example embodiment. The algorithm400shows an example use of the systems described herein.

The algorithm400starts with a measurement operation401. The measurement operation401may, for example, include a temperature measurement. Next, at operation402, a heating operation is carried out. The implementation of the heating operation402may be dependent on the output of the measurement operation401. Once the heating operation402is complete, the algorithm400returns to operation401, where the measurement operation is repeated.

The operation401may be implemented by the system60in which an impulse is applied by the impulse generation circuit62and a measurement (e.g. a temperature measurement) determined based on the output of the impulse response processor64. As discussed above, a temperature measurement may be based, for example, on a decay rate, an impulse response time, an impulse response period etc.

The operation402may be implemented by controlling the circuit40in order to heat the susceptor16of the system10. The inductive heating arrangement12may be driven at or close to the resonant frequency of the resonant circuit, in order to cause an efficient heating process. The resonant frequency may be determined based on the output of the operation401.

In one implementation of the algorithm400, the measurement operation is conducted for a first period of time, the heating operation402is conducted for a second period of time and the process is then repeated. For example, the first period of time may be 10 ms and the second period of time may be 250 ms, although other time periods are possible. In other words, the measurement operation may be performed between successive heating operations. It should also be noted that the heating operation402being conducted for the second period of time does not necessarily imply that power is supplied to the induction coil for the whole duration of the second period of time. For example, power may only be supplied for a fraction of the second period of time.

In an alternative embodiment, the algorithm400may be implemented with the heating operation402having a duration dependent on a required level of heating (with the heating duration being increased if more heating is required and reduced if less heating is required). In such an algorithm, the measurement operation401may simply be carried out when heating is not being conducted, such that the heating operation402need not be interrupted in order to conduct the measurement operation401. This interleaved heating arrangement may be referred to as a pulse-width-modulation approach to heating control. By way of example, a pulse-width modulation scheme may be provided at a frequency of the order of 100 Hz, where each period is divided into a heating portion (of variable length) and a measurement portion.

FIG.31is a flow chart, indicated generally by the reference numeral410, showing an algorithm in accordance with an example embodiment. The algorithm410may be implemented using the system60described above.

The algorithm410starts at operation411, where an impulse is applied to the resonant circuit14by the switching circuit13(e.g. the circuit40). At operation413, an impulse response (e.g. detected using the impulse response processor64) is used to determine whether an article (such as the article21) is present in the system to be heated. As discussed above, the presence of the article21affects the impulse response in a manner that can be detected.

If an article is detected at operation413, the algorithm410moves to operation415; otherwise, the algorithm terminates at operation419.

At operation415, measurement and heating operations are implemented. By way of example, the operation415may be implemented using the algorithm400described above. Of course, alternative measurement and heating arrangements could be provided.

Once a number of heating measurement and heating cycles have been conducted, the algorithm400moves to operation417, where it is determined whether heating should be stopped (e.g. if a heating period has expired, or in response to a user input). If so, the algorithm terminates at operation419; otherwise the algorithm400returns to operation411.

It should be appreciated that the above techniques for determining one or more properties of the inductive arrangement or susceptor arrangement can be applied to individual inductive elements. For systems that comprise multiple inductive elements, such as the system20, which comprises three inductive elements23a,23b, and23c, the system may be configured such that the one or more parameters, such as the temperature, can be determined for each of the inductive elements using the above described techniques. In some implementations, it may be beneficial for the system to operate using separate measurements for each of the inductive elements. In other implementations, it may be beneficial for the system to operate using only a single measurement for the plurality of inductive elements (e.g., in the case of determining whether the article21is present or not). In such situations, the system may be configured to determine an average measurement corresponding to the measurements obtained from each inductive element. In other instances, only one of the plurality of inductive elements may be used to determine the one or more properties.

Some embodiments include controlling temperature, for example of a replaceable article21. In some embodiments, the temperature may be controlled using the principles of proportional integral derivative (PID) control. This typically provides a better control performance than thermostatic control and may, for example, lead to further control advantages, such as the ability to detect failures in a replaceable article (such as damaged foils) during the temperature control phase.