Dielectric heating assembly with sensing element

Abstract

Provided is a heating assembly (130) for a dielectric heating aerosol-generating device (120). The heating assembly (130) comprising: a heating region (140) for receiving an aerosol-forming substrate (110); an electrode arrangement that forms a load capacitor for dielectrically heating an aerosol-forming substrate (110) received in the heating region (140); and a sensing element (135) configured to sense a temperature in the vicinity of the heating region (140). The sensing element (135) comprises a magnetic material having a Curie temperature corresponding to a predefined temperature point for heating an aerosol-forming substrate (110).

Description

[0001] P / 90750.W001

[0002] Dielectric Heating Assembly With Sensing Element

[0003] The present disclosure relates to heating assemblies, and specifically to heating assemblies for dielectrically heating an aerosol-forming substrate in an aerosol-generating device. The disclosure also relates to aerosol-generating devices, and aerosol-generating systems.

[0004] Known electrically operated aerosol-generating systems typically heat an aerosol-forming substrate by one or more of: conduction of heat from a heating element to an aerosol-forming substrate, radiation of heat from a heating element to an aerosol-forming substrate or drawing heated air through an aerosol-forming substrate. Most commonly, heating is achieved by passing an electrical current through an electrically resistive heating element, giving rise to Joule heating of the heating element. Inductive heating systems have also been proposed, in which Joule heating occurs as a result of eddy currents induced in a susceptor heating element.

[0005] A problem with these heating mechanisms is that they may give rise to non-uniform heating of the aerosol-forming substrate. The portion of the aerosol-forming substrate closest to the heating element is heated more quickly or to a higher temperature than portions of the aerosol-forming substrate more remote from the heating element.

[0006] Systems that dielectrically heat an aerosol-forming substrate have been proposed, which advantageously provide uniform heating of the aerosol-forming substrate. However, known dielectric heating systems are less efficient than inductive heating systems and require complex electrical circuitry in order to achieve the necessary voltages and frequencies for dielectric heating of an aerosol-forming substrate. Dielectric heating systems may also require a longer time to first puff as it can take longer to heat the aerosol-forming substrate to a vaporisation temperature when compared to inductively heated systems.

[0007] A further problem with dielectric heating systems is the difficulty in monitoring the internal temperature of the aerosol-forming substrate in order to control heating power without greatly adding to the cost and complexity of the system.

[0008] It would be desirable to provide an effective solution for monitoring aerosol-forming substrate temperatures in dielectric heating systems in order to facilitate improved temperature control.

[0009] According to the present disclosure, there is provided a heating assembly for a dielectric heating aerosol-generating device including any one or more of the features described below.

[0010] The heating assembly may comprise a heating region for receiving an aerosol-forming substrate. The heating assembly may further comprise a dielectric heating assembly for dielectrically heating an aerosol-forming substrate received in the heating region. The heating assembly may also comprise a sensing element configured to sense a temperature in the vicinity of the heating region. The sensing element may comprise a magnetic material having a Curie temperature corresponding to a predefined temperature point for heating an aerosol-forming substrate. P / 90750.W001

[0011] The heating assembly may further comprise any of the features described below alone or in combination with any other feature of the disclosure.

[0012] As used herein, the term “aerosol-generating device” relates to a device that interacts with an article comprising an aerosol-forming substrate to generate an aerosol.

[0013] As used herein, the term “aerosol-forming substrate” relates to a substrate capable of releasing volatile compounds that can form an aerosol, for example solid substrates, liquid substrates, gel-like substrates, and other. Such volatile compounds can be released by heating the aerosol-forming substrate.

[0014] As used herein, the unit "wt%" stands for "weight per cent" or " percentage by weight". That is, it denotes the mass fraction of an element within the alloy which is the ratio of the mass of that respective element to the total mass of a sample of that alloy.

[0015] According to an example of the disclosure, provided is a heating assembly for a dielectric heating aerosol-generating device. The heating assembly comprises a heating region for receiving an aerosol-forming substrate. The heating assembly further comprises a dielectric heating assembly for dielectrically heating an aerosol-forming substrate received in the heating region. The heating assembly also comprises an inductive sensing element configured to sense a temperature in the vicinity of the heating region. The inductive sensing element comprises a magnetic material having a Curie temperature corresponding to a predefined temperature point for heating an aerosol-forming substrate.

[0016] At its Curie temperature, the magnetic permeability of the magnetic material in the sensing element drops to unity leading to a change of its magnetic properties from ferro- or ferrimagnetic to paramagnetic. The change of the magnetic properties is accompanied by a temporary change of the electrical resistance of the magnetic material. Thus, by monitoring a corresponding change of the electrical current through an induction source it can be detected when the magnetic material has reached its Curie temperature and, thus, when the predefined temperature point has been reached. As such heating assemblies according to the present disclosure facilitates improved temperature control in dielectric aerosol-generating systems.

[0017] The magnetic material may comprise or consist of an Ni-Fe- alloy having 75 wt% - 85 wt% Ni and 10 wt% - 25 wt% Fe. More particular, the Ni-Fe-alloy may comprise 79 wt% - 82 wt% Ni and 13 wt% - 15 wt% Fe. Advantageously, it has been found that Ni-Fe-alloys including Ni and Fe in the above ranges exhibit only weak or even no magnetostriction. As a consequence, the magnetic material of the sensing element experiences no or only at least a reduced modification of its magnetic properties after its processing and throughout its temperature range of operation. This in turn allows for a mass production of sensing elements comprising the magnetic material with no or only little variation of its magnetic properties after processing and during subsequent operation. P / 90750.W001

[0018] In addition to the main components, the remainder of the Ni-Fe-alloy may comprise one or more of the following elements: Co, Cr, Cu, Mn, Mo, Nb, Si, Ti and V.

[0019] As used herein, the symbol Ni stands for the chemical element nickel, the symbol Fe stands for the chemical element iron, the symbol Co stands for the chemical element cobalt, the symbol Cr stands for the chemical element chromium, the symbol Cu stands for the chemical element copper, the symbol Mn stands for the chemical element manganese, the symbol Mo stands for the chemical element molybdenum, the symbol Nb stands for the chemical element niobium, the symbol Si stands for the chemical element silicon, the symbol Ti stands for the chemical element titanium, and the symbol V stands for the chemical element vanadium. According to one example, the Ni-Fe-alloy may comprise 79 wt% - 82 wt% Ni, 4 wt% - 6 wt% Mo, less than 1 wt% of Si and Mn combined together, and 13 wt% - 15 wt% Fe. As used herein, "1 wt% of Si and Mn combined together" means " Si and Mn below 1 wt% in sum".

[0020] According to another example, the Ni-Fe-alloy may comprise 77 wt% Ni, 16 wt% Fe, 5 wt% Cu, and 2 wt% of one of Cr and Mo.

[0021] According to yet another example, the Fe-Ni alloy may comprise 77 wt% Ni, 4wt% Mo, 4 wt% Cu and 14 wt% - 15 wt% Fe.

[0022] Advantageously, these specific examples of the Ni-Fe-alloy exhibit particularly weak magnetostriction.

[0023] According to yet another example, the Ni-Fe-alloy may be ASTM A 753 alloy of type 3, (similar to UNS number: N 14076) having 75 wt% - 78 wt% Ni and 10 wt% - 19 wt% Fe. The remainder may be constituted by one or more of the following elements: Co, Cr, Cu, Mn, Mo, and Si.

[0024] According to still another example, the Ni-Fe-alloy may be ASTM A 753 alloy of type 4, (similar to UNS number: N14080 and to EN numeric designation: 2.4545) having 77 wt% - 82 wt% Ni and 10 wt% - 17.5 wt% Fe (or even 9.5 wt% - 17.5 wt% Fe). The remainder may be constituted by one or more of the following elements: Co, Cr, Cu, Mn, Mo, and Si.

[0025] The magnetic material in the sensing element is configured for monitoring a temperature of the heating region of the heating assembly, that is, as a temperature marker. For this, the magnetic material is selected to have a Curie temperature which essentially corresponds to a predefined temperature point of the heating process. In particular, the magnetic material may be selected to have a Curie temperature which essentially corresponds to a predefined maximum heating temperature for an aerosol-forming substrate heated by the heating assembly. The maximum desired heating temperature may be defined to be approximately the temperature that the aerosolforming substrate should be heated to in order to generate an aerosol. However, the maximum desired heating temperature should be low enough to avoid local overheating or even burning of the aerosol-forming substrate. Preferably, the Curie temperature of the magnetic material should be below an ignition point of the aerosol forming substrate. The magnetic material may have a Curie P / 90750.W001 temperature below 500 °C, preferably equal to or below 400 °C, in particular equal to or below 390 °C. For example, the magnetic may have a Curie temperature between 150 °C and 400 °C, in particular between 150 °C and 250 °C.

[0026] In an example, the sensing element is configured to physically contact an aerosol-forming substrate when received in the heating region. Such examples may improve conduction of heat from the aerosol-forming substrate to the sensing element. In other examples a heat transfer element may be provided between the aerosol-forming substrate and the sensing element, the heat transfer element having at least one of a high thermal conductivity, a low thermal resistance, and a low heat capacity.

[0027] In some examples, the dielectric heating assembly comprises an electrode arrangement that forms a load capacitor for dielectrically heating an aerosol-forming substrate received in the heating region.

[0028] In some examples, the sensing element is situated between adjacent electrodes in the electrode arrangement. In some examples, the sensing element is situated between electrodes of the electrode arrangement, which in operation have opposing polarities.

[0029] In some examples, the sensing element is situated on an electrode of the electrode arrangement. In some examples, the sensing element is integrally formed on one or more electrodes in the electrode arrangement. In some examples, the sensing element forms a layer or coating on one or more electrodes of the electrode arrangement. In some examples, an electrode comprising the sensing element has a floating potential. In other examples, an electrode comprising the sensing element is grounded. Such examples may avoid high voltages on the electrode influencing the temperature sensing apparatus - for example an induction coil inductively coupled with the sensing element.

[0030] In some examples, the sensing element comprises a second magnetic material having a Curie temperature corresponding to a second predefined temperature point for heating an aerosolforming substrate, wherein the second predefined temperature point is different from the predefined temperature point. In some examples, the heating assembly comprises a second sensing element configured to sense a temperature in the vicinity of the heating region. In such examples, the second sensing element comprises a magnetic material having a Curie temperature corresponding to a second predefined temperature point for heating an aerosol-forming substrate, wherein the second predefined temperature point is different from the predefined temperature point. In some examples, the Curie temperature of the magnetic material of the first sensing element is one of 150, 180 or 200, while the Curie temperature of the magnetic material of the second sensing element is one of 250, 230 or 220. Such examples may be used to facilitate detection of upper and lower aerosol-forming substrate heating temperature boundaries for an aerosol-generating device to deliver precise heating control. P / 90750.W001

[0031] In some examples, the electrode arrangement comprises a first electrode aligned in parallel with a second electrode. In operation, the second electrode has an opposite polarity to the first electrode. In some examples, the first and second electrodes may be flat plate electrodes configured to heat an aerosol-forming substrate situated between the first and second electrode plates. In some examples, the first and second electrode plates may be slightly bent or rounded at the edges to create a smoother electric field distribution around the boundaries of the electrode plates. In some examples, the electrode plates may be curved. The curved electrode plates may have a radius of 15mm or greater.

[0032] In an example, the electrode arrangement comprises a first electrode comprising a tubular body having a hollow center and the second electrode comprises a rod or pin situated within the hollow center of the first electrode. In such examples, an article comprising an aerosol-forming substrate may be inserted into the electrode arrangement between the first and second electrode. In some examples, the tubular body of the first electrode may comprise one or more openings. The one or more openings may enable the aerosol generated by the dielectric heating to escape the electrode arrangement to an airflow channel. In another example, the first electrode comprises a tubular body having a hollow center and the second electrode comprises a tubular body having a hollow center, wherein the second electrode is situated within the hollow center of the first electrode. In an example, the tubular body of the second electrode comprises one or more openings. Such examples enable the inner electrode to define a central airflow passage for the generated aerosol to escape the electrode arrangement.

[0033] In some examples, the first electrode and the second electrode may each comprise a plurality of electrode portions.

[0034] In some examples, the electrode arrangement comprises a first electrode coaxially aligned with a second electrode. Advantageously, the use of coaxially aligned electrodes may provide more a more uniform electric field, and therefore more uniform dielectric heating through an aerosolforming substrate situated within the electrode arrangement.

[0035] In some examples, the electrode arrangement comprising a first electrode interdigitated with a second electrode. The term interdigitated relates to an electrode arrangement comprising a first electrode having a first polarity and a second electrode having a second polarity which is the opposite of the first polarity, wherein at least a portion of the first electrode separates two portions of the second electrode. The use of interdigitated electrodes allows for a more homogenous electric field generation, which can be used to avoid hot spots across an aerosol-forming substrate. The electrode arrangement may take on any form, providing that an electric field can be generated across an aerosol-forming substrate in the vicinity of the electrode arrangement.

[0036] In an example, the electrode arrangement may comprises a first plate comprising a first electrode portion interdigitated with a second electrode portion; and a second plate comprising a first P / 90750.W001 electrode portion interdigitated with a second electrode portion. In other examples, the first electrode and the second electrode may each comprise a cylindrical segment configured to interdigitate with the cylindrical segment of the other electrode around a cylindrical axis. In other examples, the first electrode may comprise a first plurality of cylindrical segments and the second electrode comprises a second plurality of cylindrical segments. Each of the first plurality of cylindrical segments may be positioned around the cylindrical axis separated by one of the second plurality of cylindrical segments. In some examples, the heating region for receiving an aerosol-forming substrate is situated between the first electrode and the second electrode.

[0037] In some examples, the first electrode comprises a plurality of axially aligned electrode rings and the second electrode comprises a rod or pin extending through the plurality of axially aligned electrode rings.

[0038] In some examples, the distance between the first electrode and the second electrode may vary across the electrode arrangement. This may further facilitate a more uniform electric field distribution through an aerosol-forming substrate based on the geometry of the aerosol-forming substrate and that of the heating region.

[0039] In some examples, the heating assembly further comprises a liquid transfer element in the heating region for fluidically holding an aerosol-forming substrate in the vicinity of the electrode arrangement.

[0040] In other examples, the dielectric heating assembly comprises a resonant cavity comprising the heating region for dielectrically heating an aerosol-forming substrate received within the heating region.

[0041] According to an example of the disclosure, provided is an aerosol-generating device comprising a heating assembly according to any one of the above examples. The device comprises an oscillation circuit configured to supply power to the electrode arrangement of the heating assembly for dielectrically heating an aerosol-forming substrate received in the heating region of the heating assembly. The device further comprises an inductor configured to form an inductive coupling with the sensing element of the heating assembly.

[0042] In some examples, the heating assembly is removably coupled to electrical contacts within the device. In some examples, the heating assembly may form part of an aerosol-forming article comprising an aerosol-forming substrate. In other examples, the heating assembly may be removable to facilitate easy insertion of an aerosol-forming article comprising an aerosol-forming substrate in the heating region of the heating assembly prior to connection with the device.

[0043] In some examples, the heating assembly may be coupled to, or configured to be coupled to a resonant cavity for housing an aerosol-forming substrate to be dielectrically heated via the heating assembly. P / 90750.W001

[0044] In some examples, the inductor comprises an electric field shield configured to shield the inductor from an electric field generated by the electrode arrangement.

[0045] In some examples, the inductor may be configured to form a inductive coupling with the electrode arrangement for inductively heating an aerosol-forming substrate received within the heating region of the heating assembly. In an alternative example, the device comprises a second inductor, wherein the first inductor is configured to form an inductive coupling with the sensing element and the second inductor is configured to form a inductive coupling with the electrode arrangement for inductively heating an aerosol-forming substrate received within the heating region of the heating assembly. In some examples, the second inductor is positioned on an opposite side of the heating assembly to the first inductor. Such examples may utilise combined dielectric and inductive heating using the electrode arrangement of the heating assembly as susceptor elements to inductively heat an aerosol-forming substrate.

[0046] Accordingly, the disclosed aerosol-generating devices are able to benefit from the advantages of dielectric heating while reducing the time to first puff for the aerosol-generating device. While dielectric heating may create heat substantially uniformly within an aerosol-forming substrate, inductive heating heats an external surface of the aerosol-forming substrate in the vicinity of the electrode arrangement, creating a temperature gradient across the aerosol-forming substrate. When both dielectric and inductive heating mechanism are used in combination, greater heating occurs in regions on the aerosol-forming substrate closest to the electrode arrangement to quickly reach a vaporization temperature, thereby reducing the time to first puff.

[0047] In some examples, the oscillation circuit may also be configured to supply power to the inductor for inductive heating the electrode arrangement. In an alternative example, the device may comprise a second oscillation circuit configured to supply power to the inductor for inductive heating the electrode arrangement. Advantageously, this may enable the inductive heating to be controlled independently from the dielectric heating of an aerosol-forming substrate. In some examples, one of or both the first oscillation circuit or the second oscillation circuit may be a forced oscillation circuit, wherein the power that sustains the oscillation motion is modulated externally. In some examples, the first oscillation circuit is self-oscillating and the second oscillation circuit is a forced oscillation circuit. In some examples, the inductive heating may only be engaged during a pre-heating phase to heat an aerosol-forming substrate to a vaporization temperature.

[0048] In some examples, the oscillation circuit may be self-oscillating. In some examples, the oscillation circuit may comprise a switching unit configured for inverting operation. The oscillation circuit may also comprise a feedback loop connected to the switching unit. The feedback loop may comprise the electrode arrangement of the heating assembly. The feedback loop may be configured to perform resonant oscillating operation and configured to provide a 180° phase shift between an output signal of the switching unit and an input switching signal of the switching unit. P / 90750.WG01

[0049] The oscillation circuits according to aspects of the present disclosure enable more efficient dielectric heating of an aerosol-forming substrate by facilitating the coupling of a load capacitor electrode arrangement within the feedback loop of the oscillation circuit. The resonant oscillating operation of the feedback loop is able to generate high peak voltages across the load capacitor at high frequencies to deliver dielectric heating power to an aerosol-forming substrate within the electrode arrangement while maintaining the supply voltage across the switching unit, thereby keeping switching losses to a minimum. The oscillation circuits according to aspects of the present disclosure may be configured to be self-oscillating; that is, the oscillation circuit itself controls the phase with which the external power acts on it.

[0050] Where the switching unit is configured for inverting operation, the feedback unit is configured to provide a 180° phase shift between an output signal of the switching unit and an input switching signal of the switching unit. This allows for effective resonant oscillating operation to occur.

[0051] In an example, the oscillation circuit is configured to operate a frequency of between 100MHz- 2.5GHz, and preferably between 300MHz-1 ,5GHz.

[0052] In operation, the oscillation frequency in the feedback loop may increase towards a certain resonance frequency based on the passive properties of the components in the feedback loop. However, as the oscillation frequency increases beyond a certain threshold, the feedback loop starts to lose the inductive properties that provide the necessary phase shift for effective resonant oscillating operation. Furthermore, as the oscillation frequency exceeds a certain threshold, the impedance of the feedback loop increases, reducing the dielectric heating efficiency in the load capacitor. By providing a delay element configured to impede the switching speed of the switching unit, the maximum oscillation frequency may be limited to a frequency range in which the feedback loop behaves inductively and has a low impedance for efficient dielectric heating.

[0053] In some examples, a biasing unit is coupled to an input terminal of the switching unit via the delay element. In some examples, the delay element is coupled to ground by a capacitor.

[0054] In some examples, the feedback loop comprises a capacitive element providing for a 90 degrees phase shift to a signal from the feedback loop.

[0055] In an example, the oscillation circuit is configured such that, during operation, a peak AC voltage across the electrode arrangement is greater than a supply voltage of the oscillation circuit. In some examples, the oscillation circuit is configured such that, during operation, the peak AC voltage across the electrode arrangement is greater than five times the supply voltage of the oscillation circuit. Advantageously, providing a higher voltage across the load capacitor than the supply voltage enables more power to be delivered to an aerosol-forming substrate with lower switching losses in the switching unit, and therefore directly impacts the efficiency of the aerosolgenerating device. In examples of the present disclosure, this may be achieved without the use of any voltage transformers by relying solely on resonant oscillating operation within the feedback loop. P / 90750.W001

[0056] In an example, the peak AC voltage across the electrode arrangement at the operating frequency of the oscillation circuit is from 50V to 500V, more preferably 100V to 400V, even more preferably 120V to 350V, wherein the DC supply voltage to the oscillation circuit is between 6V to 15V.

[0057] In an example, the impedance of the feedback loop at the operation frequency is matched with the impedance of the switching unit, which improves the efficiency of the oscillation circuit.

[0058] In an example, the feedback loop is suspended between a power supply and ground of the oscillation circuit, meaning that there is no direct connection between the feedback loop and the supply voltage or ground. This reduces noise and ground influences for more predictable operation in the feedback loop.

[0059] In an example, the feedback loop is connected across an output terminal and a biasing terminal of the switching unit. In some examples, the output terminal of the switching unit is coupled to the supply voltage via a radio frequency choke. The choke acts to block high frequency alternating currents while passing direct current and low frequency alternating current.

[0060] In an example, the feedback loop is configured to operate as an inductive load at an operating frequency of the oscillation circuit to provide approximately a 90° phase shift. As described above, this can be achieved by providing one or more inductors in series with the load capacitor in the feedback loop. In an example, the feedback loop further comprises a capacitive element providing for a 90° phase shift at an operating frequency of the oscillation circuit. In an example, the capacitive element comprises a capacitor connected to ground. The combination of the inductive load and capacitive element in the feedback loop provides a 180° phase shift above the resonant frequency of the oscillation circuit, which, in combination with an inverting switching unit, provides effective resonant oscillating operation for dielectric heating.

[0061] In an example, the oscillation circuit further comprises a capacitor connected between an output terminal of the switching unit and ground, the capacitor having a capacitance value that is bigger than a maximal intrinsic capacitance of the switching unit. This reduces the influence of the variation of the intrinsic properties of the switching unit due to factors such as temperature and operating frequency on the operation of the feedback loop.

[0062] In an example, the switching device comprises a single transistor. In some examples, the transistor may be a bipolar junction transistor (BJT), and the feedback loop may be connected between the collector or emitter and the base of the BJT. In other examples, the transistor may be a field effect transistor (FET) and the feedback loop may be connected between the drain or source and the gate of the FET.

[0063] In an example, the device further comprises a control unit.

[0064] In some examples, the control unit is configured to detect a change in magnetic properties of the sensing element based on a detected change in impedance or conductance of the inductor. The P / 90750.W001 control unit may then adjust a power supplied to the heating assembly based on the detected change in magnetic properties of the sensing element.

[0065] In examples wherein the heating assembly comprises a second magnetic material with a different Curie temperature to the first magnetic material, during a heating operation, the control unit may be configure to adjust a power supplied to the heating element such that the temperature of an aerosol-forming substrate is maintained between the Cuire temperatures of the first and second magnetic materials. In other examples, the first magnetic material may be selected to have a Curie temperature corresponding to a minimum operating temperature where the device is to transition from a preheating mode to an aerosolization mode, while the second magnetic material may be selected to have a Curie temperature corresponding to a maximum heating temperature for the aerosol-forming substrate.

[0066] Preferably, the temperature of the substrate is kept lower than a temperature where pyrolysis could occur in the material composition of the aerosol forming substrate. Preferably, the temperature is such that one or more active ingredients of the substrate are vaporized and thereafter aerosolized, for example simultaneously or sequentially during a heating session, for example a heating session for a duration of one puff or inhalation, for example a duration in a range between 0.5 seconds to 10 seconds, or a heating session for a duration that covers multiple puffs or inhalation, for example a duration of more than 10 seconds and less than 10 minutes, or preferably, more than 30 seconds and less than 6 minutes. In some examples, a controller of the aerosol-generating device or the settings of the oscillation circuit can be configured such that they control or set the temperature to such a range between 80°C to 365°C, more preferably between 80°C to 320°C, or more preferably 180°C to 220°C by open-loop control, or closed-loop control.

[0067] In some examples, the configuration and dimensioning of the oscillation circuit is selected to passively limit the temperature of the aerosol-forming substrate to a range between 80°C to 365°C, more preferably between 80°C to 320°C, or more preferably 180°C to 220°C, without the use of active temperature control.

[0068] In some examples in which either or both the first and second electrodes comprise a plurality of electrode portions, the aerosol-generating device may be configured to provide partial or sectional heating of an aerosol-forming substrate by selectively energizing one or more of the plurality of electrode portions for dielectric heating. This enables an aerosol-generating device to switch between different electric field distribution patterns between the first and second electrodes to adjust the heating profile across the aerosol-forming substrate. This sectional heating approach may be used to compensate for geometry and heat transfer properties of the electrode arrangement, inductive heating in the electrode arrangement (and also other components of the aerosolgenerating device) and the aerosol-forming substrate in order to avoid localized overheating or underheating in the aerosol-forming substrate. io P / 90750.W001

[0069] In some examples, both sectional dielectric and inductive heating may be utilised.

[0070] The disclosure further provides an aerosol-generating system comprising an aerosolgenerating device according to any of the above examples and an article comprising an aerosolforming substrate. The article is situated in the heating region of the heating assembly to enable dielectric heating of the aerosol-forming substrate.

[0071] It is to be appreciated that the features of the above examples of the disclosure are complementary with one another, except where stated otherwise, and so features of different examples may be readily implemented in the oscillation circuits of other examples. Further optional examples of the disclosure are set out below.

[0072] Ex1. A heating assembly for a dielectric heating aerosol-generating device, the heating assembly comprising: a heating region for receiving an aerosol-forming substrate; an electrode arrangement that forms a load capacitor for dielectrically heating an aerosolforming substrate received in the heating region; and a sensing element configured to sense a temperature in the vicinity of the heating region, wherein the sensing element comprises a magnetic material having a Curie temperature corresponding to a predefined temperature point for heating an aerosol-forming substrate.

[0073] Ex 2. A heating assembly according to Ex 1 , wherein the predefined temperature point is between 150°C and 250°C.

[0074] Ex 3. A heating assembly according to any of Ex1 or 2, wherein the sensing element is configured to physically contact an aerosol-forming substrate when received in the heating region.

[0075] Ex 4. A heating assembly according to any of Ex 1 to 3, wherein the sensing element is situated on an electrode of the electrode arrangement.

[0076] Ex 5. A heating assembly according to Ex 4, wherein the sensing element forms a layer or coating on an electrode of the electrode arrangement.

[0077] Ex 6. A heating assembly according to any of Ex 4 or 5, wherein the electrode comprising the sensing element has a floating potential.

[0078] Ex 7. A heating assembly according to any of Ex 4 or 5, wherein the electrode comprising the sensing element is grounded.

[0079] Ex 8. A heating assembly according to any preceding Ex, wherein the sensing element comprises a second magnetic material having a Curie temperature corresponding to a second predefined temperature point for heating an aerosol-forming substrate, wherein the second predefined temperature point is different from the predefined temperature point.

[0080] Ex 9. A heating assembly according to any of Ex 1 to 7, further comprising a second sensing element configured to sense a temperature in the vicinity of the heating region, wherein the second sensing element comprises a magnetic material having a Curie temperature corresponding to a P / 90750.W001 second predefined temperature point for heating an aerosol-forming substrate, wherein the second predefined temperature point is different from the predefined temperature point.

[0081] Ex 10. A heating assembly according to any preceding claims, wherein the electrode arrangement comprises a first electrode coaxially aligned with a second electrode.

[0082] Ex 11. A heating assembly according to Ex 10, wherein the first electrode comprises a tubular body having hollow centre and the second electrode comprises a rod or pin situated within the hollow centre of the first electrode.

[0083] Ex 12. A heating assembly according to Ex 1 1 , wherein the tubular body of the first electrode comprises one or more openings.

[0084] Ex 13. A heating assembly according to any of Ex 10 to 12, wherein the first electrode comprises a tubular body having a hollow centre and the second electrode comprises a tubular body having a hollow centre, wherein the second electrode is situated within the hollow centre of the first electrode.

[0085] Ex 14. A heating assembly according to Ex 13, wherein the tubular body of the second electrode comprises one or more openings.

[0086] Ex 15. A heating assembly according to any of Ex 10 to 12, wherein the first electrode comprises a plurality of axially aligned electrode rings and the second electrode comprises a rod or pin extending through the plurality of axially aligned electrode rings.

[0087] Ex 16. A heating assembly according to any of Ex 1 to 11 , wherein the electrode arrangement comprises a first electrode interdigitated with a second electrode.

[0088] Ex 17. A heating assembly according to Ex 16, wherein the electrode arrangement forms a flat plate.

[0089] Ex 18. A heating assembly according to any of Ex 16 or 17, wherein the first electrode and the second electrode each comprise a plurality of electrode portions, wherein the electrode arrangement comprises: a first plate comprising a first electrode portion interdigitated with a second electrode portion; and a second plate comprising a first electrode portion interdigitated with a second electrode portion.

[0090] Ex 19. A heating assembly according to any of Ex 16 to 18, wherein the first electrode comprises a first plurality of cylindrical segments and the second electrode comprises a second plurality of cylindrical segments, wherein each of the first plurality of cylindrical segments are positioned around the cylindrical axis separated by one of the second plurality of cylindrical segments.

[0091] Ex 20. A heating assembly according to any of Ex 16 to 18, wherein the first electrode comprises a first plurality of axially aligned electrode rings and the second electrode comprises a P / 90750.W001 second plurality of axially aligned electrode rings, wherein each of the first plurality of electrode rings are separated by one of the second plurality of electrode rings.

[0092] Ex 21 . A heating assembly according to any preceding Ex, wherein the sensing element consists entirely of the magnetic material.

[0093] Ex 22. An aerosol-generating device for dielectric heating of an aerosol forming substrate, the device comprising: a heating assembly according to any preceding Ex; and an inductor configured to form an inductive coupling with the sensing element.

[0094] Ex 23. An aerosol-generating device according to Ex 22, wherein the device further comprises a control unit configured to: detect a change in magnetic properties of the sensing element based on a detected change in impedance or conductance of the inductor; and adjust a power supplied to the heating assembly based on the detected change in magnetic properties of the sensing element.

[0095] Ex 24. An aerosol-generating device according to Ex 23, wherein the inductor is further configured to form an inductive coupling with the electrode arrangement and induce a current in the electrode arrangement for heating the aerosol-forming substrate.

[0096] Ex 25. An aerosol-generating device according to Ex 23, wherein the device further comprises a second inductor positioned in proximity with the electrode arrangement, the second inductor being configured to form an inductive coupling with the electrode arrangement and induce a current in the electrode arrangement for heating the aerosol-forming substrate.

[0097] Ex 26. An aerosol-generating device according to Ex 25, wherein the device comprises an electric field shield configured to shield the inductor from an electric field generated by the electrode arrangement.

[0098] Ex 27. A dielectric heating aerosol-generating system comprising: an aerosol-generating device according to any of Ex 23 to 26; and an aerosol-forming substrate situated in the heating region of the heating assembly.

[0099] Brief Description of Drawings

[0100] The invention will be further described, by way of example only, with reference to the accompanying drawings in which:

[0101] Figure 1 is a schematic illustration of a dielectric heating aerosol-generating system according to embodiments of the disclosure;

[0102] Figure 2 is a schematic illustration of an oscillation circuit for use in the dielectric heating aerosol-generating system of Figure 1 , according to embodiments of the disclosure; P / 90750.WQ01

[0103] Figure 3a-b are schematic illustrations of an oscillation circuit showing two different phaseshifting elements, one exemplarily implemented as a resonance circuit, one exemplarily implemented as a capacitive element, to achieve a 180 degrees phase shift;

[0104] Figure 3c is a schematic illustration of an oscillation circuit showing two different phaseshifting elements, one exemplarily implemented as a resonant cavity having parallel resonance properties, one exemplarily implemented as a capacitive element, to achieve a 180 degrees phase shift;

[0105] Figure 4 illustrates an oscillation circuit diagram according to embodiments of the disclosure;

[0106] Figure 5A-F illustrate how a Quartz-mimicking or Quartz equivalent circuit may be derived, as a non-limiting example of a parallel-resonant circuit, according to embodiments of the disclosure;

[0107] Figure 6 illustrates a frequency analyzer plot of a parallel resonant circuit showing the effect of the switching frequency on the phase shift and impedance of a parallel resonant circuit;

[0108] Figure 7 is an isometric illustration of a heating assembly, according to embodiments of the disclosure;

[0109] Figures 8A-B are cross-sectional illustrations of heating assemblies, according to embodiments of the disclosure;

[0110] Figures 9A-D are isometric and schematic illustrations of flat interdigitated electrode arrangements for use in a heating assembly, according to embodiments of the disclosure;

[0111] Figure 10 shows an isometric and schematic illustrations of tubular interdigitated electrode arrangements for use in a heating assembly, according to embodiments of the disclosure;

[0112] Figure 1 1 shows a schematic illustrations of an interdigitated electrode arrangement with a varying electrode separation distance, according to embodiments of the disclosure;

[0113] Figures 12A-D show isometric and schematic illustrations of tubular interdigitated electrode arrangements for use in a heating assembly, according to embodiments of the disclosure;

[0114] Figure 13A-D are schematic illustrations of an electrode arrangement having variable polarity control, according to embodiments of the disclosure;

[0115] Figure 14A-C are isometric illustrations of coaxial electrode arrangements for use in a heating assembly, according to embodiments of the disclosure;

[0116] Figure 15A is a schematic illustration of an inductor coil wound around an electrode arrangement, according to an embodiment of the disclosure;

[0117] Figure 15B is a schematic illustration of an inductor coil wound adjacent to an electrode arrangement, according to an embodiment of the disclosure;

[0118] Figure 16A is a schematic illustration of an inductor coil powered by a different oscillation circuit to the electrode arrangement, according to embodiments of the disclosure;

[0119] Figure 16B is a schematic illustration of an inductor coil powered by the same oscillation circuit powering the electrode arrangement, according to embodiments of the disclosure; P / 90750.W001

[0120] Figure 17 is a schematic illustration of an aerosol-forming substrate temperature sensing system comprising the electrode arrangement of figure 7, according to embodiments of the disclosure;

[0121] Figure 18 is a schematic illustration of a dielectric heating aerosol-generating system comprising a resonant cavity, according to embodiments of the disclosure.

[0122] Specific Description

[0123] Figure 1 is a schematic illustration of a combined dielectric and inductive heating aerosolgenerating system 100 according to an embodiment of the disclosure. The system 100 comprises an article 105 comprising an aerosol-forming substrate 110 and an aerosol-generating device 120 for heating the aerosol-forming substrate 1 10. The aerosol-generating device 120 comprises a heating assembly 130 having a heating region 140 for receiving the article 105. The heating region 140 and the article 105 are sized such that the aerosol-forming substrate 110 is in contact or in close proximity to an electrode arrangement within the heating assembly 130 when received within the heating region 140. Moreover, the electrode arrangement of heating assembly 130 forms part of a feedback loop of an oscillation circuit 150 via a first and second electrical contact 160, 165.

[0124] In other examples, the electrode arrangement of heating assembly 130 may form part of the article 105 comprising the aerosol-forming substrate 110. In such embodiments, a heating region between the electrode arrangement is sized such that, when the aerosol-forming article 105 is housed within the heating region 140, an electrical connection is made between the electrode arrangement and the first electrical contact 160, and with the electrode arrangement and the second electrical contact 165.

[0125] In some embodiments, the width of the article 105 comprising the aerosol-forming substrate 110 is slightly greater than the spacing between electrodes of the electrode arrangement, such that the distal end of the aerosol-generating substrate 110 is slightly compressed between the electrodes of the electrode arrangement. In some embodiments, the article 105, in an initial, uncompressed form has a width between 5-30% larger than the distance between the electrodes of the electrode arrangement. This may reduce or prevent the build-up of air between the electrodes of the electrode arrangement when the aerosol-forming article 105 is received in the heating region 140, and decrease a distance between electrodes of the electrode arrangement for dielectric heating, thereby improving dielectric properties of the load capacitor CL and the accuracy of any measurements or determinations of the dielectric properties of the aerosol-forming substrate 110 performed by the aerosol-generating device 120.

[0126] The aerosol-forming substrate 110 may comprise tobacco-based or non-tobacco based materials having an aerosol forming material therein and one or more active agents or ingredients, such as nicotine, pharmaceutical, botanicals, flavorants, liquid substrates with one or more active agents or ingredients, or a combination thereof. The aerosol-forming substrate 110 can also be a P / 90750.W001 liquid aerosol-forming substrate and thereby the aerosol-forming article 105 can be in the form of a cartridge, capsule, or liquid container, and the electrodes can be configured as a wicking element or capillary element for liquid transfer. For example, it is possible that electrodes form a capillary structure that is part of the aerosol-forming article 105 or reaches into an inner volume of the aerosolforming article 105 that can heat and vaporize a liquid aerosol-forming substrate 110 located in the inner volume. For example, the electrodes can be embodied as parallelly arranged plates separated by a distance that forms a capillary channel, for example in a range between 0.1 mm to 2mm, depending on the desired capillary strength or rise. The electrodes can be arranged as two matrices or arrays of pin-like, rod-like, or tab-like electrodes with opposite polarity, the two matrices or arrays interposed between each other, forming a capillary structure therebetween, for example with an average distance between neighbouring pin-like electrodes being in a range between 0.1 mm to 2mm, depending on the desired capillary strength or rise. In another variant, the wicking element can be a separate element that is interposed between two electrodes for example flat or slightly curved electrodes.

[0127] The aerosol-generating device 120 further comprises a power supply 170 and a controller 180 electrically coupled to the oscillation circuit 150. In this embodiment, the power supply 170 can be a rechargeable lithium ion battery, for example with one or more lithium ion battery cells, and the aerosol-generating device 120 comprises a power connector that enables the aerosol-generating device 120 to be connected to a mains power supply for recharging the power supply. Providing the aerosol-generating device 120 with a power supply, such as a battery, enables the aerosolgenerating device 120 to be portable and used outdoors or in locations in which a mains power supply is not available.

[0128] In use, power is supplied to the oscillation circuit 150 from the power supply 170 when a user activates the aerosol-generating device 120. In this embodiment, the aerosol-generating device 120 is activated by a user pressing an activation button (not shown) that can be provided on an external surface of the aerosol-generating device 120. It will be appreciated that in other embodiments, the aerosol-generating device 120 may be activated in another manner, such as on detection of a user drawing on a mouthpiece (not shown) by a puff sensor provided on the mouthpiece, or a user holding the aerosol-generating device 120. When power is supplied to the oscillation circuit 150, the oscillation circuit 150 generates an alternating electric field across the heating region 140 of heating assembly 130 to dielectrically heat the aerosol-forming substrate 1 10 in the heating region 140 to release volatile compounds.

[0129] The aerosol-generating system 100 further comprises an induction coil 190 positioned to sense a change in magnetic properties of the heating assembly 130. In some embodiments, the induction coil 190 may also be configured to inductively heat the electrode arrangement in the P / 90750.W001 heating assembly 130. In other embodiments, the inductor coil may comprise an electric field shield configured to shield the inductor from an electric field generated by the electrode arrangement.

[0130] The aerosol-generating system 100 is also configured for measuring a dielectric property of the aerosol-forming article 105 or the aerosol-forming substrate 1 10 using the electrode arrangement employed for dielectric heating of the aerosol-forming substrate 110. In some examples, the electrode arrangement can be used for dielectric measurements, either during the heating process or separately to the heating process. In this embodiment, the aerosol-generating system 100 can be configured to determine the presence of the aerosol-forming article 105 between the electrode arrangement. The aerosol-generating system can be configured to measure a dielectric property, for example an instant value, timely-evolution, or change of a dielectric property, for example to determine whether the aerosol-forming article 105 meets specific criteria or is an authentic substrate. The aerosol-generating system in this example is also configured to control the heating of the aerosol-forming substrate 110 based on the measured dielectric property of the aerosol-forming article 105.

[0131] Figure 2 is a schematic illustration of an oscillation circuit 250 for use in the aerosolgenerating system 100 of Figure 1 , according to an embodiment of the disclosure. Oscillation circuit 250 comprises a switching unit 260 interconnected with a resonator feedback loop 270 to provide for a self-oscillating signal to the switching unit 260. The switching unit 260 comprises a single transistor, such as a bipolar junction transistor (BJT) or a field effect transistor (FET).

[0132] The oscillation circuit 250 can further comprise a choke 280 that acts on an input to the feedback loop 270 to provide for a stimulation signal, for example a stimulation voltage. The oscillation circuit also comprise a biasing unit 290 acting on the feedback loop 270 for providing a variable or controllable biasing signal, for example a biasing voltage for setting the operating conditions. In the variant shown, the feedback signal can be described as a voltage. The output voltage UOUT of the switching unit 260 is coupled to the feedback loop 270 providing a feedback switching signal in the form of a voltage UIN to the switching unit 260. The configuration of the feedback loop 270 is such that the output signal, e.g. the voltage UOUT of the switching unit 260 can undergo a phase change and arrives inverted at the input UIN of the switching unit 260 for resonant oscillation. In other configurations, a current could be used as the feedback signal with a switching unit 260 comprising a BJT.

[0133] The feedback loop 270 is configured to be self-oscillating and will oscillate at or close to a given resonance frequency determined by the values of the passive components of the feedback loop 270. Feedback loop 270 is configured to provide a 180° phase shift from the output UOUT to input UIN of switching unit 260 for oscillation, and in addition, the transistor T is configured for inverting operation. P / 90750.W001

[0134] As shown in Figures 3a and 3b, feedback loop 270 includes a resonant circuit 272 comprising the load capacitor CL providing for a first 90 degrees phase shift or quarter wave shift to the feedback signal. Feedback loop 270 further includes a capacitive element 274 providing for a second 90 degrees phase shift or quarter wave shift to the feedback signal, such that the feedback signal reaching the input of the switching unit 260 is inverted and phase-shifted by 180 degrees. Switching unit 260 is itself configured for inverted switching operation to provide a 180 degree phase shift between the input UIN and the output UOUT of the switching unit 260.

[0135] Resonant circuit 272 comprises the first and second electrodes 130, 135, together forming a load capacitor CL. When an aerosol-forming substrate 110 is situated within the heating region 140 of the heating assembly 130, it forms part of the load capacitor CL. Importantly, the load capacitor CL is formed in the feedback loop 270, and not at a separate output or part of a separate circuitry that is connected to the switching unit 260. This enables a high-frequency oscillating voltage to be created across the electrodes of load capacitor CL , which is needed for sufficient and efficient dielectric heating of the aerosol-forming substrate 110, without having an additional output or circuit to the already resonating feedback loop 270, which would create unnecessary losses and circuit complexity. The resonant circuit 272 may comprise a series resonator circuit or a parallel resonator circuit, examples of which are described in greater detail below.

[0136] In an alternative embodiment, resonant circuit 272 may include a resonant cavity 272, as illustrated in Figure 3c. The resonant circuit 272 including resonant cavity may have an interior volume configured to receive an aerosol-forming substrate 1 10, for example having an opening for inserting an aerosol-forming substrate 1 10. In an example, the resonant circuit 272 including resonant cavity can be configured as a A / 4 resonator. The resonant circuit 272 including resonant cavity may be configured to behave like an RLC circuit. The inductor L and the capacitor C are arranged in parallel to each other, to have a parallel resonance or a frequency close to the parallel resonance that can be stimulated by the switching unit 260. Resonant circuit 272 including cavity may be coupled to the feedback loop 270 using one or more of a capacitive coupling, an inductive antenna coupling (magnetic coupling), a direct electric coupling, or a window coupling (e.g. coupling with a loop).

[0137] The resonant circuit 272 including resonant cavity can have any shape, but preferably has a cylindrical shape or a rectangular parallelepiped shape. In one embodiment, the resonant cavity can be configured as a split-ring resonator.

[0138] Figure 4 illustrates an oscillation circuit 350 according to a non-limiting, exemplary embodiment of the disclosure. Oscillation circuit 350 comprises a switching unit 260 in the form of a transistor T having an intrinsic capacitance Ci. Moreover, transistor T is configured for inverting operation, for example as an inverting common source FET, MOSFET, or a common emitter BJT. The source terminal of transistor T can be coupled to a DC power supply via a choke 280. Between P / 90750.W001 the gate and source terminals of transistor T extends a feedback loop 270. The feedback loop 270 comprises a resonant circuit 272 including a load capacitor CL having a first and second electrode 130, 135 separated by an aerosol-forming substrate 110. In the variant shown, the resonator circuit 272 is also connected to ground via a delay line D and a capacitor C2 connected in series to the delay line D . The circuit 350 further comprises a biasing unit 290 coupled to the gate terminal of the transistor T via the delay line DL. AS shown in Figure 4, the biasing unit 290 is electrically connected between the delay line DL and the capacitor C2, so that the biasing unit 290 is somewhat isolated from the high oscillation frequency of the feedback loop 270.

[0139] The delay line D is a time delay element, for example an element that has inductive behavior, for slowing down the arriving voltage wave from the feedback loop 270 during a period of the oscillation. This allows to tune the resonant circuit 272 to a desired switching and oscillation frequency, to move the oscillation frequency away from the natural resonant frequency given by the resonant circuit 272. This ensures that oscillation circuit 350 remains in a predefined frequency operating range to provide for the requisite inverted or 90° phase shifted feedback and also to make sure that the feedback loop has a low impedance to provide for a high gain, as described in greater detail below.

[0140] The oscillation circuit 350 is shown with electrical contacts 160, 165 that are arranged on each side of the load capacitor CL. In some embodiments, the heating assembly 130 may be removable from the oscillation circuit 350, or may form part of the aerosol-forming article 110. In such embodiments, electrical contacts 160, 165 provide an electrical connection between the heating assembly 130 and the feedback loop 270. In embodiments where the load capacitor CL is fixed within the feedback loop 270, for example, such that an aerosol-forming substrate 110 can be inserted and removed to and from the heating region 140 the heating assembly 130, electrical contacts 160, 165 provide electrical connections from the heating assembly 130to the next components in the feedback loop 270, e.g. inductors Li and L2. In the illustrated embodiment, one or both inductors Li and L2may be used to inductively heat the electrode arrangement of the heating assembly 130.

[0141] With respect to the power supply voltage, a DC power supply voltage is provided, that is preferably in a range that is suitable for battery operation with one or more standard battery cells. Preferably, the DC power supply voltage is below 14V. For example, it is possible to operate the oscillation circuit 350 on a single battery cell, for example an 18650 battery cell (Li-Ion), or a similar battery cell, that provides for 3.2V to 3.9V. However, more preferably, a voltage of one battery cell of an exemplary 3.5V to 7V for power supply can be boosted, for example by a DC-DC converter (e.g. a boost circuit), or a voltage doubler. Alternatively or in addition, two or more battery cells can be used in series, or other configurations or arrangements that allows to increase a voltage from one or more battery cell can be used. It is also possible to have a controllable output voltage (e.g. DC- DC converter, voltage regulator), to control the temperature of heating by a change to the DC supply P / 90750.W001 voltage, or to boost the voltage (for example to 10-12V) for maximum power at the preheating stage, to speed up the preheating stage with the goal to reach the aerosolization temperature quickly. Control of the DC supply voltage is one way that makes it possible to rapidly change heating power despite the oscillation circuit 350 freely oscillating.

[0142] A capacitor Ci is arranged in parallel to the transistor T and therefore in parallel with the intrinsic capacitor of the transistor T (e.g. a field effect transistor). This facilitates a less voltagedependent oscillation and frequency, stabilizes the oscillation, and also improves the overall dielectric heating efficiency. Capacitance of capacitor Ci is chosen to be larger than the maximal intrinsic capacitor Ci of transistor T at the operating conditions, so that the variation of the intrinsic transistor based on frequency, temperature, etc. has much less or negligible influence on the feedback loop 270. For example, in a non-limiting embodiment, the value can be in a range between 2pF to 10OpF, more preferably in a range between 5pF and 50pF.

[0143] Capacitive element 274 comprises a capacitor C2 arranged at the output or end of the resonant circuit 272. In one embodiment, capacitive element 274 comprises more than one capacitor. As described above, capacitive element 274 has the function of providing a 90° phase shift to the feedback voltage of feedback loop 270 with minimized losses or other undesired effects, and it therefore needs to have a high-quality factor or Q factor, preferably above 1000 at 100MHz. The capacitance value for C2 of the capacitive element 274 should be relatively high as compared to Ci, for example in a range between 500pF to 100nF, more preferably between 1 nF and 50nF, which leads to a low impedance of capacitive element 274. In one embodiment, the capacitive element 274 can be implemented as a RC network to provide for the 90° phase shift, for example using two single-resistor-capacitor networks, having two capacitors in the feedback loop, each capacitor connected to ground via a resistor.

[0144] Resonant circuit 272, together with capacitive element 274, provides for a 180° phase shift and a voltage gain from the output UOUT to the input UIN, and transistor T (for example a FET) is configured for inverting operation, thereby also providing for another 180° phase shift. This results in a resonant or close-to resonant oscillation and an amplified voltage UL across the electrodes 130 and 135 of the load capacitor CL, as compared to the DC supply voltage. When operating close to resonance, the resonant circuit 272 circuit behaves inductively, having a high Q factor. Furthermore, the feedback loop 270 is impedance-matched with the transistor T, to provide for a high gain, leading to an increased voltage across the load capacitor CL. Also, preferably, this gain is achieved without the use of an additional voltage or current amplifying passive element, such as a tapped inductor or a transformer located in the circuit that forms the feedback loop 270, as such passive elements are difficult and lossy to operate and design at frequencies greater than 50 MHz.

[0145] The combination of capacitor Ci, the feedback loop with resonant circuit 272 and capacitive element 274 can also be described as a bandpass filter or Pi or TT network that generates a 180° P / 90750.WQ01 phase shift. In the illustrated embodiment, the resonant circuit 272 of the feedback loop 270 is not connected to ground, but is suspended with ends at each capacitor Ci and C2, thereby not having a direct ground connection at either end of resonant circuit 272, reducing stray elements and ground influences for more predictable operation.

[0146] At the operating frequency, the resonant circuit 272 including load capacitor CL acts as an inductive load providing a first 90° phase shift, also referred to as a quarter-wave phase shift, and capacitive element 274 exemplarily including a high quality factor capacitor C2 connected to ground, provides for the second 90° phase shift or quarter-wave phase shift.

[0147] Oscillation circuit 350 can be described or characterized as a Pierce oscillation circuit with a modified feedback loop 270, where the physical Quartz element is replaced by a Quartz-mimicking or Quartz electric equivalent circuit to provide for an inverting feedback to the switching unit 260 that also operates in an inverted mode. In some embodiments, oscillation circuit 272 can be based on other resonant feedback loop oscillation circuit configurations, for example, but not limited to, the use of a Colpitts or Hartley type oscillator, using an inverting transistor T.

[0148] Figures 5A to 5F illustrate how a Quartz-mimicking or Quartz equivalent circuit may be derived using a variant of a parallel resonator circuit PRC, that can serve as an exemplary and nonlimiting embodiment as resonant circuit 272. A Quartz-mimicking or Quartz equivalent circuit can have a parallel resonance at a given frequency. This can be seen as a circuit with two branches, one representing the mechanical oscillation and one representing the electric behavior, as illustrated in figure 5A and 5B. The mechanical oscillation is represented by a first branch having load capacitor CL and an inductor LTOT. The electric oscillation is represented by a second branch arranged in parallel to the first branch, having a Capacitor CE. This configuration leads to a series connection of two capacitors CL and CE (seen around the loop formed by the two branches) so that CE will decrease the overall capacitive value of the equivalent circuit. Also, this circuit provides an inductive phase shift of about 90° within certain defined frequency range.

[0149] Referring now to Figure 5C, one branch of the parallel resonator circuit PRC comprises an inductor LTOT and the load capacitor CL connected in series of the first branch. This branch can be improved by splitting LTOT into two inductors Li and L2on each side of the load capacitor CL, as shown in Figure 5D, to provide a split inductor or split-coil design and a more symmetric application of the voltage UL across the load capacitor CL, thereby improving dielectric heating efficiency. To provide for parallel resonance, the capacitor CE of the second branch can be replaced with an inductor (as shown in Figure 5F) due to capacitor CE‘S minimal capacitive effect on CL.

[0150] In a non-limiting example starting from the split inductor Li and L2of the resonant circuit of Figure 5D, inductors Li and L2can be mutually magnetically coupled to form a mutual inductance M, thereby forming the parallel circuit branch or second branch of the resonant circuit 272, as shown in Figure 5E. The mutual magnetic coupling can be achieved by the close proximity of the two inductors P / 90750.WG01

[0151] L1 and L2 with alignment of winding axis of the coils, or by use of a mutual magnetic core, or both. This has the advantage of providing a parallel-resonator circuit PRC without the use of additional wires for the second branch, and without additional windings or separate magnetic cores for a second parallelly-arranged inductor. This also allows for a symmetric arrangement that favors and facilitates the inductive coupling of the two inductors Li, L2and the balancing of the voltage UL over load capacitor CL. The symmetry of the two branches in either direction with first branch Li - CL - L2and the second branch with inductor LE, representing the two mutual inductance values, facilitates the symmetrical balancing of the voltage over the electrodes of the load capacitor CL, which consequently reduces losses created at the load capacitor CL. This split inductor principle can also be referred to as a split coil resonator.

[0152] The resonant circuit 272 could also be implemented as shown in the Figure 5F, where the mutual inductance M (seen two times due to the mutuality) is replaced by a separate inductive element, for example inductor LE.

[0153] The values of components in this resonant circuit 272 are preferably chosen to be in the following exemplary and non-limiting ranges. LTOT can be a range between 10nH to 50nH, more preferably between 15nH and 40nH, which is the equivalent of Li plus L2, LEcould be in a range between 7nH and 30nH, more preferably between 10nH and 20nH, and the value of the load capacitor can be in a range between 0.5pF to 5pF, more preferably between 1 pF to 3pF.

[0154] The resonant circuit 272 can be configured as another type of tank circuit providing for the 90° phase shift in a given frequency range. In one embodiment, the resonant circuit 272 can be implemented as a series resonant circuit, having the load capacitor CL connected in series with one or more inductive elements, configured to provide for an inductive response or 90 degrees phase shift in a given frequency range that is suitable for dielectric heating.

[0155] In order to produce the required dielectric losses in the load capacitor CL, a high frequency is needed. The dielectric losses will increase somewhat proportionally to the frequency (in this case the oscillation frequency fsof the oscillation circuit) of the voltage applied to the load capacitor CL. However, higher switching frequencies fslead to greater switching losses in the transistor. Where very high switching frequencies are used, e.g. 1 GHz or more, expensive circuit designs are necessary to make the circuit operable (e.g. GaAn transistors, GHz-type circuit design e.g.).

[0156] To compensate for a lower switching frequency, a higher oscillation AC voltage UL (for example measured by the RMS or peak voltage) can be provided across the load capacitor CL to deliver the necessary power to the load capacitor CL. When a balance has to be struck between increasing the switching frequency fsand increasing the voltage over the load capacitor CL in order to increase the heating power (and therefore dielectric losses PL in the load capacitor CL which can include the aerosol-forming substrate 110), the voltage increase has a stronger effect on the heating power than frequency increase, as voltage has a second order relationship with power. The dielectric P / 90750.W001 losses in load capacitor CL are also dependent on the distance separating the two electrodes 130 and 135, which influences the electric field strength EFacross the aerosol-forming substrate 1 10.

[0157] For mobile portable designs of dielectric heater that are handled by a human, safety considerations with respect to voltage insulation and potential dielectric breakdown due to contamination and general inhomogeneous material of the substrate material S of the aerosolforming substrate 110 are a serious concern. Therefore, there are working ranges for switching frequency fs and electric field strength EF, for a hand-held and human-operated portable device The electric field strength is dependent on voltage UL applied to capacitor CL and a maximal distance d between electrodes of the electrode arrangement.

[0158] It is preferable that the switching frequency is limited to a certain range, firstly to ensure sufficient power losses PL across the load capacitor CL, and secondly to avoid excessive switching losses. Limiting the value of fsenables the use of straightforward circuit design, for example but not limited to the use of a LDMOS or other standard transistor used for RF circuits. Preferably, the switching frequency should be in a range between 100MHz and 1.2 GHz, more preferably between 150MHZ to 1 GHz, more preferably between 200MHz and 900MHz. At the same time, the maximal- value of electric field strength between the electrodes of the load capacitor CL should be limited to a reasonable value that allows for simple electric insulation materials and designs, taking into account impurities and inhomogeneous substrate designs, the use of thin electrodes that may be located in close proximity to each other (for example but not limited to 1 mm-10mm), potential exposure or close proximity to human body, and potential improper human manipulation. Preferably the average electric field strength across the electrodes of the load capacitor is maximally 120V / mm, more preferably maximally 100V / mm, even more preferably maximally 80V / mm.

[0159] Preferably, during nominal heating operation (not during a start-up or warm-up phase that lasts less than 30 seconds where the efficiency can be lower), the heating efficiency should be at least 60% (desired power losses PL versus all the other losses, which can include switching losses of transistor T, losses caused by biasing circuit and choke, inductive-resistive losses of the inductors Li and L2, capacitive-resistive losses from capacitors Ci and C2, and resistive losses of electrodes Ei and E2and the wiring). As an example, the overall power could be 10W, while the effective power or heating losses PL should be 6W or more, with 4W or less of non-heating losses or other heating losses not caused in the substrate 1 10 between the first and second electrodes 130, 135. More than 6-7W of power losses is not desirable for a handheld device. Preferably the aerosol-generating device is configured such that there are less than 5W of losses during nominal heating operation or any other operation lasting for more than 30 seconds. The average dielectric heating power density provided by the aerosol-generating device may be in a range between 1 W / cm3 to 25W / cm3 per volume of aerosol-forming substrate material over a time period of less than 15 minutes, preferably between 1.5W / cm3 and 15W / cm3. P / 90750.W001

[0160] During an initial start-up phase, the average dielectric heating power density may be controlled or set to operate in a range between 7W / cm3 to 25W / cm3. During a nominal (maintenance) heating phase, the average dielectric heating power density may be controlled or set to operate in a range between 1 W / cm3 to 7W / cm3. Preferably, during the start-up phase, the average dielectric heating power density is controlled or set to operate in a range between 8W / cm3 to 20W / cm3. Preferably, during the nominal heating phase the average dielectric heating power density is controlled or set to operate in a range between 1 W / cm3 to 5W / cm3.

[0161] To have a proper inverting effect and a 180° phase shift on the feedback loop 270 between UIN and UOUT, the oscillation circuit 350 must remain in a frequency operating range where the behavior of the feedback loop 270 is highly inductive. In the example comprising a parallel resonator circuit (PRC), the series resonance frequency fsER (resonant frequency) is relatively close to the parallel resonance frequency fpAR (antiresonant frequency). If the oscillation frequency fs of the PRC exceeds the parallel resonance frequency fPAR, the feedback loop 270 will act capacitively and not provide the necessary phase inversion to the feedback loop 270. Furthermore, the equivalent impedance of the circuit will increase to an extent that is too high for efficient dielectric heating as the oscillation circuit 350 will not be able to provide a high signal gain.

[0162] Oscillations in the feedback loop 270 will be naturally drawn towards the parallel resonance (antiresonant) frequency of the resonant circuit 272. However, the addition of a delay line D can introduce a slight time delay limiting the oscillation frequency below the parallel resonance frequency. Figure 6 shows a frequency analyzer plot of an exemplary resonant circuit 272, specifically a plot of a parallel resonator circuit PRC showing the relationship between the oscillation frequency (with a series resonance at 855 MHz and a parallel resonance at 1 .246 GHz), the phase shift across the PRC (with a relatively flat inductive 90° degrees frequency response between the two resonant frequencies) and the effective impedance of the PRC. More specifically, it can be seen from Figure 6 that the 90° phase shift starts dropping before the parallel resonance frequency fPAR is reached. After the parallel resonance frequency fpAR, the phase shift response drops below 0° to capacitive behavior and the impedance is very high, e.g. 2.4kO. The ideal operating frequency range is closer to the series resonance frequency fsER where the phase shift is still 90° and the impedance response is low. The impedance of the resonant circuits at the operating frequency of the oscillation circuit may be between 0.5Q and 10O, preferably between 10 and 50, and more preferably, between 1.50 and 30. The parallel resonance frequency fPAR can be above 1 GHz, e.g. 1 GHz to 1.5GHz, while the actual switching frequency fs can be below 1 GHz, and this lower switching frequency is caused by the delay line DL.

[0163] Ideally, the oscillation frequency fs should be set to be below the parallel resonance frequency fPAR but above the series resonance (or resonant) frequency fsER, to make sure that two conditions are fulfilled, firstly (i) that the resonant circuit behaves inductively to provide a 90° phase P / 90750.WG01 shift, and secondly (ii) to make sure that the impedance of the resonant circuit (an therefore the feedback loop 270) is low, as illustrated in the graphs of FIG. 6. For example, a resulting impedance of the feedback loop at the oscillation frequency fs of the oscillation circuit can be in a range of approximately 100mQ to 2Q. Preferably, the delay line DL is configured such that the oscillation frequency fs is closer to the series resonance frequency fsER than to the parallel resonance (or anti- resonant) frequency fPAR, thereby maintaining a low resonant circuit impedance while operating at a frequency range where the resonant circuit provides the 90° phase shift. The time delay caused by delay line DL needs to be relatively short, as the series resonance and the parallel resonance of a parallel oscillating circuit PRC are close to each other, relative to the overall frequency range. Preferably, the delay caused by delay line DL that acts of feedback loop 270 should be in a range between 5% to 35% of the period of the parallel resonance frequency fPAR, providing that the above two conditions (i) and (ii) are fulfilled. In an embodiment, the delay caused by the delay line DL that acts on feedback loop 270 is in a range between 35% and 90% of a difference between the period of the parallel resonance frequency fPAR and the period of the series resonance frequency fsER, again providing that the above two conditions (i) and (ii) are fulfilled, more preferably a range between 50% and 85%. For example, taking the illustration of FIG. 6 and as a non-limiting numerical example, assuming that a parallel resonance frequency is at 1.25 GHz, therefore having a period of 800ps (picoseconds), and a series resonance is at 855MHZ, and therefore a period of 1 169ps, there is a difference of 369ps between the period of fPAR and fsER- The time delay caused by delay line DL can be in the above range, for example at 70% of the period difference between fPARand fsER, thereby being 258ps, thereby making sure that the feedback loop 270 has the desired inductive behavior and low impedance that is necessary to provide inverting feedback at high gain.

[0164] Preferably, the delay line is implemented as a meandering conductive element having dominantly inductive behavior, for example a meandering element having from two (2) to twelve (12) meandering branches, more preferably from three (3) to eight (8) meandering branches. Such implementations exhibit minimal stray inductive and capacitive behavior. Various delay line structures can be used to provide the desired function, for example an Omega-shaped coil, single planar coil, flat inductor, wavy line, zig-zag line, or a sawtooth line. It is also possible to provide the required delay line functionality by a specific transmission line design. For example, it is possible that the physical element of the delay line DL is implemented as a conductor in a printed circuit board, for example implemented as a microstrip patch antenna. In some embodiments, a low-pass filter may be used as the delay line DL, however this will have an impact on the shape of the oscillating voltage, whereas a delay line DL that provides for a short time delay by inductive effect will not impact the wave shape. In the embodiment illustrated in Figure 4, delay line DL is placed between the feedback loop output of the resonant circuit 272 and capacitive element 274, but other arrangements are also possible. P / 90750.W001

[0165] Figure 7 shows an isometric illustration of a heating assembly 130, for use in the aerosol generating system 100 of Figure 1. The heating assembly 130 comprises a tubular electrode arrangement made up of four electrodes E1 a, E1 b, E2a, E2b. The tubular electrode arrangement defines a hollow centre which forms a heating region 140 for receiving an article 105 comprising an aerosol-forming substrate 120. The heating assembly 130 further comprises a sensing element 135 configured to sense a temperature of the heating region 140. The sensing element 135 comprises a magnetic material having a Curie temperature corresponding to a predefined temperature point for heating an aerosol-forming substrate 120.

[0166] In the embodiment illustrated in figure 7, the sensing element 135 is provided as a layer on an electrode E2a of the tubular electrode arrangement. In some embodiments, a sensing element 135 may be provided on more than one, or in some cases, all electrodes of the electrode arrangement. This may enable detection of temperature differences across different locations in the heating region 140.

[0167] Figure 8a illustrates cross-sectional illustration of a heating assembly 130, according to an embodiment of the disclosure wherein an electrode of the tubular electrode arrangement is formed from the magnetic material, thereby also forming a sensing element 135. In such embodiments, this sensing element electrode 135 may also be supplied to provide an alternative electric filed for dielectric heating. Alternatively, the sensing element electrode 135 may be used as a “dummy electrode” having a floating electrical potential, or may be grounded. In some embodiments, each electrodes of the electrode arrangement may comprise the magnetic material such that each electrode also acts as a sensing element electrode 135.

[0168] In some embodiments, such as that shown in figure 8b, the sensing element 135 may not be integral to electrodes of the electrode arrangement, but rather provided as a separate component positioned close to the heating region 140. In the embodiment of figure 8b, the sensing element 135 is configured to be in physical contact with an aerosol-forming article 105 received within the heating region 140 of the heating assembly 130. In some embodiments (not shown), the sensing element 135 may be in physical contact with a heat transfer element, which in turn, is in physical contact with an aerosol-forming article 105 received within the heating region 140 of the heating assembly 130. In some embodiments, a plurality of sensing elements 135 may be provided in different locations around the heating region 140 of the heating assembly 130. The sensing element 135 in the embodiment of figure 8b is connected to ground. In other embodiments, the sensing element may have a floating electrical potential.

[0169] As such, it will be appreciated that the sensing element 135 may take on a variety of forms and be positioned in a variety of locations within a heating assembly 130 in order to effectively sense a temperature within the heating region 140. It will also be appreciated that the disclosed sensing P / 90750.W001 element from figures 7-8 may be implemented in heating assemblies comprising numerous types of electrode arrangements, including those set out below in each of figures 9-14.

[0170] Figures 9A-D are schematic illustrations of flat interdigitated electrode arrangements for use in a heating assembly, according to embodiments of the disclosure. The use of interdigitated electrodes allows for a more homogenous electric field generation, which can be used to avoid hot spots across an aerosol-forming substrate. Figure 9A shows an electrode arrangement comprising two electrodes. A first electrode comprises one or more extended portions and a second electrode comprises a corresponding one or more recessed portions for receiving the one or more extended portions of the first electrode. In other some examples, both the first and second electrodes each comprise a combination of extended portions and recessed portions configured to align with corresponding recessed portions and extended portions in the opposing electrode.

[0171] Figures 9B and 9C show electrode arrangements comprising a plurality of electrodes for each polarity wherein each electrode is positioned adjacent to electrodes of the opposite polarity.

[0172] The shape and geometry of the electrodes may vary however, it is preferable that the edges and corners of the electrodes are rounded, e.g. having a radius in range of about 0.15 mm to 2.5 mm, to “soften” the peaks of the electric field at the edges and corners.

[0173] As shown in Figure 9D, it is possible to make an interdigitated electrode arrangement for one- side flat aerosol-forming substrate 110. However, dielectric heating may be improved by providing a second electrode arrangement identical to the electrode arrangement shown in Figure 9D on an opposite side of the aerosol-forming substrate 1 10. The electrodes of the second electrode arrangement can be configured to align with electrodes of the first electrode arrangement having an opposite polarity.

[0174] Alternatively, as shown in Figure 10, the interdigitated electrode arrangement may comprise a first and second electrode configured to interdigitate together around a cylindrical axis to form a tubular structure. In this embodiment, there are two pairs of three digits of the electrodes. Preferably, thehe tubular structure can have a diameter between 5mm to 9mm. The tangential distance between the electrodes of opposite polarity can be between 0.5 mm to 3 mm, preferably between 0.7 mm to 12.2 mm.

[0175] Figure 11 illustrates an embodiment in which the distance between electrodes of opposite polarity varies across different regions of the electrode arrangement. This may be advantageous to modify the strength of the electric field in different regions of the electrode arrangement, thereby modifying the heating power delivered to different regions of an aerosol-forming substrate 110 heated using the electrode arrangement, to provide for sectional, zoned or partial heating.

[0176] Figures 12A-B show isometric and schematic illustrations of tubular interdigitated electrode arrangements for use in a heating assembly, according to embodiments of the disclosure. The electrode arrangement in Figures 12A-B comprises a series of axially aligned electrode bands P / 90750.W001 positioned adjacent to electrode bands having opposing polarities. In such embodiments, the aerosol-forming substrate 1 10 is not positioned directly between opposing electrodes, but is still heated by the presence of the alternating electric field in its proximity. Stronger and more uniform heating of the aerosol-forming substrate 110 may be achieved using the electrode arrangement shown in Figure 12B, which is configured such that electrical field between opposing polarity electrodes is strongest across the aerosol-forming substrate 1 10. Figures 12C-D illustrate how the plurality of electrode portions from the electrode arrangements of Figure 12A-B may be electrically connected to achieve an interdigitated configuration.

[0177] Figure 13A-D are schematic illustrations of an electrode arrangement having variable polarity control for use in a heating assembly, according to embodiments of the disclosure. By the use of an analog signal demultiplexer or analog signal switch or an equivalent circuit, it is possible to selectively connect one or more pairs of electrodes to an oscillating feedback loop to deliver sectional heating to the load capacitor CL. In the illustrated embodiment, adjacent electrodes can be switched to have the same polarity, or opposing electrodes can be switched and reconfigured to the same polarity. This enables an oscillation circuit to switch between different electric field distribution patterns between the electrodes to adjust the heating profile across the aerosol-forming substrate 110. In the embodiment shown in Figures 13A to 13B, the electrodes form cylindrical segments that can be arranged around a cylindrically-shaped heating region for different electric-field patterns. This principle also works for other numbers of electrode pairs, e.g. two (2) pairs, three (3) pairs, or four (4) pairs, etc., and for sectional, zoned, or partial heating of areas or volumes of an aerosol-forming substrate 110. The analog signal switch or analog signal demultiplexer can be implemented electronically, mechanically, or electro-mechanically. For example, a semiconductor-based or solid state switch or demultiplexer can be based on JFET switches or a bilateral parallelly-arranged CMOS switch, combining PMOS and NMOS. An electromechanical based switch or demultiplexer can be based on a microelectromechanical systems (MEMS), for example using a RF MEMS switching technology, and a mechanical switch or demultiplexer can be based on relays, for example RF microrelays. In some embodiments, more than one oscillation circuit may be used. For example, a separate oscillation circuit may be provided for each pair of electrodes in the electrode arrangement.

[0178] Figure 13D illustrates how electrodes of the electrode arrangement from the system of Figure 13C may be independently energized to provide sectional, zoned, or partial heating of a cylindrical substate 110. In the illustrated embodiment, there are four (4) opposing electrodes, each neighboring pair of electrodes configured to be connected to an oscillation circuit 150, 250, 350, or another type of oscillation circuit. This enables the selective heating of a segment area or zone of the cylindrical substrate 110 with heating zones HZ that can be moved by 90 degrees for each electrode pair. The size of the heating zones may be modified by changing the geometry of the electrodes or the number of electrode pairs in the electrode arrangement. P / 90750.W001

[0179] For this configuration shown in Figure 13D and for other configurations that are intended to heat cylindrical consumables, an aerosol-forming article 105 comprising an aerosol-forming substrate 1 10 may form a hollow cylinder, having an interior hollow cylindrical volume. This aerosolforming article geometry may be beneficial since lower dielectric losses occur at areas that are located farther away from two electrode plates Ei and E2having opposite polarity. The inner hollow cylinder can have a diameter of that is in a range between 20% and 80% less that the outer diameter of the aerosol-forming article 105, more preferably in a range between 25% and 60% less that the outer diameter of the aerosol-forming article 105, even more preferably between 25% and 45% less that the outer diameter of the aerosol-forming article 105. In one embodiment, the inner core of the cylindrical aerosol-forming article 105 may be filled with an aerosol-forming material or a filler material that has a higher dielectric constant than the aerosol-forming material of the outer cylinder portion. In some embodiments, the inner core of the aerosol-forming article 105 could have a higher content of an aerosol-forming carrier liquid, such as glycerol or polypropene glycol (PPG), having high dielectric constants. Such an arrangement can increase the dielectric losses in the core area for further aerosol generation, or provide a filler material that could generated additional heat by dielectric losses, the heat capable of propagating from the inner core to the lateral sides into the outer cylindrical portion.

[0180] As another variant, it is also possible that a penetrating pin, rod, or blade is provided with the aerosol forming device 100, arranged centrally in the heating region. The penetrating pin, rod, or blade can be made or coated with a material having a high dielectric constant. The penetrating pin, rod, or blade can be configured and arranged such that it penetrates substantially into a central axis of the aerosol-forming substrate 1 10, when the aerosol-forming article 105 is inserted into the heating region. Preferably, the material chosen for the pin, rod, blade or the coating thereof should have a high dielectric constant, for example above 20, be non-conductive, and have good heat radiation properties and thermal stability, for example but not limited high-entropy or high dielectric ceramics. Such pin, rod, or blade could act as a passive heater that would heat up in the oscillating electric fields, improving the heating performance in the centre of the cylindrical aerosol-forming article 105.

[0181] Figure 14A-C shows isometric illustrations of coaxial electrode arrangements for use in a heating assembly, according to embodiments of the disclosure. The electrode arrangement of Figure 14A comprises a first electrode tube, pin, or rod Ei and a second electrode E2tube having a larger diameter than the first electrode tube, pin or rod Ei. The electrode arrangement is configured such that an aerosol-forming substrate may be situated between the first electrode Ei and second electrode E2when coaxially aligned. Aerosol generated from the aerosol-forming substrate 110 can escape in a direction that is parallel to the rotational or cylindrical axis of the substrate, or can also escape laterally from the cylindrically shaped second electrode E2. However, it is also possible that the first electrode Ei can comprise one or more openings leading to a central airflow channel running P / 90750.W001 through the centre of the first electrode Ei allowing the generated aerosol to escape laterally via the centrally-arranged electrode arrangement.

[0182] In another embodiment illustrated in Figure 14B, the first electrode Ei may be in the form of a rod situated within a tubular electrode E2. In a variant, in order to enable generated aerosol to escape laterally by the electrode arrangement, the second electrode E2may comprise one or more openings, similar to the first electrode Ei of Figure 14A. Alternatively, the tubular electrode E2may not extend entirely around the first electrode Ei, thereby creating another region for generated aerosol to laterally escape the electrode arrangement. In the electrode arrangement illustrated in Figure 14B, tubular electrode E2comprises two electrode portions separated by a gap enabling zoned or sectional heating across the length of an aerosol-forming substrate 1 10 situated between the electrodes Ei and E2. The two electrode portions of tubular electrode E2may share the same polarity or they may be independently energized with the use of an analog signal demultiplexer 11 10 or by the use of selectively applying signals of different oscillators 150, 250, 350 to provide sectional, zoned or partial heating of an aerosol-forming substrate situated between the first electrode Ei and the tubular electrode E2.

[0183] Figure 14C illustrates another electrode arrangement in which the tubular or rod-like electrode E2comprises a plurality of electrode bands axially aligned with each other and coaxially aligned with a first electrode Ei. Similarly, to the electrode arrangement illustrated in Figure 14B, separation gaps can be provided between each of the plurality of electrode bands to enable generated aerosol to escape the electrode arrangement. The plurality of electrode bands of the tubular electrode E2may be independently oscillated to provide sectional, zoned or partial heating of an aerosol-forming substrate 110 situated between the first electrode Ei and the tubular or rod-like electrode E2. Figure 14C also illustrates how the electrode arrangement can be integrated with an aerosol-generating device. A DC power supply 1090 is coupled to an oscillation circuit 1 100 which is directly connected to the first electrode Ei. In order to enable the plurality of electrode bands of the tubular electrode E2to be independently energized, the plurality of electrode bands can be connected to the oscillation circuit 1100 via an analog signal demultiplexer or analog signal switch 1110 and microprocessor 1120.

[0184] Figure 15A is a schematic illustration of an inductor coil L wound around an electrode arrangement, according to an embodiment of the disclosure. In this embodiment, the inductor coil L is configured to inductively heat both electrodes E1 and E2 of the electrode arrangement.

[0185] Figure 15B is a schematic illustration of an inductor coil wound adjacent to an electrode arrangement, according to an embodiment of the disclosure. In this embodiment, a plurality of inductor coils L1 and L2 are configured to inductively heat a region of the electrode arrangement. In the illustrated embodiment, inductor coils L1 and L2 are positioned relative to each other such that an mutual inductive coupling is formed both by the proximity of the coils and the magnetic coupling P / 90750.W001 formed by the electrodes. It will be appreciated that in other embodiments, each inductor coil may be configured to inductively heat a different electrode of the electrode arrangement. As discussed above in relation to figure 13D, sectional heating may also be applied to inductive heating of the aerosol-forming substrate by energizing an inductor coil, or a plurality of inductor coils to inductively heat a region of the electrode arrangement.

[0186] Figure 16A is a schematic illustration of an inductor coil L powered by a different oscillation circuit to the electrode arrangement 130, 135, according to embodiments of the disclosure. In this embodiment, the inductor coil L is coupled to a first oscillation circuit and the electrode arrangement 130, 135 is coupled to a second oscillation circuit, thereby enabling the inductive heating power to be controlled independently from the dielectric heating power in the aerosol-generating device. In such embodiments, a controller may be communicatively coupled with both the first oscillation circuit and the second oscillation circuit, as illustrated in figure 16A.

[0187] Figure 16B is a schematic illustration of an alternative embodiment in which the inductor coil L is powered by the same oscillation circuit as the electrode arrangement 130, 135. Such embodiments may be particularly advantageous where the inductor coil L is part of a resonant circuit with the electrode arrangement 130, 135 in a feedback loop of the oscillation circuit.

[0188] Figure 17 is a schematic illustration of an aerosol-forming substrate temperature sensing system comprising the electrode arrangement 130 of figure 7 with the power control configuration shown in figure 16A. The system comprises a first oscillation circuit OSC1 configured to supply a sensing coil. Unlike the embodiment shown in figure 16A where the inductor coil is configured to stimulate the entire electrode arrangement 130, the sensing coil in figure 17 is positioned to specifically or solely direct a magnetic field to stimulate a magnetic response of the sensing element 135 to see if the Curie temperature has been reached. In some embodiments the sensing coil may be shielded from electric fields from electrodes in the electrode arrangement. A second oscillation circuit OSC2 is configured to supplied the electrode arrangement 130. Both of the first oscillation circuit OSC1 and the second oscillation circuit OSC2 are communicatively coupled with a control unit. The control unit is configured to adjust a power supplied by the second oscillation circuit OSC2 to the electrode arrangement based on the detected magnetic response of the sensing element. In some embodiments, the control unit is configured to adjust the power supplied to the electrode arrangement by altering a switching frequency or supply voltage at the second oscillation circuit OSC2.

[0189] Figure 18 is a schematic illustration of a dielectric heating aerosol-generating system comprising a resonant cavity rather than an electrode arrangement. In this embodiment, the sensing element comprising a magnetic material having a low Curie temperature is positioned within the resonant cavity such that when an aerosol-forming substrate is received within the resonant cavity, the sensing element is in close proximity to the aerosol-forming substrate. Also housed within the P / 90750.W001 resonant cavity is an induction coil configured to form an inductive coupling with the sensing element in order to detect a change in the impedance of the sensing element when the Curie temperature of the magnetic material is reached. It will be appreciated that in other embodiments, the sensing element and induction coil may be arranged differently within the resonant cavity, so long as the sensing element is arranged close to the aerosol-forming substrate while maintaining an inductive coupling with the induction coil.

[0190] The embodiments described above are exemplary embodiments only, and various other embodiments according with this disclosure are also envisaged.

[0191] For the purpose of the present description and of the appended claims, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term “about”. Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein. In this context, therefore, a number A is understood as A ± 5% of A.

Claims

P / 90750.W001CLAIMS1 . A heating assembly for a dielectric heating aerosol-generating device, the heating assembly comprising: a heating region for receiving an aerosol-forming substrate; a dielectric heating assembly for dielectrically heating an aerosol-forming substrate received in the heating region; and an inductive sensing element configured to sense a temperature in the vicinity of the heating region, wherein the inductive sensing element comprises a magnetic material having a Curie temperature corresponding to a predefined temperature point for heating an aerosol-forming substrate.

2. A heating assembly according to claim 1 , wherein the predefined temperature point is between 150°C and 250°C.

3. A heating assembly according to any of claims 1 or 2, wherein the inductive sensing element is configured to physically contact an aerosol-forming substrate when received in the heating region.

4. A heating assembly according to any of claims 1 to 3, wherein the dielectric heating assembly comprises an electrode arrangement, wherein the inductive sensing element is situated on an electrode of the electrode arrangement.

5. A heating assembly according to claim 4, wherein the inductive sensing element forms a layer or coating on an electrode of the electrode arrangement.

6. A heating assembly according to any of claims 4 or 5, wherein the electrode comprising the inductive sensing element has a floating potential or is grounded.

7. A heating assembly according to any preceding claim, wherein the inductive sensing element comprises a second magnetic material having a Curie temperature corresponding to a second predefined temperature point for heating an aerosol-forming substrate, wherein the second predefined temperature point is different from the predefined temperature point.

8. A heating assembly according to any of claims 1 to 6, further comprising a second inductive sensing element configured to sense a temperature in the vicinity of the heating region,P / 90750.W001 wherein the second inductive sensing element comprises a magnetic material having a Curie temperature corresponding to a second predefined temperature point for heating an aerosol-forming substrate, wherein the second predefined temperature point is different from the predefined temperature point.

9. A heating assembly according to any of claims 4 to 6, wherein the electrode arrangement comprises a first electrode coaxially aligned with a second electrode.

10. A heating assembly according to any of claims 4 to 6, wherein the electrode arrangement comprises a first electrode interdigitated with a second electrode.

11. A heating assembly according to any preceding claim, wherein the inductive sensing element consists entirely of the magnetic material.

12. An aerosol-generating device for dielectric heating of an aerosol forming substrate, the device comprising: a heating assembly according to any preceding claim; and an inductor configured to form an inductive coupling with the inductive sensing element.

13. An aerosol-generating device according to claim 12, wherein the device further comprises a control unit configured to: detect a change in magnetic properties of the inductive sensing element based on a detected change in impedance or conductance of the inductor; and adjust a power supplied to the heating assembly based on the detected change in magnetic properties of the inductive sensing element.

14. An aerosol-generating device according to any of claims 12 to 13, wherein the dielectric heating assembly comprises an electrode arrangement, wherein the inductor is further configured to form an inductive coupling with the electrode arrangement and induce a current in the electrode arrangement for heating the aerosol-forming substrate.

15. A dielectric heating aerosol-generating system comprising: an aerosol-generating device according to any of claims 12 to 14; and an aerosol-forming substrate situated in the heating region of the heating assembly.

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