Dielectric heating aerosol-generating device having a resonant oscillator

Abstract

Proposed is an aerosol-generating device for dielectrically heating an aerosol-forming substrate. The device comprises: a power supply providing a DC supply voltage; and an oscillation circuit. The oscillation circuit comprises: a switching unit; and a feedback loop connected between an input and an output of the switching unit. The feedback loop includes a resonant circuit. The resonant circuit includes two electrical contacts interconnected with an electrode arrangement that forms a load capacitor CL. The load capacitor CL is configured to receive the aerosol-forming substrate for dielectric heating. In heating operation, the feedback loop is configured to heat an aerosol forming substrate received by the electrode arrangement such that a ratio between a peak voltage over the load capacitor CL and the DC supply voltage is at least 5, preferably at least 10, more preferably at least 15, even more preferably at least 20.

Description

[0001] Dielectric Heating Aerosol-generating Device having a Resonant Oscillator

[0002] The present invention relates to an aerosol-generating device, and specifically to an aerosol-generating device configured to heat an aerosol-forming substrate by dielectric heating. The present invention further relates to a system comprising the aerosol-generating device and an aerosol-generating article comprising the aerosol-forming substrate.

[0003] Background

[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 aerosolforming 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.

[0007] It would be desirable to provide a system that dielectrically heats an aerosol-forming substrate with greater efficiency, while still being realisable in a compact or handheld system.

[0008] Summary of Invention

[0009] According to a first aspect, the disclosure provides an aerosol-generating device for dielectrically heating an aerosol-forming substrate. The device comprises a power supply providing a DC supply voltage; and an oscillation circuit. The oscillation circuit comprises: a switching unit; and a feedback loop connected between an input and an output of the switching unit. The feedback loop includes a resonant circuit, the resonant circuit including two electrical contacts interconnected with an electrode arrangement that forms a load capacitor CL. The load capacitor CL is configured to receive an aerosol-forming substrate for dielectric heating, wherein in heating operation, the feedback loop is configured to heat an aerosol forming substrate received by the electrode arrangement such that a ratio between a peak voltage over the load capacitor CL and the DC supply voltage is at least 5, preferably at least 10, more preferably at least 15, even more preferably at least 20. The oscillation circuit allows for more efficient dielectric heating by maximizing losses in the load capacitor because of the presence of a resonant circuit, including two electrical contacts configured to interconnect with an electrode arrangement that forms a load capacitor CL, and because the feedback loop is configured such that there is a much higher peak AC voltage across the load capacitor as compared to the DC supply voltage.

[0010] The ratio between the peak voltage over the load capacitor CL and the DC supply voltage may be less than 100, preferably less than 50.

[0011] The feedback loop may be configured such that the peak voltage over the load capacitor CL is more than 50V, preferably more than 100V, but less than 500V, preferably less than 400V.

[0012] The electrode arrangement that forms the load capacitor CL may be fixedly interconnected to the two electrical contacts, and the electrode arrangement may be configured to removably receive the aerosol forming substrate.

[0013] The electrode arrangement that forms the load capacitor CL may be removably interconnected to the two electrical contacts, and the electrode arrangement includes the aerosol forming substrate.

[0014] The DC supply voltage may be between 3V and 13V, preferably between 6V and 12V.

[0015] A frequency of oscillation of the oscillation circuit may be in the Ultra High Frequency, UHF, range. Dielectric losses in the load capacitor CL are somewhat proportional to frequency, therefore operating in the UHF range increases heating efficiency.

[0016] The oscillation circuit may be adapted such as to minimize switching loss and maximize heat dissipation via the load capacitor CL for frequencies in the range between 100MHz and 1.2GHz, preferably between 150MHz and 1GHz, more preferably between 200MHz and 900MHz. These frequency ranges allow for the use of less expensive components and a straightforward circuit design. Furthermore, in these frequency ranges, the electric field strength is reduced, thereby reducing the risk of electric breaks so that the substrate remains stable.

[0017] The oscillation circuit may be adapted such as to channel power dissipation into the dielectric heating of the aerosol-forming substrate at an operating frequency that is close to or at a resonance frequency in the range between 200MHz and 900MHz while limiting a voltage across the load capacitor CL for reducing electric breaks.

[0018] The feedback loop may be arranged such that the oscillation circuit is self-resonant.

[0019] The resonant circuit of the feedback loop may be configured to provide for a gain that allows to provide the ratio between a peak voltage over the load capacitor CL and the DC supply voltage.

[0020] The resonant circuit may include a parallel resonant circuit PRC that includes the load capacitor CL.

[0021] The oscillation circuit may further include a capacitor Ci arranged in parallel to the switching unit, wherein a capacitance of the capacitor Ci is larger than a maximal intrinsic capacitance of the switching unit at the operating frequency. The capacitance of the capacitor Ci may be between 2pF and 100pF, preferably between 5pF and 50pF. Capacitor Ci enables the oscillation frequency to be less voltage dependent, thereby stabilizing the oscillation and increasing overall efficiency.

[0022] The resonant circuit may include two circuit branches, wherein a first branch of the two branches includes the load capacitor CL. The first branch of the resonant circuit may further include a first inductor Li connected to a first electrical contact of the two electrical contacts.

[0023] A second branch of the resonant circuit may include a parallel capacitor CE, the parallel capacitor CE being arranged parallel with the first branch of the resonant circuit.

[0024] The first branch of the resonant circuit may further comprise a second inductor L2 connected to a second electrical contact of the two electrical contacts. Having two inductors on either side of the load capacitor CL provides for a more symmetrical application of voltage across the load capacitor CL, leading to improved dielectric heating efficiency.

[0025] The first inductor Li and the second inductor L2 may be distributed relative to each other so that a mutual inductance is generated between them. This allows for the number of coil windings to be reduced and means that no magnetic core is required, thereby simplifying the circuit design.

[0026] The first inductor Li and the second inductor L2 may be arranged to have a mutual inductance between 50% and 60%. The first inductor Li and the second inductor L2 may each comprise less than 5 windings, preferably 1 or 2 windings. A capacitance value of the load capacitor CL may be between 0.5pF and 100pF, preferably between 0.5pF and 50pF, more preferably between 5pF and 50pF

[0027] The feedback loop may be implemented as a resonant cavity having an interior volume for receiving the aerosol-forming substrate.

[0028] The switching unit may include a transistor. The transistor may be one of a metal oxide semiconductor field-effect transistor (MOSFET), a laterally-diffused metal-oxide semiconductor (LDMOS) transistor, a PnP transistor, an NpN transistor, a high electron mobility transistor (HEMT) and a bipolar transistor.

[0029] The switching unit and the feedback loop may be arranged such that the switching unit performs switching at zero voltage, zero current, or a combination of zero voltage and zero current.

[0030] The feedback loop may be connected between the input and the output of the switching unit. This allows for more predictable operation and reduces stray element and ground influences.

[0031] The feedback loop may be operable to provide a phase shift of about 180° between an input and an output of the switching unit, and the switching unit is configured for inverting operation. The resonant circuit may be arranged to provide a phase shift of at least 90° and may act as an inductor at the operating frequency.

[0032] The feedback loop may further include a capacitive element that provides for a 90° phase shift. The capacitive element may include a capacitor C2 having a quality or Q-factor above 100 at 100MHz, preferably above 500 at 100MHz. The capacitive element may be connected between the first branch and to ground. A capacitance value of the capacitive element may be between 500pF and 100nF, preferably between 1 nF and 50nF. The capacitive element provides a 90° phase shift with minimal losses or other undesired effects. In view of the capacitance value of the capacitor C2 and the operating frequency of the oscillation circuit, C2 may also act as a voltage divider at the gate of transistor T of the switching unit.

[0033] The feedback loop may be impedance-matched with the switching unit. Preferably, the impedances of the resonant circuit and capacitor C2 add up to match the impedance of the switching unit, more preferably the resonant circuit is substantially impedance-matched with the switching unit. The resonant circuit of the feedback loop may have an impedance in a range of 500 mOhm to 8 Ohm, more preferably 800 mOhm to 6 Ohm, even more preferably 150 mOhm to 1.5 Ohm, even more preferably about 2 Ohm. This provides for a high gain, leading to increased voltage across the load capacitor CL. There is therefore no need for use of additional voltage or current amplifying elements in the circuitry, such as tapped inductors or transformers at the resonant circuit or at another location in the feedback loop.

[0034] The impedance of the resonant circuit of the feedback loop also depends on the operating or switching frequency of the switching unit. The operating or switching frequency of the switching unit may be defined and enforced at least by a delay line DL. The operating or switching frequency is not the parallel or series resonance of the parallel oscillating circuit PRC.

[0035] Switching conditions of the switching unit may be at least in part defined by properties of an aerosol-forming substrate coupled with the load capacitor CL.

[0036] An impedance of the load capacitor CL and remaining elements of the resonant circuit and the switching unit may be matched in order to maximize power loss in the load capacitor CL.

[0037] The feedback loop may further comprise a delay line DL (sometimes referred to as a delay element) connected between the first branch of the resonant circuit and the switching unit, to provide for a delay to define the operating frequency. However, it is to be understood that the delay line DL could be placed elsewhere, for example somewhere else in the feedback loop. The delay line acts as a time delay element and has inductive behavior to slow down the arriving voltage wave from the feedback loop during a period of the oscillation. This ensures that the feedback loop does not reach full resonance so that the oscillation circuit remains in a predefined operating frequency range to provide the requisite inverted phase shifted feedback and to make sure the feedback loop has a high gain. A delay-line oscillator is a form of electronic oscillator that uses a delay line, or delay element as its principal timing element. A delay-line oscillator may be set to oscillate by inverting the output of the delay line or delay element and feeding that signal back to the input of the delay line or delay element with appropriate amplification.

[0038] The delay element may be realized with a physical delay line (such as an LC network or a transmission line). In some examples, capacitances and inductances may be distributed across the length of the delay element. In some examples, the delay element comprises a cascade of logic gates for creating a gate delay. The timing of an oscillation circuit using a physical delay element may be much more accurate. It is also easier to get such an oscillation circuit to oscillate in the desired mode.

[0039] An increase in voltage from the power supply to the peak voltage over the load capacitor CL may not be achieved via a transformer. The feedback loop may not include a transformer. The feedback loop may not include a tapped inductor. This simplifies operation of the circuitry and reduces undesired losses, in particular at frequencies of greater than 50MHz.

[0040] According to a second aspect, there is provided a system comprising: the aerosol generating device described above; and an aerosol-generating article comprising the aerosolforming substrate.

[0041] According to a further aspect, there is provided a system comprising: an aerosol-generating article comprising an aerosol-forming substrate; and an aerosol-generating device, comprising: a power supply providing a DC supply voltage; and an oscillation circuit, wherein the oscillation circuit comprises: a switching unit; and a feedback loop connected between an input and an output of the switching unit, the feedback loop including a resonant circuit, the resonant circuit including two electrical contacts configured to be interconnected with an electrode arrangement that forms a load capacitor CL, the load capacitor CL configured to receive an aerosol-forming substrate for dielectric heating, wherein in heating operation, the feedback loop is configured to heat the aerosol forming substrate by the electrode arrangement such that a ratio between a peak voltage over the load capacitor CL and the DC supply voltage is at least 5, preferably at least 10, more preferably at least 15, even more preferably at least 20.

[0042] The electrode arrangement may form part of the aerosol-generating article.

[0043] The aerosol-forming substrate may comprise a solid substrate. The aerosol-forming substrate may comprise a liquid or gel component. The aerosol-forming substrate may be a tobacco-based substrate. The aerosol-forming substrate may not be a tobacco-based substrate. The aerosol-forming substrate may comprise an aerosol-forming material and one or more active agents. The one or more active agents may comprise one or more of nicotine, a medicament, a botanical, a flavorant. The aerosol-forming substrate may comprise a wicking element or a capillary element for liquid transfer.

[0044] In an example, the feedback loop may be 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 - e.g., there may be at least one electrical component (for examples, a resistor or capacitor) creating a non-negligible potential difference between the feedback loop and the power supply and ground in the oscillation circuit. This may reduce noise and ground influences for more predictable operation in the feedback loop.

[0045] 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.

[0046] As used herein, the term “aerosol-forming substrate” relates to a substrate capable of releasing volatile compounds that can form an aerosol. Such volatile compounds can be released by heating the aerosol-forming substrate. The aerosol-forming substrate may be solid or may comprise both solid and liquid components. An aerosol-forming substrate may be part of an aerosol-generating article.

[0047] As used herein, the term "aerosol-generating system" refers to the combination of an aerosol-generating device with an aerosol-forming substrate. When the aerosol-forming substrate forms part of an aerosol-generating article, the aerosol-generating system refers to the combination of the aerosol-generating device with the aerosol-generating article. In the aerosolgenerating system, the aerosol-forming substrate and the aerosol-generating device cooperate to generate an aerosol.

[0048] As used herein, the term “aerosol-generating article” refers to an article comprising an aerosol-forming substrate that is capable of releasing volatile compounds that can form an aerosol. An aerosol-generating article may be disposable.

[0049] An aerosol-forming substrate may comprise nicotine. An aerosol-forming substrate may comprise tobacco, for example may comprise a tobacco-containing material containing volatile tobacco flavour compounds, which are released from the aerosol-forming substrate upon heating. In preferred embodiments, an aerosol-forming substrate may comprise homogenized tobacco material, for example cast leaf tobacco. The aerosol-forming substrate may comprise both solid and liquid components. The aerosol-forming substrate may comprise a tobacco-containing material containing volatile tobacco flavour compounds, which are released from the substrate upon heating. The aerosol-forming substrate may comprise a non-tobacco material. The aerosolforming substrate may further comprise an aerosol former. Examples of suitable aerosol formers are glycerine and propylene glycol.

[0050] As used herein, the term “relative permittivity” (also known as dielectric constant) relates to the permittivity of a material that forms the aerosol-forming substrate expressed as a ratio with the permittivity of vacuum. Mathematically, relative permittivity is expressed as the following: er = e / eO. The parameters in this equation are defined as follows: e is the permittivity of a material that forms the substrate; eO is the permittivity of vacuum; and er is the relative permittivity of a material that forms the substrate. In particular, the term “relative permittivity” may also be referred to as the real part of the complex, frequency-dependent relative permittivity, measured at a temperature of 20°C, in an alternating electric field with at a very low frequency (VLF) of 1 Kilohertz or less, as defined in the international standard IEC 62631-2-1 :2018. It will be appreciated that the frequency value of 1 Kilohertz is included here solely as a general reference and other definitions may use different frequencies.

[0051] As used herein, the term “puff’ means the action of a user drawing an aerosol into their body through their mouth or nose.

[0052] The invention is defined in the claims. However, below there is provided a non-exhaustive list of non-limiting examples. Any one or more of the features of these examples may be combined with any one or more features of another example, embodiment, or aspect described herein.

[0053] Example Ex1 : An aerosol-generating device, comprising: a power supply providing a DC supply voltage; and an oscillation circuit, wherein the oscillation circuit comprises: a switching unit; and a feedback loop connected to the switching unit, the feedback loop including a resonant circuit, the resonant circuit including two electrical contacts configured to interconnect with an electrode arrangement that forms a load capacitor CL, the load capacitor CL configured to receive an aerosol-forming substrate for dielectric heating, wherein in heating operation, the feedback loop is configured such that a ratio between a peak voltage over the load capacitor CL and the DC supply voltage is at least 5, preferably at least 10, more preferably at least 15, even more preferably at least 20.

[0054] Example Ex2. The aerosol-generating device according to Ex1 , wherein the ratio between the peak voltage over the load capacitor CL and the DC supply voltage is less than 100, preferably less than 50.

[0055] Example Ex3. The aerosol-generating device according to Ex1 or Ex2, wherein the feedback loop is configured such that the peak voltage over the load capacitor CL is more than 100V, preferably more than 150V, but less than 500V, preferably less than 400V.

[0056] Example Ex4. The aerosol-generating device according to any of Ex1 to Ex3, wherein the electrode arrangement that forms the load capacitor CL is fixedly interconnected to the two contacts, and the electrode arrangement is configured to removably receive the aerosol forming substrate.

[0057] Example Ex5. The aerosol-generating device according to any of Ex1 to Ex3, wherein the electrode arrangement that forms the load capacitor CL is removably interconnected to the two contacts, and the electrode arrangement includes the aerosol forming substrate. Example Ex6. The aerosol-generating device according to any of the preceding examples, wherein the DC supply voltage is between 3V and 13V, preferably between 6V and 12 V.

[0058] Example Ex7. The aerosol-generating device according to any of the preceding examples, wherein a frequency of oscillation of the oscillation circuit is in the Ultra High

[0059] Frequency, UHF, range.

[0060] Example Ex8. The aerosol-generating device according to any of the preceding examples, wherein the oscillation circuit is adapted such as to minimize switching loss and maximize heat dissipation via the load capacitor CL for frequencies in the range between 100MHz and 1.2GHz, preferably between 150MHz and 1GHz, more preferably between 200MHz and 900MHz.

[0061] Example Ex9. The aerosol-generating device according to any of the preceding examples, wherein the oscillation circuit is adapted such as to channel power dissipation into the dielectric heating of the aerosol-forming substrate at an operating frequency that is close to or at a resonance frequency in the range between 200MHz and 900MHz while limiting a voltage across the load capacitor CL for reducing electric breaks.

[0062] Example Ex10. The aerosol-generating device according to any of the preceding examples, wherein the feedback loop is arranged such that the oscillation circuit is self-resonant.

[0063] Example Ex11. The aerosol-generating device according to any of the preceding examples, wherein the resonant circuit of the feedback loop is configured to provide for a gain that allows to provide the ratio between a peak voltage over the load capacitor CL and the DC supply voltage.

[0064] Example Ex12. The aerosol-generating device according to any of the preceding examples, wherein the resonant circuit includes a parallel resonant circuit PRC that includes the load capacitor CL.

[0065] Example Ex13. The aerosol-generating device according to any of the preceding examples, wherein the oscillation circuit further includes a capacitor Ci arranged in parallel to the switching unit, wherein a capacitance of the capacitor Ci is larger than a maximal intrinsic capacitance of the switching unit at the operating frequency.

[0066] Example Ex14. The aerosol-generating device according to Ex13, wherein the capacitance of the capacitor Ci is between 2pF and 100pF, preferably between 5pF and 50pF.

[0067] Example Ex15. The aerosol-generating device according to any of the preceding examples, wherein the resonant circuit includes two circuit branches, wherein a first branch of the two branches includes the load capacitor CL.

[0068] Example Ex16. The aerosol-generating device according to Ex15, wherein the first branch of the resonant circuit further includes a first inductor Li connected to a first electrical contact of the two electrical contacts. Example Ex17. The aerosol-generating device according to Ex15 or Ex16, wherein a second branch of the resonant circuit includes a parallel capacitor CE, the parallel capacitor CE being arranged parallel with the first branch of the resonant circuit.

[0069] Example Ex18. The aerosol-generating device according to Ex16, wherein the first branch of the resonant circuit further comprises a second inductor L2 connected to a second electrical contact of the two electrical contacts.

[0070] Example Ex19. The aerosol-generating device according to Ex18, wherein the first inductor Li and the second inductor L2 are distributed relative to each other so that a mutual inductance is generated between them.

[0071] Example Ex20. The aerosol-generating device according to Ex18 or Ex19, wherein the first inductor Li and the second inductor L2 are arranged to have a mutual inductance between 50% and 60%.

[0072] Example Ex21. The aerosol-generating device according to any of Ex18 to Ex20, wherein the first inductor Li and the second inductor L2 each comprise less than 5 windings, preferably 1 or 2 windings.

[0073] Example Ex22. The aerosol-generating device according to any of the preceding examples, wherein a capacitance value of the load capacitor CL is between 0.5pF and 100pF, preferably between 0.5pF and 50pF, more preferably between 5pF and 50pF

[0074] Example Ex23. The aerosol-generating device according to any of the preceding examples, wherein the feedback loop is implemented as a resonant cavity having an interior volume for receiving the aerosol-forming substrate.

[0075] Example Ex24. The aerosol-generating device according to any of the preceding examples, wherein the switching unit includes a transistor.

[0076] Example Ex25. The aerosol-generating device according to Ex24, wherein the transistor is one of a metal oxide semiconductor field-effect transistor (MOSFET), a laterally-diffused metal- oxide semiconductor (LDMOS) transistor, a PnP transistor, an NpN transistor, a high electron mobility transistor (HEMT) and a bipolar transistor.

[0077] Example Ex26. The aerosol-generating device according to any of the preceding examples, wherein the switching unit and the feedback loop are arranged such that the switching unit performs switching at zero voltage, zero current, or a combination of zero voltage and zero current.

[0078] Example Ex27. The aerosol-generating device according to any of the preceding examples, wherein the feedback loop is connected between the input and the output of the switching unit.

[0079] Example Ex28. The aerosol-generating device according to any of the preceding examples, wherein the feedback loop is operable to provide a phase shift of about 180° between an input and an output of the switching unit, and the switching unit is configured for inverting operation.

[0080] Example Ex29. The aerosol-generating device according to any of Ex15 to Ex28, wherein the resonant circuit is arranged to provide a phase shift of at least 90° and to act as an inductor at the operating frequency.

[0081] Example Ex30. The aerosol-generating device according to any of the preceding examples, wherein the feedback loop further includes a capacitive element that provides for a 90° phase shift.

[0082] Example Ex31. The aerosol-generating device according to Ex30, wherein the capacitive element includes a capacitor C2 having quality or Q-factor above 100 at 100MHz, preferably above 500 at 100MHz.

[0083] Example Ex32. The aerosol-generating device according to Ex30 or Ex 31 , wherein the capacitive element is connected between the first branch and to ground.

[0084] Example Ex33. The aerosol-generating device according to any of Ex30 to Ex32, wherein a capacitance value of the capacitive element is between 500pF and 100nF, preferably between 1 nF and 50nF.

[0085] Example Ex34. The aerosol-generating device according to any of the preceding examples, wherein the feedback loop is impedance-matched to the switching unit.

[0086] Example Ex35. The aerosol-generating device according to any of the preceding examples, wherein the resonant circuit of the feedback loop has an impedance in a range of 500m0hm to 80hm, more preferably 800m0hm to 60hm, even more preferably 10hm to 40hm, even more preferably about 20hm.

[0087] Example Ex36. The aerosol-generating device according to any of the preceding examples, wherein switching conditions of the switching unit are at least in part defined by properties of an aerosol-forming substrate coupled with the load capacitor CL.

[0088] Example Ex37. The aerosol-generating device according to Ex36, wherein an impedance of the load capacitor CL and remaining elements of the resonant circuit and the switching unit is matched in order to maximize power loss in the load capacitor CL.

[0089] Example Ex38. The aerosol-generating device according to any of Ex17 to Ex37, wherein the feedback loop further comprises a delay line connected between the first branch of the resonant circuit and the switching unit, to provide for a delay to define the operating frequency.

[0090] Example Ex39. The aerosol-generating device according to any of the preceding examples, wherein an increase in voltage from the power supply to the peak voltage over the load capacitor CL is not achieved via a transformer.

[0091] Example Ex40. The aerosol-generating device according to any of the preceding examples, wherein the feedback loop does not include a transformer. Example Ex 41. The aerosol-generating device according to any of the preceding claims, wherein the feedback loop does not include a tapped inductor.

[0092] Example Ex42. A system comprising: the aerosol generating device of one of Ex1 to Ex41; and an aerosol-generating article comprising the aerosol-forming substrate.

[0093] Example Ex43. The system according to Ex42, wherein the aerosol-forming substrate comprises a solid substrate.

[0094] Example Ex44. The system according to Ex42 or Ex43, wherein the aerosol-forming substrate comprises a liquid or gel component.

[0095] Example Ex45. The system according to any of Ex42 to Ex44, wherein the aerosol-forming substrate is a tobacco-based substrate.

[0096] Example Ex46. The system according to any of Ex42 to Ex44, wherein the aerosol-forming substrate is not a tobacco-based substrate.

[0097] Example Ex47. The system according to any of Ex42 to Ex46, wherein the aerosol-forming substrate comprises an aerosol-forming material and one or more active agents.

[0098] Example Ex48. The system according to Ex47, wherein the one or more active agents comprise one or more of nicotine, a medicament, a botanical, a flavorant.

[0099] Example Ex49. The system according to any of Ex44 to Ex48, wherein the aerosol-forming substrate comprises a wicking element or a capillary element for liquid transfer.

[0100] Example Ex50. An aerosol-generating device, comprising: a power supply providing a DC supply voltage; and an oscillation circuit, wherein the oscillation circuit comprises: a switching unit; and a feedback loop connected between an input and an output of the switching unit, the feedback loop including a resonant circuit, the resonant circuit including two electrical contacts interconnected with an electrode arrangement that forms a load capacitor CL, the load capacitor CL configured to receive an aerosol-forming substrate for dielectric heating, wherein in heating operation, the feedback loop is configured to heat an aerosol forming substrate received by the electrode arrangement such that a ratio between a peak voltage over the load capacitor CL and the DC supply voltage is at least 5, preferably at least 10, more preferably at least 15, even more preferably at least 20.

[0101] Example Ex51. The aerosol-generating device of Example Ex50, wherein the device is adapted according to any one of the Examples Ex2 to Ex41.

[0102] Example Ex52. A system comprising the aerosol generating device of one of Examples Ex50 or Ex51; and an aerosol-generating article comprising the aerosol-forming substrate.

[0103] Example Ex53. A system comprising: an aerosol-generating article comprising an aerosol-forming substrate; and an aerosol-generating device, comprising: a power supply providing a DC supply voltage; and an oscillation circuit, wherein the oscillation circuit comprises: a switching unit; and a feedback loop connected between an input and an output of the switching unit, the feedback loop including a resonant circuit, the resonant circuit including two electrical contacts configured to be interconnected with an electrode arrangement that forms a load capacitor CL, the load capacitor CL configured to receive an aerosol-forming substrate for dielectric heating, wherein in heating operation, the feedback loop is configured to heat the aerosol forming substrate by the electrode arrangement such that a ratio between a peak voltage over the load capacitor CL and the DC supply voltage is at least 5, preferably at least 10, more preferably at least 15, even more preferably at least 20.

[0104] Example Ex54. The system of Examples Ex52 or Ex53, wherein the system is adapted according to any one of the Examples Ex43 to Ex49.

[0105] Example Ex54. The system according to any of Examples Ex52 to Ex54, wherein the electrode arrangement forms part of the aerosol-generating article

[0106] Brief Description of Drawings

[0107] The invention will be further described, by way of example only, with reference to the accompanying drawings in which:

[0108] Figure 1 is a schematic illustration of a dielectric heating aerosol-generating system according to embodiments of the disclosure;

[0109] 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;

[0110] Figure 3a is a schematic illustration 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° phase shift;

[0111] Figure 3b 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° phase shift;

[0112] Figure 4 illustrates an oscillation circuit diagram according to embodiments of the disclosure;

[0113] 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;

[0114] 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; Figures 7A-C are isometric illustrations of inductor pairs sharing a mutual inductive coupling for use in the oscillation circuit of Figures 2 to 4, according to embodiments of the disclosure;

[0115] Figures 8A-D are isometric and schematic illustrations of flat interdigitated electrode arrangements for use in the oscillation circuit of Figures 2 to 4, according to embodiments of the disclosure;

[0116] Figure 9 shows isometric and schematic illustrations of tubular interdigitated electrode arrangements for use in the oscillation circuit of Figures 2 to 4 configured to dielectrically heat an aerosol-forming substrate 110, according to embodiments of the disclosure;

[0117] Figure 10 shows schematic illustrations of an interdigitated electrode arrangement with a varying electrode separation distance, according to embodiments of the disclosure;

[0118] Figures 11A-D show isometric and schematic illustrations of tubular interdigitated electrode arrangements for use in the oscillation circuit of Figures 2 to 4 configured to dielectrically heat an aerosol-forming substrate 110;

[0119] Figure 12A-C are schematic illustrations of electrode arrangements for dielectrically heating liquid aerosol-forming substrates configured to function as both a heater and wicking element, according to embodiments of the disclosure.

[0120] Detailed Description

[0121] The above and other features and advantages of example embodiments will become more apparent by describing in detail, example embodiments with reference to the attached drawings. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. Example embodiments may, however, be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein.

[0122] Accordingly, while example embodiments are capable of various modifications and alternative forms, embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit example embodiments to the particular forms disclosed, but to the contrary, example embodiments are to cover all modifications, equivalents, and alternatives falling within the scope of example embodiments. Like numbers refer to like elements throughout the description of the figures.

[0123] Figure 1 is a schematic illustration of a dielectric heating aerosol-generating 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 110. The aerosol-generating device 120 comprises a first electrode 130 and a second electrode 135 separated by a cavity 140 for receiving the article 105. The cavity 140 and the article 105 are sized such that the aerosol-forming substrate 110 is in contact or in close proximity to both the first electrode 130 and the second electrode 135 when received within the cavity 140. Moreover, the first electrode 130 and the second electrode 135 form part of a feedback loop of an oscillation circuit 150 via a first and second electrical contact 160, 165.

[0124] In other examples, the first electrode 130 and the second electrode 135 may form part of the article 105 comprising the aerosol-forming substrate 110. In such embodiments, a cavity between the first and second electrical contacts 160, 165 is sized such that, when the aerosolforming article 105 is housed within the cavity 140, an electrical connection is made between the first electrode 130 and the first electrical contact 160, and the second electrode 135 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 the first electrode 130 and the second electrode 135, such that the distal end of the aerosol-generating substrate 110 is slightly compressed between the first electrode 130 and the second electrode 135. In some embodiments, the article 105, in an initial, uncompressed form has a width between 5-30% larger than the distance between the first electrode 130 and the second electrode 135. This may reduce or prevent the build-up of air between the first electrode 130 and the second electrode 135 when the aerosol-forming article 105 is received in the cavity 140, and decrease a distance between first and second electrodes 130, 135 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 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 130, 135 can be configured as a wicking element or capillary element for liquid transfer. For example, it is possible that first and second electrodes 130, 135 form a capillary structure that is part of the aerosol-forming article 105 or reaches into an inner volume of the aerosol-forming article 105 that can heat and vaporize a liquid aerosol-forming substrate 110 located in the inner volume. For example, the first and second electrodes 130, 135 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 2 mm, depending on the desired capillary strength or rise. The first and second 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 neighboring pin-like electrodes being in a range between 0.1 mm to 2 mm, 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 130, 135, for example flat or slightly curved electrodes 130, 135.

[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 aerosolgenerating 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 aerosol-generating 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 first and second electrodes 130, 135 to dielectrically heat the aerosol-forming substrate 110 in the cavity 140, releasing volatile compounds.

[0129] The controller 180 may cause dielectric heating of the aerosol-forming substrate 110 that is located between the two electrodes 130, 135 with an average dielectric heating power density in a range between 1 W / cm3to 25W / cm3, preferably between 1 ,5W / cm3and 15W / cm3per volume of substrate material during a time period of less than 15 minutes. In particular, during a heat-up phase, the average dielectric heating power density may be controlled or set to be in a range between 7W / cm3to 25W / cm3, preferably between 8W / cm3to 20W / cm3. During a target heating phase (also called maintenance heating phase) during consumption, the average dielectric heating power density is in a range between 1W / cm3to 7W / cm3, preferably between 1W / cm3to 5W / cm3. In a non-limiting example, these power densities may be used in heat-not-burn (HnB) applications.

[0130] In yet another exemplary embodiment, the aerosol-generating system 100 may be configured to provide a power density between the pair of opposing electrodes 130, 135 of between 35W / cm3and 35kW / cm3. The aerosol-generating system 100 may be configured to provide a power density between the pair of opposing electrodes 130, 135 of between 50W / cm3and 10 kW / cm3, between 50W / cm3and 2.5kW / cm3or between 50W / cm3and 1.25kW / cm3. The aerosol-generating system 100 may be configured to provide a power density between the pair of opposing electrodes 130, 135 of between 170W / cm3and 2.5kW / cm3, between 250W / cm3and 2.5kW / cm3or between 500W / cm3and 2.5kW / cm3. Preferably, the aerosol-generating system 100 may be configured to provide a power density between the pair of opposing electrodes 130, 135 of between 1kW / cm3and 2kW / cm3. In a non-limiting example, these power densities may be used for heating and vaporizing liquids during a puff in a puff-on-demand application, for example for a duration in a range between 0.5 seconds to 10 seconds.

[0131] For such puff-on-demand applications, the dielectric heating losses per volume may be substantially higher than the ones of HnB applications with minute-long heating sessions. However, the heated volume may be smaller (~10 mm3in puff-on-demand applications versus -300 mm3in HnB applications).

[0132] The aerosol-generating system 100 is also configured for measuring a dielectric property of the aerosol-forming article 105 or the aerosol-forming substrate 110 using the electrodes 130, 135 that are employed for dielectric heating of the aerosol-forming substrate 110. In some examples, the first and second electrodes 130, 135 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 aerosolforming article 105 between the first electrode 130 and the second electrode 135. The aerosolgenerating 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 aerosolgenerating 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.

[0133] 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 feedback loop 270 is connected between an input and an output of 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).

[0134] The oscillation circuit 250 can further comprises 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 comprises 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.

[0135] 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.

[0136] 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° phase shift or quarter wave shift to the feedback signal. Feedback loop 270 further includes a capacitive element 274 providing for a second 90° 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°. Switching unit 260 is itself configured for inverted switching operation to provide a 180° phase shift between the input UIN and the output UOUT of the switching unit 260.

[0137] 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 between the first and second electrodes 130, 135, 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.

[0138] 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 110, for example having an opening for inserting an aerosol-forming substrate 110. 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). 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.

[0139] 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 0. 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 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 DL and a capacitor C2 connected in series to the delay line DL. 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.

[0140] The delay line DL 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.

[0141] 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 first and second electrodes 130, 135 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 first and second electrode 130, 135 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 a cavity formed in between the first and second electrodes 130, 135, electrical contacts 160, 165 provide electrical connections from the first and second electrodes to the next components in the feedback loop 270, e.g. inductors Li and L2.

[0142] 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 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. The aerosolization temperature is between 80°C and 365°C, preferably between 180°C and 320°C, more preferably between 180°C and 220°C. 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.

[0143] 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 100pF, more preferably in a range between 5pF and 50pF.

[0144] 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 1nF and 50nF, which leads to a low impedance of capacitive element 274. In a variant, 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.

[0145] 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, at an impedance of approximately 500mQ to 80, preferably around 2Q 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. Preferably, the impedances of the resonant circuit and capacitor C2 add up to match the impedance of the transistor T, more preferably the resonant circuit is substantially impedance-matched with the transistor.

[0146] When in heating operation, the ratio of the peak voltage across the electrodes 130 and 135 of the load capacitor CL and the DC supply voltage is between 5 and 100. The ratio is preferably at least 10, more preferably at least 15, even more preferably at least 20 and the ratio is preferably less than 50. The peak voltage across the electrodes 130 and 135 of the load capacitor CL is preferably more than 50V, preferably more than 100V, preferably more than 150V but less than 500V, preferably less than 400V.

[0147] 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° 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.

[0148] 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.

[0149] 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 Quartzmimicking 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.

[0150] 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 non-limiting 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 Figures 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.

[0151] 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 L2 on 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.

[0152] In a non-limiting example starting from the split inductor Li and L2 of the resonant circuit of Figure 5D, inductors Li and L2 can 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 Li 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 , L2 and the balancing of the voltage UL over load capacitor CL. The symmetry of the two branches in either direction with first branch Li - CL - L2 and 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.

[0153] 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.

[0154] 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, LE could 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. 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° 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 alternating 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. GaN 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 losses in load capacitor CL are also dependent on the distance separating the two electrodes 130 and 135, which influences the electric field strength EF across the aerosolforming substrate 110. When in heating operation, the ratio of the peak voltage provided across the load capacitor CL and the DC supply voltage is at least 5, preferably at least 10, more preferably at least 15, even more preferably at least 20. The ratio is less than 100, preferably less than 50. The peak voltage across the load capacitor CL is less than 500V, preferably less than 400V.

[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 the first and second electrodes 130, 135.

[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 1GHz, 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-10 mm), 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, at 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 E1 and E2 and 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 110 between the first and second electrodes 130, 135. More than 6-7W of power losses is not desirable for a handheld device, and more preferably there should be less than 5W, at nominal heating conditions or other operation that can last for more than 30 seconds.

[0160] T o 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 loop 270. Furthermore, the equivalent impedance of the circuit will increase to an extent that is too high for efficient dielectric heating as not providing for the requisite gain.

[0161] Oscillations in the feedback loop 270 will be naturally drawn towards the parallel resonance frequency of the resonant circuit 272. However, the addition of a delay line DL 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° 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. 2.4kQ. 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, preferably an impedance that is less than 20, more preferably less than 10. The parallel resonance frequency fPAR can be above 1GHz, e.g. 1GHz to 1.5GHz, while the actual switching frequency fscan be below 1GHz, and this lower switching frequency is caused by the delay line DL.

[0162] Ideally, the oscillation frequency fs should be set to be below the parallel resonance frequency fPAR but above the series resonance frequency fsER, to make sure that two conditions are fulfilled, firstly (i) that the resonant circuit behaves inductively to provide a 90° phase 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 Figure 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 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 Figure 6 and as a non-limiting numerical example, assuming that a parallel resonance frequency fPAR is at 1.25 GHz, therefore having a period of 800ps (picoseconds), and a series resonance frequency fsER is at 855MHZ, and therefore a period of 1169ps, 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 fPAR and 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.

[0163] 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.

[0164] Figures 7A-C are isometric illustrations of a split coil resonator having a mutual inductive coupling for use in the oscillation circuit of Figures 2 to 4, according to embodiments of the disclosure. In the example of Figure 7A, the two inductors Li and L2, are each formed as a single winding, e.g. a single loop coil. The winding central axis of each coil substantially coincides with each other, and the plane formed by each single-winding inductor is parallel to the other, and is also in close proximity. This establishes a mutual inductance between inductors Li and L2 without a magnetic core Me. If necessary, the mutual inductance M can be further increased by adding a magnetic core Me that traverses or at least partially traverses each winding of Li and L2 to reach a desired inductance level. In this respect, a distance between the two planes in which the windings are arranged can be increased, to minimize the capacitive effect between them. Preferably the windings of inductors Li and L2 are wound in the same direction around the coinciding winding central axis of, or in case a core Me is present, around the core Me or the central axis. This way, the magnetic flux caused by both coils Li and L2 is enhanced, rather than cancelled out. In other words, the two inductors Li and L2 appear as a continuously wound coil around a magnetic core Me, or around the winding central axis in case no core is used, with two winding regions forming two inductor coils Li, L2.

[0165] Figure 7B illustrates an alternative split coil resonator arrangement, wherein instead of one full loop coil for Li and L2, an omega-shaped loop is used. Other winding shapes are also possible while providing substantially the same functionality.

[0166] In some examples, it is possible to use a smaller diameter of inductor coils Li , L2, but have several loops or turns. Preferably the number of turns in each inductor coil Li , L2 is no more than five (5), preferably less than three turns, and preferably no more than one turn. To further reduce the capacitive coupling between Li and L2, the inductors Li, L2 of the split coil resonator of Figure 7B are arranged as planar coils in an omega-shape, single winding, or double winding coils, both on the same surface or plane, and are therefore not aligned in parallel to each other. This is desirable since the capacitive effect between the two inductors Li and L2 can provide for unwanted additional dielectric losses. In this embodiment, the magnetic coupling by core Me is achieved via a u-shaped core with each leg traversing a center of each planar coil Li , L2.

[0167] Both Figures 7A and 7B show an embodiment of the resonant circuit 272 as a complete parallel resonant circuit PRC by virtue of the second branch being created by the mutual inductance M between inductors Li and L2.

[0168] It is also possible that the mutual inductance M between Li and L2 are created by simple proximity of the two inductor coils Li and L2, without the use of a magnetic core Me as illustrated in Figure 7C, or by inter-winding the coils of inductors Li and L2. The electrode arrangement of Figure 7C comprises parallelly arranged electrode plates E1 and E2 having curved edges to reduce hotspots in the electric field formed around the boundaries of the electrode plates.

[0169] Figures 7A and 7B illustrate electrode arrangements comprising a pair of electrode plates 130, 135 aligned in parallel, however other electrode arrangements are also possible.

[0170] Figures 8A-D are schematic illustrations of flat interdigitated electrode arrangements for use in the oscillation circuit of Figures 2 to 4, 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 8A 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 8B and 8C 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 8D, 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 8D on an opposite side of the aerosol-forming substrate 110. 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 9, 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, the tubular structure can have a diameter between 5 mm to 9 mm. The tangential distance between the electrodes of opposite polarity can be between 0.5 mm to 3 mm, preferably between 0.7 mm to 2.2 mm.

[0175] Figure 10 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 11A-B show isometric and schematic illustrations of tubular interdigitated electrode arrangements for use in the oscillation circuit of Figures 2 and 3 configured to dielectrically heat an aerosol-forming substrate 110 positioned in a central cavity formed by the electrode arrangement. The electrode arrangement in Figures 11 A-B comprises a series of axially aligned electrode bands positioned adjacent to electrode bands having opposing polarities. In such embodiments, the aerosol-forming substrate 110 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 11 B, which is configured such that electrical field between opposing polarity electrodes is strongest across the aerosol-forming substrate 110. Figures 11C-D illustrate how the plurality of electrode portions from the electrode arrangements of Figure 11 A-B may be electrically connected to achieve an interdigitated configuration.

[0177] Figures 12A to 12C illustrate alternative electrode arrangements for use as both a heater assembly and wicking element for dielectrically heating a liquid aerosol-forming substrate. The arrangement of Figure 12A comprises a reservoir housing a liquid aerosol-forming substrate 110 and a plurality of electrode plates situated adjacent to electrode plate of the opposite polarity. The arrangement functions by generating an alternating electric field across adjacent electrode plates to dielectrically heat liquid aerosol-forming substrate situated between the adjacent electrodes. The distance between adjacent electrode plates may be selected such that the channel between adjacent electrode plates has a capillary effect drawing the liquid aerosol-forming substrate into the channel. Figures 12B-C illustrate a similar electrode arrangement which uses an array of interlocking electrode pins rather than electrode plates. Instead of pins, blades, tabs, rods, or cylinders could also be used. As better seen in Figure 12C, the array of interlocking electrode pins is configured such that adjacent electrode pins have an opposite polarity. Such electrode arrangements are particularly suited for providing uniform heating of the aerosol-forming substrate and avoiding localised overheating of the aerosol-forming substrate, which can lead to the generation of a poor quality aerosol. As with the embodiment in Figure 12A, the distance between adjacent electrode pins in the electrode array may be selected such that the region between adjacent electrode pins has a capillary effect, drawing the liquid aerosol-forming substrate into the electrode array.

[0178] It will be appreciated that the embodiments described above are exemplary embodiments only, and various other embodiments according with this disclosure are also envisaged. 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

CLAIMS:

1. An aerosol-generating device, comprising: a power supply providing a DC supply voltage; and an oscillation circuit, wherein the oscillation circuit comprises: a switching unit; and a feedback loop connected between an input and an output of the switching unit, the feedback loop including a resonant circuit, the resonant circuit including two electrical contacts interconnected with an electrode arrangement that forms a load capacitor CL, the load capacitor CL configured to receive an aerosol-forming substrate for dielectric heating, wherein in heating operation, the feedback loop is configured to heat an aerosol forming substrate received by the electrode arrangement such that a ratio between a peak voltage over the load capacitor CL and the DC supply voltage is at least 5, preferably at least 10, more preferably at least 15, even more preferably at least 20.

2. The aerosol-generating device according to claim 1 , wherein the ratio between the peak voltage over the load capacitor CL and the DC supply voltage is less than 100, preferably less than 50.

3. The aerosol-generating device according to claim 1 or 2, wherein the feedback loop is configured such that the peak voltage over the load capacitor CL is more than 100V, preferably more than 150V, but less than 500V, preferably less than 400V.

4. The aerosol-generating device according to any of claims 1 to 3, wherein the electrode arrangement that forms the load capacitor CL is fixedly interconnected to the two contacts, and the electrode arrangement is configured to removably receive the aerosol forming substrate, or wherein the electrode arrangement that forms the load capacitor CL is removably interconnected to the two contacts, and the electrode arrangement includes the aerosol forming substrate.

5. The aerosol-generating device according to any of the preceding claims, wherein the resonant circuit of the feedback loop has an impedance in a range of 500m0hm to 80hm, more preferably 800m0hm to 60hm, even more preferably 10hm to 40hm, even more preferably about 20hm.

6. The aerosol-generating device according to any of the preceding claims, wherein the oscillation circuit further includes a capacitor Ci arranged in parallel to the switching unit, wherein a capacitance of the capacitor Ci is larger than a maximal intrinsic capacitance of the switching unit at an operating frequency.

7. The aerosol-generating device according to any of the preceding claims, wherein the resonant circuit includes two circuit branches, wherein a first branch of the two branches includes the load capacitor CL.

8. The aerosol-generating device according to claim 7, wherein the first branch of the resonant circuit further includes a first inductor Li connected to a first electrical contact of the two electrical contacts, and optionally wherein the first branch of the resonant circuit further comprises a second inductor L2 connected to a second electrical contact of the two electrical contacts.

9. The aerosol-generating device according to claim 8, wherein the first inductor Li and the second inductor L2 are distributed relative to each other so that a mutual inductance is generated between them.

10. The aerosol-generating device according to claim 9, wherein the first inductor Li and the second inductor L2 are arranged to have a mutual inductance between 50% and 60%.

11. The aerosol-generating device according to any of the preceding claims, wherein the feedback loop is operable to provide a phase shift of about 180° between an input and an output of the switching unit, and the switching unit is configured for inverting operation.

12. The aerosol-generating device according to any of the preceding claims, wherein the resonant circuit is arranged to provide a phase shift of at least 90° and to act as an inductor at the operating frequency.

13. The aerosol-generating device according to any of the preceding claims, wherein the feedback loop further includes a capacitive element that provides for a 90° phase shift.

14. The aerosol-generating device according to any of claims 7 to 13, wherein the feedback loop further comprises a delay line connected between the first branch of the resonant circuit and the switching unit, to provide for a delay to define the operating frequency.

15. A system comprising: the aerosol generating device of one of claims 1 to 14; andan aerosol-generating article comprising the aerosol-forming substrate.

16. A system comprising: an aerosol-generating article comprising an aerosol-forming substrate; and an aerosol-generating device, comprising: a power supply providing a DC supply voltage; and an oscillation circuit, wherein the oscillation circuit comprises: a switching unit; and a feedback loop connected between an input and an output of the switching unit, the feedback loop including a resonant circuit, the resonant circuit including two electrical contacts configured to be interconnected with an electrode arrangement that forms a load capacitor CL, the load capacitor CL configured to receive an aerosol-forming substrate for dielectric heating, wherein in heating operation, the feedback loop is configured to heat the aerosol forming substrate by the electrode arrangement such that a ratio between a peak voltage over the load capacitor CL and the DC supply voltage is at least 5, preferably at least 10, more preferably at least 15, even more preferably at least 20.

17. The system according to claim 16, wherein the electrode arrangement forms part of the aerosol-generating article.

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