Dielectric heating aerosol-generating device with parameter detection

Abstract

Provided is an aerosol-generating device (120) for dielectrically heating an aerosol-forming substrate (110). The device (120) comprises an oscillation circuit (150) comprising a switching unit configured for inverting operation and a feedback loop connected across the switching unit. The oscillation circuit (150) is configured to provide an alternating electric field across a load capacitor when connected in the feedback loop to dielectrically heat the aerosol-forming substrate having an aerosol former received in a heating region of the device (120). The device (120) further comprises a frequency measurement unit (185) configured to measure frequency data indicative of an oscillation frequency of the alternating electric field across the load capacitor connected in the feedback loop during a dielectric heating operation. The device (120) further comprises a control unit (180) communicatively coupled with the frequency measurement unit (185). The control unit (180) is configured to receive the measured frequency data from the frequency measurement unit (185), and determine one or more parameters related to the dielectric heating operation based on the received frequency data.

Description

[0001] P / 90838.W001

[0002] Dielectric Heating Aerosol-generating Device With Parameter Detection

[0003] The present disclosure relates to aerosol-generating devices, and specifically to aerosolgenerating devices configured to heat an aerosol-forming substrate by dielectric heating. The disclosure also relates to dielectric heating aerosol-generating devices and systems with parameter detection and methods for aerosol-generation using dielectric heating systems.

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

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

[0006] Systems that dielectrically heat an aerosol-forming substrate have been proposed, which advantageously provide uniform heating of the aerosol-forming substrate. However, known dielectric heating systems are less efficient than inductive heating systems and require complex electrical circuitry in order to achieve the necessary voltages and frequencies for dielectric heating of an aerosol-forming substrate.

[0007] A further problem with dielectric heating systems is the difficulty in monitoring parameters of the heating operation in order to control heating power without greatly adding to the cost and complexity of the system.

[0008] It would be desirable to provide an effective solution for monitoring heating operation parameters in dielectric heating systems in order to facilitate improved heating power control.

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

[0010] The aerosol-generating device may comprise an oscillation circuit. The oscillation circuit may comprise a switching unit and a feedback loop connected across the switching unit. The oscillation circuit may be configured to provide an alternating electric field across a load capacitor when connected in the feedback loop to dielectrically heat an aerosol-forming substrate having an aerosol former received in a heating region of the device. The device may further comprise a frequency measurement unit configured to measure frequency data indicative of an oscillation frequency of the alternating electric field across the load capacitor connected in the feedback loop during a dielectric P / 90838.WG01 heating operation. The device may further comprise a control unit communicatively coupled with the frequency measurement unit. The control unit may be configured to: receive the measured frequency data from the frequency measurement unit; and determine one or more parameters related to the dielectric heating operation based on the received frequency data. The aerosol-generating device may further comprise any of the features described below alone or in combination with any other feature of the disclosure.

[0011] 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.

[0012] 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.

[0013] According to an example of the disclosure, provided is an aerosol-generating device for dielectrically heating an aerosol-forming substrate. The device comprises an oscillation circuit comprising a feedback loop connected across a switching unit. The oscillation circuit is configured to provide an alternating electric field across a load capacitor when connected in the feedback loop to dielectrically heat an aerosol-forming substrate having an aerosol former received in a heating region of the device. The device further comprises a frequency measurement unit configured to measure frequency data indicative of an oscillation frequency of the alternating electric field across the load capacitor connected in the feedback loop during a dielectric heating operation. The device further comprises a control unit communicatively coupled with the frequency measurement unit. The control unit is configured to: receive the measured frequency data from the frequency measurement unit; and determine one or more parameters related to the dielectric heating operation based on the received frequency data.

[0014] Aerosol formers such as glycerol, polypropene glycol (PG) and vegetable glycerin (VG) exhibit similar dielectric properties that vary with temperature and frequency. Generally, for heat-not- burn (HnB) products, the large portion of the relative permittivity of the aerosol-forming substrate is given by the infusion or presence of the aerosol former, as generally the tobacco or non-tobacco- based substrate base has a substantially lower relative permittivity (dry tobacco about 2.5 to 3). Since such aerosol formers are commonly used to infuse tobacco substrates or other non-tobacco based substrates for HnB products and as a main liquid substrate component, the dielectric response of an aerosol-forming substrate during a heating operation can be indicative of parameters associated with the heating operation.

[0015] In a dielectric heating aerosol-generating device that operates with an inverting switching unit and an LC feedback loop having the load capacitor within the feedback loop, the oscillation frequency, typically in a range between 100MHz and 1 GHz, will vary with a change of the capacitance value of the load capacitor. Given the presence of aerosol formers and some other P / 90838.W001 highly dielectric liquids such as water inside aerosol-forming substrates, the oscillation frequency of the oscillator will vary upon heating the aerosol-forming substrate.

[0016] Aerosol-generating devices according to the present disclosure are configured to collect frequency data during a heating operation in order to facilitate detection of temporal changes in the oscillation frequency analyzed over time during a dielectric heating operation. The collected frequency data is used to indirectly determine one or more parameters associated with the heating operation. This parameter determination may facilitate improved control of heating operations in the aerosol-generating device.

[0017] The frequency measurement unit may utilize one of several known mechanisms for measuring frequency data indicative of an oscillation frequency of the alternating electric field across the load capacitor connected in the feedback loop during a dielectric heating operation, including magnetic field sensors, electric field sensors, a direct measurement from a transistor signal, or inference with use of other types of measurements.

[0018] In some examples, the frequency measurement unit is configured to measure a switching frequency of the oscillation circuit. In other examples, the frequency measurement unit comprises an electric field probe configured to measure the alternating electric field in the vicinity of the load capacitor when connected in the feedback loop across the oscillation circuit. In some examples, the frequency measurement unit comprises a magnetic field probe configured to measure an alternating magnetic field departed by an inductor of the feedback loop.

[0019] In some examples, the measured frequency data is timestamped to map the frequency data to a time in the dielectric heating operation. This may facilitate the formation of a frequency profile for the dielectric heating operation.

[0020] In some examples, the control unit is further configured to determine a frequency profile for the dielectric heating operation based on the received frequency data. In some examples, the control unit is configured to determine the one or more parameters related to the dielectric heating operation based on one or more properties associated with the frequency profile.

[0021] In some examples, the control unit is configured to determine the one or more parameters based on a comparison of the frequency profile with a reference profile stored in the control unit. In some examples, the reference profile corresponds to a frequency profile from a previous dielectric heating operation.

[0022] In some examples, the control unit is configured to determine the one or more parameters based on a comparison of the one or more properties associated with the frequency profile with one or more reference frequency profile properties.

[0023] In some examples, the control unit is communicatively coupled with a database comprising stored reference data. The reference data may comprise one or more of reference profiles, reference properties and reference values. P / 90838.W001

[0024] In some examples, the control unit is configured to use a model to determine the one or more parameters related to the dielectric heating operation. In some examples, the model comprises a comparison between the frequency data and the reference data. In some examples, the model defines a relationship between frequency data properties and the one or more parameters related to the dielectric heating operation. In some examples, the model comprises a database or look-up table mapping one or more frequency data properties to one or more parameters related to the dielectric heating operation. In another examples, the model comprises a trained artificial neural network configured to map one or more frequency data properties to one or more parameters related to the dielectric heating operation.

[0025] In some examples, the one or more properties comprises a frequency change falling below a threshold value. During an initial start-up heating phase, the oscillation frequency falls as the aerosol former is heated, causing its dielectric constant to increase and consequently leading to a high load capacitance. The oscillation frequency will continue to fall until a predeterminable temperature is reached at which the aerosol former experiences no further change in relative permittivity. As such, the point at which the oscillation frequency ceases to fall can serve as a temperature and timing marker point. Such information can also be used to determine a type of aerosol-forming substrate based on the dielectric response of the aerosol former. After this point, there is a gradual increase of the oscillation frequency resulting from a decrease in relative permittivity of the aerosol-forming substrate, due to some temperature-related evacuation of liquids from the aerosol-forming substrate. With the further advancing of time, the oscillation frequency increase accelerates, as higher temperatures are reached and some vaporization begins to happen, notably the vaporization of water at 100°C. The temperature-related depletion of liquids from aerosolforming substrate thereby counteracts the temperature dependent increase of the relative permittivity. The extent of the increase in oscillation frequency during this period can be indicative of a humidity content of the aerosol-forming substrate. In some examples, the control unit is configured to detect a minimum frequency value of the measured frequency data during a preheating phase of the dielectric heating operation, and determining a temperature of the aerosolforming substrate based on the minimum frequency value. In some examples, following determination of the aerosol-forming substrate temperature, the control unit is configured to continue the pre-heating phase the aerosol-forming substrate for a predetermined time period, and initiate, after the predetermined time period has elapsed, a maintenance heat phase.

[0026] In some examples, the one or more properties comprises a frequency change exceeding a threshold value. Following the initial start-up heating phase when the device reaches a steady-state temperature, observable increases in oscillation frequency occur during user puffs. This is due to a sudden evacuation of aerosol-former from the aerosol-forming substrate, which leads to a sudden decrease of the relative permittivity of aerosol-forming substrate and causes a sharp increase in P / 90838.W001 oscillation frequency. As such, rapid increases in oscillation frequency can be used to detect not only user puff, but also user puff volumes based on the extent of the oscillation frequency increase. Such information may be collated in order to update a puff count, and a depletion status for the aerosolforming substrate. In some examples, the control unit is configured to determine a value indicative of a puff volume based on a relative increase of the frequency between a frequency at a start of a puff and a frequency at the end of the puff.

[0027] During the time between puffs, the oscillation frequency slightly decreases again due to the cooling effect to the aerosol-forming substrate from the colder incoming air drawn by the puff. Therefore, in some examples, this reduction in oscillation frequency may be used to indicate the end of a puff. Shortly after this cooling effect, the oscillation frequency starts increasing due to constant evaporation of aerosol-former at the steady-state temperature. Over subsequent heating operations, the oscillation frequency increases with increased depletion of the aerosol-forming substrate, until the difference between the oscillation frequency after and before a puff is no longer observable. Therefore, a post-puff oscillation frequency change falling below a threshold value can be used to indicate that the aerosol-forming substrate is fully depleted of aerosol-former.

[0028] The use of the first order derivative of the frequency profile (and also the second order derivative to further enhance detection and estimation results) can be used to estimate different parameters around the aerosolization process of the aerosol-forming substrate.

[0029] In some examples, the control unit is further configured to determine a first order derivative of the frequency profile, and determine the one or more parameters related to the dielectric heating operation based on one or more properties associated with the first order derivative of the frequency profile. In some examples, the one or more properties comprises a zero-crossing of the first order derivative of the frequency profile. Specifically, the zero-crossing of the first order derivative of the frequency profile can be used as a temperature and timing marker point during the initial start-up heating phase that the aerosol-forming substrate has reached an initial preheating temperature.

[0030] In some examples, the one or more properties comprises an amplitude of the first order derivative of the frequency profile. Specifically, the amplitude of the first order derivative of the frequency profile can be used to detect one or more of a puff, a puff volume, puff number and a depletion status for the aerosol-forming substrate. In some examples, the control unit is configured to detect one or more of an amplitude, a variance and a pulse width of a peak of the first order derivative of the frequency profile, and determine a puff volume based on the one or more amplitude, variance and pulse width of a peak of the first order derivative of the frequency profile.

[0031] As such parameters of the dielectric heating operation may include one or more of, aerosolforming substrate temperature, consumable article recognition, depletion level detection, puff and puff volume detection, and other features related to the dielectric heating process of the substrate, both during the heat-up phase or during the experience period or steady-state heating phase. P / 90838.W001

[0032] In some examples, the one or more parameters comprises a temperature of the aerosolforming substrate.

[0033] In some examples, the one or more parameters comprises a depletion level of the aerosolforming substrate.

[0034] In some examples, the one or more parameters comprises a type of aerosol-forming substrate.

[0035] In some examples, the one or more parameters comprises a humidity content of aerosolforming substrate.

[0036] In some examples, the one or more parameters comprises an article insertion status in the device. Specifically, imperfect article insertion may be observable in the frequency data for a heating operation following an unexpected dielectric response.

[0037] In some examples, the one or more parameters comprises a time moment when to switch from a pre-heating phase to a steady-state phase.

[0038] Based on the one or more parameters relating to the dielectric heating operation, the control unit may be configured to carry out one or more action in response.

[0039] In some examples, the control unit is configured to adjust a power supplied by the oscillation circuit to the load capacitor based on the determined one or more parameters. In an example, the control unit may be configured to transition from a pre-heating phase power to a steady-state phase power. In some examples, the aerosol-generating device may be configured to control the power delivered to the aerosol-forming substrate based on an estimated temperature of the aerosol-forming substrate based on the frequency data. The temperature generated via dielectric heating by the oscillation circuit, inside or at the substrate that is located in the heating zone of the load capacitor, for example after a pre-heating phase, can be in a range between 80°C to 365°C, more preferably between 80°C to 320°C, and more preferably between 150°C to 250°C, and more preferably between 180°C to 240°C, and more preferably between 200°C to 220°C. Preferably, the temperature of the substrate is kept lower than a temperature where pyrolysis could occur in the material composition of the aerosol forming substrate. Preferably, the temperature is such that one or more active ingredients of the substrate are vaporized and thereafter aerosolized, for example simultaneously or sequentially during a heating session, for example a heating session for a duration of one puff or inhalation, for example a duration in a range between 0.5 seconds to 10 seconds, or a heating session for a duration that covers multiple puffs or inhalation, for example a duration of more than 10 seconds and less than 10 minutes, or preferably, more than 30 seconds and less than 6 minutes. In some examples, a control unit of the aerosol-generating device or the settings of the oscillation circuit can be configured such that they control or set the temperature to such a range between 80°C to 365°C, more preferably between 80°C to 320°C, or more preferably 180°C to 250°C by open-loop control, or closed-loop control. P / 90838.W001

[0040] In some examples, the control unit is configured to select a heating profile for the aerosolforming substrate based on the determined one or more parameters. In some examples, the control unit may determine based on the frequency data that a particular type of aerosol-forming substrate is present, and selected a determined heating profile from a database based on the type of aerosolforming substrate.

[0041] In some examples, the device further comprises a user interface, wherein the control unit is configured to notify a user on the determined one or more parameters using the user interface. In some examples, the user interface comprises one or more of LEDs, haptic feedback elements, a display screen, audio feedback devices or a combination of these. Such indicators may indicate one or more of pre-heating phase completion, correct or incorrect aerosol-forming article insertion in the device, puff count, aerosol-forming substrate depletion status, fully depleted aerosol-forming substrate.

[0042] In an example, the aerosol-generating device further comprises a temperature sensor configured to detect temperature data indicative of the temperature of an aerosol-forming substrate received in the heating region. In some examples, the temperature data may be used in combination with the frequency data to enable more accurate determination of parameters related to the dielectric heating operation. In an example, the temperature sensor may be a contact sensor configured to directly measure the temperature of the aerosol-forming substrate or a component in the vicinity of the aerosol-forming substrate. In another example, the temperature sensor may be a non-contact sensor configured to capture heat radiation from the aerosol-forming substrate or a component in the vicinity of the aerosol-forming substrate. In an example, the non-contact temperature sensor is configure to capture heat radiation from a component that increases or homogenized the heat radiation and has greater thermal conductive properties than the aerosol-forming substrate.

[0043] In some examples, the configuration and dimensioning of the oscillation circuit is selected to passively limit the temperature of the aerosol-forming substrate to a range between 80°C to 365°C, more preferably between 80°C to 320°C, or more preferably 180°C to 220°C, without the use of active temperature control.

[0044] In some examples, the device further comprises a puff detection system for detecting user puffs. The control unit may be configured to use user puff information from the puff detection system in conjunction with the received frequency data to determine the one or more parameters related to the dielectric heating operation. In some examples, the user puff detection may be used as a timing marker in order to associate a specific portion of the received frequency data with a specific event in the dielectric heating operation.

[0045] In some examples, the feedback loop comprises two electrical contacts configured to interconnect with an electrode arrangement that forms a load capacitor for dielectrically heating the aerosol-forming substrate. The feedback loop is configured to perform resonant oscillating operation. P / 90838.W001

[0046] The feedback loop is configured to provide a 180° phase shift between an output signal of the switching unit and an input switching signal of the switching unit. Such oscillation circuits may enable more efficient dielectric heating of an aerosol-forming substrate by facilitating the coupling of a load capacitor electrode arrangement within the feedback loop of the oscillation circuit. The resonant oscillating operation of the feedback loop is able to generate high peak voltages across the load capacitor at high frequencies to deliver power to an aerosol-forming substrate within the electrode arrangement while maintaining the supply voltage across the switching unit, thereby keeping switching losses to a minimum. The oscillation circuits of the present disclosure may be configured to be self-oscillating; that is, the oscillation circuit itself controls the phase with which the external power acts on it.

[0047] Where the switching unit is configured for inverting operation, the feedback unit is configured to provide a 180° phase shift between an output signal of the switching unit and an input switching signal of the switching unit. This allows for effective resonant oscillating operation to occur.

[0048] In some examples, the feedback loop further comprises the electrode arrangement coupled between the two electrical contacts. In some examples, the electrode arrangement is coupled to, or configured to be coupled to a resonant cavity for housing an aerosol-forming substrate to be dielectrically heated via the electrode arrangement.

[0049] In some examples, the feedback loop comprises a first inductor having no more than five turns. The first inductor is connected in series with one of two electrical contacts configured to interconnect with an electrode arrangement that forms a load capacitor for dielectrically heating the aerosol-forming substrate.

[0050] At the operation frequency of the oscillation circuit, the first inductor in the feedback loop is configured to deliver a 90° phase shift between an output signal of the switching unit and an input switching signal of the switching unit. A further 90° phase shift may be provided by a capacitive element, as described in further detail below. By providing an inductor with no more than five turns, the required phase shift for effective resonant oscillating operation may be achieved while also minimizing the presence of parasitic inductance and capacitance in the feedback loop which negatively impact efficient dielectric heating of the aerosol-forming substrate and cause additional power losses that do not contribute to the dielectric heating.

[0051] In an example, the first inductor comprises no more than three turns. In preferred examples, the inductor has less than three turns, and preferably no more than one turn. In some examples, the first inductor may have less than one turn, for example, a half turn or omega-shaped inductor. In an example, a diameter of the turn(s) of the first inductor is less than 15 mm and more than 3 mm, preferably less than 12 mm and more than 5 mm.

[0052] In some examples, the feedback loop comprises a series connection of a first inductor, two electrical contacts configured to interconnect with an electrode arrangement that forms a load P / 90838.W001 capacitor for heating the aerosol-forming substrate, and a second inductor. Providing a first inductor coupled to a first side of the load capacitor and a second inductor coupled to a second side of the load capacitor enables more symmetrical voltages to be generated across the load capacitor, while also providing a 90° phase shift for effective resonant oscillating operation.

[0053] In some examples, the second inductor may comprise the same number of turns as the first inductor to facilitate the symmetrical generation of voltages across the load capacitor. In some examples, the turn(s) in the second inductor have the same diameter as those in the first inductor.

[0054] In some examples, the first inductor and the second inductor are inductively coupled to one another to form a mutual inductance. In order to achieve high peak voltages across the load capacitor, a high inductance is needed in the feedback loop. However, a high inductance also limits the maximum oscillation frequency attained in the feedback loop, and therefore, the power deliverable to the load capacitor. Inductively coupling the first inductor with the second inductor creates a slightly distributed inductor having an amplified effective inductance. Utilising an inductive coupling between the first and second inductors therefore enables the use of inductors having lower inductance values to mitigate the limitations on the achievable oscillation frequency in the feedback loop, while also providing a high effective inductance to amplify the peak voltages generated across the load capacitor.

[0055] In an example, the mutual inductive coupling between the first and second inductor may be between 40% and 70% (or has an inductive coupling coefficient from 0.4 to 0.7), and preferably greater than 50% (or has an inductive coupling coefficient greater than 0.5).

[0056] In an example, the mutual inductive coupling between the first and second inductors may be achieved by the close proximity between the first and second inductors. In alternative examples, a mutual inductive coupling between the first and second inductors is achieved with the use of a magnetic core extending through both the first and second inductors. The use of a magnetic core may facilitate a stronger inductive coupling between the first and second inductors than that achievable based on close proximity alone.

[0057] In an example, a coil axis of the first inductor is arranged to be in parallel with and offset from a coil axis of the second inductor to minimize a capacitive coupling between the first and second inductors. In an example, the first and second inductors are formed as planar inductors.

[0058] In an example, a coil axis of the first inductor is arranged to coaxially align with a coil axis of the second inductor.

[0059] In an example, a planar extension of the first inductor intersects the second inductor.

[0060] In some examples, the feedback loop comprises a series connection of a first inductor and two electrical contacts configured to interconnect with an electrode arrangement that forms a load capacitor for heating the aerosol-forming substrate. The oscillation circuit further comprises a delay P / 90838.WG01 element configured to impede the switching speed of the switching unit. Specifically, the delay element may delay a switching signal received by the switching unit.

[0061] An oscillation circuit comprising a delay element is sometimes referred to as a delay-line oscillator. 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.

[0062] 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.

[0063] In an example, the oscillation circuit is configured to operate a frequency of between 100MHz-2.5GHz, and preferably between 500MHz-1 ,5GHz.

[0064] In operation, the oscillation frequency in the feedback loop will increase towards a certain resonance frequency based on the passive properties of the components in the feedback loop. However, as the oscillation frequency increases beyond a certain threshold, the feedback loop starts to lose the inductive properties that provide the necessary phase shift for effective resonant oscillating operation. Furthermore, as the oscillation frequency exceeds a certain threshold, the impedance of the feedback loop increases, reducing the dielectric heating efficiency in the load capacitor. By providing a delay element configured to impede the switching speed of the switching unit, the maximum oscillation frequency may be limited to a frequency range in which the feedback loop behaves inductively and has a low impedance for efficient dielectric heating.

[0065] In some examples, a biasing unit is coupled to an input terminal of the switching unit via the delay element. In some examples, the delay element is coupled to ground by a capacitor.

[0066] In an example, the first inductor and the two electrical contacts for coupling with the load capacitor form a resonant circuit. In such examples, the delay element may be configured such that an oscillation frequency of the oscillation circuit is limited to a frequency below a parallel resonant frequency fpAR (also known as the antiresonant frequency) of the resonant circuit, but above a series resonant frequency fsER (resonant frequency) of the resonant circuit.

[0067] In an example, the time delay imposed by the delay element is between 5% to 35% of the period of the parallel resonant frequency fpAR of the resonant circuit.

[0068] In an example, the time delay imposed by delay element is between 35% and 90% of a difference between the period of the parallel resonant frequency fpAR and the period of the series P / 90838.W001 resonant frequency fsER, preferably between 50% and 85% of a difference between the period of the parallel resonant frequency fpAR and the period series resonant frequency fsER.

[0069] In an example, the delay element is configured to impose a time delay of between 50 and 500 picoseconds, preferably between 150 and 350 picoseconds, more preferably between 200 and 300 picoseconds.

[0070] In an example, the delay element comprises a low-pass filter.

[0071] In some examples, the delay element has an inductive behaviour. Advantageously, inductive delay elements may provide the required time delay without impacting the wave shape of the oscillations in the circuit. In an example, the delay element comprises a meandering electrically conductive element. In an example, the meandering electrically conductive element comprises between two and twelve meandering branches, preferably between three and ten meandering branches, more preferably three meandering branches. In an example, the meandering electrically conductive element comprises one of an omega-shaped coil, a single planar coil, a flat inductor, a wavy line, a zig-zag line, or a sawtooth line.

[0072] In an example, the oscillation circuit further comprises the electrode arrangement fixedly interconnected to the two electrical contacts to form the load capacitor, the load capacitor including or being configured to removably receive an aerosol-forming substrate. This enables an article comprising an aerosol-forming substrate to be inserted directly into a heating area in close proximity with the electrode arrangement or in a cavity within the electrode arrangement.

[0073] In an alternative example, the oscillation circuit further comprises the electrode arrangement removably interconnected to the two electrical contacts to form the load capacitor, the load capacitor including or being configured to removably receive an aerosol-forming substrate. In such examples, the electrode arrangement may form part of an article comprising an aerosolforming substrate. In other examples, the electrode arrangement may be removable to facilitate easy insertion of an article comprising an aerosol-forming substrate in a heater area on or within the electrode arrangement prior to connection with the oscillation circuit.

[0074] In an example, the oscillation circuit is configured such that, during operation, a peak AC voltage across the two electrical contacts is greater than a supply voltage of the oscillation circuit. In some examples, the oscillation circuit is configured such that, during operation, the peak AC voltage across the two electrical contacts is greater than five times the supply voltage of the oscillation circuit. Advantageously, providing a higher voltage across the load capacitor than the supply voltage enables more power to be delivered to an aerosol-forming substrate with lower switching losses in the switching unit, and therefore directly impacts the efficiency of the aerosolgenerating device. In examples of the present disclosure, this may be achieved without the use of any voltage transformers by relying solely on resonant oscillating operation within the feedback loop. In an example, the peak AC voltage across the two electrical contacts at the operating P / 90838.W001 frequency of the oscillation circuit is from 50V to 500V, more preferably 100V to 400V, even more preferably 120V to 350V, wherein the DC supply voltage to the oscillation circuit is between 6V to 15V.

[0075] In an example, the impedance of the feedback loop at the operation frequency is matched with the impedance of the switching unit, which improves the efficiency of the oscillation circuit.

[0076] In an example, the feedback loop is suspended between a power supply and ground of the oscillation circuit, meaning that there is no direct connection between the feedback loop and the supply voltage or ground - e.g., there is 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 reduces noise and ground influences for more predictable operation in the feedback loop.

[0077] In an example, the feedback loop is connected across an output terminal and a biasing terminal of the switching unit. In some examples, the output terminal of the switching unit is coupled to the supply voltage via a radio frequency choke. The choke acts to block high frequency alternating currents while passing direct current and low frequency alternating current.

[0078] In an example, the feedback loop is configured to operate as an inductive load at an operating frequency of the oscillation circuit to provide approximately a 90° phase shift. As described above, this can be achieved by providing one or more inductors in series with the load capacitor in the feedback loop. In an example, the feedback loop further comprises a capacitive element providing for a 90° phase shift at an operating frequency of the oscillation circuit. In an example, the capacitive element comprises a capacitor connected to ground. The combination of the inductive load and capacitive element in the feedback loop provides a 180° phase shift, which, in combination with an inverting switching unit, provides effective resonant oscillating operation for dielectric heating.

[0079] In an example, the oscillation circuit further comprises a capacitor connected between an output terminal of the switching unit and ground, the capacitor having a capacitance value that is bigger than a maximal intrinsic capacitance of the switching unit. This reduces the influence of the variation of the intrinsic properties of the switching unit due to factors such as temperature and operating frequency on the operation of the feedback loop.

[0080] In an example, the feedback loop comprises a resonant circuit including the two electrical contacts, such that in operation, the load capacitor is part of the resonant circuit. In some examples, the resonant circuit comprises one of a parallel resonant circuit, a series resonant circuit, or a combination of parallel and series resonant circuits. In an example, the feedback loop comprises a parallel resonant circuit which, in use, is electrically stimulated by the output signal of the switching unit. In such examples, the output signal of the switching unit may be a switched voltage across a transistor. In some examples, the impedance of the resonant circuit at the P / 90838.W001 operation frequency of the oscillation circuit is between 0.5Q and 8Q, preferably between 1 Q and 5Q, and more preferably, between 1 ,5Q and 3Q.

[0081] In an example, the switching device comprises a single transistor. In some examples, the transistor may be a bipolar junction transistor (BJT), and the feedback loop may be connected between the collector or emitter and the base of the BJT. In other examples, the transistor may be a field effect transistor (FET) and the feedback loop may be connected between the drain or source and the gate of the FET.

[0082] In an example, the oscillation circuit is configured such that the ratio of the dielectric heating losses in the load capacitor to the switching losses in the switching unit is greater than 1 1 :9, preferably greater than 13:7. Current dielectric heaters typically have heating efficiencies in the region of 50%. However, dielectric heating aerosol-generating devices incorporating the above mentioned features (e.g., incorporating the appropriate feedback loop and delay element) can achieve heating efficiencies up to 70%, which is comparable to induction heating systems known in the art.

[0083] The electrode arrangement comprises a first electrode and a second electrode. In operation, the second electrode has an opposite polarity to the first electrode. In some examples, the first and second electrodes may be flat plate electrodes configured to heat an aerosol-forming substrate situated between the first and second electrode plates. In some examples, the first and second electrode plates may be slightly bent or rounded at the edges to create a smoother electric field distribution around the boundaries of the electrode plates. In some examples, the electrode plates may be curved. The curved electrode plates may have a radius of 15mm or greater.

[0084] In some examples, the electrode arrangement comprises a first electrode interdigitated with a second electrode.

[0085] The term interdigitated relates to an electrode arrangement comprising a first electrode having a first polarity and a second electrode having a second polarity which is the opposite of the first polarity, wherein at least a portion of the first electrode separates two portions of the second electrode. The use of interdigitated electrodes allows for a more homogenous electric field generation, which can be used to avoid hot spots across an aerosol-forming substrate. The electrode arrangement may take on any form, providing that an electric field can be generated across an aerosol-forming substrate in the vicinity of the electrode arrangement.

[0086] In an example, the electrode arrangement may form a flat plate for heating an aerosol-forming substrate situated on a surface of the electrode arrangement. In some examples, the flat plate comprises a first electrode and a second electrode which is at least partially interdigitated with the first electrode. In some examples, the first electrode may comprise a first plurality of electrode portions and the second electrode may comprise a second plurality of electrode portions, wherein P / 90838.W001 each of the first plurality of electrode portions are separated by one of the second plurality of electrode portions.

[0087] In some examples, the electrode arrangement may comprise a first plate and a second plate, wherein the electrode arrangement is configured to heat an aerosol-forming substrate situated between the first plate and the second plate. In an example, the first plate comprises a first electrode and a second electrode which is at least partially interdigitated with the first electrode. In some examples, the second plate may also comprises a first electrode and a second electrode which is at least partially interdigitated with the first electrode. In some examples, the first electrode may comprise a first plurality of electrode portions and the second electrode may comprise a second plurality of electrode portions, wherein each of the first plurality of electrode portions are separated by one of the second plurality of electrode portions.

[0088] In other examples, the electrode arrangement may be cylindrical and define a central cavity for heating an aerosol-forming substrate situated within the cavity.

[0089] In one example, the electrode arrangement may comprise a first electrode and a second electrode each comprising a cylindrical segment configured to interdigitate with a cylindrical segment of the other electrode around a cylindrical axis. In some examples, the first electrode comprises a first plurality of cylindrical segments and the second electrode comprises a second plurality of cylindrical segments, wherein each of the first plurality of cylindrical segments are positioned around the cylindrical axis separated by one of the second plurality of cylindrical segments.

[0090] In another example, the first electrode comprises a first plurality of axially aligned electrode rings and the second electrode comprises a second plurality of axially aligned electrode rings, wherein each of the first plurality of electrode rings are separated by one of the second plurality of electrode rings.

[0091] In some examples, the first electrode comprises a plurality of axially aligned electrode rings and the second electrode comprises a rod or pin extending through the plurality of axially aligned electrode rings.

[0092] In some examples, the first electrode comprises a first plurality of electrode rods or pins and the second electrode comprises a second plurality of electrode rods or pins, wherein each of the first plurality of electrode rods or pins and second plurality of electrode rods or pins are alternately positioned in a grid to form an electrode array. Such examples may create a highly uniform electric field through an aerosol-forming substrate, and may be particularly suited to dielectrically heating a liquid aerosol-forming substrate in a reservoir. In some examples, the density of the electrode array may provide a wicking effect on a liquid aerosol-forming substrate to draw more liquid aerosolforming substrate from the reservoir into the electrode array as the aerosol is generated. P / 90838.W001

[0093] In some examples, the distance between the first electrode and the second electrode may vary across the electrode arrangement. This may further facilitate a more uniform electric field distribution through an aerosol-forming substrate.

[0094] In some examples, the electrode arrangement comprises a first electrode coaxially aligned with a second electrode.

[0095] Advantageously, the use of coaxially aligned electrodes may provide more a more uniform electric field, and therefore more uniform dielectric heating through an aerosol-forming substrate situated within the electrode arrangement.

[0096] In an example, the first electrode comprises a tubular body having a hollow center and the second electrode comprises a rod or pin situated within the hollow center of the first electrode. In such examples, an article comprising an aerosol-forming substrate may be inserted into the electrode arrangement between the first and second electrode. In some examples, the tubular body of the first electrode may comprise one or more openings. The one or more openings may enable the aerosol generated by the dielectric heating to escape the electrode arrangement to an airflow channel.

[0097] In another example, the first electrode comprises a tubular body having a hollow center and the second electrode comprises a tubular body having a hollow center, wherein the second electrode is situated within the hollow center of the first electrode. In an example, the tubular body of the second electrode comprises one or more openings. Such examples enable the inner electrode to define a central airflow passage for the generated aerosol to escape the electrode arrangement.

[0098] In an example, the first electrode comprises a plurality of axially aligned electrode rings and the second electrode comprises a rod or pin extending through the plurality of axially aligned electrode rings. In such examples, gaps between the electrode rings may enable aerosol to escape from the electrode arrangement to an airflow channel.

[0099] In some examples in which either or both the first and second electrodes comprise a plurality of electrode portions, the aerosol-generating device may be configured to provide partial or sectional heating of an aerosol-forming substrate by selectively energizing one or more of the plurality of electrode portions. This enables an aerosol-generating device to switch between different electric field distribution patterns between the first and second electrodes to adjust the heating profile across the aerosol-forming substrate. This sectional heating approach may be used to compensate for geometry and heat transfer properties of the electrode arrangement (and also other components of the aerosol-generating device) and the aerosol-forming substrate in order to avoid localized overheating or underheating in the aerosol-forming substrate.

[0100] In an example, the oscillation circuit further comprises one of a variable capacitor, a variable inductor, a voltage regulator, a transistor voltage biasing element. P / 90838.W001

[0101] In examples in which the oscillation circuit comprises a first and second inductor sharing a mutual inductive coupling, the aerosol-generating device may further comprise an H-field sensor configure to measure the strength of a magnetic field in the vicinity of the first and second inductors.

[0102] The disclosure further provides an aerosol-generating system comprising an aerosolgenerating device according to any of the above examples and an article comprising an aerosolforming substrate having an aerosol former. The article is arranged in the heating region of the device to enable dielectric heating of the aerosol-forming substrate.

[0103] In some examples, the aerosol former comprises at least one of glycerol, polypropene glycol and vegetable glycerin.

[0104] The disclosure further provides an aerosol generation method for an aerosol-generating system according to the disclosed examples. The method comprises measuring frequency data indicative of an oscillation frequency of the alternating electric field across the load capacitor during a dielectric heating operation. The method further comprises determining a frequency profile for the dielectric heating operation based on the frequency data; and determining one or more parameters related to the dielectric heating operation based on one or more properties of the frequency profile.

[0105] It is to be appreciated that the features of the above examples of the disclosure are complementary with one another, except where stated otherwise, and so features of different examples may be readily implemented in the oscillation circuits of other examples. Further optional examples of the disclosure are set out below.

[0106] Ex 1 . An aerosol-generating device for dielectrically heating an article comprising an aerosolforming substrate, the device comprising: an oscillation circuit comprising a feedback loop connected across a switching unit, the oscillation circuit being configured to provide an alternating electric field across a load capacitor when connected in the feedback loop to dielectrically heat an aerosol-forming substrate having an aerosol former received in a heating region of the device; a frequency measurement unit configured to measure frequency data indicative of an oscillation frequency of the alternating electric field across the load capacitor connected in the feedback loop during a dielectric heating operation; and a control unit communicatively coupled with the frequency measurement unit, wherein the control unit is configured to: receive the measured frequency data from the frequency measurement unit; and determine one or more parameters related to the dielectric heating operation based on the received frequency data.

[0107] Ex 2. An aerosol-generating device according to Ex 1 , wherein the frequency measurement unit is configured to measure a switching frequency of the oscillation circuit. P / 90838.W001

[0108] Ex 3. An aerosol-generating device according to Ex 1 , wherein the frequency measurement unit comprises a magnetic field probe configured to measure an alternating magnetic field departed by an inductor of the feedback loop.

[0109] Ex 4. An aerosol-generating device according to any preceding Ex, wherein the measured frequency data is timestamped to map the frequency data to a time in the dielectric heating operation.

[0110] Ex 5. An aerosol-generating device according to any preceding Ex, wherein the control unit is configured to determine one or more parameters related to the dielectric heating operation based on a comparison of the received frequency data with reference data.

[0111] Ex 6. An aerosol-generating device according to any preceding Ex, wherein the control unit is further configured to: determine a frequency profile for the dielectric heating operation based on the received frequency data; and determine the one or more parameters related to the dielectric heating operation based on one or more properties associated with the frequency profile.

[0112] Ex 7. An aerosol-generating device according to Ex 6, wherein the control unit is configured to determine the one or more parameters based on a comparison of the frequency profile with a reference profile stored in memory communicatively couple to the control unit.

[0113] Ex 8. An aerosol-generating device according to Ex 6, wherein the control unit is configured determine the one or more properties based on a model defining a relationship between one or more properties of a frequency profile and one or more parameters related to a dielectric heating operation.

[0114] Ex 9. An aerosol-generating device according to Ex 8, wherein the model comprises a database mapping one or more frequency profile property values to one or more parameters.

[0115] Ex 10. An aerosol-generating device according to any preceding Ex, wherein the control unit is configured to: detect a minimum frequency value of the measured frequency data during a pre-heating phase of the dielectric heating operation; determining a temperature of the aerosol-forming substrate based on the minimum frequency value.

[0116] Ex 11 . An aerosol-generating device according to Ex 10, wherein following determination of the aerosol-forming substrate temperature, the control unit is configured to: continue the pre-heating phase the aerosol-forming substrate for a predetermined time period; and initiate, after the predetermined time period has elapsed, a maintenance heat phase.

[0117] Ex 12. An aerosol-generating device according to any preceding Ex, wherein the control unit is configured to: P / 90838.W001 determine a presence of a puff based on an increase in a frequency value of the frequency data exceeding a pre-determine threshold level.

[0118] Ex 13. An aerosol-generating device according to any preceding Ex, wherein the control unit is configured to: determine a value indicative of a puff volume based on a relative increase of the frequency between a frequency at a start of a puff and a frequency at the end of the puff.

[0119] Ex 14. An aerosol-generating device according to any of Ex 6 to 13, wherein the control unit is further configured to: determine a first order derivative of the frequency profile; and determine the one or more parameters related to the dielectric heating operation based on one or more properties associated with the first order derivative of the frequency profile.

[0120] Ex 15. An aerosol-generating device according to Ex 14, wherein the one or more properties comprises a zero-crossing of the first order derivative of the frequency profile.

[0121] Ex 16. An aerosol-generating device according to Ex 14, wherein the one or more properties comprises a frequency change exceeding a pre-determined threshold value.

[0122] Ex 17. An aerosol-generating device according to Ex14, wherein the control unit is configured to: detect one or more of an amplitude, a variance and a pulse width of a peak of the first order derivative of the frequency profile; determine a puff volume based on the one or more amplitude, variance and pulse width of a peak of the first order derivative of the frequency profile.

[0123] Ex 18. An aerosol-generating device according to any preceding Ex, wherein the one or more parameters comprises one or more of a temperature of the aerosol-forming substrate, a depletion level of the aerosol-forming substrate, a type of aerosol-forming substrate, a humidity content of aerosol-forming substrate, an article insertion status in the device, and a time moment when to switch from a pre-heating phase to a steady-state phase.

[0124] Ex 19. An aerosol-generating device according to any preceding Ex, wherein the control unit is configured to adjust a power supplied by the oscillation circuit to the load capacitor based on the determined one or more parameters.

[0125] Ex 20. An aerosol-generating device according to any preceding Ex, wherein the control unit is configured to select a heating profile for the aerosol-forming substrate based on the determined one or more parameters.

[0126] Ex 21. An aerosol-generating device according to any preceding Ex, wherein the device further comprises a user interface, wherein the control unit is configured to notify a user on the determined one or more parameters using the user interface.

[0127] Ex 22. An aerosol-generating system comprising: P / 90838.WQ01 an aerosol-generating device according to any preceding Ex; and an aerosol-forming substrate comprising an aerosol former, situated in a heating region of the aerosol-generating device.

[0128] Ex 23. An aerosol generation method for an aerosol-generating system according to Ex 20, the method comprising: measuring frequency data indicative of an oscillation frequency of the alternating electric field across the load capacitor during a dielectric heating operation; determining a frequency profile for the dielectric heating operation based on the frequency data; and determining one or more parameters related to the dielectric heating operation based on one or more properties of the frequency profile.

[0129] Any of all the features of the above described oscillation circuit may be provided on a single low dielectric constant carrier material.

[0130] Brief Description of Drawings

[0131] The invention will be further described, by way of example only, with reference to the accompanying drawings in which:

[0132] Figure 1 is a schematic illustration of a dielectric heating aerosol-generating system according to embodiments of the disclosure;

[0133] 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;

[0134] Figure 3a-b are a schematic illustrations of an oscillation circuit showing two different phaseshifting elements, one exemplarily implemented as a resonance circuit, one exemplarily implemented as a capacitive element, to achieve a 180 degrees phase shift;

[0135] Figure 3c is a schematic illustration of an oscillation circuit showing two different phaseshifting elements, one exemplarily implemented as a resonant cavity having parallel resonance properties, one exemplarily implemented as a capacitive element, to achieve a 180 degrees phase shift;

[0136] Figure 4 illustrates an oscillation circuit diagram according to embodiments of the disclosure;

[0137] 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;

[0138] 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;

[0139] Figures 7A-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; P / 90838.W001

[0140] Figure 8 shows an 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;

[0141] Figure 9 shows a schematic illustrations of an interdigitated electrode arrangement with a varying electrode separation distance, according to embodiments of the disclosure;

[0142] Figures 10A-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;

[0143] Figure 11 A-D are schematic illustrations of an electrode arrangement having variable polarity control, according to embodiments of the disclosure;

[0144] 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;

[0145] Figure 13A-C are isometric illustrations of coaxial electrode arrangements for use in the oscillation circuit of Figures 2 to 4, according to embodiments of the disclosure;

[0146] Figure 14 is a schematic illustration of a control system for the dielectric heating aerosolgenerating system shown in figure 1 , according to embodiments of the disclosure;

[0147] Figure 15 is a graph illustrating how the frequency dependency of the relative permittivity of Glycerol varies with temperature.

[0148] Figure 16a is a graph illustrating an oscillation frequency profile measured during a dielectric heating operation, according to an embodiment of the disclosure;

[0149] Figure 16b is a graph illustrating a first derivative of the graph of figure 16a;

[0150] Figure 17 is a flow diagram illustrating a control process for a pre-heating phase of a dielectric heating operation, according to an embodiment of the disclosure; and

[0151] Figure 18 is a flow diagram illustrating a control process for a steady-state phase of a dielectric heating operation, according to an embodiment of the disclosure.

[0152] Specific Description

[0153] 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 aerosolforming 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 1 10 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. P / 90838.W001

[0154] In other examples, the first electrode 130 and the second electrode 135 may form part of the article 105 comprising the aerosol-forming substrate 1 10. In such embodiments, a cavity between the first and second electrical contacts 160, 165 is sized such that, when the aerosol-forming 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.

[0155] 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.

[0156] 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 aerosolforming 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 2mm, depending on the desired capillary strength or rise. The first and second electrodes can be arranged as two matrices or arrays of pinlike, 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 2mm, depending on the desired capillary strength or rise. In another variant, the wicking element can be a separate element that is interposed between two electrodes 130, 135, for example flat or slightly curved electrodes 130, 135. P / 90838.W001

[0157] The aerosol-generating device 120 further comprises a power supply 170 and a controller 180 electrically coupled to the oscillation circuit 150. The controller 180 is communicatively coupled to a frequency measurement unit 185 configured to measure frequency data indicative of an oscillation frequency of the alternating electric field across the first and second electrodes 130, 135 during a dielectric heating operation. The controller 180 is configured to receive the measured frequency data from the frequency measurement unit 185 and determine one or more parameters related to the dielectric heating operation based on the received frequency data.

[0158] In this embodiment, the power supply 170 can be a rechargeable lithium ion battery, for example with one or more lithium ion battery cells, and the aerosol-generating device 120 comprises a power connector that enables the aerosol-generating device 120 to be connected to a mains power supply for recharging the power supply. Providing the aerosol-generating device 120 with a power supply, such as a battery, enables the aerosol-generating device 120 to be portable and used outdoors or in locations in which a mains power supply is not available.

[0159] 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.

[0160] The aerosol-generating system 100 is also configured for measuring a dielectric property of the aerosol-forming article 105 or the aerosol-forming substrate 1 10 using the 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 aerosol-forming article 105 between the first electrode 130 and the second electrode 135. The aerosol-generating system can be configured to measure a dielectric property, for example an instant value, timely-evolution, or change of a dielectric property, for example to determine whether the aerosol-forming article 105 meets specific criteria or is an authentic substrate. The aerosol-generating system in this example is also configured to control the heating of the aerosol-forming substrate 110 based on the measured dielectric property of the aerosol-forming article 105. P / 90838.W001

[0161] Figure 2 is a schematic illustration of an oscillation circuit 250 for use in the aerosolgenerating system 100 of Figure 1 , according to an embodiment of the disclosure. Oscillation circuit 250 comprises a switching unit 260 interconnected with a resonator feedback loop 270 to provide for a self-oscillating signal to the switching unit 260. The switching unit 260 comprises a single transistor, such as a bipolar junction transistor (BJT) or a field effect transistor (FET).

[0162] The oscillation circuit 250 can further comprise a choke 280 that acts on an input to the feedback loop 270 to provide for a stimulation signal, for example a stimulation voltage. The oscillation circuit also comprise a biasing unit 290 acting on the feedback loop 270 for providing a variable or controllable biasing signal, for example a biasing voltage for setting the operating conditions. In the variant shown, the feedback signal can be described as a voltage. The output voltage UOUT of the switching unit 260 is coupled to the feedback loop 270 providing a feedback switching signal in the form of a voltage UIN to the switching unit 260. The configuration of the feedback loop 270 is such that the output signal, e.g. the voltage UOUT of the switching unit 260 can undergo a phase change and arrives inverted at the input UIN of the switching unit 260 for resonant oscillation. In other configurations, a current could be used as the feedback signal with a switching unit 260 comprising a BJT.

[0163] 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.

[0164] As shown in Figures 3a and 3b, feedback loop 270 includes a resonant circuit 272 comprising the load capacitor CL providing for a first 90 degrees phase shift or quarter wave shift to the feedback signal. Feedback loop 270 further includes a capacitive element 274 providing for a second 90 degrees phase shift or quarter wave shift to the feedback signal, such that the feedback signal reaching the input of the switching unit 260 is inverted and phase-shifted by 180 degrees. Switching unit 260 is itself configured for inverted switching operation to provide a 180 degree phase shift between the input UIN and the output UOUT of the switching unit 260.

[0165] 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 P / 90838.W001 circuit 272 may comprise a series resonator circuit or a parallel resonator circuit, examples of which are described in greater detail below.

[0166] In an alternative embodiment, resonant circuit 272 may include a resonant cavity 272, as illustrated in Figure 3c. The resonant circuit 272 including resonant cavity may have an interior volume configured to receive an aerosol-forming substrate 1 10, for example having an opening for inserting an aerosol-forming substrate 1 10. In an example, the resonant circuit 272 including resonant cavity can be configured as a A / 4 resonator. The resonant circuit 272 including resonant cavity may be configured to behave like an RLC circuit. The inductor L and the capacitor C are arranged in parallel to each other, to have a parallel resonance or a frequency close to the parallel resonance that can be stimulated by the switching unit 260. Resonant circuit 272 including cavity may be coupled to the feedback loop 270 using one or more of a capacitive coupling, an inductive antenna coupling (magnetic coupling), a direct electric coupling, or a window coupling (e.g. coupling with a loop).

[0167] 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.

[0168] Figure 4 illustrates an oscillation circuit 350 according to a non-limiting, exemplary embodiment of the disclosure. Oscillation circuit 350 comprises a switching unit 260 in the form of a transistor T having an intrinsic capacitance Ci. Moreover, transistor T is configured for inverting operation, for example as an inverting common source FET, MOSFET, or a common emitter BJT. The source terminal of transistor T can be coupled to a DC power supply via a choke 280. Between the gate and source terminals of transistor T extends a feedback loop 270. The feedback loop 270 comprises a resonant circuit 272 including a load capacitor CL having a first and second electrode 130, 135 separated by an aerosol-forming substrate 110. In the variant shown, the resonator circuit 272 is also connected to ground via a delay line D and a capacitor C2 connected in series to the delay line D . The circuit 350 further comprises a biasing unit 290 coupled to the gate terminal of the transistor T via the delay line DL. AS shown in Figure 4, the biasing unit 290 is electrically connected between the delay line DL and the capacitor C2, so that the biasing unit 290 is somewhat isolated from the high oscillation frequency of the feedback loop 270.

[0169] The delay line D is a time delay element, for example an element that has inductive behavior, for slowing down the arriving voltage wave from the feedback loop 270 during a period of the oscillation. This allows to tune the resonant circuit 272 to a desired switching and oscillation frequency, to move the oscillation frequency away from the natural resonant frequency given by the resonant circuit 272. This ensures that oscillation circuit 350 remains in a predefined frequency operating range to provide for the requisite inverted or 90° phase shifted feedback and also to make P / 90838.W001 sure that the feedback loop has a low impedance to provide for a high gain, as described in greater detail below.

[0170] 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 1 10 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.

[0171] 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. 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.

[0172] A capacitor Ci is arranged in parallel to the transistor T and therefore in parallel with the intrinsic capacitor of the transistor T (e.g. a field effect transistor). This facilitates a less voltagedependent oscillation and frequency, stabilizes the oscillation, and also improves the overall dielectric heating efficiency. Capacitance of capacitor Ci is chosen to be larger than the maximal intrinsic capacitor Ci of transistor T at the operating conditions, so that the variation of the intrinsic transistor based on frequency, temperature, etc. has much less or negligible influence on the feedback loop 270. For example, in a non-limiting embodiment, the value can be in a range between 2pF to 10OpF, more preferably in a range between 5pF and 50pF.

[0173] Capacitive element 274 comprises a capacitor C2arranged 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 P / 90838.WQ01 shift to the feedback voltage of feedback loop 270 with minimized losses or other undesired effects, and it therefore needs to have a high-quality factor or Q factor, preferably above 1000 at 100MHz. The capacitance value for C2 of the capacitive element 274 should be relatively high as compared to Ci, for example in a range between 500pF to 100nF, more preferably between 1 nF and 50nF, which leads to a low impedance of capacitive element 274. In one embodiment, the capacitive element 274 can be implemented as a RC network to provide for the 90° phase shift, for example using two single-resistor-capacitor networks, having two capacitors in the feedback loop, each capacitor connected to ground via a resistor.

[0174] Resonant circuit 272, together with capacitive element 274, provides for a 180° phase shift and a voltage gain from the output UOUT to the input UIN, and transistor T (for example a FET) is configured for inverting operation, thereby also providing for another 180° phase shift. This results in a resonant or close-to resonant oscillation and an amplified voltage UL across the electrodes 130 and 135 of the load capacitor CL, as compared to the DC supply voltage. When operating close to resonance, the resonant circuit 272 circuit behaves inductively, having a high Q factor. Furthermore, the feedback loop 270 is impedance-matched with the transistor T, to provide for a high gain, leading to an increased voltage across the load capacitor CL. Also, preferably, this gain is achieved without the use of an additional voltage or current amplifying passive element, such as a tapped inductor or a transformer located in the circuit that forms the feedback loop 270, as such passive elements are difficult and lossy to operate and design at frequencies greater than 50 MHz.

[0175] 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.

[0176] 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.

[0177] Oscillation circuit 350 can be described or characterized as a Pierce oscillation circuit with a modified feedback loop 270, where the physical Quartz element is replaced by a Quartz-mimicking or Quartz electric equivalent circuit to provide for an inverting feedback to the switching unit 260 that also operates in an inverted mode. In some embodiments, oscillation circuit 272 can be based on other resonant feedback loop oscillation circuit configurations, for example, but not limited to, the use of a Colpitts or Hartley type oscillator, using an inverting transistor T. P / 90838.WQ01

[0178] Figures 5A to 5F illustrate how a Quartz-mimicking or Quartz equivalent circuit may be derived using a variant of a parallel resonator circuit PRC, that can serve as an exemplary and nonlimiting embodiment as resonant circuit 272. A Quartz-mimicking or Quartz equivalent circuit can have a parallel resonance at a given frequency. This can be seen as a circuit with two branches, one representing the mechanical oscillation and one representing the electric behavior, as illustrated in figure 5A and 5B. The mechanical oscillation is represented by a first branch having load capacitor CL and an inductor LTOT. The electric oscillation is represented by a second branch arranged in parallel to the first branch, having a Capacitor CE. This configuration leads to a series connection of two capacitors CL and CE (seen around the loop formed by the two branches) so that CE will decrease the overall capacitive value of the equivalent circuit. Also, this circuit provides an inductive phase shift of about 90° within certain defined frequency range.

[0179] Referring now to Figure 5C, one branch of the parallel resonator circuit PRC comprises an inductor LTOT and the load capacitor CL connected in series of the first branch. This branch can be improved by splitting LTOT into two inductors Li and L2on each side of the load capacitor CL, as shown in Figure 5D, to provide a split inductor or split-coil design and a more symmetric application of the voltage UL across the load capacitor CL, thereby improving dielectric heating efficiency. To provide for parallel resonance, the capacitor CE of the second branch can be replaced with an inductor (as shown in Figure 5F) due to capacitor CE‘S minimal capacitive effect on CL.

[0180] In a non-limiting example starting from the split inductor Li and L2of the resonant circuit of Figure 5D, inductors Li and L2can be mutually magnetically coupled to form a mutual inductance M, thereby forming the parallel circuit branch or second branch of the resonant circuit 272, as shown in Figure 5E. The mutual magnetic coupling can be achieved by the close proximity of the two inductors L1 and L2 with alignment of winding axis of the coils, or by use of a mutual magnetic core, or both. This has the advantage of providing a parallel-resonator circuit PRC without the use of additional wires for the second branch, and without additional windings or separate magnetic cores for a second parallelly-arranged inductor. This also allows for a symmetric arrangement that favors and facilitates the inductive coupling of the two inductors Li, L2and the balancing of the voltage UL over load capacitor CL. The symmetry of the two branches in either direction with first branch Li - CL - L2and the second branch with inductor LE, representing the two mutual inductance values, facilitates the symmetrical balancing of the voltage over the electrodes of the load capacitor CL, which consequently reduces losses created at the load capacitor CL. This split inductor principle can also be referred to as a split coil resonator.

[0181] 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. P / 90838.WG01

[0182] The values of components in this resonant circuit 272 are preferably chosen to be in the following exemplary and non-limiting ranges. LTOT can be a range between 10nH to 50nH, more preferably between 15nH and 40nH, which is the equivalent of Li plus L2, LEcould be in a range between 7nH and 30nH, more preferably between 10nH and 20nH, and the value of the load capacitor can be in a range between 0.5pF to 5pF, more preferably between 1 pF to 3pF.

[0183] The resonant circuit 272 can be configured as another type of tank circuit providing for the 90° phase shift in a given frequency range. In one embodiment, the resonant circuit 272 can be implemented as a series resonant circuit, having the load capacitor CL connected in series with one or more inductive elements, configured to provide for an inductive response or 90 degrees phase shift in a given frequency range that is suitable for dielectric heating.

[0184] In order to produce the required dielectric losses in the load capacitor CL, a high frequency is needed. The dielectric losses will increase somewhat proportionally to the frequency (in this case the oscillation frequency fsof the oscillation circuit) of the voltage applied to the load capacitor CL. However, higher switching frequencies fslead to greater switching losses in the transistor. Where very high switching frequencies are used, e.g. 1 GHz or more, expensive circuit designs are necessary to make the circuit operable (e.g. GaAn transistors, GHz-type circuit design e.g.).

[0185] 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 EFacross the aerosol-forming substrate 1 10.

[0186] 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.

[0187] 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 P / 90838.W001 switching frequency should be in a range between 100MHz and 1.2 GHz, more preferably between 150MHZ to 1 GHz, more preferably between 200MHz and 900MHz. At the same time, the maximal- value of electric field strength between the electrodes of the load capacitor CL should be limited to a reasonable value that allows for simple electric insulation materials and designs, taking into account impurities and inhomogeneous substrate designs, the use of thin electrodes that may be located in close proximity to each other (for example but not limited to 1 mm-10mm), potential exposure or close proximity to human body, and potential improper human manipulation. Preferably the average electric field strength across the electrodes of the load capacitor is maximally 120V / mm, more preferably maximally 100V / mm, even more preferably maximally 80V / mm.

[0188] Preferably, during nominal heating operation (not during a start-up or warm-up phase that lasts less than 30 seconds where the efficiency can be lower), the heating efficiency should be at least 60% (desired power losses PL versus all the other losses, which can include switching losses of transistor T, losses caused by biasing circuit and choke, inductive-resistive losses of the inductors Li and L2, capacitive-resistive losses from capacitors Ci and C2, and resistive losses of electrodes Ei and E2and the wiring). As an example, the overall power could be 10W, while the effective power or heating losses PL should be 6W or more, with 4W or less of non-heating losses or other heating losses not caused in the substrate 1 10 between the first and second electrodes 130, 135. More than 6-7W of power losses is not desirable for a handheld device. Preferably the aerosol-generating device is configured such that there are less than 5W of losses during nominal heating operation or any other operation lasting for more than 30 seconds. The average dielectric heating power density provided by the aerosol-generating device may be in a range between 1 W / cm3 to 25W / cm3 per volume of aerosol-forming substrate material over a time period of less than 15 minutes, preferably between 1.5W / cm3 and 15W / cm3.

[0189] During an initial start-up phase, the average dielectric heating power density may be controlled or set to operate in a range between 7W / cm3 to 25W / cm3. During a nominal (maintenance) heating phase, the average dielectric heating power density may be controlled or set to operate in a range between 1 W / cm3 to 7W / cm3. Preferably, during the start-up phase, the average dielectric heating power density is controlled or set to operate in a range between 8W / cm3 to 20W / cm3. Preferably, during the nominal heating phase the average dielectric heating power density is controlled or set to operate in a range between 1 W / cm3 to 5W / cm3.

[0190] To have a proper inverting effect and a 180° phase shift on the feedback loop 270 between UIN and UOUT, the oscillation circuit 350 must remain in a frequency operating range where the behavior of the feedback loop 270 is highly inductive. In the example comprising a parallel resonator circuit (PRC), the series resonance frequency fsER (resonant frequency) is relatively close to the parallel resonance frequency fpAR (antiresonant frequency). If the oscillation frequency fs of the PRC exceeds the parallel resonance frequency fPAR, the feedback loop 270 will act capacitively and not P / 90838.WG01 provide the necessary phase inversion to the feedback loop 270. Furthermore, the equivalent impedance of the circuit will increase to an extent that is too high for efficient dielectric heating as the oscillation circuit 350 will not be able to provide a high signal gain.

[0191] Oscillations in the feedback loop 270 will be naturally drawn towards the parallel resonance (antiresonant) frequency of the resonant circuit 272. However, the addition of a delay line D can introduce a slight time delay limiting the oscillation frequency below the parallel resonance frequency. Figure 6 shows a frequency analyzer plot of an exemplary resonant circuit 272, specifically a plot of a parallel resonator circuit PRC showing the relationship between the oscillation frequency (with a series resonance at 855 MHz and a parallel resonance at 1 .246 GHz), the phase shift across the PRC (with a relatively flat inductive 90° degrees frequency response between the two resonant frequencies) and the effective impedance of the PRC. More specifically, it can be seen from Figure 6 that the 90° phase shift starts dropping before the parallel resonance frequency fpAR is reached. After the parallel resonance frequency fPAR, the phase shift response drops below 0° to capacitive behavior and the impedance is very high, e.g. 2.4kQ. 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. The impedance of the resonant circuits at the operating frequency of the oscillation circuit may be between 0.5Q and 10O, preferably between 10 and 50, and more preferably, between 1.50 and 30. The parallel resonance frequency fPAR can be above 1 GHz, e.g. 1 GHz to 1.5GHz, while the actual switching frequency fs can be below 1 GHz, and this lower switching frequency is caused by the delay line DL.

[0192] 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 FIG. 6. For example, a resulting impedance of the feedback loop at the oscillation frequency fs of the oscillation circuit can be in a range of approximately 10OmQ to 20. 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 P / 90838.WG01 frequency fpAR and the period of the series resonance frequency fsER, again providing that the above two conditions (i) and (ii) are fulfilled, more preferably a range between 50% and 85%. For example, taking the illustration of FIG. 6 and as a non-limiting numerical example, assuming that a parallel resonance frequency is at 1 .25 GHz, therefore having a period of 800ps (picoseconds), and a series resonance is at 855MHZ, and therefore a period of 1 169ps, there is a difference of 369ps between the period of fpAR and fsER. The time delay caused by delay line DL can be in the above range, for example at 70% of the period difference between 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.

[0193] 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.

[0194] Figures 7A-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 7A 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.

[0195] Figures 7B and 7C show electrode arrangements comprising a plurality of electrodes for each polarity wherein each electrode is positioned adjacent to electrodes of the opposite polarity. P / 90838.W001

[0196] 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.

[0197] As shown in Figure 7D, 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 7D on an opposite side of the aerosol-forming substrate 1 10. The electrodes of the second electrode arrangement can be configured to align with electrodes of the first electrode arrangement having an opposite polarity.

[0198] Alternatively, as shown in Figure 8, the interdigitated electrode arrangement may comprise a first and second electrode configured to interdigitate together around a cylindrical axis to form a tubular structure. In this embodiment, there are two pairs of three digits of the electrodes. Preferably, thehe tubular structure can have a diameter between 5mm to 9mm. The tangential distance between the electrodes of opposite polarity can be between 0.5 mm to 3 mm, preferably between 0.7 mm to 12.2 mm.

[0199] Figure 9 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.

[0200] Figures 10A-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 1 10 positioned in a central cavity formed by the electrode arrangement. The electrode arrangement in Figures 10A-B comprises a series of axially aligned electrode bands positioned adjacent to electrode bands having opposing polarities. In such embodiments, the aerosol-forming substrate 1 10 is not positioned directly between opposing electrodes, but is still heated by the presence of the alternating electric field in its proximity. Stronger and more uniform heating of the aerosol-forming substrate 110 may be achieved using the electrode arrangement shown in Figure 10B, which is configured such that electrical field between opposing polarity electrodes is strongest across the aerosol-forming substrate 1 10. Figures 10C-D illustrate how the plurality of electrode portions from the electrode arrangements of Figure 10A-B may be electrically connected to achieve an interdigitated configuration.

[0201] Figure 11 A-D are schematic illustrations of an electrode arrangement having variable polarity control, according to embodiments of the disclosure. By the use of an analog signal demultiplexer or analog signal switch or an equivalent circuit, it is possible to selectively connect one or more pairs of electrodes to an oscillating feedback loop to deliver sectional heating to the load capacitor CL. In P / 90838.W001 the illustrated embodiment, adjacent electrodes can be switched to have the same polarity, or opposing electrodes can be switched and reconfigured to the same polarity. This enables an oscillation circuit to switch between different electric field distribution patterns between the electrodes to adjust the heating profile across the aerosol-forming substrate 1 10. In the embodiment shown in Figures 1 1A to 1 1 B, the electrodes form cylindrical segments that can be arranged around a cylindrically-shaped cavity for different electric-field patterns. This principle also works for other numbers of electrode pairs, e.g. two (2) pairs, three (3) pairs, or four (4) pairs, etc., and for sectional, zoned, or partial heating of areas or volumes of an aerosol-forming substrate 1 10. The analog signal switch or analog signal demultiplexer can be implemented electronically, mechanically, or electro- mechanically. For example, a semiconductor-based or solid state switch or demultiplexer can be based on JFET switches or a bilateral parallelly-arranged CMOS switch, combining PMOS and NMOS. An electromechanical based switch or demultiplexer can be based on a microelectromechanical systems (MEMS), for example using a RF MEMS switching technology, and a mechanical switch or demultiplexer can be based on relays, for example RF micro-relays. In some embodiments, more than one oscillation circuit may be used. For example, a separate oscillation circuit may be provided for each pair of electrodes in the electrode arrangement.

[0202] Figure 11 D illustrates how electrodes of the electrode arrangement from the system of Figure 11 C may be independently energized to provide sectional, zoned, or partial heating of a cylindrical substate 110. In the illustrated embodiment, there are four (4) opposing electrodes, each neighboring pair of electrodes configured to be connected to an oscillation circuit 150, 250, 350, or another type of oscillation circuit. This enables the selective heating of a segment area or zone of the cylindrical substrate 110 with heating zones HZ that can be moved by 90 degrees for each electrode pair. The size of the heating zones may be modified by changing the geometry of the electrodes or the number of electrode pairs in the electrode arrangement.

[0203] For this configuration shown in Figure 11 D and for other configurations that are intended to heat cylindrical consumables, an aerosol-forming article 105 comprising an aerosol-forming substrate 1 10 may form a hollow cylinder, having an interior hollow cylindrical volume. This aerosolforming article geometry may be beneficial since lower dielectric losses occur at areas that are located farther away from two electrode plates Ei and E2having opposite polarity. The inner hollow cylinder can have a diameter of that is in a range between 20% and 80% less that the outer diameter of the aerosol-forming article 105, more preferably in a range between 25% and 60% less that the outer diameter of the aerosol-forming article 105, even more preferably between 25% and 45% less that the outer diameter of the aerosol-forming article 105. In one embodiment, the inner core of the cylindrical aerosol-forming article 105 may be filled with an aerosol-forming material or a filler material that has a higher dielectric constant than the aerosol-forming material of the outer cylinder portion. In some embodiments, the inner core of the aerosol-forming article 105 could have a higher P / 90838.W001 content of an aerosol-forming carrier liquid, such as glycerol or polypropene glycol (PPG), having high dielectric constants. Such an arrangement can increase the dielectric losses in the core area for further aerosol generation, or provide a filler material that could generated additional heat by dielectric losses, the heat capable of propagating from the inner core to the lateral sides into the outer cylindrical portion.

[0204] As another variant, it is also possible that a penetrating pin, rod, or blade is provided with the aerosol forming device 100, arranged centrally in the heating cavity. The penetrating pin, rod, or blade can be made or coated with a material having a high dielectric constant. The penetrating pin, rod, or blade can be configured and arranged such that it penetrates substantially into a central axis of the aerosol-forming substrate 110, when the aerosol-forming article 105 is inserted into the cavity. Preferably, the material chosen for the pin, rod, blade or the coating thereof should have a high dielectric constant, for example above 20, be non-conductive, and have good heat radiation properties and thermal stability, for example but not limited high-entropy or high dielectric ceramics. Such pin, rod, or blade could act as a passive heater that would heat up in the oscillating electric fields, improving the heating performance in the center of the cylindrical aerosol-forming article 105.

[0205] 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 substate 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 substate into the channel. Figures 13b-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 13c, 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 13a, 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 substate into the electrode array.

[0206] Figure 13 shows isometric illustrations of coaxial electrode arrangements for use in the oscillation circuit of Figures 2 and 3, according to embodiments of the disclosure. The electrode arrangement of Figure 13A comprises a first electrode tube, pin, or rod Ei and a second electrode E2tube having a larger diameter than the first electrode tube, pin or rod Ei. The electrode P / 90838.W001 arrangement is configured such that an aerosol-forming substrate may be situated between the first electrode Ei and second electrode E2when coaxially aligned. Aerosol generated from the aerosolforming substrate 110 can escape in a direction that is parallel to the rotational or cylindrical axis of the substrate, or can also escape laterally from the cylindrically shaped second electrode E2. However, it is also possible that the first electrode Ei can comprise one or more openings leading to a central airflow channel running through the centre of the first electrode Ei allowing the generated aerosol to escape laterally via the centrally-arranged electrode arrangement.

[0207] In another embodiment illustrated in Figure 13B, the first electrode Ei may be in the form of a rod situated within a tubular electrode E2. In a variant, in order to enable generated aerosol to escape laterally by the electrode arrangement, the second electrode E2may comprise one or more openings, similar to the first electrode Ei of Figure 13A. Alternatively, the tubular electrode E2may not extend entirely around the first electrode Ei, thereby creating another region for generated aerosol to laterally escape the electrode arrangement. In the electrode arrangement illustrated in Figure 13B, tubular electrode E2comprises two electrode portions separated by a gap enabling zoned or sectional heating across the length of an aerosol-forming substrate 1 10 situated between the electrodes Ei and E2. The two electrode portions of tubular electrode E2may share the same polarity or they may be independently energized with the use of an analog signal demultiplexer 11 10 or by the use of selectively applying signals of different oscillators 150, 250, 350 to provide sectional, zoned or partial heating of an aerosol-forming substrate situated between the first electrode Ei and the tubular electrode E2.

[0208] Figure 13C illustrates another electrode arrangement in which the tubular or rod-like electrode E2comprises a plurality of electrode bands axially aligned with each other and coaxially aligned with a first electrode Ei. Similarly, to the electrode arrangement illustrated in Figure 13B, separation gaps can be provided between each of the plurality of electrode bands to enable generated aerosol to escape the electrode arrangement. The plurality of electrode bands of the tubular electrode E2may be independently oscillated to provide sectional, zoned or partial heating of an aerosol-forming substrate 110 situated between the first electrode Ei and the tubular or rod-like electrode E2. Figure 13C also illustrates how the electrode arrangement can be integrated with an aerosol-generating device. A DC power supply 1090 is coupled to an oscillation circuit 1 100 which is directly connected to the first electrode Ei. In order to enable the plurality of electrode bands of the tubular electrode E2to be independently energized, the plurality of electrode bands can be connected to the oscillation circuit 1100 via an analog signal demultiplexer or analog signal switch 1110 and microprocessor 1120.

[0209] Figure 14 is a schematic illustration of a control system for the dielectric heating aerosolgenerating system shown in figure 1 , according to embodiments of the disclosure. P / 90838.WG01

[0210] An oscillation unit OSC having an inverting switching unit and an LC feedback loop is provided, the feedback loop including two inductors L1 , L2 and the load capacitor CL. The load capacitor CL comprises a removable aerosol-forming substrate S arranged within an electrode arrangement E1 , E2 for exposure to an alternating electric field, for dielectric heating. An electric field frequency probe ANT, for example an antenna, is arranged to be exposed to the alternating electric field to generate a signal that is indicative of the frequency of the alternating electric field, which is provided to a frequency counter FC. The frequency counter FC delivers its signal on the frequency to a controller, for example a microprocessor.

[0211] In some embodiments, the control system may utilize one or more of resonant antennas, microstrips, waveguides, for high-frequency sensing.

[0212] The controller can be operatively connected to a user interface Ul to allow for communication of statuses and results to a user, for example but not limited to one or more LEDs, haptic feedback, display screen, audio feedback, or a combination of those. The controller can also control or otherwise act on the electric power flow that is supplied to the oscillator unit OSC, with a power supply unit PSU. For example, the power supply unit PSU can be instructed increase or decrease a supply voltage by acting on a DC-DC converter (e.g. boost converter, buck-boost converter, buck converter, full bridge or half bridge DC-DC converter) to provide for a variable voltage to oscillator unit OSC, or by performing an on / off control to control the electric power delivery to the DC-DC converter with a fixed voltage supply, for example by bang-bang chopping control or pulse width modulation (PWM).

[0213] Figure 15 is a graph illustrating how the frequency dependency of the relative permittivity of Glycerol varies with temperature. As shown in figure 15, the relative permittivity of Glycerol increases with temperature (see e.g. at 100MHz, at 273K about 15, at 295K about 40), leading to a higher capacitance value of the load capacitor, causing the oscillation frequency of the self-oscillating oscillation circuit to drop. Conversely, the frequency-dependency of the relative permittivity of Glycerol can be seen, showing that with an increase of the oscillation frequency of the alternating electric field, the relative permittivity decreases, leading to a lower capacitance value of the load capacitor. This is due to the so-called relaxation effect of the Glycerol. This is turn will force the oscillation to increase. It can also be seen that the drop of relative permittivity can be substantial for a given frequency range.

[0214] Figure 16a illustrates the evolution of the switching frequency of the oscillation circuit over time, during a heating session including a heat-up phase and a steady state phase or session / experience phase, where the puffs are taken.

[0215] At time instant A the heating session is started with the heat-up phase, and the oscillation frequency starts at an initial value, for example, at about 500MHz. The oscillation frequency then decreases as the glycerol becomes hotter, as the dielectric constant increases (leading to a higher P / 90838.W001 value of the load capacitance), until a time instant B is reached, during which there is no change in oscillation frequency as there is no change in relative permittivity. Time instant B will happen as soon as a predeterminable temperature of the substrate has been reached and can serve as a temperature and timing marker point. As an example, at an oscillation frequency of about 500 MHz, for Glycerol as the aerosol former, the temperature can be about 73°C.

[0216] After the time instant B, there is a gradual increase of the oscillation frequency resulting from a decrease in relative permittivity of the substrate, due to some temperature-related evacuation of liquids from the substrate S. With the further advancing of time, the oscillation frequency increase accelerates, as higher temperatures are reached and some vaporization begins to happen, notably the vaporization of water at 100°C. The temperature-related depletion of liquids from substrate S thereby counteracts the temperature dependent increase of the relative permittivity. During this transition from B to START, the temperature of the substrate will reach the steady-state temperature for aerosolization, for example a temperature between 200°C and 250°C, a time moment where the experience or user session can start, allowing the user to take puffs.

[0217] After time instant START, with puff-taking events starting at 01 , C2, etc. and ending at E1 , E2, etc., respectively, with the transition D.

[0218] At a given time instant C1 , the user takes a first puff. This leads to a sudden evacuation of aerosol-former from substrate S, which leads to a sudden decrease of the relative permittivity of substrate S, leading to a sharp increase of the oscillation frequency. Therefore, upon the end of the puff at time instant E1 , the oscillator will operate at a higher frequency than at instant C1 . During the time between puffs, for example the time duration labelled as D, it shows that the oscillation frequency slightly decreases again due to the cooling effect to the substrate from the colder incoming air drawn by the puff, but shortly after starts increasing due to constant evaporation of aerosol-former at the steady-state temperature. Additional puffs that are taken at time instances C2, C3, C4, etc. show the stepwise increase of the oscillation frequency triggered by the puff, however, with the increased number of puffs (2 and more), the cooling effect by the incoming air that leads to a decrease in oscillation frequency decreases and then disappears, see, e.g. at C3 to E3.

[0219] Also, it can be seen that over the entire heating process (heat-up phase and steady state phase) the oscillation frequency increases with increased depletion of the substrate S, until there is no observable change in the oscillation frequency after and before a puff, indicating that the substrate is fully depleted of aerosol-former.

[0220] Figure 16b is a graph illustrating a first derivative of the graph of figure 16a. The use of the first order derivative (and also the second order derivative to further enhance detection and estimation results) can be used to estimate different parameters around the aerosolization process of substrate S. For example, with the zero crossing at time instant B, which occurs once the substrate S reaches a given temperature (e.g. 73°C). Furthermore, amplitude peaks (AM1 , AM2 AM3 etc...) P / 90838.W001 on the first order derivative of the measured frequency response over time may be indicative of both user puffs and puff volumes.

[0221] Figure 17 is a flow diagram illustrating a control process for a pre-heating phase of a dielectric heating operation using the control unit according to figure 14. The pre-heating phase is a time period where the heater starts heating such that the substrate is brought to a temperature for inhalation, for example 180°C to 220°C. For HnB substrates, this time period is usually about 10 seconds to 40 seconds, while for e-vapor and liquid vaporization, this time period is usually much shorter, 200ms or less.

[0222] Upon starting the heater (start pre-heat), for example by powering the oscillator unit OSC, data indicative of the frequency of the oscillator unit OSC is captured and processed, for example to normalize the date, filtered for noise, etc. Next, the data can be analyzed to detect a pre-heating frequency profile, that allows to estimate or detect one or more parameters of the pre-heating phase, for example to estimate parameters around the substrate S before the substrate S is ready for the user session. For example, the pre-heating frequency profile can be processed and compared to reference data. The pre-heating frequency profile can be processed to perform a first or second order derivative, to compare values obtained with reference data, to detect and estimate a time instant and value of the maximal frequency obtained (see time instant B above), serving as an indicator for the temperature. This reference temperature value and its timing can serve to determine a time instant when the start-up phase can be stopped, and the steady state heating phase can be performed.

[0223] Based on the analysed pre-heating frequency profile, by performing a comparison with reference data, one or more parameters related to the article can be detected. As non-limiting examples for the one or more parameters, it can be detected whether the article has been previously used and is fully or at least partially depleted (showing oscillation frequencies that are too high), whether the substrate S or article have been inserted in the correct direction (also showing too high oscillation frequencies), determine the type of substrate or article, detect humidity content of the article, determine atmospheric conditions of the environment. In the context of e-Vapor and liquid substrates, it can be determined whether there is sufficient liquid in a liquid transfer element to safely allow for a puff.

[0224] This analysis may facilitate the performance of different tasks by the controller, for example to instruct different actions, change settings or the profile of the device, or inform the user via Ul based on the one or more parameters. For example, actions can be taken such as aborting the heating if a used article or unauthorized article is being heated, determining a time moment when to switch from the pre-heating phase to the steady-state phase (e.g. predicting when the steady-state temperature of the substrate is reached). P / 90838.W001

[0225] In some embodiments, the controller may set or modify a temperature profile for the steadystate phase for the specific article, set a temperature profile based on the humidity content of the article to mitigate against a hot aerosol effect or based on different atmospheric conditions.

[0226] Parameters or data associated with the parameters can be communicated to the user with a user interface (III). For example, an error signal can be communicated, for example via a display or LED light, or instructions can be provided to the user to remedy an error situation, e.g. turning the article, inserting a new article, article identification information, etc.

[0227] Figure 18 is a flow diagram illustrating a control process for a steady-state phase of a dielectric heating operation using the control system according to figure 14.

[0228] Initially, data indicative of the oscillation frequency of the oscillator unit OSC is captured and processed, for example to normalize the data, filtered for noise, etc. Next, the data can be analyzed to detect different types of parameters, for example (1 ) parameters that are specific to an individual puff that has been taken, or (2) parameters related to the overall heating session, or both.

[0229] With respect to (1 ), a puff can be detected by a change in frequency to the oscillator unit OSC, for example by using the first order derivative and thresholding, see time instances C1 , C2, C3, etc. of figure 18a. Second order derivative can be used to enhance the detection. Amplitude and width (amplitudes AM1 , AM2, AM3, etc., pulse widths) of the first order derivative can undergo data processing to estimate puff strength and puff volume for each puff, to thereby monitor stick depletion.

[0230] In addition, with respect to (2), the measured frequency profile can be continuously analyzed with data processing to detect different parameters, for example to deduct the current temperature of the substrate S, to deduct the stick depletion level. Temperature and / or stick depletion level can be communicated to the user via the III.

[0231] The embodiments described above are exemplary embodiments only, and various other embodiments according with this disclosure are also envisaged.

[0232] 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

1. P / 90838.W001CLAIMS1. An aerosol-generating device for dielectrically heating an article comprising an aerosol-forming substrate, the device comprising: an oscillation circuit comprising a feedback loop and a switching unit, the feedback loop being connected between an input and an output of the switching unit, the oscillation circuit being configured to provide an alternating electric field across a load capacitor when connected in the feedback loop to dielectrically heat an aerosol-forming substrate having an aerosol former received in a heating region of the device; a frequency measurement unit configured to measure frequency data indicative of an oscillation frequency of the alternating electric field across the load capacitor connected in the feedback loop during a dielectric heating operation; and a control unit communicatively coupled with the frequency measurement unit, wherein the control unit is configured to: receive the measured frequency data from the frequency measurement unit; and determine one or more parameters related to the dielectric heating operation based on the received frequency data.

2. An aerosol-generating device according to claim 1 , wherein the feedback loop comprises an inductor, and wherein the frequency measurement unit comprises a magnetic field probe configured to measure an alternating magnetic field departed by the inductor.

3. An aerosol-generating device according to any preceding claim, wherein the control unit is configured to determine one or more parameters related to the dielectric heating operation based on a comparison of the received frequency data with reference data.

4. An aerosol-generating device according to any preceding claim, wherein the control unit is further configured to: determine a frequency profile for the dielectric heating operation based on the received frequency data; and determine the one or more parameters related to the dielectric heating operation based on one or more properties associated with the frequency profile.

5. An aerosol-generating device according to any preceding claim, wherein the control unit is configured to:P / 90838.W001 detect a minimum frequency value of the measured frequency data during a pre-heating phase of the dielectric heating operation; determining a temperature of the aerosol-forming substrate based on the minimum frequency value.

6. An aerosol-generating device according to claims 5, wherein following determination of the aerosol-forming substrate temperature, the control unit is configured to: continue the pre-heating phase the aerosol-forming substrate for a predetermined time period; and initiate, after the predetermined time period has elapsed, a maintenance heat phase.

7. An aerosol-generating device according to any preceding claim, wherein the control unit is configured to: determine a presence of a puff based on an increase in a frequency value of the frequency data exceeding a pre-determine threshold level.

8. An aerosol-generating device according to any preceding claim, wherein the control unit is configured to: determine a value indicative of a puff volume based on a relative increase of the frequency between a frequency at a start of a puff and a frequency at the end of the puff.

9. An aerosol-generating device according to any of claims 4 to 8, wherein the control unit is further configured to: determine a first order derivative of the frequency profile; and determine the one or more parameters related to the dielectric heating operation based on one or more properties associated with the first order derivative of the frequency profile.

10. An aerosol-generating device according to claim 9, wherein the one or more properties comprises a zero-crossing of the first order derivative of the frequency profile.1 1. An aerosol-generating device according to claim 9, wherein the control unit is configured to: detect one or more of an amplitude, a variance and a pulse width of a peak of the first order derivative of the frequency profile; determine a puff volume based on the one or more amplitude, variance and pulse width of a peak of the first order derivative of the frequency profile.P / 90838.W00112. An aerosol-generating device according to any preceding claim, wherein the one or more parameters comprises one or more of a temperature of the aerosol-forming substrate, a depletion level of the aerosol-forming substrate, a type of aerosol-forming substrate, a humidity content of aerosol-forming substrate, an article insertion status in the device, and a time moment when to switch from a pre-heating phase to a maintenance heating phase.

13. An aerosol-generating device according to any preceding claim, wherein the control unit is configured to adjust a power supplied by the oscillation circuit to the load capacitor based on the determined one or more parameters.

14. An aerosol-generating system comprising: an aerosol-generating device according to any preceding claim; and an aerosol-forming substrate comprising an aerosol former, situated in a heating region of the aerosol-generating device.

15. An aerosol generation method for an aerosol-generating system according to claim 14, the method comprising: measuring frequency data indicative of an oscillation frequency of the alternating electric field across the load capacitor during a dielectric heating operation; determining a frequency profile for the dielectric heating operation based on the frequency data; and determining one or more parameters related to the dielectric heating operation based on one or more properties of the frequency profile.

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