WO2025209891A1

WO2025209891A1 - Aerosol-generating device with dielectric heater with improved power control

Info

Publication number: WO2025209891A1
Application number: PCT/EP2025/058193
Authority: WO
Inventors: Leander Dittmann; Ana Isabel GONZALEZ FLOREZ; Nayara JORNOD
Original assignee: Philip Morris Products SA
Current assignee: Philip Morris Products SA
Priority date: 2024-04-05
Filing date: 2025-03-25
Publication date: 2025-10-09
Anticipated expiration: 2026-10-05

Abstract

An aerosol-generating device (120) for dielectrically heating an aerosol-generating article (105) comprising an aerosol-forming substrate (110). The aerosol-generating device (120) comprises: an article chamber (140); a dielectric heater; and control electronics (180). The article chamber (140) is configured to removably receive the aerosol-generating article (105). The dielectric heater is configured to generate an alternating electric field in the article chamber (140) for dielectrically heating the aerosol-generating article (105) when the aerosol-generating article (105) is received in the article chamber (140). The control electronics (180) are configured to control a supply of power to the dielectric heater for dielectrically heating the aerosol-generating article (105). The article chamber (140), the aerosol-generating article (105) received in the article chamber (140), and at least a portion of the dielectric heater form an electrically resonant oscillation system. The control electronics (180) are further configured to: measure or determine a load-dependent parameter of an electric response of the electrically resonant oscillation system to the alternating electric field generated in the article chamber (140); and control the aerosol-generating device (120) based on the load-dependent parameter of the electric response of the electrically resonant oscillation system.

Description

AEROSOL-GENERATING DEVICE WITH DIELECTRIC HEATER WITH IMPROVED POWER CONTROL

The present disclosure relates to aerosol-generating devices, and specifically to aerosolgenerating devices configured to heat an aerosol-forming substrate by dielectric or microwave heating. The disclosure also relates to dielectric or microwave heating circuits for use in a dielectric or microwave heating aerosol-generating device and an aerosol-generating system.

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 from a heating element to an aerosol-forming substrate or drawing heated air through an aerosolforming 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 heating occurs as a result of eddy currents induced by a magnetic field and magnetic hysteresis losses of the magnetic movements in a susceptor heating element.

A feature of 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.

Systems that dielectrically heat an aerosol-forming substrate have been proposed, which advantageously may provide uniform heating of the aerosol-forming substrate. For example, see WO 2021/013477 A1 , this reference is incorporated by reference in its entirety.

Dielectric heating, which is also often referred to as microwave heating, electric heating, or radiofrequency heating, generally refers to heating that arises as a result of dipole rotation of a to-be-heated material or substrate that is subjected to an alternating electric field, and particularly a high-frequency alternating electric field. When an alternating electric field is applied to materials or substrates containing polar molecules (i.e. molecules having an electrical dipole moment), the polar molecules align themselves in the electric field and rotate when the electric field alternates to maintain alignment with the electric field. This rotation (dipole rotation) results in heating of the material or substrate in the alternating electric field.

However, known dielectric heating systems are generally less efficient than inductive heating systems and require complex electrical circuitry to achieve the necessary voltages and high frequencies for dielectric or microwave heating of an aerosol-forming substrate.

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

According to the present disclosure, there is provided an aerosol-generating device for dielectrically heating an aerosol-generating article comprising an aerosol-forming substrate. The aerosolgenerating device may comprise an article chamber. The article chamber may be configured to removably receive the aerosol-generating article. The aerosol-generating device may comprise a dielectric heater. The dielectric heater may be configured to generate an alternating electric field in the article chamber. The dielectric heater may be configured to generate an alternating electric field in the article chamber for dielectrically heating the aerosol-generating article when the aerosol-generating article is received in the article chamber. The aerosol-generating device may comprise control electronics. The control electronics may be configured to control a supply of power to the dielectric heater for dielectrically heating the aerosolgenerating article. The article chamber, the aerosol-generating article received in the article chamber, and at least a portion of the dielectric heater may form an electrically resonant oscillation system. The control electronics may be further configured to measure or determine a load-dependent parameter of an electric response of the electrically resonant oscillation system to the alternating electric field generated in the article chamber. The control electronics may be further configured to control the aerosol-generating device based on the load-dependent parameter of the electric response of the electrically resonant oscillation system. The control electronics may be configured to control the aerosol-generating device by controlling the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article based on the load-dependent parameter of the electric response of the electrically resonant oscillation system.

According to the present disclosure, there is provided an aerosol-generating device for dielectrically heating an aerosol-generating article comprising an aerosol-forming substrate. The aerosolgenerating device comprises: an article chamber; a dielectric heater; and control electronics. The article chamber is configured to removably receive the aerosol-generating article. The dielectric heater is configured to generate an alternating electric field in the article chamber for dielectrically heating the aerosol-generating article when the aerosol-generating article is received in the article chamber. The control electronics are configured to control a supply of power to the dielectric heater for dielectrically heating the aerosol-generating article. The article chamber, the aerosol-generating article received in the article chamber, and at least a portion of the dielectric heater form an electrically resonant oscillation system. The control electronics are further configured to: measure or determine a load-dependent parameter of an electric response of the electrically resonant oscillation system to the alternating electric field generated in the article chamber; and control the aerosol-generating device. The control electronics may be configured to control the aerosol-generating device by controlling the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article based on the load-dependent parameter of the electric response of the electrically resonant oscillation system.

As used herein, “aerosol-generating device” refers to a device that interacts with an aerosolforming substrate to generate an aerosol. Preferably, the aerosol-generating device is a device that interacts with an aerosol-forming substrate to generate an inhalable aerosol that is directly inhalable into a user’s lungs thorough the user's mouth. Further according to the present disclosure, there is provided an aerosol-generating device for dielectrically heating an aerosol-generating article comprising an aerosol-forming substrate. The aerosolgenerating device comprises: an article chamber; a dielectric heater; and control electronics. The article chamber is configured to removably receive the aerosol-generating article. The dielectric heater is configured to generate an alternating electric field in the article chamber for dielectrically heating the aerosol-generating article when the aerosol-generating article is received in the article chamber. The control electronics are configured to control a supply of power to the dielectric heater for dielectrically heating the aerosol-generating article. The article chamber, the aerosol-generating article received in the article chamber, and at least a portion of the dielectric heater form an electrically resonant oscillation system. The control electronics are further configured to: measure or determine a load-dependent parameter of an electric response of the electrically resonant oscillation system to the alternating electric field generated in the article chamber; and control the aerosol-generating device. The control electronics may be configured to control the aerosol-generating device by controlling the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article based on the load-dependent parameter of the electric response of the electrically resonant oscillation system. The dielectric heater includes a resonant cavity or a transmission line. The resonant cavity or the transmission line is coupled to a wave source via a coupler.

As used herein, “aerosol-forming substrate” refers to a substrate capable of releasing volatile compounds that can form an aerosol. Such volatile compounds may be released by heating the aerosol-forming substrate. An aerosol-forming substrate is typically part of an aerosol-generating article.

As used herein, “aerosol-generating article” refers to an article comprising an aerosol-forming substrate that is capable of releasing volatile compounds that can form an aerosol. For example, an aerosol-generating article may be an article that generates an aerosol that is directly inhalable by the user drawing or puffing on a mouthpiece at a proximal or mouth end of the aerosol-generating article, an aerosol-generating device, or an aerosol-generating system. An aerosol-generating article may be disposable.

As used herein, “aerosol-generating system” refers to the combination of an aerosol-generating device with an aerosol-generating article. In an aerosol-generating system, the aerosol-generating article and the aerosol-generating device interact or cooperate to generate an aerosol.

As used herein, “article chamber” refers to a space or a volume that is configured to removably receive an aerosol-generating article. In other words, the article chamber is a space or a volume that is sized and shaped to receive an aerosol-generating article. In some embodiments, the article chamber is arranged between electrodes of a dielectric heater. In some embodiments, the article chamber is provided in a waveguide, or as a portion of a waveguide. In some embodiments, the article chamber is a volume or cavity of a resonant cavity. The present disclosure concerns aerosol-generating systems, and in particular aerosol-generating devices, which use dielectric heating to generate an aerosol. The aerosol-generating device comprises a dielectric heater. The dielectric heater comprises an assembly of components that enable the aerosolgenerating article to be dielectrically heated. Various types of dielectric heater are known, and any suitable type of dielectric heater is considered to be applicable to the aerosol-generating systems and aerosol-generating devices of this disclosure.

In some preferred embodiments, the dielectric heater comprises a resonant cavity. The alternating electric field may be generated in the resonant cavity and an aerosol-generating article comprising an aerosol-forming substrate is dielectrically heated when received in the resonant cavity. The resonant cavity may be coupled to a radiation source or a wave source for generating the alternating electric field in the resonant cavity. The resonant cavity may be coupled to the radiation source or the wave source via at least one of a waveguide, an antenna, and a transmission line. The dielectric heater may comprise the radiation source or the wave source. The dielectric heater may comprise the waveguide. The dielectric heater may comprise the antenna. The dielectric heater may comprise the transmission line.

In some preferred embodiments, the dielectric heater comprises a load capacitor. The load capacitor may form part of a resonant circuit. The dielectric heater may comprise the resonant circuit. An aerosol-generating article comprising an aerosol-forming substrate may form a part of the load capacitor when the aerosol-generating article is received in the article chamber. For example, the load capacitor may comprise a pair of electrodes, and the aerosol-generating article comprising the aerosol-forming substrate may form part of the load capacitor when it is arranged in close proximity to, or between, the electrodes. The alternating electric field may be generated across the load capacitor. When the aerosolgenerating article comprising the aerosol-forming substrate forms part of the load capacitor, the aerosolgenerating article may be dielectrically heated by the alternating electric field.

The alternating electric field generated in the article chamber may have any suitable frequency for dielectrically heating the aerosol-forming substrate in the aerosol-generating article. The alternating electric field may be a radio frequency, RF, electric field. As used herein, radio frequency, RF, means a frequency between 50 MHz and 300 Gigahertz. Accordingly, as used herein, RF frequencies include microwave frequencies and ultra-high frequencies, UHF. The alternating electric field may have a frequency of between 50 MHz and 300 Gigahertz, optionally a frequency of between 200 Megahertz and 50 Gigahertz, optionally a frequency of between 300 Megahertz and 30 Gigahertz, optionally a frequency of between 500 Megahertz and 20 Gigahertz, or a frequency of about 2.45 GHz.

When an alternating electric field is generated in the article chamber, the electrically resonant oscillation system exhibits an electric response. The electrical properties of the aerosol-generating article received in the article chamber affect the electric response of the oscillation system to the alternating electric field. In other words, the electrical load of the oscillation system affects the electric response of the oscillation system. The control electronics are configured to measure or determine a load-dependent parameter of the electric response of the electrically resonant oscillation system. The load-dependent parameter of the electric response is a parameter of the electric response that varies depending on the electrical load of the dielectric heater. When an aerosol-generating article is received in the article chamber, the electrical load of the dielectric heater comprises at least a portion of the aerosol-generating article received in the article chamber.

Various load-dependent parameters of the electric response may be measured or determined by the control electronics. The load-dependent parameter may be a resonant frequency of the oscillation system. The oscillation system may have one or more resonant frequencies, or resonant modes, which may be measured or determined by the control electronics. The oscillation system typically has a plurality of resonant frequencies, or resonant modes, which may be measured or determined by the control electronics. The load-dependent parameter may be a frequency shift of the electric response. The loaddependent parameter may be a frequency shift compared to a known reference value or to a measured value when no aerosol-generating article is received in the article chamber. The load-dependent parameter may be an impedance shift in the electric response The load-dependent parameter may be a quality factor, or Q-factor, of the electric response. The load-dependent parameter may be a Q-factor compared to a known reference value or to a measured value when no aerosol-generating article is received in the article chamber. The load-dependent parameter may be a bandwidth of the electric response. The load-dependent parameter may be a bandwidth compared to a known reference value or to a measured value when no aerosol-generating article is received in the article chamber. The loaddependent parameter may be a phase shift of the electric response. The load-dependent parameter may be a phase shift compared to a known reference value or to a measured value when no aerosol-generating article is received in the article chamber. The load-dependent parameter may be a gain of the electric response. The load-dependent parameter may be a gain compared to a known reference value or to a measured value when no aerosol-generating article is received in the article chamber. The loaddependent parameter may be an impedance of the electric response. The load-dependent parameter may be an impedance compared to a known reference value or to a measured value when no aerosolgenerating article is received in the article chamber.

In particular, the electric response of the electrically resonant oscillation system may be a frequency response. The load-dependent parameter of the frequency response may comprise at least one of a resonant frequency of the electrically resonant oscillation system, a frequency shift, an impedance shift, a bandwidth, and a quality factor.

Advantageously, measuring or determining a load-dependent parameter of the electric response of the electrically resonant oscillation system may enable the aerosol-generating device to distinguish between, or identify, different types of aerosol-generating article received in the article chamber, as the electric response changes depending on the electrical properties of the aerosol-generating article. Where the aerosol-generating device is able to distinguish between, or identify, different types of aerosolgenerating article received in the article chamber, the aerosol-generating device may be able to vary the power supplied to the dielectric heater for heating the aerosol-generating article depending on the type of aerosol-generating article that is determined to be received in the article chamber. This may enable the aerosol-generating device to heat different types of aerosol-generating article to different temperatures, optimising operation of the aerosol-generating system, and optimising generation of aerosol, for different types of aerosol-generating article. Such variable heating may be particularly advantageous where different types of aerosol-generating article comprise different types of aerosol-forming substrate, which require heating to different temperatures to generate the desired aerosol.

The control electronics may be configured to identify the aerosol-generating article based on the load-dependent parameter of the electric response of the electrically resonant oscillation system. The control electronics may be further configured to prevent or turn off the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article to generate an aerosol when the control electronics are unable to identify the aerosol-generating article.

The control electronics may be configured to supply different powers to the dielectric heater for heating the aerosol-generating article to different temperatures based on the measured or detected loaddependent parameter of the electric response of the electrically resonant oscillation system. In other words, the control electronics may be configured to change the power supplied to the dielectric heater for heating the aerosol-generating article based on the identity of the aerosol-generating article determined from the load-dependent parameter of the electric response of the electrically resonant oscillation system.

The control electronics may be configured to selectively supply one of: a first power to the dielectric heater for dielectrically heating the aerosol-generating article received in the article chamber; and a second power to the dielectric heater for dielectrically heating the aerosol-generating article received in the article chamber, the second power being different to the first power. The control electronics may be configured to selectively supply one of the first power and the second power to the dielectric heater based on the load-dependent parameter of the electric response of the electrically resonant oscillation system.

The control electronics may be configured to selectively supply power profiles to the dielectric heater for dielectrically heating the aerosol-generating article. At least one of the power profiles may vary with time. The selection of the power profile may be based on the load-dependent parameter of the electric response of the electrically resonant oscillation system.

The control electronics may be configured to selectively supply one of: a first power profile to the dielectric heater for dielectrically heating the aerosol-generating article received in the article chamber; and a second power profile to the dielectric heater for dielectrically heating the aerosol-generating article received in the article chamber, the second power profile being different to the first power profile. The first power profile may vary with time. The second power profile may vary with time. The selection of the first power profile or the second power profile may be based on the load-dependent parameter of the electric response of the electrically resonant oscillation system.

The control electronics may be configured to selectively supply power to the dielectric heater for dielectrically heating the aerosol-generating article to a plurality of temperatures. The selection of the temperature profile may be based on the load-dependent parameter of the electric response of the electrically resonant oscillation system.

The control electronics may be configured to selectively supply power to the dielectric heater for dielectrically heating the aerosol-generating article to a plurality of temperature profiles. At least one of the plurality of temperature profiles may vary with time. The selection of the temperature profile may be based on the load-dependent parameter of the electric response of the electrically resonant oscillation system.

The control electronics may be configured to selectively supply one of: power to the dielectric heater for dielectrically heating the aerosol-generating article received in the article chamber to a first temperature profile; and power to the dielectric heater for dielectrically heating the aerosol-generating article received in the article chamber to a second temperature profile. The second temperature profile may be different to the first power. The first temperature profile may vary with time. The second temperature profile may vary with time. The selection of the first temperature profile or the second temperature profile may be based on the load-dependent parameter of the electric response of the electrically resonant oscillation system.

In some embodiments, the at least a portion of the dielectric heater and the article chamber form an unloaded oscillation system when the aerosol-forming substrate is not received in the article chamber. In these embodiments, the control electronics may be further configured to measure or determine the load-dependent parameter of the electric response of the unloaded oscillation system. The control electronics may be further configured to determine the difference between the load-dependent parameter of the electric response of the electrically resonant oscillation system and the load-dependent parameter of the electric response of the unloaded oscillation system. The control electronics may be further configured the control the aerosol-generating device based on the difference between the load-dependent parameter of the electric response of the electrically resonant oscillation system and the load-dependent parameter of the electric response of the unloaded oscillation system. The control electronics may be configured to control the supply of power to the dielectric heater for dielectrically heating the aerosolgenerating article received in the article chamber based on the difference between the load-dependent parameter of the electric response of the electrically resonant oscillation system and the load-dependent parameter of the electric response of the unloaded oscillation system.

The control electronics may be further configured to determine whether the aerosol-forming substrate is received in the article chamber based on the difference between the load-dependent parameter of the electric response of the electrically resonant oscillation system and the load-dependent parameter of the electric response of the unloaded oscillation system. The control electronics may be further configured to control the aerosol-generating device if it is determined that the aerosol-forming substrate is not received in the article chamber. The control electronics may be configured to prevent the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article if it is determined that the aerosol-forming substrate is not received in the article chamber.

In some preferred embodiments, the load-dependent parameter is the resonant frequency. In these embodiments, where at least a portion of the dielectric heater and the article chamber form an unloaded oscillation system when the aerosol-forming substrate is not received in the article chamber, the control electronics may be further configured to measure or determine the resonant frequency of the unloaded oscillation system. The control electronics may be further configured to determine the frequency shift between the resonant frequency of the electrically resonant oscillation system and the resonant frequency of the unloaded oscillation system. The control electronics may be further configured to control the aerosol-generating device based on the frequency shift. The control electronics may be configured to control the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article based on the frequency shift. The control electronics may be further configured to determine whether the aerosol-forming substrate is received in the article chamber based on the frequency shift. The control electronics may be configured to control the aerosolgenerating device if it is determined that the aerosol-forming substrate is not received in the article chamber. The control electronics may be configured to prevent the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article if it is determined that the aerosol-forming substrate is not received in the article chamber.

In some embodiments, the control electronics are further configured to: determine the difference between the load-dependent parameter of the electric response of the electrically resonant oscillation system and a reference value. The control electronics may be further configured to control the aerosolgenerating device based on the difference between the load-dependent parameter of the electric response of the loaded oscillation system and the reference value. The control electronics may be configured to control the supply of power to the dielectric heater for dielectrically heating the aerosolgenerating article based on the difference between the load-dependent parameter of the electric response of the loaded oscillation system and the reference value.

The control electronics may be further configured to determine whether the aerosol-forming substrate is received in the article chamber based on the difference between the load-dependent parameter of the electric response of the electrically resonant oscillation system and the reference value. The control electronics may be configured to control the aerosol-generating device if it is determined that the aerosol-forming substrate is not received in the article chamber. The control electronics may be configured to prevent the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article if it is determined that the aerosol-forming substrate is not received in the article chamber.

In some preferred embodiments, the load-dependent parameter is the resonant frequency. In some of these embodiments, the control electronics are further configured to: determine the frequency shift between the resonant frequency of the electrically resonant oscillation system and a reference value. The control electronics may be further configured to control the aerosol-generating device based on the frequency shift. The control electronics may be configured to control the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article based on the frequency shift.

The control electronics may be further configured to determine whether the aerosol-forming substrate is received in the article chamber based on the frequency shift. The control electronics may be configured to control the aerosol-generating device if it is determined that the aerosol-forming substrate is not received in the article chamber. The control electronics may be configured to prevent the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article if it is determined that the aerosol-forming substrate is not received in the article chamber.

The reference value may be a known value corresponding to an expected load-dependent parameter. The reference value may be stored in a memory of the control electronics. The reference value may be obtained in a calibration procedure before use of the aerosol-generating device, and stored in a memory of the aerosol-generating device.

The reference value may be a plurality of reference values. The reference value may be a mapping function. The mapping function may map a measured or determined load-dependent parameter to known types of aerosol-generating articles.

The control electronics are configured to measure or determine the load-dependent parameter of the electric response of the electrically resonant oscillation system.

In some embodiments, the measuring or determining the load-dependent parameter may comprise measuring or determining at least two load-dependent parameters of the electric response of the electrically resonant oscillation system. In these embodiments, the controlling the aerosol-generating device may comprise controlling the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article based on the at least two load-dependent system parameters of the electrically resonant oscillation system.

Advantageously, using two or more load-dependent parameters of the electric response of the electrically resonant oscillation system to identify an aerosol-generating article may improve the reliability of the identification compared to identification based on a single load-dependent parameter of the electric response.

In some preferred embodiments, the measuring or determining the load-dependent parameter of the electric response of the electrically resonant oscillation system comprises measuring or determining the resonant frequency of the electrically resonant oscillation system, and measuring or determining at least one of the quality factor of the electrically resonant oscillation system and the bandwidth of the electrically resonant oscillation system. In these embodiments, the controlling the aerosol-generating device comprises controlling the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article based on the resonant frequency and the at least one of the quality factor and the bandwidth of the electrically resonant oscillation system.

According to the disclosure, there is provided an aerosol-generating device for dielectrically heating an aerosol-generating article comprising an aerosol-forming substrate. The aerosol-generating device comprises: an article chamber; a dielectric heater; and control electronics. The article chamber is configured to receive the aerosol-generating article. The dielectric heater is configured to generate an alternating electric field in the article chamber for dielectrically heating the aerosol-generating article when the aerosol-generating article is received in the article chamber. The control electronics are configured to control a supply of power to the dielectric heater for dielectrically heating the aerosol-generating article. The article chamber, the aerosol-forming substrate received in the article chamber, and at least a portion of the dielectric heater form an electrically resonant oscillation system. The control electronics are further configured to: measure or determine at least two load-dependent parameters of an electric response of the electrically resonant oscillation system to the alternating electric field generated in the article chamber; and identify the aerosol-generating article based on the at least two load-dependent parameters of the electric response of the electrically resonant oscillation system.

As mentioned above, the dielectric heater may comprise any suitable type of dielectric heater for heating the aerosol-forming substrate of an aerosol-generating article to generate an aerosol.

In some preferred embodiments, the dielectric heater comprises a load capacitor for dielectrically heating the aerosol-generating article.

In some of these preferred embodiments, the dielectric heater comprises a first electrode and a second electrode. The second electrode may be spaced apart from the first electrode. The first electrode and the second electrode may be arranged such that when the aerosol-forming substrate is received in the article chamber, at least a portion of the aerosol-forming substrate is arranged between the first electrode and the second electrode. The load capacitor may be formed by the first electrode, the second electrode and the aerosol-forming substrate received in the article chamber between the first electrode and the second electrode.

Preferably, the dielectric heater comprises a resonant circuit including the load capacitor and an inductor.

In some preferred embodiments, the dielectric heater further comprises: a switching unit configured for inverting operation; and a feedback loop connected to the switching unit. The feedback loop may comprise two electrical contacts configured to connect with an electrode arrangement that forms the load capacitor for dielectrically heating the aerosol-generating article. The feedback loop may be configured to perform resonant oscillating operation and configured to provide a 180° phase shift between an output signal of the switching unit and an input switching signal of the switching unit. The dielectric heater may further comprise the electrode arrangement connected to the two electrical contacts to form the load capacitor. The feedback loop may comprise a resonant circuit that provides for a 90 degrees phase shift circuit at an operating frequency of the oscillator circuit.

The resonant circuit may comprise a resonant cavity. The resonant circuit may comprise a parallel resonant circuit, which is electrically stimulated by the output signal of the switching unit. The feedback loop may have substantially the same impedance as the switching unit. The switching unit may include a frequency measurement device to measure a switching frequency of a transistor of the switching unit.

In some other preferred embodiments, the dielectric heater comprises a resonant cavity or a resonator. In some preferred embodiments, the dielectric heater comprises a transmission line. In some preferred embodiments, the dielectric heater comprises a combination of both a resonant cavity/resonator and a transmission line. The resonant cavity/resonator, transmission line, or both may at least partially include the article chamber. The article chamber may be arranged in the resonant cavity, or transmission line, or both. The resonant cavity or transmission line may be arranged in the article chamber. The article chamber may be the resonant cavity or the transmission line or a combination of a resonant cavity and a transmission line. The resonant cavity may be configured as a quarter wavelength resonator. The transmission line may be configured as a quarter wavelength resonator.

Preferably, the dielectric heater further comprises a radiation source or a wave source. The resonant cavity or the transmission line may be coupled directly or indirectly to the radiation source or wave source. The resonant cavity or transmission line may be coupled to the radiation source or wave source by any suitable means. The resonant cavity or transmission line may be coupled to the radiation source or wave source via a coupler. The resonant cavity or transmission line may be coupled to the radiation source or wave source via at least one of a waveguide, an antenna, and a transmission line. The radiation source or wave source may be coupled to the resonant cavity or the transmission line using at least one of a capacitive coupling, an inductive coupling, a direct electric coupling or a window coupling.

In some preferred embodiments, the dielectric heater comprises a resonant circuit including the resonant cavity, transmission line, or both, for example as an element of the resonant circuit. The resonant cavity or transmission line may be coupled to the radiation source or wave source using at least one of a capacitive coupling, an inductive coupling, a direct electric coupling or a window coupling.

In some preferred embodiments comprising a resonant cavity, transmission line, or both, a coupler to the resonant cavity may perform the function of a probe or antenna to measure a parameter of the electric field generated in the article chamber.

In some other preferred embodiments, the aerosol-generating device further comprises a probe or antenna to measure a parameter of the electric field generated in the article chamber. The parameter measured by the probe or antenna may be the frequency of the electric field generated in the article chamber. The control electronics may be associated with the probe or antenna and configured to derive the load-dependent parameter from the measured parameter of the electric field.

The probe or antenna may include at least one of: a transverse electromagnetic (TEM) transmission line, a microstrip, an inductor, or an antenna. The probe or antenna may include a resonant cavity or a transmission line.

The probe or antenna may comprise a quarter wavelength coaxial cavity resonator. The quarter wavelength coaxial cavity resonator may comprise an inner wire, wherein the inner wire has an impurity- doped insulator.

The resonant cavity or transmission line may be arranged in the article chamber. The resonant cavity or transmission line may be the article chamber.

The aerosol-generating device may further comprise a signal processing unit configured to convert an output provided by the resonant cavity, the transmission line, or both to a signal that is receivable by the control electronics. The signal processing unit may comprise a rectifier connected to the resonant cavity to generate a DC signal from the output of the cavity resonator. The signal processing unit may comprise an impedance element on which the DC signal is applied, and a voltage sensor to measure a voltage over the impedance element that is fed to the control electronics.

The dielectric heater may comprise a radiation source or a wave source. The radiation source or wave source may be any suitable type of radiation source or wave source configured to cause an alternating electric field in the article chamber. The radiation source or wave source may be any suitable type of radiation source or wave source configured to generate a radio frequency (RF) electric field and provide it to the article chamber, for example via a waveguide and coupler. The radiation source or wave source may be a voltage-controlled oscillator (VCO). The signal source may be a synthesizer.

The dielectric heater may comprise one or more solid state RF components, such as a solid state RF transistor. In particular, a radiation source or wave source may comprise one or more solid state RF components. Preferably, the radiation source or wave source comprises a solid state RF transistor. The solid state RF transistor may be part of a VCO. The solid state RF transistor may be part of a synthesizer.

The use of a solid state RF transistor, and other solid state RF components, allows the aerosolgenerating device to be compact, as compared to a solution where a magnetron is used as a radiation source or wave source. The conventional means for producing RF frequency radiation for heating, such as in domestic microwave ovens, is a magnetron. Magnetrons are bulky and require high voltages to operate. Furthermore, magnetrons have a relatively unstable frequency output and have a relatively short service life. A RF transistor can provide for consistent operation over many more usage cycles and requires much lower operating voltages.

Advantageously, one or more solid state RF transistor may be configured to generate and amplify the RF electric field. Using a single transistor to provide both the generating and amplification of the RF electric field allows for the aerosol-generating device to be compact. The solid state RF transistor may be, for example, a LDMOS transistor, a GaAs FET, a SiC MESFET or a GaN HFET.

Although it is preferable that the radiation source or wave source comprises a solid state RF transistor, it is envisaged that in some embodiments the radiation source or wave source may comprise a magnetron or other suitable radiation source or wave source capable of generating a RF electromagnetic field.

The aerosol-generating device comprises control electronics. The control electronics may comprise a microprocessor, which may be a programmable microprocessor, a microcontroller, or an application specific integrated chip (ASIC) or other electronic circuitry capable of providing control. The control electronics may comprise further electronic components. The control electronics may be configured to regulate a supply of power to the dielectric heater. Power may be supplied to the dielectric heater continuously following activation of the aerosol-generating device or may be supplied intermittently, such as on a puff by puff basis. The control electronics may advantageously comprise DC/AC inverter, which may comprise a Class-D orClass-E power amplifier, or any other suitable amplifier.

In some preferred embodiments, the aerosol-generating device further comprises a power supply.

The aerosol-generating device may further comprise a power supply. The control electronics may be configured to control the aerosol-generating device. The control electronics may be configured to control the aerosol-generating device by controlling the supply of power from the power supply to the dielectric heater.

The power supply may be a DC power supply. The power supply may comprise at least one of a battery and a capacitor. In one embodiment, the power supply is a DC power supply having a DC supply voltage in the range of about 2.5 Volts to about 4.5 Volts and a DC supply current in the range of about 1 Amp to about 10 Amps (corresponding to a DC power supply in the range of about 2.5 Watts to about 45 Watts).

The control electronics may comprise a power sensing system configured to detect a power consumption value drawn from the power supply. The power consumption value may be used as the load-dependent parameter. The power consumption value may be indicative of a supply current, in particular a DC supply current, drawn from the power supply. The power sensing system may comprise a shunt to derive the supply current. The control electronics may be configured to control the frequency of the electric field generated in the article chamber by the dielectric heater.

The control electronics may be configured to control the aerosol-generating device based on the measured or determined load-dependent parameter. The control electronics may be configured to control the aerosol-generating device in response to a measurement or determination of the loaddependent parameter, or in response to a calculation using the load-dependent parameter, a comparison of the load-dependent parameter to a reference value, or in response to the input of the load-dependent parameter into a mapping function. The control electronics may be configured to control the aerosol-generating device in any suitable manner.

In some embodiments, the control electronics are configured to control the aerosol-generating device by controlling the supply of power to the dielectric heater for dielectrically heating the aerosolgenerating article. The control electronics may be configured to control the aerosol-generating device by selectively supplying power or power profiles to the dielectric heater for dielectrically heating the aerosol-generating article. The control electronics may be configured to selectively supply power to the dielectric heater for dielectrically heating the aerosol-generating article to a plurality of temperatures or temperature profiles.

The control electronics may be configured to control the supply of power to the dielectric heater by any suitable means. For example, the control electronics may be configured to control the power supplied to the dielectric heater by at least one of controlling the instantaneous source power level, by pulse width modulation, and by controlling forward/reflected power, for example by impedance tuning.

In some embodiments, the control electronics are configured to control the aerosol-generating device by preventing or inhibiting the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article. The control electronics may be configured to control the aerosol-generating device by preventing or inhibiting the heating of the aerosol-generating article by the dielectric heater.

In some embodiments, the control electronics are configured to control the aerosol-generating device by notifying a user. The control electronics may notify a user in any suitable manner. The control electronics may notify a user by issuing a visual notification. The aerosol-generating device may comprise a display, and the control electronics may notify a user by displaying information to a user on the display. The aerosol-generating device may comprise a light, such as an LED, and the control electronics may notify a user by turning on or off the light or altering the colour of the light. The control electronics may notify a user by issuing an audible notification. The aerosol-generating device may comprise a loudspeaker or a buzzer, and the control electronics may notify a user by generating a sound from the loudspeaker or buzzer.

The control electronics may be configured to notify a user of the identity or authenticity of an aerosol-generating article received in the article chamber based on the load-dependent parameter. In some embodiments, the control electronics are configured to identify the aerosol-generating article received in the article chamber based on the load-dependent parameter. In these embodiments, the control electronics may be configured to control the aerosol-generating device by notifying a user of the identity or type of aerosol-generating article received in the article chamber.

In some embodiments, the control electronics may be configured to vary the frequency of the alternating electric field generated in the article chamber.

The control electronics are configured to measure or determine the load-dependent parameter. The measuring or determining the load-dependent parameter may comprise the control electronics being configured to: supply power to the dielectric heater to generate an alternating electric field in the article chamber; control the supply of power to the dielectric heater to vary the frequency of the generated alternating electric field; and measure a parameter of the electrically resonant oscillation system at a plurality of frequencies of the alternating electric field.

The control electronics may be further configured to control the supply of power to the dielectric heater to vary the frequency of the generated alternating electric field over a predetermined frequency range. The measuring or determining the load-dependent parameter may comprise the control electronics being further configured to determine the load-dependent parameter based on the measured parameter of the electrically resonant oscillation system at the plurality of frequencies.

Advantageously, varying the frequency of the alternating electric field in the article chamber may enable load-dependent parameters, such as the resonant frequency, to be identified.

The measuring or determining the load-dependent parameter may comprise the control electronics being configured to generate a frequency plot from the parameter measured or determined at the plurality of frequencies. The control electronics may be configured to determine the load-dependent parameter based on the frequency plot.

The load-dependent parameter may be the parameter measured at the plurality of frequencies.

The control electronics may further comprise a probe or antenna to measure a frequency of oscillation of the oscillation circuit.

The probe or antenna may include a transverse electromagnetic (TEM) transmission line, a microstrip, an inductor, or an antenna.

The aerosol-generating device may further include a power sensing system to detect a power consumption value drawn from the power source. In some embodiments, the power consumption value may be used as the load-dependent parameter, or as a proxy for the load-dependent parameter.

The detected power consumption value may be indicative for the resonant frequency of the oscillation circuit because a change in the resonant frequency may be proportional to the power loss of the dielectric heating element. This relationship may enable identification ofthe type of aerosol-generating article based on the power consumption value drawn from the power source rather than from a frequency measurement device. Using a power sensing system instead of a frequency measurement device, like an antenna or probe, may enable for a compact product.

The power consumption value may be indicative of a supply current, in particular a DC supply current, drawn from the power source.

Variations in the humidity, or water content, of an aerosol-forming substrate in an aerosolgenerating article may have an undesirable effect on the load-dependent parameter measured or determined when the aerosol-generating article is received in the article chamber. This is because of the relatively high dielectric constant of water, compared to typical aerosol-formers in aerosol-forming substrates, such as polypropene glycol and glycerine. As a result, variations in humidity, or water content, of an aerosol-forming substrate may reduce the accuracy and reliability of the identification of an aerosolgenerating article based on the load-dependent parameter of the electric response of the electrically resonant oscillation system including the aerosol-generating article.

To reduce any unwanted effects of variations in humidity, or water content, of an aerosol-forming substrate, the control electronics may be configured to perform a pre-heating phase before measurement or determination of the load-dependent parameter to drive off unwanted moisture. The pre-heating phase may have any suitable duration, and may heat the aerosol-generating article to any suitable temperature. Fore example, the pre-heating phase may have a duration of 20 seconds or less, heating for at least a part of that time slightly above 100°C.

It may also be possible to generate mapping functions indicating the impact of humidity, or water content, variations on the loa-dependent parameter to compensate for such variations.

According to the disclosure, there is also provided an aerosol-generating system comprising: an aerosol-generating device as described above; and an aerosol-generating article comprising an aerosolforming substrate.

In some preferred embodiments, the aerosol-generating article comprises a load-capacitor comprising the aerosol-forming substrate. In these embodiments, the aerosol-generating article comprises a portion of the dielectric heater.

The load capacitor may comprise a first electrode and a second electrode. The second electrode may be spaced apart from the first electrode. At least a portion of the aerosol-forming substrate may be arranged between the first electrode and the second electrode. The load capacitor may be formed by the first electrode, the second electrode, and the aerosol-forming substrate.

The load-capacitor of the aerosol-generating article may be electrically connected to the aerosolgenerating device when the aerosol-generating article is received in the article chamber of the aerosolgenerating device, and form part of the dielectric heater. The aerosol-generating device may comprise electrodes configured to connect to the electrodes of the load capacitor when the aerosol-generating article is received in the article chamber.

In some preferred embodiments, the aerosol-generating article comprises a dielectric marker.

The dielectric marker may be configured to significantly alter the dielectric constant of the aerosolgenerating article compared to when the dielectric marker is not present in the aerosol-generating article. For example, the dielectric marker may double, triple, or quadruple the dielectric constant of the aerosolgenerating article compared to the aerosol-generating article without the dielectric marker. Advantageously, the provision of such a dielectric marker may result in an electric response of the electrically resonant oscillation system to the alternating electric field when the aerosol-generating article with the dielectric marker is in the article chamber that is substantially different from the electric response when other types of aerosol-generating article without such a dielectric marker are in the article chamber. Advantageously, the provision of such a dielectric marker may make identification of the aerosolgenerating article with the dielectric marker more accurate and reliable.

According to the disclosure there is also provided an aerosol-generating article for use in an aerosol-generating system, the aerosol-generating article comprising: an aerosol-forming substrate; and a dielectric marker.

The dielectric marker may be any suitable element that causes the desired electric response of the electrically resonant oscillation system to the alternating electric field when the aerosol-generating article with the dielectric marker is in the article chamber.

The dielectric marker may comprise a material having a dielectric constant that is at least two times greater than the dielectric constant of the aerosol-forming substrate.

The dielectric marker may comprise an electrical component. The dielectric marker may comprise at least one of: a coil, a partial coil, and a capacitive element.

The dielectric marker may be provided in any suitable location in the aerosol-generating article. The dielectric marker may be provided in the aerosol-forming substrate. The dielectric marker may be provided in or on a wrapper circumscribing the aerosol-forming substrate. The dielectric marker may be provided as a separate element from the aerosol-forming substrate. The dielectric marker may be comprised in the aerosol-forming substrate, as a constituent part of the aerosol-forming substrate.

The aerosol-generating article comprises an aerosol-forming substrate.

Preferably, the aerosol-forming substrate is a solid aerosol-forming substrate. However, the aerosol-forming substrate may comprise both solid and liquid components. Alternatively, the aerosolforming substrate may be a liquid aerosol-forming substrate.

Preferably, the aerosol-forming substrate comprises nicotine. More preferably, the aerosolforming substrate comprises tobacco. Alternatively or in addition, the aerosol-forming substrate may comprise a non-tobacco material or tobacco-substitute material containing aerosol-forming material.

If the aerosol-forming substrate is a solid aerosol-forming substrate, the solid aerosol- forming substrate may comprise, for example, one or more of: powder, granules, pellets, shreds, strands, strips, or sheets containing one or more of: herb leaf, tobacco leaf, tobacco ribs, expanded tobacco and homogenised tobacco. In some embodiments, the aerosol-forming substrate is a gel.

Optionally, the solid aerosol-forming substrate may contain tobacco or non-tobacco volatile flavour compounds, which are released upon heating of the solid aerosol-forming substrate. The solid aerosol-forming substrate may also contain one or more capsules that, for example, include additional tobacco volatile flavour compounds or non-tobacco volatile flavour compounds and such capsules may melt during heating of the solid aerosol-forming substrate.

Optionally, the solid aerosol-forming substrate may be provided on or embedded in a thermally stable carrier. The carrier may take the form of powder, granules, pellets, shreds, strands, strips, or sheets. The solid aerosol-forming substrate may be deposited on the surface of the carrier in the form of, for example, a sheet, foam, gel, or slurry. The solid aerosol-forming substrate may be deposited on the entire surface of the carrier, or alternatively, may be deposited in a pattern in order to provide a non- uniform flavour delivery during use.

In a preferred embodiment, the aerosol-forming substrate comprises homogenised tobacco material. As used herein, the term “homogenised tobacco material” refers to a material formed by agglomerating particulate tobacco.

Preferably, the aerosol-forming substrate comprises a gathered sheet of homogenised tobacco material. As used herein, the term “sheet” refers to a laminar element having a width and length substantially greater than the thickness thereof. As used herein, the term “gathered” is used to describe a sheet that is convoluted, folded, or otherwise compressed or constricted substantially transversely to the longitudinal axis of the aerosol-generating article. Preferably, the aerosol-forming substrate comprises an aerosol former. As used herein, the term “aerosol former” is used to describe any suitable known compound or mixture of compounds that, in use, facilitates formation of an aerosol and that is substantially resistant to thermal degradation at the operating temperature of the aerosol-generating article.

Suitable aerosol-formers are known in the art and include, but are not limited to: polyhydric alcohols, such as propylene glycol, triethylene glycol, 1 ,3-butanediol and glycerine; esters of polyhydric alcohols, such as glycerol mono-, di- or triacetate; and aliphatic esters of mono-, di- or polycarboxylic acids, such as dimethyl dodecanedioate and dimethyl tetradecanedioate. Preferred aerosol formers are polyhydric alcohols or mixtures thereof, such as propylene glycol, triethylene glycol, 1 ,3-butanediol and, most preferred, glycerine.

The aerosol-forming substrate may comprise a single aerosol former. Alternatively, the aerosolforming substrate may comprise a combination of two or more aerosol formers.

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.

1 . An aerosol-generating device for dielectrically heating an aerosol-generating article comprising an aerosol-forming substrate, the aerosol-generating device comprising: an article chamber configured to removably receive the aerosol-generating article; a dielectric heater configured to generate an alternating electric field in the article chamber for dielectrically heating the aerosol-generating article when the aerosol-generating article is received in the article chamber; and control electronics configured to control a supply of power to the dielectric heater for dielectrically heating the aerosol-generating article, wherein the article chamber, the aerosol-generating article received in the article chamber, and at least a portion of the dielectric heater form an electrically resonant oscillation system; and wherein the control electronics are further configured to: measure or determine a load-dependent parameter of an electric response of the electrically resonant oscillation system to the alternating electric field generated in the article chamber; and control the aerosol-generating device based on the load-dependent parameter of the electric response of the electrically resonant oscillation system.

2. An aerosol-generating device according to example 1 , wherein the load-dependent parameter of the electric response of the electrically resonant oscillation system includes at least one of a resonant frequency, a frequency shift, an impedance shift, a quality factor, a bandwidth, a phase shift, and a gain of the electrically resonant oscillation system.

3. An aerosol-generating device according to example 1 or example 2, wherein the control electronics are further configured to identify the aerosol-generating article based on the load-dependent parameter of the electric response of the electrically resonant oscillation system, and optionally wherein the control electronics are further configured to control the aerosol-generating device by preventing or turning off the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article to generate an aerosol when the control electronics are unable to identify the aerosol-generating article.

4. An aerosol-generating device according to any one of examples 1 to 3, wherein the control electronics are configured to control the aerosol-generating device by controlling the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article, and optionally by selectively supplying one of: a first power to the dielectric heater for dielectrically heating the aerosolgenerating article received in the article chamber; and a second power to the dielectric heater for dielectrically heating the aerosol-generating article received in the article chamber, the second power being different to the first power; and wherein the control electronics are configured to selectively supply one of the first power and the second power to the dielectric heater based on the load-dependent parameter of the electric response of the electrically resonant oscillation system.

5. An aerosol-generating device according to any one of examples 1 to 4, wherein the control electronics are configured to control the aerosol-generating device by selectively supplying power profiles to the dielectric heater for dielectrically heating the aerosol-generating article; wherein at least one of the power profiles varies with time; and wherein the selection of the power profile is based on the load-dependent parameter of the electric response of the electrically resonant oscillation system.

6. An aerosol-generating device according to example 5, wherein the control electronics are configured to control the aerosol-generating device by selectively supplying one of: a first power profile to the dielectric heater for dielectrically heating the aerosol-generating article received in the article chamber; and a second power profile to the dielectric heater for dielectrically heating the aerosolgenerating article received in the article chamber, the second power profile being different to the first power profile; wherein the first power profile varies with time; and wherein the selection of the first power profile or the second power profile is based on the load-dependent parameter of the electric response of the electrically resonant oscillation system, and optionally wherein the second power profile varies with time.

7. An aerosol-generating device according to any one of examples 1 to 6, wherein the control electronics are configured to control the aerosol-generating device by selectively supplying power to the dielectric heater for dielectrically heating the aerosol-generating article to a plurality of temperature profiles; wherein at least one of the plurality of temperature profiles varies with time; and wherein the selection of the temperature profile is based on the load-dependent parameter of the electric response of the electrically resonant oscillation system.

8. An aerosol-generating device according to example 7, wherein the control electronics are configured to control the aerosol-generating device by selectively supplying one of: power to the dielectric heater for dielectrically heating the aerosol-generating article received in the article chamber to a first temperature profile; and power to the dielectric heater for dielectrically heating the aerosolgenerating article received in the article chamber to a second temperature profile, the second temperature profile being different to the first power; wherein the first temperature profile varies with time; and wherein the selection of the first temperature profile or the second temperature profile is based on the load-dependent parameter of the electric response of the electrically resonant oscillation system; and optionally wherein the second temperature profile varies with time.

9. An aerosol-generating device according to any one of examples 1 to 8, wherein: the at least a portion of the dielectric heater and the article chamber form an unloaded oscillation system when the aerosol-forming substrate is not received in the article chamber; and the control electronics are further configured to: measure or determine the load-dependent parameter of the electric response of the unloaded oscillation system; determine the difference between the load-dependent parameter of the electric response of the electrically resonant oscillation system and the load-dependent parameter of the electric response of the unloaded oscillation system; and control the aerosol-generating device by controlling the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article received in the article chamber based on the difference between the load-dependent parameter of the electric response of the electrically resonant oscillation system and the load-dependent parameter of the electric response of the unloaded oscillation system.

10. An aerosol-generating device according to example 9, wherein the control electronics are further configured to determine whether the aerosol-forming substrate is received in the article chamber based on the difference between the load-dependent parameter of the electric response of the electrically resonant oscillation system and the load-dependent parameter of the electric response of the unloaded oscillation system; and optionally wherein the control electronics are configured to control the aerosolgenerating device by preventing the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article if it is determined that the aerosol-forming substrate is not received in the article chamber.

11. An aerosol-generating device according to any one of examples 1 to 8, wherein: the load-dependent parameter is the resonant frequency, at least a portion of the dielectric heater and the article chamber form an unloaded oscillation system when the aerosol-forming substrate is not received in the article chamber; and the control electronics are further configured to: measure or determine the resonant frequency of the unloaded oscillation system; determine the frequency shift between the resonant frequency of the electrically resonant oscillation system and the resonant frequency of the unloaded oscillation system; and control the aerosol-generating device by controlling the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article based on the frequency shift; and optionally wherein the control electronics are further configured to determine whether the aerosol-forming substrate is received in the article chamber based on the frequency shift; and optionally wherein the control electronics are configured to control the aerosolgenerating device by preventing the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article if it is determined that the aerosol-forming substrate is not received in the article chamber.

12. An aerosol-generating device according to any one of examples 1 to 8, wherein the control electronics are further configured to: determine the difference between the load-dependent parameter of the electric response of the electrically resonant oscillation system and a reference value ; and control the aerosol-generating device by controlling the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article based on the difference between the loaddependent parameter of the electric response of the loaded oscillation system and the reference value.

13. An aerosol-generating device according to claim 12, wherein the control electronics are further configured to determine whether the aerosol-forming substrate is received in the article chamber based on the difference between the load-dependent parameter of the electric response of the electrically resonant oscillation system and the reference value; and optionally wherein the control electronics are configured to control the aerosol-generating device by preventing the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article if it is determined that the aerosol-forming substrate is not received in the article chamber. 14. An aerosol-generating device according to any one of examples 1 to 8, wherein: the load-dependent parameter is the resonant frequency; and the control electronics are further configured to: determine the frequency shift between the resonant frequency of the electrically resonant oscillation system and a reference value; and control the aerosol-generating device by controlling the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article based on the frequency shift; and optionally wherein the control electronics are further configured to determine whether the aerosol-forming substrate is received in the article chamber based on the frequency shift; and optionally wherein the control electronics are configured to control the aerosolgenerating device by preventing the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article if it is determined that the aerosol-forming substrate is not received in the article chamber.

15. An aerosol-generating device according to any one of examples 1 to 14, wherein: the measuring or determining the load-dependent parameter of the electric response of the electrically resonant oscillation system comprises measuring or determining at least two load-dependent parameters of the electric response of the electrically resonant oscillation system; and the controlling the aerosol-generating device comprises controlling the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article based on the at least two load-dependent system parameters of the electrically resonant oscillation system.

16. An aerosol-generating device according to any one of examples 1 to 15, wherein: the measuring or determining the load-dependent parameter of the electric response of the electrically resonant oscillation system comprises measuring or determining the resonant frequency of the electrically resonant oscillation system, and measuring or determining at least one of the quality factor of the electrically resonant oscillation system and the bandwidth of the electrically resonant oscillation system; and the controlling the aerosol-generating device comprises controlling the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article based on the resonant frequency and the at least one of the quality factor and the bandwidth of the electrically resonant oscillation system.

17. An aerosol-generating device for dielectrically heating an aerosol-generating article comprising an aerosol-forming substrate, the aerosol-generating device comprising: an article chamber configured to receive the aerosol-generating article; a dielectric heater configured to generate an alternating electric field in the article chamber for dielectrically heating the aerosol-generating article when the aerosol-generating article is received in the article chamber; and control electronics configured to control a supply of power to the dielectric heater for dielectrically heating the aerosol-generating article, wherein the article chamber, the aerosol-forming substrate received in the article chamber, and at least a portion of the dielectric heater form an electrically resonant oscillation system; and wherein the control electronics are further configured to: measure or determine at least two load-dependent parameters of an electric response of the electrically resonant oscillation system to the alternating electric field generated in the article chamber; and identify the aerosol-generating article based on the at least two load-dependent parameters of the electric response of the electrically resonant oscillation system.

18. An aerosol-generating device according to example 17, wherein the at least two loaddependent parameters include at least one of: the resonant frequency, the quality factor, and the bandwidth of the electrically resonant oscillation system; and optionally wherein the control electronics are further configured to control the aerosol-generating device by preventing the supply of power to the dielectric heater for dielectrically heating the aerosolgenerating article when the control electronics are unable to identify the aerosol-generating article.

19. An aerosol-generating device according to any one of examples 1 to 18, wherein the alternating electric field generated in the article chamber has a frequency of between 50 MHz and 300 Gigahertz, optionally a frequency of between 200 Megahertz and 50 Gigahertz, optionally a frequency of between 500 Megahertz and 30 Gigahertz, optionally a frequency of between 900 megahertz and 20 Gigahertz, or a frequency of about 2.45 GHz.

20. An aerosol-generating device according to any one of examples 1 to 19, wherein the dielectric heater comprises a load capacitor for dielectrically heating the aerosol-generating article.

21 . An aerosol-generating device according to any one of examples 1 to 19, wherein the dielectric heater comprises a first electrode and a second electrode, the second electrode being spaced apart from the first electrode; wherein the first electrode and the second electrode are arranged such that when the aerosol-forming substrate is received in the article chamber, at least a portion of the aerosol-forming substrate is arranged between the first electrode and the second electrode; and wherein a load capacitor is formed by the first electrode, the second electrode and the aerosol-forming substrate received in the article chamber between the first electrode and the second electrode.

22. An aerosol-generating device according to example 20 or example 21 , wherein the dielectric heater comprises a resonant circuit including the load capacitor and an inductor. 23. An aerosol-generating device according to any one of examples 20 to 22, wherein the dielectric heater comprises: a switching unit configured for inverting operation; and a feedback loop connected to the switching unit, the feedback loop comprising two electrical contacts configured to connect with an electrode arrangement that forms the load capacitor for dielectrically heating the aerosol-generating article, the feedback loop being configured to perform resonant oscillating operation and configured to provide a 180° phase shift between an output signal of the switching unit and an input switching signal of the switching unit.

24. An aerosol-generating device according to example 23, wherein the dielectric heater further comprises the electrode arrangement connected to the two electrical contacts to form the load capacitor.

25. An aerosol-generating device according to example 23 or example 24, wherein the feedback loop comprises a resonant circuit that provides for a 90 degrees phase shift circuit at an operating frequency of the oscillator circuit.

26. An aerosol-generating device according to example 25, wherein the resonant circuit comprises a resonant cavity.

27. An aerosol-generating device according to example 25, wherein the resonant circuit comprises a parallel resonant circuit which is electrically stimulated by the output signal of the switching unit.

28. An aerosol-generating device according to any one of examples 23 to 27, wherein the feedback loop has substantially the same impedance as the switching unit.

29. An aerosol-generating device according to any one of examples 23 to 28, wherein the switching unit includes a frequency measurement device to measure a switching frequency of a transistor of the switching unit.

30. An aerosol-generating device according to any one of examples 1 to 19, wherein the dielectric heater comprises a resonant cavity that at least partially includes the article chamber, optionally wherein the resonant cavity is arranged in the article chamber, optionally wherein the article chamber is the resonant cavity, and optionally wherein the resonant cavity is configured as a quarter wavelength resonator.

31 . An aerosol-generating device according to example 30, wherein the dielectric heater further comprises a radiation source or a wave source and at least one of a waveguide, an antenna, and a transmission line, wherein the resonant cavity is coupled to the radiation source or the wave source via the at least one of a waveguide, an antenna, and a transmission line, and optionally wherein the resonant cavity is coupled to the radiation source or the wave source using at least one of a capacitive coupling, an inductive coupling, a direct electric coupling or a window coupling. 32. An aerosol-generating device according to example 30 or example 31 , wherein the dielectric heater comprises a resonant circuit including the resonant cavity.

33. An aerosol-generating device according to example 32, wherein the resonant cavity is coupled to the radiation source or the wave source using at least one of a capacitive coupling, an inductive coupling, a direct electric coupling or a window coupling.

34. An aerosol-generating device according to any one of examples 1 to 33, wherein the aerosol-generating device further comprises a probe or antenna to measure a parameter of the electric field generated in the article chamber, and optionally wherein the parameter measured by the probe or antenna is the frequency of the electric field generated in the article chamber.

35. An aerosol-generating device according to example 34, wherein the control electronics are associated with the probe or antenna and are configured to derive the load-dependent parameter from the measured parameter of the electric field.

36. An aerosol-generating device according to example 34 or example 35, wherein the probe or antenna includes at least one of: a transverse electromagnetic (TEM) transmission line, a microstrip, an inductor, or an antenna.

37. An aerosol-generating device according to any one of examples 34 to 36, wherein the probe or antenna includes a resonant cavity.

38. An aerosol-generating device according to example 37, wherein the resonant cavity comprises a quarter wavelength coaxial cavity resonator, and optionally wherein the quarter wavelength coaxial cavity resonator comprises an inner wire, wherein the inner wire has an impurity-doped insulator.

39. An aerosol-generating device according to example 37 or example 38, wherein the resonant cavity has at least one of: a resonant frequency of in between 8 gigahertz to 12 gigahertz, optionally about 10 GHz; a quarter wavelength of in between 6.3 mm to 9.4 mm, and optionally about 7.5 mm.

40. An aerosol-generating device according to any one of examples 37 to 39, wherein the resonant cavity is arranged in the article chamber.

41 . An aerosol-generating device according to any one of examples 37 to 40, wherein the aerosol-generating device further comprises a signal processing unit configured to convert an output provided by the resonant cavity to a signal that is receivable by the control electronics.

42. An aerosol-generating device according to example 41 , wherein the signal processing unit comprises: a rectifier connected to the resonant cavity to generate a DC signal from the output of the cavity resonator; and an impedance element on which the DC signal is applied, and a voltage sensor to measure a voltage over the impedance element that is fed to the controller. 43. An aerosol-generating device according to any one of examples 1 to 42, wherein the aerosol-generating device further comprises a power supply, wherein the control electronics are configured to control the aerosol-generating device by controlling the supply of power from the power supply to the dielectric heater; and wherein the control electronics comprise a power sensing system configured to detect a power consumption value drawn from the power supply, and wherein the power consumption value is used as the load-dependent parameter.

44. An aerosol-generating device according to example 43, wherein the power consumption value is indicative of a supply current, in particular a DC supply current, drawn from the power supply.

45. An aerosol-generating device according to example 43 or example 44, wherein the power sensing system comprises a shunt to derive the supply current.

46. An aerosol-generating device according to any one of examples 1 to 45, wherein the control electronics are configured to control the frequency of the electric field generated in the article chamber by the dielectric heater.

47. An aerosol-generating device according to any one of examples 1 to 46, wherein the measuring or determining the load-dependent parameter comprises the control electronics being configured to: supply power to the dielectric heater to generate an alternating electric field in the article chamber; and control the supply of power to the dielectric heater to vary the frequency of the generated alternating electric field; and measure a parameter of the electrically resonant oscillation system at a plurality of frequencies of the alternating electric field.

48. An aerosol-generating device according to example 47, wherein the control electronics are further configured to control the supply of power to the dielectric heater to vary the frequency of the generated alternating electric field over a predetermined frequency range.

49. An aerosol-generating device according to example 47 or example 48, wherein the measuring or determining the load-dependent parameter comprises the control electronics being further configured to determine the load-dependent parameter based on the measured parameter of the electrically resonant oscillation system at the plurality of frequencies.

50. An aerosol-generating device according to example 47 or example 48, wherein the measuring or determining the load-dependent parameter comprises the control electronics being further configured to generate a frequency plot from the parameter measured or determined at the plurality of frequencies, and determine the load-dependent parameter based on the frequency plot.

51 . An aerosol-generating device according to example 47 or example 48, wherein the loaddependent parameter is the parameter measured at the plurality of frequencies.

52. An aerosol-generating system comprising: an aerosol-generating device according to any one of examples 1 to 51 ; and an aerosol-generating article comprising an aerosol-forming substrate.

53. An aerosol-generating system according to example 53, wherein the aerosol-generating article comprises a load-capacitor comprising the aerosol-forming substrate.

54. An aerosol-generating system according to example 53, wherein the load capacitor comprises a first electrode and a second electrode, the second electrode being spaced apart from the first electrode, and at least a portion of the aerosol-forming substrate arranged between the first electrode and the second electrode.

55. An aerosol-generating system according to example 53 or example 54, wherein the loadcapacitor of the aerosol-generating article is electrically connected to the aerosol-generating device when the aerosol-generating article is received in the article chamber of the aerosol-generating device, and forms a part of the dielectric heater.

56. An aerosol-generating system according to any one of examples 53 to 55, wherein the aerosol-generating article comprises a dielectric marker.

57. An aerosol-generating system according to example 56, wherein the dielectric marker comprises a material having a dielectric constant that is at least two times greater than the dielectric constant of the aerosol-forming substrate.

58. An aerosol-generating system according to example 56, wherein the dielectric marker comprises an electrical component, and optionally wherein the dielectric marker comprises at least one of: a coil, a partial coil, and a capacitive element.

59. An aerosol-generating article for use in an aerosol-generating system, the aerosolgenerating article comprising: an aerosol-forming substrate; and a dielectric marker.

60. An aerosol-generating article according to example 59, the dielectric marker comprises a material having a dielectric constant that is at least two times greater than the dielectric constant of the aerosol-forming substrate.

61 . An aerosol-generating article according to example 59, wherein the dielectric marker comprises an electrical component, and optionally wherein the dielectric marker comprises at least one of: a coil, a partial coil, and a capacitive element.

62. An aerosol-generating article according to any one of examples 59 to 61 , wherein the aerosol-generating article comprises a load-capacitor comprising the aerosol-forming substrate.

63. An aerosol-generating article according to example 62, wherein the load capacitor comprises a first electrode and a second electrode, the second electrode being spaced apart from the first electrode, and at least a portion of the aerosol-forming substrate arranged between the first electrode and the second electrode. The invention will be further described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a schematic illustration of a dielectric heater for an aerosol-generating system according to an embodiment of the disclosure;

Figure 2 is a schematic illustration of a closed-loop control system for an aerosol-generating system having a dielectric heater according to an embodiment of the disclosure;

Figure 3 is a schematic illustration of an aerosol-generating system having a dielectric heater according to an embodiment of the disclosure;

Figure 4 is a schematic illustration of an oscillation circuit for use in the aerosol-generating system of Figure 3;

Figures 5a, 5b and 5c are schematic illustrations of oscillation circuits showing phase shifting elements configured to achieve a 180 degrees phase shift, Figure 5a shows an oscillation circuit comprising a phase shifting element comprising a resonant circuit and a capacitive element, which together are configured to achieve a 180 degree phase shift, Figure 5b shows one embodiment of the resonant circuit of Figure 5a, in which the resonant circuit comprises a capacitive element, and Figure 5c shows another embodiment of the resonant circuit of Figure 5a, in which the resonant circuit comprises a resonant cavity;

Figure 5d is a schematic illustration of a resonant cavity of a dielectric heater in accordance with an embodiment of the disclosure;

Figure 6 illustrates a circuit diagram of an exemplary embodiment of the oscillation circuit of Figure 5a and Figure 5c;

Figures 7A-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;

Figure 8 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;

Figure 9 is a schematic illustration of control electronics comprising a frequency sensing system, the control electronics being configured to control the aerosol-generating device by controlling the power supplied to the dielectric heater based on a frequency of a detected alternating electric field, according to an embodiment of the disclosure;

Figure 10 shows a flow diagram of a method of operating an aerosol-generating device in accordance with an embodiment of the disclosure; and

Figures 11a, 11 b and 11c are schematic illustrations of frequency responses of an electrically resonant oscillation system according to an embodiment of the disclosure.

The present disclosure concerns aerosol-generating systems, and in particular aerosol-generating devices, which use dielectric heating to generate an aerosol. Various types of dielectric heater are known, and any suitable type of dielectric heater is considered to be applicable to the aerosol-generating systems and aerosol-generating devices of this disclosure. In particular, examples of two different types of dielectric heater are described below. The first type of dielectric heater, as shown in Figures 1 , 2 and 5a/c, comprises a resonant cavity coupled to a wave source, such as via at least one of waveguides, antennae, or transmission lines, wherein an aerosol-generating article comprising an aerosol-forming substrate is dielectrically heated when received in the resonant cavity. The second type of dielectric heater, as shown in Figures 3-4, 5a/b, and 6-8, comprises a load capacitor in a resonant circuit, wherein an aerosol-generating article comprising an aerosol-forming substrate is dielectrically heated when in close proximity, or between the electrodes of, to the load capacitor.

Figure 1 is a schematic illustration of an exemplary system for dielectric heating using radio frequency (RF) electromagnetic radiation. The system comprises a wave source 10 configured to generate a radio frequency signal, a power amplifier 12 connected to the wave source 10 to amplify the radio frequency signal, and antennas 16 positioned inside a resonant cavity 14, the antennas 16 being connected to an output of the power amplifier 12. The output of the power amplifier 12 is fed back to the wave source 10 to provide closed-loop control. Although in this embodiment the wave source 10 is coupled to the resonant cavity 14 via antennas, it will be appreciated that in other embodiments the wave source 10 may be coupled to the resonant cavity another suitable means, such as a single antenna, a waveguide, or a transmission line.

An aerosol-generating article 18, which is to be heated, is placed in the resonant cavity 14, which in this embodiment defines an article chamber, and is subjected to radio frequency electromagnetic radiation. Polar molecules within the aerosol-generating article 18 align with the oscillating electromagnetic field and so are agitated by the electromagnetic field as it oscillates. This causes an increase in temperature of the aerosol-generating article 18. This kind of heating has the advantage that it may be configured to be uniform throughout the aerosol-generating article 18 (provided that the polar molecules are uniformly distributed and the resonant cavity is designed accordingly). It also has the advantage of being a non-contact form of heating, which does not require conduction or convection of heat from high temperature heating element.

Figure 2 illustrates a control scheme that may be used for the dielectric heater of Figure 1 . The system comprises control electronics for the dielectric heater. In the example of Figure 2, an electric field generator 11 comprises a solid state RF LDMOS transistor that performs the function of both the wave source 10 (a RF signal generator) and the power amplifier 12, to amplify the generated RF electric signal. The output of the RF solid state transistor is passed to an antenna 16, which is positioned in a resonant cavity 14, and generate an oscillating electric field in the resonant cavity 14. In this embodiment, the resonant cavity 14 forms an article chamber, and an aerosol-generating article 18, comprising an aerosolforming substrate 20, is received in the resonant cavity 14, and exposed to the oscillating electric field.

The control electronics comprises a microcontroller 26 that can control both the frequency and the power output of the RF solid state transistor. One or more sensors provide input to the microcontroller 26. The microcontroller 26 adjusts the frequency or the power output, or both the frequency and the power output, of the electromagnetic field generator 11 based on the sensor inputs. In the example shown in Figure 2, there is a temperature sensor 28 positioned to sense the temperature within the article chamber 14. A sampling antenna 30 may be provided in the article chamber 14 as an alternative, or in addition, to the temperature sensor 28. The sampling antenna 30 is configured as a receiver and can detect perturbation of the electric field in the article chamber 14, which is an indication of the efficiency of the energy absorption by the aerosol-forming substrate 20. A RF power sensor 32 is also provided to detect the power output from the electric field generator 11. It will be appreciated that in some embodiments a sampling antenna 30 may not be required, and the antenna 16 may be used to detect perturbation of the electric field in the article chamber 14.

The microcontroller 26 receives signals from the RF power sensor 32, the temperature sensor 28 and the sampling antenna 30. The signals can be used to determine at least one of: whether the temperature is too low, whether the temperature is too high, if there is a fault, and if there is no substrate, or a substrate with inappropriate dielectric properties, in the resonant cavity 14.

Based on the determination made by the microcontroller 26, the frequency and power of the electromagnetic filed generated by the RF solid state transistor is adjusted or the electric filed is switched off. Typically, it is desirable to provide for a stable and consistent volume of aerosol, which means maintaining the aerosol-forming substrate within a particular temperature range. However, the desired target temperature may vary with time as the composition of the aerosol-forming substrate changes and the temperature of the surrounding system changes. Also, the dielectric properties of the aerosol-forming substrate change with temperature and so the electromagnetic field may need to be adjusted as temperature increases or decreases.

When the aerosol-generating article 18 is received in the resonant cavity 14, the resonant cavity 14 and the aerosol-generating article 18 together form an electrically resonant oscillation system. When power is supplied to the electromagnetic field generator 11 to generate an RF electric signal, an alternating electric field is generated in the resonant cavity 14. The electrically resonant oscillation system exhibits an electric response to the alternating electric field. The control electronics are configured to measure load-dependent parameters of the electric response of the electrically resonant oscillation system to the alternating electric field generated in the resonant cavity 14. The control electronics are further configured to control the aerosol-generating device by controlling the supply of power to the antenna 16 to dielectrically heat the aerosol-generating article based on the load-dependent parameter of the electric response of the electrically resonant oscillation system to the alternating electric field, as described in more detail below, with reference to Figures 10a-c.

Figure 3 is a schematic illustration of an aerosol-generating system 100 according to an embodiment of the disclosure. The aerosol-generating system 100 comprises an aerosol-generating article 105 comprising an aerosol-forming substrate 110. The aerosol-generating system 100 further comprises an aerosol-generating device 120 for heating the aerosol-generating article 105. The aerosolgenerating device 120 comprises an article chamber 140 that is configured to removably receive the aerosol-generating article 105. The aerosol-generating device 120 further comprises a dielectric heater that is configured to generate an alternating electric field in the article chamber 140.

In this embodiment, the dielectric heater comprises a first electrode 130 and a second electrode 135, separated by the article chamber 140. The article chamber 140 and the aerosol-generating article 105 are configured such that the aerosol-forming substrate 110 is in contact with or in close proximity to both the first electrode 130 and the second electrode 135 when the aerosol-generating article 105 is received in the article chamber 140. When the aerosol-generating article 105 is received in the article chamber 140, with the aerosol-forming substrate 110 arranged between the first electrode 130 and the second electrode 135, the first electrode 130, the second electrode 135, and the aerosol-forming substrate 110 form a load capacitor CL.

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. The oscillation circuit 150 is also part of the dielectric heater.

In some embodiments, the width of the aerosol-generating article 105 is slightly greater than the space between the first electrode 130 and the second electrode 135, such that the distal end of the aerosol-forming substrate 110 is slightly compressed between the first electrode 130 and the second electrode 135. In some embodiments, the aerosol-generating 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-generating article 105 is received in the article chamber 140, and may decrease the distance between first and second electrodes 130, 135 for dielectric heating, thereby improving dielectric properties of the load capacitor CL formed by the first and second electrodes 130, 135 and the aerosol-forming substrate 110.

In this embodiment, the aerosol-generating device 120 comprises the first electrode 130 and the second electrode 135. However, it will be appreciated that in other embodiments, the aerosol-generating article 105 may comprise the first electrode 130 and the second electrode 135. In these embodiments, the space between the first and second electrical contacts 160, 165 is sized such that, when the aerosolgenerating article 105 is received in the article chamber 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.

The aerosol-forming substrate 110 may comprise tobacco, tobacco-based materials or nontobacco 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 may also be a liquid aerosol-forming substrate. Where the aerosol-forming substrate 110 is a liquid aerosol-forming substrate, the aerosol-generating article 105 may be configured as a cartridge, capsule, or liquid container. Where the aerosol-forming substrate 110 is a liquid aerosol-forming substrate, the first and second electrodes 130, 135 may be configured as wicking elements or capillary elements 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-generating article 105 or reaches into an inner volume of the aerosol-generating article 105 that can heat and vaporize a liquid aerosol-forming substrate 110 located in the inner volume. For example, the first and second electrodes 130, 135 can be embodied as parallelly arranged plates separated by a distance that forms a capillary channel, for example in a range between 0.1 mm to 2mm, depending on the desired capillary strength or rise. The first and second electrodes can be arranged as two matrices or arrays of pin-like, rod-like, or tab-like electrodes with opposite polarity, the two matrices or arrays interposed between each other, forming a capillary structure therebetween, for example with an average distance between neighbouring pin-like electrodes being in a range between 0.1 mm to 2mm, depending on the desired capillary strength or rise. In another variant, the wicking element can be a separate element that is interposed between two electrodes 130, 135, for example flat or slightly curved electrodes 130, 135.

The aerosol-generating device 120 further comprises a power supply 170, control electronics 180 electrically coupled to the oscillation circuit 150, and user interface 182, in the form of a touch screen display, electrically coupled to the control electronics 180. In this embodiment, the power supply 170 is a rechargeable lithium ion battery, for example with one or more lithium ion battery cells, and the aerosolgenerating 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.

In use, power is supplied to the oscillation circuit 150 from the power supply 170 when a user activates the aerosol-generating device 120. The control electronics 180 controls the supply of power from the power supply 170 to the oscillation circuit 150.

In this embodiment, the aerosol-generating device 120 is activated by a user pressing an activation button (not shown), which is 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 the aerosol-generating article 110 or on a mouthpiece (not shown) of the aerosol-generating device 120 by a puff sensor. When power is supplied to the oscillation circuit 150, the oscillation circuit 150 generates an alternating electric field in the article chamber 140, between the first and second electrodes 130, 135 for dielectrically heating the aerosolgenerating article 105, and in particular for dielectrically heating the aerosol-forming substrate 110, in the article chamber 140, to release volatile compounds from the aerosol-forming substrate, which condense to form an aerosol that is inhalable by a user of the aerosol-generating system 100. When the aerosol-generating article 105 is received in the article chamber 140, the article chamber 140, the portion of the aerosol-generating article 105 received in the article chamber 140, and the oscillation circuit 150 forming the dielectric heater, together form an electrically resonant oscillation system. When power is supplied to the oscillation circuit 150, an alternating electric field is generated in the article chamber 140. The electrically resonant oscillation system exhibits an electric response to the alternating electric field. The control electronics 180 are configured to measure load-dependent parameters of the electric response of the electrically resonant oscillation system to the alternating electric field generated in the article chamber 140. The control electronics 180 are further configured to control the aerosol-generating device 120 by controlling the supply of power to the oscillation circuit to dielectrically heat the aerosol-generating article 105 based on the load-dependent parameter of the electric response of the electrically resonant oscillation system, as described in more detail below, with reference to Figures 10 and 11a-c.

Figure 4 is a schematic illustration of an oscillation circuit 250 for use in the aerosol-generating system 100 of Figure 3, according to an embodiment of the disclosure. Oscillation circuit 250 comprises a switching unit 260 interconnected with a resonator feedback loop 270 to provide 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).

The oscillation circuit 250 further comprises a choke 280 that acts on an input to the feedback loop 270 to provide for a stimulation signal, for example a stimulation voltage. The oscillation circuit also 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 U IN 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 arrive 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.

The feedback loop 270 is configured to be self-oscillating and will oscillate at or close to a resonant 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 U IN of switching unit 260 for oscillation, and in addition, the transistor of the switching unit 260 is configured for inverting operation.

As shown in Figures 5a and 5b, feedback loop 270 includes a resonant circuit 272 comprising the load capacitor CL, which provides for a first 90 degrees phase shift or quarter wave shift to the feedback signal. Feedback loop 270 further includes a capacitive element 274, which provides for a second 90 degree 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 U IN and the output UOUT of the switching unit 260.

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

In an alternative embodiment, as shown in Figure 5c, the resonant circuit 272 includes a resonant cavity, rather than the load capacitor. In this embodiment, the resonant cavity forms the article chamber 140. In other words, the resonant cavity has an interior volume configured to receive the aerosol-forming substrate 110, and has an opening for inserting the aerosol-forming substrate 110. Preferably, the resonant cavity is configured as a A/4 resonator. In this embodiment, the resonant circuit 272 including the resonant cavity is configured to behave as a RLC circuit. The inductor L and the capacitor C of the equivalent RLC circuit 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.

In this embodiment, the resonant circuit 272 including the resonant cavity is coupled to the feedback loop 270 using an inductive antenna coupling (magnetic coupling). It will be appreciated that in other embodiments the resonant circuit 272 including the resonant cavity may be coupled to the feedback loop 270 by any suitable type of coupling, such as a capacitive coupling, an inductive antenna coupling (magnetic coupling), a direct electric coupling, or a window coupling (e.g. coupling with a loop).

In this embodiment, the resonant cavity has a cylindrical shape. However, the resonant cavity may have any suitable shape, such as a rectangular parallelepiped shape. In some embodiments, the resonant cavity is configured as a split-ring resonator.

Figure 5d is a schematic illustration of a resonant cavity 280, or resonator, of a dielectric heater in accordance with an embodiment of the disclosure. The resonator 280 may be part of a resonant circuit, such as the resonant circuit 272 of Figure 5c.

In this embodiment, resonator 278 includes a resonator casing 279 surrounding two transmission lines 280. The resonator casing 279 defines an article chamber configured to receive at least a portion of an aerosol-generating article. The resonator casing 279 comprises an opening 281 . The opening 281 is configured to enable a portion of an aerosol-generating article to be inserted into the article chamber, between the transmission lines 280. Each transmission line 280 includes a first, lower portion 282, and a second, upper portion 283. The separation between the upper portions 283 is narrower than the separation between the lower portions 282. The lower portions 282 of the two transmission lines 280 are connected to each other at the end opposite the upper portion 283 by an intermediate portion 284.

Each transmission lines 280 is connected to a feed 285 at the lower portion 282. The feed 285 connects the transmission line 280 to an oscillation circuit (not shown).

In particular, one of the transmission lines 280 is connected to a first feed 286, and the other transmission line 280 is connected to a second feed 287. Each feed 286, 287 has a coaxial structure comprising a signal line 288, and a grounded shielding 289. The signal line 288 of each feed 286, 287 extends through the resonator casing 279 at a through-hole on opposing sides of the casing 279. The resonator casing 279 is connected to ground via the grounded shielding 289 of the feeds 286, 287. The transmission lines 280 are connected to the feeds 285 via the signal lines 288.

When an aerosol-generating article is received in the article chamber of the resonator 278, the resonator 278, the portion of the aerosol-generating article received in the article chamber, and the oscillation circuit together form an electrically resonant oscillation system.

In use, the oscillation circuit drives an alternating signal through the feeds 285, which generates an alternating electric field 290 in the article cavity, between the transmission lines 280. The generated alternating electric field 290 propagates from one transmission line 280 through the portion of the aerosol-generating article received between the transmission lines 280 into the other transmission line 280.

Preferably, each transmission line las a length that is around one-quarter of a wavelength of the generated alternating electric field 290.

Figure 6 illustrates an oscillation circuit 350 for an aerosol-generating system, such as the aerosolgenerating system 100 of Figure 3, 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 Cj. 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, arranged in an article chamber of the aerosol-generating system. In the variant shown, the resonator circuit 272 is also connected to ground via a delay line DL, and a capacitor C2 connected in series to the delay line DL. The oscillation 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 6, 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. The delay line DL is a time delay element, for example an element that has inductive behaviour, for slowing down the arriving voltage wave from the feedback loop 270 during a period of the oscillation. This allows for tuning to a desired switching and oscillation frequency of the resonant circuit 272, to move the oscillation frequency away from the natural resonant frequency given by the resonant circuit 272. This ensures that oscillation circuit 350 remains in a predefined frequency operating range to provide for the requisite inverted or 90° phase shifted feedback and also to make sure that the feedback loop has a low impedance to provide for a high gain, as described in greater detail below.

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-generating article 110. In such embodiments, electrical contacts 160, 165 provide an electrical connection between the first and second electrodes 130, 135 and the feedback loop 270. In embodiments where the load capacitor CL is fixed within the feedback loop 270, for example, such that an aerosol-forming substrate 110 can be inserted into and removed from an article chamber formed 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, such as inductors L1 and L2.

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 14 volts. 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, which provides for 3.2 volts to 3.9 volts. However, more preferably, a voltage of one battery cell of an exemplary 3.5 volts to 7 volts for power supply can be boosted, for example by a DC-DC converter (e.g. a boost circuit), or a voltage doubler. It will be appreciated that two or more battery cells can be used in series, or in other configurations or arrangements which allow for an increasing 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 dielectric heating of the aerosol-forming substrate 110 by a change to the DC supply voltage, or to boost the voltage (for example to 10-12V) for maximum power in a 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 power to the load capacitor CL for heating of the aerosol-forming substrate 110 despite the oscillation circuit 350 freely oscillating.

A capacitor C1 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 voltage-dependent oscillation and frequency, stabilizes the oscillation, and also improves the overall dielectric heating efficiency. Capacitance of capacitor C1 is chosen to be larger than the maximal intrinsic capacitor Cj of transistor T at the operating conditions, so that the variation of the intrinsic transistor based on frequency, temperature, etc. has much lower or negligible influence on the feedback loop 270. For example, in a non-limiting embodiment, the value can be in a range between 2pF to 100pF, more preferably in a range between 5pF and 50pF.

Capacitive element 274 comprises a capacitor C2 arranged at the output or end of the resonant circuit 272. In one embodiment, capacitive element 274 comprises more than one capacitor. As described above, capacitive element 274 has the function of providing a 90° phase shift to the feedback voltage of feedback loop 270 with minimized losses or other undesired effects, and it therefore needs to have a high-quality factor or Q factor, preferably above 1000 at 100MHz. The capacitance value for C2 of the capacitive element 274 should be relatively high as compared to C1 , 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.

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 U IN, 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.

The combination of capacitor C1 , 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 C1 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.

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.

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.

Figures 7A to 7F illustrate how a Quartz-mimicking or Quartz equivalent circuit may be derived using a variant of a parallel resonator circuit PRC, which can serve as an exemplary and non-limiting embodiment as resonant circuit 272. A Quartz-mimicking or Quartz equivalent circuit can have a parallel resonance at a given frequency. This can be seen as a circuit with two branches, one representing the mechanical oscillation and one representing the electric behaviour, as illustrated in figure 7A and 7B. 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.

Referring now to Figure 7C, 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 L1 and L2 on each side of the load capacitor CL, as shown in Figure 7D, 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 7F) due to capacitor CE‘S minimal capacitive effect on CL.

In a non-limiting example starting from the split inductor L1 and L2 of the resonant circuit of Figure 7D, inductors L1 and L2 can be mutually magnetically coupled to form a mutual inductance M, thereby forming the parallel circuit branch or second branch of the resonant circuit 272, as shown in Figure 7E. 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 favours and facilitates the inductive coupling of the two inductors L1 , L2 and the balancing of the voltage UL over load capacitor CL. The symmetry of the two branches in either direction with first branch L1 - CL - L2 and the second branch with inductor LE, representing the two mutual inductance values, facilitates the symmetrical balancing of the voltage over the electrodes of the load capacitor CL, which consequently reduces losses created at the load capacitor CL. This split inductor principle can also be referred to as a split coil resonator. The resonant circuit 272 could also be implemented as shown in the Figure 7F, where the mutual inductance M (seen two times due to the mutuality) is replaced by a separate inductive element, for example inductor LE.

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 L1 plus L2, LE could be in a range between 7nH and 30nH, more preferably between 10nH and 20nH, and the value of the load capacitor can be in a range between 0.5pF to 5pF, more preferably between 1 pF to 3pF.

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

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 f_s of the oscillation circuit) of the voltage applied to the load capacitor CL. However, higher switching frequencies f_s lead 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).

To compensate for a lower switching frequency, a higher oscillation AC voltage U L (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 f_s and 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 aerosolforming substrate 110), the voltage increase has a stronger effect on the heating power than frequency increase, as voltage has a second order relationship with power. The dielectric losses in load capacitor CL are also dependent on the distance separating the two electrodes 130 and 135, which influences the electric field strength EF across the aerosol-forming substrate 110.

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 aerosol-forming substrate 110 are a serious concern. Therefore, there are working ranges for switching frequency f_s and dielectric field strength EF, for a hand-held and human-operated portable device The dielectric field strength is dependent on voltage UL applied to capacitor CL and a maximal distance d between the first and second electrodes 130, 135. 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 f_s enables the use of straightforward circuit design, for example but not limited to the use of a LDMOS or other standard transistor used for RF circuits. Preferably, the switching frequency should be in a range between 100MHz and 1.2 GHz, more preferably between 150MHZ to 1GHz, more preferably between 200MHz and 900MHz. At the same time, the maximal-value of dielectric 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 dielectric field strength across the electrodes of the load capacitor is maximally 120V/mm, more preferably maximally 100V/mm, even more preferably maximally 80V/mm.

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 L1 and L2, capacitive-resistive losses from capacitors C1 and C2 , and resistive losses of electrodes E1 and E2 and the wiring). As an example, the overall power could be 10W, while the effective power or heating losses PL should be 6W or more, with 4W or less of non-heating losses or other heating losses not caused in the substrate 110 between the first and second electrodes 130, 135. More than 6-7W of power losses is not desirable for a handheld device. 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.

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.

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

Oscillations in the feedback loop 270 will be naturally drawn towards the parallel resonance frequency of the resonant circuit 272. However, the addition of a delay line DL can introduce a slight time delay limiting the oscillation frequency below the parallel resonance frequency. Figure 8 shows a frequency analyser 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 8 that the 90° phase shift starts dropping before the parallel resonance frequency f_PAR is reached. After the parallel resonance frequency f_PAR, the phase shift response drops below 0° to capacitive behaviour and the impedance is very high, e.g. 2.4kQ. The ideal operating frequency range is closer to the series resonance frequency fsE 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 10Q, preferably between 1 Q and 5Q, and more preferably, between 1 ,5Q and 3Q. The parallel resonance frequency f_PAR can be above 1 GHz, e.g. 1 GHz to 1 ,5GHz, while the actual switching frequency f_s can be below 1 GHz, and this lower switching frequency is caused by the delay line DL.

Ideally, the oscillation frequency f_s should be set to be below the parallel resonance frequency fp_AR 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 (and therefore the feedback loop 270) is low, as illustrated in the graphs of FIG. 8. For example, a resulting impedance of the feedback loop at the oscillation frequency f_s of the oscillation circuit can be in a range of approximately 100mQ to 2Q. Preferably, the delay line DL is configured such that the oscillation frequency f_s is closer to the series resonance frequency fsER than to the parallel resonance frequency f_PAR, 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 f_PAR, providing that the above two conditions (i) and (ii) are fulfilled. In an embodiment, the delay caused by the delay line DL that acts on feedback loop 270 is in a range between 35% and 90% of a difference between the period of the parallel resonance frequency (PAR 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. 8 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 1169ps, there is a difference of 369ps between the period of fpA 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 behaviour and low impedance that is necessary to provide inverting feedback at high gain.

Preferably, the delay line is implemented as a meandering conductive element having dominantly inductive behaviour, 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 behaviour. 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, zigzag 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 6, 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.

Figure 9 is a schematic illustration of control electronics utilizing a frequency sensing system for controlling the power supplied to the dielectric heater based on a frequency of the alternating electric field in the article chamber, according to some embodiments of the disclosure, such as the embodiments described above in relation to Figures 3 to 8.

The control electronics comprise a sensing resonant cavity (or resonator, e.g., quarter wavelength resonator) having a peak resonance frequency above the switching frequency of the feedback loop. The sensing resonant cavity is prepared, for example by the use of impurities or mechanical imperfections, to provide a wide range frequency response showing a variation between the different frequencies, such that the operational range of frequencies is covered by a resonance response. In one embodiment, the sensing resonant cavity comprises a quarter wavelength coaxial cavity resonator with an inner wire. The sensing resonant cavity comprises an impurity-doped insulator. The sensing resonant cavity is situated at a location within the electric field generated by the load capacitor CL, for example at a peripheral area of the load capacitor CL, or within the resonant cavity, or within an area of the article chamber that would not obstruct the aerosol-forming substrate. The sensing resonant cavity is connected via a direct electric coupler to a rectifier for generating a DC signal. The generated DC signal is fed to a resistor/impedance to be measured by a voltage measurement device. The voltage measurements are transmitted to a controller/microprocessor for calibration and/or further processing.

In alternative embodiments, the system may utilize one or more of resonant antennas, microstrips, waveguides, for high-frequency sensing.

It will be appreciated that such a frequency sensing system may not be a part of the control electronics, and may be used as a calibration system to generate a mapping function MF.

The change in resonant frequency may be proportional to the power loss of the load capacitor CL. Hence, measurements of the power consumption may alternatively provide an indication of whether there is an aerosol-generating article received in the article chamber, and the type of aerosol-generating article that is received in the article chamber. In this respect, it is possible to simply use a frequency sensor for calibration purposes, for example at a factory level, to correlate different power consumption patterns (e.g. of DC supply current that is fed from a power source of a calibration device) with the frequency of oscillation. Thereafter, the aerosol-generating device itself may not need to have a frequency sensor or frequency sensing system anymore.

Accordingly, based on previously made frequency measurements and calibration, a mapping function MF may be generated and pre-stored in the aerosol-generating device so that it is possible to use a power consumption value (DC supply current, DC supply voltage, or both) as a load-dependent parameter that is indicative of whether there is an aerosol-generating article received in the article chamber, and the type of aerosol-generating article that is received in the article chamber.

It will be appreciated that in other embodiments, the control electronics may include a frequency detection unit to measure or derive a frequency of the alternating electric field in the article chamber. The measured frequency may then be fed to a pre-stored mapping function MF that maps the measured frequency, in particular a resonant frequency of the oscillation circuit 150, to those of known types of aerosol-generating article.

The system may utilize one or more of resonant antennas, microstrips, waveguides, for high- frequency sensing.

Figure 10 shows a flow diagram of a method of operating the aerosol-generating device 120 of Figure 3, in accordance with an embodiment of the disclosure. It will be appreciated that this method is also applicable to other embodiments in accordance with the disclosure.

In a first step, 301 , the control electronics 180 of the aerosol-generating device 120 supply power to the dielectric heater to generate an alternating electric field in the article chamber 140, and measure a parameter of the electric response of the electrically resonant oscillation system to the alternating electric field. The parameter may be a load-dependent parameter of the electrical response, or may be associated with a load-dependent parameter. Where the measured parameter is associated with the load-dependent parameter, the control electronics determine the load-dependent parameter from the measured parameter.

In a second step, 302, the control electronics 180 determine a difference between the measured or determined load-dependent parameter and a reference, 303, stored in a memory of the control electronics. In this embodiment, the reference 303 is a pre-stored reference value, or mapping function, determined in a calibration procedure following assembly of the device. It will be appreciated that in some embodiments the reference 303 may be a value or mapping function determined by the device when no aerosol-generating article is received in the article chamber 140, and stored in the memory of the control electronics.

The control electronics 180 subsequently control the aerosol-generating device 120 based on the difference between the measured or determined load-dependent parameter and the reference. In this embodiment, the control electronics 180 control the aerosol-generating device 120 in two ways.

In a third step, 304, the control electronics 180 control the aerosol-generating device 120 by controlling the power supplied to the dielectric heater for heating the aerosol-generating article 105 received in the article chamber 140. Where the measured or determined load-dependent parameter is not recognised by the control electronics 180 (i.e. does not match a stored reference), the control electronics 180 prevent heating by preventing the supply of power to the dielectric heater for heating the aerosol-generating article 105 received in the article chamber 140. Similarly, where the measured or determined load-dependent parameter indicates that no aerosol-generating article 105 is received in the article chamber 140, the control electronics 180 prevent heating by preventing the supply of power to the dielectric heater for heating aerosol-generating article 105 received in the article chamber 140. Where the measured or determined load-dependent parameter matches a stored reference 303, such that the control electronics 180 are able to identify the aerosol-generating article 105 received in the article chamber 140, the control electronics 180 supply a predetermined power to the dielectric heater to heat the aerosol-generating article 105 to a predetermined temperature. The control electronics 180 store multiple references 303 such that multiple different aerosol-generating articles 105 may be recognised by the control electronics 180. Each stored reference 303 is associated in the memory of the control electronics 180 with a predetermined power, such that the power supplied to the dielectric heater is varied depending on the load-dependent parameter measured or determined by the control electronics 180. This enables the aerosol-generating device 120 to heat different aerosol-generating articles 105 to different temperatures.

In a fourth step, 305, the control electronics 180 control the aerosol-generating device 120 by notifying a user of the aerosol-generating device 120 of the identity of the aerosol-generating article 105 received in the article chamber 140. The control electronics 180 notify a user of the identity of the aerosolgenerating article 105 by displaying article identifying information on the user interface 182. Where the control electronics 180 determine that no aerosol-generating article 105 is received in the article chamber, the control electronics 180 notify a user that no article is received in the article chamber 140 by displaying an empty notification on the user interface 182.

It will be appreciated that in other embodiments the control electronics 180 may be configured to notify a user in alternative ways, such as via an audible notification, or a haptic notification, or by another visual notification, such as by controlling one or more LEDs.

It will be appreciated that in other embodiments, the control electronics 180 may be configured to control the aerosol-generating device in other ways based on the difference between the measured or determined load-dependent parameter and the reference. For example, the control electronics 180 may be configured to perform only one of the third step 304 and the fourth step 305.

Figures 11a, 11b, and 11c show different load-dependent parameters of the electric response of an electrically resonant oscillation system of an aerosol-generating device, according to embodiments of the disclosure. Each of Figures 11a, 11 b, and 11c show frequency responses of the electrically resonant oscillation system of an aerosol-generating device (i.e. the dependence of the signal strength on the frequency of the applied electric field) in different configurations.

Figure 11a shows the frequency response of an electrically resonant oscillation system when an aerosol-generating article is received in the article chamber and when an aerosol-generating article is not received in the article chamber. As shown in Figure 11a, the frequency response of the electrically resonant oscillation system when an aerosol-generating article is received in the article chamber is different to the frequency response of the electrically resonant oscillation system when an aerosolgenerating article is received in the article chamber. The frequency response of the electrically resonant oscillation system when an aerosol-generating article is received in the article chamber is shifted, such that the resonant frequency, co_r, (i.e. the peak of the response) when an aerosol-generating article is received in the article chamber occurs at a different frequency to the resonant frequency, coo, when an aerosol-generating article is not received in the article chamber. This frequency shift can be measured and used to determine when an aerosol-generating article is received in the article chamber. The magnitude of the frequency shift can also vary depending on the electrical properties of the aerosolgenerating article received in the article chamber. As such, the magnitude of the frequency shift can also be used to determine the type of aerosol-generating article received in the article chamber.

Figure 11 b shows a frequency response of an electrically resonant oscillation system when an aerosol-generating article is received in the article chamber. The frequency response has a bandwidth, Aco. The bandwidth, Aco, of the frequency response can also be indicative of the type of aerosolgenerating article received in the article chamber. As such, the bandwidth of the frequency response may be used to determine the type of aerosol-generating article received in the article chamber.

Figure 11c shows three different frequency responses of an electrically resonant oscillation system, when a first aerosol-generating article is received in the article chamber, when a second aerosolgenerating article is received in the article chamber, and when no aerosol-generating article is received in the article chamber. As shown in Figure 11c, each of the frequency responses is different. For each frequency response, the frequency shift and the bandwidth is unique. Accordingly, a combination of the frequency shift and the bandwidth of the frequency response may be used to determine whether an aerosol-generating article is received in the article chamber, and the type of aerosol-generating article received in the article chamber. Using more than one load-dependent property of the frequency response of the electrically resonant oscillation system may provide a more accurate determination of whether an aerosol-generating article is received in the article chamber, and the type of aerosol-generating article received in the article chamber, compared to using a single load-dependent parameter.

In some embodiments, the control electronics are configured to measure load-dependent parameters by varying the frequency of the alternating electric field generated in the article chamber. Accordingly, the control electronics are configured to control the aerosol-generating device by controlling the supply power to the dielectric heater to generate an alternating electric field in the article chamber with a varying frequency, the frequency varying in a sweep over a predetermined range of frequencies. The control electronics monitor the electric response of the oscillation system across the range of varying frequencies, and generate a frequency plot, which enables load-dependent parameters, such as the resonant frequency, to be identified, and used to identify the type of aerosol-generating article that is received in the article chamber.

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

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

Claims

1 . An aerosol-generating device for dielectrically heating an aerosol-generating article comprising an aerosol-forming substrate, the aerosol-generating device comprising: an article chamber configured to removably receive the aerosol-generating article; a dielectric heater configured to generate an alternating electric field in the article chamber for dielectrically heating the aerosol-generating article when the aerosol-generating article is received in the article chamber; and control electronics configured to control a supply of power to the dielectric heater for dielectrically heating the aerosol-generating article, wherein the article chamber, the aerosol-generating article received in the article chamber, and at least a portion of the dielectric heater form an electrically resonant oscillation system; and wherein the control electronics are further configured to: measure or determine a load-dependent parameter of an electric response of the electrically resonant oscillation system to the alternating electric field generated in the article chamber; and control the aerosol-generating device based on the load-dependent parameter of the electric response of the electrically resonant oscillation system, wherein the dielectric heater includes a resonant cavity or a transmission line that is coupled to a wave source via a coupler.

2. An aerosol-generating device according to claim 1 , wherein the load-dependent parameter of the electric response of the electrically resonant oscillation system includes at least one of a resonant frequency, a frequency shift, an impedance shift, a quality factor, a bandwidth, a phase shift, and a gain of the electrically resonant oscillation system.

3. An aerosol-generating device according to claim 1 or claim 2, wherein the control electronics are further configured to identify the aerosol-generating article based on the load-dependent parameter of the electric response of the electrically resonant oscillation system, and optionally wherein the control electronics are configured to control the aerosol-generating device by preventing the generation of aerosol by the dielectric heater or by preventing or turning off the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article to generate an aerosol when the control electronics are unable to identify the aerosol-generating article.

4. An aerosol-generating device according to any one of claims 1 to 3, wherein the control electronics are configured to control the aerosol-generating device by controlling the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article, and optionally by selectively supplying one of: a first power to the dielectric heater for dielectrically heating the aerosol-generating article received in the article chamber; and a second power to the dielectric heater for dielectrically heating the aerosol-generating article received in the article chamber, the second power being different to the first power; and wherein the control electronics are configured to selectively supply one of the first power and the second power to the dielectric heater based on the load-dependent parameter of the electric response of the electrically resonant oscillation system.

5. An aerosol-generating device according to any one of claims 1 to 4, wherein the control electronics are configured to control the aerosol-generating device by selectively supplying power to the dielectric heater for dielectrically heating the aerosol-generating article to a plurality of temperature profiles; wherein at least one of the plurality of temperature profiles varies with time; and wherein the selection of the temperature profile is based on the load-dependent parameter of the electric response of the electrically resonant oscillation system.

6. An aerosol-generating device according to any one of claims 1 to 5, wherein: the at least a portion of the dielectric heater and the article chamber form an unloaded oscillation system when the aerosol-forming substrate is not received in the article chamber; and the control electronics are further configured to: measure or determine the load-dependent parameter of the electric response of the unloaded oscillation system; determine the difference between the load-dependent parameter of the electric response of the electrically resonant oscillation system and the load-dependent parameter of the electric response of the unloaded oscillation system; and control the supply of power to the dielectric heater for dielectrically heating the aerosolgenerating article received in the article chamber based on the difference between the loaddependent parameter of the electric response of the electrically resonant oscillation system and the load-dependent parameter of the electric response of the unloaded oscillation system; and optionally wherein the control electronics are further configured to determine whether the aerosol-forming substrate is received in the article chamber based on the difference between the load-dependent parameter of the electric response of the electrically resonant oscillation system and the load-dependent parameter of the electric response of the unloaded oscillation system; and optionally wherein the control electronics are configured to control the aerosolgenerating device by preventing the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article if it is determined that the aerosol-forming substrate is not received in the article chamber.

7. An aerosol-generating device according to any one of claims 1 to 5, wherein: the load-dependent parameter is the resonant frequency, at least a portion of the dielectric heater and the article chamber form an unloaded oscillation system when the aerosol-forming substrate is not received in the article chamber; and the control electronics are further configured to: measure or determine the resonant frequency of the unloaded oscillation system; determine the frequency shift between the resonant frequency of the electrically resonant oscillation system and the resonant frequency of the unloaded oscillation system; and control the aerosol-generating device by controlling the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article based on the frequency shift; and optionally wherein the control electronics are further configured to determine whether the aerosol-forming substrate is received in the article chamber based on the frequency shift; and optionally wherein the control electronics are configured to control the aerosolgenerating device by preventing the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article if it is determined that the aerosol-forming substrate is not received in the article chamber.

8. An aerosol-generating device according to any one of claims 1 to 5, wherein the control electronics are further configured to: determine the difference between the load-dependent parameter of the electric response of the electrically resonant oscillation system and a reference value ; and control the aerosol-generating device by controlling the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article based on the difference between the loaddependent parameter of the electric response of the loaded oscillation system and the reference value; and optionally wherein the control electronics are further configured to determine whether the aerosol-forming substrate is received in the article chamber based on the difference between the loaddependent parameter of the electric response of the electrically resonant oscillation system and the reference value; and optionally wherein the control electronics are configured to control the aerosol-generating device by preventing the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article if it is determined that the aerosol-forming substrate is not received in the article chamber.

9. An aerosol-generating device according to any one of claims 1 to 8, wherein: the load-dependent parameter is the resonant frequency; and the control electronics are further configured to: determine the frequency shift between the resonant frequency of the electrically resonant oscillation system and a reference value; and control the aerosol-generating device by controlling the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article based on the frequency shift; and optionally wherein the control electronics are further configured to determine whether the aerosol-forming substrate is received in the article chamber based on the frequency shift; and optionally wherein the control electronics are configured to control the aerosolgenerating device by preventing the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article if it is determined that the aerosol-forming substrate is not received in the article chamber.

10. An aerosol-generating device according to any one of claims 1 to 9, wherein: the measuring or determining the load-dependent parameter of the electric response of the electrically resonant oscillation system comprises measuring or determining at least two load-dependent parameters of the electric response of the electrically resonant oscillation system; and the controlling the aerosol-generating device comprises controlling the supply of power to the dielectric heater for dielectrically heating the aerosol-generating article based on the at least two loaddependent system parameters of the electrically resonant oscillation system.

11. An aerosol-generating device according to any one of claims 1 to 10, wherein the dielectric heater comprises a first electrode and a second electrode, the second electrode being spaced apart from the first electrode; wherein the first electrode and the second electrode are arranged such that when the aerosol-forming substrate is received in the article chamber, at least a portion of the aerosolforming substrate is arranged between the first electrode and the second electrode; and wherein a load capacitor is formed by the first electrode, the second electrode and the aerosol-forming substrate received in the article chamber between the first electrode and the second electrode.

12. An aerosol-generating device according to any one of claims 1 to 10, wherein the dielectric heater comprises a resonant cavity that at least partially includes the article chamber, optionally wherein the resonant cavity is arranged in the article chamber, optionally wherein the article chamber is the resonant cavity, and optionally wherein the resonant cavity is configured as a quarter wavelength resonator.

13. An aerosol-generating device according to claim 12, wherein the dielectric heater further comprises a radiation source or a wave source and at least one of a waveguide, an antenna, and a transmission line, wherein the resonant cavity is coupled to the radiation source or the wave source via the at least one of a waveguide, an antenna, and a transmission line, and optionally wherein the resonant cavity is coupled to the radiation source or the wave source using at least one of a capacitive coupling, an inductive coupling, a direct electric coupling or a window coupling.

14. An aerosol-generating device according to any one of claims 1 to 13, wherein the control electronics are configured to control the frequency of the electric field generated in the article chamber by the dielectric heater.

15. An aerosol-generating system comprising: an aerosol-generating device according to any one of claims 1 to 14; and an aerosol-generating article comprising an aerosol-forming substrate.

16. An aerosol-generating system according to example 15, wherein the aerosol-generating article comprises a load-capacitor comprising the aerosol-forming substrate, the load capacitor comprising a first electrode and a second electrode, the second electrode being spaced apart from the first electrode, and at least a portion of the aerosol-forming substrate arranged between the first electrode and the second electrode.

17. An aerosol-generating system according to claim 15 or claim 16, wherein the aerosol-generating article comprises a dielectric marker.