Temperature sensing means for dielectric heating

Abstract

There is provided an aerosol-generating device (200) for dielectrically heating an aerosol-forming substrate (301) to generate an aerosol therefrom. The aerosol-generating device (200) comprising: a heating chamber (211) configured to receive the aerosol-forming substrate (301), a dielectric heating element (205, 222) configured to heat the aerosol-forming substrate (301) by subjecting it to an alternating electric field inside the heating chamber (211), a temperature sensor (213, 214, 228, 229) comprising an electrically conductive material with temperature-dependent resistivity connected to provide an electrical parameter as a value indicative of a temperature of the aerosol-forming substrate (301), and a controller (203) configured to apply an electrical pulse to the electrically conductive material to measure the electrical parameter. At least a portion of the electrically conductive material is arranged within the heating chamber (211).

Description

[0001] Temperature Sensing Means for Dielectric Heating

[0002] 1. Technical field

[0003] 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 an aerosol-generating system having the aerosol-generating device, a method of operating the aerosol-generating device and a use of a resistance temperature detector for such an aerosol-generating device.

[0004] 2. Background

[0005] Known electrically operated aerosol-generating systems typically heat an aerosol-forming substrate by one or more of: conduction of heat from a heating element to an aerosol-forming substrate, radiation of heat from a heating element to an aerosol-forming substrate or drawing heated air through an aerosol-forming substrate. Most commonly, heating is achieved by passing an electrical current through an electrically resistive heating element, giving rise to Joule heating of the heating element. Inductive heating systems have also been proposed, in which 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.

[0006] A problem with these heating mechanisms is that they may give rise to non-uniform heating of the aerosol-forming substrate. The portion of the aerosol-forming substrate closest to the heating element is heated more quickly or to a higher temperature than portions of the aerosol-forming substrate more remote from the heating element.

[0007] Systems that dielectrically heat an aerosol-forming substrate have been proposed, using a resonant cavity that is fed with a microwave from a wave source via a microwave coupler, which advantageously provides uniform heating of the aerosol-forming substrate. For example, see WO 2021 / 013477 and WO 2022 / 128290, these references are herewith incorporated by reference in their entirety.

[0008] Dielectric heating, which is also often referred to as microwave heating, electric heating, or radio-frequency heating, generally refers to heating that arises as a result of dipole rotation of a to-be-heated material or substance 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 substances 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 substance in the alternating electric field.

[0009] For effective aerosol generation, precise heating and temperature control are crucial. Traditionally, feedback control systems are employed, where the heating output is adjusted based on the difference between a setpoint value and a measured temperature. A dynamic response from a temperature sensor, which monitors the temperature of the aerosol-forming material, is essential for proper feedback control. Known temperature sensors include infrared sensors and optical fiber thermometers. However, these solutions tend to be relatively complex and expensive.

[0010] It would be preferable to provide an aerosol-generating device that dielectrically heats an aerosol-forming substrate in an efficient and accurate manner, while still being realizable in a compact or handheld design.

[0011] 3. Summary

[0012] According to a first aspect, there is provided an aerosol-generating device for dielectrically heating an aerosol-forming substrate to generate an aerosol therefrom, the aerosol-generating device comprising: a heating chamber configured to receive the aerosol-forming substrate, a dielectric heating element configured to heat the aerosol-forming substrate by subjecting it to an alternating electric field inside the heating chamber, and a temperature sensor comprising an electrically conductive material with temperature-dependent resistivity connected to provide an electrical parameter as a value indicative of a temperature of the aerosol-forming substrate. At least a portion of the electrically conductive material is arranged within the heating chamber.

[0013] Arranging the electrically conductive material of the temperature sensor within the heating chamber, e.g. so that the electrically conductive material or a part thereof is arranged within an interior of the heating chamber or forms an interior surface of the heating chamber, and thus next to the aerosol-forming substrate allows for accurate temperature measurements, that can allow to deduct the actual temperature of the substrate that is being heated by dielectric heating, with a less expensive, small and compact in size, and less complex measurement system compared to known measurement systems in the field of dielectric heating, for example optical or heat radiation based measurements. It has been found that, in contrast to a widely spread prejudice, the electromagnetic field present in the heating chamber during aerosolization does not interfere with the electrically conductive material, e.g. by inducing eddy currents, in a manner that resistance temperature detectors (RTDs) would lead to incorrect or at least unusable temperature measurements and therefore cannot be used.

[0014] The electrically conductive material may have a positive or negative temperature coefficient a, with an absolute value of a in a range from 0.001 to 0.01 1 / K, preferably from 0.002 to 0.008 1 / K, in particular from 0.003 to 0.006 1 / K.

[0015] The electrically conductive material may be selected from a group of metals, preferably including one or more of: platinum, nickel, and / or copper.

[0016] The electrical parameter may be a temperature-caused resistance change of the electrically conductive material. The electrical parameter may be a voltage drop across the electrically conductive material that is indicative of a temperature-caused resistance change of the electrically conductive material.

[0017] The electrically conductive material may have a lengthwise extension to extend within the heating chamber, such as in the form of a track, wire, or plate.

[0018] By having an electrically conductive material that acts as a temperature sensor to extended lengthwise into or along a longitudinal direction of the heating chamber allows for better coverage and more precise temperature measurement over a larger area within the chamber.

[0019] The electrical parameter may be an electrical impedance of a circuit or a part of a circuit, which can provide insights into characteristics such as resistance, capacitance, and inductance. In such configuration, the aerosol-generating device may include an impedance measurement device. The sensitivity of the impedance measurement device may depend on their ability to detect small changes in impedance, which may be often influenced by the frequency of the input signal, as impedance can vary with frequency. Achieving high sensitivity in impedance measurements may involve using high-quality, stable measurement circuits, and accurate frequency control.

[0020] A. Electrically Conductive Track

[0021] The temperature sensor may comprise an electrically insulating base substrate and an electrically conductive track patterned on the electrically insulating base substrate. At least a part of the electrically conductive track may be arranged to be in the heating chamber. Said part of the electrically conductive track may be made of the electrically conductive material.

[0022] The electrically conductive track may be formed as a PT100 or PT1000 element.

[0023] The electrically conductive track may form a loop inside the heating chamber.

[0024] The electrically conductive track may be designed in a pattern with one or more windings. Specifically, the pattern may define a loop with multiple windings. The windings may be arranged in a planar configuration.

[0025] The electrically conductive track may be etched or printed on the electrically insulating base substrate.

[0026] The electrically conductive track may have a thickness of less than 200 micrometers, preferably less than 100 micrometers, and more preferably less than 70 micrometers.

[0027] The electrically conductive track may have a thickness from 10 to 200 micrometers, preferably from 20 to 100 micrometers, and more preferably from 30 to 70 micrometers.

[0028] The electrically conductive track may have a width or diameter of less than 2 millimeters, preferably less than 1 millimeter.

[0029] The electrically conductive track may have a width or diameter from 0.1 to 2 millimeters, preferably from 0.2 to 2 millimeters, more preferably from 0.5 to 1.5 millimeters. By having a track with minimal mass may ensure to reduce the time delay in thermal response due to its relatively small thermal capacity. Preferably, the track may be made of a thin layer and is not very wide, to avoid too much thermal capacity that could add a time delay to the temperature measurements.

[0030] The electrically conductive track and the dielectric heating element, preferably electrodes of a load capacitor, may be arranged on the electrically insulating base substrate, preferably in one or more of the following configurations: on a same layer of the electrically insulating base substrate, and / or on different layers to form a multilayer structure.

[0031] By having the track and the dielectric heating element arranged on the same substrate, conventional PCB techniques may be utilized to manufacture a dielectric heater together with the temperature sensor (RTD track). For example, a heater module can include the dielectric heating element and the electrically conductive track, the heater module may be made from a material that has a low-dielectric constant (low relative permittivity), high-temperature resistivity (about 400°C), electrically non-conductive properties, and / or is food-grade microwave-safe, for example a plastic, ceramic, or glass. The heater module can be structurally shaped to form a space or cavity that can be used as a heating chamber. The dielectric heating element, for example electrode pairs forming the load capacitor, and / or the electrically conductive track can be placed on an interior surface of the material that forms the heater module.

[0032] In a variant, the material used for the heater module could be a relatively soft, bendable material, for example a thin layer (e.g. less than 200pm) of low-dielectric (e.g. low relative permittivity) high-temperature resistant polymer, for example PEEK (Polyether Ether Ketone) or PEI (Polyetherimide) to thereby allow to bendably, foldably, or rollably form a heating chamber. This may also allow to form the heater module, or at least a part thereof, by printed circuit board (PCB) manufacturing techniques.

[0033] In another variant, the heater module may be made of a glass material such as quartz glass, or a rigid layer or structure of a plastic, or other material such as low-dielectric microwave ceramics that can allow to form a heating chamber and at the same time can be used as a substrate for the dielectric heating element and the electrically conductive track.

[0034] The temperature sensor may include a first electrically conductive track portion and a second electrically conductive track portion. At least a part of the first electrically conductive track portion may not be arranged to be in the heating chamber. At least a part of the second electrically conductive track portion may be arranged to be in the heating chamber. A material of the second track portion may be made of the electrically conductive material.

[0035] A material of the first track portion may be same or different to the material of the second track portion. The electrically insulating base substrate may be a flexible substrate film, preferably a flexible printed circuit board (FPCB). The electrically insulating base substrate may comprise or may be made of an adhesive layer.

[0036] The electrically insulating base substrate may adhere to the heating chamber via the adhesive layer.

[0037] The electrically insulating base substrate may comprise a polymer, preferably a thermoplastic polymer, for example PEEK (Polyether Ether Ketone) and / or PEI (Polyetherimide).

[0038] The electrically insulating base substrate may have a low relative permittivity, preferably in a range from 1.5 to 10, preferably from 2 to 6, in particular from 2 to 4.B. Attachment of temperature sensor

[0039] The heating chamber may comprise one or more peripheral walls. The one or more peripheral walls may define an interior of the heating chamber. The electrically conductive material may be provided on the one or more peripheral walls or between the peripheral walls.

[0040] At least one of the one or more peripheral walls may comprise an opening, such as a slot. The electrically conductive material of the temperature sensor may protrude through the opening into the heating chamber.

[0041] The one or more peripheral walls and the temperature sensor may together define a smooth inner surface of the heating chamber.

[0042] The temperature sensor may be firmly attached on the one or more peripheral walls or between the peripheral walls.

[0043] The one or more peripheral walls may comprise one or more sidewalls arranged along a longitudinal direction of the heating chamber. The electrically conductive material may be provided on the one or more sidewalls or between the sidewalls.

[0044] A longitudinal position of the electrically conductive material of the temperatures sensor may correspond to a longitudinal position of at least a portion of the aerosol-forming substrate in an assembled state.

[0045] C. Plurality of Temperature Sensors and Arrangement

[0046] The aerosol-generating device may comprise a plurality of temperature sensors. Each may comprise an electrically conductive material disposed at least partially within the heating chamber. A second temperature sensor may be arranged symmetrically to a first temperature sensor with respect to a central axis of the heating chamber, so as to face each other.

[0047] Each of the plurality of temperature sensors may comprise an electrically conductive material disposed at least partially within the heating chamber and distributed along a longitudinal direction of the heating chamber. A third temperature sensor may be arranged in a longitudinal distance to the first temperature sensor, to enable a temperature measurement of different aero- sol-forming substrate portions of the aerosol-forming substrate. The third temperature sensor may be located to measure a temperature of a second aero- sol-forming substrate portion. The first temperature sensor may be located to measure a temperature of a first aerosol-forming substrate portion of the aerosol-forming substrate.

[0048] D. Heating chamber i) Shape of Heating chamber:

[0049] The heating chamber may be configured as a blind cavity having an open end and a closed end, the heating chamber configured to receive, via the open end, at least part of the length of an aerosol-forming article comprising the aerosol-forming substrate.

[0050] The heating chamber may comprise one or more sidewalls arranged between the open end and the closed end, along the longitudinal axis of the heating chamber.

[0051] The heating chamber may have an elongated shape.

[0052] The heating chamber may have a cylindrical shape.

[0053] The heating chamber may have a rectangular cuboid shape.

[0054] The heating chamber may have an oval, round, or rectangular cross-section along the longitudinal direction.

[0055] The heating chamber may have an inner diameter substantially matching an outer diameter of at least a portion of the aerosol-forming article. ii) Retaining mechanism

[0056] The heating chamber may include a retaining mechanism to hold the aerosol-forming substrate in the heating chamber. The retaining mechanism may include retaining elements in form of one or more protrusions extending from a peripheral wall of the heating chamber in a direction towards the center of the heating chamber.

[0057] E. Dielectric heating element i) Load capacitor

[0058] The dielectric heating element may comprise a load capacitor, the load capacitor comprises first and second electrodes arranged to receive the aerosol-forming substrate therebetween.

[0059] The first and second electrodes may define the heating chamber.

[0060] The at least one of the first and second electrodes may define a sidewall of the heating chamber. ii) Resonant cavity

[0061] The dielectric heating element may comprise a resonant cavity.

[0062] The aerosol-generating device may comprise a dielectric filling arranged within an interior of the resonant cavity. The dielectric filling may define the heating chamber for receiving the aerosol-forming substrate.

[0063] The dielectric filling may define a sidewall of the heating chamber. The aerosol-generating device may comprise an antenna coupled to the resonant cavity. The antenna may be configured to convey radio-frequency (RF) electromagnetic radiation to the resonant cavity.

[0064] F. Power Electronics, Power Source, and Oscillation Circuit

[0065] The aerosol-generating device may comprise power electronics including: a power source, and an oscillation circuit powered by the power source. The dielectric heating element may be fed by the oscillation circuit.

[0066] The oscillation circuit may comprise a switching unit.

[0067] The oscillation circuit may comprise the dielectric heating element.

[0068] The oscillation circuit may comprise a resonant feedback circuit including the dielectric heating element, so that the oscillation circuit may be self-resonating.

[0069] The oscillation circuit may resonate at a radio frequency (RF).

[0070] G. Controller

[0071] The aerosol-generating device may comprise a controller.

[0072] The controller may be connected to receive a signal from the temperature sensor and connected to control operation of the dielectric heating element in dependence of the signal from the temperature sensor. i) Temperature Control

[0073] The controller may be configured to control a temperature of the aerosol-forming substrate by changing a parameter or configuration of the aerosol-generating device based on the signal from the temperature sensor, preferably by using feedback control, such as P, PI, PD, or PID control.

[0074] PID (Proportional, Integral, Derivative) control may adjust the microwave power by calculating an error value as the difference between a set point and the measured temperature. The control then adjusts the process input at a rate proportional to this error, integrated over time, and the derivative of the error. The simplicity and effectiveness of PID controllers in maintaining process stability may make them highly desirable for processes where the relationship between input power and temperature change is linear or near-linear, as supposed in the aerosol-generating device. Another variant is to control the temperature of the aerosol-forming substrate may be on / off control of the e-field power, for example through a bang-bang control.

[0075] Alternatively, reinforcement learning may be used to control a temperature of the aerosolforming substrate. Reinforcement learning may use algorithms to learn the best actions to take, in real-time, based on past performance and given feedback. In this context, the algorithm may dynamically adjust microwave power based on the temperature sensor data to optimize process outcomes. Reinforcement learning can potentially handle complex, non-linear systems more effectively than PID controls, adapting to changes in the system’s behavior that might be unforeseen in traditional models.

[0076] Changing a parameter or configuration of the aerosol-generating device may include controlling power supply to the dielectric heating element.

[0077] The controller may be configured to control the temperature of the aerosol-forming substrate by first applying a preheating phase to reach a temperature above an aerosolization temperature of the aerosol forming material. Thereafter the controller may perform a puff heating phase where the temperature may be controlled to be maintained constant.

[0078] The controller may be operable to control the temperature of the heating element during a puff heating phase in a temperature range in between 150 and 400 °C, preferably in between 180 and 300 °C, in particular in between 220 and 240 °C. ii) Shifted Heating Control

[0079] The controller may be configured to control operation of the dielectric heating element such that the center of heat generation shifts along a longitudinal direction, preferably along an insertion direction of the aerosol-forming article in the heating chamber, thereby heating a second aerosol-forming substrate portion before a first aerosol-forming substrate portion. Additionally, the controller may be configured to control a temperature of the second aerosol-forming substrate portion based on a signal from a third temperature sensor located in proximity of the second aerosol-forming substrate portion, and a temperature of the first aerosol-forming substrate portion based on a signal from a first temperature sensor located in proximity of the first aerosol-forming substrate portion.

[0080] The first and second aerosol-forming substrate portions may be two portions of the same or different aerosol-forming substrate.

[0081] The operation to shift heating may comprise changing an operation frequency of the RF electromagnetic field.

[0082] The dielectric heating element may be a resonant cavity configuration with one or more gaps, and wherein the resonant cavity configuration is operated to shift heating.

[0083] The dielectric heating element may comprise multiple distinct dielectric heating elements. The multiple distinct dielectric heating elements may be distributed along a longitudinal direction of the heating chamber which are connected to be operated independently to shift heating. iii) Obtain Temperature

[0084] The controller may be configured to apply an electrical pulse or signal to the electrically conductive material to measure the electrical parameter. The electrical pulse may be a current pulse and / or a voltage pulse. The measuring may include applying a current pulse on the electrically conductive material and detecting a voltage drop indicative of a resistance change of the electrically conductive material, or applying a voltage pulse on the electrically conductive material and detecting a resulting current or current change.

[0085] The electrical pulse may be a transient change in the amplitude of an electrical signal from a baseline value to a higher or lower value, followed by a return to the baseline value. The electrical pulse may be any of a rectangular pulse, cosine squared (raised cosine) pulse, dirac pulse, sine pulse, gaussian pulse or can have other suitable pulse shapes allowing to measure the electrical parameter.

[0086] The controller may be configured to apply periodic electrical pulses to the electrically conductive material in order to measure the electrical parameter. The periodic electrical pulses may comprise a continuously repeating sequence of identical electrical pulses.

[0087] The controller may apply the electrical pulse and / or the periodic electrical pulses to the electrically conductive material within a measurement cycle, in which the dielectric heating power is reduced or the dielectric heating is turned-off, and / or during a heating cycle, for example during temperature control and / or shifted heating control, in which the aerosol-forming substrate is heated to generate aerosol.

[0088] Specifically, during the measurement cycle, the dielectric heating may be turned off, for example by interrupting the power supply to the oscillation circuit, disabling the oscillation circuit by other means, for example by reducing or setting the oscillation frequency to zero, or by reducing the power delivered to the dielectric heating element. Preventing the temperature sensor from being exposed to electric fields, or reducing the strength of the electric field, may improve the accuracy of the temperature measurement, since subjecting the temperature sensor to a relatively strong electric field can result in erroneous temperature readings.

[0089] Preferably, the controller may be configured to obtain a temperature of the aerosol-forming substrate, by sending a current pulse to the electrically conductive material, obtain a voltage or voltage drop across the electrically conductive material, and determine an actual temperature of the substrate based on a predefined relationship associated with the voltage or voltage drop.

[0090] The controller may be configured to determine a centre temperature of the aerosol-forming substrate by adding to the measured temperature a predefined bias value that is indicative of a temperature difference between temperatures on the periphery of the aerosol-forming substrate and centre caused by thermal conduction losses.

[0091] According to a second aspect, there is provided an aerosol-generating system for delivering aerosol to a user, the system comprising: an aerosol-generating device according to the first aspect, and an aerosol-forming article comprising an aerosol-forming substrate.

[0092] The aerosol-forming substrate may be solid or may comprise a solid material.

[0093] The aerosol-forming substrate may comprise tobacco or a tobacco containing material. The aerosol-forming article may comprise a wrapper enclosing the aerosol-forming substrate to define a rod, the rod having a mouth end and a distal end. The wrapper may be paperbased.

[0094] The aerosol-forming article may comprise a first aerosol-forming substrate portion and a second aerosol-forming substrate portion. A distance between the second aerosol-forming substrate portion and the mouth end may be smaller than a distance between the first aerosol-forming substrate portion and the mouth end.

[0095] The first and second substrate portions may include the same or different materials and / or material compositions.

[0096] H. Arrangement of Temperature Sensor in Relation to Substrate / Article

[0097] The electrically conductive material of the temperature sensor may be arranged to be in a distance to the aerosol-forming substrate in an assembled state, in which at least part of the length of the aerosol-forming article comprising the aerosol-forming substrate is arranged in the heating chamber, so that in use, aerosol can be generated.

[0098] Said distance may be in a range from 0.001 to 10 millimetres, preferably from 0.005 to 1 millimetres, in particular from 0.01 to 0.4 millimetres.

[0099] Said distance may be equal to or greater than a thickness of a wrapper of the aerosolforming article, the wrapper encloses the aerosol-forming substrate. The wrapper may have a thickness from 0.01 to 0.4 millimetres.

[0100] In other words, in some examples, the aerosol-forming article and the electrically conductive material are in direct contact. In an alternative example, there may be only an air gap arranged between the aerosol-forming article and the electrically conductive material. With respect to the aerosol-forming substrate, in some examples, there may be only a wrapper material of the aero- sol-forming article arranged between the aerosol-forming substrate and the electrically conductive material. In an alternative example, there may be only the wrapper material of the aerosol-forming article and an air gap arranged between the aerosol-forming article and the electrically conductive material.

[0101] The electrically conductive material of the temperature sensor may be arranged to be in contact with an outer surface portion of the aerosol-forming article that houses the aerosol-forming substrate in an assembled state, in which at least part of the length of the aerosol-forming article comprising the aerosol-forming substrate is arranged in the heating chamber, so that in use, aerosol can be generated.

[0102] According to a third aspect, there is provided a method of dielectrically heating an aerosolforming substrate by means of an aerosol-generating device according to the first aspect, the method comprising the following steps: dielectrically heating the aerosol-forming substrate by subjecting it to an alternating electric field; measuring an electrically parameter indicative of a temperature of the aerosol-forming substrate; and controlling the temperature of the aerosol-forming substrate by changing a parameter or configuration of the aerosol-generating device based on the measured value.

[0103] The measuring may include applying an electrical pulse to the electrically conductive material to measure the electrical parameter.

[0104] Specifically, the measuring may include applying a current pulse on the electrically conductive material and detecting a voltage drop indicative of a resistance change of the electrically conductive material.

[0105] According to a fourth aspect, there is provided a method of manufacturing an aerosol-generating device according to the first aspect, wherein the electrically conductive material and / or electrically conductive track, and the dielectric heating element, preferably electrodes of a load capacitor, may be manufactured on a same substrate using printed circuit board (PCB) manufacturing techniques, preferably such that the electrically conductive material and the dielectric heating element are arranged on a same layer of the substrate, and / or on different layers to form a multilayer structure.

[0106] The substrate may comprise a polymer, preferably a thermoplastic polymer, for example PEEK (Polyether Ether Ketone) and / or PEI (Polyetherimide).

[0107] By leveraging PCB manufacturing techniques, the integration of the dielectric heating element and temperature sensor (RTD track) into the same substrate may be streamlined, enhancing efficiency and precision in the manufacturing process.

[0108] According to a fifth aspect, there is provided a use of a resistance temperature detector (RTD) within a heating chamber of an aerosol-generating device, preferably according to the aerosol-generating device of the first aspect, for dielectrically heating an aerosol-forming substrate received in the heating chamber.

[0109] I. Thin-film thermistor

[0110] The temperature sensor may be a thermistor, specifically a thin-film thermistor. Thin-film thermistor may differ from conventional RTDs, which include relatively tick metal wires, in that a thin electrically conductive track or electrically conductive foil is applied, for example etched or printed, on a flexible thin sheet forming the electrically insulating base substrate. The electrically conductive material used for the foil or track may comprise or consist of a metal and / or a semiconductor, such as certain ceramics or polymers, whose electrical resistance changes with temperature. Thin thin-film thermistor may offer a fast response time and minimal thermal mass, which allow temperatures to be measured without significantly affecting the surrounding components and self-overheating.

[0111] The temperature sensitivity of the thermistor may be defined by its temperature coefficient, which can either be negative or positive. Factors affecting thermistor sensitivity may be: material properties of the electrically conductive material, the geometrical design of the thermistor, and the operating temperature range.

[0112] In contrast to commonly used thermocouples, which consist of two different metal wires joined at one end and open at the other end, allowing measurement of a voltage that indicates a temperature difference due to the thermoelectric effect known as the Seebeck effect, and which can measure a wide temperature range from about 200°C to 1750°C, the thermistors may be suitable for measuring a narrower temperature range, typically from about -55°C to 250°C. This range may be sufficient for monitoring a maximum temperature at the peripheral wall of the heating chamber, where temperatures of up to approximately 230°C may occur. Furthermore, thermistors may be relatively sensitive and may detect temperature changes as small as 0.01 °C.

[0113] The thin-film thermistor may be flexible. The flexible thin-film thermistor may be smoothly affixed to an inner surface of the heating chamber, for example, to an inner surface of a sidewall of the heating chamber. The main extension direction of the thermistor may be parallel to the longitudinal axis of the heating chamber.

[0114] The electrically insulating base substrate may comprise kapton, polyimide, PEEK, PEI, silicone rubber or any other material producing low losses in the RF environment and also flexible such that it can be wrapped on a surface, for example on an inner side of the heating chamber.

[0115] J. Manufacturing of the temperature sensor through etching and printing

[0116] Etched temperature sensor may be manufactured by etching an electrically conductive track or electrically conductive foil onto the electrically insulating base substrate. The etching process may allow for precise control over the sensor's dimensions and hence its resistance, providing accurate temperature measurements.

[0117] Printed temperature sensors may be created using printing technigues, where electrically conductive inks may be applied to the electrically insulating base substrate. The manufacturing method may include screen printing, inkjet printing, or other printing technologies The process may be faster and less costly than etching, suitable for mass production and thus for handheld devices, like aerosol-generating devices.

[0118] 4. Terms and Definitions

[0119] As used herein, the term “aerosol-generating device” refers to a device that interacts with an aerosol-forming substrate of an aerosol-forming article to generate an aerosol. Preferably, the aerosol-generating device is a smoking device that interacts with an aerosol-forming substrate of an aerosol-forming article to generate an aerosol that is directly inhalable into user’s lungs through a user's mouth. The aerosol-generating device may be a holder for a smoking article.

[0120] Preferably, the aerosol-forming article is a smoking article that generates an aerosol that is directly inhalable into the user’s lungs through the user's mouth. More preferably, the aerosolforming article is a smoking article that generates a nicotine-containing aerosol that is directly inhalable into the user’s lungs through the user's mouth.

[0121] As used herein, the term “aerosol-generating system” refers to a combination of an aerosolgenerating device and an aerosol-forming article, in which the aerosol-forming article and the aerosol-generating device cooperate to generate and deliver an aerosol to a user of the system.

[0122] As used herein, the term “aerosol-forming substrate” refers to a substrate consisting of or comprising an aerosol-forming material that is capable of releasing volatile compounds upon heating to generate an aerosol.

[0123] As used herein, the term “assembled state” refers to an operation state, in which at least part of the length of an aerosol-forming article comprising the aerosol-forming substrate is arranged in the heating chamber, so that in use, an aerosol can be generated.

[0124] As used herein, a “longitudinal axis” may refer to an axis along which the heating chamber has its greatest length. The longitudinal axis may be or may be parallel to a “central axis” of the heating chamber.

[0125] As used herein, the term “radio frequency (RF)” means a frequency between 300 MHz and 300 GHz, preferably between 300 MHz and 100 GHz, and includes microwaves. Preferably, the RF electromagnetic field has a frequency between 500 MHz and 50 GHz, more preferably between 900 MHz and 30 GHz. The RF electromagnetic field may have a frequency between 900 MHz and 5 GHz. In one embodiment the RF electromagnetic field has a frequency of about 2.4 GHz or 4.8 GHz.

[0126] As used herein, the term “RTD (Resistance Temperature Detector)” refers to a temperature sensor that measures a temperature based on a change in electrical resistance of an electrically conductive material, such as a metal (typically platinum) as the temperature varies. The resistance may increases substantially linearly with temperature. The RTD may be constructed to include wire-wound RTDs or thin-film RTDs. In a thin-film RTD, an electrically conductive track (e.g. metal track) or an electrically conductive layer (e.g., metal layer) is disposed on a base substrate. In a wire-wound RTD, an electrically conductive track (e.g. metal track) is wound around a core.

[0127] As used herein, the term “temperature-dependent resistivity” (i.e., temperature coefficient of resistance a) of the electrically conductive material describes the relative change of resistivity of the electrically conductive material that is associated with a given change in temperature. The relationship may be given by the formula: R(T) = RO (1 + aT) where R is resistance, RO is the resistance at a given temperature (usually 0 °C), T is the temperature, and a is the temperature coefficient of the electrically conductive material.

[0128] As used herein, the term “predefined relationship associated with the voltage drop” to obtain the actual temperature of the aerosol-forming substrate based on a predefined relationship associated with a measured voltage drop may be given by the formula: where:

[0129] T is the actual temperature,

[0130] R(T) is the resistance of the electrically conductive material at the actual temperature, i.e., the value of the voltage drop AURdivided by the value of the current pulse Ipulse,

[0131] RO is the resistance at a reference temperature TO (usually 0 °C), a is the temperature coefficient of a material of the electrically conductive track, and AT is the change in temperature from the reference temperature.

[0132] As used herein, the term “sensitivity” refers to a ratio of the change in the output signal of a measurement system to the change in the input quantity being measured.

[0133] List of non-limiting examples

[0134] The invention is defined in the claims. However, below there is provided a non-exhaustive list of non-limiting examples. Any one or more of the features of these examples may be combined with any one or more features of another example, embodiment, or aspect described herein.

[0135] Example Ex1. An aerosol-generating device for dielectrically heating an aerosol-forming substrate to generate an aerosol therefrom, the aerosol-generating device comprising: a heating chamber configured to receive the aerosol-forming substrate, a dielectric heating element configured to heat the aerosol-forming substrate by subjecting it to an alternating electric field inside the heating chamber, a temperature sensor comprising an electrically conductive material with temperature-dependent resistivity connected to provide an electrical parameter as a value indicative of a temperature of the aerosol-forming substrate, wherein at least a portion of the electrically conductive material is arranged within the heating chamber.

[0136] Example Ex1.1. The aerosol-generating device according to the preceding example, wherein the electrically conductive material has a positive or negative temperature coefficient a, with an absolute value of a in a range from 0.001 to 0.01 1 / K, preferably from 0.002 to 0.008 1 / K, in particular from 0.003 to 0.006 1 / K.

[0137] Example Ex1 .2. The aerosol-generating device according to any of the preceding examples, wherein the electrically conductive material is selected from a group of metals, preferably including one or more of: platinum, nickel, and / or copper.

[0138] Example Ex1 .3. The aerosol-generating device according to any of the preceding examples, wherein the electrical parameter is a temperature-caused resistance change of the electrically conductive material.

[0139] Example Ex1.3.1. The aerosol-generating device according to the preceding example, wherein the electrical parameter is a voltage drop across the electrically conductive material that is indicative of a temperature-caused resistance change of the electrically conductive material .

[0140] Example Ex1 .4. The aerosol-generating device according to any of the preceding examples, wherein the electrically conductive material that acts as a temperature sensor has a lengthwise extension to extend within the heating chamber, such as in the form of a track, wire, or plate.

[0141] A. Electrically Conductive Track

[0142] Example Ex2. The aerosol-generating device according to any of the preceding examples, wherein the temperature sensor comprises an electrically insulating base substrate and an electrically conductive track patterned on the electrically insulating base substrate, wherein at least a part of the electrically conductive track is arranged to be in the heating chamber, wherein said part of the electrically conductive track is made of the electrically conductive material.

[0143] Example Ex2.1. The aerosol-generating device according to the preceding example, wherein the electrically conductive track is formed as a PT100 or PT1000 element.

[0144] Example Ex2.2. The aerosol-generating device according to any of Ex2 to Ex2.1 , wherein the electrically conductive track is designed in a pattern with one or more windings.

[0145] Example Ex2.3. The aerosol-generating device according to any of Ex2 to Ex2.2, wherein the electrically conductive track has a thickness of less than 200 micrometers, preferably less than 100 micrometers, and more preferably less than 70 micrometers.

[0146] Example Ex2.4. The aerosol-generating device according to any of Ex2 to Ex2.3, wherein the electrically conductive track has a thickness from 10 to 200 micrometers, preferably from 20 to 100 micrometers, and more preferably from 30 to 70 micrometers.

[0147] Example Ex2.5. The aerosol-generating device according to any of Ex2 to Ex2.4, wherein the electrically conductive track has a width or diameter of less than 2 millimeters, preferably less than 1 millimeter.

[0148] Example Ex2.6. The aerosol-generating device according to any of Ex2 to Ex2.5, wherein the electrically conductive track has a width or diameter from 0.1 to 2 millimeters, preferably from 0.2 to 2 millimeters, more preferably from 0.5 to 1.5 millimeters. Example Ex2.7. The aerosol-generating device according to any of Ex2 to Ex2.6, wherein the electrically conductive track and the dielectric heating element, preferably electrodes of a load capacitor, are arranged on the electrically insulating base substrate, preferably in one or more of the following configurations: on a same layer of the electrically insulating base substrate, and / or on different layers to form a multilayer structure.

[0149] Example Ex2.8. The aerosol-generating device according to any of Ex2 to Ex2.7, wherein the temperature sensor includes a first electrically conductive track portion and a second electrically conductive track portion, wherein at least a part of the first electrically conductive track portion is not arranged to be in the heating chamber, wherein at least a part of the second electrically conductive track portion is arranged to be in the heating chamber, wherein a material of the second track portion is made of the electrically conductive material.

[0150] Example Ex2.8.1. The aerosol-generating device according the preceding example, wherein a material of the first track portion is same or different to the material of the second track portion.

[0151] Example Ex2.9. The aerosol-generating device according to any of Ex2 to Ex2.8.1 , wherein the electrically insulating base substrate is a flexible substrate film, preferably a flexible printed circuit board (FPCB).

[0152] Example Ex2.9.1. The aerosol-generating device according to the preceding example, wherein the electrically insulating base substrate comprises or is made of an adhesive layer.

[0153] Example Ex2.9.1.1. The aerosol-generating device according to the preceding example, wherein the electrically insulating base substrate is adhered to the heating chamber via the adhesive layer.

[0154] Example Ex2.10. The aerosol-generating device according to any of Ex.2 to Ex2.9.1.1 , wherein the electrically insulating base substrate has a low relative permittivity, preferably in a range from 1.5 to 10, preferably from 2 to 6, in particular from 2 to 4.

[0155] Example Ex2.11. The aerosol-generating device according to any of Ex2 to Ex2.10, wherein the electrically insulating base substrate comprises a polymer, preferably a thermoplastic polymer, for example PEEK (Polyether Ether Ketone) and / or PEI (Polyetherimide).

[0156] B. Attachment of temperature sensor

[0157] Example Ex3. The aerosol-generating device according to any of the preceding examples, wherein the heating chamber comprises one or more peripheral walls, the one or more peripheral walls define an interior of the heating chamber, wherein the electrically conductive material is provided on the one or more peripheral walls or between the peripheral walls.

[0158] Example Ex3.1. The aerosol-generating device according to the preceding example, wherein at least one of the one or more peripheral walls comprise an opening, such as a slot, wherein the electrically conductive material of the temperature sensor protrudes through the opening into the heating chamber. Example Ex3.2. The aerosol-generating device according to any of Ex3 to Ex.3.1 , wherein the one or more peripheral walls and the temperature sensor together define a smooth inner surface of the heating chamber.

[0159] Example Ex3.3. The aerosol-generating device according to any of Ex3 to Ex.3.2, wherein the temperature sensor is firmly attached on the one or more peripheral walls or between the peripheral walls.

[0160] Example Ex3.4. The aerosol-generating device according to any of Ex3 to Ex.3.3, wherein the one or more peripheral walls comprise one or more sidewalls arranged along a longitudinal direction of the heating chamber, wherein the electrically conductive material is provided on the one or more sidewalls or between the sidewalls.

[0161] Example Ex3.4.1. The aerosol-generating device according to any of Ex3 to Ex3.4, wherein a longitudinal position of the electrically conductive material of the temperatures sensor corresponds to a longitudinal position of at least a portion of the aerosol-forming substrate in an assembled state.

[0162] C. Plurality of Temperature Sensors and Arrangement

[0163] Example Ex4. The aerosol-generating device according to any of the preceding examples, wherein the aerosol-generating device comprises a plurality of temperature sensors, each comprising an electrically conductive material disposed at least partially within the heating chamber, wherein a second temperature sensor is arranged symmetrically to a first temperature sensor with respect to a central axis of the heating chamber, so as to face each other.

[0164] Example Ex5. The aerosol-generating device according to any of the preceding examples, wherein the aerosol-generating device comprises a plurality of temperature sensors, each comprising an electrically conductive material disposed at least partially within the heating chamber and distributed along a longitudinal direction of the heating chamber, wherein a third temperature sensor is arranged in a longitudinal distance to the first temperature sensor, to enable temperature measurement of different aerosol-forming substrate portions of the aerosol-forming substrate.

[0165] Example Ex5.1. The aerosol-generating device according to the preceding example, wherein the third temperature sensor is located to measure a temperature of a second aerosolforming substrate portion and the first temperature sensor is located to measure a temperature of a first aerosol-forming substrate portion of the aerosol-forming substrate.

[0166] D. Heating chamber i) Shape of Heating chamber:

[0167] Example Ex6. The aerosol-generating device according to any of the preceding examples, wherein the heating chamber is configured as a blind cavity having an open end and a closed end, the heating chamber configured to receive, via the open end, at least part of the length of an aerosol-forming article comprising the aerosol-forming substrate. Example Ex7. The aerosol-generating device according to any of the preceding examples, wherein the heating chamber comprises one or more sidewalls arranged between the open end and the closed end, along the longitudinal axis of the heating chamber.

[0168] Example Ex8. The aerosol-generating device according to any of the preceding examples, wherein the heating chamber has an elongated shape.

[0169] Example Ex9. The aerosol-generating device according to any of the preceding examples, wherein the heating chamber has a cylindrical shape.

[0170] Example Ex10. The aerosol-generating device according to any of the preceding examples, wherein the heating chamber has a rectangular cuboid shape.

[0171] Example Ex11 . The aerosol-generating device according to any of the preceding examples, wherein the heating chamber has an oval, round, or rectangular cross-section along the longitudinal direction.

[0172] Example Ex12. The aerosol-generating device according to any of the preceding examples, wherein the heating chamber has an inner diameter substantially matching an outer diameter of at least a portion of the aerosol-forming article. ii) Retaining mechanism

[0173] Example Ex13. The aerosol-generating device according to any of the preceding examples, wherein the heating chamber includes a retaining mechanism to hold the aerosol-forming substrate in the heating chamber.

[0174] Example Ex13.1. The aerosol-generating device according to the preceding example, wherein the retaining mechanism includes retaining elements in form of one or more protrusions extending from a peripheral wall of the heating chamber in a direction towards the center of the heating chamber.

[0175] E. Dielectric heating element i) Load capacitor

[0176] Example Ex14. The aerosol-generating device according to any of the preceding examples, wherein the dielectric heating element comprises a load capacitor, the load capacitor comprises first and second electrodes arranged to receive the aerosol-forming substrate therebetween.

[0177] Example Ex14.1. The aerosol-generating device according to the preceding example, wherein the first and second electrodes define the heating chamber

[0178] Example Ex14.2. The aerosol-generating device according to any of Ex14 to Ex14.1 , wherein at least one of the first and second electrodes define a sidewall of the heating chamber. ii) Resonant cavity

[0179] Example Ex15. The aerosol-generating device according to any of Ex1 to Ex13.1 , wherein the dielectric heating element comprises a resonant cavity. Example Ex15.1. The aerosol-generating device according to the preceding example, further comprising a dielectric filling arranged within an interior of the resonant cavity, the dielectric filling defining a heating chamber for receiving the aerosol-forming substrate.

[0180] Example Ex15.2. The aerosol-generating device according to any of Ex15 to Ex15.1 , wherein the dielectric filling defines a sidewall of the heating chamber.

[0181] Example Ex15.3. The aerosol-generating device according to any of Ex15 to Ex15.2, further comprising an antenna coupled to the resonant cavity, wherein the antenna is configured to convey radio-frequency (RF) electromagnetic radiation to the resonant cavity.

[0182] F. Power Electronics, Power Source, and Oscillation Circuit

[0183] Example Ex16. The aerosol-generating device according to any of the preceding examples, further comprising power electronics including: a power source, and an oscillation circuit powered by the power source, wherein the dielectric heating element being fed by the oscillation circuit.

[0184] Example Ex16.1. The aerosol-generating device according to the preceding example, wherein the oscillation circuit comprises a switching unit.

[0185] Example Ex16.2. The aerosol-generating device according to any of Ex16 to Ex16.1 , wherein the oscillation circuit comprises the dielectric heating element.

[0186] Example Ex16.3. The aerosol-generating device according to any of Ex16 to Ex16.2, wherein the oscillation circuit comprises a resonant feedback circuit including the dielectric heating element, so that the oscillation circuit may be self-resonating.

[0187] Example Ex16.4. The aerosol-generating device according to any of Ex16 to Ex16.3, wherein the oscillation circuit resonates at a radio frequency (RF).

[0188] G. Controller

[0189] Example Ex17. The aerosol-generating device according to any of the preceding examples, further comprising a controller, preferably connected to receive a signal from the temperature sensor and connected to control operation of the dielectric heating element in dependence of the signal from the temperature sensor. i) Temperature Control

[0190] Example Ex17.1. The aerosol-generating device according to the preceding example, wherein the controller is configured to control a temperature of the aerosol-forming substrate by changing a parameter or configuration of the aerosol-generating device based on the signal from the temperature sensor, preferably by using feedback control.

[0191] Example Ex17.1.1. The aerosol-generating device according to the preceding example, wherein changing a parameter or configuration of the aerosol-generating device includes controlling power supply to the dielectric heating element.

[0192] Example Ex17.2. The aerosol-generating device according to any of Ex17.1 to Ex17.1.1 , wherein the controller is configured to control the temperature of the aerosol-forming substrate by first applying a preheating phase to reach a temperature above an aerosolization temperature of an aerosol forming material, and thereafter performing a puff heating phase where the temperature is to be maintained constant.

[0193] Example Ex17.2.1. The aerosol-generating device according to the preceding example, wherein the controller is operable to control temperature of the heating element during a puff heating phase in a temperature range in between 150 and 400 °C, preferably in between 180 and 300 °C, in particular in between 220 and 240 °C. ii) Shifted Heating Control

[0194] Example Ex17.3. The aerosol-generating device according to any of Ex17 to Ex17.2.1 , wherein the controller is configured to control operation of the dielectric heating element such that the center of heat generation shifts along a longitudinal direction, preferably along an insertion direction of the aerosol-forming article in the heating chamber, thereby heating a second aerosolforming substrate portion before a first aerosol-forming substrate portion and wherein the controller is configured to control a temperature of the second aerosol-forming substrate portion based on a signal from a third temperature sensor located in proximity of the second aerosol-forming substrate portion, and a temperature of the first aerosol-forming substrate portion based on a signal from a first temperature sensor located in proximity of the first aerosol-forming substrate portion.

[0195] Example Ex17.3.1. The aerosol-generating device according to the preceding example, wherein the first and second aerosol-forming substrate portions are two portions of the same or different aerosol-forming substrate.

[0196] Example Ex17.3.2. The aerosol-generating device according to any of Ex17.3 to Ex17.3.1 , wherein the operation to shift heating comprises changing an operation frequency of the RF electromagnetic field.

[0197] Example Ex17.3.3. The aerosol-generating device according to any of Ex17.3 to Ex17.3.2, wherein the dielectric heating element is a resonant cavity configuration with one or more gaps, and wherein the resonant cavity configuration is operated to shift heating.

[0198] Example Ex17.3.4. The aerosol-generating device according to any of Ex17.3 to Ex17.3.3, wherein the dielectric heating element comprises multiple distinct dielectric heating elements distributed along a longitudinal direction of the heating chamber which are connected to be operated independently to shift heating. iii) Obtain Temperature

[0199] Example Ex17.4. The aerosol-generating device according to any of Ex17 to Ex17.3.4, wherein the controller is configured to apply an electrical pulse to the electrically conductive material to measure the electrical parameter. Example Ex17.5. The aerosol-generating device according to the preceding example wherein the electrical pulse is a current pulse and / or a voltage pulse.

[0200] Example Ex17.6. The aerosol-generating device according to any of Ex17 to Ex17.5, wherein the controller is configured to obtain a temperature of the aerosol-forming substrate, by sending a current pulse to the electrically conductive material, obtain a voltage drop across the electrically conductive material, and determine an actual temperature of the substrate based on a predefined relationship associated with the voltage drop.

[0201] Example Ex17.6.1. The aerosol-generating device according to the preceding example, wherein the controller is configured to determine a centre temperature of the aerosol-forming substrate by adding to the measured temperature a predefined bias value that is indicative of a temperature difference between temperatures on the periphery of the aerosol-forming substrate and centre caused by thermal conduction losses.

[0202] SYSTEM

[0203] Example Ex18. An aerosol-generating system for delivering an aerosol to a user, the system comprising: an aerosol-generating device according to any of the preceding examples, and an aerosol-forming article comprising an aerosol-forming substrate.

[0204] Example Ex18.1. The aerosol-generating system according to the preceding example, wherein the aerosol-forming substrate comprises a solid material.

[0205] Example Ex18.2. The aerosol-generating system according to any of Ex18 to Ex18.1 , wherein the aerosol-forming substrate comprises tobacco or a tobacco containing material.

[0206] Example Ex18.3. The aerosol-generating system according to any of Ex18 to Ex18.2, wherein the aerosol-forming article comprises a wrapper enclosing the aerosol-forming substrate to define a rod, the rod having a mouth end and a distal end.

[0207] Example Ex18.3.1. The aerosol-generating system according to the preceding example, wherein the wrapper is paper-based.

[0208] Example Ex18.4. The aerosol-generating system according to any of Ex18 to Ex18.3.1 , wherein the aerosol-forming article comprises a first aerosol-forming substrate portion and a second aerosol-forming substrate portion, wherein a distance between the second aerosol-forming substrate portion and the mouth end is smaller than a distance between the first aerosol-forming substrate portion and the mouth end.

[0209] Example Ex18.4.1. The aerosol-generating system according to the preceding example, wherein the first and second substrate portions include the same or different materials and / or material compositions.

[0210] H. Arrangement of Temperature Sensor in Relation to Substrate / Article Example Ex18.5. The aerosol-generating system according to any of Ex18 to Ex18.4.1 , wherein the electrically conductive material of the temperature sensor is arranged to be in a distance to the aerosol-forming substrate in an assembled state, in which at least part of the length of the aerosol-forming article comprising the aerosol-forming substrate is arranged in the heating chamber, so that in use, an aerosol can be generated.

[0211] Example Ex18.5.1. The aerosol-generating system according to the preceding example, wherein the distance is equal to or greater than a thickness of a wrapper of the aerosolforming article, the wrapper encloses the aerosol-forming substrate.

[0212] Example Ex18.5.2. The aerosol-generating system according to any of Ex18 to Ex18.5.1 , wherein the distance is in a range from 0.001 to 10 millimetres, preferably from 0.005 to 1 millimetres, in particular from 0.01 to 0.4 millimetres.

[0213] Example Ex18.6. The aerosol-generating system according to any of Ex18 to Ex18.5.2, wherein the electrically conductive material of the temperature sensor is arranged to be in contact with an outer surface portion of the aerosol-forming article that houses the aerosol-forming substrate in an assembled state, in which at least part of the length of the aerosol-forming article comprising the aerosol-forming substrate is arranged in the heating chamber, so that in use, an aerosol can be generated.

[0214] OPERATION METHOD

[0215] Example Ex19. A method of dielectrically heating an aerosol-forming substrate by means of an aerosol-generating device according to any one of the preceding examples directed to the aerosol-generating device, the method comprising the following steps: dielectrically heating the aerosol-forming substrate by subjecting it to an alternating electric field; measuring an electrically parameter indicative of a temperature of the aerosol-forming substrate; and controlling the temperature of the aerosol-forming substrate by changing a parameter or configuration of the aerosolgenerating device based on the measured value.

[0216] Example Ex19.1. The method according to the preceding example, wherein the measuring includes applying an electrical pulse to the electrically conductive material to measure the electrical parameter.

[0217] Example Ex19.2. The method according to the example Ex19 or Ex19.1 , wherein measuring incudes: applying a current pulse on the electrically conductive material and detecting a voltage drop indicative of a resistance change of the electrically conductive material.

[0218] MANUFACTURING METHOD

[0219] Example Ex20. A method of manufacturing an aerosol-generating device according to any one of the preceding examples directed to the aerosol-generating device, wherein the electrically conductive material and the dielectric heating element are manufactured on a same substrate using printed circuit board (PCB) manufacturing techniques, preferably such that the electrically conductive material and the dielectric heating element are arranged on a same layer of the substrate, and / or on different layers to form a multilayer structure.

[0220] Example Ex20.1. The method according to the preceding example, wherein the substrate comprises a polymer, preferably a thermoplastic polymer, for example PEEK (Polyether Ether Ketone) and / or PEI (Polyetherimide).

[0221] USE

[0222] Example Ex21. Use of a resistance temperature detector (RTD) within a heating chamber of an aerosol-generating device, preferably according to any one of the preceding examples directed to the aerosol-generating device, for dielectrically heating an aerosol-forming substrate received in the heating chamber.

[0223] 5. Brief Description of Drawings

[0224] The invention will be further described, by way of example only, with reference to the accompanying drawings in which:

[0225] Figure 1 is a schematic illustration of an aerosol-generating system having an aerosol-generating device with a resonant cavity for dielectric heating according to an embodiment of the invention.

[0226] Figure 2 is a schematic illustration of a control circuit to control a temperature of an aerosolforming substrate, which may be used in the aerosol-generating system of Figure 1.

[0227] Figure 3 is a schematic illustration of a portion of an aerosol-generating system having an aerosol-generating device with a load capacitor for dielectric heating according to an embodiment of the invention.

[0228] Figure 4 is a schematic illustration of a portion of an aerosol-generating system having an aerosol-generating device according to an embodiment of the invention, which may be used in the aerosol-generating system of Figure 1.

[0229] Figure 5 is a diagram showing experimental temperature measurements obtained during an experiment using a temperature sensor having an electrically conductive track arranged within a heating chamber where an RF electric field is applied for heating, compared to temperature measurements using an optical fiber thermometer.

[0230] 6. Detailed Description

[0231] The above and other features and advantages of example embodiments will become more apparent by describing in detail, example embodiments with reference to the attached drawings. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. The example embodiments may, however, be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein. Accordingly, while the example embodiments are capable of various modifications and alternative forms, embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the example embodiments to the particular forms disclosed, but to the contrary, the example embodiments are to cover all modifications, equivalents, and alternatives falling within the scope of example embodiments. Like numbers refer to like elements throughout the description of the Figures.

[0232] Although the temperature sensors are carried out as thin-film RTDs with an electrically conductive track in the below examples and Figures, the present disclosure is not limited thereto. In alternative examples, other suitable RTDs with a different configuration may be used; for example, a wire-wound RTD or a thin-film RTD with an electrically conductive layer. In yet other variants, the temperature sensor may be embodied as a thin-film thermistor. The thin-film thermistor may differ from a thin-film RTD in that the resistive element is configured as a foil rather than a patterned track, and / or in that the resistive element may comprise or consist of semiconductors, such as certain ceramics or polymers, whose electrical resistance changes with temperature.

[0233] Figure 1 is a schematic illustration of an aerosol-generating system 100 using radiofrequency (RF) electromagnetic radiation, sometimes referred to as dielectric heating. The aerosolgenerating system 100 has an aerosol-generating device 200 and an aerosol-forming article 300 comprising an aerosol-forming substrate 301 . In a variant, the aerosol-forming substrate 301 may be heated in its centre to a temperature up to 400°C, preferably in a range from 250°C to 400°C.

[0234] The aerosol-generating device 200 has an elongate housing 201. The elongate housing 201 houses power electronics including a power source 202 and an oscillation circuit (not shown), such as an RF electromagnetic field generator, that is powered by the power source 202. The elongate housing 201 further houses control electronics, such as a controller 203, and a resonant cavity 205. The electromagnetic field generator may include a solid state transistor. The power source 202 is coupled to the controller 203 and the RF electromagnetic field generator to provide power thereto. In the illustrated example, the power source 202 is a rechargeable battery, such as a lithium-ion battery. However, in alternative examples, other suitable power sources may be used; for example, an alternative form of battery or a capacitor. An outer shell of the elongate housing 201 that is visible to a user in normal use is made of a metal, preferably aluminum.

[0235] The resonant cavity 205 is defined by a peripheral wall 206, which is generally cylindrical in form. For the non-limiting illustrated example, the peripheral wall 206 may be formed of copper. The resonant cavity 205 is arranged so that the length of the resonant cavity 205 lies generally along a longitudinal axis 207 of the elongate housing 201. The resonant cavity 205 defines a blind cavity, with an opening 208 at one end of the cavity and an opposite end 209 of the cavity being closed. A dielectric filling 210 formed of ceramic material, such as alumina, is provided within the resonant cavity 205. The dielectric filling 210 is provided as an annular sleeve circumscribing a heating chamber 211 within the resonant cavity 205.

[0236] The heating chamber 211 is formed as a blind cavity having an open end and a peripheral end wall 218, such as protrusions extending from the dielectric filling 210, and configured to stop the aerosol-forming article 300 when inserted into the heating chamber 211 via the open end, thereby holding the aerosol-forming article 300 in the assembled state shown in Figure 1. One or more sidewalls 217 extend between the open end and the peripheral end wall 218. In the present example, there is one generally cylindrical sidewall 217 existing, which is formed by the dielectric filling 210.

[0237] The dielectric filling 210 has a relative permittivity er greater than 1. The provision of the dielectric filling 210 having a relative permittivity er of greater than one within the interior of the resonant cavity 205 has been found to have a beneficial effect of reducing the resonant frequency of the resonant cavity 205 compared to the same resonant cavity lacking any filling (i.e. relative to a resonant cavity which is entirely hollow and contains only air). In general terms, for a resonant cavity 205 of a given size, the greater the relative permittivity er of the filling, the smaller the resonant frequency of the resonant cavity 205. So, where the resonant cavity 205 has a size consistent with the aerosol-generating device 200 being handheld and portable, the filling which is used can be selected to tune the resonant frequency of the resonant cavity 205 to correspond with an operation frequency for the RF electromagnetic radiation generated by the RF electromagnetic field generator. An antenna 212 extends from the RF electromagnetic field generator into the interior of the resonant cavity 205.

[0238] Airflow inlets (not shown) may be provided in the elongate housing 201 to allow air to be drawn into the aerosol-generating device 200, through the heating chamber 211 and out through a mouthpiece of the aerosol-forming article 300.

[0239] The aerosol-generating device 200 comprises a first temperature sensor 213 and a second temperature sensor 214 to measure a temperature of the aerosol-forming substrate 301 .

[0240] Each of the temperature sensors 213, 214 comprises an electrically conductive track 215 made of an electrically conductive material patterned on an electrically insulating base substrate

[0241] 216. The electrically insulating base substrate 216 is adhered to an inner surface of the sidewall

[0242] 217, so that the respective electrically conductive track 215 is in contact with an outer surface portion (e.g. paper wrapper 302) of the aerosol-forming article 300 that houses the aerosol-forming substrate 301. The electrically insulating base substrate 216 may be a flexible substrate film, in particular a flexible printed circuit board (FPCB). In alternative examples, the electrically conductive material and / or the electrically conductive track 215 may be integrated in the dielectric filling 211 , thereby avoiding the need for the electrically insulating base substrate 216. The electrically conductive track 215 of a respective temperature sensor 213, 214 is arranged on a front-surface side 219 of the electrically insulating base substrate 216, so as to be in contact with the aerosol-forming article 300 in use. In other embodiments, the electrically conductive track 215 comprises a first electrically conductive track portion arranged on the front-surface side 219 and a second electrically conductive track portion (not shown) provided on a back-surface side 220 of the electrically insulating base substrate 216. In yet other embodiments, the temperature sensors 213, 214 may be at least partially integrated within the dielectric filling 210, so that the second electrically conductive track portion may be arranged outside the heating chamber 211 (i.e. , within the dielectric filling 210) and the first electrically conductive track portion may be provided on the front-surface side 219 of the electrically insulating base substrate 216, so as to generate a smooth surface with the sidewall 217 of the heating chamber 211.

[0243] As shown in Figure 1 , the electrically conductive track 215 may be formed in a loop with multiple windings on the electrically insulating base substrate 216. However, other forms are possible, as long as a predefined resistance of the electrically conductive track 215 can be established by the form and electrically conductive material used, for example, 1000 or 100 Ohm at 0°C.

[0244] The electrically conductive material has an appropriate temperature coefficient a of resistance characteristic, since this will mean that a relatively small change in temperature results in a large change in resistance associated with a given change in temperature. The relationship may be given by the formula:

[0245] R(T) = R0 (1 + aT) where R(T) is resistance, R0 is the resistance at a given temperature (usually 0 °C), T is the actual temperature, and a is the temperature coefficient of the electrically conductive material. Suitable materials having a large value of a include platinum, nickel, and copper.

[0246] In the shown example, the second temperature sensor 214 is arranged symmetrically to the first temperature sensor 213 with respect to a central axis of the heating chamber 211 , so that the first temperature sensor 213 and the second temperature sensor 214 face each other. Nonetheless, it will be understood that only one temperature sensor could also be used. The provision of two temperature sensors may improve the accuracy of the temperature measurement.

[0247] The first temperature sensor 213 and the second temperature sensor 214 are connected to the controller 203 via sensor wires 221.

[0248] Referring to Figure 2, in use, the controller 203 sends current pulses to the first temperature sensor 213 (and optionally to the second temperature sensor 214), and receives as output a voltage response associated to the temperature at the periphery of the aerosol-forming substrate 301. The controller 203 then obtains the actual temperature of the aerosol-forming substrate 301 based on a predefined relationship associated with a measured voltage response, for example, based on the following formula: where:

[0249] - T is the actual temperature,

[0250] - R(T) is the resistance of the electrically conductive material at the actual temperature, i.e. , the value of the voltage response (voltage drop) AURdivided by the value of the current pulse IpUise ■

[0251] - RO is the resistance at a reference temperature TO (usually 0 °C),

[0252] - a is the temperature coefficient of a material of the electrically conductive track, and

[0253] - AT is the change in temperature from the reference temperature.

[0254] In some non-limiting examples, the controller 203 determines a mean temperature value over responses from the multiple temperature sensors 213, 214. In some non-limiting examples, the controller 203 determines a centre temperature of the aerosol-forming substrate 301 by adding to the measured temperature a predefined bias value that is indicative of a temperature difference between temperatures on the periphery of the aerosol-forming substrate 301 and centre caused by thermal conduction losses. Based on the measured temperature, the controller 203 drives the power electronics and thus the dielectric heating element to control and / or regulate the temperature of the aerosol-forming substrate 301. The temperature control operation may include standard feedback loop control with an error value coming from the difference between the measured temperature and a setpoint. Current pulses may be sent periodically to the temperature sensors 213, 214 during the temperature control. The frequency of the measurement may be optimized to best control the heating without significant energy depletion.

[0255] Figure 3 shows a partially schematic view of an embodiment of an aerosol-generating system, where instead of a resonant cavity-based type dielectric heating element as shown in Figure 1 , a load capacitor 222 with a first electrode 223 and second electrode 224 are used as a dielectric heating element. The electrodes 223, 224 are plate-shaped and are arranged in parallel so as to form a heating chamber 211 to receive the aerosol-forming substrate 301 accommodated in the aerosol-forming article 300 . However, in alternative examples, other suitable electrode shapes may be used; for example, as disclosed in European patent application No. 23201984.4, which is herewith incorporated by reference in its entirety. An oscillation circuit 225 is connected to the electrodes 223, 224 to generate, in use, an RF electric field between them, thereby causing dielectric heating of the aerosol-forming substrate 301.

[0256] Similar to the embodiment shown in Figure 1 , a temperature sensor 226 with an electrically conductive track 227 made of an electrically conductive material is arranged within the heating chamber 211. In the present example, the electrically conductive track 227 forms a loop without additional windings. In other examples, the electrically conductive track 227 may have the form of as shown in Figure 1 . The temperature sensor 226 is arranged in the heating chamber 211 so that the electrically conductive track 227 is in close proximity or in contact with the aerosol-forming substrate 301. In a preferred example, the electrically conductive track 227 is in contact with an outer surface portion (e.g., a paper wrapper 302) of the aerosol-forming article 300 that houses the aerosol-forming substrate 301.

[0257] Figure 4 shows an arrangement of an aerosol-generating system 100 where, in addition to a first sensor couple defined by the first temperature sensor 213 and the second temperature sensor 214 shown in Figure 1 , a second sensor couple of a third temperature sensor 228 and a fourth temperature sensor 229 is provided and disposed in a longitudinal distance to the first sensor couple. The first sensor couple is positioned in correspondence of a first aerosol-forming substrate portion 303 (distal portion) of the aerosol-forming substrate 301. Similarly, the second sensor couple is positioned in correspondence of a second aerosol-forming substrate portion 304 (proximal portion) of the aerosol-forming substrate 301.

[0258] Such arrangement may be particularly useful for localized heating of local portions of the aerosol-forming substrate 301 and shifted heating.

[0259] In a non-limiting example, localized heating is realized by powering the dielectric heating element (here: resonant cavity 205) with different radio frequencies (so called RF mode), thereby enabling to choose in which region of the heating chamber 211 the electromagnetic field may have the highest intensity. In other examples, multiple distinct dielectric heating elements, such as load capacitors, may be arranged along the longitudinal axis of the heating chamber 211.

[0260] Shifted heating includes localized heating of the aerosol-forming substrate portion 301 in steps along the longitudinal axis 207. For example, as indicated by a rectangle in the upper part of Figure 4, a first RF mode is applied to heat the second aerosol-forming substrate portion 304 (proximal portion) of the aerosol-forming substrate 301 whose temperature is monitored by the second sensor couple of the third temperature sensor 228 and the fourth temperature sensor 229. Similarly, as indicated by a rectangle in the lower part of Figure 4, a second RF mode is applied to heat the first aerosol-forming substrate portion 303 (distal portion) of the aerosol-forming substrate 301 whose temperature is monitored by the first sensor couple of the first temperature sensor 213 and the second temperature sensor 214. Figure 5 is a diagram showing experimental temperature measurements obtained during an experiment using a temperature sensor having an electrically conducive track (solid line) arranged within a heating chamber where an RF electric field is applied to for heating, compared to temperature measurements using an optical fiber thermometer (dashed line).

[0261] In this non-limiting implementation, a cylindrical resonating cavity that was excited by a pin coupler that was powered by an RF signal source (ADF4350 synthesizer with VCO), a pre-amplifier (MAX2092 VGA), and a power amplifier (ZHL-2425-250X). Control was done by a microcontroller (STM32F411), and amplifier-integrated power meters measured forward and reflected power to keep track of the shift of resonance frequency during a heating cycle. The resonant cavity had an opening to insert an aerosol-generating article at the cavity’s center axis. Used was a cast leaf aerosol-forming article (stick). Other implementations would be the use of a load capacitor with two opposing electrode plates or other electrodes forming a heating volume between the capacitor plates, or a transmission line structure (for example within a resonant cavity) forming an area between two or more transmission lines.

[0262] The experiment is carried out as follows: Power is turned on at t=20 s; at t=70 s power is increased to overcompensate for the flattening of the temperature rise. Att=105 s power is turned off and at t= 130 s turned on again to showcase the dynamic response of the temperature measurement sensor. Fast dynamic response is important for the use of such temperature sensors to be used as a feedback to control the heating operation. At 175 sec power is turned off.

[0263] The solid measurement line is obtained by a temperature sensor having an electrically conducive track (solid line) with a negative temperature coefficient sensor (NTC) arranged in the heating chamber I resonant cavity.

[0264] The dashed measurement line is obtained by using an optical fiber thermometer during the same experiment. The optical fiber thermometer was placed inside the aerosol-forming substrate of the aerosol-generating article. Optical fiber temperature sensors provide relatively accurate results, but are substantially more expensive than an electrically conducive track temperatures sensor, and requires substantially more complex signal analysis for the measurement. In turn, it can be said that electrically conductive track temperatures sensors arranged in a heating chamber, although being exposed to high RF field therein, provide reliable and dynamic temperature measurements, while being less expensive and complex compared to known optical fiber thermometers.

Claims

CLAIMS1. An aerosol-generating device for dielectrically heating an aerosol-forming substrate to generate an aerosol therefrom, the aerosol-generating device comprising: a heating chamber configured to receive the aerosol-forming substrate, a dielectric heating element configured to heat the aerosol-forming substrate by subjecting it to an alternating electric field inside the heating chamber, and a temperature sensor comprising an electrically conductive material with temperature-dependent resistivity connected to provide an electrical parameter as a value indicative of a temperature of the aerosol-forming substrate, and a controller configured to apply an electrical pulse to the electrically conductive material to measure the electrical parameter, wherein at least a portion of the electrically conductive material is arranged within the heating chamber.

2. The aerosol-generating device according to the preceding claim, wherein the temperature sensor comprises an electrically insulating base substrate and an electrically conductive track patterned on the electrically insulating base substrate, wherein at least a part of the electrically conductive track is arranged to be in the heating chamber, wherein said part of the electrically conductive track is made of the electrically conductive material.

3. The aerosol-generating device according to the preceding claim, wherein the electrically insulating base substrate is a flexible substrate film, preferably a flexible printed circuit board (FPCB).

4. The aerosol-generating device according to any one of the preceding claims, wherein the heating chamber comprises one or more peripheral walls, the one or more peripheral walls define an interior of the heating chamber, wherein the electrically conductive material is provided on the one or more peripheral walls or between the peripheral walls.

5. The aerosol-generating device according to the preceding claim, wherein the one or more peripheral walls comprise one or more sidewalls arranged along a longitudinal direction of the heating chamber, wherein the electrically conductive material is provided on the one or more sidewalls or between the sidewalls.

6. The aerosol-generating device according to any one of the preceding claims, wherein the aerosol-generating device comprises a plurality of temperature sensors, each comprising an electrically conductive material disposed at least partially within the heating chamber, wherein a second temperature sensor is arranged symmetrically to a first temperature sensor with respect to a central axis of the heating chamber, so as to face each other.

7. The aerosol-generating device according to any one of the preceding claims, wherein the aerosol-generating device comprises a plurality of temperature sensors, each comprising an electrically conductive material disposed at least partially within the heating chamber and distributed along a longitudinal direction of the heating chamber, wherein a third temperature sensor is arranged in a longitudinal distance to a first temperature sensor, to enable temperature measurement of different aerosol-forming substrate portions of the aerosol-forming substrate.

8. The aerosol-generating device according to any one of the preceding claims, wherein the dielectric heating element comprises a load capacitor, the load capacitor comprises first and second electrodes arranged to receive the aerosol-forming substrate therebetween.

9. The aerosol-generating device according to any one of the preceding claims, wherein the controller is connected to receive a signal from the temperature sensor and is connected to control operation of the dielectric heating element in dependence of the signal from the temperature sensor.

10. The aerosol-generating device according to the preceding claim, wherein the controller is configured to control operation of the dielectric heating element such that the center of heat generation shifts along a longitudinal direction, preferably along an insertion direction of the aerosol-forming article in the heating chamber, thereby heating a second aerosol-forming substrate portion before a first aerosol-forming substrate portion and wherein the controller is configured to control a temperature of the second aerosol-forming substrate portion based on a signal from a third temperature sensor located in proximity of the second aerosol-forming substrate portion, and a temperature of the first aerosol-forming substrate portion based on a signal from a first temperature sensor located in proximity of the first aerosolforming substrate portion.

11. An aerosol-generating system for delivering an aerosol to a user, the system comprising: an aerosol-generating device according to any one of the preceding claims or claims 15 to 18, and an aerosol-forming article comprising an aerosol-forming substrate.

12. The aerosol-generating system according to the preceding claim, wherein the electrically conductive material of the temperature sensor is arranged to be in a distance to the aero- sol-forming substrate in an assembled state, in which at least part of the length of the aerosolforming article comprising the aerosol-forming substrate is arranged in the heating chamber, so that in use, aerosol can be generated.

13. The aerosol-generating system according to claim 11 or 12, wherein the electrically conductive material of the temperature sensor is arranged to be in contact with an outer surface portion of the aerosol-forming article that houses the aerosol-forming substrate in an assembled state, in which at least part of the length of the aerosol-forming article comprising the aerosolforming substrate is arranged in the heating chamber, so that in use, aerosol can be generated.

14. A method of dielectrically heating an aerosol-forming substrate by means of an aerosol-generating device according to any one of claims 1 to 10 or 15 to 18, the method comprising the following steps: dielectrically heating the aerosol-forming substrate by subjecting it to an alternating electric field; measuring an electrically parameter indicative of a temperature of the aerosol-forming substrate; and controlling the temperature of the aerosol-forming substrate by changing a parameter or configuration of the aerosol-generating device based on the measured value, wherein the measuring includes applying an electrical pulse to the electrically conductive material to measure the electrical parameter.

15. The aerosol-generating device according to any one of claims 1 to 10, wherein the electrical pulse may be a current pulse and / or a voltage pulse.

16. The aerosol-generating device according to any one of claims 1 to 10 or 15, wherein the controller is configured to apply periodic electrical pulses to the electrically conductive material in order to measure the electrical parameter.

17. The aerosol-generating device according to any one of claims 1 to 10 or 15 or 16, wherein the controller is configured to apply the electrical pulse and / or the periodic electrical pulses to the electrically conductive material within a measurement cycle, in which the dielectric heating power is reduced or the dielectric heating is turned-off.

18. The aerosol-generating device according to any one of claims 1 to 10 or 15 to 17, wherein the electrically conductive track may form a loop inside the heating chamber.

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