Inductive heater assembly equipped with a temperature sensor

Abstract

An inductive heater assembly (10) for an aerosol generating device is provided, wherein the inductive heater assembly comprises: at least one inductor coil (12) configured to generate a variable magnetic field when a variable current flows through at least one inductor coil; at least one susceptor (11) arranged to be penetrated by the variable magnetic field generated by the at least one inductor coil to heat the susceptor; and at least one temperature sensor (13) arranged to determine the temperature of the at least one susceptor; wherein the at least one temperature sensor comprises a first resistance sensing element (41) and a second resistance sensing element (42), wherein the first resistance sensing element is connected to the second resistance sensing element, and the first resistance sensing element is positioned relative to the second resistance sensing element, so that the current induced in the first resistance sensing element by the variable magnetic field is opposed to the current induced in the second resistance sensing element by the variable magnetic field.

Description

Technology Field

[0001] The present invention The present invention relates to an inductive heater assembly for an aerosol generating device. In particular, but not exclusively, one or more embodiments of the present invention may relate to an inductive heater assembly having a temperature sensor capable of reducing the effect of noise operating in a variable magnetic field. The present invention also relates to an aerosol generating device comprising an inductive heater assembly. Background Technology

[0002] A number of electrically operated aerosol generators having an electric heater for heating an aerosol-forming material, such as a cigarette plug, are proposed in the art. The goal of such aerosol generators is to reduce known harmful smoke components of the type produced by the combustion and thermal degradation of tobacco in conventional cigarettes. Typically, the aerosol-generating material is provided as part of an aerosol-generating article inserted into the chamber or cavity of the aerosol generator.

[0003] In some disclosed devices, in order to heat an aerosol-forming substrate to a temperature at which volatile components capable of forming an aerosol can be released, a resistive heating element, such as a heating blade, is inserted into or around the aerosol-forming substrate when the article is received in an aerosol generating device.

[0004] Other aerosol generators use inductive heaters rather than resistive heating elements. An inductive heater typically comprises an inductor forming part of the aerosol generator and a conductive susceptor element arranged in thermal proximity to the aerosol-forming substrate. The inductor generates a variable magnetic field, causing eddy currents and hysteresis losses in the susceptor element, thereby heating the susceptor element and consequently heating the aerosol-forming substrate. Induction heating can allow aerosol generation without exposing the heater to the aerosol-forming article. This can improve the ease with which the heater can be cleaned.

[0005] In an aerosol generator, it may be useful to determine the temperature of an electric heater to ensure that the temperature does not exceed the temperature at which harmful smoke components begin to be generated. The measured temperature can be used, for example, as part of a feedback loop, to control the amount of power supplied to the heater to maintain the heater at a target temperature.

[0006] Determining the temperature of a resistive heating element is relatively simple. For example, a temperature sensor can be used, or the resistance of the resistive heating element can be measured, and the temperature can be determined based on the known relationship between temperature and resistance. However, determining the temperature of a susceptor in an inductive heater is more challenging. For instance, since a susceptor is typically not connected to a control circuit, its resistance cannot be easily measured. Furthermore, using a temperature sensor in a variable magnetic field introduces a high level of noise into the sensor signal, which can render the signal unusable or result in an inaccurate temperature determination. The problem to be solved

[0007] It would be desirable to provide an inductive heater assembly having a temperature sensor that can determine the temperature of the susceptor more accurately and is less affected by noise. means of solving the problem

[0008] According to the present disclosure, an inductive heater assembly for an aerosol generating device is provided. The inductive heater assembly may include at least one inductor coil. The at least one inductor coil may be configured to generate a variable magnetic field when a variable current flows through the at least one inductor coil. The inductive heater assembly may include at least one susceptor. The at least one susceptor may be arranged to be penetrated by the variable magnetic field generated by the at least one inductor coil and to heat the susceptor. The inductive heater assembly may include at least one temperature sensor. The at least one temperature sensor may be arranged to determine the temperature of the at least one susceptor. The at least one temperature sensor may include a first resistance sensing element and a second resistance sensing element. The first resistance sensing element may be connected to the second resistance sensing element. The first resistance sensing element may be positioned relative to the second resistance sensing element such that the current induced within the first resistance sensing element by the variable magnetic field opposes the current induced within the second resistance sensing element by the variable magnetic field.

[0009] According to the present disclosure, an inductive heater assembly for an aerosol generating device is provided, wherein the inductive heater assembly comprises: at least one inductor coil configured to generate a variable magnetic field when a variable current flows through at least one inductor coil; at least one susceptor arranged to be penetrated by the variable magnetic field generated by the at least one inductor coil to heat the susceptor; and at least one temperature sensor arranged to determine the temperature of the at least one susceptor; wherein the at least one temperature sensor comprises a first resistance sensing element and a second resistance sensing element, the first resistance sensing element is connected to the second resistance sensing element, and the first resistance sensing element is positioned relative to the second resistance sensing element, so that a current induced in the first resistance sensing element by the variable magnetic field is opposed to a current induced in the second resistance sensing element by the variable magnetic field.

[0010] The temperature sensor of the aforementioned inductive heater assembly is configured such that the current induced in the first resistance sensing element by the variable magnetic field opposes the current induced in the second resistance sensing element by the variable magnetic field. That is, the current induced in the second resistance sensing element flows in the opposite direction to the current induced in the first resistance sensing element. Consequently, the magnetic field generated by the second resistance sensing element is substantially identical and opposite to the magnetic field generated by the first resistance sensing element, so that the magnetic fields of the first and second resistance sensing elements cancel each other out to a significant degree. Therefore, the self-inductance of the temperature sensor is substantially reduced, and the noise effect caused by operating the temperature sensor in a variable magnetic field is also reduced. This arrangement of temperature sensors helps improve the accuracy of temperature measurement even when operating in a variable magnetic field.

[0011] The inductor coil can have any suitable shape. For example, the inductor coil can be a flat inductor coil. A flat inductor coil can be wound spirally in a substantially flat plane. Preferably, the inductor coil is a tubular inductor coil. Typically, a tubular inductor coil is wound spirally around a longitudinal axis. The inductor coil can be slender. Particularly preferably, the inductor coil can be a slender tubular inductor coil. The inductor coil can have any suitable cross-section. For example, the inductor coil can have a circular, elliptical, square, rectangular, triangular, or other polygonal cross-section.

[0012] The inductor coil can be formed from any suitable material. The inductor coil is formed from an electrically conductive material. Preferably, the inductor coil is formed from a metal or a metal alloy.

[0013] As used herein, "electrical conductivity" is 1 x 10⁻⁶ at 20°C. -4 It refers to a material having an electrical resistivity of Ωm or less.

[0014] As described herein, a variable current may refer to a current that varies at a frequency of about 5 kHz to about 500 kHz. In some embodiments, the variable current is a high-frequency variable current. As used herein, the term “high-frequency variable current” means a variable current having a frequency of about 500 kHz to about 30 MHz. The high-frequency variable current may have a frequency of about 1 MHz to about 30 MHz, such as about 1 MHz to about 10 MHz, or about 5 MHz to about 8 MHz. The variable current may be alternating current.

[0015] As used herein, the term “susceptor” refers to an element comprising a material capable of converting magnetic energy into heat. When the susceptor is placed within a variable magnetic field, such as a variable magnetic field generated by an inductor coil, the susceptor is heated. The heating of the susceptor may be the result of at least one of hysteresis loss or eddy current induced in the susceptor, depending on the electrical and magnetic properties of the susceptor material.

[0016] The susceptor may comprise any suitable material. The susceptor may be formed of any material capable of inductive heating to a temperature sufficient to release volatile compounds from the aerosol-forming substrate. A preferred susceptor may be heated to a temperature exceeding 250°C. A preferred susceptor may be formed of an electrically conductive material. Suitable materials for an elongated susceptor include graphite, molybdenum, silicon carbide, stainless steel, niobium, aluminum, nickel, nickel-containing compounds, titanium, and composites of metallic materials. A preferred susceptor comprises metal or carbon. Some preferred susceptors comprise ferromagnetic materials, such as ferritic iron, ferromagnetic alloys like ferromagnetic steel or stainless steel, ferromagnetic particles, and ferrite. Some preferred susceptors are made of ferromagnetic materials. A suitable susceptor may comprise aluminum. A suitable susceptor may be composed of aluminum. The susceptor may contain at least about 5%, at least about 20%, at least about 50%, or at least about 90% of a ferromagnetic or paramagnetic material.

[0017] Preferably, the susceptor is formed of a material that is substantially impermeable to gas. That is, preferably, the susceptor is formed of a material that is not permeable to gas.

[0018] At least one susceptor of the inductive heater assembly may have any suitable shape. For example, the susceptor may be elongated. The susceptor may have any suitable cross-section. For example, the susceptor may have a circular, elliptical, square, rectangular, triangular, or other polygonal cross-section. The susceptor may be tubular.

[0019] In some preferred embodiments, the susceptor may include a susceptor layer provided on a support body. When the susceptor is placed in a variable magnetic field, eddy currents are induced very close to the surface of the susceptor due to an effect referred to as the skin effect. Thus, it is possible to form the susceptor from a relatively thin layer of susceptor material so that the susceptor is effectively heated in the presence of a variable magnetic field. Making the susceptor from a support body and a relatively thin susceptor layer can facilitate the manufacture of a simple, inexpensive, and robust aerosol-generating article.

[0020] The support body can be formed by a manufacturing process that is not sensitive to induction heating. Advantageously, this can reduce heating of the surface of the susceptor that does not come into contact with the aerosol-forming substrate, and the surface of the support body forms the surface of the susceptor that does not come into contact with the aerosol-forming substrate.

[0021] The support body may comprise an electrically insulating material. As used herein, "electrically insulating" is at least 1 x 10⁻⁶ at 20°C. 4 It refers to a material having an electrical resistivity of Ωm.

[0022] Forming a support body from a thermal insulating material can provide a thermal insulating barrier between the susceptor layer and other components of an inductive heater assembly, such as an inductor coil surrounding the induction heating element. Advantageously, this can reduce heat transfer between the susceptor and other components of the induction heating system.

[0023] Thermal insulating materials also, as measured using the laser flash method, at approximately 0.01 square centimeters (cm²) per second. 2 It can have a bulk thermal diffusivity of less than / s. Providing a support body having such a thermal diffusivity can result in a support body having high thermal inertia, which can reduce heat transfer between the susceptor layer and the support body and reduce temperature changes of the support body.

[0024] The susceptor may have any suitable dimensions. The susceptor may have a length of about 5 mm to about 15 mm, for example, about 6 mm to about 12 mm, or about 8 mm to about 10 mm. The susceptor may have a width of about 1 mm to about 8 mm, for example, about 3 mm to about 5 mm. The susceptor may have a thickness of about 0.01 mm to about 2 mm. If the susceptor has a constant cross-section, for example, a circular cross-section, the susceptor may have a preferred width or diameter of about 1 mm to about 5 mm.

[0025] The inductive heater assembly may include at least one external heating element. The at least one external heating element may include at least one susceptor. As used herein, the term “external heating element” refers to a heating element configured to heat the external surface of an aerosol-forming substrate. The at least one external heating element may at least partially surround a cavity to accommodate the aerosol-forming substrate.

[0026] The inductive heater assembly may include at least one internal heating element. The internal heating element may include at least one susceptor. As used herein, the term "internal heating element" refers to a heating element configured to be inserted into an aerosol-forming substrate. The internal heating element may be in the form of a blade, a fin, and a cone. At least one internal heating element may extend into a cavity to receive the aerosol-forming substrate.

[0027] In some embodiments, the inductive heater assembly includes at least one internal heating element and at least one external heating element.

[0028] The first and second resistance sensing elements may each include an electrically resistive wire having first and second ends arranged adjacent to each other along their respective lengths. This arrangement helps to reduce or eliminate the magnetic field of the first and second resistance sensing elements.

[0029] The first and second resistance sensing elements may be formed of platinum, gold, silver, tungsten, nickel, and copper.

[0030] The first and second resistance sensing elements may be formed from other suitable electrically resistive materials. Suitable electrically resistive materials include, but are not limited to, semiconductors such as doped ceramics, electrically "conductive" ceramics (e.g., molybdenum disilicide), carbon, graphite, metals, metal alloys, and composite materials made of ceramic and metal materials. Such composite materials may include doped ceramics or undoped ceramics. Examples of suitable doped ceramics include doped silicon carbide. Examples of suitable metals include titanium, zirconium, tantalum, platinum, gold, and silver. Examples of suitable metal alloys include stainless steel, nickel-, cobalt-, chromium-, aluminum-, titanium-, zirconium-, hafnium-, niobium-, molybdenum-, tantalum-, tungsten-, tin-, gallium-, manganese-, gold-, and iron-containing alloys, and superalloys based on nickel, iron, cobalt, stainless steel, Timetal®, and iron-manganese-aluminum alloys. In composite materials, the electrically resistive material may be optionally embedded in the insulating material, encapsulated or coated with the insulating material, or vice versa, depending on energy transfer dynamics and required external physicochemical properties.

[0031] The first and second resistance sensing elements can be wound together to form a bifilar coil. This has been found to be a particularly effective arrangement for reducing or eliminating the magnetic field of the first and second resistance sensing elements.

[0032] As used herein, the term “bifiler coil” refers to a coil comprising two closely spaced or adjacent parallel windings. The coil may be made of double wire having two closely spaced or adjacent filaments or strands. Alternatively, the coil may be made by winding two separate wires in a closely spaced or adjacent arrangement.

[0033] Each circuit of the bifiler coil can be spaced apart from its adjacent circuit(s). This reduces the magnetic shielding effect of the temperature sensor on the susceptor. The spacing between the circuits of the bifiler coil allows the variable magnetic field to pass through the temperature sensor in a less restricted manner, allowing the susceptor to be penetrated by more variable magnetic fields. This arrangement is particularly advantageous when the temperature sensor extends along the entire length of the susceptor.

[0034] The first and second resistance sensing elements can be electrically connected in series at their respective second ends. This allows current to pass through the second resistance sensing element in the opposite direction to the current passing through the first resistance sensing element.

[0035] The first end of each of the first and second resistance sensing elements can be arranged to be connected to a control circuit. This allows the resistance of the temperature sensor to be determined by the control circuit.

[0036] The temperature sensor may be arranged around at least a portion of the outer surface of the susceptor. Preferably, the ratio of the length of the temperature sensor to the length of the susceptor is less than 0.5:1, more preferably less than 0.4:1, more preferably less than 0.3:1, more preferably less than 0.2:1, and more preferably less than 0.1:1.

[0037] Each circuit of the temperature sensor's bifiler coil can make contact with its adjacent circuit(s). This helps to distribute the temperature evenly across the sensor, thereby avoiding temperature "hot spots" at specific locations on the sensor.

[0038] As used herein, the term “adjacent” is used to mean “side” or “next”. This includes not only arrangements where lines are in direct contact, but also arrangements where two or more lines are separated by a gap, such as an air gap or gap, which includes one or more intermediate components between adjacent lines.

[0039] The temperature sensor can extend along substantially the entire length of the susceptor. This allows the average temperature of the entire susceptor to be determined.

[0040] The temperature sensor can come into contact with the susceptor. This provides improved thermal contact between the temperature sensor and the susceptor.

[0041] The temperature sensor further includes a forming agent around which a bifiler coil is wound. This allows the coil to be formed before it is integrated into the inductive heater assembly, which can provide easier fabrication and assembly. The forming agent may be resistant to variable magnetic fields so as not to affect the magnetic field or shield the susceptor.

[0042] The inductive heater assembly may include multiple inductor coils, and a separate temperature sensor is provided for each inductor coil. This allows different susceptors or different susceptor regions to be heated at different times or to different temperatures.

[0043] An inductive heater assembly may include multiple susceptors, and a separate inductor coil and a separate temperature sensor are provided for each inductor coil. This allows different susceptors to be heated at different times or to different temperatures.

[0044] An inductive heater assembly may include a single susceptor, multiple inductor coils, and corresponding temperature sensors. This allows different susceptor regions to be heated at different times or to different temperatures.

[0045] According to the present disclosure, an aerosol generating device is provided. The aerosol generating device may include an inductive heater assembly as described above. The aerosol generating device may include a control circuit. The aerosol generating device may include a power source. The control circuit may be configured to control the supply of current from the power source to the inductive heater assembly to controllably heat the susceptor. The control circuit may be connected to at least one temperature sensor of the inductive heater assembly. The control circuit may be configured to determine the temperature of the susceptor by determining the resistance of at least one temperature sensor.

[0046] According to the present disclosure, an aerosol generating device is provided, the device comprising an inductive heater assembly as described above; a control circuit; and a power source; the control circuit is configured to control the supply of current from the power source to the inductive heater assembly to controllably heat a susceptor; and the control circuit is configured to determine the temperature of the susceptor by determining the resistance of at least one temperature sensor connected to at least one temperature sensor of the inductive heater assembly.

[0047] As used herein, the "aerosol generating device" relates to a device capable of generating an aerosol by interacting with an aerosol-forming substrate or an aerosol-generating article.

[0048] As used herein, the term "aerosol-forming substrate" relates to a substrate capable of releasing a volatile compound capable of forming an aerosol. Such volatile compounds may be released by heating the aerosol-forming substrate.

[0049] As used herein, the term "aerosol generating article" refers to an article comprising an aerosol-forming material that releases a volatile compound capable of forming an aerosol when heated within an aerosol generating device. The aerosol generating article is separate from the aerosol generating device for heating the aerosol generating article and is configured to be combined with the aerosol generating device.

[0050] The aerosol-forming substrate may contain nicotine. The nicotine-containing aerosol-forming substrate may be a nicotine salt matrix.

[0051] The aerosol-forming substrate may be a liquid. The aerosol-forming substrate may include a solid component and a liquid component. Preferably, the aerosol-forming substrate may be a solid.

[0052] The aerosol-forming substrate may include a plant-based material. The aerosol-forming substrate may include tobacco. The aerosol-forming substrate may include a tobacco-containing material containing a volatile tobacco flavor compound that is released from the aerosol-forming substrate upon heating. The aerosol-forming substrate may include a non-tobacco material. The aerosol-forming substrate may include a homogenized plant-based material. The aerosol-forming substrate may include a homogenized tobacco material. The homogenized tobacco material may be formed by aggregating fine tobacco particles. In a particularly preferred embodiment, the aerosol-forming substrate comprises a crimped sheet of homogenized tobacco material. As used herein, the term 'crimped sheet' refers to a sheet having a plurality of substantially parallel ridges or wavy folds.

[0053] The aerosol-forming substrate may comprise at least one aerosol-forming agent. The aerosol-forming agent is any suitable known compound or mixture of compounds that facilitates the formation of a dense and stable aerosol upon use and substantially resists thermal degradation at the operating temperature of the system. Suitable aerosol-forming agents are well known in the art and include, but are not limited to, polyhydric alcohols such as triethylene glycol, 1,3-butanediol, and glycerin; 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-forming agents may comprise polyhydric alcohols or mixtures thereof, such as triethylene glycol and 1,3-butanediol. Preferably, the aerosol-forming agent is glycerin. The homogenized tobacco material may have an aerosol-forming agent content of 5% by weight or more based on dry weight, such as 5% by weight to 30% by weight, where present. The aerosol-forming agent may include other additives and components, such as flavoring agents.

[0054] At least one temperature sensor may be connected in series with a reference resistor to form a potential divider, and the output signal from at least one temperature sensor is taken from a connection point between at least one temperature sensor and the reference resistor. This provides the output signal as a voltage that can be processed by a control circuit, for example, by an analog-to-digital converter of a microcontroller.

[0055] At least one temperature sensor can be connected in a Wheatstone bridge array. This provides a very accurate means for determining the resistance of the temperature sensor.

[0056] The control circuit may further include a capacitor for filtering the output signal from at least one temperature sensor to reduce noise within the output signal. This helps to reduce any residual noise in the temperature sensor signal that is not removed by the configuration of the temperature sensor itself.

[0057] A capacitor can form part of a low-pass filter. The cut-off frequency of the low-pass filter can be configured to filter frequencies within the frequency range of the variable magnetic field. The capacitor can be connected in parallel across a reference resistor. The capacitor can be configured to reduce noise within the frequency range of the variable magnetic field.

[0058] The capacitance of the capacitor may be in the range of 1 nF to 100 μF. Preferably, the capacitance is about 10 μF or less, more preferably about 1 μF or less, more preferably about 100 nF or less, and more preferably 94 nF.

[0059] The aerosol generating device may further include a cavity for receiving an aerosol generating article or an aerosol forming substrate so that the aerosol generating article or the aerosol forming substrate is thermally close to an inductive heater assembly.

[0060] The aerosol generating device may include a device housing. The device housing may at least partially define a cavity for receiving an aerosol-forming substrate or an aerosol-generating article. Preferably, the cavity for receiving the aerosol-forming substrate or the aerosol-generating article is located at the proximal end of the device.

[0061] When the susceptor is a tubular susceptor, the tubular susceptor may at least partially define a cavity for receiving an aerosol-forming substrate. When the susceptor includes a support body, the support body may be a tubular support body, and the susceptor layer may be provided on the inner surface of the tubular support body. Providing the susceptor layer on the inner surface of the support body allows the susceptor layer to be positioned adjacent to the aerosol-forming substrate within the cavity for receiving the aerosol-forming substrate, thereby improving heat transfer between the susceptor layer and the aerosol-forming substrate.

[0062] The device housing may be elongated. Preferably, the device housing has a cylindrical shape. The device housing may comprise any suitable material or a combination of materials. Examples of suitable materials include metals, alloys, plastics, or composite materials comprising one or more of these materials, or thermoplastic resins suitable for food or pharmaceutical applications, such as polypropylene, polyetheretherketone (PEEK), and polyethylene. The material is preferably lightweight and non-brittle.

[0063] Preferably, the aerosol generator is portable. The aerosol generator may have a size similar to a conventional cigar or cigarette. The aerosol generator may have a total length of about 30 mm to about 150 mm. The aerosol generator may have an outer diameter of about 5 mm to about 30 mm. The aerosol generator may be a handheld device. That is, the aerosol generator may have a size and shape that fits in the user's hand.

[0064] The aerosol generator may include a power supply configured to provide a variable current to an inductor coil.

[0065] The power supply unit may be a DC power supply unit. In a preferred embodiment, the power supply unit is a battery. The power supply unit may be a nickel-hydrogen alloy battery, a nickel-cadmium battery, or a lithium-based battery, such as a lithium-cobalt, lithium-iron-phosphate, or lithium-polymer battery. However, in some embodiments, the power supply unit may be another type of charge storage device, such as a capacitor. The power supply unit may require recharging and may have a capacity that allows for the storage of sufficient energy for one or more user experiences. For example, the power supply unit may have a capacity sufficient to allow continuous heating of an aerosol-forming substrate for a period of about 6 minutes, corresponding to the usual time taken to smoke a conventional cigarette, or for a period of several times 6 minutes. In another example, the power supply unit may have a capacity sufficient to allow for the individual activation of a predetermined number of puffs or aerosol generators. In another example, the power supply unit may have a capacity sufficient to allow for a predetermined number of device uses or individual activations. In one embodiment, the power supply is a DC power supply having a DC supply voltage in the range of about 2.5 V to about 4.5 V and a DC supply current in the range of about 1 A to about 10 A (corresponding to a DC power source in the range of about 2.5 W to about 45 W).

[0066] The aerosol generator may include at least one inductor coil and a control circuit or controller connected to a power supply. The control circuit may be configured to control the power supply from the power supply to at least one inductor coil. The control circuit may include a programmable microprocessor, a microcontroller, an application-specific integrated circuit (ASIC), or a microprocessor capable of providing control. The control circuit may further include electronic components. The control circuit may be configured to regulate the current supply to at least one inductor coil. The current may be supplied to at least one inductor coil continuously following the activation of the aerosol generator, or intermittently, for example, on a puff-by-puff basis.

[0067] Advantageously, the control circuit may include a DC / AC inverter that may include a D-class or E-class power amplifier.

[0068] The control circuit may be configured to supply a variable current to at least one inductor coil. The variable current may be from about 5 kHz to about 500 kHz. In some embodiments, the variable current is a high-frequency variable current, i.e., a current from about 500 kHz to about 30 MHz. The high-frequency variable current may have a frequency from about 1 MHz to about 30 MHz, such as from about 1 MHz to about 10 MHz, or from about 5 MHz to about 8 MHz.

[0069] In some embodiments, the device housing includes a mouthpiece. The mouthpiece may include at least one air inlet and at least one air outlet. The mouthpiece may include more than one air inlet. One or more of the air inlets may reduce the temperature of the aerosol before the aerosol is delivered to the user and may reduce the concentration of the aerosol before the aerosol is delivered to the user.

[0070] In some embodiments, a mouthpiece may be provided as part of an aerosol generating article. As used herein, the term “mouthpiece” refers to a part of an aerosol generating system that is placed in the user’s mouth to directly inhale an aerosol generated by the aerosol generating system from an aerosol generating article received by an aerosol generating device.

[0071] The aerosol generating device may include a user interface for activating the device, for example, a button for initiating heating of an aerosol generating article.

[0072] The aerosol generating device may include a display for indicating the state of the device or the aerosol forming substrate.

[0073] Additionally, an aerosol generating system is described herein. As used herein, the term “aerosol generating system” refers to a combination of an aerosol generating device and one or more aerosol forming substrates or aerosol generating articles for use with said device. An aerosol generating system may include additional components, such as a charging unit for recharging an on-board electric power supply for an electric-operated or electric aerosol generating device.

[0074] An aerosol-generating article may be an article that generates an aerosol that can be inhaled directly by a user inhaling or puffing over a mouthpiece at the proximal end of the system or at the user end. An aerosol-generating article may be disposable. An article comprising an aerosol-forming material including tobacco may be referred to herein as a tobacco stick.

[0075] The aerosol generating article may have any suitable shape. The aerosol generating article may be substantially cylindrical in shape. The aerosol generating article may be substantially elongated. The aerosol generating article may have a length and a circumference substantially perpendicular to this length.

[0076] An aerosol-forming substrate may be provided as an aerosol-generating segment containing an aerosol-forming substrate. The aerosol-generating segment may include a plurality of aerosol-forming substrates. The aerosol-generating segment may include a first aerosol-forming substrate and a second aerosol-forming substrate. In some embodiments, the second aerosol-forming substrate is substantially identical to the first aerosol-forming substrate. In some embodiments, the second aerosol-forming substrate is different from the first aerosol-forming substrate.

[0077] If the aerosol generating segment comprises a plurality of aerosol-forming substrates, the number of aerosol-forming substrates may be equal to the number of susceptors in the induction heating element. Similarly, the number of aerosol-forming substrates may be equal to the number of inductor coils in the induction heater assembly.

[0078] The aerosol generating segment may have a substantially cylindrical shape. The aerosol generating segment may be substantially elongated. The aerosol generating segment may also have a length and a circumference substantially perpendicular to that length.

[0079] When an aerosol generating segment comprises a plurality of aerosol forming substrates, the aerosol forming substrates may be arranged in a single end-to-end manner along the axis of the aerosol generating segment. In some embodiments, the aerosol generating segment may include a separator between adjacent aerosol forming substrates.

[0080] In some preferred embodiments, the aerosol generating article may have a total length of about 30 mm to 100 mm. In some embodiments, the aerosol generating article has a total length of about 45 mm. The aerosol generating article may have an outer diameter of about 5 mm to about 12 mm. In some embodiments, the aerosol generating article may have an outer diameter of about 7.2 mm.

[0081] The aerosol generating segment may have a length of about 7 mm to about 15 mm. In some embodiments, the aerosol generating segment may have a length of about 10 mm or 12 mm.

[0082] The aerosol generating segment preferably has an outer diameter approximately equivalent to the outer diameter of the aerosol generating article. The outer diameter of the aerosol generating segment may be about 5 mm to about 12 mm. In one embodiment, the aerosol generating segment may have an outer diameter of about 7.2 mm.

[0083] The aerosol generating article may include a filter plug. The filter plug may be located at the proximal end of the aerosol generating article. The filter plug may be a cellulose acetate filter plug. In some embodiments, the filter plug may have a length of about 5 mm to about 10 mm. In some preferred embodiments, the filter plug may have a length of about 7 mm.

[0084] The aerosol generating article may include an outer wrapper. The outer wrapper may be formed of paper. The outer wrapper may be gas permeable in the aerosol generating segment. In particular, in an embodiment comprising a plurality of aerosol generating substrates, the outer wrapper may include perforations or other air inlets at the interface between adjacent aerosol generating substrates. If a separation portion is provided between adjacent aerosol generating substrates, the outer wrapper may include perforations or other air inlets upon separation. This may allow the aerosol generating substrate to directly provide air that is not drawn in through other aerosol generating substrates. This may increase the amount of air received by each aerosol generating substrate. This may improve the characteristics of the aerosol generated from the aerosol generating substrate.

[0085] Additionally, the aerosol generating article may include a separator between the aerosol forming substrate and the filter plug. The separator may be about 18 mm, but may be in the range of about 5 mm to about 25 mm.

[0086] Features described in connection with one or more examples of the present disclosure may be equally applied to other examples of the present invention. In particular, features described in connection with an aerosol generating system may be equally applied to an aerosol generating article or an aerosol generating device, and The opposite It could be. Brief explanation of the drawing

[0087] Now, embodiments of the present invention will be described merely by reference to the attached drawings, and among the attached drawings, FIG. 1 is a schematic partial cross-sectional view of a heater assembly according to an example of the present invention. FIG. 2 is an enlarged and simplified drawing of a temperature sensor of a heater assembly according to an example of the present invention. FIG. 3 is a schematic partial cross-sectional view of a heater assembly including a temperature sensor according to another example of the present invention. FIG. 4 is a schematic partial cross-sectional view of a heater assembly according to another example of the present invention. FIG. 5 is a schematic partial cross-sectional view of a heater assembly according to another example of the present invention. FIG. 6 is a schematic partial cross-sectional view of an aerosol generating device according to another example of the present invention and an aerosol generating article for use in the device. FIG. 8 illustrates the upper part of the aerosol generating device of FIG. 7 when an aerosol generating article is received within the device. FIGS. 8a to 8c illustrate various filter circuits for an aerosol generating device according to another example of the present invention for filtering. Figure 9 shows the filter circuit of Figure 8b connected to a microcontroller. Specific details for implementing the invention

[0088] FIG. 1 illustrates an inductive heater assembly (10) comprising a susceptor (11) and an inductor coil (12). The inductor coil (12) is configured to generate a variable magnetic field when a variable current flows through the inductor coil (12). The susceptor (11) is arranged relative to the inductor coil (12) in such a way that the susceptor (11) can be heated by the penetration of a variable magnetic field that can be generated by the inductor coil (12). The susceptor (11) is configured to heat an aerosol-forming substrate. Alternatively, when the susceptor (11) is heated by the penetration of a variable magnetic field, the aerosol-forming substrate can be heated by the susceptor. The aerosol-forming substrate that can be heated by the susceptor can be accommodated within a cavity (14) of the inductive heater assembly (10). In the example of FIG. 1, the susceptor (11) is a tubular susceptor, and the tubular susceptor (11) defines a cavity (14) for receiving an aerosol-forming substrate.

[0089] A temperature sensor (13) is provided in thermal contact or proximity to the susceptor (11) at a position along the length of the susceptor. As a result, the temperature sensor (13) can be used to measure the temperature of the susceptor (11). The temperature sensor (13) is a resistance temperature sensor that changes its resistance as a function of its temperature. The resistance of the temperature sensor (13) increases as the temperature increases according to a known or determinable relationship. By measuring the resistance of the temperature sensor (13), the temperature of the temperature sensor (13) can be determined based on the relationship between temperature and resistance, which provides a temperature indication of the susceptor (11).

[0090] The temperature sensor (13) is in the form of a bifiler coil of copper wire wound around the susceptor (11). The copper wire has a diameter of approximately 60 μm, and each circuit of the bifiler coil contacts its adjacent circuit(s). The copper wire is insulated or enameled to prevent electrical short circuits between the circuits. The temperature sensor (13) is approximately 4.5 mm long and wraps around about 10% of the length of the susceptor (11). The inner diameter of the temperature sensor (13) is approximately 7.2 mm. The free end (13a) of the bifiler coil of the temperature sensor (13) extends out of the heater assembly (10) so that it can be connected to a control circuit (not shown).

[0091] FIG. 2 shows an enlarged and simplified drawing of the temperature sensor (13) of the heater assembly (10) of FIG. 1. For clarity, only a few lines of the bifiler coil are shown. The temperature sensor comprises a first resistance sensing element (41) and a second resistance sensing element (42) arranged adjacent to each other along their respective lengths and wound together in a bifiler coil around the susceptor (11). The first resistance sensing element (41) and the second resistance sensing element (42) each have a first end (41a, 42a) and a second end (41b, 42b), respectively. The first resistance sensing element (41) and the second resistance sensing element (42) are electrically connected in series at their respective second ends (41b, 42b). The first ends (41a, 41b) can be used to connect the temperature sensor (13) to a control circuit (not shown).

[0092] The current (I1) induced in the first resistance sensing element (41) by the variable magnetic field generated by the inductor coil (12) is opposite to the current (I2) induced in the second resistance sensing element (42) by the variable magnetic field. As can be seen from FIG. 2, the current (I2) induced in the second resistance sensing element (42) flows in the opposite direction to the current (I1) induced in the first resistance sensing element (41). Consequently, the magnetic field generated by the second resistance sensing element (42) is substantially the same and opposite to that generated by the first resistance sensing element (41), so the magnetic fields of the first resistance sensing element (41) and the second resistance sensing element (42) cancel each other out to a significant degree. Therefore, the self-inductance of the temperature sensor (13) is substantially reduced, and the noise effect caused by operating the temperature sensor in a variable magnetic field is also reduced. Thus, the temperature sensor (13) can accurately determine the temperature even when operating in a variable magnetic field.

[0093] FIG. 3 illustrates a heater assembly (100) according to a different example of the present invention. The heater assembly (100) is substantially identical to the heater assembly (10) of FIG. 1 and includes a susceptor (111), an inductor coil (112), and a temperature sensor (113) in the form of a bifiler coil. The only difference in this arrangement is that the circuits of the bifiler coil are spaced apart and the temperature sensor extends substantially along the entire length of the susceptor (111). In this example, the spacing between the circuits of the bifiler coil helps to reduce shielding of the susceptor (111) from the variable magnetic field so that the susceptor (111) can be penetrated by the variable magnetic field. That is, the spacing between the circuits of the bifiler coil allows the variable magnetic field to pass through the temperature sensor (113) to the susceptor (111).

[0094] FIG. 4 illustrates an inductive heater assembly (10) comprising a first susceptor (11) and a second susceptor (15). The inductive heater assembly (10) also comprises a first inductor coil (12) and a second inductor coil (16). The first inductor coil (12) is configured to generate a first variable magnetic field when a first variable current flows through the first inductor coil (12). The second inductor coil (16) is configured to generate a second variable magnetic field when a second variable current flows through the second inductor coil (16). The first susceptor (11) is arranged relative to the first inductor coil (12) in such a way that the first susceptor (11) can be heated by the penetration of the first variable magnetic field. The second susceptor (15) is arranged with respect to the second inductor coil (16) in such a way that the second susceptor (15) can be heated by the penetration of the second variable magnetic field. Thus, when the first susceptor (11) is heated by the penetration of the first variable magnetic field, an aerosol-forming substrate (not shown) located within the first susceptor (11) can be heated by the first susceptor (11). Likewise, when the second susceptor (15) is heated by the penetration of the second variable magnetic field, an aerosol-forming substrate (not shown) located within the second susceptor (15) can be heated by the second susceptor (15).

[0095] The inductive heater assembly (10) of FIG. 4 includes a first temperature sensor (13) and a second temperature sensor (17). The first (13) and second (17) temperature sensors of FIG. 4 are identical to the temperature sensor (13) of FIG. 1 and FIG. 2. The first temperature sensor (13) is provided in thermal contact with the first susceptor (11). As a result, the first temperature sensor (13) can be used to measure the temperature of the first susceptor (11). The second temperature sensor (17) is provided in thermal contact with the second susceptor (15). As a result, the second temperature sensor (17) can be used to measure the temperature of the second susceptor (15).

[0096] In the example of FIG. 4, the first susceptor (11) is a tubular susceptor, and the tubular susceptor defines a first hollow portion (14) for receiving an aerosol-forming material. Likewise, the second susceptor (15) is a tubular susceptor, and the tubular susceptor defines a second hollow portion (18) for receiving an aerosol-forming material.

[0097] The arrangement of FIG. 4 enables selective heating of the first susceptor (11) and the second susceptor (15). This selective heating allows the inductive heater assembly (10) to heat different parts of the aerosol-forming substrate at different times when the aerosol-forming substrate is accommodated in the common first (14) and second (18) portions. Additionally, the arrangement of FIG. 4 enables one of the susceptors (11, 15) to be heated to a different temperature than the other susceptor (15, 11). These temperatures can advantageously be measured by using temperature sensors (13 and 17).

[0098] FIG. 5 illustrates an inductive heater assembly (10) comprising a single susceptor (11) having a first region (111) and a second region (112). The inductive heater assembly (10) also comprises a first inductor coil (12) and a second inductor coil (16). The first inductor coil (12) is configured to generate a first variable magnetic field when a first variable current flows through the first inductor coil (12). The second inductor coil (16) is configured to generate a second variable magnetic field when a second variable current flows through the second inductor coil (16). The first region (111) is arranged relative to the first inductor coil (12) in such a way that the first region (111) can be heated by the penetration of the first variable magnetic field. The second region (112) is arranged with respect to the second inductor coil (16) in such a way that the second region (112) can be heated by the penetration of the second variable magnetic field. Thus, when the first region (111) is heated by the penetration of the first variable magnetic field, an aerosol-forming substrate (not shown) located within the first region (111) can be heated by the first region (111). Likewise, when the second region (112) is heated by the penetration of the second variable magnetic field, an aerosol-forming substrate (not shown) located within the second region (112) can be heated by the second region (112).

[0099] The inductive heater assembly of FIG. 5 includes a first temperature sensor (13) and a second temperature sensor (17). The first (13) and second (17) temperature sensors of FIG. 5 are identical to the temperature sensor (13) of FIG. 1 and FIG. 2. The first temperature sensor (13) is provided in thermal contact with a first region (111). As a result, the first temperature sensor (13) can be used to measure the temperature of the first region (111). The second temperature sensor (17) is provided in thermal contact with a second region (112). As a result, the second temperature sensor (17) can be used to measure the temperature of the second region (112).

[0100] In the arrangement of FIG. 5, the susceptor (11) is a tubular susceptor, and the tubular susceptor defines a cavity (14) for receiving an aerosol-forming substrate. The inductive heater assembly (10) of FIG. 5 enables selective heating of a first region (111) and a second region (112). This selective heating allows the inductive heater assembly (10) to heat different parts of the aerosol-forming substrate at different times when the aerosol-forming substrate is received within the cavity (14). Additionally, the inductive heater assembly (10) of FIG. 5 enables one of the regions (111, 112) to be heated to a temperature different from that of the other region (112, 111). This temperature can advantageously be measured by using temperature sensors (13 and 17).

[0101] FIG. 6 illustrates a schematic cross-section of an aerosol generating device (200) and an aerosol generating article (300) for use with the aerosol generating device (200). The aerosol generating article (300) and the aerosol generating device (200) together comprise an aerosol generating system.

[0102] The aerosol generator (200) comprises a substantially cylindrical device housing (202) having a shape and size similar to a conventional cigar. The aerosol generator (200) further comprises a power supply unit (206) in the form of a rechargeable battery, a control circuit (208) including a microcontroller, an electrical connector (209), and the aforementioned inductive heater assembly (10). In the example of FIG. 6, the inductive heater assembly (10) is similar to that of FIG. 4. However, other inductive heater assemblies may be used. In particular, an inductive heater assembly comprising one inductor coil and one susceptor may be used. Alternatively, an inductive heater assembly comprising more than two inductor coils and more than two susceptors may be used. In a preferred alternative, an inductive heater assembly comprising one susceptor, two inductor coils, and two temperature sensors may be used; in particular, the inductive heater assembly of FIG. 5 may be used.

[0103] The power supply unit (206), control circuit (208), and inductive heater assembly (10) are all housed within the device housing (202). The inductive heater assembly (10) of the aerosol generating device (200) is arranged at the proximal end of the device (200). An electrical connector (209) is arranged at the distal end of the device housing (202).

[0104] As used herein, the term “proximal” refers to the user end or mouse end of an aerosol generator or aerosol generating article. The proximal end of a component of an aerosol generator or aerosol generating article is the end of the component closest to the user end or mouse end of the aerosol generator or aerosol generating article. As used herein, the term “distal” refers to the end opposite to the proximal end.

[0105] The control circuit (208) is configured to control the power supply from the power supply unit (206) to the inductive heater assembly (10). The control circuit (208) further includes a DC / AC inverter including a Class D power amplifier. The control circuit (208) is also configured to control the recharging of the power supply unit (206) from the electrical connector (209). The control circuit (208) further includes a puff sensor (not shown) configured to detect when a user inhales the aerosol generator.

[0106] The inductive heater assembly (10) includes a first inductor coil (12) and a second inductor coil (16). The inductive heater assembly (10) also includes a first susceptor (11) and a second susceptor (15). As described with reference to FIG. 4, the first susceptor (11) is a tubular susceptor, and the tubular susceptor defines a first cavity (14) for receiving an aerosol-forming substrate. Likewise, the second susceptor (15) is a tubular susceptor, and the tubular susceptor defines a second cavity (18) for receiving an aerosol-forming substrate. The first inductor coil (12) and the second inductor coil (16) are also tubular in the example of FIG. 6, and the inductor coils are arranged concentrically around the first susceptor (11) and the second susceptor (15), respectively.

[0107] The first inductor coil (12) is connected to a control circuit (208) and a power supply unit (206), and the control circuit (208) is configured to supply a first variable current to the first inductor coil (12). When the first variable current is supplied to the first inductor coil (12), the first inductor coil (12) generates a first variable magnetic field, which heats the first susceptor (11) by induction.

[0108] The second inductor coil (16) is connected to a control circuit (208) and a power supply unit (208), and the control circuit (208) is configured to supply a second variable current to the second inductor coil (16). When the second variable current is supplied to the second inductor coil (16), the second inductor coil (16) generates a second variable magnetic field, which heats the second susceptor (15) by induction.

[0109] The inductive heater assembly (10) includes a first temperature sensor (13) that is in thermal contact with the first susceptor (11). The inductive heater assembly (10) includes a second temperature sensor (17) that is in thermal contact with the second susceptor (15). The first temperature sensor (13) and the second temperature sensor (17) can be used to measure the temperatures of the first susceptor (11) and the second susceptor (15), respectively, as described with reference to FIG. 4.

[0110] The device housing (202) also defines an air inlet (280) near the distal end of the first part (14) of the cavity for receiving an aerosol-forming material. The air inlet (280) is configured so that ambient air can be drawn into the device housing (202).

[0111] The aerosol generating article (300) illustrated in FIG. 6 is generally in the form of a cylindrical rod having a diameter similar to the inner diameter of a cavity (14, 18) for receiving an aerosol-forming substrate. The aerosol generating article (300) comprises a cylindrical aerosol generating segment (310) wrapped together by a cylindrical cellulose acetate filter plug (304) and an outer wrapper (320) of a cigarette paper.

[0112] A filter plug (304) is arranged at the proximal end of an aerosol generating article (200) and forms a mouthpiece of an aerosol generating system that allows a user to inhale aerosol generated by the system.

[0113] The aerosol generating segment (310) is arranged at the distal end of the aerosol generating article (300) and has a length substantially equal to the combined length of the first part (14) and the second part (18). The aerosol generating segment (310) comprises a plurality of aerosol generating substrates, including a first aerosol generating substrate (312) at the distal end of the aerosol generating article (300) and a second aerosol generating substrate (314) at the proximal end of the aerosol generating segment (310) adjacent to the first aerosol generating substrate (312). In some embodiments, it will be understood that two or more aerosol generating substrates may be formed from the same material. However, in this embodiment, each aerosol generating substrate (312, 314) is different. The aerosol generating substrate (312) comprises a pleated and crimped sheet of homogenized tobacco material without additional flavoring. The second aerosol-forming substrate (314) comprises a pleated and crimped sheet of homogenized tobacco material containing a flavoring in the form of menthol. In another embodiment, the aerosol-forming substrate may contain a flavoring in the form of menthol and does not contain tobacco material or any other nicotine source. Each of the aerosol-forming substrates (312, 314) may also contain one or more aerosol-forming agents and additional components such as water, so that the aerosol-forming substrate is heated to produce an aerosol having desirable sensory characteristics.

[0114] The proximal end of the first aerosol-forming substrate (312) is exposed because it is not covered by the outer wrapper (320). The outer wrapper (320) includes a line of perforations (322) surrounding the aerosol-generating article (300) at the interface between the first aerosol-forming substrate (312) and the second aerosol-forming substrate (314). The perforations (322) allow air to be drawn into the aerosol-generating segment (310).

[0115] In the example of FIG. 6, the first aerosol-forming substrate (312) and the second aerosol-forming substrate (314) are arranged end-to-end. However, in other embodiments, it is expected that a separation portion may be provided between the first aerosol-forming substrate (312) and the second aerosol-forming substrate (314).

[0116] FIG. 7 shows an enlarged view of the proximal end of the aerosol generating device (200) of FIG. 6 in which an aerosol generating article (300) is accommodated inside. The aerosol generating article (300) is accommodated such that a first aerosol forming material (312) is located in the first part (14) of the cavity and a second aerosol forming material (314) is located in the second part (18) of the cavity.

[0117] When in use, the user inhales the filter plug (304), which in turn inhales air through the air inlet (280), which is detected by a puff detector (not shown). In response, a control circuit (not shown in FIG. 7) heats one or more of the susceptors (11 and 15) by activating one or more of the inductor coils (12 and 16) to generate an aerosol from one or more of the first (312) and second (314) aerosol-forming materials. Air flows from the air inlet (280) along a defined airflow path (indicated by a straight arrow in FIG. 7) through the aerosol generating device (200) and the aerosol generating article (300). The generated aerosol is carried by droplets from the aerosol generating article (300) through the filter (304) into the user's mouth.

[0118] FIGS. 8a through 8c illustrate various filter circuits (400a through 400c) for filtering signals generated by the temperature sensor (13) of the aforementioned inductive heater assembly (10) when operating in a variable magnetic field. The filter circuits (400a through 400c) help to reduce residual noise that is not removed by the dual array of the temperature sensor (13).

[0119] In each filter circuit (400a to 400c), a temperature sensor (13) having a resistance (Rs) is placed in series with a reference resistor (51) having a known resistance (Rr). In the examples of FIGS. 8a to 8c, the reference resistor (51) has a value of 100 Ω. The temperature sensor (13) and the reference resistor (51) form a potential divider between the supply voltage (Vcc) and ground. An output signal or voltage (Vo) is taken from the connection point between the temperature sensor (13) and the reference resistor (51).

[0120] Each filter circuit (400a to 400c) also includes a capacitor (53) having a capacitance (C) to assist in filtering residual noise from a variable magnetic field. The capacitor (53) is combined with a reference resistor (51) to form a low-pass filter for filtering noise in the frequency range of the variable magnetic field, i.e., a frequency range of 5 kHz to 500 kHz or higher. A filter circuit based on the example of FIG. 8b using a capacitor (53) having a capacitance (C) of 94 nF has been found to be particularly effective in reducing residual noise in a signal.

[0121] FIG. 9 illustrates the filter circuit (400b) of FIG. 8b connected to a microcontroller (220) that forms part of the control circuit (208) of FIG. 6. The microcontroller (220) can be used to determine the resistance (Rs) of the temperature sensor (13) by determining the output voltage (Vo) using an integrated analog-to-digital converter. Once the output voltage (Vo) is determined, the microcontroller can calculate the resistance (Rs) as follows.

[0122] The current (I) through the reference resistor (51) is equal to Vo divided by Rr (i.e., I = Vo / Rr). The current (I) passing through the temperature sensor (13) is equal to the difference between the supply voltage (Vcc) and the output voltage (Vo) divided by the resistance (Rs) of the temperature sensor (13) (i.e., I = (Vcc - Vo) / Rs). Assuming that the current (I) through the temperature sensor (13) is equal to the current (I) through the reference resistor (51), an equation for the resistance (Rs) is provided by making the two aforementioned equations equal and rearranging them:

[0123] Rs = Rr x (Vcc - Vo) / Vo

[0124] Once Rs is determined, the temperature of the temperature sensor (13) and the susceptor accordingly can be determined by applying a function related to temperature and resistance or by using a lookup table of resistance and corresponding temperature values.

[0125] In the test, the temperature sensor (13) of FIG. 1 has a nominal resistance of 10.5 Ω at 23°C and 0.00288 K -1 It was found to have a resistance temperature coefficient of (Cu: 0.00386 K -1 (Compared to the theoretical value for ). This showed an approximate linear relationship between temperature and resistance over a temperature range of 0 to 200℃.

Claims

Claim 1 An inductive heater assembly for an aerosol generator comprises: at least one inductor coil configured to generate a variable magnetic field when a variable current flows through at least one inductor coil; at least one susceptor arranged to be penetrated by the variable magnetic field generated by the at least one inductor coil to heat the susceptor; and at least one temperature sensor arranged to determine the temperature of the at least one susceptor, wherein the at least one temperature sensor comprises a first resistance sensing element and a second resistance sensing element, the first resistance sensing element is connected to the second resistance sensing element, and the first resistance sensing element is positioned relative to the second resistance sensing element such that a current induced in the first resistance sensing element by the variable magnetic field is opposed to a current induced in the second resistance sensing element by the variable magnetic field, and the first resistance sensing element and the second resistance sensing element each comprise a resistive wire having a first end and a second end, respectively, arranged adjacent to each other along the length of each, and the first resistance sensing element and the second resistance sensing element are wound together to form a bifiler coil. Inductive heater assembly. Claim 2 delete Claim 3 delete Claim 4 An inductive heater assembly, wherein each circuit of the bifiler coil is spaced apart from its adjacent circuit. Claim 5 An inductive heater assembly according to claim 1 or 4, wherein the first and second resistance sensing elements are electrically connected in series at their respective second ends. Claim 6 In claim 1 or 4, the temperature sensor is an inductive heater assembly arranged around at least a portion of the outer surface of the susceptor. Claim 7 An inductive heater assembly according to claim 6, wherein the length of the temperature sensor is less than 50% of the length of the susceptor. Claim 8 In paragraph 6, the temperature sensor is an inductive heater assembly extending along the entire length of the susceptor. Claim 9 In claim 1 or 4, the temperature sensor is an inductive heater assembly in contact with the susceptor. Claim 10 An inductive heater assembly according to claim 1 or 4, wherein the inductive heater assembly comprises a plurality of inductor coils and a separate temperature sensor is provided for each of the inductor coils. Claim 11 An aerosol generating device comprising: an inductive heater assembly according to claim 1 or 4; a control circuit; and a power source; wherein the control circuit is configured to control the supply of current from the power source to the inductive heater assembly to controllably heat the susceptor; and wherein the control circuit is configured to determine the temperature of the susceptor by connecting to at least one temperature sensor of the inductive heater assembly and determining the resistance of the at least one temperature sensor. Claim 12 An aerosol generating device according to claim 11, wherein the at least one temperature sensor is connected in series with a reference resistor to form a potential divider, and the output signal from the at least one temperature sensor is taken from a connection point between the at least one temperature sensor and the reference resistor. Claim 13 An aerosol generating device according to claim 11, wherein the control circuit further comprises a capacitor that filters an output signal from at least one temperature sensor to reduce noise in the output signal. Claim 14 In paragraph 13, the above capacitor is connected in parallel across a reference resistor, an aerosol generating device. Claim 15 In paragraph 13, the aerosol generating device wherein the capacitor is configured to reduce noise in the frequency range of the variable magnetic field.

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