HEATER FOR AEROSOL FORMING SUBSTRATE COMPRISING POSITIVE TEMPERATURE COEFFICIENT THERMISTOR - Patent application

Abstract

A heater (10) for heating an aerosol-forming substrate. The heater (10) includes a heating element configured to heat the aerosol-forming substrate, the heating element including at least one PTC thermistor (24, 25, 260, 261, 262, 263, 264, 265, 27). The resistance of the at least one PTC thermistor (24, 25, 260, 261, 262, 263, 264, 265, 27) increases as the temperature of the at least one PTC thermistor (24, 25, 260, 261, 262, 263, 264, 265, 27) increases within a stabilization temperature range. The lower end of the stabilization temperature range is a reference temperature (CT) at which the resistance of the at least one PTC thermistor (24, 25, 260, 261, 262, 263, 264, 265, 27) is twice the value of the lowest resistance of the at least one PTC thermistor (24, 25, 260, 261, 262, 263, 264, 265, 27).

Description

[Technical field]

[0001] The present invention relates to a heater for heating an aerosol-forming substrate, and to an aerosol generating device and an aerosol generating system including the heater. [Background technology]

[0002] Aerosol-generating articles in which an aerosol-forming substrate, such as a tobacco-containing substrate, is heated rather than combusted are known in the art. The purpose of such heated aerosol-generating articles is to reduce the potentially harmful by-products produced by the combustion and thermal decomposition of tobacco in conventional cigarettes.

[0003] In heated aerosol-generating articles, inhalable aerosols are typically generated by heat transfer from a heater to an aerosol-forming substrate. During heating, volatile compounds are released from the aerosol-forming substrate and entrained in the air. For example, volatile compounds may be entrained in air that passes through, passes through, around, or is otherwise drawn near the aerosol-generating article. As the released volatile compounds cool, they condense to form an aerosol. The aerosol can be inhaled by a user. The aerosol can contain aromas, flavors, nicotine, and other desirable elements.

[0004] The heating element may be included in an aerosol generating device. The combination of the aerosol generating article and the aerosol generating device may form an aerosol generating system.

[0005] The heating element may be a resistive heating element that may be inserted into or disposed around the aerosol-forming substrate when the article is received in the aerosol generating device. However, it may be difficult to adjust the temperature of the resistive heating element to provide the desired heating profile, as the resistive heating element may exhibit a slow thermal response. It may also be difficult to avoid the possibility of overheating without providing additional elements.

[0006] It would be desirable to provide a heater whose operating temperature can be controlled in an efficient manner. It would also be desirable to provide a heater whose operating temperature is limited by the heater's configuration. Summary of the Invention

[0007] A heater for heating an aerosol-forming substrate is provided. The heater may comprise a heating element configured to heat the aerosol-forming substrate. The heating element may include at least one positive temperature coefficient (PTC) thermistor. The resistance of the at least one PTC thermistor may increase as the temperature of the at least one PTC thermistor increases within a stabilization temperature range. The lower end of the stabilization temperature range may be a reference temperature at which the resistance of the at least one PTC thermistor is twice the value of the lowest resistance of the at least one PTC thermistor.

[0008] In the disclosure, a heater for heating an aerosol-forming substrate is provided, the heater comprising a heating element configured to heat the aerosol-forming substrate, the heating element comprising at least one PTC thermistor such that the resistance of the at least one PTC thermistor increases as the temperature of the at least one PTC thermistor increases within a stabilization temperature range, the lower end of the stabilization temperature range being a reference temperature at which the resistance of the at least one PTC thermistor is twice the value of the minimum resistance of the at least one PTC thermistor.

[0009] The heating element may comprise at least one PTC thermistor. The at least one PTC thermistor is a thermally sensitive resistor that can be heated when an electric current is supplied to the at least one PTC thermistor. When the at least one PTC thermistor is heated, the temperature and resistance of the at least one PTC thermistor can change according to a function related to both parameters. The at least one PTC thermistor can have a good thermal response when the temperature changes according to such a function. Thus, the operating temperature of the at least one PTC thermistor can be controlled in an efficient manner. In particular, the at least one PTC thermistor may be heated to a temperature corresponding to a minimum resistance of the at least one PTC thermistor.

[0010] Similarly, the at least one PTC thermistor may be heated to a temperature corresponding to twice the minimum resistance of the at least one PTC thermistor. If the at least one PTC thermistor is heated to a temperature higher than the temperature corresponding to twice the minimum resistance of the at least one PTC thermistor, the resistance of the at least one PTC thermistor increases as the temperature of the at least one PTC thermistor increases within the stabilization temperature range. The stabilization temperature range is therefore bounded by a lower end corresponding to a temperature at which the resistance of the at least one PTC thermistor is twice the value of the minimum resistance of the at least one PTC thermistor. This lower end of the stabilization temperature range is usually called the reference temperature of the at least one PTC thermistor. Within the stabilization temperature range, as the temperature of the at least one PTC thermistor increases, the increase in the resistance of the at least one PTC thermistor is sufficiently sharp to allow a very slow fluctuation of the temperature of the at least one PTC thermistor. It should be noted that as used herein, a "stabilized temperature range" should be interpreted as the range of temperatures of a PTC thermistor over which the temperature is not necessarily constant, even though changes in temperature of the PTC thermistor are negligible relative to changes in the resistance of the PTC thermistor.

[0011] Thus, the at least one PTC thermistor may be stabilized at substantially a reference temperature (or just above the reference temperature) within the stabilization temperature range for a period that may be longer than the normal operating period of an aerosol-generating device that includes a heater of the present disclosure, thereby providing a more consistent heating profile of the aerosol-forming substrate, where the maximum temperature of the heating element during the operating period can be determined and controlled by providing an appropriate PTC thermistor.

[0012] The reference temperature may correspond substantially to the Curie temperature of a dielectric PTC thermistor, such as a semiconducting ceramic, which is typically defined as the threshold temperature above which a particular material transitions from ferroelectric to paraelectric.

[0013] A heating element including at least one PTC thermistor may be less susceptible to overheating because the temperature of the at least one PTC thermistor does not significantly exceed a reference temperature, and by providing the PTC thermistor with a reference temperature below such threshold, the heater may not require additional dedicated elements to reduce the potentially damaging effects of temperatures above a given temperature threshold.

[0014] Because the reference temperature can be an inherent property of the at least one PTC thermistor, the heater may not require a dedicated element, such as a sensor, to measure and regulate the temperature of the heating element. Thus, even in the absence of such a dedicated element, the heating element can be configured to operate at a maximum temperature that does not substantially exceed the reference temperature of the at least one PTC thermistor.

[0015] The heater may comprise an external heating element, and at least one PTC thermistor is included in the external heating element. As used herein, the term "external heating element" refers to a heating element configured to heat an outer surface of the aerosol-forming substrate. The external heating element may at least partially surround a cavity for receiving the aerosol-forming substrate.

[0016] The heater may include an internal heating element, and at least one PTC thermistor is included within the internal heating element. As used herein, the term "internal heating element" refers to a heating element configured to be inserted into the aerosol-forming substrate. The internal heating element may be in the form of a blade, a pin, and a cone. The internal heating element may extend into a cavity for receiving the aerosol-forming substrate.

[0017] In some embodiments, the heater includes an internal heating element and an external heating element.

[0018] The heater is configured to heat the aerosol-forming substrate.

[0019] As used herein, the term "aerosol-forming substrate" refers to a substrate capable of releasing volatile compounds capable of forming an aerosol. Such volatile compounds may be released by heating the aerosol-forming substrate. The aerosol-forming substrate is typically part of an aerosol-generating article.

[0020] The aerosol-forming substrate may comprise nicotine. The nicotine-containing aerosol-forming substrate may be a nicotine salt matrix.

[0021] The aerosol-forming substrate may be a liquid. The aerosol-forming substrate may comprise a solid component and a liquid component. The aerosol-forming substrate is preferably a solid.

[0022] The aerosol-forming substrate may comprise a plant-derived material. The aerosol-forming substrate may comprise tobacco. The aerosol-forming substrate may comprise a tobacco-containing material comprising volatile tobacco flavour compounds that are released from the aerosol-forming substrate upon heating. The aerosol-forming substrate may comprise a non-tobacco material. The aerosol-forming substrate may comprise a homogenised plant-derived material. The aerosol-forming substrate may comprise a homogenised tobacco material. The homogenised tobacco material may be formed by agglomerating particulate tobacco. In a particularly preferred embodiment, the aerosol-forming substrate comprises an assembly of crimped sheets of homogenised tobacco material. As used herein, the term "crimped sheet" means a sheet having a plurality of substantially parallel ridges or corrugations.

[0023] The aerosol-forming substrate may include at least one aerosol former. The aerosol former is any suitable known compound or mixture of compounds that facilitates the formation of a dense, stable aerosol during use and is substantially resistant to thermal decomposition at the operating temperature of the system. Suitable aerosol formers are well known in the art and include, but are not limited to, polyhydric alcohols (such as triethylene glycol, 1,3-butanediol, glycerin, etc.), esters of polyhydric alcohols (such as glycerol monoacetate, diacetate, or triacetate, etc.), and aliphatic esters of mono-, di-, or polycarboxylic acids (such as dimethyl dodecanedioate, dimethyl tetradecanedioate, etc.). Preferred aerosol formers may include polyhydric alcohols or mixtures thereof (such as triethylene glycol, 1,3-butanediol, etc.). Preferably, the aerosol former is glycerin. When present, the homogenized tobacco material may have an aerosol former content of about 5 weight percent or more on a dry weight basis, for example, from about 5 weight percent to about 30 weight percent on a dry weight basis. The aerosol-forming substrate may contain other additives and ingredients such as flavourings.

[0024] The reference temperature of the at least one PTC thermistor can be from about 100 degrees Celsius to about 350 degrees Celsius when a constant voltage of 3.3 volts is applied to the at least one PTC thermistor.

[0025] This range of reference temperatures may be beneficial for heating the aerosol-forming substrate sufficiently to release certain substances that may be contained in the aerosol-forming substrate, such as nicotine or processed tobacco.

[0026] More preferably, the reference temperature of the at least one PTC thermistor may be between about 200 degrees Celsius and about 250 degrees Celsius.

[0027] This range of reference temperatures may be sufficient to heat the aerosol-forming substrate sufficiently to release certain substances that may be contained in the aerosol-forming substrate, such as, for example, nicotine-containing e-liquids and gel-like substances.

[0028] The heating element may be configured to be inserted into the aerosol-forming substrate.

[0029] In other words, the heating element may be an internal heating element. The internal heating element may penetrate the aerosol-forming substrate. The internal heating element may also be received in an internal cavity of the aerosol-forming substrate. The heater may comprise a cavity for receiving the aerosol-forming substrate when the internal heating element is inserted into the aerosol-forming substrate. When an electric current is supplied to the internal heating element, the temperature of the internal heating element rises until it reaches a reference temperature of at least one PTC thermistor contained in the internal heating element. If the supply of electric current is maintained after this moment, the temperature of the internal heating element stabilizes at a temperature that substantially corresponds to the reference temperature of at least one PTC thermistor contained in the internal heating element. Thus, the internal heating element may be used to heat the aerosol-forming substrate substantially to the reference temperature of the at least one PTC thermistor. The reference temperature may be adjusted to optimize the release of volatile compounds from the substrate.

[0030] The heating element may be configured to heat the outer surface of the aerosol-forming substrate.

[0031] In other words, the heating element may be an external heating element. The external heating element may comprise a cavity for receiving the aerosol-forming substrate. The cavity may include an inner wall configured to be in thermal contact with the outer surface of the aerosol-forming substrate. When an electric current is supplied to the external heating element, the temperature of the external heating element rises until it reaches a reference temperature of at least one PTC thermistor contained in the external heating element. If the supply of electric current is maintained after this moment, the temperature of the external heating element stabilizes at a temperature that substantially corresponds to the reference temperature of at least one PTC thermistor contained in the external heating element. Thus, the external heating element may be used to heat the aerosol-forming substrate substantially at the reference temperature of the at least one PTC thermistor. The reference temperature may be adjusted to optimize the release of volatile compounds from the substrate.

[0032] The heater may comprise a heater housing having a peripheral portion extending transversely between a peripheral inner wall and a peripheral outer wall, and a bottom portion extending longitudinally between a bottom inner wall and a bottom outer wall, the cavity being for receiving an aerosol-forming substrate extending longitudinally between the open end and the bottom inner wall, the cavity being bounded transversely by the peripheral inner wall.

[0033] The peripheral and bottom inner walls may have suitable dimensions and shapes to define a cavity for receiving the aerosol-forming substrate such that the transfer of heat from the heating element to the aerosol-forming substrate may be optimized.

[0034] The at least one PTC thermistor may be a PTC disc disposed within the base.

[0035] This may allow for a heater that is easy to manufacture and assemble, while still providing a satisfactory heating profile for the aerosol-forming substrate when the substrate is received within the cavity of the heater housing. In this embodiment, the temperature of the peripheral inner wall may not be significantly different from the temperature of the PTC disk. Thus, adequate transfer of heat between the PTC disk and the aerosol-forming substrate may be achieved.

[0036] The at least one PTC thermistor may comprise a PTC tube disposed within the peripheral portion so as to surround the inner peripheral wall.

[0037] In this arrangement, the temperature of the peripheral inner wall may be substantially the same as the temperature of the PTC tube, which may result in enhanced heat transfer between the PTC tube and the aerosol-forming substrate.

[0038] The peripheral outer wall includes at least one PTC thermistor including at least three planar sections, at least one PTC plate disposed on at least one of the at least three planar sections.

[0039] The provision of at least three planar sections on the peripheral outer wall may be advantageous in that the at least one PTC plate, which may be easy to manufacture, may be arranged on one or more planes of the at least three planar sections. This arrangement may result in optimized heat transfer from the at least one PTC plate to the aerosol-forming substrate when the substrate is received within the cavity of the heater housing. The PTC plate is planar.

[0040] The peripheral wall may define, in cross section, a regular or irregular polygon, hi one embodiment, the polygon is one of a triangle, a rectangle, a square, a pentagon, and a hexagon.

[0041] The at least one PTC thermistor may include at least three PTC plates, each of the at least three PTC plates being disposed on a different planar section, such that the number of PTC plates is equal to the number of planar sections.

[0042] In this embodiment, a PTC plate is disposed on each planar section, which may contribute to improving the transfer of heat from the PTC plate to the aerosol-forming substrate when the substrate is received within the cavity of the heater housing.

[0043] At least two of the at least three PTC plates may have different reference temperatures.

[0044] This can be useful for heating different sections of the aerosol-forming substrate to different temperatures when the substrate is received within the cavity of the heater housing. This can be used to provide sequential heating to different sections of the aerosol-forming substrate, which may help reduce the mass of evaporated aerosol that can occur due to depletion of the substrate in contact with the heater housing.

[0045] The at least three PTC plates may be electrically connected in parallel with each other.

[0046] This may reduce the overall electrical resistance of the heater and therefore increase power consumption when using small size batteries, such as batteries having a voltage of 3.0 volts to 6.0 volts.

[0047] The peripheral outer wall may comprise six planar sections.

[0048] It has been found that an arrangement having six planar sections may provide a compromise between optimal transfer of heat from the PTC plate to the aerosol-forming substrate when the substrate is received within the cavity of the heater housing and ease of fabrication of the planar sections.

[0049] The heater housing may comprise a conductive material, such as a conductive metal, and the heater housing forms a first electrode in electrical contact with the at least one PTC plate. The heater may further comprise at least one external electrical contact, comprising a conductive material, such as a conductive metal, and forming a second electrode in electrical contact with the at least one PTC plate.

[0050] By using the heater housing as the first electrode of at least one PTC plate, the current supply can be integrated into the heater in a more compact manner. The conductive material contained within the housing may be a metal, such as aluminum.

[0051] Similarly, at least one external electrical contact is advantageous in that it may allow for an easy-to-assemble arrangement for the current supply.

[0052] In an embodiment in which the PTC thermistor comprises at least three PTC plates, such that each of the at least three PTC plates is disposed on a different planar section, at least three external electrical contacts may be provided, each external electrical contact being in electrical contact with a different PTC plate. This arrangement may allow for an adequate current supply to the at least three PTC plates. In particular, in an embodiment including six PTC plates, and therefore six external electrical contacts, it may be possible to reach a temperature substantially equal to the reference temperature of each PTC plate in 30 seconds.

[0053] In one embodiment, the at least one PTC plate may have a length of about 7 millimeters. The at least one PTC plate may have a width of about 3.8 millimeters. The at least one PTC plate may have a thickness of about 0.5 millimeters.

[0054] The at least one PTC thermistor may include a ceramic semiconductor such as barium titanate.

[0055] Providing a suitable ceramic semiconductor may allow for tuning of the reference temperature of the at least one PTC thermistor. When the at least one PTC thermistor is made from a ceramic semiconductor, the reference temperature of the PTC semiconductor may correspond substantially to the Curie temperature of the ceramic semiconductor.

[0056] The at least one PTC thermistor may comprise a polymeric material.

[0057] The provision of a polymeric material may be advantageous in that it allows for simplified assembly of at least one PTC thermistor within the heater due to the high flexibility that some polymeric materials may have. This may also lead to a less fragile heater. This may also produce a heater with a lower thermal mass, which may result in lower thermal latency during heating.

[0058] The polymeric material may include polyethylene. The polymeric material may include carbon particles, carbon ink, or other suitable conductive grains. The carbon particles may include carbon black. The carbon particles may include nickel powder.

[0059] The polymeric material may include a polymeric film.

[0060] The heater may include a laminate backing that may be attached directly to the polymeric film. The laminate backing may include a metal such as copper.

[0061] The at least one PTC thermistor may include a blend of barium titanate and an alkaline earth metal element, such as strontium or bismuth element. The at least one PTC thermistor may include a blend of barium titanate and lead titanate. These blends may allow for additional adjustment of the reference temperature of the at least one PTC thermistor.

[0062] Additionally, an additive may be added to the at least one PTC thermistor to adjust the reference temperature of the at least one PTC thermistor to a desired level.

[0063] Provided in the disclosure is an aerosol-generating device that includes any of the heaters disclosed above. As used herein, the term "aerosol-generating device" refers to a device that interacts with an aerosol-forming substrate to generate an aerosol.

[0064] Since the aerosol generating device of the present disclosure includes a heater according to the previous disclosure, the advantages identified above for the heater also apply to the device itself.

[0065] The aerosol generating device may comprise a device housing. The device housing may at least partially define a cavity for receiving the aerosol-forming substrate. The cavity for receiving the aerosol-forming substrate is preferably at a proximal end of the device.

[0066] The device housing may be elongated. The device housing is preferably cylindrical in shape. The device housing may comprise any suitable material or combination of materials. Examples of suitable materials include metals, alloys, plastics, or composites containing one or more of these materials, or thermoplastics suitable for food or pharmaceutical applications, such as polypropylene, polyetheretherketone (PEEK), and polyethylene. Preferably, the material is light and not brittle.

[0067] The aerosol generating device is preferably portable. The aerosol generating device may have a size comparable to a conventional cigar or cigarette. The aerosol generating device may have an overall length of about 30 mm to about 150 mm. The aerosol generating device may have an outer diameter of about 5 mm to about 30 mm. The aerosol generating device may be a handheld device. In other words, the aerosol generating device may be sized and shaped to be held in a user's hand.

[0068] The aerosol generating device may include a power source configured to provide electrical current to the heating element.

[0069] The power source may be a DC power source. In a preferred embodiment, the power source is a battery. The power source may be a nickel metal hydride battery, a nickel cadmium battery, or a lithium-based battery (e.g., lithium cobalt, lithium iron phosphate, or lithium polymer battery). However, in some embodiments, the power source may be another form of charge storage device, such as a capacitor. The power source may require recharging and may have a capacity that allows for storage of sufficient energy for one or more user actions. For example, the power source may have a capacity sufficient to allow continuous heating of the aerosol-forming substrate for approximately six minutes, or a multiple of six minutes, corresponding to the typical time it takes to smoke one conventional cigarette. In another example, the power source may have a capacity sufficient to allow a predetermined number of puffs or discontinuous activation of the aerosol generator. In another example, the power source may have a capacity sufficient to allow a predetermined number of uses of the device or discontinuous activation. In one embodiment, the power supply is a DC power supply having a DC supply voltage in the range of about 2.5 volts to about 4.5 volts, and a DC supply current in the range of about 1 amp to about 10 amps (corresponding to a DC power supply in the range of about 2.5 watts to about 45 watts).

[0070] The aerosol generating device may include a controller connected to the heating element and a power source. The controller may be configured to control the power supply from the power source to the heating element. The controller may include a microprocessor, which may be a programmable microprocessor, a microcontroller, or an application specific integrated circuit chip (ASIC) or other electronic circuit capable of providing control. The controller may include further electronic components. The controller may be configured to regulate the current supply to the heating element. Current may be supplied to the heating element continuously following activation of the aerosol generating device, or may be supplied intermittently, such as between puffs.

[0071] The controller may advantageously include a DC / AC inverter, which may include a class D or class E power amplifier.

[0072] In some embodiments, the device housing includes a mouthpiece. The mouthpiece may comprise at least one air inlet and at least one air outlet. The mouthpiece may comprise two or more air inlets. One or more of the air inlets may reduce the temperature of the aerosol before it is delivered to the user and may reduce the concentration of the aerosol before it is delivered to the user.

[0073] In some embodiments, a mouthpiece is provided as part of the aerosol-generating article. As used herein, the term "mouthpiece" refers to a portion of an aerosol-generating system that is placed into the mouth of a user to directly inhale aerosol generated by the aerosol-generating system from an aerosol-generating article received by the aerosol generating device.

[0074] The aerosol generating device may include a user interface for activating the device, for example a button to initiate heating of the aerosol generating article.

[0075] The aerosol generating device may include a display that indicates the status of the device or the aerosol-forming substrate.

[0076] The disclosure provides an aerosol generating system comprising any of the above-mentioned aerosol generating devices, the aerosol generating system further comprising an aerosol-generating article comprising an aerosol-forming substrate.

[0077] As used herein, the term "aerosol-generating article" refers to an article that includes an aerosol-forming substrate capable of releasing a volatile compound capable of forming an aerosol. For example, the aerosol-generating article may be an article that generates an aerosol that can be directly inhaled by a user sucking or puffing on a mouthpiece at the proximal or user end of the system. The aerosol-generating article may be disposable.

[0078] As used herein, the term "aerosol generating system" refers to the combination of an aerosol-generating article and an aerosol-generating device that work together to generate a respirable aerosol.

[0079] Because the aerosol generating system of the present disclosure includes a heater according to the foregoing disclosure, the advantages identified above for the heater also apply to the system itself.

[0080] 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 the length.

[0081] The aerosol-forming substrate may be provided as an aerosol-generation segment containing the aerosol-forming substrate. The aerosol-generation segment may comprise a plurality of aerosol-forming substrates. The aerosol-generation segment may comprise 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.

[0082] The aerosol-generation segment may be substantially cylindrical in shape. The aerosol-generation segment may be substantially elongated. The aerosol-generation segment may also have a length and a circumference substantially perpendicular to the length.

[0083] Where the aerosol-generation segment comprises more than one aerosol-forming substrate, the aerosol-forming substrates may be arranged end-to-end along the axis of the aerosol-generation segment, hi some embodiments, the aerosol-generation segment may comprise separations between adjacent aerosol-forming substrates.

[0084] In some preferred embodiments, the aerosol-generating article may have an overall length of about 30 millimeters to about 100 millimeters. In some embodiments, the aerosol-generating article has an overall length of about 45 millimeters. The aerosol-generating article may have an outer diameter of about 5 millimeters to about 12 millimeters. In some embodiments, the aerosol-generating article may have an outer diameter of about 7.2 millimeters.

[0085] The aerosol-generation segment may have a length of about 7 millimeters to about 15 millimeters, in some embodiments, the aerosol-generation segment may have a length of about 10 millimeters or about 12 millimeters.

[0086] The aerosol-generation segment preferably has an outer diameter approximately equal to the outer diameter of the aerosol-generating article. The outer diameter of the aerosol-generation segment may be from about 5 millimeters to about 12 millimeters. In one embodiment, the aerosol-generation segment may have an outer diameter of about 7.2 millimeters.

[0087] The aerosol-generating article may include a filter plug. The filter plug may be located at a 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 millimeters to about 10 millimeters. In some preferred embodiments, the filter plug may have a length of about 7 millimeters.

[0088] The aerosol-generating article may comprise an outer wrapper. The outer wrapper may be formed from paper. The outer wrapper may be gas permeable in the aerosol-generating segment. In particular in embodiments including a plurality of aerosol-forming substrates, the outer wrapper may include perforations or other air inlets at the joints between adjacent aerosol-forming substrates. If a separation is provided between adjacent aerosol-forming substrates, the outer wrapper may include perforations or other air inlets at the separation. This may allow the aerosol-forming substrate to be provided directly with air that has not been drawn through another aerosol-forming substrate. This may increase the amount of air received by each aerosol-forming substrate. This may improve the characteristics of the aerosol generated from the aerosol-forming substrate.

[0089] The aerosol-generating article may also include a separation between the aerosol-forming substrate and the filter plug, which may be about 18 millimeters, but may be in the range of about 5 millimeters to about 25 meters.

[0090] Disclosure provides a method of operating any of the above aerosol generating systems. The method may include determining a maximum operating temperature of an aerosol-forming substrate included in the aerosol-generating article. The method may include supplying, by a power source, a current having a constant voltage to at least one PTC thermistor. The constant voltage may be such that a reference temperature of the PTC thermistor is substantially the maximum operating temperature of the aerosol-forming substrate.

[0091] The present disclosure provides a method of operating any of the above aerosol generating systems, the method comprising: - determining a maximum operating temperature of an aerosol-forming substrate included in the aerosol-generating article; - supplying an electric current by a power source to at least one PTC thermistor, the electric current having a constant voltage, the constant voltage being such that a reference temperature of the PTC thermistor is substantially the maximum operating temperature of the aerosol-forming substrate.

[0092] These steps may be controlled by a controller. The aerosol-generating device may comprise the controller. Alternatively, the controller may be provided in a device external to the aerosol-generating system, such as a computer or a mobile phone. The controller may be configured to detect the type of aerosol-forming substrate in the aerosol-generating system. The controller may store a maximum operating temperature for each type of aerosol-forming substrate to enhance the formation of the aerosol when the aerosol-forming substrate is heated. The controller may be configured to receive external data to determine the maximum operating temperature of the aerosol-forming substrate. The controller may determine the maximum operating temperature of the aerosol-forming substrate using any other suitable configuration.

[0093] The resistance of the at least one PTC thermistor may depend on the grain resistance and grain boundary transition resistance of the grains forming the material contained in the at least one PTC thermistor. The higher the voltage applied to the at least one PTC thermistor, the lower the resistance of the at least one PTC thermistor. The decrease in the resistance of the at least one PTC thermistor with a higher voltage may be more significant at temperatures higher than the reference temperature of the at least one PTC thermistor, since the breakdown of the barrier between the grains may be more likely, and similarly, a portion of the applied voltage may not be absorbed by the grain resistance. However, it has been found that the decrease in the resistance of the at least one PTC thermistor with an increased voltage may be more significant at temperatures below the reference temperature or the reference temperature of the at least one PTC thermistor. Due to this effect, it has been found that the reference temperature of the at least one PTC thermistor may depend on the voltage applied to the at least one PTC thermistor.

[0094] The method of the present disclosure may advantageously utilize variation of the reference temperature of the at least one PTC thermistor with a voltage applied to the at least one PTC thermistor. To accomplish this, the controller may control the power source to supply a current to the at least one PTC thermistor with a constant voltage. The constant voltage selected may be determined by the controller to ensure that the reference temperature of the PTC thermistor is substantially the maximum operating temperature of the aerosol-forming substrate. The controller may store a table relating the voltage applied to the at least one PTC thermistor to the reference temperature of the at least one PTC thermistor.

[0095] Thus, the method of the present disclosure may enable at least one PTC thermistor of the aerosol-generating system to be substantially stabilized at the maximum operating temperature of the aerosol-forming substrate. The temperature at which the at least one PTC thermistor stabilizes is substantially the same as or sufficiently close to the temperature applied to the aerosol-forming substrate when the aerosol-generating system is used to heat the aerosol-forming substrate. Thus, the temperature at which the PTC thermistor stabilizes may be selected to optimize the formation of the aerosol. This may be beneficial for providing an optimized aerosol experience.

[0096] In the disclosure, a method of operating any of the above aerosol generating systems is provided. The method may include measuring a puff intensity when a puff is drawn during use of the aerosol generating system. The method may include determining a puff intensity threshold. When the puff intensity is equal to or greater than the puff intensity threshold, the method may include determining a first maximum operating temperature and a second maximum operating temperature of an aerosol-forming substrate included in the aerosol-generating article. The method may include selecting the first maximum operating temperature or the second maximum operating temperature. When the first maximum operating temperature is selected, the method may include supplying a current by a power source to at least one PTC thermistor, the current having a first constant voltage, and the first constant voltage is such that a reference temperature of the PTC thermistor is substantially the first maximum operating temperature of the aerosol-forming substrate. When the second maximum operating temperature is selected, the method may include supplying a current by a power source to at least one PTC thermistor, the current having a second constant voltage, and the second constant voltage is such that a reference temperature of the PTC thermistor is substantially the second maximum operating temperature of the aerosol-forming substrate.

[0097] The present disclosure provides a method of operating any of the above aerosol generating systems, the method comprising: - measuring the intensity of a puff as the puff is drawn during use of the aerosol generating system; determining a puff intensity threshold, when the puff intensity is equal to or exceeds the puff intensity threshold, the method further comprising: - determining a first maximum operating temperature and a second maximum operating temperature of an aerosol-forming substrate included in the aerosol-generating article; - selecting a first maximum operating temperature or said second maximum operating temperature, - if a first maximum operating temperature is selected, supplying a current by a power source to at least one PTC thermistor, the current having a first constant voltage, the first constant voltage being supplied such that a reference temperature of the PTC thermistor is substantially the first maximum operating temperature of the aerosol-forming substrate; - if a second maximum operating temperature is selected, supplying a current by a power source to at least one PTC thermistor, the current having a second constant voltage, the second constant voltage being supplied such that a reference temperature of the PTC thermistor is substantially the second maximum operating temperature of the aerosol-forming substrate.

[0098] As explained with respect to the method of the previous disclosure, variation of the reference temperature of the at least one PTC thermistor may be achieved by varying the voltage applied to the at least one PTC thermistor, thereby allowing the reference temperature to be adjusted to substantially correspond to the maximum operating temperature of the aerosol-forming substrate, thus optimizing the formation of the aerosol.

[0099] For some aerosol-forming substrates, it may be advantageous to vary the maximum operating temperature, thereby allowing the formation of the aerosol to be tailored to a given aerosol experience, which may be selected according to the preferences of a user of the aerosol generating system.

[0100] However, as shown in the previously disclosed methods, the variation in the reference temperature of the at least one PTC thermistor by varying the voltage applied to the at least one PTC thermistor may be relatively small, in other words, the presently disclosed methods may allow for variation in the reference temperature of the at least one PTC thermistor within a typically small temperature range.

[0101] The method of the present disclosure includes measuring a puff intensity as a puff is drawn during use of the aerosol generating system. The method also includes determining a puff intensity threshold. These steps may also be performed by a controller.

[0102] The controller may be configured to determine a reference temperature of the at least one PTC thermistor by determining a voltage applied to the at least one PTC thermistor only when the puff intensity is equal to or greater than the puff intensity threshold. When the puff intensity is less than the puff intensity threshold, the temperature of the at least one PTC thermistor may typically be a function of the puff intensity. The function may be stored in the controller.

[0103] When the puff intensity is equal to or greater than the puff intensity threshold, the controller may adjust a voltage applied to the at least one PTC thermistor to determine a reference temperature of the at least one PTC thermistor. The controller may control the power supply to supply a first constant voltage to the at least one PTC thermistor, the first constant voltage resulting in a first reference temperature of the at least one PTC thermistor. The controller may control the power supply to supply a second constant voltage, different from the first constant voltage, to the at least one PTC thermistor, the second constant voltage resulting in a second reference temperature of the at least one PTC thermistor. Preferably, the first reference temperature and the second reference temperature are equal to or greater than a temperature corresponding to a threshold puff intensity in a function relating the temperature of the at least one PTC thermistor and the puff intensity.

[0104] By limiting the adjustment of the reference temperature of the at least one PTC thermistor to puff intensities equal to or greater than the puff intensity threshold, the specific range of reference temperatures that can be achieved by varying the voltage supplied to the at least one PTC thermistor focuses on temperatures that may result in overheating of the aerosol generating device or the production of a lower quality aerosol. Even if the variation in the reference temperature of the at least one PTC thermistor within such a specific range is relatively small, the corresponding variation in the maximum operating temperature of the aerosol-forming substrate may advantageously allow substantial variation in the characteristics of the aerosol formed, thereby allowing an aerosol experience that may be optimized or customized. The control device may select the first reference temperature or the second reference temperature to achieve the desired characteristics in the aerosol formed.

[0105] Similarly, the first reference temperature and the second reference temperature of the PTC thermistor may be equal to or greater than a temperature corresponding to a puff intensity threshold of a function relating the temperature of the at least one PTC thermistor and the puff intensity, such that when a puff having an intensity below the puff intensity threshold is drawn, an aerosol generating system including at least one PTC thermistor may be configured to modify the temperature of the at least one PTC thermistor in accordance with such function without reaching a stabilization temperature range.

[0106] The methods of the present disclosure may also allow for the determination and selection of additional reference temperatures, such as a third reference temperature, a fourth reference temperature, a fifth reference temperature, a seventh reference temperature, an eighth reference temperature, a ninth reference temperature, a tenth reference temperature, or any other reference temperature.

[0107] Although the method disclosed above includes providing a constant voltage, the controller may also be configured to control the power supply to use pulse width modulation or pulse frequency modulation when current is supplied to the at least one PTC thermistor. In such a case, the resulting method is the same as the method disclosed above, except that it is the respective pulse width or pulse frequency that is associated with a given reference temperature of the at least one PTC thermistor. Thus, the reference temperature of the at least one PTC thermistor may be adjusted by adjusting the pulse width or pulse frequency of the current supplied to the at least one PTC thermistor.

[0108] These and other features and advantages of the present invention will become more apparent in the light of the following detailed description of preferred embodiments, given by way of illustrative and non-limiting example only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0109] [Figure 1] FIG. 1 shows a temperature / resistance diagram of a PTC thermistor contained in a heating element. [Diagram 2] FIG. 2 shows a longitudinal section of the heater including the heater housing and the PTC disc. [Diagram 3] FIG. 3 shows a longitudinal section of the heater including the heater housing and the PTC tube. [Figure 4] FIG. 4 depicts a longitudinal section of the heater including the heater housing and internal heating element. [Diagram 5] FIG. 5 then shows a perspective view of the heater housing which includes six planar sections. [Figure 6] FIG. 6 shows a cross section of the heater housing of FIG. [Figure 7] FIG. 7 shows a number of external electrical contacts. [Figure 8] FIG. 8 shows a perspective view of a heater including the heater housing of FIG. 5 and the multiple external electrical contacts of FIG. [Figure 9]FIG. 9 shows the temperature of the peripheral inner wall of four examples of the heater of FIG. [Figure 10] FIG. 10 shows an aerosol generating system including an aerosol generating article and an aerosol generating device equipped with the heater of FIG. [Figure 11] FIG. 11 illustrates the aerosol-generating system of FIG. 10 in which the aerosol-generating article is received within a cavity in the heater housing. [Figure 12] FIG. 12 illustrates an embodiment of an aerosol-generating article. [Figure 13] FIG. 13 represents the evolution of the temperature of the peripheral inner wall and of the temperature of the PTC tube of the heater of FIG. [Figure 14] FIG. 14 shows the evolution of the temperature of the peripheral inner wall and of the PTC disc of the heater of FIG. [Figure 15] FIG. 15 shows three temperature / resistance diagrams of a PTC thermistor contained in a heating element when three different constant voltages are applied to the PTC thermistor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0110] FIG. 1 shows a temperature T / resistance R diagram of a PTC thermistor included in a heating element of a heater for heating an aerosol-forming substrate.

[0111] When a current is applied to the PT thermistor, the PTC thermistor heats up. As the PTC thermistor heats up, its temperature T and resistance R change according to the functions shown in FIG.

[0112] In particular, the PTC thermistor may be heated to a temperature TMR that corresponds to the minimum resistance MR of the PTC thermistor.

[0113] When the PTC thermistor is heated to a temperature T below the temperature corresponding to the minimum resistance TMR, the resistance R of the PTC thermistor decreases slightly as the temperature T of the PTC thermistor increases, according to the function of Figure 1. For some PTC thermistors, the resistance R of the PTC thermistor remains substantially constant, at a resistance slightly above the minimum resistance MR of the PTC thermistor, until the temperature corresponding to the minimum resistance TMR of the PTC thermistor is reached.

[0114] Similarly, when a PTC thermistor is heated to a temperature T above the temperature corresponding to a minimum resistance TMR, the resistance R of the PTC thermistor increases as the temperature T of the PTC thermistor increases, according to the function of FIG.

[0115] If the PTC thermistor is heated to a temperature above the temperature corresponding to twice the minimum resistance TMR, the increase in the resistance of the PTC thermistor becomes very significant as the temperature of the PTC thermistor increases, and the temperature of the PTC thermistor is substantially stabilized at a temperature T corresponding to twice the minimum resistance MR. Such a temperature is usually referred to as the reference temperature CT of the PTC thermistor. In other words, the PTC thermistor has a high positive temperature coefficient a within a stabilized temperature range bounded at the lower end by the reference temperature CT. For a dielectric material, the reference temperature CT may substantially correspond to the Curie temperature of the dielectric material.

[0116] A temperature T substantially exceeding the reference temperature CT can be reached if a current is supplied to the PTC thermistor for a time sufficient to reach a maximum resistance of the PTC thermistor. However, it should be considered that FIG. 1 shows the resistance R on a logarithmic scale. Thus, the time period required to reach such a maximum resistance is generally substantially longer than a conventional operation time of a heater for heating an aerosol-forming substrate. This ensures that the PTC thermistor is effectively stabilized at a temperature that does not significantly exceed the reference temperature CT.

[0117] FIG. 2 shows the heater 10 comprising a heater housing 20. The heater housing 20 comprises a transversely extending peripheral portion 21 between a peripheral inner wall 210 and a peripheral outer wall 211. The heater housing 20 comprises a longitudinally extending bottom portion 22 between a bottom inner wall 220 and a bottom outer wall 221. A cavity 23 for receiving an aerosol-forming substrate extends longitudinally between an open end 230 of the heater housing 20 and the bottom inner wall 220, the cavity 23 being bounded transversely by the peripheral inner wall 210. In the embodiment of FIG. 2, the heater comprises a heating element formed of a PTC disk 24 arranged in the bottom portion 22. When an electric current is supplied to the PTC disk 24, the temperature of the PTC disk 24 increases until a reference temperature of the PTC disk 24 is reached. If the supply of electric current is maintained after this moment, the temperature of the PTC disk 24 stabilizes at a temperature that substantially corresponds to the reference temperature of the PTC disk 24. Thus, the peripheral inner wall 210 reaches a temperature that may not be significantly different from the temperature at which the PTC disc 24 stabilizes. Thus, when an aerosol-forming substrate is received within the cavity 23, the aerosol-forming substrate may be heated to the temperature of the peripheral inner wall 210 such that an inhalable aerosol is formed.

[0118] FIG. 3 shows a heater 10 comprising a heater housing 20. The heater housing 20 comprises a peripheral portion 21 extending transversely between a peripheral inner wall 210 and a peripheral outer wall 211. The heater housing 20 comprises a bottom portion 22 extending longitudinally between a bottom inner wall 220 and a bottom outer wall 221. A cavity 23 for receiving an aerosol-forming substrate extends longitudinally between an open end 230 of the heater housing 20 and the bottom inner wall 220, the cavity 23 being bounded transversely by the peripheral inner wall 210. In the embodiment of FIG. 3, the heater comprises a heating element formed from a PTC tube 25 arranged in the peripheral portion 21. When an electric current is supplied to the PTC tube 25, the temperature of the PTC tube 25 increases until it reaches a reference temperature of the PTC tube 25. If the supply of electric current is maintained after this moment, the temperature of the PTC tube 25 stabilizes at a temperature that substantially corresponds to the reference temperature of the PTC tube 25. Thus, the peripheral inner wall 210 reaches a temperature that substantially corresponds to the reference temperature of the PTC tube 25. Thus, when an aerosol-forming substrate is received in the cavity 23, the aerosol-forming substrate may be heated to a temperature that substantially corresponds to the reference temperature of the PTC tube 25 such that an inhalable aerosol is formed.

[0119] FIG. 4 shows the heater 10 comprising a heater housing 20. The heater housing 20 comprises a transversely extending peripheral portion 21 between a peripheral inner wall 210 and a peripheral outer wall 211. The heater housing 20 comprises a longitudinally extending bottom portion 22 between a bottom inner wall 220 and a bottom outer wall 221. A cavity 23 for receiving an aerosol-forming substrate extends longitudinally between an open end 230 of the heater housing 20 and the bottom inner wall 220, the cavity 23 being bounded transversely by the peripheral inner wall 210. In the embodiment of FIG. 4, the heater comprises a heating element formed of a PTC blade 27 extending longitudinally into the cavity 23 such that the PTC blade 27 is configured to penetrate the aerosol-forming substrate when the substrate is received in the cavity 23. When an electric current is supplied to the PTC blade 27, the temperature of the PTC blade 27 increases until it reaches a reference temperature of the PTC blade 27. If the supply of electric current is maintained after this moment, the temperature of the PTC blade 27 stabilizes at a temperature that substantially corresponds to the reference temperature of the PTC blade 27. The PTC blade 27 can therefore be used to heat an aerosol-forming substrate substantially at the reference temperature of the PTC blade, such that an inhalable aerosol is formed.

[0120] FIG. 5 shows a perspective view of the heater housing 20. The heater housing 20 comprises a transversely extending peripheral portion 21 between a peripheral inner wall 210 and a peripheral outer wall 211. The peripheral outer wall 211 comprises six planar sections 2110, 2111, 2112, 2113, 2114, 2115, configured such that at least one PTC plate can be arranged on at least one of the planar sections 2110, 2111, 2112, 2113, 2114, 2115. The PTC plates may be circular, square or polygonal plates. The plates are planar. FIG. 6 represents a cross section of the heater housing 20 of FIG. 5. A cavity 23 for receiving an aerosol-forming substrate extends longitudinally between an open end 230 and a bottom inner wall 220 (not represented in FIGS. 5 and 6), the cavity 23 being bounded transversely by the peripheral inner wall 210. In the embodiment of Figures 5 and 6, the cavity 23 bounded by the inner peripheral wall 210 is cylindrical, i.e. the inner peripheral wall 23 has a circular cross-section as shown in Figure 5. Such a shape may be convenient for receiving a cylindrical aerosol-forming substrate.

[0121] In a preferred embodiment, the heater housing 20 of FIGS. 5 and 6 comprises six PTC plates, one on each planar section 2110, 2111, 2112, 2113, 2114, 2115, thus forming the heater 10.

[0122] In one embodiment, the heater housing 20 comprises a conductive material, such as a conductive metal. The heater housing 20 then forms a first electrode that is configured to be in electrical contact with the six PTC plates.

[0123] The heater 10 may also include at least one external electrical contact 30 comprising an electrically conductive material, such as an electrically conductive metal, forming a second electrode configured to be in electrical contact with the six PTC plates. Figure 7 depicts the at least one external electrical contact 30 including six elongated external electrical contacts 310, 311, 312, 313, 314, 315, each configured to be in electrical contact with a PTC plate disposed on the planar sections 2110, 2111, 2112, 2113, 2114, 2115.

[0124] Figure 8 shows a heater 10 including the heater housing 20 of Figures 5 and 6 and the elongated external electrical contacts 310, 311, 312, 313, 314, 315 of Figure 7. Six PTC plates 260, 261, 262, 263, 264, 265 are provided, one on each planar section 2110, 2111, 2112, 2113, 2114, 2115. The six PTC plates 260, 261, 262, 263, 264, 265 form the heating element of the heater 10. The PTC plates 260, 261, 262, 263, 264, 265 are in electrical contact with the planar sections 2110, 2111, 2112, 2113, 2114, 2115 of the heater housing 20, such that the heater housing 20 serves as a first electrode for the PTC plates 260, 261, 262, 263, 264, 265. The elongated external electrical contacts 310, 311, 312, 313, 314, 315, which are in electrical contact with the PTC plates 260, 261, 262, 263, 264, 265, serve as second electrodes for the PTC plates 260, 261, 262, 263, 264, 265.

[0125] When current is supplied to the first and second electrodes, as shown in Figure 1, the temperature of the PTC plates 260, 261, 262, 263, 264, 265 increases until it reaches the reference temperature of the PTC plates 260, 261, 262, 263, 264, 265. After such a moment, the temperature of the PTC plates 260, 261, 262, 263, 264, 265 stabilizes substantially at the reference temperature of the PTC plates 260, 261, 262, 263, 264, 265 (or just above the reference temperature) for a period of time that is typically longer than the operation time of the aerosol generating device. This allows for a consistent and predictable heating profile of the aerosol-forming substrate when the substrate is received within cavity 23, where the maximum temperature during operation of each of PTC plates 260, 261, 262, 263, 264, 265 can be determined and controlled by selecting the reference temperatures of the PTC plates 260, 261, 262, 263, 264, 265. The PTC plates 260, 261, 262, 263, 264, 265 may have the same or different reference temperatures.

[0126] FIG. 9 illustrates the temperature of the peripheral inner wall 210 for four embodiments of the heater 10 of FIG. 8, where the reference temperatures of the six PTC plates 260, 261, 262, 263, 264, 265 are the same.

[0127] In the first embodiment CT190, the reference temperature of the six PTC plates 260, 261, 262, 263, 264, 265 is 190 degrees Celsius. When current is supplied to the first electrode and the second electrode, the six PTC plates 260, 261, 262, 263, 264, 265 reach the reference temperature of 190 degrees Celsius after about 30 seconds and stabilize at a temperature slightly above the reference temperature. Heat is transferred through the heater housing 20 so that the temperature of the inner wall 210 is substantially the same as the temperature of the six PTC plates 260, 261, 262, 263, 264, 265, i.e., slightly above 190 degrees Celsius, as shown in FIG. When an aerosol-forming substrate is received within cavity 23 after inner wall 210 has reached a temperature of substantially 190 degrees Celsius, this temperature is consistently applied to the aerosol-forming substrate during the operation of heater 10, thus forming an inhalable aerosol.

[0128] In the second embodiment CT200, the reference temperature of the six PTC plates 260, 261, 262, 263, 264, 265 is 200 degrees Celsius. When the first electrode and the second electrode are supplied with current, the six PTC plates 260, 261, 262, 263, 264, 265 reach the reference temperature of 200 degrees Celsius after about 30 seconds and stabilize at a temperature slightly above the reference temperature. Heat is transferred through the heater housing 20 so that the temperature of the inner wall 210 is substantially the same as the temperature of the six PTC plates 260, 261, 262, 263, 264, 265, i.e., slightly above 200 degrees Celsius, as shown in FIG. When an aerosol-forming substrate is contained within the cavity 23 after the inner wall 210 has reached a temperature of substantially 200 degrees Celsius, this temperature is consistently applied to the aerosol-forming substrate during the operating time of the heater 10, thus forming an inhalable aerosol.

[0129] In the third embodiment CT210, the reference temperature of the six PTC plates 260, 261, 262, 263, 264, 265 is 210 degrees Celsius. When the first electrode and the second electrode are supplied with current, the six PTC plates 260, 261, 262, 263, 264, 265 reach the reference temperature of 210 degrees Celsius after about 30 seconds and stabilize at a temperature slightly above the reference temperature. Heat is transferred through the heater housing 20 so that the temperature of the inner wall 210 is substantially the same as the temperature of the six PTC plates 260, 261, 262, 263, 264, 265, i.e., slightly above 210 degrees Celsius, as shown in FIG. When an aerosol-forming substrate is contained within the cavity 23 after the inner wall 210 has reached a temperature of substantially 210 degrees Celsius, this temperature is consistently applied to the aerosol-forming substrate during the operation time of the heater 10, thus forming an inhalable aerosol.

[0130] In the fourth embodiment CT220, the reference temperature of the six PTC plates 260, 261, 262, 263, 264, 265 is 220 degrees Celsius. When the first electrode and the second electrode are supplied with current, the six PTC plates 260, 261, 262, 263, 264, 265 reach their reference temperature of 220 degrees Celsius after about 30 seconds and stabilize at a temperature slightly above the reference temperature. Heat is transferred through the heater housing 20 so that the temperature of the inner wall 210 is substantially the same as the temperature of the six PTC plates 260, 261, 262, 263, 264, 265, i.e., slightly above 220 degrees Celsius, as shown in FIG. 9. When an aerosol-forming substrate is contained within the cavity 23 after the inner wall 210 has reached a temperature of substantially 220 degrees Celsius, this temperature is consistently applied to the aerosol-forming substrate during the operation time of the heater 10, thus forming an inhalable aerosol.

[0131] 10 and 11 show schematic cross-sectional views of an aerosol-generating device 200 and an aerosol-generating article 300. The aerosol-generating device 200 and the aerosol-generating article 300 form an aerosol generation system.

[0132] The aerosol generating device 200 comprises a substantially cylindrical device housing 202 having a shape and size similar to a conventional cigar.

[0133] The aerosol generating device 200 further includes a power source 206 in the form of a rechargeable nickel-cadmium battery, a PCB (printed circuit board) controller 208 including a microprocessor and memory, an electrical connector 209, and a heater 10. In the embodiment of Figures 10 and 11, the heater 10 is similar to that of Figure 3. However, other heaters may be used. In particular, the heaters of Figures 2, 4 and 8 may be used.

[0134] The power supply 206, controller 208, and heater 10 are all contained within the device housing 202. The heater 10 of the aerosol generation device 200 is disposed at the proximal end of the device 200. An electrical connector 209 is disposed at the distal end of the device housing 202.

[0135] As used herein, the term "proximal" refers to the user end or mouth end of the aerosol generating device or aerosol generating article, i.e., the end of the aerosol generating device or aerosol generating article that is configured to be closest to the mouth of a user during normal use of the aerosol generating device or aerosol generating system that includes the aerosol generating device and the aerosol generating article. The proximal end of a component of the aerosol generating device or aerosol generating article is the end of the component closest to the user end or mouth end of the aerosol generating device or aerosol generating article. As used herein, the term "distal" refers to the end opposite the proximal end.

[0136] The controller 208 is configured to control the supply of power from the power source 206 to the heater 10. The controller 208 further includes a DC / AC inverter including a class D power amplifier. The controller 208 is also configured to control the recharging of the power source 206 from an electrical connector 209. The controller 208 further includes a puff sensor (not shown) configured to detect when a user withdraws an aerosol-generating article received within the cavity 23.

[0137] As illustrated in Figure 3, the heater 10 includes a heater housing 20. The heater housing 20 includes a transversely extending peripheral portion 21 between a peripheral inner wall 210 and a peripheral outer wall 211. The heater housing 20 includes a longitudinally extending bottom portion 22 between a bottom inner wall 220 and a bottom outer wall 221. A cavity 23 for receiving an aerosol-forming substrate extends longitudinally between an open end 230 and the bottom inner wall 220, the cavity 23 being transversely bounded by the peripheral inner wall 210. A PTC tube 25 is disposed within the peripheral portion 21 so as to surround the peripheral inner wall 210.

[0138] The device housing 202 also defines an air inlet 280 proximate the distal end of the cavity 23 for receiving the aerosol-forming substrate. The air inlet 280 is configured to allow ambient air to be drawn into the device housing 202. An airflow path (not shown) is defined through the device 200 to allow air to be drawn from the air inlet 280 into the cavity 23.

[0139] The aerosol-generating article 300 is generally in the form of a cylindrical rod having a diameter similar to that of the inner peripheral wall 210. The aerosol-generating article 300 includes a cylindrical cellulose acetate filter plug 304 and a cylindrical aerosol-generating segment 310 that are wrapped together in an outer wrapper 320 of cigarette paper.

[0140] A filter plug 304 is disposed at the proximal end of the aerosol-generating article 300 and forms the mouthpiece of the aerosol-generating system over which a user pulls to receive aerosol generated by the system.

[0141] The aerosol-generating segment 310 is disposed at the distal end of the aerosol-generating article 300 and has a length substantially equal to the length of the cavity 23. Although the aerosol-generating segment 310 of Figures 10 and 11 includes only one aerosol-forming substrate, the aerosol-generating segment may equally include several aerosol-forming substrates. When there are multiple aerosol-forming substrates, the substrates may be arranged end-to-end with respect to one another along the longitudinal axis of the aerosol-generating article 300. However, it is envisioned that in other embodiments, separations may be provided between the aerosol-forming substrates. It may be appreciated that in some embodiments, two or more aerosol-forming substrates may be formed from the same material, while in other embodiments, the aerosol-forming substrates are each different. For example, one or more aerosol-forming substrates may include an aggregated and crimped sheet of homogenized tobacco material that includes a flavorant in the form of menthol. One or more aerosol-forming substrates may include a flavorant in the form of menthol and may not include tobacco material or any other source of nicotine. The one or more aerosol-forming substrates may also comprise one or more aerosol formers and further components, such as water, such that heating of the aerosol-forming substrate produces an aerosol having desirable organoleptic properties.

[0142] The proximal end of the aerosol-generation segment 310 is exposed as it is not covered by the outer wrapper 320. When the aerosol-generation segment 310 comprises several aerosol-forming substrates, the outer wrapper 320 may include a perforation line that surrounds the aerosol-generating article 300 at the interface between the aerosol-forming substrates. The perforations allow air to be drawn into the aerosol-generation segment 310.

[0143] FIG. 12 shows an aerosol-generating article 300 similar to that of FIGS. 10 and 11. However, the filter plug 304 is a filter assembly 304 in the form of a rod. The filter assembly 304 includes three segments: a cooling segment 307, a filter segment 309, and an oral end segment 311. In the embodiment of FIG. 12, the cooling segment 307 is disposed between the second aerosol-generation segment 310 and the filter segment 309 such that the cooling segment 307 is in adjacent relationship with the aerosol-generation segment 310 and the filter segment 309. In other examples, there may be separations between the aerosol-generation segment 310 and the cooling segment 307, and between the cooling segment 307 and the filter segment 309. The filter segment 309 is disposed between the cooling segment 307 and the oral end segment 311. The oral end segment 311 is disposed adjacent the filter segment 309 toward the proximal end of the article 300. 12, filter segment 309 is in abutting relationship with oral end segment 311. In one embodiment, the overall length of filter assembly 304 is between 37 millimeters and 45 millimeters, and more preferably, the overall length of filter assembly 304 is 41 millimeters.

[0144] In one example of the embodiment of Figure 12, the length of the aerosol-generation segment 310 is between 34 millimeters and 50 millimeters, more preferably the length of the aerosol-generation segment 310 is between 38 millimeters and 46 millimeters, and even more preferably the length of the aerosol-generation segment 310 is 42 millimeters.

[0145] In one example of the embodiment of FIG. 12, the overall length of article 300 is between 71 millimeters and 95 millimeters, more preferably, the overall length of article 300 is between 79 millimeters and 87 millimeters, and even more preferably, the overall length of article 300 is 83 millimeters.

[0146] In one embodiment, the cooling segment 307 is an annular tube and defines a void within the cooling segment 307. The void provides a chamber for the flow of heated volatile components generated from the aerosol-generation segment 310. The cooling segment 307 is hollow, thereby providing a chamber for aerosol accumulation while still providing sufficient rigidity to withstand axial compressive forces and bending moments that may occur during manufacture and use of the article 300 upon insertion into the aerosol generation device 200. In one embodiment, the wall thickness of the cooling segment 307 is about 0.29 millimeters.

[0147] The cooling segment 307 provides a physical displacement between the aerosol-generation segment 310 and the filter segment 309. The physical displacement provided by the cooling segment 307 provides a thermal gradient across the length of the cooling segment 307. In one embodiment, the cooling segment 307 is configured to provide a temperature difference of at least 40 degrees Celsius between the heated volatile components entering the distal end of the cooling segment 307 and the heated volatile components exiting the proximal end of the cooling segment 307. In one embodiment, the cooling segment 307 is configured to provide a temperature difference of at least 60 degrees Celsius between the heated volatile components entering the distal end of the cooling segment 307 and the heated volatile components exiting the proximal end of the cooling segment 307. This temperature difference across the length of the cooling segment 307 protects the temperature sensitive filter segment 309 from the high temperatures of the aerosol formed from the aerosol-generation segment 310.

[0148] In one embodiment of article 300 of Figure 12, the length of cooling segment 307 is at least 15 millimeters. In one embodiment, the length of cooling segment 307 is between 20 millimeters and 30 millimeters, more specifically between 23 millimeters and 27 millimeters, more specifically between 25 millimeters and 27 millimeters, and more specifically 25 millimeters.

[0149] The cooling segment 307 is made from paper, meaning that it is made of a material that does not produce compounds of concern. In one embodiment of the article 300 of FIG. 12, the cooling segment 307 is manufactured from a spirally wound paper tube that provides a hollow interior chamber while maintaining mechanical rigidity. A spirally wound paper tube can meet the stringent dimensional accuracy requirements of high speed manufacturing processes for tube length, outer diameter, roundness, and straightness. In another embodiment, the cooling segment 307 is a recess made from a stiff plug wrap or tipping paper. The stiff plug wrap or tipping paper is manufactured to have a rigidity sufficient to withstand axial compressive forces and bending moments that may occur during manufacturing and use of the article 300 during insertion into the aerosol generating device 200.

[0150] For each of the examples of cooling segment 307, the dimensional accuracy of the cooling segment is sufficient to meet the dimensional accuracy requirements of rapid manufacturing processes.

[0151] Filter segment 309 may be formed of any filter material sufficient to remove one or more volatile components from the heated volatile components from aerosol-generation segment 310. In one embodiment of article 300 of Figure 12, filter segment 309 is made of a monoacetate material, such as cellulose acetate. Filter segment 309 provides cooling and reduced irritation from the heated volatile components without depleting the amount of the heated volatile components to an unsatisfactory level for the user.

[0152] The density of the cellulose acetate tow material of filter segment 309 controls the pressure drop across filter segment 309, which in turn controls the resistance to withdrawal of article 300. Thus, the selection of material for filter segment 309 is important in controlling the resistance to withdrawal of article 300. Additionally, the filter segment performs the filtration function of article 300.

[0153] The presence of filter segment 309 provides an insulating effect by providing additional cooling to the heated volatile components exiting cooling segment 307. This additional cooling effect reduces the contact temperature of a user's lips on the surface of filter segment 309.

[0154] One or more flavorants may be added to filter segment 309 either by direct injection of a flavored liquid into filter segment 309 or by embedding or disposing one or more flavored frangible capsules or other flavored carriers within the cellulose acetate tow of filter segment 309. In one embodiment of article 300 of FIG. 12, filter segment 309 has a length of between 6 millimeters and 10 millimeters, more preferably 8 millimeters.

[0155] The oral end segment 311 is an annular tube and defines a void within the oral end segment 311. The void provides a chamber for heated volatile components flowing from the filter segment 309. The oral end segment 311 is hollow, thereby providing a chamber for aerosol accumulation while providing sufficient rigidity to withstand axial compressive forces and bending moments that may occur during manufacture and use of the article upon insertion into the aerosol generating device 200. In one embodiment, the wall thickness of the oral end segment 311 is about 0.29 millimeters.

[0156] In one embodiment, the length of the oral end segment 311 is between 6 millimeters and 10 millimeters, and more preferably, 8 millimeters.

[0157] The mouth end segment 311 may be manufactured from a spirally wound paper tube that provides a hollow interior chamber while maintaining significant mechanical rigidity. A spirally wound paper tube can meet the stringent dimensional accuracy requirements of high speed manufacturing processes for tube length, outside diameter, roundness, and straightness.

[0158] The mouth end segment 311 serves the function of preventing any liquid condensate that accumulates at the outlet of the filter segment 309 from coming into direct contact with the user.

[0159] It should be understood that in one embodiment, the mouth end segment 311 and the cooling segment 307 may be formed from a single tube, with the filter segment 309 located within that tube separating the mouth end segment 311 and the cooling segment 307.

[0160] 12, vents 317 are positioned within cooling segment 307 to facilitate cooling of article 300. In one embodiment, vents 317 include one or more rows of holes, preferably each row of holes disposed circumferentially around article 300 in a cross section substantially perpendicular to the longitudinal axis of article 300.

[0161] In one embodiment of article 300 of FIG. 12, there are one to four rows of vent holes 317 to provide ventilation to article 300. Each row of vent holes 317 can have between 12 and 36 vent holes 317. The diameter of vent holes 317 can be, for example, between 100 and 500 micrometers. In one embodiment, the axial separation between rows of vent holes 317 is between 0.25 millimeters and 0.75 millimeters, and more preferably, the axial separation between rows of vent holes 317 is 0.5 millimeters.

[0162] In one embodiment of article 300 of FIG. 12, vents 317 are of uniform size. In another embodiment, vents 317 vary in size. Vents 317 may be created using any suitable technique, for example, one or more of laser techniques, mechanical drilling of cooling segment 307, or pre-drilling of cooling segment 307 before it is formed in article 300. Vents 317 are positioned to provide effective cooling to article 300.

[0163] 12, the row of vents 317 is located at least 11 millimeters from the proximal end of article 300, and more preferably, vents 317 are located 17-20 millimeters from the proximal end of article 300. The locations of vents 317 are positioned such that a user does not block vents 317 when article 300 is in use.

[0164] Advantageously, providing a row of vent holes 17-20 mm from the proximal end of article 300 allows vent holes 317 to be located on the exterior of aerosol generation device 200 when article 300 is fully inserted into aerosol generation device 200. By locating vent holes 317 on the exterior of device 200, unheated air can enter article 300 from outside device 200 through the vent holes to facilitate cooling of article 300.

[0165] The length of cooling segment 307 is such that when article 300 is fully inserted into apparatus 200 , cooling segment 307 will be partially inserted into apparatus 200 .

[0166] In use, when the aerosol-generating article 300 is received within the cavity 23, a user may suck on the proximal end of the aerosol-generating article 300 to inhale the aerosol generated by the aerosol generation system. When the user draws on the proximal end of the aerosol-generating article 300, air is drawn into the device housing 202 at the air inlet 280 and into the aerosol-generating segment 310 of the aerosol-generating article 300.

[0167] 11 and 12, the controller 208 of the aerosol generating device 200 is configured to supply current to the PTC tube 25 disposed within the peripheral portion 21 of the heater housing 20. The temperature of the PTC tube 25 increases until it reaches a reference temperature of the PTC tube 25. After such a moment, the temperature of the PTC tube 25 stabilizes at a temperature substantially equal to the reference temperature of the PTC tube 25 for a time period that typically exceeds the duration of a user's session with the aerosol generating device 200. Thus, the heating profile of the aerosol-forming substrate contained within the aerosol-generating segment 310 of the aerosol-generating article 300 received within the cavity 23 can be determined in function of the reference temperature of the PTC tube 25.

[0168] In the heaters of Figures 3 and 10, the temperature of the PTC tube TE is substantially the same as the temperature of the peripheral inner wall TI, i.e., substantially the same as the temperature applied to the aerosol-forming substrate. This is represented diagrammatically in Figure 13. The reference temperature of the PTC tube 25 of the heater 10 of Figure 13 is 200 degrees Celsius, which substantially corresponds to the temperature of the PTC tube TE and the temperature of the peripheral inner wall after the stabilization time TI.

[0169] In the case of the heater of Fig. 8, the temperature TE of the six PTC plates also substantially corresponds to the temperature TI of the peripheral inner wall. However, unlike the case of Fig. 12, the stabilization time may be poor. In particular, the temperature TE of the six PTC plates and the temperature TI of the peripheral inner wall may be substantially stabilized at the reference temperature of the six PTC plates in 30 seconds.

[0170] Figure 14 represents the evolution of the temperature TE of the PTC disk and the temperature TI of the peripheral inner wall with time of the heater 10 of Figure 2. It will be understood that in this embodiment the temperature TI of the peripheral inner wall is lower than the temperature TE of the PTC disk. In particular, for a PTC disk 24 with a reference temperature of 220 degrees Celsius, the temperature TI of the peripheral inner wall stabilizes at 210.

[0171] FIG. 15 shows a temperature T / resistance R diagram of a PTC thermistor included in a heating element of a heater for heating an aerosol-forming substrate when different constant voltages V are supplied to the PTC thermistor. In FIG. 15, a first voltage V1 is greater than a second voltage V2, which in turn is greater than a third voltage V3. As can be seen in FIG. 15, the reference temperature CT of the PTC thermistor depends on the voltage V applied to the PTC thermistor. In particular, the first voltage V1 leads to a first reference temperature CT1, the second voltage V2 leads to a second reference temperature CT2, and the third voltage V3 leads to a third reference temperature CT3, so that the first reference temperature CT1 is greater than the second reference temperature CT2, which in turn is greater than the third reference temperature CT3.

[0172] The controller may control the power supply to supply a current to the PTC thermistor with a first voltage V1, a second voltage V2, a third voltage V3, or any other suitable voltage. Thus, the reference temperature of the PTC thermistor is adjusted to a first reference temperature CT1, a second reference temperature CT2, a third reference temperature CT3, or any other suitable temperature. The relationship between the supply voltage V and the reference temperature CT for a particular PTC thermistor may be stored in the controller, and in a preferred embodiment, such relationship may be stored in a memory included in the controller. Similarly, the first reference temperature CT1, the second reference temperature CT2, the third reference temperature CT3, or any other suitable temperature may be determined to correspond to a desired maximum operating temperature of one or more aerosol-forming substrates. The controller may also store one or more maximum operating temperatures of a given aerosol-forming substrate, and in a preferred embodiment, such maximum operating temperatures may be stored in a memory included in the controller.

[0173] Thus, the PTC thermistor of the aerosol-generating system may be substantially stabilized at a maximum operating temperature determined by the controller for a given aerosol-forming substrate. As described for the heater of the above embodiment, the temperature at which the PTC thermistor stabilizes is substantially the same as, or sufficiently close to, the temperature applied to the aerosol-forming substrate when the aerosol-generating system is used to heat the aerosol-forming substrate. Thus, the temperature at which the PTC thermistor stabilizes may be selected to optimize the formation of the aerosol. This may be beneficial for providing an optimized aerosol experience.

Claims

1. A heater for heating an aerosol-forming substrate, the heater comprising a heating element configured to heat the aerosol-forming substrate, the heating element comprising at least one positive temperature coefficient (PTC) thermistor, the at least one PTC thermistor configured to be supplied with an electric current so as to heat the at least one PTC thermistor; a resistance of the at least one PTC thermistor increases as the temperature of the at least one PTC thermistor increases within a stabilization temperature range, a lower end of the stabilization temperature range being a reference temperature at which the resistance of the at least one PTC thermistor is twice the value of a minimum resistance of the at least one PTC thermistor when a constant voltage is applied to the at least one PTC thermistor, and the reference temperature is between about 100 degrees Celsius and about 350 degrees Celsius when a constant voltage of 3.3 volts is applied to the at least one PTC thermistor.

2. 2. The heater of claim 1, wherein the reference temperature is between about 200 degrees Celsius and about 250 degrees Celsius when a constant voltage of 3.3 volts is applied to the at least one PTC thermistor.

3. A heater according to claim 1 or 2, wherein the heating element is configured to be inserted into the aerosol-forming substrate.

4. A heater according to any one of claims 1 to 3, wherein the heating element is configured to heat an outer surface of the aerosol-forming substrate.

5. 5. The heater according to claim 1, further comprising a cavity for receiving the aerosol-forming substrate, the heater being configured to heat the aerosol-forming substrate when the aerosol-forming substrate is received within the cavity.

6. 6. The heater of claim 5, comprising a heater housing, the heater housing having a peripheral portion extending transversely between a peripheral inner wall and a peripheral outer wall, and a bottom portion extending longitudinally between a bottom inner wall and a bottom outer wall, the cavity for receiving the aerosol-forming substrate extending longitudinally between an open end and the bottom inner wall, the cavity being bounded transversely by the peripheral inner wall.

7. The heater of claim 6 , wherein the at least one PTC thermistor comprises a PTC disk disposed within the base.

8. 8. The heater of claim 6 or 7, wherein the at least one PTC thermistor comprises a PTC tube disposed within the peripheral portion so as to surround the inner peripheral wall.

9. 8. The heater of claim 6 or 7, wherein the peripheral outer wall comprises at least three planar sections, and the at least one PTC thermistor comprises at least one PTC plate disposed on at least one of the at least three planar sections.

10. A heater according to any preceding claim, wherein the at least one PTC thermistor comprises a ceramic semiconductor such as barium titanate.

11. A heater according to any preceding claim, wherein at least one PTC thermistor comprises a polymeric material.

12. A heater housing comprising: a peripheral portion extending transversely between a peripheral inner wall and a peripheral outer wall; and a bottom portion extending longitudinally between a bottom inner wall and a bottom outer wall; a cavity for receiving the aerosol-forming substrate extending longitudinally between an open end and the bottom inner wall, the cavity being bounded in the transverse direction by the peripheral inner wall; Equipped with the peripheral outer wall comprises at least three planar sections, and the at least one PTC thermistor comprises at least three PTC plates, each of the at least three PTC plates being disposed on a different planar section such that the number of PTC plates is equal to the number of planar sections; At least two of the at least three PTC plates have different reference temperatures; The heater of claim 1.

13. An aerosol generating device, comprising: - a heater according to any one of claims 1 to 12, - a device housing, a power source electrically connected to the heating element and supplying a current to the at least one PTC thermistor.

14. 1. An aerosol generation system comprising: an aerosol-generating article comprising the aerosol-forming substrate as described above; - an aerosol generating system comprising an aerosol generating device according to claim 13.

15. 15. A method of operating an aerosol generating system according to claim 14, said method comprising: - determining the maximum operating temperature of the aerosol-forming substrate comprised in the aerosol-generating article; - supplying a current by the power source to the at least one PTC thermistor, the current having a constant voltage, such that as the temperature of the at least one PTC thermistor increases within a stabilization temperature range, the resistance of the at least one PTC thermistor increases, the lower end of the stabilization temperature range is a reference temperature at which the resistance of the at least one PTC thermistor is twice the value of the minimum resistance of the at least one PTC thermistor, and the constant voltage is supplied such that the reference temperature of the PTC thermistor is substantially the maximum operating temperature of the aerosol-forming substrate.

16. 15. A method of operating an aerosol generating system according to claim 14, said method comprising: - measuring the intensity of a puff as it is drawn during use of said aerosol generating system; determining a puff intensity threshold, when said puff intensity is equal to or exceeds said puff intensity threshold, the method further comprising: - determining a first maximum operating temperature and a second maximum operating temperature of an aerosol-forming substrate comprised in said aerosol-generating article; - selecting said first maximum operating temperature or said second maximum operating temperature, when the first maximum operating temperature is selected, supplying a current by the power source to the at least one PTC thermistor, the current having a first constant voltage, such that as the temperature of the at least one PTC thermistor increases within a stabilization temperature range, the resistance of the at least one PTC thermistor increases, the lower end of the stabilization temperature range being a reference temperature at which the resistance of the at least one PTC thermistor is twice the value of the minimum resistance of the at least one PTC thermistor, and the first constant voltage being supplied such that the reference temperature of the PTC thermistor is substantially the first maximum operating temperature of the aerosol-forming substrate, when the second maximum operating temperature is selected, supplying a current by the power source to the at least one PTC thermistor, the current having a second constant voltage, such that as the temperature of the at least one PTC thermistor increases within a stabilization temperature range, the resistance of the at least one PTC thermistor increases, the lower end of the stabilization temperature range is a reference temperature at which the resistance of the at least one PTC thermistor is twice the value of the minimum resistance of the at least one PTC thermistor, and the second constant voltage is supplied such that the reference temperature of the PTC thermistor is substantially the second maximum operating temperature of the aerosol-forming substrate.

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