Induction heating aerosol generating article comprising an aerosol forming substrate and a susceptor assembly

Abstract

The present invention relates to an induction-heated aerosol generating article (100) comprising an aerosol-forming substrate (130) and a susceptor assembly (120) for induction-heating the aerosol-forming substrate under the influence of an alternating magnetic field. The susceptor assembly comprises a first susceptor (121) and a second susceptor (122). The first susceptor comprises a first susceptor material having a positive resistance temperature coefficient. The second susceptor comprises a ferromagnetic or ferrimagnetic second susceptor material having a negative resistance temperature coefficient. The present invention also relates to an aerosol generating system comprising such article and an aerosol generating device (10) for use with the article.

Description

Technology Field

[0001] The present invention relates to an induction-heated aerosol generating article comprising an aerosol-forming substrate and a susceptor assembly for inductively heating said substrate under the influence of an alternating magnetic field. The present invention also relates to an aerosol generating system comprising an aerosol generating article and an aerosol generating device for use with said article. Background Technology

[0002] Aerosol generating systems are generally known from the prior art—based on the induction heating of an aerosol-forming substrate capable of forming an inhalable aerosol upon heating. To heat the substrate, the article may be housed within an aerosol generating device comprising an electric heater. The heater may be an inductive heater comprising an induction source. The induction source is configured to generate an alternating electromagnetic field that induces at least one of a heat-generating vortex or a hysteresis loss in a susceptor. The susceptor element itself may be an integral part of the article and may be arranged to be in thermal proximity or in physical direct contact with the substrate to be heated.

[0003] To control the temperature of the substrate, a susceptor assembly comprising first and second susceptors made of different materials is proposed. The first susceptor material is optimized for heat loss and consequently heating efficiency. In contrast, the second susceptor material is used as a temperature marker. For this purpose, the second susceptor material is selected to have a Curie temperature corresponding, for example, to a predetermined operating temperature of the susceptor assembly. At its Curie temperature, the magnetic properties of the second susceptor change from ferromagnetic or ferrimagnetic to paramagnetic, accompanied by a transient change in its electrical resistance. Thus, by monitoring the corresponding change in the electric current absorbed by an inducer, it can be detected when the second susceptor material reaches its Curie temperature, and consequently when the predetermined operating temperature is reached.

[0004] However, when monitoring changes in the electric current absorbed by the inducer, it may prove difficult to distinguish between the situation when the second susceptor material reaches its Curie temperature and the situation when the user takes a puff, particularly the initial puff, during which the electric current exhibits similar characteristic changes. The change in electric current during the user's puff is due to the cooling of the susceptor assembly caused by the air inhaled through the aerosol generating item when the user takes a puff. Cooling causes a transient change in the electrical resistance of the susceptor assembly. This ultimately causes a corresponding change in the electric current absorbed by the inducer. Typically, the cooling of the susceptor assembly during the user's puff is neutralized toward the controller by temporarily increasing the heating power. Furthermore, this controller-induced transient increase in heating power can adversely cause unnecessary overheating of the susceptor assembly if the monitored change in electric current—actually due to the second susceptor material reaching its Curie temperature—is misidentified as the user's puff.

[0005] Therefore, it would be desirable to have an induction-heated aerosol generating article comprising a susceptor assembly that possesses the advantages of the solution of the prior art but not its limitations. In particular, it would be desirable to have an induction-heated aerosol generating article comprising a susceptor assembly that allows for improved temperature control. means of solving the problem

[0006] According to the present invention, an induction-heated aerosol generating article is provided, comprising an aerosol-forming substrate and a susceptor assembly, wherein the susceptor assembly is configured to induction-heat the aerosol-forming substrate under the influence of an alternating magnetic field. The susceptor assembly comprises a first susceptor and a second susceptor. The first susceptor comprises a first susceptor material having a positive resistance temperature coefficient. The second susceptor comprises a second ferromagnetic or ferrimagnetic susceptor material having a negative resistance temperature coefficient.

[0007] According to the present invention, it has been recognized that a susceptor assembly comprising two susceptor materials having opposite resistance temperature coefficients has a resistance-over-temperature profile including a minimum of resistance at ±5°C around the Curie temperature of the second susceptor material, for example, the Curie temperature of the second susceptor material. Preferably, this minimum is a global minimum of the resistance-over-temperature profile. The minimum is caused by the opposite temperature behavior of the electrical resistances of the first and second susceptor materials and the magnetic properties of the second susceptor material. When the susceptor assembly is heated from room temperature, the resistance of the first susceptor material increases, while the resistance of the second susceptor material decreases as the temperature increases. The total apparent resistance of the susceptor assembly is given by the combination of the respective resistances of the first and second susceptor materials—as shown by the induction source used to induce heating the susceptor assembly. When the Curie temperature of the second susceptor material is reached from below, the decrease in resistance of the second susceptor material typically dominates the increase in resistance of the first susceptor material. Consequently, the total apparent resistance of the susceptor assembly decreases below the Curie temperature of the second susceptor material, particularly in the temperature range near the Curie temperature. At the Curie temperature, the second susceptor material loses its magnetic properties. This causes an increase in the skin layer available for eddy currents within the second susceptor material, accompanied by a sharp drop in its resistance. Therefore, when the temperature of the susceptor assembly is further increased beyond the Curie temperature of the second susceptor material, the contribution of the resistance of the second susceptor material to the total apparent resistance of the susceptor assembly can be less or more negligible. Thus, after passing a minimum value around the Curie temperature of the second susceptor material, the total apparent resistance of the susceptor assembly is given primarily by the increasing resistance of the first susceptor material. In other words, the total apparent resistance of the susceptor assembly increases again.Advantageously, the decrease and subsequent increase in the resistance-over-temperature profile around the minimum value of the Curie temperature of the second susceptor material can be sufficiently distinguished from the transient change in the total apparent resistance during a user puff. As a result, the minimum value of resistance around the Curie temperature of the second susceptor material can be reliably used as a temperature marker to control the heating temperature of the aerosol-forming substrate without the risk of being mistaken for a user puff. Thus, the aerosol-forming substrate can be effectively prevented from unnecessary overheating.

[0008] Preferably, the second susceptor material is selected to have a Curie temperature of less than 350°C, particularly less than 300°C, preferably less than 250°C, and most preferably less than 200°C. These values ​​are well below the conventional operating temperature used to heat the aerosol-forming substrate within the aerosol-generating article. Thus, proper identification of the temperature marker is further improved due to a sufficiently large temperature gap between the minimum value of the resistance-over-temperature profile for the Curie temperature of the second susceptor material and the operating temperature at which a change in apparent total resistance during a user's puff typically occurs.

[0009] The operating temperature used to heat the aerosol-forming substrate may be at least 300°C, particularly at least 350°C, preferably at least 370°C, most preferably at least 400°C. This temperature is a conventional operating temperature for heating the aerosol-forming substrate without burning it.

[0010] Accordingly, preferably, the second susceptor material has a Curie temperature below at least 20°C, particularly at least 50°C, more specifically at least 100°C, preferably at least 150°C, and most preferably at least 200°C of the operating temperature of the heating assembly.

[0011] As used herein, the term “susceptor” refers to an element capable of converting electromagnetic energy into heat when subjected to an alternating electromagnetic field. This may be the result of hysteresis losses and / or eddy currents induced in the susceptor, depending on the electrical and magnetic properties of the susceptor material. Hysteresis losses occur in ferromagnetic or ferrimagnetic susceptors due to magnetic domains within the material that are switched under the influence of an alternating electromagnetic field. Eddy currents may be induced when the susceptor is electrically conductive. In the case of electrically conductive ferromagnetic or ferrimagnetic susceptors, heat may be generated due to both eddy currents and hysteresis losses.

[0012] According to the present invention, the second susceptor material is at least ferrimagnetic or ferromagnetic having a specific Curie temperature. The Curie temperature is the temperature at which a ferrimagnetic or ferromagnetic material loses its ferrimagnetic or ferromagnetic properties, respectively, and becomes paramagnetic. In addition to being ferrimagnetic or ferromagnetic, the second susceptor material may also be electrically conductive.

[0013] Preferably, the second susceptor material may comprise either mu-metal or permalloy. Mu-metal is a nickel-iron soft ferromagnetic alloy. Permalloy is a nickel-iron magnetic alloy having, for example, about 80% nickel and 20% iron content.

[0014] While the second susceptor is configured primarily to monitor the temperature of the susceptor assembly, the first susceptor is preferably configured to heat the aerosol-forming substrate. To this end, the first susceptor can be optimized with respect to heat loss and, accordingly, with respect to heating efficiency. Thus, the first susceptor material may be electrically conductive and / or paramagnetic, ferromagnetic, or ferrimagnetic. If the first susceptor material is ferromagnetic or ferrimagnetic, the corresponding Curie temperature of the first susceptor material is preferably distinct from the Curie temperature of the second susceptor and is higher than any conventional operating temperature mentioned above, particularly for heating the aerosol-forming substrate. For example, the first susceptor material may have a Curie temperature of at least 400°C, particularly at least 500°C, preferably at least 600°C.

[0015] For example, the first susceptor material may include one of aluminum, gold, iron, nickel, copper, bronze, cobalt, conductive carbon, graphite, ordinary-carbon steel, stainless steel, ferritic stainless steel, martensitic stainless steel, or austenitic stainless steel.

[0016] Preferably, the first susceptor and the second susceptor are in close physical contact with each other. In particular, the first and second susceptors can form a single susceptor assembly. Therefore, the first and second susceptors essentially have the same temperature. As a result, temperature control of the first susceptor by the second susceptor is very precise. Close contact between the first susceptor and the second susceptor can be achieved by any suitable means. For example, the second susceptor may be plated, deposited, coated, clad, or welded onto the first susceptor. Preferred methods include electroplating (galvanic plating), cladding, dip coating, or roll coating.

[0017] The susceptor assembly according to the present invention is preferably configured to be driven by an alternating current, particularly a high-frequency electromagnetic field. As referred to herein, the high-frequency electromagnetic field may be within the range of 500 kHz (kilohertz) to 30 MHz (megahertz), particularly 5 MHz (megahertz) to 15 MHz (megahertz), preferably 5 MHz (megahertz) to 10 MHz (megahertz).

[0018] To optimize heat transfer from the susceptor assembly to the aerosol-forming substrate, at least one of the first susceptor and the second susceptor, or the entire susceptor assembly, may be at least thermally close to, preferably thermally in contact with, or even physically in direct contact with, the aerosol-forming substrate to be heated. In particular, at least one of the first susceptor and the second susceptor, or the entire susceptor assembly, is arranged within the aerosol-forming substrate. Preferably, at least the first susceptor is arranged within the aerosol-forming substrate.

[0019] Each of the first susceptor and the second susceptor, or the susceptor assembly, may include various geometric configurations. At least one of the first susceptor and the second susceptor, or the susceptor assembly, may be a particulate susceptor, or a susceptor filament, or a susceptor mesh, or a susceptor wick, or a susceptor pin, or a susceptor rod, or a susceptor blade, or a susceptor strip, or a susceptor sleeve, or a susceptor cup or a cylindrical susceptor, or a flat susceptor.

[0020] In one embodiment, at least one of the first susceptor or the second susceptor or the susceptor assembly may be a microparticle. The particles may have an equivalent spherical diameter of 10 μm to 100 μm. The particles may be distributed homogeneously throughout the aerosol-forming substrate, or have local concentration peaks or are distributed according to a concentration gradient.

[0021] In one embodiment, at least one of the first susceptor, the second susceptor, or the susceptor assembly may be a filament susceptor, a mesh susceptor, or a wick susceptor. Such a susceptor may have advantages regarding its manufacture, its geometric regularity and reproducibility, as well as its wicking function. Geometric regularity and reproducibility may prove to have advantages in both temperature control and controlled local heating. The wicking function may prove to be advantageous for use with a liquid aerosol forming substrate. With respect to the liquid aerosol forming substrate, the aerosol generating article may include a reservoir, be a cartridge for storing the liquid aerosol forming substrate, or be filled with the liquid aerosol forming substrate. In particular, the aerosol generating article may include the liquid aerosol forming substrate and a filament susceptor, a mesh susceptor, or a wick susceptor that is in at least partial contact with the liquid aerosol forming substrate.

[0022] At least one of the first susceptor, the second susceptor, or the susceptor assembly may be a susceptor blade, a susceptor rod, or a susceptor pin. Preferably, the first susceptor and the second susceptor together form a susceptor blade, a susceptor rod, or a susceptor pin. For example, one of the first or second susceptors may form the core or inner layer of the susceptor blade, a susceptor rod, or a susceptor pin, while the other of each of the first or second susceptors may form the jacket or envelope of the susceptor blade, a susceptor rod, or a susceptor pin. The susceptor blade, a susceptor rod, or a susceptor pin may be arranged within an aerosol-forming substrate. One extreme end of the susceptor blade, a susceptor rod, or a susceptor pin may be tapered or pointed to facilitate, for example, the insertion of the susceptor blade, a susceptor rod, or a susceptor pin into the aerosol-forming substrate of the article. The susceptor blade, susceptor rod, or susceptor pin may have a length ranging from 8 mm to 16 mm, particularly from 10 mm to 14 mm, preferably 12 mm. In the case of the susceptor blade, the first susceptor, and / or the second susceptor, the susceptor assembly in particular may have a width ranging from, for example, 2 mm to 6 mm, particularly from 4 mm to 5 mm. Likewise, the thickness of the blade-shaped first susceptor and / or the second susceptor, particularly the blade-shaped susceptor assembly, is preferably in the range of 0.03 mm to 0.15 mm, more preferably from 0.05 mm to 0.09 mm.

[0023] At least one of the first susceptor, the second susceptor, or the susceptor assembly may be a cylindrical susceptor, a susceptor sleeve, or a susceptor cup. The cylindrical susceptor, the susceptor sleeve, or the susceptor cup surrounds at least a portion of the aerosol-forming substrate to be heated, and thus may realize a heating oven or a heating chamber. In particular, the cylindrical susceptor, the susceptor sleeve, or the susceptor cup may form at least a portion of the shell, wrapper, casing, or housing of the aerosol-generating article.

[0024] The susceptor assembly may be a multilayer susceptor assembly. In this regard, the first susceptor and the second susceptor may form layers, particularly adjacent layers of the multilayer susceptor assembly.

[0025] In a multilayer susceptor assembly, the first susceptor and the second susceptor can be in close physical contact with each other. As a result, temperature control of the first susceptor by the second susceptor is sufficiently accurate because the first and second susceptors essentially have the same temperature.

[0026] The second susceptor may be plated, deposited, coated, cladded, or welded onto the first susceptor. Preferably, the second susceptor is applied onto the first susceptor by spraying, dip coating, roll coating, electroplating, or cladding.

[0027] It is desirable for the second susceptor to exist as a dense layer. The dense layer has a higher magnetic permeability than the porous layer and makes it easier to detect minute changes at the Curie temperature.

[0028] Individual layers of a multilayer susceptor assembly may be exposed to or revealed to the environment on the circumferential outer surface of the multilayer susceptor assembly when viewed in any direction parallel to and / or across the layer. Alternatively, the multilayer susceptor assembly may be coated with a protective coating.

[0029] Multilayer susceptor assemblies can be used to realize different geometric configurations of susceptor assemblies.

[0030] For example, the multilayer susceptor assembly may be an elongated susceptor strip or susceptor blade having a length of 8 mm to 16 mm, particularly 10 mm to 14 mm, preferably 12 mm. The width of the susceptor assembly may be in the range of, for example, 2 mm to 6 mm, particularly 4 mm to 5 mm. The thickness of the susceptor assembly is preferably in the range of 0.03 mm to 0.15 mm, more preferably 0.05 mm to 0.09 mm. The multilayer susceptor blade may have a free-tapered end.

[0031] As an example, the multilayer susceptor assembly may be an elongated strip having a first susceptor which is a strip of Grade 430 stainless steel having a length of 12 mm (millimeters), a width of 4 mm (millimeters) to 5 mm (millimeters), for example, 4 mm (millimeters), and a thickness of about 50 μm (micrometers). The Grade 430 stainless steel may be coated with a layer of mu-metal or permalloy as a second susceptor having a thickness of 5 μm (micrometers) to 30 μm (micrometers), for example, 10 μm (micrometers).

[0032] The term “thickness” is used herein to refer to a dimension extending between the top and bottom sides, for example, between the top and bottom sides of a layer or between the top and bottom sides of a multilayer susceptor assembly. The term “width” is used herein to refer to a dimension extending between two opposing lateral sides. The term “length” is used herein to refer to a dimension extending between the front and rear or between two other opposing sides orthogonal to the two opposing lateral sides forming the width. Thickness, width, and length may be orthogonal to each other.

[0033] Likewise, the multilayer susceptor assembly may be a multilayer susceptor rod or a multilayer susceptor pin, particularly as described above. In this configuration, one of the first or second susceptors may form a core layer surrounded by a peripheral layer formed by the other of the first or second susceptors. Preferably, the first susceptor is the one forming the peripheral layer when the first susceptor is optimized for heating the substrate. Thus, heat transfer to the peripheral aerosol-forming substrate is enhanced.

[0034] Alternatively, the multilayer susceptor assembly may be a multilayer susceptor sleeve, a multilayer susceptor cup, or a cylindrical multilayer susceptor, particularly as described above. One of the first or second susceptors may form the inner wall of the multilayer susceptor sleeve, a multilayer susceptor cup, or the cylindrical multilayer susceptor. The other of each of the first or second susceptors may form the outer wall of the multilayer susceptor sleeve, a multilayer susceptor cup, or the cylindrical multilayer susceptor. Preferably, the first susceptor forms the inner wall, particularly when the first susceptor is optimized for heating the substrate. As described above, the multilayer susceptor sleeve, a multilayer susceptor cup, or the cylindrical multilayer susceptor may surround at least a portion of the aerosol-forming substrate to be heated, and in particular may form at least a portion of the shell, wrapper, casing, or housing of the aerosol-generating article.

[0035] For example, for the purpose of manufacturing an aerosol-generating article, it may be desirable for the first and second susceptors to have similar geometric configurations as described above.

[0036] Alternatively, the first susceptor and the second susceptor may have different geometric configurations. Thus, the first and second susceptors can be tailored to their specific functions. Preferably, the first susceptor, having a heating function, may have a geometric configuration that provides a large surface area to the aerosol-forming substrate to enhance heat transfer. In contrast, the second susceptor, preferably having a temperature control function, does not need to have a very large surface area. If the first susceptor material is optimized for heating the substrate, it may be desirable not to have a larger volume of the second susceptor material than is necessary to provide a detectable Curie point.

[0037] According to this embodiment, the second susceptor may include one or more second susceptor elements. Preferably, one or more second susceptor elements are significantly smaller than the first susceptor, that is, have a volume smaller than the volume of the first susceptor. Each of the one or more second susceptor elements may be in close physical contact with the first susceptor. As a result, the first and second susceptors essentially have the same temperature, which improves the accuracy of temperature control of the first susceptor through the second susceptor acting as a temperature marker.

[0038] For example, the first susceptor may be in the form of a susceptor blade, a susceptor strip, a susceptor sleeve, or a susceptor cup, while the second susceptor material may be in the form of individual patches plated, deposited, or welded onto the first susceptor material.

[0039] According to another example, the first susceptor may be a strip susceptor, a filament susceptor, or a mesh susceptor, while the second susceptor is a particulate susceptor. Both the filament or mesh-type first susceptor and the particulate second susceptor may be embedded within an aerosol generating article that is in direct physical contact with, for example, an aerosol forming substrate to be heated. In this particular configuration, the first susceptor may extend through the center of the aerosol generating article within the aerosol forming substrate, while the second susceptor may be homogeneously distributed throughout the aerosol forming substrate.

[0040] The first and second susceptors do not need to be in close physical contact with each other. The first susceptor may be a susceptor blade or strip that realizes a heating blade or strip arranged within an aerosol-forming substrate to be heated. Likewise, the first susceptor may be a susceptor sleeve or susceptor cup that realizes a heating oven or heating chamber. In either of these configurations, the second susceptor may be located at a different location within the aerosol-generating article that is spaced apart from the first susceptor and the aerosol-forming substrate but remains thermally close to the first susceptor.

[0041] The first and second susceptors can form different parts of the susceptor assembly. For example, the first susceptor can form a side wall portion or a sleeve portion of the cup-shaped susceptor assembly, whereas the second susceptor forms a bottom portion of the cup-shaped susceptor assembly.

[0042] At least a portion of at least one of the first susceptor and the second susceptor may include a protective cover. Likewise, at least a portion of the susceptor assembly may include a protective cover. The protective cover may be formed by glass, ceramic, or an inert metal formed or coated on at least a portion of each of the first susceptor and / or the second susceptor, or the susceptor assembly. Advantageously, the protective cover may be configured to do at least one of avoiding the aerosol-forming substrate adhering to the surface of the susceptor assembly, avoiding material diffusion from the susceptor material into the aerosol-forming substrate, e.g., metal diffusion, and improving the mechanical strength of the susceptor assembly. Preferably, the protective cover is electrically nonconductive.

[0043] As used herein, the term “aerosol-forming substrate” refers to a substrate comprising or formed therefrom an aerosol-forming material capable of releasing volatile compounds upon heating to generate an aerosol. The aerosol-forming substrate is intended to be heated rather than burned to release aerosol-forming volatile compounds. The aerosol-forming substrate may be a solid or a liquid aerosol-forming substrate. In both cases, the aerosol-forming substrate may comprise both solid and liquid components. The aerosol-forming substrate may comprise a tobacco-containing material containing volatile tobacco flavor compounds released from the substrate upon heating. Alternatively or additionally, the aerosol-forming substrate may comprise a non-tobacco material. The aerosol-forming substrate may further comprise an aerosol-forming agent. Examples of suitable aerosol-forming agents are glycerin and propylene glycol. The aerosol-forming substrate may also comprise other additives and components, such as nicotine or flavoring agents. The aerosol-forming material may also be a paste-like material, a sachet of porous material containing the aerosol-forming material, or loose tobacco mixed with a gelling agent or adhesive, which may include a common aerosol-forming agent such as glycerin, for example, and subsequently compressed or molded into a plug.

[0044] As used herein, the term “aerosol generating article” refers to an article comprising at least one aerosol-forming material that releases a volatile compound capable of forming an aerosol when heated. Preferably, the aerosol generating article is a heated aerosol generating article. That is, the aerosol generating article comprises at least one aerosol-forming material intended to be heated rather than burned to release a volatile compound capable of forming an aerosol. The aerosol generating article may be a consumable, in particular a consumable to be discarded after a single use. The aerosol generating article may be a tobacco article. For example, the article may be a cartridge comprising a liquid or solid aerosol-forming material to be heated. Alternatively, the article may be a rod-shaped article, in particular a tobacco article, similar to a conventional cigarette and comprising a solid aerosol-forming material.

[0045] Preferably, the induction-heated aerosol-forming article according to the present invention has a circular, elliptical, or egg-shaped cross section. However, the article may also have a square, rectangular, triangular, or polygonal cross section.

[0046] In addition to the aerosol-forming substrate and the susceptor assembly, the article may further include different elements.

[0047] In particular, the article may include a mouthpiece. As used herein, the term “mouthpiece” refers to a part of the article placed into the user’s mouth to inhale an aerosol directly from the article. Preferably, the mouthpiece includes a filter.

[0048] In particular, regarding an aerosol generating article having a rod-shaped article similar to a conventional cigarette and / or comprising a solid aerosol-forming substrate, the article may further comprise a support element having a central air passage, an aerosol cooling element, and a filter element. The filter element preferably serves as a mouthpiece. In particular, the article may comprise a substrate element comprising an aerosol-forming substrate and a susceptor assembly in contact with the aerosol-forming substrate. Any one or any combination of these elements may be arranged sequentially with respect to the aerosol-forming rod segment. Preferably, the substrate element is arranged at the distal end of the article. Likewise, the filter element is preferably arranged at the proximal end of the article. The support element, the aerosol cooling element, and the filter element may have the same external cross-section as the aerosol-forming rod segment.

[0049] Furthermore, the article may include a casing or wrapper that surrounds at least a portion of the aerosol-forming substrate. In particular, the article may include a wrapper that surrounds at least a portion of the different segments and elements mentioned above to hold them together and maintain the required cross-sectional shape of the article.

[0050] The casing or wrapper may include a susceptor assembly. Advantageously, this allows for homogeneous and symmetrical heating of an aerosol-forming substrate surrounded by the susceptor assembly.

[0051] Preferably, the casing or wrapper forms at least a portion of the outer surface of the article. The casing may form a cartridge comprising a reservoir containing an aerosol-forming substrate, for example, a liquid aerosol-forming substrate. The wrapper may be a paper wrapper, particularly a paper wrapper made of cigarette paper. Alternatively, the wrapper may be a foil made of plastic, for example. The wrapper may be fluid-permeable, for example, to allow vaporized aerosol-forming substrate to be released from the article or to allow air to be drawn into the article through the circumference of the article. Furthermore, the wrapper may comprise at least one volatile substance that is activated and released from the wrapper upon heating. For example, the wrapper may be impregnated with a flavor volatile substance.

[0052] Additionally, the present invention relates to an aerosol generating system comprising an induction-heated aerosol generating article according to the present invention and as described herein. The system further comprises an induction-heated aerosol generating device for use with said article.

[0053] As used herein, the term “aerosol generating device” is used to describe an electrically operated device capable of interacting with at least one aerosol-forming substrate, in particular an aerosol-forming substrate provided within an aerosol generating article, in order to generate an aerosol by heating the substrate. Preferably, the aerosol generating device is a puffing device for generating an aerosol that can be inhaled directly by a user through the user’s mouth. In particular, the aerosol generating device is a handheld aerosol generating device.

[0054] The above device may include a receiving cavity for at least partially receiving an aerosol generating article. The receiving cavity may be embedded within the housing of the aerosol generating device.

[0055] The device may further include an induction source configured to generate an alternating electromagnetic field, preferably a high-frequency electromagnetic field. As referred to herein, the high-frequency electromagnetic field may be in the range of 500 kHz (kilohertz) to 30 MHz (megahertz), particularly 5 MHz (megahertz) to 15 MHz (megahertz), preferably 5 MHz (megahertz) to 10 MHz (megahertz).

[0056] To generate an alternating electromagnetic field, the inductor may include at least one inductor, preferably at least one induction coil. The at least one inductor may be configured and arranged to generate an alternating electromagnetic field within the receiving cavity to inductively heat the susceptor assembly of the article when the article is received within the receiving cavity.

[0057] The induction source may include a single induction coil or multiple induction coils. The number of induction coils may depend on the number of susceptors and / or the size and shape of the susceptor assembly. The induction coil or coils may have a shape that corresponds to the shape of the first and / or second susceptor or susceptor assembly, respectively. Likewise, the induction coil or coils may have a shape that corresponds to the shape of the housing of the aerosol generator.

[0058] The inductor may be a helical coil or a flat planar coil, particularly a pancake coil or a curved planar coil. Using a flat helical coil enables a compact design that is robust and inexpensive to manufacture. Using a helical induction coil can advantageously generate a homogeneous alternating electromagnetic field. As used herein, “flat helical coil” generally refers to a coil that is planar, wherein the winding axis of the coil is normal to the surface on which the coil is placed. A flat helical induction may have any desired shape within the plane of the coil. For example, a flat helical coil may have a circular shape or generally a rectangular or square shape. However, as used herein, the term “flat helical coil” includes both planar coils and flat helical coils shaped to conform to a curved surface. For example, the induction coil may be a “curved” planar coil arranged preferably on the circumference of a cylindrical coil support, for example, a ferrite core. Furthermore, the flat spiral coil may comprise, for example, two layers of four-turn flat spiral coils or a single layer of four-turn flat spiral coils.

[0059] The first and / or second induction coils may be retained within either the housing or the main body of the aerosol generator. The first and / or second induction coils may preferably be wound around a cylindrical coil support, for example, a ferrite core.

[0060] The inductor may include an alternating current (AC) generator. The AC generator may be powered by the power supply of the aerosol generator. The AC generator is operably coupled to at least one inductor. In particular, at least one inductor may be an integral part of the AC generator. The AC generator is configured to generate a high-frequency oscillating current to pass through the inductor to generate an alternating electromagnetic field. The AC current may be supplied to the inductor continuously after activation of the system, or intermittently, for example, whenever puffing occurs.

[0061] Preferably, the inductor includes a DC / AC converter connected to a DC power supply including an LC network, and the LC network includes a series connection of capacitors and inductors.

[0062] The aerosol generating device may include a full controller for controlling the operation of the device.

[0063] The controller may be configured to control the operation of an induction source, particularly in a closed-loop configuration, to control the heating of the aerosol-forming substrate to an operating temperature. The operating temperature used to heat the aerosol-forming substrate may be at least 300°C, particularly at least 350°C, preferably at least 370°C, most preferably at least 400°C. These temperatures are typical operating temperatures for heating the aerosol-forming substrate without burning.

[0064] The controller may include a microprocessor, for example, a programmable microprocessor, a microcontroller, or an application-specific integrated chip (ASIC), or other electronic circuitry capable of providing control. The controller may include additional electronic components, such as at least one DC / AC inverter and / or power amplifier, for example, a Class-D or Class-E power amplifier. In particular, an inductor may be part of the controller.

[0065] As described above, the aerosol generating device may be configured to heat an aerosol-forming substrate to a predetermined operating temperature. Preferably, the second susceptor material has a Curie temperature below the operating temperature by at least 20°C, particularly at least 50°C, more specifically at least 100°C, preferably at least 150°C, and most preferably at least 200°C. Advantageously, this ensures that the temperature gap between the temperature marker around the Curie temperature of the second susceptor material and the operating temperature is sufficiently large.

[0066] The controller may be configured to determine the minimum value of apparent resistance occurring in a temperature range of ±5°C around the Curie temperature of the second susceptor material during the preheating of the susceptor assembly—starting from room temperature toward the operating temperature. Advantageously, this enables the appropriate identification of a temperature marker around the Curie temperature of the second susceptor material. To this end, the controller may be configured to determine the actual apparent resistance of the susceptor assembly, which indicates the actual temperature of the susceptor assembly, from a supply voltage, particularly a DC supply voltage, and a supply current, particularly a DC supply current, which are typically drawn from a power supply.

[0067] Additionally, the controller may be configured to control the operation of the inductor in a closed-loop configuration such that the actual apparent resistance corresponds to a determined minimum value of apparent resistance + a predetermined offset value of apparent resistance to control the heating of the aerosol-forming substrate to the operating temperature.

[0068] In relation to this embodiment, the control of the heating temperature is preferably based on the principle of offset locking or offset control, using a predetermined offset value of the apparent resistance to bridge the gap between the apparent resistance measured at the marker temperature and the apparent resistance at the operating temperature. Advantageously, this can avoid direct control of the heating temperature based on a predetermined target value of the apparent resistance at the operating temperature, and thus avoid misinterpretation of the measured resistance characteristics. Furthermore, offset control of the heating temperature is more stable and reliable than temperature control based on the measured absolute value of the apparent resistance at the required operating temperature. This is due to the fact that the measured absolute value of the apparent resistance, as determined from the supply voltage and supply current, depends on various factors, such as the resistance of the inductor's electrical circuit and various contact resistances. These factors are susceptible to environmental effects and may change conditionally during manufacturing over time and / or between different inductors and susceptor assemblies of the same type. Advantageously, these effects substantially eliminate the difference between the two measured absolute values ​​of the apparent resistance. Therefore, using the offset value of the apparent resistance to control temperature is less susceptible to these negative effects and deformations.

[0069] The offset value of the apparent resistance for controlling the heating temperature of the aerosol-forming substrate to the operating temperature can be determined in advance, for example, by calibration measurements during the manufacture of the device.

[0070] Preferably, the minimum value around the Curie temperature of the second susceptor material is the global minimum value of the resistance-over-temperature profile.

[0071] As used herein, the term “starting at room temperature” means that, preferably, the minimum value around the Curie temperature of the second susceptor material occurs in the resistance-over-temperature profile during the heating of the susceptor assembly at room temperature toward the operating temperature at which the aerosol-forming substrate must be heated.

[0072] As used herein, room temperature can correspond to a temperature in the range of 18°C ​​to 25°C, particularly a temperature of 20°C.

[0073] At least some of the controller and inductors, particularly inductors spaced apart from the inductor, can be arranged on a common printed circuit board. This proves to be particularly advantageous for compact design.

[0074] To determine the actual apparent resistance of the susceptor assembly indicating the actual temperature of the susceptor assembly, the controller of the heating assembly may include at least one of a voltage sensor for measuring a supply voltage drawn from a power supply, in particular a DC supply voltage, in particular a DC voltage sensor, or a current sensor for measuring a supply current drawn from a power supply, in particular a DC supply current, in particular a DC current sensor.

[0075] As described above, the aerosol generator may include a power supply unit, specifically a DC power supply unit configured to provide a DC supply voltage and a DC supply current to an inducer. Preferably, the power supply unit is a battery, such as a lithium iron phosphate battery. Alternatively, the power supply unit may be another form of charge storage device, such as a capacitor. The power supply unit may require recharging, that is, the power supply unit may be rechargeable. The power supply unit may have a capacity that allows for the storage of sufficient energy for one or more user experiences. For example, the power supply unit may have a capacity sufficient to continuously generate aerosols for a period of about 6 minutes, or for a period of several times 6 minutes. In another example, the power supply unit may have a capacity sufficient to allow for the individual activation of a predetermined number of puffs or inducers.

[0076] The aerosol generating device may preferably include a main body comprising at least one of an inductor, an inductor, a controller, a power supply, and at least one part of a receiving cavity.

[0077] In addition to the main body, the aerosol generating device may further include a mouthpiece, particularly where the aerosol generating article to be used with the device does not include a mouthpiece. The mouthpiece may be mounted on the main body of the device. The mouthpiece may be configured to close a receiving cavity when the mouthpiece is mounted on the main body. To attach the mouthpiece to the main body, the proximal end portion of the main body may include a magnetic or mechanical mounting, such as a bayonet mount or a snap-fit ​​mounting, which engages with a corresponding portion at the distal end portion of the mouthpiece. Where the device does not include a mouthpiece, the aerosol generating article to be used with the aerosol generating device may include a mouthpiece, such as a filter plug.

[0078] The aerosol generating device may include at least one air outlet, for example (if present) an air outlet within the mouthpiece.

[0079] Preferably, the aerosol generating device includes an air path extending from at least one air inlet through a receiving cavity, and, if possible, additionally, to an air outlet in a mouthpiece, if present. Preferably, the aerosol generating device includes at least one air inlet in fluid communication with the receiving cavity. Thus, the aerosol generating system may include an air path extending from at least one air inlet to the receiving cavity, and possibly through an aerosol-forming material in an article and a mouthpiece into the user's mouth.

[0080] The aerosol generating device may be, for example, the device described in WO 2015 / 177256 A1.

[0081] Further features and advantages of the aerosol generating device according to the present invention have been described with respect to the aerosol generating article and will not be repeated. Brief explanation of the drawing

[0082] The present invention will be further described merely for illustrative purposes with reference to the accompanying drawings, where FIG. 1 is a schematic diagram of an induction-heated aerosol generating article according to a first embodiment of the present invention comprising a susceptor element; FIG. 2 is a schematic diagram of an exemplary embodiment of an aerosol generating system comprising an aerosol generating device and an aerosol generating article according to FIG. 1; FIG. 3 is a perspective view of a susceptor assembly contained within an aerosol-generating article according to FIG. 1; FIG. 4 is a diagram schematically illustrating the resistance-over-temperature profile of a susceptor assembly according to the present invention. FIG. 5 is a perspective view of an alternative embodiment of a susceptor assembly according to the present invention for use with the article according to FIG. 1 and FIG. 2; FIG. 6 is a perspective view of another alternative embodiment of a susceptor assembly for use with the article according to FIG. 1 and FIG. 2; FIG. 7 is a perspective view of another alternative embodiment of a susceptor assembly for use with the article according to FIG. 1 and 2; FIG. 8 is a schematic diagram of an induction-heated aerosol generating article according to a second exemplary embodiment of the present invention comprising a susceptor element; FIG. 9 is a schematic diagram of an induction-heated aerosol generating article according to a third exemplary embodiment of the present invention comprising a susceptor element; and FIG. 10 is a schematic diagram of an induction-heated aerosol generating article according to a fourth exemplary embodiment of the present invention comprising a susceptor element. Specific details for implementing the invention

[0083] FIG. 1 schematically illustrates a first exemplary embodiment of an induction-heated aerosol generating article (100) according to the present invention. The aerosol generating article (100) has a substantially rod shape and comprises an aerosol generating rod portion (110) comprising a susceptor assembly (120) and an aerosol generating substrate (130), which are four elements arranged sequentially in coaxial alignment, a support element (140) having a central air passage (141), an aerosol cooling element (150), and a filter element (160) serving as a mouthpiece. The aerosol generating rod segment (110) is arranged at the distal end (102) of the article (100), while the filter element (160) is arranged at the distal end (103) of the article (100). Each of these four elements is substantially cylindrical, and all of them have substantially the same diameter. Additionally, the four elements are enclosed by an outer wrapper (170) to hold the four elements together, for example, and maintain the required circular cross-sectional shape of the rod-like article (100). The wrapper (170) is preferably made of paper. Further details of the article, in particular the four elements, are disclosed in WO 2015 / 176898 A1—separate from details of the susceptor assembly (120) within the rod segment (110).

[0084] As illustrated in FIG. 2, an aerosol generating article (100) is configured to be used with an induction heating aerosol generating device (10). The device (10) and the article (100) together form an aerosol generating system (1). The aerosol generating device (10) includes a cylindrical receiving cavity (20) defined within the proximal portion (12) of the device (10) to accommodate at least the distal portion of the article (100). The device (10) further includes an induction source comprising an induction coil (30) for generating an alternating current, particularly a high-frequency electromagnetic field. In this embodiment, the induction coil (30) is a helical coil that circumferentially surrounds the cylindrical receiving cavity (20). The coil (30) is arranged so that the susceptor assembly (120) of the aerosol generating article (100) experiences the electromagnetic field when the article (100) is engaged with the device (10). Accordingly, when the induction source is activated, the susceptor assembly (120) is heated due to eddy currents and / or hysteresis losses induced by an alternating electromagnetic field, depending on the magnetic and electrical properties of the susceptor material of the susceptor assembly (120). The susceptor assembly (120) is heated until it reaches an operating temperature sufficient to vaporize the aerosol-forming substrate (130) surrounding the susceptor assembly (120) within the article (100). Within the distal portion (13), the aerosol generator (10) further includes a DC power supply (40) and a controller (50) (exemplified only schematically in FIG. 2) for supplying power and controlling the heating process. The induction source—separate from the induction coil (30)—is preferably at least partially integral with the controller (50). Details of temperature control will be further described below.

[0085] FIG. 3 shows a detailed view of a susceptor assembly (120) used in an aerosol generating article illustrated in FIG. 1. According to the present invention, the susceptor assembly (120) comprises a first susceptor (121) and a second susceptor (122). The first susceptor (121) comprises a first susceptor material having a positive resistance temperature coefficient, while the second susceptor (122) comprises a second ferromagnetic or ferrimagnetic susceptor material having a negative resistance temperature coefficient. Due to the first and second susceptor materials having opposing resistance temperature coefficients and due to the magnetic properties of the second susceptor material, the susceptor assembly (120) has a resistance-over-temperature profile including a minimum value of resistance around the Curie temperature of the second susceptor material.

[0086] The corresponding resistance-over-temperature profile is illustrated in FIG. 4. When the susceptor assembly (120) begins to be heated at room temperature (T_R), the resistance of the first susceptor material increases, while the resistance of the second susceptor material decreases with increasing temperature (T). The total apparent resistance (R_a) of the susceptor assembly (120) is given by the combination of the respective resistances of the first and second susceptor materials—as seen by the induction source of the device (10) used to induction heat the susceptor assembly (120). When the Curie temperature (T_C) of the second susceptor material is reached from below, the decrease in the resistance of the second susceptor material typically dominates the increase in the resistance of the first susceptor material. Accordingly, the total apparent resistance (R_a) of the susceptor assembly (120) decreases below the Curie temperature (T_C) of the second susceptor material, particularly in the temperature range approaching the Curie temperature. At the Curie temperature (T_C), the second susceptor material loses its magnetic properties. This causes an increase in the skin layer available for eddy currents within the second susceptor material, accompanied by a sharp drop in its resistance. Therefore, when the temperature (T) of the susceptor assembly (120) is further increased beyond the Curie temperature (T_C) of the second susceptor material, the contribution of the resistance of the second susceptor material to the total apparent resistance (R_a) of the susceptor assembly (120) may be less or more negligible. Accordingly, after delivering a minimum value (R_min) around the Curie temperature (T_C) of the second susceptor material, the total apparent resistance (R_a) of the susceptor assembly (120) is given mainly by the increasing resistance of the first susceptor material. That is, the total apparent resistance (R_a) of the susceptor assembly (120) increases again toward the operating resistance (R_op) at the operating temperature (T_op). Advantageously, the decrease and subsequent increase of the resistance-over-temperature profile around the minimum value (R_min) for the Curie temperature (T_C) of the second susceptor material can be sufficiently distinguished from the transient change in total apparent resistance during the user's puff.As a result, the minimum value of the resistance value (R_a) around the Curie temperature (T_C) of the second susceptor material can be reliably used as a temperature marker to control the heating temperature of the aerosol-forming substrate without the risk of being mistaken for a user's puff. Thus, the aerosol-forming substrate can be effectively prevented from unnecessary overheating.

[0087] To control the heating temperature of an aerosol-forming substrate to correspond to a required operating temperature (T_op), the controller (50) of the device (10) shown in FIG. 2 is configured to control the operation of an inducer in a closed-loop offset configuration to maintain, for example, the actual apparent resistance at a value corresponding to a determined minimum value (R_min) of apparent resistance (R_a) + a predetermined offset value (ΔR_offset). The offset value (ΔR_offset) bridges the gap between the apparent resistance (R_min) measured at the marker temperature (T_C) and the operating resistance (R_op) at the operating temperature (T_op). Advantageously, this avoids direct control of the heating temperature based on a predetermined target value of apparent resistance at the operating temperature (T_op). Furthermore, offset control of the heating temperature is more stable and reliable than temperature control based on the measured absolute value of apparent resistance at the required operating temperature.

[0088] When the actual apparent resistance is equal to or exceeds the determined minimum value of the apparent resistance plus a predetermined offset value of the apparent resistance, the heating process can be stopped by ceasing the generation of the alternating electromagnetic field, that is, by switching off the inductor or at least reducing the output power of the inductor. When the actual apparent resistance is less than the determined minimum value of the apparent resistance plus a predetermined offset value of the apparent resistance, the heating process can be resumed by restarting the generation of the alternating electromagnetic field, that is, by switching the inductor back on or increasing the output power of the inductor again.

[0089] In this embodiment, the operating temperature is about 370°C. This temperature is a typical operating temperature for heating the aerosol-forming substrate without burning. To ensure a sufficiently large temperature gap of at least 20°C between the marker temperature at the Curie temperature (T_C) of the second susceptor material and the operating temperature (T_op), the second susceptor material is selected to have a Curie temperature of, for example, less than 350°C.

[0090] As illustrated in FIG. 3, the susceptor assembly (120) in the article of FIG. 1 is a multilayer susceptor assembly, more specifically a two-layer susceptor assembly. It comprises a first layer constituting a first susceptor (121), and a second layer constituting a second susceptor (122) arranged on the first layer and closely coupled to the first layer. The first susceptor (121) is optimized for heat loss and thus heating efficiency, while the second susceptor (122) is a functional susceptor used primarily as a temperature marker, as previously described. The susceptor assembly (120) is in the form of an elongated strip having a length (L) of 12 mm and a width (W) of 4 mm, that is, both layers have a length (L) of 12 mm and a width (W) of 4 mm. The first susceptor (121) is a strip made of stainless steel, for example, Grade 430 stainless steel, having a Curie temperature exceeding 400°C. It has a thickness of about 35 μm. The second susceptor (122) is a strip of mu metal or permalloy having a Curie temperature below the operating temperature. It has a thickness of about 10 μm. The susceptor assembly (120) is formed by cladding the second susceptor strip to the first susceptor strip.

[0091] FIG. 5 illustrates an alternative embodiment of a strip-shaped susceptor assembly (220) similar to the embodiment of the susceptor assembly (120) shown in FIG. 1 and 2. In contrast to the latter, the susceptor assembly (220) according to FIG. 5 is a three-layer susceptor assembly comprising—in addition to first and second susceptors (221, 222) forming the first and second layers, respectively—a third susceptor (223) forming the third layer. All three layers are arranged in layers, and adjacent layers are tightly coupled to each other. The first and second susceptors (221, 222) of the three-layer susceptor assembly shown in FIG. 5 are identical to the first and second susceptors (121, 122) of the two-layer susceptor assembly (120) shown in FIG. 1 and 2. The third susceptor (223) is identical to the first susceptor (221). That is, the third layer (223) contains the same material as the first susceptor (221). Additionally, the layer thickness of the third susceptor (223) is equal to the layer thickness of the first susceptor (221). Therefore, the thermal expansion behavior of the first and third susceptors (221, 223) is substantially the same. Advantageously, this provides a highly symmetric layer structure that essentially does not exhibit out-of-plane deformation. Furthermore, the three-layer susceptor assembly according to FIG. 5 provides higher mechanical stability.

[0092] FIG. 6 illustrates another embodiment of a strip-shaped susceptor assembly (320) that can be used alternatively within the article of FIG. 1 instead of the two-layer susceptor (120). The susceptor assembly (320) according to FIG. 6 is formed by a first susceptor (321) closely coupled to a second susceptor (322). The first susceptor (321) is a strip of Grade 430 stainless steel having dimensions of 12 mm x 4 mm x 35 μm. Thus, the first susceptor (321) defines the basic shape of the susceptor assembly (320). The second susceptor (322) is a patch of mu metal or permalloy with dimensions of 3 mm x 2 mm x 10 μm. The patch-shaped second susceptor (322) is electroplated onto the strip-shaped first susceptor (321). Although the second susceptor (322) is significantly smaller than the first susceptor (321), it is still sufficient to allow for precise control of the heating temperature. Advantageously, the susceptor assembly (320) according to FIG. 6 provides significant savings in the second susceptor material. In additional embodiments (not shown), there may be more than one patch of the second susceptor positioned in close contact with the first susceptor.

[0093] FIG. 7 illustrates another embodiment of a susceptor assembly (1020) for use with the article illustrated in FIG. 1. According to this embodiment, the susceptor assembly (1020) forms a susceptor rod. The susceptor rod is cylindrical with a circular cross-section. Preferably, the susceptor rod is arranged at the center within the aerosol-forming substrate to extend the longitudinal axis of, for example, the aerosol-generating article illustrated in FIG. 1. As can be seen from one of its end faces, the susceptor assembly (1020) includes an inner core susceptor forming a second susceptor (1022) according to the present invention. The core susceptor is surrounded by a jacket susceptor forming a first susceptor (1021) according to the present invention. Since the first susceptor (1021) preferably has a heating function, this configuration proves advantageous for direct heat transfer to the surrounding aerosol-forming substrate. In addition, the cylindrical shape of the susceptor pin provides a highly symmetrical heating profile that can be advantageous for rod-shaped aerosol-generating articles.

[0094] FIGS. 8-10 schematically illustrate different aerosol-generating articles (400, 500, 600) according to the second, third, and fourth embodiments of the present invention. The articles (400, 500, 600) are very similar to the article (100) shown in FIG. 1, particularly with respect to the general configuration of the articles. Accordingly, similar or identical features are indicated by the same reference numbers as in FIG. 1, but are increased by 300, 400, and 500, respectively.

[0095] In contrast to the article (100) illustrated in FIG. 1, the aerosol generating article (400) according to FIG. 8 comprises a filament susceptor assembly (420). That is, the first and second susceptors (421, 422) are filaments that are twisted together to form, for example, a pair of twisted filaments. The pair of filaments is arranged within an aerosol generating substrate (430) that is in direct contact with the substrate (430). The pair of filaments extends substantially along the length extension of the article (400). The first susceptor (421) is a filament made of ferromagnetic stainless steel and thus primarily has a heating function. The second susceptor (422) is a filament made of mu metal or permalloy and thus primarily serves as a temperature marker.

[0096] The aerosol generating article (500) according to FIG. 9 includes a particulate susceptor assembly (520). Both the first susceptor (521) and the second susceptor (522) include a plurality of susceptor particles diffused within the aerosol forming substrate (530) of the article (500). Thus, the susceptor particles are in direct physical contact with the aerosol forming substrate (530). The susceptor particles of the first susceptor (521) are made of ferromagnetic stainless steel and thus serve to primarily heat the surrounding aerosol forming substrate (530). In contrast, the susceptor particles of the second susceptor (422) are made of mu metal or permalloy and thus serve primarily as temperature markers.

[0097] The aerosol generating article (600) according to FIG. 10 comprises a susceptor assembly (600) comprising a first susceptor (621) and a second susceptor (622) having different geometric configurations. The first susceptor (621) is a microparticle susceptor comprising a plurality of susceptor particles diffused within an aerosol-forming substrate (630). Due to the microparticle nature, the first susceptor (621) provides a large surface area to the surrounding aerosol-forming substrate (630), which advantageously enhances heat transfer. Accordingly, the microparticle configuration of the first susceptor (621) is specifically selected for the heating function. In contrast, the second susceptor (622) primarily has a temperature control function and therefore does not need to have a very large surface area. Accordingly, the second susceptor (622) of the present embodiment is a susceptor strip extending within the aerosol-forming substrate (630) through the center of the aerosol-generating article (600).

Claims

Claim 1 An induction-heating aerosol generating article comprising an aerosol forming substrate and a susceptor assembly for inductively heating the aerosol forming substrate under the influence of an alternating magnetic field, wherein the susceptor assembly comprises a first susceptor and a second susceptor, wherein the first susceptor comprises a first susceptor material having a positive resistance temperature coefficient, and the second susceptor comprises a ferromagnetic or ferrimagnetic second susceptor material having a negative resistance temperature coefficient. Claim 2 An aerosol generating article according to claim 1, wherein the second susceptor material has a Curie temperature of less than 350°C. Claim 3 An aerosol generating article according to claim 1 or 2, wherein the second susceptor material comprises one of mu-metal or permalloy. Claim 4 An aerosol generating article according to claim 1 or 2, wherein the first susceptor material is one of paramagnetic, ferromagnetic, or ferrimagnetic. Claim 5 An aerosol generating article according to claim 1 or 2, wherein the first susceptor material comprises one of aluminum, iron, nickel, copper, bronze, cobalt, ordinary-carbon steel, stainless steel, ferritic stainless steel, martensitic stainless steel, or austenitic stainless steel. Claim 6 An aerosol generating article according to claim 1 or 2, wherein the first susceptor and the second susceptor are in close physical contact with each other. Claim 7 An aerosol generating article according to claim 1 or 2, wherein the first susceptor or the second susceptor or both the first and second susceptors or the susceptor assembly is one of a particulate susceptor, or a susceptor filament, or a susceptor mesh, or a susceptor wick, or a susceptor pin, or a susceptor rod, or a susceptor blade, or a susceptor strip, or a susceptor sleeve, or a cylindrical susceptor, or a flat susceptor. Claim 8 An aerosol generating article according to claim 1 or 2, wherein the susceptor assembly is a multilayer susceptor assembly, and the first susceptor and the second susceptor form layers. Claim 9 An aerosol generating article according to claim 1 or 2, wherein the second susceptor comprises one or more second susceptor elements, each of which is in close physical contact with the first susceptor. Claim 10 An aerosol generating article according to claim 1 or 2, wherein at least one of the first susceptor and the second susceptor, or the entire susceptor assembly, is arranged within the aerosol forming substrate. Claim 11 An aerosol generating article according to claim 1 or 2, further comprising a casing surrounding at least a portion of the aerosol-forming substrate. Claim 12 An aerosol generating article according to claim 1 or 2, further comprising a mouthpiece. Claim 13 An aerosol generating article according to claim 1 or 2, wherein at least a portion of at least one of the first susceptor and the second susceptor, or at least a portion of the susceptor assembly, comprises a protective cover. Claim 14 An aerosol generating system comprising an aerosol generating article according to paragraph 1 or 2, and an aerosol generating device for use with said aerosol generating article. Claim 15 An aerosol generating system according to claim 14, wherein the system is configured to heat an aerosol-forming substrate to a predetermined operating temperature, and the second susceptor material has a Curie temperature at least 20°C below the operating temperature.

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