Multi-layer susceptor arrangement for inductively heating an aerosol-forming substrate - Patent Application 20070123633

Abstract

The present invention relates to a multi-layer susceptor arrangement for inductively heating an aerosol-forming substrate. The susceptor arrangement comprises at least a first layer comprising a first susceptor material and a second layer comprising a second susceptor material. The second susceptor material comprises or consists of a Ni-Fe alloy comprising 75% to 85% by weight Ni and 10% to 25% by weight Fe. The present invention also relates to an inductively heatable aerosol-generating article comprising an aerosol-forming substrate and a multi-layer susceptor arrangement for heating the substrate. The present invention further relates to an aerosol-generating system comprising such an aerosol-generating article and an inductively heated aerosol generator for use with the article.

Description

[Technical field]

[0001] The present invention relates to a multi-layer susceptor arrangement for inductively heating an aerosol-forming substrate, and to an inductively heatable aerosol-generating article comprising an aerosol-forming substrate and such a multi-layer susceptor arrangement for heating the substrate. The present invention further relates to an aerosol-generating system comprising such an aerosol-generating article and an inductively heated aerosol generator for use with the article. [Background technology]

[0002] It is generally known from the prior art to generate aerosols by inductive heating of an aerosol-forming substrate capable of forming an inhalable aerosol upon heating. To heat the substrate, the substrate may be part of an aerosol-generating article that is received in an aerosol-generating device. The device may comprise an induction source for generating an alternating magnetic field that is used to inductively heat the susceptor arrangement by inducing at least one of eddy currents and hysteresis losses in the susceptor material. The susceptor arrangement may be an integral part of the article and may be arranged in thermal proximity or in direct physical contact with the substrate to be heated.

[0003] To control the temperature of the substrate, a multi-layer susceptor arrangement is proposed, comprising at least a first layer and a second layer firmly bonded together. The first layer comprises a first susceptor material that is optimized with respect to heat loss and therefore heating efficiency, while the second layer comprises a second susceptor material that is used as a temperature marker. For this, the second susceptor material is chosen to be magnetic (ferromagnetic or ferrimagnetic) and to have a Curie temperature that corresponds to a predetermined temperature point for heating the substrate. At that Curie temperature, the magnetic permeability of the second susceptor material drops to 1, leading to a change in its magnetic properties from ferromagnetic or ferrimagnetic to paramagnetic. The change in magnetic properties is accompanied by a temporary change in the electrical resistance of the susceptor arrangement. Therefore, by monitoring the corresponding change in the current through the induction source, it is possible to detect when the second susceptor material has reached its Curie temperature and therefore when the predetermined temperature point has been reached.

[0004] The desired properties of the susceptor materials are typically selected for the individual materials in an unassembled state. However, it has been observed that when a first susceptor material and a second susceptor material are assembled together to form a multi-layer susceptor arrangement, certain properties of the layers, particularly the magnetic properties, may change compared to the unassembled state. In many cases, it has been observed that combining the layers and further processing the susceptor arrangement may even destroy the original desirable properties and effects of the layer materials. Summary of the Invention [Problem to be solved by the invention]

[0005] It would therefore be desirable to have a multi-layer susceptor arrangement for inductively heating an aerosol-forming substrate that has the advantages of, but mitigates the limitations of, the prior art solutions. In particular, it would be desirable to have a multi-layer susceptor arrangement that has no or only minimal variation in its magnetic properties after processing and during subsequent operation. [Means for solving the problem]

[0006] According to the present invention there is provided a multi-layer susceptor arrangement for inductively heating an aerosol-forming substrate, the susceptor arrangement comprising at least a first layer comprising a first susceptor material and a second layer comprising a second susceptor material, the second susceptor material comprising or consisting of a Ni-Fe alloy comprising 75% to 85% by weight Ni and 10% to 25% by weight Fe.

[0007] According to the present invention, it has been found that the variations in magnetic properties observed in multi-layer susceptor arrangements known from the prior art are caused by a combination of magnetostrictive properties and internal mechanical stresses present in the susceptor arrangement after its processing and throughout the temperature range of its operation. In particular, it has been found that the specific nature of such a multi-layer susceptor arrangement, in particular the different thermal expansion coefficients between the various layers, can result in thermal stresses. For example, the processing of a multi-layer susceptor arrangement may involve intimately connecting the various layer materials to each other at a given temperature, followed by a heat treatment (such as annealing) of the assembled susceptor arrangement. During the subsequent cooling of the susceptor arrangement, the individual layers try to shrink according to their specific thermal expansion coefficients, which may differ from each other. However, taking into account the fact that the layers are firmly bonded to each other, the layers cannot shrink freely, i.e. independently of each other. Inevitably, this results in internal mechanical stresses and thermal deformations of the susceptor arrangement. Most ferromagnetic or ferrimagnetic materials are subject to magnetostriction, so mechanical stresses have a consequent effect on the magnetic properties of the magnet layer; that is, when exposed to a magnetic field, these materials may expand or contract. Conversely, when the free thermal expansion or contraction is restricted, the magnetization of such materials is altered, i.e. strengthened or weakened. This is particularly true for the magnetic susceptor material of the second susceptor layer, which is used as a temperature marker.

[0008] In fact, the effect of limited free movement between the various susceptor layers on magnetostriction is difficult to control during mass production of such susceptor arrangements. In particular, these undesirable effects may vary across different locations of the precursor laminate material from which the multiple multi-layer susceptor arrangements are ultimately made. As a result, the magnetic properties may vary between different susceptor arrangements, even when made with the same precursor material.

[0009] To reduce these undesirable effects, the susceptor arrangement according to the invention comprises a second susceptor material comprising or consisting of a Ni-Fe alloy having 75% to 85% by weight Ni and 10% to 25% by weight Fe. More specifically, the Ni-Fe alloy may comprise 79% to 82% by weight Ni and 13% to 15% by weight Fe. Advantageously, it has been found that Ni-Fe alloys with Ni and Fe within the above ranges exhibit only weak or no magnetostriction. As a result, the second susceptor material of the functional second layer experiences no or at least reduced modification of its magnetic properties after its processing and throughout the temperature range of its operation. This consequently allows mass production of multi-layer susceptor arrangements with functional magnetic layers that have no or only negligible variations in their magnetic properties after processing and during subsequent operation.

[0010] As used herein, processing of a multi-layer susceptor arrangement may include at least one of intimately connecting layer materials to each other at a given temperature or heat treating (such as annealing) the multi-layer susceptor arrangement. Specifically, the susceptor arrangement may be a heat-treated susceptor arrangement. In either case, during the processing referred to herein, the temperature of the layers or the temperature of the assembly, respectively, is different from the operating temperature of the susceptor arrangement when it is being used to inductively heat the aerosol-forming substrate. Typically, the temperature during intimately connecting layer materials to each other or during heat treating the multi-layer susceptor arrangement is higher than the operating temperature of the susceptor arrangement during inductive heating of the aerosol-forming substrate.

[0011] As used herein, the unit "weight % (wt%)" stands for "weight percent" or "percent by weight", i.e., it indicates the mass fraction of an element in the alloy, which is the ratio of the mass of the respective element to the total mass of the alloy sample.

[0012] In addition to the main constituents, the remainder of the Ni-Fe alloy may contain one or more of the elements Co, Cr, Cu, Mn, Mo, Nb, Si, Ti, V.

[0013] As used herein, the symbol Ni represents the chemical element nickel, the symbol Fe represents the chemical element iron, the symbol Co represents the chemical element cobalt, the symbol Cr represents the chemical element chromium, the symbol Cu represents the chemical element copper, the symbol Mn represents the chemical element manganese, the symbol Mo represents the chemical element molybdenum, the symbol Nb represents the chemical element niobium, the symbol Si represents the chemical element silicon, the symbol Ti represents the chemical element titanium, and the symbol V represents the chemical element vanadium.

[0014] According to one embodiment, the Ni-Fe-alloy comprises 79% to 82% by weight Ni, 4% to 6% by weight Mo, less than 1% by weight Si and Mn combined together, and 13% to 15% by weight Fe. As used herein, "1% by weight Si and Mn combined together" means less than 1% by weight Si and Mn in total.

[0015] According to yet another embodiment, the Ni-Fe alloy may include 77% Ni, 16% Fe, 5% Cu, and 2% one of Cr and Mo by weight.

[0016] According to yet another embodiment, the Fe-Ni alloy may include 77 wt% Ni, 4 wt% Mo, 4 wt% Cu, and 14 wt% to 15 wt% Fe.

[0017] Advantageously, these particular examples of Ni-Fe alloys exhibit particularly weak magnetostriction.

[0018] According to yet another embodiment, the Ni-Fe-alloy may be ASTM A 753 alloy type 3 (similar to UNS number: N14076) with 75% to 78% by weight Ni and 10% to 19% by weight Fe, the remainder being structured by one or more of the elements Co, Cr, Cu, Mn, Mo, Si.

[0019] According to yet another embodiment, the Ni-Fe-alloy may be ASTM A 753 alloy type 4 (similar to UNS number: N14080, and EN numerical designation: 2.4545) with 77% to 82% by weight Ni and 10% to 17.5% by weight Fe (or even 9.5% to 17.5% by weight Fe), the remainder being structured by one or more of the elements Co, Cr, Cu, Mn, Mo, Si.

[0020] As mentioned above, the second susceptor material is preferably configured to monitor the temperature of the susceptor arrangement (i.e. as a temperature marker). For this purpose, the second susceptor material may be selected to have a Curie temperature that essentially corresponds to a predetermined temperature point of the heating process. In particular, the second susceptor material may be selected to have a Curie temperature that essentially corresponds to a predetermined maximum heating temperature of the susceptor arrangement. The maximum desired heating temperature may be defined to be approximately the temperature to which the susceptor arrangement should be heated to generate an aerosol from the aerosol-forming substrate. However, the maximum desired heating temperature should be low enough to avoid local overheating or even combustion of the aerosol-forming substrate. The Curie temperature of the second susceptor material should preferably be below the ignition point of the aerosol-forming substrate. The second susceptor material may have a Curie temperature below 500° C., preferably below 400° C., in particular below 390° C. For example, the second susceptor may have a Curie temperature of 150° C. to 400° C., specifically 200° C. to 400° C. Although the second layer is primarily a functional layer that provides a temperature marker via the Curie temperature of the second susceptor material, it may also contribute to the inductive heating of the susceptor arrangement.

[0021] Moreover, it is preferably the first layer comprising a first susceptor material that is configured primarily for heating the aerosol-forming substrate, for which reason the first susceptor material may be optimized with respect to heat losses and therefore with respect to heating efficiency.

[0022] The term "susceptor material" as used herein refers to a material that has the ability to convert electromagnetic energy into heat when subjected to an alternating magnetic field. This may be the result of at least one of hysteresis loss and eddy currents induced in the susceptor material, depending on its electrical and magnetic properties. Hysteresis loss occurs in ferromagnetic or ferrimagnetic susceptor materials due to magnetic domains in the material being switched under the influence of the alternating electromagnetic field. Eddy currents may be induced if the susceptor material is electrically conductive. In the case of an electrically conductive ferromagnetic susceptor or an electrically conductive ferrimagnetic susceptor, heat can be generated due to both eddy currents and hysteresis losses.

[0023] As a result, the first susceptor material may be at least one of electrically conductive or magnetic (i.e., either ferromagnetic or ferrimagnetic). If the first susceptor material is electrically conductive, it may also be paramagnetic. If the first susceptor material is magnetic (ferromagnetic or ferrimagnetic), it is preferably selected to have a Curie temperature different from, and specifically higher than, the Curie temperature of the second susceptor material. In this specific configuration, the first susceptor material may have a first Curie temperature and the second susceptor material may have a second Curie temperature.

[0024] The first susceptor material is preferably made of a corrosion-resistant material and is therefore advantageously resistant to any corrosive influences, which is of particular interest when the susceptor arrangement is embedded in an aerosol-generating article that is in direct physical contact with the aerosol-forming substrate.

[0025] Preferably, the first susceptor material comprises a metal, such as ferritic iron, or stainless steel, particularly a ferromagnetic stainless steel, such as a ferritic stainless steel. It may be particularly preferred that the first susceptor material comprises a 400 series stainless steel (such as grade 410 stainless steel, or grade 420 stainless steel, or grade 430 stainless steel, or a similar grade stainless steel).

[0026] Alternatively, the first susceptor material may comprise a suitable non-magnetic material, in particular a paramagnetic conductive material, such as aluminum (Al), in which inductive heating occurs solely by resistive heating due to eddy currents.

[0027] Alternatively, the first susceptor material may comprise a non-conductive ferrimagnetic material, such as a non-conductive ferrimagnetic ceramic, in which case heat is generated solely by hysteresis losses.

[0028] The second layer may be intimately connected to the first layer. The term "intimately connected" as used herein refers to a mechanical connection between two layers in a multi-layer susceptor arrangement, such that mechanical forces may be transmitted between the two layers, particularly in a direction parallel to the layer structure. The connection may be a layered, two-dimensional, area connection, or a full-area connection, i.e., a connection on both sides of the respective opposing surfaces of the two layers. The connection may be a direct connection. Specifically, the two layers that are intimately connected to each other may be in direct contact with each other. Alternatively, the connection may be an indirect connection. Specifically, the two layers may be indirectly connected via at least one intermediate layer. The second layer is disposed on the first layer and intimately connected to the first layer, particularly preferably directly connected to the first layer.

[0029] The multi-layer susceptor arrangement may further comprise a third layer. The third layer may be intimately connected to the second layer. In this context, the term "intimately connected" is used in the same manner as defined above with respect to the first and second layers.

[0030] Preferably, the third layer is a protective layer configured to at least one of prevent the aerosol-forming substrate from sticking to the surface of the susceptor arrangement, or prevent material diffusion (e.g., metal migration) from the susceptor material into the aerosol-forming substrate, or prevent or reduce thermal bending due to differences in thermal expansion between the layers, or protect other layers (specifically the second layer) from any corrosive effects.

[0031] The latter is particularly important when the susceptor arrangement is embedded in the aerosol-forming substrate of the aerosol-generating article, i.e., when the susceptor arrangement is in direct physical contact with the aerosol-forming substrate. For this reason, the third layer preferably comprises or consists of a corrosion-resistant material. Advantageously, the corrosion-resistant material improves the aging properties of those portions of the outer surface of the second layer that are not corrosion-resistant that are covered by the third layer and therefore are not directly exposed to the environment.

[0032] The term "third layer" as used herein refers to a layer different from and in addition to the first and second layers. Specifically, any possible oxide layer on the surface of the first or second layer resulting from oxidation of the first or second susceptor material should not be considered a third layer (specifically, a third layer including or consisting of a corrosion-resistant material).

[0033] The third layer may comprise or consist of the same material as the first susceptor material of the first layer. Due to this, the multi-layer susceptor arrangement comprises at least two layers having the same thermal expansion coefficient, which results in reduced deformation of the susceptor arrangement throughout the operating temperature range. This is especially true when the susceptor arrangement comprises only the first layer, the second layer, and the third layer, and when the second layer is sandwiched symmetrically between the first layer and the third layer.

[0034] As a result, the third layer may comprise a metal, such as ferritic iron, or stainless steel, such as a ferritic stainless steel, in particular a 400 series stainless steel (such as grade 410 stainless steel, or grade 420 stainless steel, or grade 430 stainless steel, or a similar grade stainless steel). Alternatively, the third layer may comprise a suitable non-magnetic material, in particular a paramagnetic conductive material (such as aluminum (Al)). Similarly, the third layer may comprise a non-conductive ferrimagnetic material, such as a non-conductive ferrimagnetic ceramic.

[0035] It is also possible that the third layer comprises or consists of austenitic stainless steel. Advantageously, austenitic stainless steel, due to its paramagnetic properties and high electrical resistance, slightly shields the second layer from the magnetic field applied to the first and second susceptor materials. By way of example, the third layer may comprise or consist of X5CrNi18-10 (designation according to EN (European Standards), material number 1.4301, also known as V2A steel) or X2CrNiMo17-12-2 (designation according to EN (European Standards), material number 1.4571 or 1.4404, also known as V4A steel). In particular, the third layer may comprise or consist of one of 301 stainless steel, 304 stainless steel, 304L stainless steel, 316 stainless steel, or 316L stainless steel (designation according to SAE steel grades [Society of Automotive Engineers]).

[0036] In general, the various layers of a multi-layer susceptor arrangement may have either the same layer thickness or different layer thicknesses. The term "thickness" as used herein refers to a dimension extending between an upper side and a lower side, e.g., between an upper side and a lower side of a layer, or between an upper side and a lower side of a multi-layer susceptor arrangement. Similarly, the term "width" is used herein to refer to any dimension extending between two opposing lateral sides of a layer or susceptor arrangement. The term "length" is used herein to refer to any dimension extending between a front side and a back side, or between two other opposing sides, perpendicular to the two opposing lateral sides forming the width. The width extension is preferably greater than the thickness extension. Similarly, the width extension may be less than the length extension. The thickness, width, and length may be perpendicular to each other.

[0037] The first layer may have a layer thickness in the range of 20 micrometers to 60 micrometers, in particular 30 micrometers to 50 micrometers, preferably 40 micrometers.

[0038] The second layer may have a layer thickness in the range of 4 micrometers to 20 micrometers, in particular 8 micrometers to 16 micrometers, preferably 10 micrometers to 15 micrometers.

[0039] If present, the third layer may have a layer thickness in the range of 2 micrometers to 6 micrometers, in particular 3 micrometers to 5 micrometers, preferably 3 micrometers to 4 micrometers.

[0040] The thickness of the third layer may be 0.05 to 1.5 times, specifically 0.1 to 1.25 times or 0.95 to 1.05 times, or specifically 1 time, the thickness of the first layer, or the thickness of the third layer may be 0.02 to 0.2 times, specifically 0.03 to 0.2 times, or 0.03 to 0.1 times the thickness of the first layer.

[0041] In the case of a symmetrical or nearly symmetrical layer configuration, the first layer as well as the third layer may have a thickness in the range of 2 micrometers to 20 micrometers, specifically 3 micrometers to 10 micrometers, preferably 3 micrometers to 6 micrometers.

[0042] The second layer may then have a thickness in the range of 5 micrometers to 50 micrometers, specifically 10 micrometers to 40 micrometers, preferably 20 micrometers to 40 micrometers.

[0043] In general, the multi-layer susceptor arrangements described herein may be used to achieve different geometric configurations of the susceptor arrangement.

[0044] Preferably, the multi-layer susceptor arrangement may be an elongated, particularly strip-like, susceptor arrangement. The elongated susceptor arrangement may have a thickness in the range of 0.03 mm to 0.15 mm, more preferably 0.05 mm to 0.09 mm. The elongated susceptor arrangement may have a width in the range of 2 mm to 6 mm, particularly 4 mm to 5 mm. Similarly, the elongated susceptor arrangement may have a length in the range of 8 mm to 19 mm, particularly 10 mm to 14 mm, preferably 10 mm to 12 mm.

[0045] Alternatively, the multi-layer susceptor arrangement may be a multi-layer susceptor rod, or a multi-layer susceptor pin, or a multi-layer susceptor sleeve, or a multi-layer susceptor cup, or a cylindrical multi-layer susceptor.

[0046] The terms "first layer", "second layer", and "third layer" as used herein are merely nominal, without necessarily designating a particular order or sequence of the respective layers. The first layer, second layer, and third layer are preferably adjacent layers of a multi-layer susceptor arrangement. In this case, the first layer, second layer, and third layer may be in intimate direct physical contact with each other. In particular, the second layer may be sandwiched between the first layer and the third layer. More particularly, the third layer may be disposed on the second layer and intimately connected to the second layer. The second layer may in turn be disposed on the first layer and intimately connected to the first layer. At least one of the first layer or the third layer may be an edge layer of the multi-layer susceptor arrangement.

[0047] With regard to the fabrication of the susceptor arrangement, and in particular with regard to the assembly of the various layers, each of the layers may be plated, deposited, coated, clad, or welded onto the respective adjacent layers. In particular, any of these layers may be applied onto the respective adjacent layers by spraying, dip coating, roll coating, electroplating, or cladding. This is particularly true for the first layer, the second layer, the third layer, and, if present, at least one intermediate layer. Either way, any of the above configurations or layer structures fall within the scope of the term "intimately connected" as used herein and further defined above.

[0048] According to the present invention there is also provided an inductively heatable aerosol-generating article comprising an aerosol-forming substrate and a multi-layer susceptor arrangement according to the present invention and as described herein, which is constructed and arranged to inductively heat the substrate.

[0049] The term "aerosol-generating article" as used herein refers to an article comprising at least one aerosol-forming substrate capable of releasing a volatile compound capable of forming an aerosol when heated. The aerosol-generating article is preferably a heated aerosol-generating article, i.e. an aerosol-generating article comprising at least one aerosol-forming substrate intended to be heated rather than burned. The aerosol-generating article may be a consumable product, in particular a consumable product that is discarded after a single use. For example, the article may be a cartridge comprising a liquid aerosol-forming substrate to be heated. As another example, the article may be a rod-shaped article resembling a conventional cigarette, in particular a tobacco article.

[0050] The term "aerosol-forming substrate" as used herein means a substrate formed from or including an aerosol-forming material capable of releasing a volatile compound upon heating to generate an aerosol. The aerosol-forming substrate is preferably intended to be heated, rather than combusted, to release the aerosol-forming volatile compound. The aerosol-forming substrate may be a solid aerosol-forming substrate, a liquid aerosol-forming substrate, a gel-like aerosol-forming substrate, or any combination thereof. For example, the aerosol-forming substrate may include both solid and liquid components. The aerosol-forming substrate may include a tobacco-containing material that contains volatile tobacco flavor compounds that are released from the substrate upon heating. Alternatively, or additionally, the aerosol-forming substrate may include a non-tobacco material. The aerosol-forming substrate may further include an aerosol former. Examples of suitable aerosol formers are glycerin and propylene glycol. The aerosol-forming substrate may also include other additives and ingredients, such as nicotine or flavorings. The aerosol-forming substrate may also be a paste-like material, a sachet of porous material containing the aerosol-forming substrate, or loose tobacco mixed with, for example, a gelling or adhesive agent, which may include a common aerosol former such as glycerin, which is compressed or molded into a plug.

[0051] The article is preferably an elongated or rod-shaped article. The elongated or rod-shaped article may have a shape that resembles the shape of a conventional cigarette.

[0052] Aerosol-generating articles, in particular elongated or rod-shaped articles, may have a circular or elliptical or oval or square or rectangular or triangular or polygonal cross-section.

[0053] In one embodiment, the aerosol-generating article may be a rod-shaped article, specifically a cylindrical article comprising one or more of a distal front plug element, a base element, a first tube element, a second tube element, and a filter element.

[0054] The substrate element preferably comprises at least one aerosol-forming substrate to be heated and a susceptor arrangement in thermal contact or in thermal proximity to the aerosol-forming substrate. The substrate element may have a length of 10 mm to 14 mm, for example 12 mm.

[0055] The first tube element is distal to the second tube element. Preferably, the first tube element is proximal to the base element and the second tube element is proximal to the first tube element and distal to the filter element, i.e. between the first tube element and the filter element. At least one of the first tube element and the second tube element may comprise a central air passage. The cross section of the central air passage of the second tube element may be larger than the cross section of the central air passage of the first tube element. Preferably, at least one of the first tube element and the second tube element may comprise a hollow cellulose acetate tube. At least one of the first tube element and the second tube element may have a length of 6 mm to 10 mm, for example 8 mm.

[0056] The filter element preferably functions as a mouthpiece or as part of a mouthpiece together with a second tube element. As used herein, the term "mouthpiece" refers to the portion of the article through which the aerosol exits the aerosol-generating article. The filter element may have a length of 10 millimeters to 14 millimeters, for example 12 millimeters.

[0057] The distal forward plug element may be used to cover and protect the distal forward end of the base element. The distal forward plug element may have a length of 3 mm to 6 mm, for example 5 mm. The distal forward plug element may be made of the same material as the filter element.

[0058] All of the aforementioned elements may be disposed consecutively along the length axis of the article in the order described above, with the distal forward plug element preferably disposed at the distal end of the article and the filter element preferably disposed at the proximal end of the article. Each of the aforementioned elements may be substantially cylindrical. Specifically, all of the elements may have the same external cross-sectional shape and / or dimensions.

[0059] In addition, the elements may be surrounded by one or more outer wrappers, such as to hold the elements together and to maintain the desired cross-sectional shape of the rod-like article. The wrapper is preferably made of paper. The wrapper may further comprise an adhesive that bonds the overlapping free ends of the wrappers to each other. For example, the distal forward plug element, the base element, and the first tube element may be surrounded by a first wrapper, and the second tube element and the filter element may be surrounded by a second wrapper. The second wrapper may also surround at least a portion of the first tube element (after being wrapped by the first wrapper) to connect the distal forward plug element, the base element, and the first tube element surrounded by the first wrapper to the second tube element and the filter element. The second wrapper may comprise perforations around its circumference.

[0060] Further features and advantages of the aerosol-generating article according to the present invention have been described with respect to multi-layer susceptor arrangements and therefore apply equally.

[0061] According to the present invention there is provided an inductively heated aerosol generating device for use with an aerosol generating article, as well as an aerosol generating system comprising an inductively heatable aerosol generating article according to the present invention.

[0062] The term "aerosol generating device" as used herein describes an electrically actuated device for interaction with an aerosol-generating article according to the present invention to generate an aerosol by inductively heating an aerosol-forming substrate via a susceptor arrangement. The aerosol generating device is preferably a smoke extractor for generating an aerosol that is directly inhalable by a user through the user's mouth. In particular, the aerosol generating device is a handheld aerosol generating device.

[0063] The device may comprise a receiving cavity for removably receiving at least a portion of the aerosol-generating article.

[0064] The aerosol generating device comprises an induction heating arrangement constructed and arranged to generate an alternating magnetic field in a receiving cavity for inductively heating the susceptor arrangement when an article is received in the aerosol generating device. To generate the alternating magnetic field, the induction heating arrangement may comprise at least one induction coil surrounding at least a portion of the susceptor arrangement when an article is received in the cavity of the device. The at least one induction coil may be a helical coil or a flat planar coil, in particular a pancake coil or a curved planar coil.

[0065] The induction heating arrangement may further comprise an alternating current (AC) generator. The AC generator may be powered by a power supply of the aerosol generating device. The AC generator is operably coupled to the at least one induction coil. In particular, the at least one induction coil may be an integral part of the AC generator. The AC generator is configured to generate a high frequency oscillating current that passes through the at least one induction coil to generate an alternating magnetic field. The AC current may be continuously supplied to the at least one induction coil after activation of the system, or may be intermittently supplied (e.g., after every puff). The induction heating arrangement comprises a DC / AC converter including an LC network, the LC network preferably comprising a series connection of a capacitor and an inductor. The DC / AC converter may be connected to a DC power source.

[0066] The induction heating arrangement is preferably configured to generate a high frequency magnetic field, which as referred to herein may be in the range of 500 kHz to 30 MHz, particularly 5 MHz to 15 MHz, preferably 5 MHz to 10 MHz.

[0067] The aerosol generating device may further comprise a controller configured to control the operation of the heating process, preferably in a closed loop configuration, to specifically control the heating of the aerosol-forming liquid to a predetermined operating temperature.

[0068] The controller may be the overall controller of the aerosol generating device or may be part of the overall controller of the aerosol generating device. The controller may comprise a microprocessor (e.g., a programmable microprocessor), a microcontroller, or an application specific integrated circuit (ASIC) or other electronic circuitry capable of providing control. The controller may comprise further electronic components, such as at least one DC / AC inverter and / or a power amplifier (e.g., a class C power amplifier, or a class D power amplifier, or a class E power amplifier). In particular, the inductive source may be part of the controller.

[0069] The aerosol generating device may also include a power source, specifically a DC power source configured to provide a DC supply voltage and a DC supply current to the induction source. The power source is preferably a battery, such as a lithium iron phosphate battery. The power source may be rechargeable. The power source may have a capacity that allows for storage of sufficient energy for one or more user experiences. For example, the power source may have a capacity sufficient to allow continuous generation of aerosol for about six minutes, or a multiple of six minutes. In another embodiment, the power source may have a capacity sufficient to allow a predetermined number of puffs, or discontinuous activation of the induction source.

[0070] Further features and advantages of the aerosol-generating system according to the present invention have been described with respect to the susceptor arrangement and the aerosol-generating article and therefore apply equally.

[0071] The present invention is defined in the claims. However, below is provided a non-exhaustive list of non-limiting examples. Any one or more of the features of these examples may be combined with any one or more features of any other example, embodiment, or aspect described herein.

[0072] Example 1: A multi-layer susceptor arrangement for inductively heating an aerosol-forming substrate, comprising at least: a first layer comprising a first susceptor material; a second layer comprising a second susceptor material, the second susceptor material comprising or consisting of a Ni-Fe alloy comprising 75% to 85% by weight of Ni and 10% to 25% by weight of Fe. Example 2: A multi-layer susceptor arrangement as described in example 1, wherein the Ni-Fe-alloy further comprises one or more of the elements Co, Cr, Cu, Mn, Mo, Nb, Si, Ti, V. Example 3: A multi-layer susceptor arrangement according to any one of Examples 1-2, wherein the Ni-Fe alloy comprises 79-82 wt. % Ni and 13-15 wt. % Fe. Example 4: A multilayer susceptor arrangement according to any one of Examples 1 to 3, wherein the Ni-Fe alloy comprises 79% to 82% by weight Ni, 4% to 6% by weight Mo, less than 1% by weight Si and Mn combined together, and 13% to 15% by weight Fe. Example 5: A multi-layer susceptor arrangement as described in any one of Example 1 or Example 2, wherein the Ni-Fe alloy comprises 77 wt.% Ni, 16 wt.% Fe, 5 wt.% Cu, and 2 wt.% of one of Cr and Mo. Example 6: A multi-layer susceptor arrangement according to any one of Examples 1 or 2, wherein the Ni-Fe alloy comprises 77 wt.% Ni, 14-15 wt.% Fe, 4 wt.% Cu, and 4 wt.% Mo. Example 7: The multi-layer susceptor arrangement of any one of Examples 1-6, wherein the first susceptor material comprises a metal, such as ferritic iron, or stainless steel, specifically grade 410, grade 420, or grade 430 stainless steel. Example 8: The multi-layer susceptor arrangement of any one of Examples 1-7, wherein the second layer is intimately connected to the first layer. Example 9: A multi-layer susceptor arrangement according to any one of Examples 1 to 8, wherein the first layer has a layer thickness in the range of 20 micrometers to 60 micrometers, specifically 30 micrometers to 50 micrometers, preferably 40 micrometers. Example 10: A multi-layer susceptor arrangement according to any one of Examples 1 to 9, wherein the second layer has a layer thickness in the range of 4 micrometers to 20 micrometers, specifically 8 micrometers to 16 micrometers, preferably 10 micrometers to 15 micrometers. Example 11: The multi-layer susceptor arrangement of any one of Examples 1-10, further comprising a third layer intimately connected to the second layer. Example 12: The multi-layer susceptor arrangement of example 11, wherein the third layer comprises or consists of a corrosion resistant material. Example 13: The multi-layer susceptor arrangement of any one of Example 11 or Example 12, wherein the third layer comprises or consists of the same material as the first susceptor material of the first layer. Example 14: A multi-layer susceptor arrangement according to any one of Examples 11 to 13, wherein the third layer comprises or consists of a metal, such as ferritic iron, or stainless steel, in particular grade 410, grade 420, or grade 430 stainless steel. Example 15: The multi-layer susceptor arrangement of any one of Examples 11-12, wherein the third layer comprises or consists of an austenitic stainless steel. Example 16: The multi-layer susceptor arrangement of Example 15, wherein the third layer comprises, or consists of, X5CrNi18-10 or X2CrNiMo17-12-2. Example 17: The multi-layer susceptor arrangement of example 15, wherein the third layer comprises or consists of one of 301 stainless steel, 304 stainless steel, 304L stainless steel, 316 stainless steel, or 316L stainless steel. Example 18: A multilayer susceptor arrangement according to any one of Examples 11 to 17, wherein the layer thickness of the third layer is within the range of 0.05 to 1.5 times, specifically 0.1 to 1.25 times, or 0.95 to 1.05 times, specifically 1 time, the layer thickness of the first layer. Example 19: A multi-layer susceptor arrangement according to any one of Examples 11 to 17, wherein the layer thickness of the third layer is equal to the layer thickness of the first layer. Example 20: A multi-layer susceptor arrangement according to any one of Examples 11 to 19, wherein the third layer has a layer thickness in the range of 2 micrometers to 6 micrometers, specifically 3 micrometers to 5 micrometers, preferably 3 micrometers to 4 micrometers. Example 21: The multi-layer susceptor arrangement of any one of Examples 11-20, wherein the first layer, the second layer, and the third layer are adjacent layers of the multi-layer susceptor arrangement. Example 22: An inductively heatable aerosol-generating article comprising an aerosol-forming substrate and a multi-layer susceptor arrangement as defined in any one of Examples 1-21. Example 23: An aerosol-generating article according to Example 22, wherein the susceptor arrangement is located within the aerosol-forming substrate. Example 24: An aerosol generating system comprising an inductively heatable aerosol generating article according to any one of Example 22 or Example 23 and an inductively heatable aerosol generator for use with the aerosol generating article.

[0073] The embodiments will now be further described with reference to the following figures: [Brief description of the drawings]

[0074] [Figure 1] FIG. 1 illustrates generally one exemplary embodiment of an inductively heatable aerosol-generating article comprising a multi-layer susceptor arrangement according to the present invention. [Diagram 2] FIG. 2 illustrates a schematic diagram of an exemplary embodiment of an aerosol-generating system comprising an aerosol-generating article according to FIG. [Diagram 3] FIG. 3 shows details of the multi-layer susceptor arrangement of the aerosol-generating article of FIG. [Figure 4] FIG. 4 shows details of another embodiment of a multi-layer susceptor arrangement according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0075] 1 illustrates in schematic form (not to scale) an exemplary embodiment of an inductively heatable aerosol-generating article 100 according to the present invention. The aerosol-generating article 100 is a substantially rod-shaped consumable comprising five elements arranged consecutively in coaxial alignment: a distal forward plug element 150, a base element 110, a first tube element 140, a second tube element 145, and a filter element 160. The distal forward plug element 150 is arranged at the distal end 102 of the article 100 and covers and protects the distal forward end of the base element 110, while the filter element 160 is arranged at the proximal end 103 of the article 100. Both the distal forward plug element 150 and the filter element 160 may be made of the same filter material. The filter element 160 preferably functions as a mouthpiece, preferably as part of the mouthpiece together with the second tube element 145. The filter element may have a length of 10 mm to 14 mm, for example 12 mm, while the distal front plug element 150 may have a length of 3 mm to 6 mm, for example 5 mm. The base element 110 comprises not only the aerosol-forming substrate 130 to be heated, but also the multi-layer susceptor arrangement 120 according to a first embodiment of the invention, which is configured and arranged to heat the substrate 130. For this purpose, the susceptor arrangement 120 is fully embedded in the substrate 130 so as to be in direct thermal contact with the substrate 130. The base element 110 may have a length of 10 mm to 14 mm, for example 12 mm. Each of the first tube element 140 and the second tube element 145 is a hollow cellulose acetate tube having a central air passage 141, 146, the cross section of the central air passage 146 of the second tube element 145 being larger than the cross section of the central air passage 141 of the first tube element 140. The first pipe element 140 and the second pipe element 145 may have a length between 6 mm and 10 mm, for example 8 mm.

[0076] In use, an aerosol formed by volatile compounds released from the substrate element 110 is drawn through the first and second tube elements 140, 145, and the filter element 160 toward the proximal end 103 of the article 100. Each of the aforementioned elements 150, 110, 140, 145, 160 may be substantially cylindrical. Specifically, all of the elements 150, 110, 140, 145, 160 may have the same external cross-sectional shape and dimensions.

[0077] In addition, the elements may be surrounded by one or more outer wrappers, such as to keep the elements together and to maintain a desired cross-sectional shape of the rod-like article. In this embodiment, the distal forward plug element 150, the base element 110, and the first tube element 140 are surrounded by the first wrapper 140, while the second tube element 145 and the filter element 160 are surrounded by the second wrapper 172. The second wrapper 172 also surrounds at least a portion of the first tube element 140 (after being wrapped by the first wrapper 171) to connect the distal forward plug element 150, the base element 110, and the first tube element 140 surrounded by the first wrapper 171 to the second tube element 145 and the filter element 160. The first wrapper 171 and the second wrapper 172 are preferably made of paper. In addition, the second wrapper 172 may be provided with perforations around its circumference (not shown). The wrappers 171, 172 may further comprise an adhesive that adheres the overlapping free ends of the wrappers to one another.

[0078] As shown in FIG. 2, the aerosol-generating article 100 is configured for use with an inductively heated aerosol generating device 10. The device 10 and the article 100 together form an aerosol generating system 1 according to the present invention. The aerosol generating device 10 comprises a cylindrical receiving cavity 20 defined in a proximal portion 12 of the device 10, in which at least a distal portion of the article 100 is received. The device 10 further comprises an inductive heating arrangement including an induction coil 30 for generating an alternating magnetic field, specifically a high-frequency alternating magnetic field, in the cavity 20. In this embodiment, the induction coil 30 is a helical coil circumferentially surrounding the cylindrical receiving cavity 20. The coil 30 is arranged such that the susceptor arrangement 120 of the aerosol-generating article 100 is exposed to the magnetic field upon insertion of the article 100 into the cavity 20 of the device 10. Thus, when the induction heating arrangement is activated, depending on the magnetic and electrical properties of the susceptor material of the susceptor arrangement 120, the susceptor arrangement 120 heats up due to eddy currents and / or hysteresis losses induced by the alternating magnetic field. The susceptor arrangement 120 is heated until it reaches an operating temperature sufficient to vaporize the aerosol-forming substrate 130 surrounding the susceptor arrangement 120 in the article 100. In the distal portion 13, the aerosol generating device 10 further comprises a DC power supply 40 and a controller 50 (shown only diagrammatically in FIG. 2) for supplying power and controlling the heating process. Apart from the induction coil 30, the induction heating arrangement is preferably an at least partially integral part of the controller 50.

[0079] Figure 3 shows a detailed view (not to scale) of the susceptor arrangement 120 used in the aerosol-generating article shown in Figure 1. According to the invention, the susceptor arrangement 120 is a multi-layer susceptor arrangement 120 comprising at least a first layer 121 and a second layer 122. In the present invention, the multi-layer susceptor arrangement 120 comprises only two layers, namely the first layer 121 and the second layer 122. The first layer 121 comprises a first susceptor material that is optimized with respect to heat loss and therefore heating efficiency, while the second layer 122 comprises a second susceptor material that acts as a temperature marker. For this purpose, the second susceptor material is chosen to be ferromagnetic and to have a Curie temperature that corresponds to a predetermined temperature point for heating the substrate 130. At its Curie temperature, the magnetic permeability of the second susceptor material drops to 1, leading to a change in its magnetic properties from ferromagnetic to paramagnetic. The change in magnetic properties is accompanied by a temporal change in the electrical resistance of the susceptor arrangement 120. Therefore, by monitoring the corresponding change in the current absorbed by the induction heating arrangement of the apparatus 10, it is possible to detect when the second susceptor material has reached its Curie temperature, and hence a predetermined temperature point. In this manner, the first layer is primarily used to heat the substrate, while the second layer may be considered to be the functional layer.

[0080] In this embodiment, the first layer 121 comprises 400 series stainless steel (such as grade 410 stainless steel, or grade 420 stainless steel, or grade 430 stainless steel, or a similar grade stainless steel). The use of stainless steel proves advantageous with regard to the aging properties of the first layer 121, which is in direct contact with the aerosol-forming substrate 130 in the base element 110.

[0081] As can be further seen in FIG. 3, the multi-layer susceptor arrangement 120 is in the form of an elongated strip, where the second layer 122 is intimately connected to the first layer 121 thereon. The strip-like susceptor arrangement has a length L of 10-12 mm and a width W of 4-5 mm. That is, both layers have a length L of 10-12 mm and a width W of 4-5 mm, yet different layer thicknesses. The first layer 121 has a layer thickness of 50 micrometers, while the second layer 122 has a layer thickness of 10 micrometers. Thus, the total thickness T of the susceptor arrangement 120 is 60 micrometers. The susceptor arrangement 120 is formed by cladding the second susceptor material of the second layer 122 onto the first susceptor material of the first layer 121.

[0082] However, the fact that the first and second layers are intimately connected to each other, but typically have different thermal expansion coefficients, may give rise to undesirable internal stresses. As mentioned above, these internal stresses will cause modifications of the magnetic properties of the susceptor arrangement if the second susceptor material exhibits magnetostriction. In order to reduce these undesirable effects, the susceptor arrangement according to the invention comprises a second susceptor material that exhibits only weak or no magnetostriction. According to the invention, this has been found to be the case for a Ni-Fe alloy having 75% to 85% by weight Ni and 10% to 25% by weight Fe. The remainder of the alloy may comprise one or more of the elements Co, Cr, Cu, Mn, Mo, Nb, Si, Ti, V.

[0083] In this embodiment, the second layer 122 is made of a Ni-Fe-alloy (as the second susceptor material) containing 79% to 82% by weight Ni, 4% to 6% by weight Mo, less than 1% by weight Si and Mn combined together, and 13% to 15% by weight Fe.

[0084] Alternatively, the Ni-Fe alloy may comprise 77% by weight Ni, 16% by weight Fe, 5% by weight Cu, and 2% by weight of one of Cr and Mo. According to yet another alternative, the Ni-Fe alloy may comprise 77% by weight Ni, 14-15% by weight Fe, 4% by weight Cu, and 4% by weight Mo.

[0085] FIG. 4 shows a detail of a multi-layer susceptor arrangement 220 according to another embodiment of the invention (not to scale). In contrast to the susceptor arrangement 120 according to FIGS. 1-3, the multi-layer susceptor arrangement 220 according to FIG. 4 comprises, in addition to the first layer 221 and the second layer 222, a third layer 223. The third layer 223 is intimately connected to (on) the second layer 222, which in turn is intimately connected to (on) the first layer 221. The third layer 223 is a protective layer made of a corrosion-resistant material to protect the second layer, which is not corrosion-resistant, from any corrosive influences. This is particularly important since, as shown in FIG. 1, the susceptor arrangement 220 is typically in direct physical contact with the aerosol-forming substrate. In addition, the third layer 223 avoids material diffusion, e.g. metal diffusion, from the second susceptor material into the aerosol-forming substrate. Additionally, the third layer 223 helps to avoid or reduce thermal bending due to differences in thermal expansion between the layers 221 , 222 , 223 .

[0086] The susceptor arrangement 220 may be formed by first cladding the second susceptor material onto the material of the first layer 221. The material of the third layer 223 may then be clad onto the second layer 222.

[0087] The third layer 223 preferably comprises or consists of the same material as the first layer 221. Thus, the multi-layer susceptor arrangement 220 comprises at least two layers 221, 223 having the same thermal expansion coefficient, which results in reduced deformation of the susceptor arrangement 220 throughout its operating temperature range. As a result, both the first layer 221 and the third layer 223 of the susceptor arrangement 220 shown in Figure 4 may comprise 400 series stainless steel (such as grade 410 stainless steel, or grade 420 stainless steel, or grade 430 stainless steel, or a similar grade stainless steel).

[0088] Alternatively, the third layer 223 may include or consist of an austenitic stainless steel. By way of example, the third layer 223 may include or consist of X5CrNi18-10 or X2CrNiMo17-12-2 (designations according to EN (European Standards)). In particular, the third layer 223 may include or consist of one of 301 stainless steel, 304 stainless steel, 304L stainless steel, 316 stainless steel, or 316L stainless steel (designations according to SAE steel grades [Society of Automotive Engineers]). Advantageously, austenitic stainless steel, due to its paramagnetic properties and high electrical resistivity, slightly shields the second susceptor material of the second layer 222 from magnetic fields applied thereto.

[0089] As in the case of Fig. 3, the second layer 222 according to Fig. 4 may consist of a Ni-Fe-alloy (as the second susceptor material) containing 79% to 82% by weight Ni, 4% to 6% by weight Mo, less than 1% by weight of Si and Mn combined together, and 13% to 15% by weight Fe. Alternatively, the Ni-Fe-alloy may contain 77% by weight Ni, 16% by weight Fe, 5% by weight Cu, and one of 2% by weight Cr and Mo. According to yet another alternative, the Ni-Fe-alloy may contain 77% by weight Ni, 14-15% by weight Fe, 4% by weight Cu, and 4% by weight Mo.

[0090] The layer thickness of the third layer 223 may be between 3 micrometers and 5 micrometers, for example 3.5 micrometers. The layer thickness of the second layer 222 may be between 15 micrometers and 16 micrometers. The layer thickness of the first layer 221 may be between 40 micrometers and 42 micrometers, in particular between 40.5 micrometers and 41.5 micrometers. In total, the multilayer susceptor arrangement 220 according to Fig. 4 may have a thickness of 60 micrometers.

[0091] For the purposes of this specification and the appended claims, unless otherwise indicated, all numbers expressing amounts, quantities, percentages, and the like, should be understood in all cases as modified by the term "about." Also, all ranges include the maximum and minimum points disclosed, and include any intermediate ranges therein, which may or may not be specifically recited herein. Thus, in this context, the number A is understood as A±5%. Within this context, the number A may be considered to include a numerical value that is within the general standard error for the measurement of the property that the number A modifies. The number A may deviate by the percentages recited above, in some cases as used in the appended claims, provided that the amount by which A deviates does not materially affect the basic and novel property(ies) of the claimed invention. Also, all ranges include the maximum and minimum points disclosed, and include any intermediate ranges therein, which may or may not be specifically recited herein.

Claims

1. 1. A multi-layer susceptor arrangement for inductively heating an aerosol-forming substrate, comprising at least a first layer comprising a first susceptor material; a second layer comprising a second susceptor material, said second susceptor material comprising: 79% to 82% by weight of Ni and 13% to 15% by weight of Fe, or 79% to 82% by weight Ni, 4% to 6% by weight Mo, less than 1% by weight Si and Mn combined together, and 13% to 15% by weight Fe, or 77% by weight Ni, 16% by weight Fe, 5% by weight Cu, and 2% by weight of one of Cr and Mo, or a second layer comprising or consisting of a Ni-Fe-alloy containing one of the following by weight: 77% Ni, 14-15% Fe, 4% Cu, and 4% Mo.

2. 2. The multi-layer susceptor arrangement of claim 1, wherein the first susceptor material comprises a metal, such as ferritic iron, or stainless steel, specifically grade 410, grade 420, or grade 430 stainless steel.

3. 3. The multi-layer susceptor arrangement of claim 1 or 2, wherein the second layer is intimately connected to the first layer.

4. 3. The multilayer susceptor arrangement according to claim 1 or 2, wherein the first layer has a layer thickness in the range of 20 micrometers to 60 micrometers, in particular in the range of 30 micrometers to 50 micrometers, preferably 40 micrometers, and the second layer has a layer thickness in the range of 4 micrometers to 20 micrometers, in particular in the range of 8 micrometers to 16 micrometers, preferably in the range of 10 micrometers to 15 micrometers.

5. 3. The multi-layer susceptor arrangement of claim 1 or 2, further comprising a third layer intimately connected to the second layer.

6. The multi-layer susceptor arrangement of claim 5 , wherein the third layer comprises or consists of a corrosion resistant material.

7. The multi-layer susceptor arrangement of claim 5 , wherein the third layer comprises or consists of the same material as the first susceptor material of the first layer.

8. 6. The multi-layer susceptor arrangement of claim 5, wherein the third layer comprises or consists of an austenitic stainless steel, specifically one of 301 stainless steel, 304 stainless steel, 304L stainless steel, 316 stainless steel, or 316L stainless steel.

9. 6. The multi-layer susceptor arrangement according to claim 5, wherein the third layer has a layer thickness in the range of 2 micrometers to 6 micrometers, in particular 3 micrometers to 5 micrometers, preferably 3 micrometers to 4 micrometers.

10. The multi-layer susceptor arrangement of claim 5 , wherein the first layer, the second layer, and the third layer are adjacent layers of the multi-layer susceptor arrangement.

11. 3. An inductively heatable aerosol-generating article comprising an aerosol-forming substrate and the multi-layer susceptor arrangement of claim 1 or 2.

12. 1. A multi-layer susceptor arrangement for inductively heating an aerosol-forming substrate, comprising at least a first layer comprising a first susceptor material; a second layer intimately connected to said first layer and comprising a second susceptor material, said second susceptor material comprising or consisting of a Ni-Fe alloy comprising 75% to 85% by weight Ni and 10% to 25% by weight Fe; a third layer intimately connected to said second layer, A multi-layer susceptor arrangement, wherein the first layer has a layer thickness in the range of 20 micrometers to 60 micrometers and the third layer has a layer thickness in the range of 2 micrometers to 6 micrometers.

13. 13. The multi-layer susceptor arrangement of claim 12, wherein the Ni-Fe-alloy further comprises one or more of the elements Co, Cr, Cu, Mn, Mo, Nb, Si, Ti, V.

14. 14. The multi-layer susceptor arrangement according to claim 12 or 13, wherein said Ni-Fe-alloy comprises 79% to 82% by weight of Ni and 13% to 15% by weight of Fe, specifically said Ni-Fe-alloy comprises 79% to 82% by weight of Ni, 4% to 6% by weight of Mo, less than 1% by weight of Si and Mn combined together, and 13% to 15% by weight of Fe.

15. 14. The multi-layer susceptor arrangement of claim 12 or 13, wherein the Ni-Fe-alloy comprises 77% by weight Ni, 16% by weight Fe, 5% by weight Cu, and 2% by weight of one of Cr and Mo.

16. 14. The multi-layer susceptor arrangement according to claim 12 or 13, wherein the Ni-Fe-alloy comprises 77% Ni, 14-15% Fe, 4% Cu, and 4% Mo by weight.

17. 14. The multi-layer susceptor arrangement of claim 12 or 13, wherein the first susceptor material comprises a metal, such as ferritic iron, or stainless steel, in particular grade 410, grade 420, or grade 430 stainless steel.

18. A multi-layer susceptor arrangement according to claim 12 or 13, wherein the first layer has a layer thickness in the range of 30 micrometers to 50 micrometers, preferably 40 micrometers.

19. 14. A multi-layer susceptor arrangement according to claim 12 or 13, wherein the second layer has a layer thickness in the range of 4 micrometers to 20 micrometers, in particular 8 micrometers to 16 micrometers, preferably 10 micrometers to 15 micrometers.

20. 14. The multi-layer susceptor arrangement of claim 12 or 13, wherein the third layer comprises or consists of a corrosion resistant material.

21. 14. The multi-layer susceptor arrangement of claim 12 or 13, wherein the third layer comprises or consists of the same material as the first susceptor material of the first layer.

22. 14. The multi-layer susceptor arrangement of claim 12 or 13, wherein the third layer comprises or consists of an austenitic stainless steel, specifically one of 301 stainless steel, 304 stainless steel, 304L stainless steel, 316 stainless steel, or 316L stainless steel.

23. A multi-layer susceptor arrangement according to claim 12 or 13, wherein the third layer has a layer thickness in the range of 3 micrometers to 5 micrometers, preferably 3 micrometers to 4 micrometers.

24. 14. The multi-layer susceptor arrangement of claim 12 or 13, wherein the first layer, the second layer, and the third layer are adjacent layers of the multi-layer susceptor arrangement.

25. 14. An inductively heatable aerosol-generating article comprising an aerosol-forming substrate and a multi-layer susceptor arrangement according to claim 12 or 13.

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