Multilayer susceptor arrangement for inductively heating an aerosol-forming substrate

Abstract

The present invention relates to a multi-layer susceptor arrangement (120) for inductively heating an aerosol-forming substrate (130), the susceptor arrangement (120) comprising or consisting of a first layer (121) including or consisting of a first susceptor material, a second layer (122) including or consisting of a second susceptor material, and a third layer (123) including or consisting of a third material. The second layer (122) is sandwiched between the first and third layers. The second susceptor material includes or consists of a Ni-Fe alloy having a Ni content of 65% by weight or less. The third layer has a thickness of 8 micrometers or less. The present invention relates to an aerosol-generating article (100) and an aerosol-generating system including the 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 relates to an aerosol-generating article and an aerosol-generating system comprising the aerosol-generating article and an inductively heated aerosol generator for use with the article. [Background technology]

[0002] It is generally known in the prior art to generate aerosols by inductively heating 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 housed within an aerosol-generating device. The device may include an induction source for generating an alternating magnetic field used to inductively heat the susceptor arrangement by inducing at least one of eddy currents and hysteresis losses in the material of the susceptor arrangement. The susceptor arrangement may be an integral part of the article or may be disposed in thermal proximity or direct physical contact with the substrate to be heated. Alternatively, the susceptor arrangement may be part of the device and may be disposed in thermal proximity or direct physical contact with the substrate when the article is engaged with the device.

[0003] To control the temperature of a substrate, a multi-layer susceptor arrangement has been proposed, comprising a first layer and a second layer tightly bonded together. The first layer comprises a first susceptor material optimized for heat loss and therefore heating efficiency, while the second layer comprises a second susceptor material used as a temperature marker. To this end, the second susceptor material is selected to be magnetic (ferromagnetic or ferrimagnetic) and have a Curie temperature corresponding to a predetermined temperature point for heating the substrate. At that Curie temperature, the magnetic permeability of the second susceptor material decreases monotonically, leading to a change in its magnetic properties from ferromagnetic or ferrimagnetic to paramagnetic. This 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 current through an 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. Summary of the Invention [Problem to be solved by the invention]

[0004] Depending on the specific compositions of the first and second susceptors, such susceptor arrangements may result in diffusion of material from the susceptor material to the aerosol-forming substrate and material degradation, particularly corrosion. Additionally, depending on the material pairing resulting from the specific materials of the first and second layers, such susceptor arrangements may result in changes in the magnetic properties of the susceptor material and thermal bending due to differences in thermal expansion between the layers.

[0005] Therefore, what is desired is a susceptor arrangement for inductively heating an aerosol-forming substrate that provides the advantages of prior art solutions while reducing their limitations. Specifically, what is desired is a susceptor arrangement and an aerosol-generating article including such a susceptor arrangement that has improved properties at least with respect to material diffusion and material degradation from the susceptor material to the aerosol-forming substrate. [Brief explanation of the drawings]

[0006] [Figure 1]FIG. 1 illustrates schematically one exemplary embodiment of an inductively heatable aerosol-generating article comprising a multi-layer susceptor arrangement according to the present invention. [Figure 2] FIG. 2 illustrates schematically an exemplary embodiment of an aerosol-generating system comprising an aerosol-generating article according to FIG. [Figure 3] FIG. 3 shows in perspective view a detail of the multi-layer susceptor arrangement of the aerosol-generating article of FIG. [Figure 4] FIG. 4 shows in cross-section a detail of the multi-layer susceptor arrangement of the aerosol-generating article of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0007] According to the present invention, there is provided a multi-layer susceptor arrangement for inductively heating an aerosol-forming substrate, the susceptor arrangement comprising or consisting of a first layer including or consisting of a first susceptor material, a second layer including or consisting of a second susceptor material, and a third layer including or consisting of a third material. The second layer is sandwiched between the first and third layers. The second susceptor material includes or consists of a Ni-Fe alloy having a Ni content of 65 wt% or less. The third layer has a thickness of 8 micrometers or less.

[0008] According to the present invention, it has been found that the properties of a susceptor arrangement can be readily improved by adding a third layer to the second layer opposite the first layer, such that the second layer is sandwiched between the first and third layers. The third layer can thus function as a protective layer configured to at least one of prevent material diffusion, e.g., migration of metals from the second susceptor material into the aerosol-forming substrate, or protect other layers, particularly the second layer, from degradation, particularly, e.g., corrosion. Both aspects are particularly important when the susceptor arrangement is intended to be embedded in the aerosol-forming substrate of the aerosol-generating article, i.e., when the susceptor arrangement is intended to be disposed in direct physical contact with the aerosol-forming substrate.

[0009] Specifically, the third layer allows for more selective and freer selection of the composition of the second susceptor material with respect to its magnetic properties, particularly with respect to the desired Curie temperature, while at the same time being less constrained by limitations related to material degradation and material diffusion. For example, the third layer allows for the deliberate selection of a material with low corrosion resistance as the temperature marker material for the second layer, but with a desired Curie temperature close to or equal to the predetermined temperature point for heating the substrate.

[0010] It has further been found that the thickness of the third layer can be relatively thin, i.e., 8 micrometers or less. A thin third layer is advantageous not only in terms of saving material, but also in that the second layer is less likely to be shielded from the alternating magnetic field of an induction source used to inductively heat the susceptor arrangement. As a result, when the second susceptor material is used as a temperature marker, the above-mentioned change in the magnetic properties of the second susceptor material near its Curie temperature has a more pronounced effect on the current passing through the induction source. Advantageously, this allows for a more reliable determination of when the second susceptor material has reached its Curie temperature, and therefore when a predetermined temperature point has been reached.

[0011] As used herein, the term "thickness" refers to the dimension extending between the upper and lower surfaces, for example, between the upper and lower surfaces of a layer, or between the upper and lower surfaces of a multi-layer susceptor arrangement.

[0012] Basically, the thinner the third layer, the more material savings and the more reliable the temperature monitoring. Therefore, the thickness of the third layer may be 7 micrometers or less, specifically 7 micrometers or less, more specifically 6 micrometers or less, more specifically 5 micrometers or less, preferably 4 micrometers or less, or 3 micrometers or less.

[0013] Relatively, the thickness of the third layer may be 50% or less, specifically 40% or less, more specifically 30% or less, preferably 25% or less, more preferably 20% or less, even more preferably 15% or less, and most preferably 10% or less of the thickness of the first layer.

[0014] Conversely, the third layer should not be too thin to adequately perform its protective function. Specifically, if the third layer is too thin, it may be fragile and prone to failure. Therefore, the thickness of the third layer may be at least 0.75 micrometers, specifically at least 1 micrometer.

[0015] Considering the above upper and lower limits, it can be advantageous if the layer thickness of the third layer is preferably in the range of 0.75 micrometers to 8 micrometers, specifically 1 micrometer to 5 micrometers, more specifically 2 micrometers to 4 micrometers, for example 3.5 micrometers.

[0016] As used herein, the term "susceptor material" refers to a material that has the ability to convert magnetic field 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 magnetic 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 loss.

[0017] As noted above, the first layer comprising the first susceptor material preferably functions as the primary susceptor for heating the aerosol-forming substrate, and to this end, the first susceptor material may be optimized with respect to heat loss and hence heating efficiency.

[0018] At least a portion of the outer surface of the first layer is unprotected, i.e., bare, and exposed to the environment or in direct contact with the environment. Specifically, when the susceptor arrangement is embedded in the aerosol-forming substrate, at least a portion of the outer surface of the first layer is exposed to the aerosol-forming substrate and is in direct physical contact with the aerosol-forming substrate. Advantageously, this allows for good heat transfer to the aerosol-forming substrate, which is preferably heated primarily by the first layer. All portions of the outer surface of the first layer are unprotected, bare, or exposed to the environment unless they are in close physical contact with another layer, specifically the second layer. Advantageously, this ensures maximum heat transfer to the aerosol-forming substrate.

[0019] The first susceptor material may be at least one of electrically conductive and 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.

[0020] The first susceptor material is preferably made of a corrosion resistant material and is therefore advantageously resistant to any corrosive influences itself.

[0021] Preferably, the first susceptor material comprises or consists of 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 for the first susceptor material to comprise or consist of 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.

[0022] Alternatively, the first susceptor material may comprise or consist of a suitable non-magnetic material, in particular a paramagnetic conductive material, such as aluminum (Al), in which induction heating occurs solely through resistive heating due to eddy currents.

[0023] Alternatively, the first susceptor material may include or consist of a non-conductive ferrimagnetic material, such as a non-conductive ferrimagnetic ceramic, in which case heat is generated solely by hysteresis losses.

[0024] As described above, the second susceptor material preferably functions as a temperature marker. That is, the second susceptor material is preferably configured to monitor the temperature of the susceptor arrangement. To this end, the second susceptor material may be selected to have a Curie temperature that essentially corresponds to a predetermined temperature point in the heating process. Specifically, 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 sufficiently low 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 heated aerosol-forming substrate. The second susceptor material, specifically a Ni-Fe alloy of the second susceptor material, may have a Curie temperature of less than 500°C, preferably less than 400°C, and particularly less than 390°C. For example, the second susceptor, specifically the Ni-Fe alloy of the second susceptor material, may have a Curie temperature in the range of 180°C to 420°C, particularly 210°C to 380°C, and preferably 250°C to 380°C. The second layer may be primarily a functional layer that provides a temperature marker by virtue of the Curie temperature of the second susceptor material, but may also contribute to inductive heating of the susceptor arrangement. Preferably, the second layer is a first layer including a first susceptor material that is primarily configured to heat the aerosol-forming substrate.

[0025] As defined above, the second susceptor material comprises or consists of a Ni-Fe alloy having a Ni content of 65 wt% or less. As used herein, the term "wt% (wt%)" refers to "weight percent" or "weight percentage." That is, it refers to 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.

[0026] Advantageously, most Ni-Fe alloys with a Ni content of 65 wt. % or less have Curie temperatures in the range below 600° C., making them highly suitable as temperature markers for a wide range of heated, non-combustion substrates, most of which have ignition points above 600° C. Furthermore, most Ni-Fe alloys with a Ni content of 65 wt. % or less still possess a sufficiently large magnetic permeability that they exhibit a clearly detectable decrease in magnetic permeability when the temperature of the material approaches the Curie point.

[0027] The Ni content may be much less than 65 wt %. Thus, the Ni-Fe alloy of the second susceptor material has an Ni content of 50 wt % or less, specifically 44 wt % or less, more specifically an Ni content in the range of 36 wt % to 44 wt %, preferably in the range of 36 wt % to 40 wt %, for example 36.1 wt %, 36.4 wt %, or 40 wt %, with the remainder preferably being Fe.

[0028] The Ni-Fe alloy of the second susceptor material may be a binary Ni-Fe alloy, ie, a Ni-Fe alloy consisting only of Ni and Fe.

[0029] Alternatively, the Ni-Fe alloy may include one or more of the following elements: Co, Cr, Cu, Mn, Mo, Nb, Si, Ti and V.

[0030] 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.

[0031] Advantageously, the Curie temperature of the Ni-Fe alloy may be selectively adjusted by adding chromium. Therefore, the Ni-Fe alloy of the second susceptor material may further contain chromium. Specifically, the second susceptor material may include or consist of a Ni-Fe-Cr alloy. The higher the chromium content, the lower the Curie temperature of the alloy. Furthermore, adding chromium affects the corrosion resistance of the Ni-Fe alloy. Generally, corrosion resistance can be improved by increasing the chromium content. As a specific example, the Ni-Fe alloy of the second susceptor material may further contain 8% to 12% by weight of Cr, particularly 9% to 11% by weight of Cr. Depending on the actual Ni content, the Curie temperature of the Ni-Fe alloy further containing 8% to 12% by weight of Cr, particularly 9% to 11% by weight of Cr, can be advantageously adjusted to be within the range of 200°C to 300°C.

[0032] According to one example, a Ni-Fe alloy may contain or consist of 50% Ni, 9% Cr by weight, and the remainder Fe. This alloy is commercially available, for example, under the trade name Phytherm 260, and has a Curie temperature of 260°C. According to another example, a Ni-Fe alloy may contain or consist of 50% Ni, 10% Cr by weight, and the remainder Fe. This alloy may be commercially available, for example, under the trade name Phytherm 220, and has a Curie temperature of 230°C. According to yet another example, a Ni-Fe alloy may contain or consist of 50% Ni, 11% Cr by weight, and the remainder Fe. This alloy is also commercially available, for example, under the trade name Phytherm 210, and has a Curie temperature of 210°C. Advantageously, all of the aforementioned alloys (Phytherm alloys) are corrosion-resistant materials.

[0033] The Ni-Fe alloy may also contain one or more other elements in addition to chromium.

[0034] According to one example, the Ni-Fe alloy of the second susceptor material may include or consist of 50 wt% Ni, 9 wt% Cr, up to 1 wt% Si, and up to 1 wt% Mn, with the remainder being Fe. According to another example, the Ni-Fe alloy of the second susceptor material may include or consist of 50 wt% Ni, 10 wt% Cr, up to 1 wt% Si, and up to 1 wt% Mn, with the remainder being Fe. According to yet another example, the Ni-Fe alloy of the second susceptor material may include or consist of 50 wt% Ni, 11 wt% Cr, up to 1 wt% Si, and up to 1 wt% Mn, with the remainder being Fe.

[0035] As described above, the Ni-Fe alloy of the second susceptor material may have a Ni content even less than 50% by weight. Specifically, the Ni-Fe alloy of the second susceptor material may have a Ni content of 44% by weight or less, more specifically, a Ni content in the range of 36% to 44% by weight, preferably 36% to 40% by weight, e.g., 36.1% by weight, 36.4% by weight, or 40% by weight, with the remainder preferably being Fe. As an example, the Ni-Fe alloy may be an alloy available from Hitachi under the designation "MS-10," which has a Ni content of 36.1% by weight and a Curie temperature of 213°C. Similarly, the Ni-Fe alloy may be an alloy available from Hitachi under the designation "MS-16," which has a Ni content of 36.4% by weight and a Curie temperature of 221.5°C.

[0036] As used herein, the term "third layer" refers to the first and second layers as well as layers different from 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).

[0037] Preferably, the third material comprises or consists of a corrosion-resistant material, which advantageously improves the aging properties of those portions of the outer surface of the second layer that are not directly exposed to the environment because they are covered by the third layer.

[0038] The third layer may include or consist of the same material as the first susceptor material of the first layer. That is, the third material may be identical to the first susceptor material. 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 particularly true when the susceptor arrangement comprises only a first layer, a second layer, and a third layer, such that the second layer is symmetrically sandwiched between the first and third layers.

[0039] Alternatively, the third material may be different from the first susceptor material, and in this manner, the properties of the first and third layers may be independently selected to best suit their respective purposes.

[0040] In particular, when the third material is the same as the first susceptor material, the third material may comprise or consist of a metal, such as ferritic iron, or stainless steel, such as 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.

[0041] Alternatively, the third susceptor material may comprise or consist of a suitable non-magnetic material, in particular a paramagnetic conductive material, such as aluminum (Al). Similarly, the third material may comprise or consist of a non-conductive ferrimagnetic material, such as a non-conductive ferrimagnetic ceramic.

[0042] The third material may also include or consist of austenitic stainless steel. Advantageously, austenitic stainless steel, due to its paramagnetic properties and high electrical resistivity, slightly shields the second layer from magnetic fields applied to the first and second susceptor materials. By way of example, the third material may include or consist of X5CrNi18-10 (material number 1.4301, also known as V2A steel, under the EN (European Standard) nomenclature) or X2CrNiMo17-12-2 (material number 1.4571 or 1.4404, also known as V4A steel, under the EN (European Standard) nomenclature). Specifically, the third material may include or consist of one of 301 stainless steel, 304 stainless steel, 304L stainless steel, 316 stainless steel, or 316L stainless steel (SAE steel grade [Society of Automotive Engineers] nomenclature).

[0043] The thickness of the first layer may be in the range of 20 micrometers to 60 micrometers, particularly 30 micrometers to 50 micrometers, for example 40 micrometers or 42.5 micrometers.

[0044] Similarly, the layer thickness of the second layer may be in the range of 4 micrometers to 20 micrometers, in particular 8 micrometers to 18 micrometers, preferably 10 micrometers to 16 micrometers, for example 10 micrometers or 14 micrometers.

[0045] Relatively, the thickness of the first layer may be 1.5 to 5 times, particularly 2 to 4 times, preferably 2.5 to 3.5 times, and more preferably about 3 times, the thickness of the second layer. To this extent, it has been found that the thickness of the second layer does not need to be significantly greater than that of the first layer, i.e., the temperature marker layer does not need to be significantly greater than the primary heating layer.

[0046] Similarly, the third layer may be 70% or less of the second layer, specifically 60% or less, more specifically 50% or less, even more specifically 45% or less, preferably 40% or less, more preferably 35% or less, even more preferably 30% or less, and most preferably 25% or less.

[0047] As defined above, the second layer is sandwiched between the first layer and the third layer. This does not necessarily mean that the first, second, and third layers are adjacent layers. That is, there may be one or more additional layers between the first and second layers, and / or between the second and third layers, and / or above the third layer opposite the second layer, and / or below the first layer opposite the second layer.

[0048] Furthermore, the first, second and third layers are preferably immediately adjacent layers of a multi-layer susceptor arrangement, and specifically are in direct physical contact with one another.

[0049] At least one of the first layer or the third layer may be an edge layer of a multi-layer susceptor arrangement.

[0050] More specifically, the multi-layer susceptor arrangement may consist of only a first layer, a second layer, and a third layer, i.e., the multi-layer susceptor arrangement is preferably a three-layer susceptor arrangement.

[0051] When a first layer and a second layer are immediately adjacent layers, the second layer may be intimately connected to the first layer, specifically on top of the first layer. Similarly, when a second layer and a third layer are immediately adjacent layers, the third layer may be intimately connected to the second layer, specifically on top of the second layer.

[0052] With respect to the fabrication of the susceptor arrangement, and particularly with respect to the assembly of the various layers, each of the layers may be plated, deposited, coated, clad, or welded onto its respective adjacent layer. Specifically, each of these layers may be applied onto its respective adjacent layer by spraying, dip coating, roll coating, electroplating, or cladding. This is particularly true for the first layer, second layer, third layer, and, if present, at least one additional layer. In any event, any of the above configurations or layer structures fall within the term "intimately coupled" as used herein.

[0053] Generally, the multi-layer susceptor arrangement may have various shapes. Specifically, the susceptor arrangement may have the form of a blade, a strip, or a sheet. Preferably, the multi-layer susceptor arrangement may be an elongated, specifically a strip-like susceptor arrangement.

[0054] The overall thickness of the susceptor arrangement may be in the range of 24 micrometers to 88 micrometers, in particular 50 micrometers to 65 micrometers, preferably 54 micrometers to 62 micrometers, for example 56 micrometers or 60 micrometers.

[0055] The width of the susceptor arrangement in a direction perpendicular to its overall thickness may be in the range of 3 mm to 7 mm, in particular 4 mm to 6 mm, for example 5 mm.

[0056] The length of the susceptor arrangement in a direction perpendicular to its overall thickness may be in the range of 10 mm to 15 mm, in particular 11 mm to 13 mm, for example 12 mm.

[0057] The term "thickness" as used herein refers to the dimension extending between the upper and lower surfaces, e.g., between the upper and lower surfaces of a layer, or between the upper and lower surfaces 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 the front and back surfaces, or between two other opposing sides, perpendicular to the two opposing lateral sides that form 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.

[0058] According to another aspect of the present invention, there is provided a two-layer susceptor arrangement for inductively heating an aerosol-forming substrate, the susceptor arrangement comprising a first layer comprising or consisting of a first susceptor material and a second layer comprising or consisting of a second susceptor material, the first layer and the second layer being intimately connected to each other, the second susceptor material comprising or consisting of a Ni-Fe alloy having a Ni content of 65 wt % or less and a Cr content of 13 wt % or more, and the thickness of the second layer being in the range of 1 micrometer to 22 micrometers.

[0059] According to this aspect of the present invention, it has been discovered that Ni-Fe alloys with a Ni content of 65 wt. % or less and a Cr content of 13 wt. % or more exhibit sufficient corrosion resistance due to their chemical composition, primarily the chromium content, such that a protective layer on the second layer (opposite the first layer) can be omitted. This represents a beneficial material-saving advantage. Corrosion resistance is provided by the relatively high chromium content, which is passivated by reaction with oxygen, thereby forming a microscopically thin, inert chromium oxide surface film. This passive film prevents further corrosion by blocking oxygen diffusion to the second layer surface, thereby preventing corrosion from spreading to the bulk of the metal. The passive film is self-repairing even if it is damaged or temporarily disturbed by abnormal environmental conditions. Preferably, the thickness of the second layer in a two-layer susceptor arrangement may be in the range of 1 micrometer to 15 micrometers, specifically 4 micrometers to 15 micrometers, or 1 micrometer to 11 micrometers, more specifically 4 micrometers to 11 micrometers. The thickness of the first layer of the bilayer susceptor arrangement may be in the range of 20 micrometers to 60 micrometers, particularly 30 micrometers to 50 micrometers, e.g., 40 micrometers or 42.5 micrometers. The overall thickness of the bilayer susceptor arrangement may be in the range of 21 micrometers to 75 micrometers or 21 micrometers to 82 micrometers, particularly 24 micrometers to 71 micrometers, more particularly 44 micrometers to 55 micrometers.

[0060] According to the present invention there is also provided an inductively heatable aerosol-generating article comprising at least one aerosol-forming substrate and a multi-layer susceptor arrangement according to the present invention and as described herein.

[0061] As used herein, the term "aerosol-generating article" refers to an article comprising at least one aerosol-forming substrate capable of emitting a volatile compound capable of forming an aerosol when heated. Preferably, the aerosol-generating article is 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. Such articles are sometimes referred to as non-heat-burn aerosol-generating articles, and the substrate is sometimes referred to as a non-heat-burn aerosol-forming substrate. The aerosol-generating article may be a consumable product, specifically a consumable product that is discarded after a single use. The aerosol-generating article may also be a tobacco article. For example, the article may be a cartridge containing a liquid aerosol-forming substrate to be heated. As another example, the article may be an elongated or rod-shaped article. The elongated or rod-shaped article may have a shape similar to that of a conventional cigarette. Specifically, such an article may have a circular, elliptical, oval, square, rectangular, triangular, or polygonal cross section.

[0062] As used herein, the term "aerosol-forming substrate" refers to a substrate formed from or containing an aerosol-forming material capable of releasing a volatile compound upon heating to generate an aerosol. Preferably, the aerosol-forming substrate is 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 contain both solid and liquid components. The aerosol-forming substrate may include a tobacco-containing material containing 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 flavoring agents). 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.

[0063] The multi-layer susceptor arrangement is preferably embedded in the aerosol-forming substrate.

[0064] 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.

[0065] The substrate element preferably comprises at least one aerosol-forming substrate to be heated and a susceptor arrangement in thermal contact with or in thermal proximity to the aerosol-forming substrate. The substrate element may have a length of 10 to 14 millimeters, for example 12 millimeters. The susceptor arrangement may extend along the entire length of the substrate element, or the length of the extension may be shorter than the length of the substrate element.

[0066] 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 to 10 millimeters, for example 8 millimeters.

[0067] The filter element preferably functions as the mouthpiece or is part of the mouthpiece together with the 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 to 14 millimeters, for example 12 millimeters.

[0068] The distal front plug element may be used to cover and protect the distal front end of the base element. The distal front plug element may have a length of 3 to 6 millimeters, for example 5 millimeters. The distal front plug element may be made of the same material as the filter element.

[0069] All of the aforementioned elements may be disposed consecutively along the longitudinal axis of the article in the order described above, with the distal front 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.

[0070] Additionally, the elements may be surrounded by one or more outer wrappers to hold the elements together and maintain the desired cross-sectional shape of the rod-shaped 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 one another. For example, the distal forward plug element, the base element, and the first tubing element may be surrounded by a first wrapper, and the second tubing 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 tubing element (after being wrapped by the first wrapper, i.e., on top of the first wrapper) and connect the distal forward plug element, the base element, and the first tubing element surrounded by the first wrapper to the second tubing element and the filter element. The second wrapper may comprise perforations around its circumference.

[0071] Further features and advantages of the aerosol-generating article according to the invention have already been explained above with respect to the susceptor arrangement according to the invention and apply analogously.

[0072] According to one aspect of the present invention, there is also provided an aerosol generation system comprising an inductively heatable aerosol-generating article according to the present invention and as described herein, and an inductively heated aerosol generator for use with the aerosol-generating article.

[0073] According to another aspect of the present invention, there is provided an aerosol generation system comprising an inductively heated aerosol generator and an aerosol-generating article for use with the aerosol-generating device, wherein the aerosol-generating device comprises a multi-layer susceptor arrangement according to the present invention and as described herein, and the aerosol-generating article comprises an aerosol-forming substrate heated by the multi-layer susceptor arrangement.

[0074] That is, according to one aspect of the present invention (first configuration of the system), the susceptor arrangement is part of the aerosol-generating article, while according to another aspect of the present invention (second configuration of the system), the susceptor arrangement is part of the aerosol-generating device.

[0075] As used herein, the term "aerosol-generating device" refers to an electrically operated device that interacts with an aerosol-generating article, in any configuration, to generate an aerosol by heating an aerosol-forming substrate through the interaction of an alternating magnetic field generated by the aerosol-generating device with a susceptor arrangement. The aerosol-generating device is preferably a smoking device for generating an aerosol that can be directly inhaled by a user through the user's mouth. Specifically, the aerosol-generating device is a handheld aerosol-generating device.

[0076] In either configuration of the system, the device may comprise a receiving cavity for removably receiving at least a portion of each aerosol-generating article.

[0077] In either configuration of the system, the aerosol generating device may include an induction heating arrangement constructed and arranged to generate an alternating magnetic field within the receiving cavity to inductively heat the susceptor arrangement.

[0078] To generate the alternating magnetic field, the induction heating arrangement may include at least one induction coil that surrounds at least a portion of the susceptor arrangement when the system is in use. The at least one induction coil may be a helical coil or a flat, planar coil, specifically a pancake coil or a curved, planar coil. In a first configuration, the aerosol generating device and the aerosol-generating article are preferably configured such that the susceptor arrangement is disposed within the device's volume, specifically within the interior space of the at least one induction coil, so that the susceptor arrangement is subjected to the alternating magnetic field when the article is housed in the aerosol generating device. Similarly, in a second configuration, the susceptor arrangement is preferably fixedly disposed within the device's volume, specifically within the interior space of the at least one induction coil, so that the susceptor arrangement is subjected to the alternating magnetic field.

[0079] 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 at least one induction coil. Specifically, 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 supplied to the at least one induction coil continuously after activation of the system, or may be supplied intermittently (e.g., with each puff). The induction heating arrangement may comprise 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.

[0080] The induction heating arrangement is preferably configured to generate a high frequency magnetic field, which as referred to herein may have a frequency in the range of 500 kHz (kilohertz) to 30 MHz (megahertz), in particular 5 MHz (megahertz) to 15 MHz (megahertz), preferably 5 MHz (megahertz) to 10 MHz (megahertz).

[0081] In any configuration of the system, the aerosol generating device may further comprise a controller configured to control the operation of the heating process. The controller may be the overall controller of the aerosol generating device or may be part of it. The controller may comprise a microprocessor (e.g., a programmable microprocessor), a microcontroller, or an application specific integrated circuit (ASIC) or other electronic circuit capable of providing control. The controller may also comprise other electronic components, such as at least one DC / AC converter and / or a power amplifier, such as a Class C power amplifier, a Class D power amplifier, or a Class E power amplifier. Specifically, the inductive source may be part of the controller.

[0082] In any configuration of the system, 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 energy sufficient for one or more user experiences. For example, the power source may have a capacity sufficient to allow continuous generation of aerosol for approximately six minutes, or a multiple of six minutes. In another embodiment, the power source may have a capacity sufficient to allow for a predetermined number of puffs, or for discontinuous activation of the induction source.

[0083] Further features and advantages of the aerosol-generating system according to any aspect of the present invention have been described with respect to the susceptor arrangement and the aerosol-generating article and therefore apply analogously.

[0084] 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.

[0085] Example 1: 1. A multi-layer susceptor arrangement for inductively heating an aerosol-forming substrate, the susceptor arrangement comprising: a first layer comprising or consisting of a first susceptor material; a second layer comprising or consisting of a second susceptor material; a third layer comprising or consisting of a third material, A multi-layer susceptor arrangement, wherein the second layer is sandwiched between the first layer and the third layer, the second susceptor material comprises or consists of a Ni-Fe alloy having a Ni content of 65 wt% or less, and the third layer has a thickness of 8 micrometers or less. Example 2: The multilayer susceptor arrangement of Example 1, wherein the thickness of the third layer is 7 micrometers or less, particularly 6 micrometers or less, more particularly 5 micrometers or less, preferably 4 micrometers or less, or 3 micrometers or less. Example 3: The multilayer susceptor arrangement of any one of Examples 1 or 2, wherein the thickness of the third layer is in the range of 0.75 micrometers to 8 micrometers, specifically 1 micrometer to 5 micrometers, preferably 2 micrometers to 4 micrometers, for example 3.5 micrometers. Example 4: The multilayer susceptor arrangement according to any one of Examples 1 to 3, wherein the thickness of the first layer is 1.5 to 5 times, specifically 2 to 4 times, preferably 2.5 to 3.5 times, and more preferably about 3 times the thickness of the second layer. Example 5: 5. The multi-layer susceptor arrangement of any one of Examples 1-4, wherein the first susceptor material comprises or consists of a metal, such as ferritic iron, or stainless steel, specifically grade 410, grade 420, or grade 430 stainless steel. Example 6: The multi-layer susceptor arrangement of any one of Examples 1 to 5, wherein the Ni-Fe alloy of the second susceptor material further comprises 8 wt% to 12 wt% Cr, specifically 9 wt% to 11 wt% Cr. Example 7: 7. A multilayer susceptor arrangement according to any one of Examples 1 to 6, wherein the Ni-Fe alloy of the second susceptor material has a Ni content of 50 wt% or less, specifically 44 wt% or less, more specifically in the range of 36 wt% to 44 wt%, preferably in the range of 36 wt% to 40 wt%, for example 36.1 wt% or 36.4 wt% or 40 wt%, with the remainder preferably being Fe. Example 8: The second susceptor material is a Ni-Fe alloy. 50% by weight Ni, 9% by weight Cr, the remainder being Fe, 50% by weight Ni, 10% by weight Cr, the remainder being Fe, 50% by weight Ni, 11% by weight Cr, the remainder being Fe, 50% by weight of Ni, 9% by weight of Cr, max. 1% by weight of Si and max. 1% by weight of Mn, the remainder being Fe; 50% by weight of Ni, 10% by weight of Cr, max. 1% by weight of Si and max. 1% by weight of Mn, the remainder being Fe; 7. The multilayer susceptor arrangement of any one of Examples 1-6, comprising or consisting of one of: 50 wt.% Ni, 11 wt.% Cr, max. 1 wt.% Si and max. 1 wt.% Mn, the remainder being Fe. Example 9: The multilayer susceptor arrangement according to any one of Examples 1 to 8, wherein the Ni-Fe alloy of the second susceptor material has a Curie temperature in the range of 180°C to 420°C, specifically 210°C to 380°C, preferably 250°C to 380°C. Example 10: The multi-layer susceptor arrangement of any one of Examples 1-9, wherein the third material comprises or consists of a corrosion-resistant material. Example 11: The multi-layer susceptor arrangement of any one of Examples 1-10, wherein the third material is the same as the first susceptor material. Example 12: The multi-layer susceptor arrangement of any one of Examples 1-10, wherein the third material is different from the first susceptor material. Example 13: The multilayer susceptor arrangement of any one of Examples 1 to 12, wherein the thickness of the first layer is in the range of 20 micrometers to 60 micrometers, specifically 30 micrometers to 50 micrometers, for example, 40 micrometers or 42.5 micrometers. Example 14: The multilayer susceptor arrangement according to any one of Examples 1 to 13, wherein the thickness of the second layer is in the range of 4 micrometers to 20 micrometers, specifically 8 micrometers to 18 micrometers, preferably 10 micrometers to 16 micrometers, for example, 10 micrometers or 14 micrometers. Example 15: The multilayer susceptor arrangement of any one of Examples 1 to 14, wherein the thickness of the third layer is 50% or less of the thickness of the first layer, specifically 40% or less, more specifically 30% or less, preferably 25% or less, more preferably 20% or less, even more preferably 15% or less, and most preferably 10% or less. Example 16: The multi-layer susceptor arrangement of any one of Examples 1 to 15, wherein the third layer has a thickness of at least 0.75 micrometers, specifically at least 1 micrometer. Example 17: 17. The multi-layer susceptor arrangement of any one of Examples 1-16, wherein the second layer is intimately bonded to the first layer, specifically on top of the first layer. Example 18: The multi-layer susceptor arrangement of any one of Examples 1-17, wherein the third layer is intimately bonded to the second layer, specifically on top of the second layer. Example 19: The multi-layer susceptor arrangement of any one of Examples 1-18, wherein the first layer, the second layer, and the third layer are immediately adjacent layers of the multi-layer susceptor arrangement. Example 20: 20. The multi-layer susceptor arrangement of any one of Examples 1-19, wherein the susceptor arrangement has the form of a blade or strip or sheet. Example 21: 21. The multilayer susceptor arrangement of any one of Examples 1 to 20, wherein the overall thickness of the susceptor arrangement is in the range of 24 micrometers to 88 micrometers, specifically 50 micrometers to 65 micrometers, preferably 54 micrometers to 62 micrometers, e.g., 56 micrometers or 60 micrometers. Example 22: A multilayer susceptor arrangement according to any one of Examples 1 to 21, wherein the width of the susceptor arrangement in a direction perpendicular to the overall thickness of the susceptor arrangement is in the range of 3 millimeters to 7 millimeters, specifically 4 millimeters to 6 millimeters, for example 5 millimeters. Example 23: A multi-layer susceptor arrangement according to any one of Examples 1 to 22, wherein the length of the susceptor arrangement in a direction perpendicular to the overall thickness of the susceptor arrangement is in the range of 10 millimeters to 15 millimeters, specifically 11 millimeters to 13 millimeters, for example 12 millimeters. Example 24: An inductively heatable aerosol-generating article comprising an aerosol-forming substrate and the multi-layer susceptor arrangement of any one of Examples 1-23. Example 25: 25. The aerosol-generating article of example 24, wherein the multi-layer susceptor arrangement is embedded in the aerosol-forming substrate. Example 26: An aerosol generating system comprising the inductively heatable aerosol-generating article according to any one of Examples 24 to 25, and an inductively heatable aerosol generator used together with the aerosol-generating article. Example 27: An aerosol generating system comprising: an induction-heated aerosol generating apparatus, wherein the aerosol generating apparatus comprises the multi-layer susceptor arrangement described in any one of Examples 1 to 23, and the aerosol-generating article comprises an aerosol-forming substrate heated by the multi-layer susceptor arrangement; and an aerosol-generating article for use with the aerosol-generating apparatus.

[0086] The embodiments will now be further described with reference to the figures.

[0087] FIG. 1 illustrates, in a schematic representation (not to scale), one 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 product 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 disposed 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 disposed 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 160 may have a length of 10 to 14 millimeters, e.g., 12 millimeters, while the distal front plug element 150 may have a length of 3 to 6 millimeters, e.g., 5 millimeters. The base element 110 comprises an aerosol-forming substrate 130 to be heated and a multilayer susceptor arrangement 120 for heating the substrate 130 according to an exemplary embodiment of the present invention. Here, the susceptor arrangement 120 has the shape of a blade or strip 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 to 14 millimeters, e.g., 12 millimeters. As shown in FIG. 1 , the susceptor arrangement 120 extends along the entire length of the base element 110, but may alternatively have an extension of a length shorter than the length of the base element 110. Each of the first and second tube elements 140, 145 is a hollow cellulose acetate tube having a central air passage 141, 146, the cross section of which is larger than the cross section of the central air passage 141 of the first tube element 140. The first and second tube elements 140, 145 may have a length of 6 to 10 millimeters, for example 8 millimeters. Each of the aforementioned elements 150, 110, 140, 145, 160 may be substantially cylindrical.In particular, all elements 150, 110, 140, 145, 160 may have the same external cross-sectional shape and dimensions.

[0088] Additionally, elements 150, 110, 140, 145, 160 may be surrounded by one or more outer wrappers to hold the elements together and maintain the desired cross-sectional shape of the rod-shaped article. In this embodiment, distal forward plug element 150, base element 110, and first tube element 140 are surrounded by a first wrapper 171, while second tube element 145 and filter element 160 are surrounded by a second wrapper 172. Second wrapper 172 also surrounds at least a portion of first tube element 140 (after being wrapped by first wrapper 171) to connect distal forward plug element 150, base element 110, and first tube element 140 surrounded by first wrapper 171 to second tube element 145 and filter element 160. First and second wrappers 171, 172 are preferably made of paper. Additionally, the second wrapper 172 may include perforations around its periphery (not shown). The wrappers 171, 172 may further include an adhesive that adheres the overlapping free ends of the wrappers 171, 172 to one another.

[0089] As shown in FIG. 2 , the aerosol-generating article 100 is configured for use with an induction-heating aerosol-generating device 10. The device 10 and the article 100 together form an aerosol-generation system 1 according to the present invention. The aerosol-generating device 10 comprises a cylindrical receiving cavity 20 defined within a proximal portion 12 of the device 10, for receiving at least a distal portion of the article 100 therein. The device 10 further comprises an induction-heating arrangement comprising an induction coil 30 for generating a high-frequency alternating magnetic field within 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, when the article 100 is inserted into the cavity 20 of the device 10, the susceptor arrangement 120 of the aerosol-generating article 100 is exposed to the alternating magnetic field. Thus, upon activation of the induction heating arrangement, depending on the magnetic and electrical properties of the susceptor material of the susceptor arrangement 120, the susceptor arrangement 120 heats 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 within the article 100. In use, an aerosol formed by volatile compounds released from the heated substrate 130 is drawn through the first and second tube elements 140, 145 and through the filter element 160 toward the proximal end 103 of the article 100.

[0090] Within 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.

[0091] 3 and 4 show detailed views (not to scale) of the susceptor arrangement 120 used in the aerosol-generating article shown in FIG. 1. In accordance with the present invention, the susceptor arrangement 120 is a multi-layer susceptor arrangement 120 comprising a first layer 121, a second layer 122, and a third layer 123, which are arranged such that the second layer 122 is sandwiched between the first layer 121 and the third layer 123. In the present invention, the multi-layer susceptor arrangement 120 is a three-layer susceptor arrangement 120 consisting of only these three layers 121, 122, and 123. Thus, the first and third layers 121 and 123, respectively, form edge layers of the susceptor arrangement 120.

[0092] 3 and 4, the second layer 122 is intimately connected to the first layer 121, and the third layer 123 is intimately connected to the opposite side of the second layer 121 from the first layer 121. In terms of manufacturing, the susceptor arrangement 120 can be formed, for example, by first coating the material of the second layer 122 onto the material of the first layer 121. The material of the third layer 123 can then be coated onto the second layer 122.

[0093] The first layer 121 is primarily used for heating purposes. To this end, it is made of a first susceptor material optimized for heat loss and thus heating efficiency. Here, the first susceptor material is a 400 series stainless steel, such as grade 410 stainless steel, grade 420 stainless steel, grade 430 stainless steel, or a similar grade. The use of stainless steel proves advantageous in terms of the aging properties of the first layer 121, which is in direct contact with the aerosol-forming substrate 130 in the base element 110.

[0094] While the first layer 121 is primarily used to heat the substrate 130, the second layer 122 is a functional layer that primarily functions as a temperature marker. To this end, the second layer 122 is composed of a ferromagnetic second susceptor material selected to have a Curie temperature corresponding to a predetermined temperature point for heating the substrate 130. At that Curie temperature, the magnetic permeability of the second susceptor material decreases monotonically, leading to a change in its magnetic properties from ferromagnetic to paramagnetic. This change in magnetic properties is accompanied by a temporary change in the electrical resistance of the susceptor arrangement 120. Therefore, by monitoring the corresponding change in 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 therefore, when the predetermined temperature point has been reached.

[0095] As defined above, the second susceptor material comprises or consists of a Ni-Fe alloy with a Ni content of 65% by weight or less. Here, the Ni-Fe alloy comprises 50% by weight Ni, 9% by weight Cr, and the remainder Fe. This alloy is commercially available, for example, under the trade name Phytherm 260, and has a Curie temperature of 260°C. If a lower Curie temperature is desired, the Ni-Fe alloy may alternatively comprise or consist of 50% by weight Ni, 10% by weight Cr, and the remainder Fe. This alloy has a Curie temperature of 230°C and is also commercially available, for example, under the trade name Phytherm 220. According to yet another alternative, the Ni-Fe alloy may comprise or consist of 50% by weight Ni, 11% by weight Cr, and the remainder Fe. This alloy is also commercially available, for example, under the trade name Phytherm 210, and has a Curie temperature of 210°C. Advantageously, all of the aforementioned alloys (Phytherm alloys) are corrosion resistant materials.

[0096] Although the Phytherm alloy is already a corrosion-resistant material, the second layer 122 is preferably protected not only from one side but also from the other side by the first layer 121. This is achieved by the third layer 123, which includes or consists of a third material. Specifically, the third layer 123 can reduce material diffusion, e.g., metal diffusion, from the second susceptor material into the surrounding aerosol-forming substrate 130. Furthermore, the third layer 123 can help avoid or reduce thermal bending due to differences in thermal expansion between the various layers 121, 122, and 123.

[0097] Preferably, the third layer 123 comprises or consists of the same material as the first layer 121. Thus, the multi-layer susceptor arrangement 120 comprises at least two layers 121, 123 having the same thermal expansion coefficient, thereby reducing deformation of the susceptor arrangement 120 throughout its operating temperature range. Thus, in this embodiment, the third material of the third layer 123 is also preferably 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.

[0098] Alternatively, the third material of the third layer 123 may be an austenitic stainless steel. As an example, the third material of the third layer 123 may be X5CrNi18-10 or X2CrNiMo17-12-2 (according to the EN (European Standard) nomenclature). Specifically, the third material of the third layer 123 may be one of 301 stainless steel, 304 stainless steel, 304L stainless steel, 316 stainless steel, or 316L stainless steel (SAE steel grade [Society of Automotive Engineers] nomenclature). 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.

[0099] As further described above, it has been further discovered that the thickness of the third layer 123 can be relatively thin, i.e., 8 micrometers or less. A thin third layer is advantageous not only in terms of material savings, but also in that the second layer 122 is less likely to be shielded from the alternating magnetic field of the induction source used to inductively heat the susceptor arrangement 120. As a result, when the second susceptor material is used as a temperature marker, the above-described changes in the magnetic properties of the second susceptor material have a more pronounced effect on the current passing through the induction source. Advantageously, this allows for a more reliable determination of when the second susceptor material has reached its Curie temperature, and therefore when a predetermined temperature point has been reached. In this embodiment, the thickness of the first layer 121 is in the range of 42 micrometers to 43 micrometers, and the thickness of the third layer 123 is in the range of 3 micrometers to 4 micrometers. Therefore, the thickness of the third layer 123 is approximately 7% to 9% of the thickness of the first layer 121.

[0100] The thickness of the second layer 122 may be between the thickness of the first layer 121 and the thickness of the third layer 123. Here, the thickness of the second layer 122 is within a range of 10 micrometers to 16 micrometers, or 13 micrometers to 15 micrometers, and is preferably about 10 micrometers or about 14 micrometers.

[0101] As can be seen specifically in FIG. 3 , the multilayer susceptor arrangement 120 according to this embodiment is in the form of an elongated strip. The strip-like susceptor arrangement 120 has a length L of 10 to 12 millimeters and a width W of 4 to 5 millimeters. That is, the three layers 121, 122, and 123 all have lengths L of 10 to 12 millimeters and widths W of 4 to 5 millimeters, but different layer thicknesses. Considering the above values ​​for each layer thickness, the total thickness T of the susceptor arrangement 120 is in the range of 55 micrometers to 63 micrometers, e.g., about 56 micrometers or about 60 micrometers.

[0102] For 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 instances to be modified by the term "about." Also, all ranges include the disclosed maximum and minimum points, 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 typical standard error for the measurement of the property that the number A modifies. In some cases, as used in the appended claims, the number A may deviate by the percentages recited above, provided that the amount by which A deviates does not materially affect the basic and novel characteristics of the claimed invention. Also, all ranges include the disclosed maximum and minimum points, 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, said susceptor arrangement comprising: a first layer comprising or consisting of a first susceptor material; a second layer comprising or consisting of a second susceptor material; a third layer comprising or consisting of a third material, The multi-layer susceptor arrangement, wherein the second layer is sandwiched between the first layer and the third layer, the second susceptor material comprises or consists of a Ni—Fe alloy having a Ni content of 65 wt % or less, and the third layer has a thickness of 8 micrometers or less.

2. 2. The multilayer susceptor arrangement according to claim 1, wherein the thickness of the third layer is 7 micrometers or less, in particular 6 micrometers or less, more particularly 5 micrometers or less, preferably 4 micrometers or less, or 3 micrometers or less.

3. 3. The multilayer susceptor arrangement of claim 1, wherein the thickness of the first layer is in the range of 1.5 to 5 times, particularly 2 to 4 times, preferably 2.5 to 3.5 times, and more preferably about 3 times, the thickness of the second layer.

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

5. 5. The multi-layer susceptor arrangement of claim 1, wherein the Ni-Fe alloy of the second susceptor material further comprises 8 wt% to 12 wt% Cr, specifically 9 wt% to 11 wt% Cr.

6. 6. A multi-layer susceptor arrangement according to any one of claims 1 to 5, wherein the Ni-Fe alloy of the second susceptor material has a Ni content of 50 wt% or less, in particular 44 wt% or less, more particularly in the range of 36 wt% to 44 wt%, preferably in the range of 36 wt% to 40 wt%, for example 36.1 wt% or 36.4 wt% or 40 wt%, the remainder preferably being Fe.

7. The Ni—Fe alloy of the second susceptor material is 50% by weight Ni, 9% by weight Cr, the remainder Fe, 50% by weight Ni, 10% by weight Cr, the remainder Fe, 50% by weight Ni, 11% by weight Cr, the remainder Fe, 50% by weight Ni, 9% by weight Cr, max. 1% by weight Si and max. 1% by weight Mn, the remainder being Fe, 50% by weight Ni, 10% by weight Cr, max. 1% by weight Si and max. 1% by weight Mn, the remainder being Fe, 6. A multilayer susceptor arrangement according to any one of claims 1 to 5, comprising or consisting of one of the following: 50% by weight Ni, 11% by weight Cr, max. 1% by weight Si and max. 1% by weight Mn, the remainder being Fe.

8. 8. A multi-layer susceptor arrangement according to any one of claims 1 to 7, wherein the Ni-Fe alloy of the second susceptor material has a Curie temperature in the range of 180°C to 420°C, in particular 210°C to 380°C, preferably 250°C to 380°C.

9. The multi-layer susceptor arrangement of any one of claims 1 to 8, wherein the third material comprises or consists of a corrosion resistant material.

10. The multi-layer susceptor arrangement of any one of claims 1 to 9, wherein the third material is the same as the first susceptor material or the third material is different from the first susceptor material.

11. 11. The multilayer susceptor arrangement according to claim 1, wherein the first layer has a thickness in the range of 20 micrometers to 60 micrometers, particularly 30 micrometers to 50 micrometers, for example 40 micrometers or 42.5 micrometers.

12. 12. The multilayer susceptor arrangement according to any one of claims 1 to 11, wherein the second layer has a thickness in the range of 4 micrometers to 20 micrometers, in particular 8 micrometers to 18 micrometers, preferably 10 micrometers to 16 micrometers, for example 10 micrometers or 14 micrometers.

13. 13. The multilayer susceptor arrangement of claim 1, wherein the thickness of the third layer is 50% or less, specifically 40% or less, more specifically 30% or less, preferably 25% or less, more preferably 20% or less, even more preferably 15% or less, and most preferably 10% or less of the thickness of the first layer.

14. The multilayer susceptor arrangement according to any one of claims 1 to 13, wherein the third layer has a layer thickness of at least 0.75 micrometers, in particular at least 1 micrometer.

15. An inductively heatable aerosol-generating article comprising an aerosol-forming substrate and a multi-layer susceptor arrangement according to any one of claims 1 to 14.

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