A SET OF SUSCEPTORS COMPRISING ONE OR MORE COMPOSITE SUSCEPTOR PARTICLES

Abstract

This description relates to an assembly of susceptors comprising one or more composite susceptor particles for induction heating an aerosol-forming substrate under the influence of an alternating magnetic field. Each of the one or more susceptor particles comprises a particle core and a particle shell that completely encapsulates the particle core. The particle core comprises or is made of a ferromagnetic or ferrimagnetic core material having a relative magnetic permeability of at least 200 for frequencies up to 10 kHz at a temperature of 20 degrees Celsius. The particle shell comprises or is made of an electrically conductive shell material. The description further relates to an aerosol-generating article comprising such a susceptor unit, as well as to an aerosol-generating system comprising such an article and an aerosol-generating device.Furthermore, the description refers to a method of manufacturing such a set of susceptors.

Description

A SUSCEPTOR ASSEMBLY COMPRISING ONE OR MORE COMPOSITE SUSCEPTOR PARTICLES This description relates to a susceptor unit comprising one or more composite susceptor particles for induction heating an aerosol-forming substrate under the influence of an alternating magnetic field. The description further relates to an aerosol-generating article comprising such a susceptor unit, as well as to an aerosol-generating system comprising such an article and an aerosol-generating device. Additionally, the description relates to a method of manufacturing such a susceptor assembly. The generation of inhalable aerosols by inductive heating of heated aerosol-forming substrates is generally known by prior art. For this, the substrate may be arranged in thermal proximity or direct physical contact with a susceptor capable of generating heat due to at least one eddy current or hysteresis loss when exposed to an alternating magnetic field. For example, the susceptor may comprise one or more susceptor particles incorporated into the aerosol-forming substrate. Together, the substrate and the susceptor may be part of an aerosol-generating article configured for insertion into an aerosol-generating device comprising an induction source for generating the alternating magnetic field. To control the substrate temperature, susceptor assemblies have been proposed, comprising a first and a second susceptor made of different materials. The first susceptor material can be optimized with respect to heat loss and, therefore, heating efficiency. Conversely, the second susceptor material can be used as a temperature marker. For this purpose, the material of the second susceptor is chosen so that it has a Curie temperature corresponding to a predefined operating temperature of the susceptor assembly. At its Curie temperature, the magnetic properties of the second susceptor change from ferromagnetic or ferrimagnetic to paramagnetic, accompanied by a temporary change in its electrical resistance.Therefore, by monitoring the corresponding change in the electrical current drawn by the induction source, it is possible to detect when the second susceptor material has reached its Curie temperature and, consequently, when the predefined operating temperature has been reached. To prevent rapid overheating, the heating process should be controlled by actively reducing or switching off the heating power once the operating temperature has been reached. 1} LC ίη / ΖΖΠΖ / Ε / ΥΙΛΙ It would be desirable to have a susceptor assembly, an aerosol generating article, and an aerosol generating system that combines the advantages of prior art solutions while mitigating their limitations. In particular, it would be desirable to have a susceptor assembly, an aerosol generating article, and an aerosol generating device system that has improved heating efficiency and enhanced temperature control capabilities. According to one aspect of the present invention, a susceptor unit is provided for inductively heating an aerosol-forming substrate under the influence of an alternating magnetic field. The susceptor assembly comprises one or more composite susceptor particles. Each of the one or more susceptor particles comprises a particle core and a particle shell that completely encapsulates the particle core. The particle core comprises or is made of a ferromagnetic or ferrimagnetic core material having a relative magnetic permeability of at least 200 at a frequency of 10 kHz (kilohertz), particularly for frequencies up to 10 kHz (kilohertz), and at a temperature of 20 degrees Celsius.That is, the particle core comprises or is made of a ferromagnetic or ferrimagnetic core material having a relative magnetic permeability of at least 200 when penetrated by an alternating magnetic field with a frequency of 10 kHz (kilohertz), in particular, a frequency up to 10 kHz (kilohertz), at a temperature of 20 degrees Celsius. The particle shell comprises or is made of an electrically conductive shell material. According to the invention, it has been discovered that susceptor particles comprising a magnetic core with high magnetic permeability and an electrically conductive shell provide both improved heating efficiency and enhanced temperature control with self-regulating properties. To date, it has been found that a magnetic core with high magnetic permeability acts as a flux concentrator, increasing the magnetic flux through the particle shell. According to Faraday's law of induction, an increase in magnetic flux causes an increase in electromotive force around a closed path through the electrically conductive shell material, which, in turn, causes an increase in eddy current losses in the particle shell.Therefore, the high magnetic permeability of the magnetic core increases the amount of heat generated in the particle coating during use. Advantageously, this also allows the particle coating to be quite thin, thus saving material and costs in the manufacture of the susceptor particles. 1} LC ίη / ΖΖΠΖ / Ε / ΥΙΛΙ Furthermore, it has been discovered that the magnetic core can be used to control the amount of heat generated in the particle shell as a function of the actual temperature of the susceptor array. This is due to the fact that the magnetic properties of the particle core change from ferromagnetic or ferrimagnetic to paramagnetic at the Curie temperature of the core material. Consequently, the overall effective magnetic permeability of the composite susceptor particle drops to unity when the susceptor array reaches the Curie temperature of the core material. This causes a cessation of heat generation in the particle core due to hysteresis losses as the magnetic hysteresis of the core material disappears.Furthermore, the change in magnetic permeability also affects heat generation in the particle shell, as decreased magnetic permeability leads to a decrease in magnetic flux through the electrically conductive shell. This, in turn, leads to a reduction in electromotive force and, therefore, a reduction in heat-generating eddy current losses in the particle shell when the susceptor array reaches the Curie temperature of the core material. Additionally, the particle shell skin depth, which is a measure of how much electrical conduction occurs in the electrically conductive shell material when exposed to an alternating magnetic field, depends on the overall effective magnetic permeability of the composite susceptor particle.Therefore, a decrease in the overall effective magnetic permeability of the susceptor particle caused a decrease in the magnetic permeability of the particle core, leading to an increase in the skin depth of the coating. This, in turn, causes a decrease in the effective resistance of the electrically conductive particle coating. Consequently, upon reaching the Curie temperature of the core material, heat generation in the particle coating also decreases due to the reduction in effective resistance, which also results in a reduction of eddy current losses in the coating material. Therefore, at the Curie temperature, heat generation from eddy current losses in the particle coating is reduced due to both a reduction in magnetic flux through the particle coating and a reduction in the effective resistance of the coating material.Furthermore, overall heat generation is reduced due to hysteresis losses in the particle core that disappear at the Curie temperature of the core material. More importantly, the reduction in overall heat generation occurs automatically when the susceptor array reaches the Curie temperature of the core material. As a result, rapid overheating of the aerosol-forming substrate can be effectively avoided, preferably without the need for active temperature control. Furthermore, the heating efficiency of the composite susceptor particles according to the present invention is greater than that of a susceptor particle made solely from ferromagnetic or ferrimagnetic core material. This is due to the shell material, in which a significant portion of the heat is generated due to improved eddy current losses. The sheath material can be paramagnetic. In this case, heat generation in the electrically conductive shell material is caused solely by eddy currents. Alternatively, the sheath material can be ferromagnetic or ferrimagnetic. Consequently, heat can also be generated in the sheath material due to hysteresis losses. Advantageously, this increases the heating efficiency of the susceptor assembly. Preferably, if magnetic, the Curie temperature of the sheath material is less than or equal to the Curie temperature of the ferromagnetic or ferrimagnetic core material. Advantageously, this ensures that heat generation in the sheath material due to hysteresis losses only occurs below or up to the Curie temperature of the core material—that is, only below or up to a predefined operating temperature.It is also possible that the Curie temperature of the shell material is higher than the Curie temperature of the ferromagnetic or ferrimagnetic core material. The shell material can be aluminum, stainless steel, electrically conductive carbon, or bronze. Aluminum is particularly suitable as it allows for sintering at low temperatures, which in turn can facilitate the fabrication of the composite susceptor particles, as will be described in more detail below. Preferably, the core material is electrically non-conductive. In this case, heat generation in the core material is caused solely by hysteresis losses. Consequently, when the Curie temperature of the core material is reached, heat generation in the susceptor core ceases completely. This is particularly advantageous for self-regulating temperature control of the susceptor array. It is also possible for the core material to be electrically conductive. As mentioned previously, the Curie temperature of the core material preferably corresponds to the predefined operating temperature of the susceptor array. The actual operating temperature depends on the specific type of aerosol-forming substrate being heated. For solid aerosol-forming substrates containing tobacco material, the temperature of 1} LC ίη / ZZΖΠZ / E / YΙΛΙ The operating temperature can be in a range between 200 degrees Celsius and 360 degrees Celsius. For gel-type aerosol-forming substrates, the operating temperature can be in a range between 160 degrees Celsius and 240 degrees Celsius. Accordingly, the core material can have a Curie temperature in a range between 160 degrees Celsius and 400, in particular between 160 degrees Celsius and 360 degrees Celsius, preferably between 200 degrees Celsius and 360 degrees Celsius or between 160 degrees Celsius and 240 degrees Celsius. The heating efficiency of the susceptor assembly increases with higher values ​​of relative magnetic permeability. Therefore, the core material can have a relative magnetic permeability even greater than 200. Consequently, the core material can have a relative magnetic permeability of at least 300, or at least 400, or at least 500, or at least 700, in particular at least 1000, preferably at least 10,000, or at least 50,000, or at least 80,000. These values ​​refer to the maximum values ​​of relative magnetic permeability at a frequency of 10 kHz (kilohertz), in particular for frequencies up to 10 kHz (kilohertz), and a temperature of 25 degrees Celsius.As will be described later, the alternating magnetic field used to inductively heat the susceptor array can be in the range of 500 kHz to 30 MHz, particularly between 5 MHz and 15 MHz, preferably between 5 MHz and 10 MHz. For these frequencies, the minimum relative magnetic permeability of the core material can be lower. For example, the core material can have a relative magnetic permeability of at least 80, particularly at least 100, preferably at least 120 at a frequency of 7 MHz and a temperature of 25 degrees Celsius. Likewise, the core material can have a relative magnetic permeability of at least 40, in particular at least 50, preferably at least 60 at a frequency of 15 MHz (megahertz) and a temperature of 25 degrees Celsius. The core material may comprise or be a ferrite, in particular a ferrite powder. As used herein, a ferrite is a ceramic material made by mixing and firing large proportions of iron(III) oxide (FezCh) mixed with small proportions of one or more additional metallic elements, such as barium, manganese, nickel, and zinc. For example, the core material can be one of a manganese-magnesium ferrite, a nickel-zinc ferrite, or a cobalt-zinc barium ferrite. For example, the core material may comprise or consist of a composition of the type MgxMnyFezÜ4, where x = 0.4 - 1.1, y = 0.3 - 0.9, yz = 1 - 2, and where the atomic fraction x, 5 yyz of the metal cations Mg, Mn, and Fe is such that the total charge of the metal cations balances the total charge of the oxygens. In particular, the core material may comprise or be one of: Mgo.77 Mno.58 Fei.65 O4, with a Curie temperature of approximately 270 degrees Celsius; Mgo.55 Mno.88 Fei.55 O4; which has a Curie temperature of approximately 262 degrees Celsius; Mg1.03 Mno.35 Fei.37 O4; which has a Curie temperature of approximately 190 degrees Celsius; Nickel-zinc ferrite, as mentioned above, may comprise or consist of a composition of the type NiₓZnₓxFe₂O₄, where x = 0.3–0.7 and the atomic fraction of the metal cations Ni, Zn, and Fe is such that the total charge of the metal cations balances the total charge of the oxygen anions. In particular, the inductively heated, open-porous ceramic material may comprise or be, for example, NiₓZnₓFe₂O₄, which has a Curie temperature of approximately 258 degrees Celsius. Cobalt-zinc barium ferrite - as mentioned above - may comprise or consist of C01.75 Zno.25 Ba2 Fe2 O22, which has a Curie temperature of approximately 279 degrees Celsius. Advantageously, ferrites are easy and inexpensive to manufacture. Furthermore, ferrites are not electrically conductive. Consequently, heat generation in the core material is solely due to hysteresis losses and is therefore self-regulating once the Curie temperature is reached. Additionally, ferrites are inert and therefore not critical for use in aerosol-generating articles comprising aerosol-forming substrates. The particle core is preferably a solid particle core. In particular, the particle core may be spherical. Similarly, the particle shell may preferably be a solid particle shell. In particular, the particle shell may be spherical. Each of the one or more susceptor particles may have an equivalent particle diameter in the range of 10 micrometers to 500 micrometers, particularly between 20 micrometers and 250 micrometers, and more specifically between 35 micrometers and 75 micrometers, for example, 55 micrometers. The equivalent spherical diameter is used in combination with irregularly shaped particles and is defined as the diameter of a sphere of equivalent volume. The particle size may depend, among other factors, on the aerosol-forming substrate to be heated.Furthermore, for six safety reasons, the particle size must be large enough to prevent the susceptor particles from passing through a filter in an aerosol-generating device in which they might be used. Therefore, each of the one or more susceptor particles may have a particle diameter of at least 20 micrometers, preferably at least 35 micrometers. Consequently, the particle core can have an equivalent spherical core diameter in the range of 5 micrometers to 499 micrometers, particularly between 15 micrometers and 220 micrometers, and more specifically between 30 micrometers and 55 micrometers, for example, 35 micrometers. The equivalent particle diameter can be given primarily by the equivalent spherical core diameter. An equivalent spherical core diameter in the range of 30 micrometers to 55 micrometers is particularly suitable since such particles are small enough to be barely visible on the substrate, yet large enough not to pass through a filter in an aerosol-generating device in which the susceptor particles might be used. Due to the flow-enhancing effect of the core material on the coating, the coating thickness can be quite small. Advantageously, this allows for material and cost savings in the manufacture of the susceptor particles. The particle coating thickness can range from 2.5 micrometers to 15 micrometers, particularly between 5 and 12 micrometers, for example, 10 micrometers. The coating thickness may depend, among other things, on the particle coating material, especially the inductive heating rate and the specific material requirements for coating production. For example, the coating thickness might be 10 micrometers for aluminum, while it might be less than 10 micrometers for steel. Larger L-values ​​of the coating thickness are particularly suitable for particle coatings with a porous or sintered structure. The above values ​​may refer to the mean core diameter, mean coat thickness, and mean particle diameter of all the susceptor particles in the susceptor set. Consequently, some susceptor particles may have at least one smaller core diameter, a smaller coat thickness, or a smaller particle diameter than other susceptor particles in the susceptor set. 1} LC ίη / ΖΖΠΖ / Ε / ΥΙΛΙ Preferably, the particle shell is in physical contact with the particle core. This allows for good heat exchange between the shell and the core, ensuring they are at approximately the same temperature. The particle core can be a sintered particle core. In particular, the core material can be a sintered material. Sintering is the process of compacting and forming a solid mass of material by means of heat or pressure without melting it to the liquefaction point. Advantageously, sintering allows for the production of particle cores of almost any shape and size. Sintering also produces susceptor particles with good strength properties. Furthermore, a sintered particle core facilitates good bonding between the shell and the core. Consequently, the particle shell preferentially bonds tightly to the particle core. That is, a substance-to-substance bond can exist between the particle shell and the particle core. A tight bond provides good mechanical stability and efficient heat transfer between the particle shell and the particle core. In particular, the cover material may be plated, deposited, coated, or coated onto the particle core such as to form the particle cover. The susceptor assembly according to the present invention is preferably configured to be driven by an alternating magnetic field, particularly a high-frequency field. As mentioned herein, the high-frequency magnetic field may be in the range of 500 kHz (kilohertz) to 30 MHz (megahertz), particularly between 5 MHz (megahertz) and 15 MHz (megahertz), preferably between 5 MHz (megahertz) and 10 MHz (megahertz). The susceptor particle may comprise a coating, in particular a protective coating. The coating may be formed from glass, ceramic, or an inert metal, formed or coated onto at least a portion of the susceptor particles, respectively.Advantageously, the coating can be configured to at least one of the following: to prevent the aerosol-forming substrate from adhering to the surface of the susceptor assembly, or conversely, to increase the adhesion of the aerosol-forming substrate, particularly liquid aerosol-forming substrate, to the susceptor assembly; to provide a porous surface, particularly for storing a flavoring substance or liquid aerosol-forming substrate; to provide a flavoring substance or coating that enhances aerosolization; to prevent diffusion of material, for example, metal diffusion, from the susceptor materials into the aerosol-forming substrate; or to improve the mechanical strength of the susceptor particles. To provide a flavoring substance or coating for 8. 1} LC ίη / ZZΖΠZ / E / YΙΛΙ To improve aerosolization, the coating may comprise a flavoring substance or a substance to enhance aerosolization. Preferably, the coating is electrically non-conductive. As used in this description, the term susceptor particle refers to an element capable of converting electromagnetic energy into heat when subjected to an alternating magnetic field. This can result from at least one of the hysteresis losses or eddy currents induced in the susceptor particle, depending on the electrical and magnetic properties of the materials comprising the particle. Hysteresis losses occur in ferromagnetic or ferrimagnetic susceptor materials because the magnetic domains within the material change under the influence of an alternating electromagnetic field. Eddy currents can be induced if the susceptor material is electrically conductive. In the case of an electrically conductive ferromagnetic or ferrimagnetic susceptor material, heat can be generated due to both eddy currents and hysteresis losses. In accordance with another aspect of the present invention, an aerosol generating article is provided for use with an induction-heated aerosol generating device. The article comprises at least one aerosol-forming substrate and a susceptor assembly according to the present invention and as described herein. The one or more susceptor particles of the susceptor assembly are incorporated into the aerosol-forming substrate. Susceptor particles can be distributed throughout the aerosol-forming substrate. They can be distributed evenly, i.e., homogeneously. Alternatively, they can be distributed with local concentration peaks or according to a concentration gradient, such as a distribution gradient from the central axis of the aerosol-forming article to its periphery. As used herein, the term aerosol-generating article refers to an article comprising at least one aerosol-forming substrate that, when heated, releases volatile compounds capable of forming an aerosol. Preferably, the aerosol-generating article is a heated aerosol-generating article. That is, an aerosol-generating article comprising at least one aerosol-forming substrate that is intended to be heated, rather than burned, in order to release volatile compounds capable of forming an aerosol. The aerosol-generating article may be a consumable, particularly a consumable that is discarded after a single use. For example, the article may be a cartridge that includes an aerosol-forming substrate. 1} LC ίη / ZZΖΠZ / E / YΙΛΙ heatable gel-like aerosol. Alternatively, the article may be a rod-shaped article, in particular a tobacco article, resembling conventional cigarettes.As used herein, the term aerosol-forming substrate denotes a substrate formed from or comprising an aerosol-forming material capable of releasing volatile compounds upon heating to generate an aerosol. The aerosol-forming substrate is intended to be heated, rather than burned, to release the volatile aerosol-forming compounds. The aerosol-forming substrate may be a solid aerosol-forming substrate, a liquid aerosol-forming substrate, a gel-type aerosol-forming substrate, or any combination thereof. That is, the aerosol-forming substrate may comprise, for example, both solid and liquid components. The aerosol-forming substrate may comprise a tobacco-containing material containing volatile tobacco flavor compounds, which are released from the substrate upon heating.Alternatively or additionally, the aerosol-forming substrate may comprise a non-tobacco material. The aerosol-forming substrate may further comprise an aerosol former. Examples of suitable aerosol formers are glycerin and propylene glycol. The aerosol-forming substrate may further comprise other additives and ingredients, such as nicotine or flavorings. The aerosol-forming substrate may also be a paste-like material, a pouch of porous material comprising an aerosol-forming substrate, or, for example, loose tobacco mixed with a gelling or adhesive agent, which could include a common aerosol former such as glycerin, and which is compressed or molded into a cap. By way of example, the aerosol-generating article may comprise the following elements: a substrate element, a support element, a cooling element, and a filter element. All of the aforementioned elements may be arranged sequentially along the length of a longitudinal axis of the article in the order described above, where the substrate element is located at a distal end of the article and the filter element is located at a proximal end. In particular, the substrate element is located downstream of the support element with respect to an airflow passing through the article during system use. Each of the aforementioned elements may be essentially cylindrical. In particular, all elements may have the same external cross-sectional shape.Furthermore, the elements may be enclosed by an outer wrapping that holds them together and maintains the convenient cross-sectional shape of the bar-shaped article. Preferably, the wrapping is made of paper. ! LC ίη / ΖΖΠΖ / Ε / ΥΙΛΙ The substrate element preferably comprises at least one aerosol-forming substrate to be heated and the susceptor assembly, i.e., the one or more susceptor particles incorporated into the aerosol-forming substrate. The support element may comprise a hollow cellulose acetate tube having a free central air passage. The aerosol cooling element can be an element with a large surface area and low pull-out resistance, for example, from 15 mmHg (millimeter water gauge) to 20 mmHg (millimeter water gauge). During use, an aerosol formed by volatile compounds released from the substrate element is drawn through the aerosol cooling element before being transported to the proximal end of the aerosol-generating article. The filter element preferably serves as a nozzle, or as part of a nozzle in conjunction with the aerosol cooling element. As used herein, the term “nozzle” refers to a portion of the article through which the aerosol exits the aerosol-generating article. According to another example, the aerosol-generating article may comprise the following elements: a distal support element, a substrate element, a proximal support element, a cooling element, and a filter element. All of the aforementioned elements may be arranged sequentially along the length of a longitudinal axis of the article in the order described above, wherein the distal support element is located at a distal end of the article and the filter element is located at a proximal end of the article. That is, the substrate element is located between the proximal support element and the distal support element. In particular, the substrate element is located downstream of the proximal support element and upstream of the distal support element with respect to an airflow passing through the article during use.Each of the aforementioned elements can be essentially cylindrical. In particular, all elements can have the same external cross-sectional shape. Furthermore, the elements can be enclosed by an outer wrapping that holds them together and maintains the desired cross-sectional shape of the bar-shaped article. Preferably, the wrapping is made of paper. The substrate element, the cooling element, and the filter element may correspond to the respective elements in accordance with the example mentioned above. The distal and proximal support element may comprise a hollow cellulose acetate tube having a free central air passage. Alternatively, the distal support element may comprise a cellulose acetate plug (without a free central air passage). The cellulose acetate plug may be used to cover and protect the distal front end of the substrate element. Other features and advantages of the aerosol generating article according to the present invention have already been described above with respect to the susceptor assembly according to the present invention and apply equally. In accordance with another aspect of the present invention, an aerosol generating system is provided comprising an aerosol generating article according to the present invention and as described herein, as well as an inductively heated aerosol generating device for use with the device. As used herein, the term inductively heated aerosol generating device is used to describe an electrically operated device capable of interacting with at least one aerosol-generating article, which includes at least one aerosol-forming liquid, to generate an aerosol by inductively heating the susceptor assembly and, consequently, the aerosol-forming substrate within the article. Preferably, the aerosol generating device is a mouth-sucking device for generating an aerosol that a user can inhale directly through the user's mouth. In particular, the aerosol generating device is a portable aerosol generating device. The device may comprise a receiving cavity to detachably receive at least a portion of the aerosol-generating article. The inductively heated aerosol generating device may comprise at least one induction source configured and arranged to generate an alternating magnetic field in the receiving cavity to inductively obtain an aerosol-forming substrate in the aerosol-generating article when the article is received in the aerosol-generating device. To generate the alternating magnetic field, the induction source may comprise at least one inductor, preferably at least one induction coil arranged around the receiving cavity. The induction coil may be arranged so as to surround the susceptor assembly, i.e., the susceptor particle(s), when the article is received into the receiving cavity. The induction coil can be either a helical coil or a flat coil, specifically a pancake coil or a curved flat coil. Using a flat helical coil allows for a compact design that is robust and inexpensive to manufacture. Using a helical induction coil advantageously allows for the generation of a homogeneous alternating magnetic field. As used in this description, a flat helical coil means a coil that is generally flat, where the winding axis of the coil is perpendicular to the surface on which the coil is located. The flat helical induction coil can have any desired shape within the plane of the coil. For example, the flat helical coil can be circular, or it can have a generally oblong or rectangular shape.However, the phrase "flat spiral coil," as used herein, covers both flat coils and flat spiral coils formed to fit a curved surface. For example, the induction coil may be a curved flat coil arranged on the circumference of a preferably cylindrical coil support, such as a ferrite core. Furthermore, the flat spiral coil may comprise, for example, two layers of a four-turn flat spiral coil or a single layer of a four-turn flat spiral coil. The at least one induction coil may be contained within a main body or housing of the aerosol generating device. The induction source may comprise an alternating current (AC) generator. The AC generator may be powered by a power supply from the aerosol generating device. The AC generator is operatively coupled to at least one induction coil. In particular, the at least one induction coil may be an integrated part of the AC generator. The AC generator is configured to generate a high-frequency oscillating current to pass through 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 system activation or may be supplied intermittently, such as puff by puff. Preferably, the induction source comprises a DC / AC converter connected to the DC power supply which includes an LC network, wherein the LC network comprises a series connection of a capacitor and the inductor. The induction source is preferably configured to generate a high-frequency magnetic field. As mentioned in this description, the high-frequency magnetic field can be in the range between 500 kHz (kilohertz) and 30 MHz (megahertz), particularly between 5 MHz (megahertz) and 15 MHz (megahertz), preferably between 5 MHz (megahertz) and 10 MHz (megahertz). The aerosol generating device may further comprise a controller configured to control the operation of the heating process, preferably in a closed-loop configuration, in particular to control the heating of the aerosol-forming liquid to a predetermined operating temperature. The operating temperature used to heat the aerosol-forming substrate may be in the range of 200°C to 360°C, particularly between 160°C and 240°C. These temperatures are typical operating temperatures for heating, but not for burning, the aerosol-forming substrate. The controller may be, or may be in the art, a general-purpose controller for the aerosol generating device. The controller may comprise a microprocessor, for example, a programmable microprocessor, a microcontroller, or an application-specific integrated circuit (ASIC), or other electronic circuitry capable of providing control. The controller may comprise other electronic components, such as at least one DC / AC inverter and / or power amplifiers, for example, a class C power amplifier, a class D power amplifier, or a class E power amplifier. In particular, the induction source may be part of the controller. The aerosol-generating device may comprise a power supply, in particular a DC power supply configured to provide a DC supply voltage and a DC supply current to the induction source. Preferably, the power supply is a battery such as a lithium iron phosphate battery. Alternatively, the power supply may be another form of charge storage device, such as a capacitor. The power supply may require recharging; that is, the power supply may be rechargeable. The power supply may have a capacity that allows for the storage of sufficient energy for one or more user experiences. For example, the power supply may have sufficient capacity to allow for continuous aerosol generation for a period of approximately six minutes or for a period that is a multiple of six minutes.In another example, the power supply may have sufficient capacity to allow a predetermined number of discrete puffs or activations of the induction source. The aerosol generating device may further comprise a flow concentrator arranged around at least a portion of the induction coil and configured to distort the alternating magnetic field of at least one inductive source toward the receiving cavity. Therefore, when the item is received in the receiving cavity, the alternating magnetic field is distorted toward the inductively heated liquid conduit, if present. Preferably, the flow concentrator comprises a flow concentrator sheet, in particular a multilayer flow concentrator sheet. ! LC ίη / ΖΖΠΖ / Ε / ΥΙΛΙ Additional features and advantages of the aerosol generating system according to the present invention have already been described with respect to the susceptor assembly and the aerosol generating article according to the present invention and are therefore equally applicable. According to the invention, a method of manufacturing a susceptor assembly comprising one or more composite susceptor particles for induction heating an aerosol-forming substrate is also provided, wherein each of the one or more susceptor particles comprises a particle core and a particle shell that completely encapsulates the particle core. The method comprises: - provide one or more particle cores comprising or manufactured from a ferromagnetic or ferrimagnetic core material; - coat each of the one or more particle nuclei with an electrically conductive shell material such as to form a particle shell around each of the one or more particle nuclei. As described above with respect to the susceptor assembly according to the present invention, the particle core may be a sintered particle core. Accordingly, providing one or more particle cores may comprise: - to form from the ferromagnetic or ferrimagnetic core material one or more green bodies that have the shape corresponding to the shape of the particle core; - synthesize one or more green bodies by heating one or more green bodies. As described above with respect to the susceptor assembly according to the present invention, the coating material may be plated, deposited, coated, or covered onto the particle core such that it forms the particle coating. Accordingly, coating each of the one or more particle cores with an electrically conductive coating material may comprise plated, deposited, coated, or covered onto the one or more particle cores. In particular, the electrically conductive coating material may be applied to the particle core by vapor deposition, suspension, or flat fluid bath, wherein the suspension and the flat fluid bath comprise the coating material to be applied. Other features and advantages of the method according to the present invention have already been described above with respect to the susceptor assembly according to the present invention and apply equally. ! LC ίη / ΖΖΠΖ / Ε / ΥΙΛΙ The invention is defined in the claims. However, a non-exhaustive list of non-limiting examples is provided below. Any or more of the features of these examples may be combined with any one or more features of another example, embodiment, or aspect described herein. Example Ex 1: An array of receptors for inductively heating an aerosol-forming substrate under the influence of an alternating magnetic field, the array of receptors comprising one or more composite receptor particles, wherein each of the one or more receptor particles comprises a particle core and a particle shell that completely encapsulates the particle core, wherein the particle core comprises or is made of a ferromagnetic or ferrimagnetic core material having a relative magnetic permeability of at least 200 at a frequency of 10 kHz (kilohertz), particularly for frequencies up to 10 kHz (kilohertz), and at a temperature of 20 degrees Celsius, and wherein the particle shell comprises or is made of an electrically conductive shell material. Example Ej2: Set of receptors in accordance with example Exl, wherein the cover material is paramagnetic. Example Ej3: Assembly of receptors in accordance with any of the above examples, wherein the cover material is one of aluminum, stainless steel, electrically conductive carbon, or bronze. Example Ej4: Set of receptors in accordance with any of the above examples, wherein the core material is electrically non-conductive. Example Ej5: Assembly of susceptors in accordance with any of the above examples, wherein the core material has a Curie temperature in a range between 160 degrees Celsius and 400, in particular between 160 degrees Celsius and 360 degrees Celsius, preferably between 200 degrees Celsius and 360 degrees Celsius or between 160 degrees Celsius and 240 degrees Celsius. Example Ej6: Set of susceptors in accordance with any of the above examples, wherein the core material is a ferrite powder. Example Ej7: Susceptor assembly in accordance with any of the above examples, wherein the core material is a manganese-magnesium ferrite, a nickel-zinc ferrite, or a cobalt-zinc barium ferrite. Example Ej8: Set of susceptors in accordance with any of the above examples, wherein each of the one or more susceptor particles is essentially ball-shaped. ! LC ίη / ΖΖΠΖ / Ε / ΥΙΛΙ Example Ej9: Set of susceptors in accordance with any of the above examples, wherein each of the one or more susceptor particles has an equivalent spherical particle diameter in a range between 10 micrometers and 500 micrometers, in particular between 20 micrometers and 250 micrometers, more particularly between 35 micrometers and 75 micrometers, for example 55 micrometers. Example EjlO: A set of susceptors in accordance with any of the above examples, wherein the particle nucleus has an equivalent spherical nucleus diameter in a range between 5 micrometers and 499 micrometers, in particular between 15 micrometers and 220 micrometers, more particularly between 30 micrometers and 55 micrometers, for example 35 micrometers. Example Ejl 1: Set of susceptors in accordance with any of the above examples, wherein the particle coating has a coating thickness in a range between 1 micrometer and 100 micrometers, in particular between 2.5 micrometers and 15 micrometers, more particularly between 5 micrometers and 12 micrometers, for example 10 micrometers. Example Ejl2: Set of susceptors in accordance with any of the above examples, wherein the particle core is a sintered particle core, in particular wherein the core material is a sintered material. Example Ejl3: Set of susceptors in accordance with any of the above examples, where the particle shell is in physical contact with the particle core. Example Ejl4: A set of susceptors in accordance with any of the above examples, wherein the particle shell is firmly attached to the particle core. Example Ex 15: Assembly of susceptors in accordance with any of the above examples, wherein the coating material is plated, deposited, coated or covered over the particle core such as to form the particle coating. Example Ex 16: Aerosol generating article for use with an inductively heated aerosol generating device, wherein the article comprises at least one aerosol forming substrate and a susceptor assembly in accordance with any of the preceding examples, wherein the one or more susceptor particles of the susceptor assembly are incorporated into the aerosol forming substrate, are distributed particularly along the aerosol forming substrate, for example, homogeneously distributed or distributed with local concentration peaks or distributed with a distribution gradient, in particular from a central axis of the aerosol forming article to the periphery thereof. Example Ex 17: Aerosol generating system comprising an aerosol generating article in accordance with any of the above examples and an inductively heated aerosol generating device for use with the device. Example Ex 18: Method of manufacturing a susceptor assembly comprising one or more composite susceptor particles for inductively heating an aerosol-forming substrate, wherein each of the one or more susceptor particles comprises a particle core and a particle shell that completely encapsulates the particle core, the method comprising: - providing one or more particle cores comprising or manufactured from a ferromagnetic or ferrimagnetic core material; - coat each of the one or more particle nuclei with an electrically conductive shell material such as to form a particle shell around each of the one or more particle nuclei. Example Ejl9: Method in accordance with Example Exl8, wherein providing the one or more particle nuclei comprises: - to form from the ferromagnetic or ferrimagnetic core material one or more green bodies that have the shape corresponding to the shape of the particle core; - sintering one or more green bodies by heating one or more green bodies. Example Ej20: Method in accordance with any one of Examples Exl8 or Exl9, wherein coating each of the one or more particle cores with an electrically conductive covering material comprises plating, depositing, coating or cladding the covering material onto the one or more particle cores. Example Ej21: Method in accordance with any one of Examples Exl8 to Ex20, wherein coating each of the one or more particle cores with an electrically conductive coating material comprises applying the coating material onto the particle core by steam deposit, winding in suspension or in a flat fluid bath, wherein the suspension and the flat fluid bath comprise the coating material to be applied. Now, examples will also be described with reference to the figures in which: Figure 1 schematically illustrates an aerosol generating article that can be heated by induction according to a first illustrative embodiment of the present invention comprising a set of susceptors; ! LC ίη / ΖΖΠΖ / Ε / ΥΙΛΙ Figure 2 schematically illustrates an illustrative embodiment of an aerosol generating system comprising an aerosol generating device and the aerosol generating article in accordance with Figure 1; Figure 3 shows a susceptor particle from the susceptor assembly included in the aerosol generating article according to Figure 1; and Figure 4 schematically illustrates an aerosol generating article that can be heated by induction in accordance with a second illustrative embodiment of the present invention. Figure 1 schematically illustrates a first embodiment of an inductively heated aerosol generating article 100 according to the present invention. The aerosol generating article 100 is essentially rod-shaped and comprises four elements arranged sequentially in coaxial alignment: an aerosol forming rod segment 110, a support element 140 having a central air passage 141, an aerosol cooling element 150, and a filter element 160 serving as a nozzle. The aerosol forming rod segment 110 is arranged at a distal end 102 of the article 100, while the filter element 160 is arranged at a distal end 103 of the article 100. Each of these four elements is essentially cylindrical, and all of them have essentially the same diameter.Furthermore, the four elements are enclosed by an outer wrapper 170 so as to hold the four elements together and maintain the convenient circular cross-sectional shape of the bar-shaped article 100. The wrapper 170 is preferably made of paper. With respect to the present invention, the aerosol-forming bar segment 110 comprises an aerosol-forming substrate 130 and a susceptor assembly 120 for heating the substrate 130 when exposed to an alternating magnetic field. As can be seen in Figure 1, the susceptor assembly 120 comprises a plurality of susceptor particles 123 that are evenly distributed along the aerosol-forming substrate 130. Due to their particle-like nature, the susceptor particles 123 present a large surface area to the surrounding aerosol-forming substrate 130, which advantageously enhances heat transfer. Details of the susceptor particles 123 will be described in more detail below with reference to Figure 3. As illustrated in Figure 2, the aerosol generating article 100 is configured for use with an inductively heated aerosol generating device 10. Together, the device 10 and article 100 form an aerosol generating 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 to receive at least a distal portion of article 100. The device 10 further comprises an induction source including an induction coil 30 for generating a high-frequency alternating magnetic field. In the present embodiment, the induction coil 30 is a helical coil circumferentially surrounding the cylindrical receiving cavity 20.The coil 30 is arranged so that the susceptor assembly 120 of the aerosol generating article 100 experiences the alternating magnetic field when the article 100 is coupled to the device 10. Therefore, when the induction source is activated, the susceptor assembly 120 is heated by induction heating. As will be described in more detail below with reference to Figure 3, the susceptor assembly 120 is heated to an operating temperature sufficient to vaporize the aerosol-forming substrate 130 in the aerosol-forming bar segment 110. Within a distal portion 13, the aerosol generating device 10 further comprises a DC power supply 40 and a controller 50 (illustrated schematically in Figure 2 only) for powering and controlling the heating process.In addition to the induction coil 30, the induction source is preferably at least partially an integral part of the controller 50 of device 10. Figure 3 shows a detailed cross-sectional view of one of the susceptor particles 123 used in the aerosol-generating article shown in Figure 1. According to the invention, each of the susceptor particles 123 comprises a particle core 121 and a particle shell 122 that completely encapsulates the particle core 121. The particle core 121 comprises or is made of a ferromagnetic or ferrimagnetic core material having a relative magnetic permeability of at least 200 for frequencies up to 10 kHz (kilohertz) at a temperature of 20 degrees Celsius. In the present embodiment, the particle core 121 is made of a nickel-zinc ferrite, i.e., a non-electrically conductive ferrimagnetic material. Conversely, the particle shell 122 is made of an electrically conductive shell material.In this embodiment, the particle 122 shell is made of aluminum, which is paramagnetic. Therefore, in general, when exposed to the alternating magnetic field of the induction coil 32, the particle 122 shell heats up due to eddy currents, while the particle 121 core heats up due to hysteresis losses. According to the present invention, the magnetic core has another important function: Due to its high magnetic permeability, particle 121 acts as a flux concentrator, increasing the magnetic flux through the particle coating 122. According to Faraday's law of induction, an increase in magnetic flux leads to an increase in eddy current losses in the particle coating 122. Therefore, the high magnetic permeability of the magnetic particle core 121 increases the amount of heat generated in the particle coating during use. Advantageously, this also allows the particle coating to be quite thin, thus saving material and costs in the manufacture of the susceptor particles. Upon reaching approximately the Curie temperature of the core material, the magnetic properties of the particle core 121 change from ferrimagnetic to paramagnetic.As a consequence, the overall effective magnetic permeability of the magnetic particle core 121 drops to unity. This causes heat generation in the particle core 121 to cease as the magnetic hysteresis of the core material disappears. Furthermore, the change in magnetic permeability also affects heat generation in the particle shell 122, since the decrease in the magnetic permeability of the magnetic particle core 121 leads to a decrease in magnetic flux through the electrically conductive particle shell 122. This, in turn, leads to a reduction in electromotive force and, therefore, a reduction in the eddy current losses that generate heat in the particle shell 122 when the susceptor array reaches the Curie temperature of the core material. Furthermore, the change in magnetic permeability also affects heat generation in the particle 122 coating because the decrease in magnetic permeability leads to an increase in skin depth in the particle 122 coating, as described earlier. This, in turn, causes a decrease in the effective resistance of the aluminum 122 particle coating. Therefore, when the Curie temperature of the core material is reached, heat generation in the particle 122 coating also decreases, since the reduction in effective resistance also leads to a reduction in eddy current losses in the coating material. Consequently, at the Curie temperature, heat generation from eddy current losses in the particle 122 coating is reduced due to both a reduction in magnetic flux through the particle coating and a reduction in the effective resistance of the coating material. Furthermore, overall heat generation is reduced due to hysteresis losses in the particle 121 core, which disappear at the Curie temperature from the core material. In particular, the reduction in overall heat generation results in rapid overheating of the aerosol-forming substrate being effectively prevented, preferably without the need for active temperature control. Preferably, the specific core material is chosen such that it has a Curie temperature of approximately a predefined operating temperature of the susceptor assembly 120 in which the aerosol-forming substrate 130 is to be heated. For solid aerosol-forming substrates containing tobacco material, the operating temperature may be in the range of 200 degrees Celsius to 360 degrees Celsius. As can also be seen in Figure 3, the susceptor particle 123 is essentially spherical. The particle diameter 124 can range from 50 micrometers to 75 micrometers. In the present embodiment, the mean particle diameter of all susceptor particles 123 is approximately 555 micrometers, resulting in a core diameter 125 of approximately 35 micrometers for particle 121 and a shell thickness 126 of approximately 10 micrometers. The particle core can be fabricated by sintering a green body of ferromagnetic or ferrimagnetic core material, and subsequently applying the shell material over the particle core 121, for example, by vapor deposition such as to provide a particle shell 122 that bonds tightly to the particle core 121. Figure 4 shows a second embodiment of an aerosol-generating article 200 according to the present invention. In general, the aerosol-generating article 200 according to Figure 4 is very similar to the aerosol-generating article 100 shown in Figure 1 and Figure 2. Therefore, identical or similar features are denoted by the same reference symbols, but increased by 100. Unlike the first embodiment shown in Figure 1, the article 400 according to Figure 4 has a particle distribution of the susceptor particles 223 with a distribution gradient from a central axis 207 of the aerosol-forming article 200 to its periphery, in particular with a maximum local concentration along the central axis 207 of the article 200, so that the aerosol-forming substrate 230 is heated mainly in a central portion of the rod segment 210. For the purposes of this description and the appended claims, unless otherwise stated, all numbers expressing quantities, percentages, etc., shall be understood to be modified in all cases by the term "approximately". Furthermore, all intervals include the maximum and minimum points described and include any intermediate intervals therewith, which may or may not be specifically enumerated in this description. In this context, therefore, a number A is understood to be A + 5 percent of A. Within this context, a number A may be considered to include numerical values ​​that are within the general standard error of the measurement of the property that modifies the number A.The number A, in some cases as used in the appended claims, may deviate by the percentages listed above, provided that the amount by which A deviates does not materially affect the basic and novel feature(s) of the claimed invention. Furthermore, all intervals include the maximum and minimum points described and include any intermediate intervals therein, which may or may not be specifically listed herein.

Claims

CLAIMS 1. An assembly of susceptors for inductively heating an aerosol-forming substrate under the influence of an alternating magnetic field, the assembly of susceptors comprising one or more composite susceptor particles, wherein each of the one or more susceptor particles comprises a particle core and a particle shell that completely encapsulates the particle core, wherein the particle core comprises or is made of a ferromagnetic or ferrimagnetic core material having a relative magnetic permeability of at least 200 for frequencies up to 10 kHz at a temperature of 20 degrees Celsius, and wherein the particle shell comprises or is made of an electrically conductive shell material.

2. A set of receptors according to claim 1, wherein the cover material is paramagnetic.

3. A susceptor assembly according to any of the preceding claims, wherein the cover material is aluminum, stainless steel, electrically conductive carbon, or bronze.

4. A set of receptors according to any of the preceding claims, wherein the core material is electrically non-conductive.

5. Susceptor assembly according to any of the preceding claims, wherein the core material has a Curie temperature in the range of 160 degrees Celsius to 400, in particular between 160 degrees Celsius and 360 degrees Celsius, preferably between 200 degrees Celsius and 360 degrees Celsius or between 160 degrees Celsius and 240 degrees Celsius.

6. Susceptor assembly according to any of the preceding claims, wherein the core material is a ferrite powder.

7. Susceptor assembly according to any of the preceding claims, wherein the core material is a manganese-magnesium ferrite, a nickel-zinc ferrite, or a cobalt-zinc barium ferrite.

8. A set of receptors according to any of the preceding claims, wherein each of the one or more receptor particles is essentially ball-shaped.

9. A susceptor assembly according to any of the preceding claims, wherein each of the one or more susceptor particles has an equivalent spherical particle diameter in the range of 10 micrometers to 500 micrometers, particularly between 20 micrometers and 250 micrometers, more particularly between 35 micrometers and 75 micrometers, for example 55 micrometers.

10. A susceptor assembly according to any of the preceding claims, wherein the particle core has an equivalent spherical core diameter in the range of 5 micrometers to 499 micrometers, particularly between 15 micrometers and 220 micrometers, more particularly between 30 micrometers and 55 micrometers, for example 35 micrometers.

11. A susceptor assembly according to any of the preceding claims, wherein the particle coating has a coating thickness in the range of 1 micrometer to 100 micrometers, in particular between 2.5 micrometers and 15 micrometers, more particularly between 5 micrometers and 12 micrometers, for example 10 micrometers.

12. Assembly of susceptors according to any of the preceding claims, wherein the particle core is a sintered particle core, in particular wherein the core material is a sintered material.

13. A susceptor assembly according to any preceding claim, wherein the coating material is plated, deposited, coated, or covered onto the particle core such as to form the particle coating. 1 ! LC ίη / ZZΖΠZ / E / YΙΛΙ 14. Aerosol generating article for use with an inductively heated aerosol generating device, wherein the article comprises at least one aerosol forming substrate and a susceptor assembly according to any preceding claim, wherein the one or more susceptor particles of the susceptor assembly are incorporated into the aerosol forming substrate, distributed particularly along the aerosol forming substrate, preferably with a distribution gradient from a central axis of the aerosol forming article to the periphery thereof.

15. Aerosol generating system comprising an aerosol generating article according to any of the preceding claims and an induction heating aerosol generating device for use with the device.

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