Susceptor assembly comprising one or more composite susceptor particles

Abstract

To provide a susceptor assembly comprising one or more composite susceptor particles for inductively heating an aerosol-forming substrate under the influence of an alternating magnetic field.SOLUTION: Each one of the one or more susceptor particles comprises a particle core and a particle shell entirely encapsulating 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 degree Celsius. The particle shell comprises or is made of an electrically conductive shell material. The disclosure further relates to an aerosol-generating article comprising such a susceptor assembly as well as to an aerosol-generating system comprising such an article and an aerosol-generating device. In addition, the disclosure relates to a method of manufacturing such a susceptor assembly.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a susceptor assembly comprising one or more composite susceptor particles for inductively heating an aerosol-forming substrate under the influence of an alternating magnetic field. The present disclosure further relates to an aerosol-generating article comprising such a susceptor assembly, as well as an aerosol-generating system comprising such an article and an aerosol-generating device. Additionally, the present disclosure relates to a method of manufacturing such a susceptor assembly. [Background technology]

[0002] It is generally known in the prior art to generate inhalable aerosols by inductively heating an aerosol-forming substrate. To this end, the substrate may be disposed in thermal proximity to or in direct physical contact with a susceptor, which may be capable of generating heat due to at least one of eddy currents or hysteresis losses when exposed to an alternating magnetic field. For example, the susceptor may include one or more susceptor particles embedded within the aerosol-forming substrate. Together, the substrate and susceptor may be part of an aerosol-generating article configured to be inserted into an aerosol-generating device that includes an induction source for generating the alternating magnetic field.

[0003] To control the temperature of a substrate, a susceptor assembly has been proposed, comprising a first susceptor and a second susceptor made of different materials. The first susceptor material may be optimized for heat loss and therefore heating efficiency. In contrast, the second susceptor material may be used as a temperature marker. To this end, the second susceptor material is selected to have a Curie temperature corresponding to a predefined operating temperature of the susceptor assembly. At that 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 current absorbed by the induction source, it is possible to detect when the second susceptor material has reached its Curie temperature, and therefore, when the predefined operating temperature has been reached. To avoid rapid overheating, the heating process must be controlled by actively reducing or switching off the heating power when the operating temperature is reached.

[0004] It would be desirable to have susceptor assemblies, aerosol-generating articles, and aerosol-generating systems that have the advantages of prior art solutions while mitigating their limitations. In particular, it would be desirable to have susceptor assemblies, aerosol-generating articles, and aerosol-generating systems that have improved heating efficiency and improved temperature control capabilities. Summary of the Invention

[0005] According to an embodiment of the present invention, a susceptor assembly for inductively heating an aerosol-forming substrate under the influence of an alternating magnetic field is provided. The susceptor assembly includes one or more composite susceptor particles. Each of the one or more susceptor particles includes a particle core and a particle shell completely enclosing the particle core. The particle core includes 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), specifically up to 10 kHz (kilohertz), and at a temperature of 20 degrees Celsius. That is, the particle core includes or is made of a ferromagnetic or ferrimagnetic core material having a relative magnetic permeability of at least 200 at a temperature of 20 degrees Celsius when penetrated by an alternating magnetic field having a frequency of 10 kHz (kilohertz), specifically up to 10 kHz (kilohertz). The particle shell includes or is made of a conductive shell material.

[0006] According to the present invention, it has been discovered that susceptor particles comprising a magnetic core with a high magnetic permeability and a conductive shell provide both improved heating efficiency and improved temperature control with self-regulating properties. To this extent, it has been discovered that the magnetic core with a high magnetic permeability acts as a magnetic 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 the electromotive force around a closed path through the conductive shell material, which in turn causes an increase in eddy current losses within the particle shell. Thus, a high magnetic permeability of the magnetic core increases the amount of heat generated within the particle shell during use. Advantageously, this also allows the particle shell to be made rather thin, thereby saving material and costs for the manufacture of susceptor particles.

[0007] Furthermore, it has been found that a magnetic core can be used to control the amount of magnetic flux generated within the particle shell as a function of the actual temperature of the susceptor assembly. 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. As a result, the overall effective magnetic permeability of the composite susceptor particle decreases to 1 when the susceptor assembly reaches the Curie temperature of the core material. This causes the magnetic hysteresis of the core material to disappear, resulting in the cessation of heat generation in the particle core due to hysteresis losses. Furthermore, the change in magnetic permeability also affects heat generation in the particle shell because the decrease in magnetic permeability causes a decrease in magnetic flux through the conductive shell. This results in a reduction in electromotive force and therefore in heat-generating eddy current losses within the particle shell when the susceptor assembly reaches the Curie temperature of the core material. In addition, the skin depth of the particle shell (which is a measure of the extent to which electrical conduction occurs within the conductive shell material when exposed to an alternating magnetic field) depends on the overall effective magnetic permeability of the composite susceptor particle. Thus, a decrease in the overall effective magnetic permeability of the susceptor particles causes a decrease in the magnetic permeability of the particle core, leading to an increase in the skin depth in the shell. This, in turn, causes a decrease in the effective resistance of the conductive particle shell. As a result, when the Curie temperature of the core material is reached, heat generation in the particle shell also decreases due to the decrease in effective resistance, and also causes a decrease in eddy current losses in the shell material. As a result, at the Curie temperature, heat generation due to eddy current losses in the particle shell decreases due to both the decrease in magnetic flux through the particle shell and the decrease in effective resistance of the shell material. In addition, overall heat generation decreases due to the disappearance of hysteresis losses in the particle core at the Curie temperature of the core material. Most importantly, the reduction in overall heat generation occurs automatically when the susceptor assembly 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.

[0008] Furthermore, the heating efficiency of the composite susceptor particles according to the present invention is greater than that of susceptor particles consisting of only ferromagnetic or ferrimagnetic core materials, as most of the heat is generated from the shell material due to enhanced eddy current losses.

[0009] The shell material may be paramagnetic. In this case, heat generation in the conductive shell material occurs only due to eddy currents. Similarly, the shell material may be ferromagnetic or ferrimagnetic. As a result, heat may also be generated in the shell material due to hysteresis losses. Advantageously, this increases the heating efficiency of the susceptor assembly. Preferably, if magnetic, the Curie temperature of the shell material is equal to or lower than the Curie temperature of the ferromagnetic or ferrimagnetic core material. Advantageously, this ensures that heat generation in the shell material due to hysteresis losses occurs only at temperatures below the Curie temperature of the core material, i.e., below the predefined operating temperature. It is also possible for the Curie temperature of the shell material to be higher than the Curie temperature of the ferromagnetic or ferrimagnetic core material.

[0010] The shell material may be one of aluminum, stainless steel, conductive carbon, or bronze. Aluminum is particularly suitable because it allows for low temperature sintering, which may result in easier fabrication of composite susceptor particles, as described in more detail below.

[0011] Preferably, the core material is non-conductive. In this case, heat generation in the core material is caused only by hysteresis losses. As a result, when the Curie temperature of the core material is reached, heat generation in the susceptor core completely stops. This clearly proves particularly beneficial for self-regulating temperature control of the susceptor assembly. It is also possible for the core material to be conductive.

[0012] As mentioned above, the Curie temperature of the core material preferably corresponds to the predefined operating temperature of the susceptor assembly. The actual operating temperature depends on the specific type of aerosol-forming substrate being heated. For solid aerosol-forming substrates containing tobacco material, the operating temperature may be within the range of 200°C to 360°C. For gel-like aerosol-forming substrates, the operating temperature may be within the range of 160°C to 240°C. As a result, the core material may have a Curie temperature within the range of 160°C to 400°C, specifically 160°C to 360°C, preferably 200°C to 360°C, or 160°C to 240°C.

[0013] The heating efficiency of the susceptor assembly increases with higher values ​​of relative magnetic permeability. Thus, the core material may even have a relative magnetic permeability higher than 200. As a result, the core material may have a relative magnetic permeability of at least 300, or at least 400, or at least 500, or at least 700, specifically at least 1000, preferably at least 10,000, or at least 50,000, or at least 80,000. These values ​​refer to maximum relative magnetic permeability values ​​at a frequency of 10 kHz (specifically for frequencies up to 10 kHz) and a temperature of 25 degrees Celsius. As described further below, the alternating magnetic field used for induction heating of the susceptor assembly may be in the range of 500 kHz (kilohertz) to 30 MHz (megahertz), specifically 5 MHz to 15 MHz (megahertz), preferably 5 MHz to 10 MHz (megahertz). For these frequencies, the minimum relative permeability of the core material may be lower. For example, the core material may have a relative permeability of at least 80, specifically at least 100, and preferably at least 120, at a frequency of 7 MHz (megahertz) and a temperature of 25 degrees Celsius. Similarly, the core material may have a relative permeability of at least 40, specifically at least 50, and preferably at least 60, at a frequency of 15 MHz (megahertz) and a temperature of 25 degrees Celsius.

[0014] The core material may include or be ferrite, specifically ferrite powder. As used herein, ferrite is a ceramic material made by mixing and firing a major proportion of iron (III) oxide (FeO) with a minor proportion of one or more additional metallic elements, such as barium, manganese, nickel, and zinc.

[0015] By way of example, the core material may be one of manganese magnesium ferrite, nickel zinc ferrite, or cobalt zinc barium ferrite.

[0016] For example, the core material is Mg x Mn y Fe z It may comprise or consist of an O4 type composition, where x=0.4-1.1, y=0.3-0.9, z=1-2, and the atomic fractions x, y, and z of the metal cations Mg, Mn, and Fe are such that the total charge of the metal cations balances the total charge of the oxygen anions.

[0017] Specifically, the core material is: -Mg, which has a Curie temperature of about 270 degrees Celsius 0.77 Mn 0.58 Fe 1.65 O4, -Mg, which has a Curie temperature of approximately 262 degrees Celsius 0.55 Mn 0.88 Fe 1.55 O4, -Mg, which has a Curie temperature of about 190 degrees Celsius 1.03 Mn 0.35 Fe 1.37 O4, may comprise or consist of.

[0018] The nickel zinc ferrite described above is x Zn 1-xIt may comprise or consist of a Fe2O4 type composition, where x=0.3-0.7, and the atomic fractions of the metal cations Ni, Zn, and Fe are such that the total charge of the metal cations is balanced by the total charge of the oxygen anions. In particular, the open-pore inductively heatable ceramic material may comprise, for example, Ni, Zn, Fe, which has a Curie temperature of about 258 degrees Celsius. 0.5 Zn 0.5 It may comprise or be Fe2O4.

[0019] Cobalt zinc barium ferrite, as described above, has a Curie temperature of about 279 degrees Celsius. 1.75 Zn 0.25 Ba2Fe 12 O 22 It may comprise or consist of.

[0020] Advantageously, ferrites are simple and inexpensive to manufacture. In addition, ferrites are non-conductive. As a result, heat generation in the core material is due solely to hysteresis losses and is therefore self-regulating when the Curie temperature is reached. Furthermore, ferrites are inert and therefore not critical for use in aerosol-generating articles, including aerosol-forming substrates.

[0021] The particle core is preferably a solid particle core. In particular, the particle core may have a ball shape. Similarly, the particle shell is preferably a solid particle shell. In particular, the particle may be a spherical shell.

[0022] Each of the one or more susceptor particles may have an equivalent particle diameter in the range of 10 micrometers to 500 micrometers, specifically 20 micrometers to 250 micrometers, and more specifically 35 micrometers to 75 micrometers, e.g., 55 micrometers. The equivalent spherical diameter is used in conjunction with irregularly shaped particles and is defined as the diameter of a sphere of equivalent volume. The particle size may depend, among other things, on the aerosol-forming substrate being heated. Additionally, for safety reasons, the particle size should be large enough to prevent the susceptor particles from passing through filters in the aerosol-generating article in which the susceptor particles may be used. Consequently, each of the one or more susceptor particles may have a particle diameter of at least 20 micrometers, preferably at least 35 micrometers.

[0023] As a result, the particle cores may have an equivalent spherical core diameter in the range of 5 micrometers to 499 micrometers, specifically 15 micrometers to 220 micrometers, and more specifically 30 micrometers to 55 micrometers, for example, 35 micrometers. The equivalent particle diameter may be given primarily by the equivalent spherical core diameter. Equivalent spherical core diameters in the range of 30 micrometers to 55 micrometers are particularly suitable because such particles are small enough to be nearly invisible within the substrate, yet large enough to bypass filters in aerosol-generating articles in which the susceptor particles may be used.

[0024] Due to the flux-strengthening effect of the core material within the shell, the shell thickness may be somewhat small. Advantageously, this allows for material and cost savings in the production of susceptor particles. The particle shell may have a shell thickness of 2.5 micrometers to 15 micrometers, specifically 5 micrometers to 12 micrometers, for example, 10 micrometers. The shell thickness may depend, among other things, on the particle shell material, particularly the induction heating rate and material-specific requirements for shell production. For example, the shell thickness may be 10 micrometers for aluminum, while the shell thickness may be less than 10 micrometers for steel. Larger shell thickness values ​​are particularly appropriate for particle shells with porous or sintered structures.

[0025] The above values ​​may refer to the average core diameter, average shell thickness, and average particle diameter of all susceptor particles in the susceptor assembly, such that some susceptor particles may have at least one of a smaller core diameter, a smaller shell thickness, or a smaller particle diameter than other susceptor particles in the susceptor assembly.

[0026] The particle shell is preferably in physical contact with the particle core, which allows good heat exchange between the particle shell and the particle core so that they are at approximately the same temperature.

[0027] The particle core may be a sintered particle core. Specifically, the core material may be a sintered material. Sintering is a process of consolidating and forming a solid mass of material by heat or pressure without melting to the liquidus point. Advantageously, sintering makes it possible to produce particle cores with almost any shape and size. Sintering also results in susceptor particles with good strength properties. In addition, sintered particle cores facilitate good bonding between the particle shell and the particle core.

[0028] As a result, the particle shell is preferably firmly bonded to the particle core, i.e., there may be a material-to-material bond between the particle shell and the particle core. A strong bond provides good mechanical stability and good heat exchange between the particle shell and the particle core.

[0029] In particular, the shell material may be plated, deposited, coated, or clad onto the particle core, such as to form a particle shell.

[0030] The susceptor assembly according to the present invention is preferably configured to be driven by an alternating magnetic field, particularly a high frequency magnetic field, which as referred to herein may be in the range of 500 kHz (kilohertz) to 30 MHz (megahertz), particularly 5 MHz (megahertz) to 15 MHz (megahertz), preferably 5 MHz (megahertz) to 10 MHz (megahertz).

[0031] The susceptor particles may be provided with a cover, particularly a protective cover. The cover may be made of glass, ceramic, or an inert metal, and may be formed or coated on the outside of at least a portion of the susceptor particles, respectively. Advantageously, the cover may be configured for at least one of the following purposes: to prevent the aerosol-forming substrate from sticking to the surface of the susceptor assembly or vice versa; to increase adhesion of the aerosol-forming substrate, particularly a liquid aerosol-forming substrate, to the susceptor assembly; to store a flavoring substance or a liquid aerosol-forming substrate; to provide a flavoring substance or an aerosolization-enhancing cover; to prevent diffusion of a substance, e.g., metal diffusion, from the susceptor material to the aerosol-forming substrate; or to improve the mechanical strength of the susceptor particles. To provide a flavoring substance or an aerosolization-enhancing cover, the cover may include a flavoring substance or an aerosolization-enhancing substance. The cover is preferably non-conductive.

[0032] As used herein, the term "susceptor particle" refers to an element capable of converting electromagnetic energy into heat when subjected to an alternating magnetic field. This may be the result of at least one of hysteresis loss or eddy currents induced within the susceptor particle, depending on the electrical and magnetic properties of the material contained within the susceptor particle. Hysteresis loss occurs in ferromagnetic or ferrimagnetic susceptor materials due to magnetic domains within the material being switched under the influence of the alternating electromagnetic field. Eddy currents may be induced if the susceptor material is electrically conductive. In the case of electrically conductive ferromagnetic or ferrimagnetic susceptor materials, heat can be generated due to both eddy currents and hysteresis loss.

[0033] According to another aspect of the present invention, there is provided an aerosol-generating article for use with an inductively heated aerosol-generating device, the article comprising at least one aerosol-forming substrate and at least one susceptor assembly according to the present invention and as described herein, wherein one or more susceptor particles of the susceptor assembly are embedded within the aerosol-forming substrate.

[0034] The susceptor particles may be dispersed throughout the aerosol-forming substrate. The susceptor particles may be dispersed evenly, i.e., uniformly, throughout the aerosol-forming substrate. The susceptor particles may also be dispersed throughout the aerosol-forming substrate with local concentration peaks or according to a concentration gradient, for example, a dispersion gradient from the central axis of the aerosol-forming article to its periphery.

[0035] As used herein, the term "aerosol-generating article" refers to an article comprising at least one aerosol-forming substrate that, when heated, releases a volatile compound capable of forming an aerosol. The aerosol-generating article is preferably a heated aerosol-generating article, i.e., an aerosol-generating article comprising at least one aerosol-forming substrate that is intended to be heated, rather than combusted, to release a volatile compound capable of forming an aerosol. The aerosol-generating article may be a consumable product, particularly one that is disposed of after a single use. For example, the article may be a cartridge comprising a gel-like aerosol-forming substrate that is heated. Alternatively, the article may be a rod-shaped article (particularly a tobacco article) that resembles a conventional cigarette.

[0036] As used herein, the term "aerosol-forming substrate" refers to a substrate formed from or including an aerosol-forming material capable of releasing a volatile compound upon heating to form an aerosol. 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, or a gel-like aerosol-forming substrate, or any combination thereof. That is, the aerosol-forming substrate may, for example, include 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, for example, loose tobacco mixed with a gelling or adhesive agent, which may include a common aerosol former such as glycerin, which is compressed or molded into a plug.

[0037] As an 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 longitudinal axis of the article in the order described above, with the substrate element being arranged at the distal end of the article and the filter element being arranged at the proximal end of the article. Specifically, the substrate element is located downstream of the support element with respect to airflow passing through the article when the system is in use. Each of the aforementioned elements may be substantially cylindrical. Specifically, all of the elements may have the same outer cross-sectional shape. Additionally, the elements may be surrounded by an outer wrapper to hold the elements together and maintain the desired cross-sectional shape of the rod-shaped article. The wrapper is preferably made of paper.

[0038] The substrate element preferably comprises at least one aerosol-forming substrate which is heated, and a susceptor assembly, i.e., one or more susceptor particles embedded in the aerosol-forming substrate.

[0039] The support element may comprise a hollow cellulose acetate tube with an empty central air passage.

[0040] The aerosol cooling element may be an element having a large surface area and a low draw resistance (e.g., 15 mmWG (millimeter gauge pressure of water column) to 20 mmWG (millimeter gauge pressure of water column). In use, the aerosol formed by the volatile compounds released from the substrate element is drawn through the aerosol cooling element before being conveyed to the proximal end of the aerosol-generating article.

[0041] The filter element preferably functions as a mouthpiece or as part of a mouthpiece together with the aerosol cooling element. As used herein, the term "mouthpiece" refers to the portion of the article through which the aerosol exits the aerosol-generating article.

[0042] According to another embodiment, 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 sequentially arranged along the longitudinal axis of the article in the aforementioned order, with the distal support element disposed at the distal end of the article and the filter element disposed at the proximal end of the article. That is, the substrate element is located between the proximal and distal support elements. Specifically, the substrate element is located downstream of the proximal support element and upstream of the distal support element with respect to airflow passing through the article in use. Each of the aforementioned elements may be substantially cylindrical. Specifically, all elements may have the same outer cross-sectional shape. Additionally, the elements may be surrounded by an outer wrapper to hold the elements together and maintain the desired cross-sectional shape of the rod-shaped article. The wrapper is preferably made of paper.

[0043] The substrate element, the cooling element and the filter element may correspond to the respective elements according to the previous embodiments.

[0044] The distal and proximal support elements may comprise hollow cellulose acetate tubes with an empty central air passage. Alternatively, the distal support element may comprise a cellulose acetate plug (without an empty central air passage). The cellulose acetate plug may be used to cover and protect the distal forward end of the base element.

[0045] Further features and advantages of the aerosol-generating article according to the invention have already been described above with respect to the susceptor assembly according to the invention and apply equally well.

[0046] According to another aspect of the present invention, there is provided an inductively heated aerosol generating device for use with the device, as well as an aerosol generating system comprising an aerosol-generating article according to the present invention and as described herein.

[0047] 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 containing at least one aerosol-forming liquid to generate an aerosol by inductively heating a susceptor assembly, and hence an aerosol-forming substrate within the article. The aerosol generating device is preferably a smoking device for generating an aerosol that is inhalable by a user directly through the user's mouth. In particular, the aerosol generating device is a handheld aerosol generating device.

[0048] The device may comprise a receiving cavity for removably receiving at least a portion of the aerosol-generating article.

[0049] The inductively heated aerosol generating device may comprise at least one induction source constructed and arranged to generate an alternating magnetic field within the receiving cavity to inductively heat an aerosol-forming substrate within the aerosol-generating article when the article is received within the aerosol generating device.

[0050] To generate the alternating magnetic field, the induction source may include at least one inductor, preferably at least one induction coil, disposed around the receiving cavity, the induction coil being arranged to surround the susceptor assembly, i.e., one or more susceptor particles, when the article is received in the receiving cavity.

[0051] 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. The use of a flat spiral coil allows for a compact design that is robust and inexpensive to manufacture. The use of a helical induction coil advantageously allows for the generation of a homogeneous alternating magnetic field. As used herein, a "flat spiral coil" refers to a generally planar coil in which the axis of the coil's windings is perpendicular to the surface on which the coil is placed. A flat spiral induction coil can have any desired shape within the plane of the coil. For example, a flat spiral coil may have a circular shape or a generally elliptical or rectangular shape. However, as used herein, the term "flat spiral coil" encompasses both planar coils as well as flat spiral coils shaped to fit curved surfaces. For example, the induction coil may be a "curved" planar coil disposed around a preferably cylindrical coil support (e.g., a ferrite core). Furthermore, the flat spiral coil may comprise, for example, two layers of a four-turn flat spiral coil, or may comprise a single layer of a four-turn flat spiral coil. At least one induction coil may be held within one of the main bodies or housings of the aerosol generating device.

[0052] The induction source may 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., after each puff).

[0053] The inductive source preferably comprises a DC / AC converter connected to a DC power source including an LC network, the LC network comprising a series connection of a capacitor and an inductor.

[0054] The induction source is preferably configured to generate a radio frequency magnetic field, which as referred to herein may be in the range of 500 kHz (kilohertz) to 30 MHz (megahertz), specifically 5 MHz (megahertz) to 15 MHz (megahertz), preferably 5 MHz (megahertz) to 10 MHz (megahertz).

[0055] The aerosol-generating device may further comprise a controller configured to control the operation of the heating process, preferably in a closed-loop configuration, particularly 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 160°C to 240°C. These temperatures are typical operating temperatures for heating but not burning the aerosol-forming substrate.

[0056] The controller may be the overall controller of the aerosol generating device or may be part of the technical field of the overall controller of the aerosol generating device. The controller may comprise a microprocessor, such as a programmable microprocessor, a microcontroller, or an application specific integrated circuit chip (ASIC) or other electronic circuit capable of providing control. The controller may comprise further electronic components, such as at least one DC / AC inverter and / or a power amplifier (e.g., a class C power amplifier, a class D power amplifier, or a class E power amplifier). In particular, the induction source may be part of the controller.

[0057] The aerosol generating device may 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. Alternatively, the power source may be another form of charge storage device, such as a capacitor. The power source may require recharging, i.e., 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.

[0058] The aerosol generating device may also further comprise a flux concentrator disposed around at least a portion of the induction coil and configured to distort the alternating magnetic field of the at least one induction source towards the receiving cavity. Thus, when an article is received in the receiving cavity, the alternating magnetic field, if present, is distorted towards the inductively heatable liquid conduit. Preferably, the flux concentrator comprises a flux concentrator foil, in particular a multi-layer flux concentrator foil.

[0059] Further features and advantages of the aerosol-generating system according to the invention have already been described with respect to the susceptor assembly and aerosol-generating article according to the invention and therefore apply equally.

[0060] According to the present invention, there is also provided a method of manufacturing a susceptor assembly for inductively heating an aerosol-forming substrate, the susceptor assembly including one or more composite susceptor particles, each of the one or more susceptor particles including a particle core and a particle shell completely encapsulating the particle core, the method comprising: - providing one or more particle cores comprising or made from a ferromagnetic or ferrimagnetic core material; - completely enveloping each of the one or more particle cores with a conductive shell material so as to form a particle shell around each of the one or more particle cores.

[0061] As further described above with respect to the susceptor assembly according to the present invention, the particle cores may be sintered particle cores. As a result, providing one or more particle cores may include: - forming one or more green bodies from a ferromagnetic or ferrimagnetic core material, the green bodies having a shape corresponding to the shape of the particle cores; - sintering the one or more green bodies by heating the one or more green bodies.

[0062] As further described above with respect to the susceptor assembly according to the present invention, the shell material may be plated, deposited, coated, or clad onto the particle cores to form the particle shells. Thus, completely encasing each of the one or more particle cores with the conductive shell material may include plating, depositing, coating, or cladding the shell material onto the one or more particle cores. In particular, the conductive shell material may be applied onto the particle cores by vapor deposition, roller application in a slurry, or in a flat fluid bath, the slurry and flat fluid bath including the applied shell material.

[0063] Further features and advantages of the method according to the invention have already been mentioned above with respect to the susceptor assembly according to the invention and apply equally.

[0064] 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.

[0065] Example Ex1: A susceptor assembly for inductively heating an aerosol-forming substrate under the influence of an alternating magnetic field, the susceptor assembly comprising one or more composite susceptor particles, each of the one or more susceptor particles comprising a particle core and a particle shell completely enclosing the particle core, the particle core comprising or made of a ferromagnetic or ferrimagnetic core material having a relative magnetic permeability of at least 200 at a temperature of 20 degrees Celsius and a frequency of 10 kHz (kilohertz), particularly at frequencies up to 10 kHz (kilohertz), and the particle shell comprising or made of a conductive shell material.

[0066] Example Ex2: A susceptor assembly according to example Ex1, wherein the shell material is paramagnetic.

[0067] Example Ex3: A susceptor assembly according to any one of the preceding examples, wherein the shell material is one of aluminum, stainless steel, conductive carbon, or bronze.

[0068] Example Ex4: A susceptor assembly according to any one of the preceding examples, wherein the core material is non-conductive.

[0069] Example Ex5: A susceptor assembly according to any one of the preceding examples, wherein the core material has a Curie temperature in the range of 160 degrees Celsius to 400 degrees Celsius, specifically 160 degrees Celsius to 360 degrees Celsius, preferably 200 degrees Celsius to 360 degrees Celsius, or 160 degrees Celsius to 240 degrees Celsius.

[0070] Example Ex6: A susceptor assembly according to any one of the preceding examples, wherein the core material is a ferrite powder.

[0071] Example Ex7: A susceptor assembly according to any one of the preceding examples, wherein the core material is of manganese-magnesium ferrite, nickel-zinc ferrite, or cobalt-zinc barium ferrite.

[0072] Example Ex8: A susceptor assembly according to any one of the preceding examples, wherein each of the one or more susceptor particles has a substantially ball shape.

[0073] Example Ex9: A susceptor assembly according to any one of the preceding examples, wherein each of the one or more susceptor particles has an equivalent spherical particle diameter in the range of 10 micrometers to 500 micrometers, specifically 20 micrometers to 250 micrometers, more specifically 35 micrometers to 75 micrometers, e.g., 55 micrometers.

[0074] Example Ex10: A susceptor assembly according to any one of the preceding examples, wherein the particle cores have an equivalent spherical core diameter in the range of 5 micrometers to 499 micrometers, specifically 15 micrometers to 220 micrometers, more specifically 30 micrometers to 55 micrometers, e.g., 35 micrometers.

[0075] Example Ex11: A susceptor assembly according to any one of the preceding examples, wherein the particle shell has a shell thickness in the range of 1 micrometer to 100 micrometers, specifically 2.5 micrometers to 15 micrometers, more specifically 5 micrometers to 12 micrometers, for example 10 micrometers.

[0076] Example Ex12: A susceptor assembly according to any one of the preceding examples, wherein the particle cores are sintered particle cores, in particular the core material is a sintered material.

[0077] Example Ex13: A susceptor assembly according to any one of the preceding examples, wherein the particle shells are in physical contact with the particle cores.

[0078] Example Ex14: A susceptor assembly according to any one of the preceding examples, wherein the particle shells are firmly bonded to the particle cores.

[0079] Example Ex15: A susceptor assembly according to any one of the preceding examples, wherein the shell material is plated, deposited, coated, or clad onto the particle core to form the particle shell.

[0080] Example Ex16: An aerosol-generating article for use with an induction-heated aerosol-generating device, the article comprising at least one aerosol-forming substrate and a susceptor assembly according to any one of the preceding examples, wherein one or more susceptor particles of the susceptor assembly are embedded within the aerosol-forming substrate and, in particular, are dispersed throughout the aerosol-forming substrate, for example, homogeneously dispersed or dispersed with a local concentration peak, or, in particular, dispersed with a dispersion gradient from the central axis of the aerosol-forming article to its periphery.

[0081] Example Ex17: An aerosol generating system comprising an aerosol-generating article according to any one of the preceding examples and an inductively heated aerosol generator for use with the apparatus.

[0082] Example Ex18: A 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 completely enclosing the particle core, comprising: providing one or more particle cores comprising or made from a ferromagnetic or ferrimagnetic core material; completely encasing each of the one or more particle cores with a conductive shell material so as to form a particle shell around each of the one or more particle cores.

[0083] Example Ex19: Providing one or more particle cores forming one or more green bodies from a ferromagnetic or ferrimagnetic core material having a shape corresponding to the shape of the particle cores; Sintering the one or more green bodies by heating the one or more green bodies.

[0084] Example Ex20: The method according to any one of examples Ex18 or Ex19, wherein completely encasing each of the one or more particle cores with the conductive shell material comprises plating, depositing, coating, or cladding the shell material onto the one or more particle cores.

[0085] Example Ex21: The method according to any one of examples Ex18 to Ex20, wherein the completely enveloping of each of the one or more particle cores with the conductive shell material is by vapor deposition, by roller application in the form of a slurry, or by applying the shell material onto the particle cores in a flat fluid bath, wherein the slurry and the flat fluid bath comprise the applied shell material.

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

[0087] [Figure 1] FIG. 1 illustrates schematically an inductively heatable aerosol-generating article comprising a susceptor assembly according to a first exemplary embodiment of the present invention. [Figure 2] FIG. 2 illustrates schematically an exemplary embodiment of an aerosol generation system comprising an aerosol generating device and an aerosol-generating article according to FIG. [Figure 3] FIG. 3 shows one susceptor particle of a susceptor assembly contained within the aerosol-generating article according to FIG. [Figure 4] FIG. 4 illustrates schematically an inductively heatable aerosol-generating article according to a second exemplary embodiment of the present invention.

[0088] FIG. 1 schematically illustrates a first exemplary embodiment of an inductively heatable aerosol-generating article 100 according to the present invention. The aerosol-generating article 100 has a substantially rod-shape and comprises four elements sequentially arranged 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 functioning as a mouthpiece. The aerosol-forming rod segment 110 is disposed at the distal end 102 of the article 100, while the filter element 160 is disposed at the distal end 103 of the article 100. Each of these four elements is a substantially cylindrical element, all of which have substantially the same diameter. Additionally, the four elements are surrounded by an outer wrapper 170 to hold the four elements together and maintain the desired circular cross-sectional shape of the rod-like article 100. The wrapper 170 is preferably made of paper.

[0089] For the present invention, the aerosol-forming rod segment 110 includes not only an aerosol-forming substrate 130, but also a susceptor assembly 120 for heating the substrate 130 when exposed to an alternating magnetic field. As can be seen in FIG. 1 , the susceptor assembly 120 comprises a plurality of susceptor particles 123 evenly distributed throughout the aerosol-forming substrate 130. Due to their particulate nature, the susceptors 123 present a large surface area to the surrounding aerosol-forming substrate 130, which advantageously enhances heat transfer. Details of the susceptor particles 123 are described in further detail below with respect to FIG. 3 .

[0090] As illustrated 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 includes 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 includes an induction source including an induction coil 30 for generating a high-frequency alternating magnetic field. In this embodiment, the induction coil 30 is a helical coil circumferentially surrounding the cylindrical receiving cavity 20. The coil 30 is disposed such that a susceptor assembly 120 of the aerosol-generating article 100 experiences the alternating magnetic field upon engagement of the article 100 with the device 10. Thus, when the induction source is activated, the susceptor assembly 120 heats up due to induction heating. As described in more detail further below with respect to Figure 3, the susceptor assembly 120 is heated to an operating temperature sufficient to vaporize the aerosol-forming substrate 130 within the aerosol-forming rod segment 110. Within the distal portion 13, the aerosol-generating device 10 further comprises a DC power supply 40 and a controller 50 (illustrated only diagrammatically in Figure 2) for supplying power and controlling the heating process. Apart from the induction coil 30, the induction source is preferably at least partially an integral part of the controller 50 of the device 10.

[0091] FIG. 3 shows a detailed cross-sectional view of one of the susceptor particles 123 used in the aerosol-generating article shown in FIG. 1 . According to the present invention, each susceptor particle 123 comprises a particle core 121 and a particle shell 122 that completely encapsulates the particle core 121. The particle core 121 includes or is made of a ferromagnetic or ferrimagnetic core material having a relative permeability of at least 200 for frequencies up to 10 kHz (kilohertz) at a temperature of 20 degrees Celsius. In this embodiment, the particle core 121 is made of nickel-zinc ferrite, a non-conductive ferrimagnetic material. In contrast, the particle shell 122 is made of a conductive shell material. In this embodiment, the particle shell 122 is made of aluminum, which is paramagnetic. Thus, generally, when exposed to the alternating magnetic field of the induction coil 32, the particle shell 122 heats due to eddy currents, while the particle core 121 heats due to hysteresis losses.

[0092] According to the present invention, the magnetic core has another important function: due to its high magnetic permeability, the particles 121 act as a magnetic flux concentrator, increasing the magnetic flux through the particle shell 122. According to Faraday's law of induction, an increase in magnetic flux causes an increase in eddy current losses within the particle shell 122. Thus, the high magnetic permeability of the magnetic particle core 121 increases the amount of heat generated within the particle shell during use. Advantageously, this also allows the particle shell to be rather thin, and therefore saves material and costs for the manufacture of susceptor particles.

[0093] When the Curie temperature of the core material is nearly reached, the magnetic property of the particle core 121 changes from ferrimagnetic to paramagnetic. As a result, the overall effective permeability of the magnetic particle core 121 decreases to 1. This causes heat generation in the particle core 121 to cease because the magnetic hysteresis of the core material disappears. Furthermore, the change in permeability also affects heat generation in the particle shell 122 because the decrease in permeability of the magnetic particle core 121 causes a decrease in magnetic flux through the conductive particle shell 122. This results in a reduction in the electromotive force and, therefore, in the heat-generating eddy current losses in the particle shell 122 when the susceptor assembly reaches the Curie temperature of the core material.

[0094] Additionally, the change in magnetic permeability also affects heating of the particle shells 122, as a decrease in magnetic permeability causes an increase in the skin depth within the particle shells 122, as described further above. This, in turn, causes a decrease in the effective resistivity of the aluminum particle shells 122. Thus, when the Curie temperature of the core material is reached, a decrease in effective resistivity also occurs, reducing heating in the particle shells 122 and therefore reducing eddy current losses in the shell material.

[0095] As a result, at the Curie temperature, heat generation due to eddy current losses in the particle shell 122 is reduced due to both the reduced magnetic flux through the particle shell and the reduced effective resistance of the shell material. In addition, overall heat generation is reduced because hysteresis losses in the particle core 121 disappear at the Curie temperature of the core material. Specifically, the overall heat generation reduction is a result of this in itself, as rapid overheating of the aerosol-forming substrate can be effectively avoided, preferably without the need for active temperature control.

[0096] The particular core material is preferably selected to have a Curie temperature around the predefined operating temperature of the susceptor assembly 120 to which the aerosol-forming substrate 130 is 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.

[0097] As can be further seen in Figure 3, the susceptor particles 123 have a substantially ball shape. Particle diameter 124 may be in the range of 50 micrometers to 75 micrometers. In this embodiment, the average particle diameter of all susceptor particles 123 is about 55 micrometers, resulting from particle cores 121 having a core diameter 125 of about 35 micrometers and particle shells 122 having a shell thickness 126 of about 10 micrometers.

[0098] The particle cores may be manufactured by sintering a green body of ferromagnetic or ferrimagnetic core material and then applying a shell material, for example by vapor deposition, onto the particle cores 121 to provide particle shells 122 firmly bonded to the particle cores 121.

[0099] 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 Figures 1 and 2. Accordingly, identical or similar features are designated with the same reference numerals, but with the addition of 100. In contrast to the first embodiment shown in Figure 1, the article 400 according to Figure 4 has an aerosol-forming substrate 230 that is heated primarily at the central portion of the rod segment 210, and therefore has a particle distribution of susceptor particles 223 that has a dispersion gradient with a local concentration maximum from the central axis 207 of the aerosol-forming article 200 to its periphery, specifically along the central axis 207 of the article 200.

[0100] For purposes of this specification and the appended claims, unless otherwise indicated, all numbers expressing amounts, quantities, percentages, and the like should be understood to be modified in all instances 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 percent of A. Within this context, the number A may be considered to include values ​​that are within the common standard error of measurement for the property that it 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 property(ies) 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. A susceptor assembly for inductively heating an aerosol-forming substrate under the influence of an alternating magnetic field, the susceptor assembly comprising one or more composite susceptor particles, each of the one or more susceptor particles comprising a particle core and a particle shell completely enclosing the particle core, the particle core comprising or made of a ferromagnetic or ferrimagnetic core material having a relative magnetic permeability of at least 200 at a temperature of 20 degrees Celsius and for frequencies up to 10 kHz, and the particle shell comprising or made of a conductive shell material.

2. The susceptor assembly of claim 1 , wherein the shell material is paramagnetic.

3. The susceptor assembly of any one of claims 1 to 2, wherein the shell material is one of aluminum, stainless steel, conductive carbon, or bronze.

4. The susceptor assembly of any one of claims 1 to 3, wherein the core material is non-conductive.

5. 5. The susceptor assembly according to claim 1, wherein the core material has a Curie temperature in the range of 160 to 400 degrees Celsius, particularly 160 to 360 degrees Celsius, preferably 200 to 360 degrees Celsius, or 160 to 240 degrees Celsius.

6. The susceptor assembly of any one of claims 1 to 5, wherein the core material is a ferrite powder.

7. The susceptor assembly of any one of claims 1 to 6, wherein the core material is manganese-magnesium ferrite, nickel-zinc ferrite, or cobalt-zinc barium ferrite.

8. The susceptor assembly of any one of claims 1 to 7, wherein each of the one or more susceptor particles has a substantially ball shape.

9. 9. The susceptor assembly of claim 1, wherein each of the one or more susceptor particles has an equivalent spherical particle diameter in the range of 10 micrometers to 500 micrometers, specifically 20 micrometers to 250 micrometers, more specifically 35 micrometers to 75 micrometers, for example 55 micrometers.

10. 10. The susceptor assembly of claim 1, wherein the particle cores have an equivalent spherical core diameter in the range of 5 micrometers to 499 micrometers, specifically 15 micrometers to 220 micrometers, more specifically 30 micrometers to 55 micrometers, e.g., 35 micrometers.

11. 11. The susceptor assembly of claim 1, wherein the particle shell has a shell thickness in the range of 1 micrometer to 100 micrometers, specifically 2.5 micrometers to 15 micrometers, more specifically 5 micrometers to 12 micrometers, for example 10 micrometers.

12. The susceptor assembly according to any one of claims 1 to 11, wherein the particle cores are sintered particle cores, in particular, the core material is a sintered material.

13. The susceptor assembly of any one of claims 1 to 12, wherein the shell material is plated, deposited, coated, or clad onto the particle core to form the particle shell.

14. 14. An aerosol-generating article for use with an induction-heated aerosol-generating device, the article comprising at least one aerosol-forming substrate and a susceptor assembly according to any one of claims 1 to 13, wherein the one or more susceptor particles of the susceptor assembly are embedded within the aerosol-forming substrate, particularly dispersed throughout the aerosol-forming substrate, preferably with a dispersion gradient from a central axis of the aerosol-forming article to its periphery.

15. An aerosol generating system comprising an aerosol-generating article according to any one of claims 1 to 14 and an inductively heated aerosol generating device for use with said device.

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