A susceptor assembly comprising one or more composite material susceptor particles

Abstract

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. Each of the one or more susceptor particles comprises a particle core and a particle shell completely enclosing 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 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 for manufacturing such a susceptor assembly.

Description

Technical Field

[0001] The present disclosure relates to a susceptor assembly comprising one or more composite material 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 to an aerosol-generating system comprising such an article and an aerosol-generating device. In addition, the present disclosure relates to a method for manufacturing such susceptor assemblies.

Background Art

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

[0003] To control the temperature of the substrate, susceptor assemblies have been proposed that include a first susceptor and a second susceptor made of different materials. The first susceptor material may be optimized with respect to heat loss and, thus, heating efficiency. In contrast, the second susceptor material may be used as a temperature marker. For this purpose, 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 magnetism of the second susceptor changes 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 reaches its Curie temperature and, thus, when the predefined operating temperature is 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 reducing their limitations. In particular, it would be desirable to have susceptor assemblies, aerosol generating articles, and aerosol generating device systems that have improved heating efficiency and improved temperature control capabilities. SUMMARY OF THE INVENTION

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

[0006] According to the present invention, it has been found that susceptor particles comprising a magnetic core with a high permeability and a conductive shell provide both an improvement in heating efficiency and an improvement in temperature control with self-regulating properties. To this extent, the magnetic core with a high permeability has been found to act as a magnetic flux concentrator that increases the magnetic flux through the particle shell. According to Faraday's law of induction, the 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, the high 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 thinner and, therefore, saves on materials and costs for the manufacture of the susceptor particles.

[0007] Furthermore, it has been found that a magnetic core may be used to control the amount generated within the particle shell as a function of the actual temperature of the susceptor assembly. This is due to the fact that the magnetism of the particle core changes from ferromagnetic or ferrimagnetic to paramagnetic at the Curie temperature of the core material. As a result, the overall effective permeability of the composite susceptor particles decreases to 1 when the susceptor assembly reaches the Curie temperature of the core material. This causes the cessation of heat generation in the particle core due to hysteresis loss as the magnetic hysteresis of the core material disappears. Even further, the change in permeability affects the heat generation in the particle shell because the decrease in permeability causes a decrease in the magnetic flux through the conductive shell. This results in a reduction of the induced electromotive force and, consequently, a reduction of the eddy current loss heat generation in the particle shell when the susceptor assembly reaches the Curie temperature of the core material. In addition, the skin thickness of the particle shell (which is a measure of how far electrical conduction occurs within the conductive shell material when exposed to an alternating magnetic field) depends on the overall effective permeability of the composite susceptor particles. Thus, the decrease in the overall effective permeability of the susceptor particles causes a decrease in the permeability of the particle core and leads to an increase in the skin thickness in the shell. This results in a decrease in the effective resistance of the conductive particle shell. As a result, when the Curie temperature of the core material is reached, the heat generation in the particle shell is reduced due to the decrease in the effective resistance, causing a reduction of the eddy current loss in the shell material. As a result, at the Curie temperature, the heat generation due to eddy current loss in the particle shell is reduced due to both the reduction of the magnetic flux through the particle shell and the reduction of the effective resistance of the shell material. In addition, the overall heat generation is reduced due to the disappearance of the hysteresis loss of the particle core at the Curie temperature of the core material. Most importantly, the reduction of the overall heat generation occurs by itself when the susceptor assembly reaches the Curie temperature of the core material. As a result, the rapid overheating of the aerosol-forming substrate can preferably be effectively avoided without the need for active temperature control.

[0008] Furthermore, the heating efficiency of the composite material susceptor particles according to the present invention is higher than that of susceptor particles consisting only of a ferromagnetic or ferrimagnetic core material. This is due to the shell material, where most of the heat is generated 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 by eddy currents. Similarly, the shell material may be ferromagnetic or ferrimagnetic. As a result, heat may also be generated by hysteresis losses within the shell material. Advantageously, this increases the heating efficiency of the susceptor assembly. Preferably, when magnetic, the Curie temperature of the shell material is preferably below 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 a 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 for enabling sintering at low temperatures, which may result in facilitating the manufacture of the composite material susceptor particles, as described in more detail below.

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

[0012] As described above, the Curie temperature of the core material preferably corresponds to a predefined operating temperature of the susceptor assembly. The actual operating temperature depends on the specific type of aerosol-forming substrate 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. For gel-like aerosol-forming substrates, the operating temperature may be in the range of 160 degrees Celsius to 240 degrees Celsius. As a result, the core material may have 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.

[0013] The heating efficiency of the susceptor assembly increases with a higher value of relative permeability. Thus, the core material may even have a relative permeability higher than 200. As a result, the core material may have a relative permeability of at least 300, or at least 400, or at least 500, or at least 700, specifically at least 1000, preferably at least 10000, or at least 50000, or at least 80000. These values refer to the maximum value of the relative permeability at a frequency of 10 kHz (kilohertz) (specifically, for a frequency up to 10 kHz (kilohertz)) and a temperature of 25 degrees Celsius. As further described below, the alternating magnetic field used for inductive heating of the susceptor assembly 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). 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, 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, 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 may be, ferrite, specifically ferrite powder. As used herein, ferrite is a ceramic material made by mixing and firing a large proportion of iron(III) oxide (Fe2O3) with one or more additional metal elements such as a small proportion of barium, manganese, nickel, and zinc.

[0015] As an 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 may contain, or may consist of, a composition of the Mg x Mn y Fe z O4 type, where x = 0.4 to 1.1, y = 0.3 to 0.9, z = 1 to 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 0.77 Mn 0.58 Fe 1.65 O4 having a Curie temperature of about 270 degrees Celsius, - Mg 0.55 Mn 0.88 Fe 1.55 O4 having a Curie temperature of about 262 degrees Celsius, - Mg 1.03 Mn 0.35 Fe 1.37 O4 having a Curie temperature of about 190 degrees Celsius, and may contain, or may consist of, the same.

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

[0019] Cobalt zinc barium ferrite as described above has Co with a Curie temperature of about 279 degrees Celsius 1.75 Zn 0.25 Ba2Fe 12 O 22 and may contain or consist of it.

[0020] Advantageously, the ferrite is easy and inexpensive to manufacture. In addition, the ferrite is non-conductive. As a result, the heat generation in the core material is due only to hysteresis loss and is therefore self-regulating when the Curie temperature is reached. Furthermore, the ferrite is inert and is therefore not of great importance for use in aerosol-generating articles containing an aerosol-forming substrate.

[0021] The particle core is preferably a solid particle core. Specifically, 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, more specifically 35 micrometers to 75 micrometers, for example 55 micrometers. The equivalent spherical diameter is used in combination with particles of irregular shape and is defined as the diameter of a sphere of equivalent volume. The particle size may depend, inter alia, on the aerosol-forming substrate to be heated. Additionally, for safety reasons, the particle size should be large enough so that the susceptor particles do not pass through the filter of the aerosol-generating article in which the susceptor particles may be used. As a result, 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 core may 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, for example 35 micrometers. The equivalent particle diameter may be mainly given by the equivalent spherical core diameter. An equivalent spherical core diameter in the range of 30 micrometers to 55 micrometers is particularly appropriate since such particles are small enough to be hardly visible within the substrate but still large enough not to pass through the filter of the aerosol-generating article 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 enables material and cost savings for the production of susceptor particles. The particle shell may have a shell thickness in the range of 2.5 micrometers to 15 micrometers, specifically 5 micrometers to 12 micrometers, for example, a shell thickness of 10 micrometers. The shell thickness may depend, inter alia, on the material of the particle shell, in particular the induction heating rate and material-specific requirements for the production of the shell. For example, the shell thickness may be 10 micrometers for aluminum, while the shell thickness may be lower than 10 micrometers for steel. Larger values of the shell thickness are particularly suitable for particle shells having a porous or sintered structure.

[0025] The above values may refer to the average core diameter, average shell thickness, and average particle diameter of all susceptor particles of the susceptor assembly. As a result, 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 of the susceptor assembly.

[0026] The particle shell preferably physically contacts the particle core. This enables good heat exchange between the particle shell and the particle core so that the particle shell and the particle core reach 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 melting point. Advantageously, sintering enables the production of particle cores having almost any shape and dimension. Sintering also results in susceptor particles having good strength characteristics. In addition, the sintered particle core facilitates good bonding between the particle shell and the particle core.

[0028] As a result, it is preferable that the particle shell is firmly bonded to the particle core. That is, there may be a bond between substances between the particle shell and the particle core. A firm bond provides good mechanical stability and good heat exchange between the particle shell and the particle core.

[0029] Specifically, the shell material may be plated, deposited, coated, or clad on the particle core, such as to form the particle shell.

[0030] The susceptor assembly according to the present invention is preferably configured to be driven particularly by a high-frequency alternating magnetic field. As mentioned herein, the high-frequency magnetic field 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).

[0031] The susceptor particles may comprise a cover, particularly a protective cover. The cover may be formed of glass, ceramic, or an inert metal and may be formed or coated respectively on the outside of at least a part of the susceptor particles. Advantageously, the cover is configured for at least one of avoiding the aerosol-forming substrate from sticking to the surface of the susceptor assembly or vice versa, increasing the adhesion of the aerosol-forming substrate, specifically a liquid aerosol-forming substrate, to the susceptor assembly, specifically storing a flavoring substance or a liquid aerosol-forming substrate, providing a flavoring substance or an aerosolization-enhancing cover, avoiding the diffusion of substances, such as metal diffusion, from the susceptor material to the aerosol-forming substrate, or improving the mechanical strength of the susceptor particles. To provide a flavoring substance or an aerosolization-enhancing cover, the cover may contain 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 having the ability to convert electromagnetic energy into heat when subjected to an alternating magnetic field. This may be the result of at least one of a susceptor, hysteresis losses induced within the particle, or eddy currents, depending on the electrical and magnetic properties of the material contained within the susceptor particle. Hysteresis losses occur in ferromagnetic or ferrimagnetic susceptor materials due to magnetic domains within the material that are switched under the influence of an alternating electromagnetic field. Eddy currents may be induced if the susceptor material is conductive. In the case of a conductive ferromagnetic or ferrimagnetic susceptor material, heat can be generated due to both eddy currents and hysteresis losses.

[0033] According to another aspect of the invention, there is provided an aerosol generating article for use with an induction heating aerosol generator. The article comprises at least one aerosol forming substrate and at least one susceptor assembly according to the invention and as described herein. 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 evenly, i.e., uniformly, dispersed throughout the aerosol forming substrate. Also, the susceptor particles may be dispersed throughout the aerosol forming substrate having local concentration peaks or according to a concentration gradient, for example, a dispersion gradient from the central axis of the aerosol generating 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 releases a volatile compound capable of forming an aerosol when heated. The aerosol-generating article is preferably a heated aerosol-generating article. That is, it is 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, particularly a consumable that is discarded after single use. For example, the article may be a cartridge containing a gel-like aerosol-forming substrate that is heated. Alternatively, the article may be a rod-shaped article (particularly a tobacco article) similar to a conventional cigarette.

[0036] As used herein, the term "aerosol-forming substrate" means a substrate formed from, or comprising, 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 an aerosol-forming volatile compound. The aerosol-forming substrate may be a solid aerosol-forming substrate or a liquid aerosol-forming substrate or a gel-like aerosol-forming substrate, or any combination thereof. That is, the aerosol-forming substrate may comprise, for example, both a solid component and a liquid component. The aerosol-forming substrate may comprise a tobacco-containing material containing a volatile tobacco flavor compound 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 also contain other additives and ingredients (such as nicotine or flavorants). The aerosol-forming substrate may also be a paste-like material, a sachet of a porous material containing the aerosol-forming substrate, or, for example, loose tobacco mixed with a gelling agent or adhesive, which may contain a common aerosol former such as glycerin and which is compressed or shaped into a plug.

[0037] As an example, the aerosol-generating article may comprise the following elements, namely a base element, a support element, a cooling element, and a filter element. All of the aforementioned elements may be sequentially arranged along the length axis of the article in the order described above, the base 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 base element is located downstream of the support element with respect to the airflow passing through the article during use of the system. Each of the aforementioned elements may be substantially cylindrical. Specifically, all of the elements may have the same outer cross-sectional shape. In addition, the elements may be surrounded by an outer wrapper so as to hold the elements together and to maintain the desired cross-sectional shape of the rod-shaped article. The wrapper is preferably made of paper.

[0038] The base element preferably includes at least one aerosol-forming substrate to be heated and a susceptor assembly, namely one or more susceptor particles embedded in the aerosol-forming substrate.

[0039] The support element may comprise a hollow cellulose acetate tube having a central air passage with nothing in it.

[0040] The aerosol cooling element may be an element having a large surface area and a low draw resistance (e.g., 15 mmWG (millimeter water column gauge pressure) to 20 mmWG (millimeter water column gauge pressure)). During use, the aerosol formed by the volatile compounds released from the base 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 part of the article through which the aerosol passes and exits the aerosol-generating article.

[0042] According to another embodiment, the aerosol generating article may comprise the following elements, namely a distal support element, a base element, a proximal support element, a cooling element, and a filter element. All of the aforementioned elements may be sequentially arranged along the length axis of the article in the order described above, with the distal support element being arranged at the distal end of the article and the filter element being arranged at the proximal end of the article. That is, the base element is located between the proximal support element and the distal support element. Specifically, the base element is located downstream of the proximal support element and upstream of the distal support element with respect to the air flow passing through the article during use. Each of the aforementioned elements may be substantially cylindrical. Specifically, all of the elements may have the same outer cross-sectional shape. In addition, the elements may be surrounded by an outer wrapper so as 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 base element, the cooling element, and the filter element may correspond to their respective elements according to the aforementioned embodiments.

[0044] The distal support element and the proximal support element may comprise a hollow cellulose acetate tube having a central air passage that is empty. Alternatively, the distal support element may comprise a cellulose acetate plug (having no central air passage that is empty). The cellulose acetate plug may be used to cover and protect the distal front end of the base element.

[0045] Further 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 equally applicable thereto.

[0046] According to another aspect of the present invention, there is provided an induction heating aerosol generating device for use with an apparatus, 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 "induction heating aerosol generator" is used to describe an electrically-operated device having the ability to interact with at least one aerosol-generating article containing at least one aerosol-forming liquid so as to generate an aerosol by induction heating the susceptor assembly and hence the aerosol-forming substrate within the article. The aerosol generator is preferably a smoking device for generating an aerosol that can be directly inhaled by a user through the user's mouth. In particular, the aerosol generator is a hand-held aerosol generator.

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

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

[0050] 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 to surround the susceptor assembly, i.e., one or more susceptor particles, when the article is received within the receiving cavity.

[0051] 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 robust and inexpensive compact design. 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" generally means a planar coil in which the axis of the coil winding is perpendicular to the surface on which the coil is placed. The flat spiral induction coil can have any desired shape within the plane of the coil. For example, the flat spiral coil may have a circular shape, or generally an elliptical or rectangular shape. However, as used herein, the term "flat spiral coil" encompasses not only planar coils but also flat spiral coils shaped to conform to a curved surface. For example, the induction coil may preferably be a "curved" planar coil disposed around a cylindrical coil support (e.g., a ferrite core). Further, 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. At least one induction coil may be held within one of the main body or housing of the aerosol generator.

[0052] The induction source may comprise an alternating current (AC) generator. The AC generator may be powered by the power supply of the aerosol generator. The AC generator is operably connected to at least one induction coil. Specifically, 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 at least one induction coil to generate an alternating magnetic field. The AC current may be continuously supplied to at least one induction coil after startup of the system, or intermittently (such as for each puff).

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

[0054] The induction source is preferably configured to generate a high-frequency magnetic field. As mentioned in this specification, the high-frequency magnetic field 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 generator may further comprise a controller configured to control the operation of the heating process, preferably in a closed-loop configuration, specifically for controlling the heating of the aerosol-forming liquid to a predetermined operating temperature. The operating temperature used for heating the aerosol-forming substrate may be in the range of 200 degrees Celsius to 360 degrees Celsius, specifically 160 degrees Celsius to 240 degrees Celsius. These temperatures are typical operating temperatures for heating the aerosol-forming substrate without combustion.

[0056] The controller may be the overall controller of the aerosol generator or in the technical field of the overall controller of the aerosol generator. 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 having the ability to provide control. The controller may further comprise additional electronic components such as at least one DC / AC inverter and / or a power amplifier (e.g., class C power amplifier, or class D power amplifier, or class E power amplifier). Specifically, the induction source may be part of the controller.

[0057] The aerosol generating device may comprise a power source, specifically a DC power source configured to provide a DC supply voltage and a DC supply current to an 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 sufficient energy storage for one or more user experiences. For example, the power source may have a capacity sufficient to allow for 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 puffings, or 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 an alternating magnetic field of at least one induction source towards the receiving cavity. Therefore, when an article is received within the receiving cavity, the alternating magnetic field, if present, is distorted towards the inductively heatable liquid conduit. The flux concentrator preferably comprises a flux concentrator foil, particularly a multi-layer flux concentrator foil.

[0059] Further features and advantages of the aerosol generation 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.

[0060] According to the present invention, there is also provided a method of manufacturing a susceptor assembly comprising one or more composite material susceptor particles for inductively heating an aerosol forming substrate, each of the one or more susceptor particles comprising a particle core and a particle shell completely encapsulating the particle core. The method comprises - providing one or more particle cores comprising or made from a ferromagnetic or ferrimagnetic core material, and - completely wrapping 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 core may be a sintered particle core. As a result, providing one or more particle cores - forming one or more green bodies having a shape corresponding to the shape of the particle core from a ferromagnetic or ferrimagnetic core material, - 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 core so as to form a particle shell. As a result, completely wrapping each of the one or more particle cores with a 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 deposited, applied with a roller in a slurry state, or applied onto the particle core in a flat fluid bath, and the slurry and the flat fluid bath contain the shell material to be applied.

[0063] Further 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 are equally applicable.

[0064] The present invention is defined in the claims. However, a non-exhaustive list of non-limiting examples is provided below. Any one or more of the features of these examples may be combined with any one or more of the features of another 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 material 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 being made of a ferromagnetic or ferrimagnetic core material having a relative permeability of at least 200 at a temperature of 20 degrees Celsius and a frequency of 10 kHz (kilohertz), specifically up to a frequency of 10 kHz (kilohertz), and the particle shell comprising or being 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 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 spherical 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, for example, 55 micrometers.

[0074] Example Ex10: A susceptor assembly according to any one of the preceding examples, wherein the particle core has 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, for example, 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 core is a sintered particle core, and 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 shell is in physical contact with the particle core.

[0078] Example Ex14: A susceptor assembly according to any one of the preceding examples, wherein the particle shell is firmly bonded to the particle core.

[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 so as to form a particle shell.

[0080] Example Ex16: An aerosol generating article for use with an induction heating aerosol generator, 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, specifically dispersed throughout the aerosol-forming substrate, for example, homogeneously dispersed, or dispersed with local concentration peaks, or specifically dispersed with a dispersion gradient from the central axis to the periphery of the aerosol generating article.

[0081] Example Ex17: An aerosol generating system comprising an aerosol generating article according to any one of the preceding examples and an induction heating aerosol generator for use with the device.

[0082] Example Ex18: A method of manufacturing a susceptor assembly for inductively heating an aerosol-forming substrate, the susceptor assembly comprising one or more composite material susceptor particles for inductively heating the aerosol-forming substrate, each of the one or more susceptor particles comprising a particle core and a particle shell completely encapsulating the particle core. providing one or more particle cores comprising or made from a ferromagnetic or ferrimagnetic core material; completely encapsulating 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 core; A method according to Example Ex18, comprising sintering one or more green bodies by heating the one or more green bodies.

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

[0085] Example Ex21: A method according to any one of Examples Ex18 to Ex20, wherein completely wrapping each of the one or more particle cores with a conductive shell material is by vapor deposition, coating with a roller in a slurry state, or applying the shell material onto the particle cores in a flat fluid bath, the slurry and the flat fluid bath containing the shell material to be applied.

[0086] Here, the examples will be further described with reference to the drawings.

Brief Description of the Drawings

[0087]

Figure 1

Figure 2

Figure 3

Figure 4

[0088] Figure 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 a coaxial alignment, namely, 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, and all of them have substantially the same diameter. In addition, the four elements are surrounded by an outer wrapper 170 so as 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] Regarding 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 Figure 1, the susceptor assembly 120 comprises a plurality of susceptor particles 123 evenly dispersed throughout the aerosol-forming substrate 130. Due to their particulate nature, the susceptor 123 presents 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 more detail below with respect to Figure 3.

[0090] As illustrated in FIG. 2, the aerosol generating article 100 is configured to be used with an induction heating aerosol generating device 10. The device 10 and the article 100 together form an aerosol generating system 1 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 the present embodiment, the induction coil 30 is a helical coil that circumferentially surrounds the cylindrical receiving cavity 20. The coil 30 is arranged such that the susceptor assembly 120 of the aerosol generating article 100 experiences an alternating magnetic field as the article 100 engages with the device 10. Therefore, when the induction source is activated, the susceptor assembly 120 is heated due to induction heating. As will be described in more detail below with respect to FIG. 3, the susceptor assembly 120 is heated until it reaches 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 includes a DC power supply 40 and a controller 50 (only schematically illustrated in FIG. 2) for supplying power and controlling the heating process. Separate 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] Figure 3 shows a detailed cross-sectional view of one of the susceptor particles 123 used within the aerosol-generating article shown in Figure 1. According to the present 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 permeability of at least 200 with respect to a frequency of 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, i.e., 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 is heated due to eddy currents, while the particle core 121 is heated due to hysteresis losses.

[0092] According to the present invention, the magnetic core has another important function: due to its high permeability, the particle 121 acts as a magnetic flux concentrator that increases the magnetic flux passing through the particle shell 122. According to Faraday's law of induction, the increase in magnetic flux causes an increase in eddy current losses within the particle shell 122. Thus, the high permeability of the magnetic particle core 121 increases the amount of heat generated within the particle shell during use. Advantageously, this also makes it possible to make the particle shell rather thinner and, therefore, to save on materials and costs for the manufacture of the susceptor particles.

[0093] When the temperature of the core material almost reaches the Curie temperature, the magnetism of the particle core 121 changes from ferromagnetic to paramagnetic. As a result, the overall effective magnetic permeability of the magnetic particle core 121 decreases to 1. This causes the heat generation in the particle core 121 to stop because the magnetic hysteresis of the core material disappears. Furthermore, the change in magnetic permeability also affects the heat generation in the particle shell 122 because the decrease in the magnetic permeability of the magnetic particle core 121 causes a decrease in the magnetic flux passing through the conductive particle shell 122. This results in a reduction in the electromotive force and, consequently, a reduction in the eddy current loss heat generation in the particle shell 122 when the susceptor assembly reaches the Curie temperature of the core material.

[0094] In addition, the change in magnetic permeability also affects the heat generation in the particle shell 122 because the decrease in magnetic permeability causes an increase in the skin depth in the particle shell 122 as further described above. This results in a decrease in the effective resistance of the aluminum particle shell 122. Therefore, when the Curie temperature of the core material is reached, a decrease in the effective resistance also occurs and the heat generation in the particle shell 122 is reduced, resulting in a reduction in the eddy current loss in the shell material.

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

[0096] The specific core material is preferably selected so as to have a Curie temperature around the predefined operating temperature of the susceptor assembly 120 where the aerosol-forming substrate 130 is heated. For a solid aerosol-forming substrate 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 FIG. 3, the susceptor particles 123 substantially have a ball shape. The particle diameter 124 may be in the range of 50 micrometers to 75 micrometers. In this embodiment, the average particle diameter of all the susceptor particles 123 is about 55 micrometers, which results from a particle core 121 having a core diameter 125 of about 35 micrometers and a particle shell 122 having a shell thickness 126 of about 10 micrometers.

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

[0099] FIG. 4 shows a second embodiment of the aerosol generating article 200 according to the present invention. Generally, the aerosol generating article 200 according to FIG. 4 is very similar to the aerosol generating articles 100 shown in FIGS. 1 and 2. Therefore, the same or similar features are denoted by the same reference numerals, with 100 added. In contrast to the first embodiment shown in FIG. 1, the article 400 according to FIG. 4 has a particle distribution of susceptor particles 223 having a dispersion profile with a maximum local concentration along the central axis 207 of the article 200, specifically from the central axis 207 of the aerosol generating article 200 to its periphery, because the aerosol forming substrate 230 is mainly heated at the central portion of the rod segment 210.

[0100] For the purposes of this specification and the appended claims, unless otherwise indicated, all numbers expressing amounts, quantities, percentages, etc. are to be understood as being modified in all instances by the term "about." Also, all ranges include the disclosed maximum and minimum points, and any intermediate ranges therebetween, whether or not specifically enumerated herein. Thus, in this context, number A is understood as A ± 5 percent of A. Within this context, number A may be considered to include numerical values within the general standard error of the measurement of the property that number A modifies. In some instances, as used in the appended claims, number A may deviate by the percentages recited above, provided that the amount by which A deviates does not substantially affect the basic and novel characteristic(s) of the claimed invention. Also, all ranges include the disclosed maximum and minimum points, and any intermediate ranges therebetween, whether or not specifically enumerated herein.

Claims

1. A susceptor assembly for inductively heating an aerosol-forming substrate under the influence of an alternating magnetic field, said susceptor assembly comprising one or more composite material susceptor particles, each of said one or more susceptor particles comprising a particle core and a particle shell completely encapsulating said particle core, said particle core comprising or being made of a ferromagnetic or ferrimagnetic core material having a relative permeability of at least 200 at a temperature of 20 degrees Celsius with respect to a frequency of up to 10 kHz, and said particle shell comprising or being made of a conductive shell material.

2. The susceptor assembly according to claim 1, wherein said shell material is paramagnetic.

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

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

5. The susceptor assembly according to any one of claims 1 to 4, wherein said core material has a Curie temperature in the range of 160 degrees Celsius to 400 degrees Celsius.

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

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

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

9. The susceptor assembly according to any one of claims 1 to 8, wherein each of said one or more susceptor particles has an equivalent spherical particle diameter in the range of 10 micrometers to 500 micrometers.

10. The susceptor assembly according to any one of claims 1 to 9, wherein said particle core has an equivalent spherical core diameter in the range of 5 micrometers to 499 micrometers.

11. The susceptor assembly according to any one of claims 1 to 10, wherein said particle shell has a shell thickness in the range of 1 micrometer to 100 micrometers.

12. The susceptor assembly according to any one of claims 1 to 11, wherein said particle core is a sintered particle core.

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

14. An aerosol generating article for use with an induction heating aerosol generator, 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.

15. An aerosol generating system comprising an aerosol generating article according to any one of claims 1 to 14 and an induction heating aerosol generator for use with the aerosol generating article.

Images