SUSCEPTOR ASSEMBLY COMPRISING ONE OR MORE COMPOSITE SUSCEPTOR PARTICLES

Abstract

A susceptor assembly is provided for inductively heating an aerosol-forming substrate under an influence of an alternating magnetic field, the susceptor assembly including: one or more composite susceptor particles, each one of the one or more composite susceptor particles including a particle core and a particle shell entirely encapsulating the particle core, in which the particle core includes or is made of a ferromagnetic or ferrimagnetic core material having a relative magnetic permeability of at least 200 for frequencies up to 10 kHz at a temperature of 20 degrees Celsius, and in which the particle shell includes or is made of an electrically conductive shell material. An aerosol-generating article for an inductively heating aerosol-generating device, and an aerosol-generating system including an aerosol-generating article, are also provided.

Claims

1.-15. (canceled)

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

17. The susceptor assembly according to claim 16, wherein a material of the particle shell is paramagnetic.

18. The susceptor assembly according to claim 16, wherein a material of the particle shell is one of aluminum, stainless steel, electrically conductive carbon, or bronze.

19. The susceptor assembly according to claim 16, wherein a material of the core is electrically non-conductive.

20. The susceptor assembly according to claim 16, wherein a material of the core has a Curie temperature in a range between 160 degrees Celsius and 400 degrees Celsius.

21. The susceptor assembly according to claim 16, wherein a material of the core has a Curie temperature in a range between 160 degrees Celsius and 240 degrees Celsius.

22. The susceptor assembly according to claim 16, wherein a material of the core is a ferrite powder.

23. The susceptor assembly according to claim 16, wherein a material of the core is of a manganese-magnesium ferrite, a nickel-zinc ferrite, or a cobalt-zinc barium ferrite.

24. The susceptor assembly according to claim 16, wherein each one of the one or more composite susceptor particles substantially has a ball shape.

25. The susceptor assembly according to claim 16, wherein each one of the one or more composite susceptor particles has an equivalent spherical particle diameter in a range between 10 micrometers and 500 micrometers.

26. The susceptor assembly according to claim 16, wherein each one of the one or more composite susceptor particles has an equivalent spherical particle diameter in a range between 35 micrometers and 75 micrometers.

27. The susceptor assembly according to claim 16, wherein the particle core has an equivalent spherical core diameter in a range between 5 micrometers and 499 micrometers.

28. The susceptor assembly according to claim 16, wherein the particle core has an equivalent spherical core diameter in a range between 30 micrometers and 55 micrometers.

29. The susceptor assembly according to claim 16, wherein the particle shell has a shell thickness in a range between 1 micrometer and 100 micrometers.

30. The susceptor assembly according to claim 16, wherein the particle shell has a shell thickness in a range between 5 micrometers and 12 micrometers.

31. The susceptor assembly according to claim 16, wherein the particle core is a sintered particle core, and wherein a material of the particle core is a sintered material.

32. The susceptor assembly according to claim 16, wherein a material of the particle shell is plated, deposited, coated, or cladded onto the particle core such as to form the particle shell.

33. An aerosol-generating article for an inductively heating aerosol-generating device, the aerosol-generating article comprising: at least one aerosol-forming substrate and a susceptor assembly according to claim 16, wherein the one or more susceptor particles of the susceptor assembly are embedded in the aerosol-forming substrate.

34. The aerosol-generating article according to claim 33, wherein the one or more susceptor particles of the susceptor assembly are distributed throughout the aerosol-forming substrate with a distribution gradient from a central axis of the aerosol-forming article to a periphery thereof.

35. An aerosol-generating system comprising an aerosol-generating article according to claim 16 and an inductively heating aerosol-generating device for the inductively heating aerosol-generating device.

Description

[0096] Examples will now be further described with reference to the figures in which:

[0097] FIG. 1 schematically illustrates an inductively heatable aerosol-generating article according to a first exemplary embodiment of the present invention comprising a susceptor assembly;

[0098] FIG. 2 schematically illustrates an exemplary embodiment of an aerosol-generating system comprising an aerosol-generating device and the aerosol-generating article according to FIG. 1;

[0099] FIG. 3 shows one susceptor particle of the susceptor assembly included in the aerosol-generating article according to FIG. 1; and

[0100] FIG. 4 schematically illustrates an inductively heatable aerosol-generating article according to a second exemplary embodiment of the present invention.

[0101] 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 substantially has a rod-shape and comprises four elements which are 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 which serves as a mouthpiece. The aerosol-forming rod segment 110 is arranged at a distal end 102 of the article 100, whereas the filter element 160 is arranged at a distal end 103 of the article 100. Each of these four elements is a substantially cylindrical element, all of them having substantially the same diameter. In addition, the four elements are circumscribed by an outer wrapper 170 such as to keep the four elements together and to maintain the desired circular cross-sectional shape of the rod-like article 100. The wrapper 170 preferably is made of paper.

[0102] As regard the present invention, the aerosol-forming rod segment 110 comprises an aerosol-forming substrate 130 as well as a susceptor assembly 120 for heating the substrate 130 when being exposed to an alternating magnetic field. As can be seen in FIG. 1, the susceptor assembly 120 comprises a plurality of susceptor particles 123 which are equally distributed throughout the aerosol-forming substrate 130. Due to their particulate nature, the susceptor particles 123 present a large surface area to the surrounding aerosol-forming substrate 130 which advantageously enhances heat transfer. Details of the susceptor particles 123 will be described in more detail 123 further below with regard to FIG. 3

[0103] As illustrated in FIG. 2, the aerosol-generating article 100 is configured for use with an inductively heating aerosol-generating device 10. Together, the device 10 and the article 100 form an aerosol-generating system 1 according to the present invention. The aerosol-generating device 10 comprises a cylindrical receiving cavity 20 defined within a proximal portion 12 of the device 10 for receiving a least a distal portion of the article 100 therein. The device 10 further comprises an induction source including an induction coil 30 for generating an alternating high-frequency magnetic field. In the present embodiment, the induction coil 30 is a helical coil circumferentially surrounding the cylindrical receiving cavity 20. The coil 30 is arranged such that the susceptor assembly 120 of the aerosol-generating article 100 experiences the alternating magnetic field upon engaging the article 100 with the device 10. Thus, when activating the induction source, the susceptor assembly 120 heats up due induction heating. As will be described in more detail 123 further below with regard to FIG. 3, the susceptor assembly 120 is heated until reaching an operating temperature sufficient to vaporize the aerosol-forming substrate 130 in the aerosol-forming rod segment 110. Within a distal portion 13, the aerosol-generating device 10 further comprises a DC power supply 40 and a controller 50 (illustrated in FIG. 2 schematically only) for powering and controlling the heating process. Apart from the induction coil 30, the induction source preferably is at least partially integral part of the controller 50 of the device 10.

[0104] FIG. 3 shows a detailed cross-sectional view through one of the susceptor particles 123 of used within the aerosol-generating article shown in FIG. 1. According to the invention, each one of the susceptor particles 123 comprises a particle core 121 and a particle shell 122 entirely encapsulating the particle core 121. The particle core 121 comprises or is made of a ferromagnetic or ferrimagnetic core material having a relative magnetic permeability of at least 200 for frequencies up to 10 kHz (kilo-Hertz) at a temperature of 20 degree Celsius. In the present embodiment, the particle core 121 is made of a nickel-zinc ferrite, that is, of an electrically non-conductive ferrimagnetic material. In contrast, the particle shell 122 is made of an electrically conductive shell material. In the present embodiment, the particle shell 122 is made of aluminium, which is paramagnetic. Hence, in general, when exposed to the alternating magnetic field of the induction coil 32, the particle shell 122 heats up due to eddy currents, whereas the particle core 121 heats up due to hysteresis losses.

[0105] According to the present invention, the magnetic core has another important function: Due its high magnetic permeability, the particle 121 acts as a flux concentrator which increases the magnetic flux through the particle shell 122. According to Faraday's law of induction, an increase of the magnetic flux causes an increase of eddy current losses in the particle shell 122. Hence, the high magnetic permeability of the magnetic particle core 121 increases the amount of heat generated in particle shell during use. Advantageously, this also allows to make the particle shell rather thin, and thus to save material and costs for the manufacturing of the susceptor particles.

[0106] When reaching about the Curie temperature of the core material, the magnetic properties of the particle core 121 change from ferrimagnetic to paramagnetic. As a consequence, the overall effective magnetic permeability of the magnetic particle core 121 drops to unity. This causes the heat generation in the particle core 121 to stop as the magnetic hysteresis of the core material disappears. Even more, the change in the magnetic permeability also affects the heat generation in the particle shell 122 as the decrease of the magnetic permeability of the magnetic particle core 121 causes a decrease of the magnetic flux through the electrically conductive particle shell 122. This in turn leads to a reduction of the electromotive force and thus to a reduction of heat generating eddy current losses in the particle shell 122, when the susceptor assembly reaches the Curie temperature of the core material.

[0107] In addition, the change in the magnetic permeability affects the heat generation in the particle shell 122 also because the decrease of the magnetic permeability causes an increase of the skin depth in the particle shell 122 as described further above. This in turn causes the effective resistance of the aluminum particle shell 122 to decrease. Hence, when reaching the Curie temperature of the core material, heat generation in the particle shell 122 is also reduced since the decrease of the effective resistance also causes a reduction of eddy current losses in the shell material.

[0108] Accordingly, at the Curie temperature, the heat generation by eddy current losses in the particle shell 122 is reduced due to both, a reduction of the magnetic flux through the particle shell and a reduction of the effective resistance of the shell material. In addition, the overall heat generation is reduced due to the hysteresis losses in the particle core 121 disappearing at the Curie temperature of the core material. In particular, the reduction of the overall heat generation results by itself, so that rapid overheating of the as aerosol-forming substrate can be effectively avoided, preferably without the need for an active temperature control.

[0109] Preferably, the specific core material is chosen such as to have a Curie temperature at about a predefined operating temperature of the susceptor assembly 120 at which the aerosol-forming substrate 130 is to be heated. For solid aerosol forming substrates containing tobacco material, the operating temperature may be in a range between 200 degree Celsius and 360 degree Celsius.

[0110] As be further seen in FIG. 3, the susceptor particle 123 substantially has a ball shape. The particle diameter 124 may be in a range between 50 micrometer and 75 micrometer. In the present embodiment, the mean particle diameter of all susceptor particles 123 is about 555 micrometer which results from the particle core 121 having a core diameter 125 of about 35 micrometer, and the particle shell 122 having a shell thickness 126 of about 10 micrometer.

[0111] The particle core may be manufactured may sintering a green body of the ferromagnetic or ferrimagnetic core material, and subsequently applying the shell material onto the particle core 121, for example, by vapor deposition such as to provide a particle shell 122 that is firmly bonded to the particle core 121.

[0112] FIG. 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 FIG. 4 is very similar to the aerosol-generating article 100 shown in FIG. 1 and FIG. 2. Therefore, identical or similar features are denoted with the same reference signs, yet incremented by 100. In contrast to the first embodiment shown in FIG. 1, the article 400 according to FIG. 4 has a particle distribution of the susceptor particles 223 with a distribution gradient from a central axis 207 of the aerosol-forming article 200 to the periphery thereof, in particular with a local concentration maximum along the center axis 207 of the article 200, in order to have the aerosol-forming substrate 230 mainly heated in a center portion of rod segment 210.

[0113] For the purpose of the present description and of the appended claims, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term “about”. Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein. In this context, therefore, a number A is understood as A ±5 percent of A. Within this context, a number A may be considered to include numerical values that are within general standard error for the measurement of the property that the number A modifies. The number A, in some instances as used in the appended claims, may deviate by the percentages enumerated above provided that the amount by which A deviates does not materially affect the basic and novel characteristic(s) of the claimed invention. Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein.