EP4364595A1

EP4364595A1 - Aerosol generating devices and induction heating assemblies therefor

Info

Publication number: EP4364595A1
Application number: EP23207489.8A
Authority: EP
Inventors: Tilen CEGLAR; Jaakko MCEVOY
Original assignee: JT International SA
Current assignee: JT International SA
Priority date: 2022-11-02
Filing date: 2023-11-02
Publication date: 2024-05-08

Abstract

An aerosol generating system (16) comprising: an aerosol generation device (18) comprising a region arranged for receiving a consumable comprising an aerosol-forming substance (20), an induction heating assembly (14) comprising an induction coil (22) and a susceptor (60", 80, 110), said susceptor having a footprint (100), the induction heating assembly being configured to heat said aerosol-forming substance in the consumable to generate an aerosol that may be inhaled by a user, wherein the susceptor comprises at least one out of plane structure (64) that forms one or more airflow deflection features shaped to control an airflow path around said aerosol-forming substrate.

Description

Technical Field

The present invention relates generally to an aerosol generating system including an induction heating assembly, such as an induction coil. The invention relates particularly, but not exclusively, to susceptors for use in such a heating assembly.

Technical Background

Aerosol generating devices (also known as vaporisers) which heat, rather than burn or combust, an aerosol generating substrate to produce an aerosol for inhalation by a user of the device have become popular with consumers in recent years as an alternative to the use of traditional tobacco products.
Various devices and systems are available which can use one of a number of different approaches to provide heat to the aerosol generating substrate. One such approach is to provide an induction heating assembly. Such assemblies employ an electromagnetic field generator, such as an induction coil, to generate an alternating electromagnetic field that couples with, and inductively heats, a heat transfer component in the form of a susceptor heating element. Heat from the susceptor is transferred, for example by conduction, to the substrate and an aerosol is generated as the substrate is heated for inhalation by a user of the device. A susceptor may be included within an aerosol generating device, for example as a wall of a heating chamber within the device. Alternatively, or additionally, a susceptor may be included in a consumable for use in an aerosol generating device.
In such a system, efficient heat transfer through the susceptor to the aerosol generating substrate is important in order to ensure efficient heating of the aerosol generating substrate. Typically susceptors are provided as one or more thin strips of susceptor material, which can result in inefficient heating due to uneven heat distribution through a transversal cross-section of a usually cylindrical aerosol generating substrate. There is therefore a need to improve thermal efficiency within an induction heated aerosol generating system.

Summary

According to a first aspect of the invention, we provide an aerosol generating system comprising:

an aerosol generation device comprising a region arranged for receiving a consumable comprising an aerosol-forming substance,
an induction heating assembly comprising an induction coil and a susceptor, said susceptor having a footprint, the induction heating assembly being configured to heat said aerosol-forming substance in the consumable to generate an aerosol that may be inhaled by a user,
wherein the susceptor comprises at least one out of plane structure that forms one or more airflow deflection features shaped to control an airflow path around said aerosol-forming substrate.

Many susceptors used currently are relatively simple in geometry, being either a single strip of metal or multiple strips of metal - that is, being thin, such prior art susceptors are essentially two-dimensional surfaces. This leads to inefficiencies when heating a target aerosol generating material due to inefficient heat transfer from the susceptor to an aerosol-forming substance, which may not have a flat surface. In contrast, a susceptor as described above is a three-dimensional surface which includes one or more out of plane structures that are shaped to control an airflow path (e.g. to control a direction and/or speed of the airflow). Such features may improve the efficiency of heat transfer between the susceptor and the aerosol-forming substrate, for example, by increasing one or more of turbulence, mixing or recirculation in the airflow.
The susceptor may comprise a plurality of out of plane structures. For example, the susceptor may comprise a periodically repeating pattern of out of plane structures. The pattern may comprise a plurality of rows of out of plane structures. Such a pattern may disrupt air as it flows across the surface of the susceptor, so promoting mixing, turbulence and/or recirculation in the airflow, as compared with a flat susceptor. The out of plane structures in each row may be aligned with respect to a bulk airflow direction through the system (i.e. located one behind the other). Alternatively, the out of plane structures in a first row may be offset from the out of plane structures in a second row with respect to the bulk airflow direction through the system.
The at least one out of plane structure may comprise one or more recesses, protrusions, ridges, channels or corrugations. For example, the susceptor may comprise a periodically repeating pattern of protrusions. Such features may be particularly effective at controlling (e.g. disrupting) airflow so as to promote mixing.
The susceptor may further comprises a plurality of roughness enhancing microstructures. Such microstructures may further increase turbulence and mixing in the flow, which may improve the heat transfer further. The roughness enhancing microstructures may comprise micro-scale protrusions, which may for example have semi-circular or triangular cross sections. The micro-scale protrusions may be provided randomly, or may be provided in a regular pattern similar to that discussed above. The plurality of roughness enhancing microstructures may be located on the entire surface of the susceptor, or may be provided in selected locations. The plurality of roughness enhancing microstructures may be located on the out of plane structures, between the out of plane structures, or both. Using micro-scale structures in addition to macro-scale out of plane structures may permit better control of airflow through the system.
The induction coil may be operable to generate an alternating magnetic field having a region of high magnetic flux density and a region of low magnetic flux density. The susceptor may comprise at least one out of plane structure shaped to place a greater surface area and/or volume of the susceptor in the region of high magnetic flux as compared with a planar susceptor having the same footprint. The out of plane structure that is shaped to place greater surface area and/or volume of the susceptor in the region of high magnetic flux may additionally be shaped to control an airflow path around the susceptor. Such a susceptor may be shaped to increase electromagnetic coupling between the induction coil and the susceptor, as compared with a planar susceptor having the same footprint, for example by ensuring that more susceptor material is located in the region of high magnetic flux density as compared with a planar susceptor.
The induction coil may be a transverse coil, and the susceptor may be located adjacent the coil and shaped such that a normal distance between an out of plane structure at an edge region of the susceptor and the coil is less than or equal to a normal distance between a planar region of the susceptor and the coil. Such a susceptor preferably comprises a longitudinal axis, and at least one out of plane structure (and preferably two out of plane structures) may run parallel to the longitudinal axis at opposing edges of the susceptor such that the susceptor has a generally U-shaped cross section.
The aerosol generating system may further comprise the consumable, and the susceptor may be comprised in the consumable. For example, the consumable may comprise a solid aerosol-forming substance, and the susceptor may be positioned within the solid aerosol-forming substance.
The solid aerosol-forming substance may include a defined airflow path, and the susceptor may act as at least one wall of the defined airflow path. The defined airflow path may be generally aligned with a longitudinal axis of the consumable. At least one out of plane structure may protrudes into the defined airflow path, so as to influence the airflow within the defined airflow path.
The consumable may be generally planar in shape and may comprise a first generally planar body of aerosol-forming substance and a second generally planar body of aerosol-forming substance, with the susceptor being sandwiched between the first and second generally planar bodies of aerosol forming substance.
The solid aerosol-forming substance may include a plurality of defined airflow paths, a first group of which are formed in the first generally planar body of aerosol-forming substance and bounded on one wall by a first surface of the susceptor, and a second group of which are formed in the second generally planar body of aerosol-forming substance and bounded on one wall by a second surface of the susceptor. Each of the defined airflow paths may be generally aligned with the longitudinal axis of the consumable. The first group of defined airflow paths may be offset from the second group of airflow paths. At least one out of plane structure may protrude into one or more of the defined airflow paths, so as to influence the airflow within said defined airflow path(s).
The susceptor may comprise a lip at an edge, which is operable to fold around a side wall of the first generally planar body of aerosol-forming substance. The susceptor may comprise a second lip at an opposing edge which is operable to fold around a second side wall of the first generally planar body of aerosol-forming substance. Such a susceptor may have a generally U-shaped cross section.
The at least one out of plane structure may be embossed into the susceptor. The plurality of roughness enhancing microstructures may be embossed into the susceptor.
According to a second aspect of the invention, we provide an aerosol generating system comprising:

an aerosol generation unit comprising a region arranged for receiving a consumable comprising an aerosol-forming substance,
an induction heating assembly comprising an induction coil and a susceptor, said susceptor having a footprint, the induction heating assembly being configured to heat said aerosol-forming substance in the consumable to generate an aerosol that may be inhaled by a user,
wherein the induction coil is operable to generate an alternating magnetic field having a region of high magnetic flux density and a region of low magnetic flux density, and
wherein the susceptor comprises at least one out of plane structure that is shaped to place a greater surface area and/or volume of the susceptor in the region of high magnetic flux as compared with a planar susceptor having the same footprint.

As used herein, the term "footprint" means the shape and area resulting from a projection of susceptor onto a planar surface, when viewed in plan view. For example, the footprint produced by a circular planar disc will necessarily be a circle having the same area as the disc. However, other non-planar structures could produce that same footprint, such as a cone having the same diameter at its base (i.e. at its widest point) as the diameter of the disc. Put another way, the planar footprint is the area taken up by the susceptor when it is placed on a planar surface.
In some applications it can also be useful to consider the susceptor footprint in a cylindrical coordinate system. In that case, the radius (or largest in-plane dimension) of the susceptor can be used as a footprint. For example, an aerosol generating device having a helical induction coil is typically adapted to receive a generally cylindrical consumable within a heating chamber. The consumable may be rotated inside the device around its central axis in a manner that is substantially invariant between different consumables. The largest in-plane dimension of a susceptor included within the consumable defines the radius of a circle that is swept out by rotation of the consumable (and so the susceptor) within the device. This radial footprint can also be used as a reference for comparing susceptors in accordance with the disclosure herein with known susceptors.
The susceptors discussed herein are three dimensional bodies, having at least one out of plane structure, as opposed to being two dimensional surfaces. Many susceptors used currently are relatively simple in geometry, being either a single strip of metal or multiple strips of metal - that is, being thin, such prior art susceptors are essentially two dimensional surfaces. This leads to inefficiencies when heating a target aerosol generating material due to inefficient heat transfer from the susceptor to an aerosol-forming substance, which may not have a flat surface. Further inefficiencies also arise due to non-ideal coupling between the susceptor and the electromagnetic field generator (e.g. induction coil), which commonly has a circular cross section. Thus, by ensuring that a susceptor has a three dimensional shape that is complementary to a shape of the induction coil electromagnetic coupling between the induction coil and the susceptor may be improved, by ensuring that more of susceptor material is located in the region of high magnetic flux density as compared with a planar susceptor.
The susceptor may be shaped to increase electromagnetic coupling between the induction coil and the susceptor, as compared with a planar susceptor having the same footprint, for example by ensuring that more susceptor material is located in the region of high magnetic flux density as compared with a planar susceptor.
The susceptor may comprise a plurality of out of plane structures, for example one, two, three, four, or more out of plane structures. The at least one out of plane structure may comprise one or more recesses, protrusions, ridges, channels or corrugations. By use of a plurality of out of plane structures the shape of the susceptor may conveniently be tailored to the shape of the induction coil.
The susceptor may comprise a longitudinal axis, and the at least one out of plane structure may run the length of the longitudinal axis such that the susceptor comprises a constant axial cross section. The susceptor may have a generally S or U shaped cross section, or may be corrugated. A susceptor of such a structure places more susceptor material in the region of high magnetic flux density along the entire length of the susceptor, thus consistently improving electromagnetic coupling along the length of the susceptor, permitting even heating.
The induction coil may be a helical coil having a coil axis, and the susceptor may be located within the coil such that the coil axis lies in a plane defined by the susceptor footprint, wherein the at least one out of plane structure does not lie on a radius of the coil. The at least one out of plane structure may be an edge region of the susceptor that is curved or bent so as to form an angle of greater than 10 degrees with a radius of the coil, preferably greater than 20 degrees, and most preferably greater than 30 degrees, or 40 degrees, or 50 degrees, or 60 degrees, or 70 degrees, or 80 degrees. The at least one out of plane structure is preferably curved or bent so that an edge region of the susceptor is substantially perpendicular to a radius of the coil (i.e. parallel to a tangent to the coil). Such an arrangement ensures that an edge region of the susceptor is closer to the coil than it would be in a planar susceptor of the same footprint, so improving electromagnetic coupling to the coil.
The induction coil may be a transverse coil, and the susceptor may be located adjacent the coil. The susceptor may be shaped such that a normal distance between an out of plane structure at edge region of the susceptor and the coil is less than or equal to a normal distance between a planar region of the susceptor and the coil. Such an arrangement ensures that an edge region of the susceptor is closer to the coil than it would be in a planar susceptor of the same footprint, so improving electromagnetic coupling to the coil.
At least 20% of the susceptor may lie out of the plane defined by the susceptor footprint, preferably at least 40%, and most preferably at least 50%, or more. Where a greater volume of susceptor material lies out of plane, proportionately more susceptor material may be located in the region of high magnetic flux density, so improving electromagnetic coupling to the coil.
The at least one out of plane structure may be shaped to form one or more airflow deflection features. For example, the out of plane structure(s) may define one or more channels which deflect air or fluid within the device, so increasing the efficiency of the device.
The at least one out of plane structure may be embossed into the susceptor. Embossing typically refers to a continuous process whereby a starting material is continuously fed between two rollers, which may be heated and/or pressurised, in order to produce deformations in the surface of the sheet material.
Embossing can quickly and cheaply produce a large deformation on one or both sides of a sheet, with local elongation of the sheet under pressure from an embossing tool. Typically embossed features may have a minimum dimension of 0.1 mm or greater, for example between 0.5-10 mm. Embossing can thus be used to produce a susceptor having a relatively complex geometry, and may be used to shape a planar starting material to form an embossed material having a three dimensional shape. In such a manner a three dimensional susceptors may be produced from a planar starting material.
The starting material comprises a first axis (also termed herein a longitudinal axis) and a second axis perpendicular to the first axis which together define a plane. The embossed material may lie only partially within the plane of the starting material, such that less than 70% of the embossed material lies in the plane, or less than 50%, or less than 30%, or less than 20%, or less than 10%.
The susceptor may comprise a thermally and electrically conductive material. The susceptor may comprise one or more of, but not limited to, graphite, molybdenum, silicon carbide, niobium, aluminium, iron, nickel, nickel containing compounds, titanium, mild steel, stainless steel, low carbon steel and alloys thereof, e.g., nickel chromium or nickel copper, and composites of metallic materials.
The susceptor may have a thickness of less than 500µm and greater than 10µm. Materials that can be considered "soft" such as aluminium can have a thickness of below 500µm, and more preferably below 200µm and even more preferably below 100µm. Materials that can be considered "hard" such as stainless steel can have a thickness of below 200µm, more preferably below 100µm and even more preferably below 50µm to prevent wear and damage to the rollers. Such susceptors are particular suited to the embossing process mentioned above.
The susceptor may be comprised in said consumable.
The susceptor may be in direct contact with said aerosol-forming substance.
The features set out above may be combined together in any combination. In particular, the features of the second aspect of the invention may be combined with features from the first aspect of the invention, and vice versa, and also with features selected from the detailed description below.

Brief description of the drawings

There now follows a detailed description of the invention, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 schematically shows an aerosol generating system including an aerosol generating device and an aerosol generating substrate;
Figures 2a and 2b respectively schematically show a plan view of a prior art heating assembly and a plan view of a heating assembly according to the invention for comparison;
Figure 3 illustrates a normalized surface current density for a flat susceptor located axially within an axial induction coil;
Figure 4 illustrates a normalized surface current density for a susceptor comprising at least one out of plane structure located axially within an axial induction coil;
Figure 5 schematically shows an embossing system;
Figure 6 illustrates a method of manufacturing a susceptor;
Figure 7 shows cross-sectional views for ten susceptors each comprising at least one out of plane structure;
Figure 8 illustrates (a) a flat circular induction coil, (b) a circular susceptor comprising at least one out of plane structure for use with the flat circular induction coil shown in image (a); and (c) a cut away view showing both the circular susceptor and the flat circular induction coil;
Figure 9 illustrates (a) a flat rectangular induction coil, (b) a rectangular susceptor comprising at least one out of plane structure for use with the flat rectangular induction coil shown in image (a); and (c) a cut away view showing both the rectangular susceptor and the flat rectangular induction coil;
Figure 10 illustrates a normalized surface current density for a flat susceptor located adjacent a flat induction coil;
Figure 11 illustrates a normalized surface current density for a susceptor comprising at least one out of plane structure located adjacent a flat induction coil;
Figure 12 schematically shows a first susceptor comprising at least one three dimensional surface structure;
Figure 13 schematically shows a second susceptor comprising at least one three dimensional surface structure;
Figure 14 schematically shows a third susceptor comprising at least one three dimensional surface structure and an induction coil;
Figure 15 schematically shows a fourth susceptor comprising at least one three dimensional surface structure;
Figure 16 shows a perspective view of a fifth susceptor comprising at least one out of plane structure;
Figure 17 schematically shows an aerosol generating system including the fifth susceptor;
Figure 18 shows a perspective view of a sixth susceptor comprising at least one out of plane structure; and
Figure 19 schematically shows an aerosol generating system including the sixth susceptor.

Detailed Description

As shown diagrammatically in Figure 1, a susceptor 10 is useable as a heating element 12 as part of an induction heating assembly 14 of an aerosol generating system 16. The aerosol generating system 16 comprises an aerosol generating device 18 (also known as a vaporiser) and an aerosol generating substrate 20, also termed herein an aerosol-forming substance 20. The aerosol generating device 18 is a hand-held, portable device, by which it is meant that a user is able to hold and support the device 18 unaided, in a single hand. The aerosol generating substrate 20 may be comprised in a consumable.
In use, an induction coil 22, i.e., an electromagnetic field generator, comprised in the induction heating assembly 14 is arranged to be energised to generate an alternating electromagnetic field that couples with, and inductively heats, the susceptor 10 due to eddy currents and magnetic hysteresis losses resulting in a conversion of energy from electromagnetic to heat. Heat from the susceptor 10 is transferred, for example by conduction, radiation and convection, to the aerosol generating substrate 20 to heat the aerosol generating substrate 20 (without burning or combusting the aerosol generating substrate 20) thereby generating a vapour which cools and condenses to form an aerosol for inhalation by a user of the aerosol generating device 18. Aerosolised substrate is entrained in air drawn into the system through one or more air inlets (not shown) as said air flows past or through the heated substrate 20, for example during a user's inhalation. Typically, air follows a continuous airflow path extending through the system 16 from the air inlet(s), through the consumable, to an aerosol outlet (not shown), which may be defined by a mouthpiece of the consumable.
In general terms, a vapour is a substance in the gas phase at a temperature lower than its critical temperature, which means that the vapour can be condensed to a liquid by increasing its pressure without reducing the temperature, whereas an aerosol is a suspension of fine solid particles or liquid droplets, in air or another gas. It should, however, be noted that the terms 'aerosol' and 'vapour' may be used interchangeably in this specification, particularly with regard to the form of the inhalable medium that is generated for inhalation by a user.
The induction coil 22 is energised by a power source 24 of the aerosol generating device 18, such as a battery. Aerosol generating devices 18 typically include a controller 26 and a user interface for controlling the operation of the aerosol generating device 18 via the controller 26.
The controller 26 is configured to detect the initiation of use of the aerosol generating device 18, for example, in response to a user input, such as a button press to activate the aerosol generating device 18, and/or in response to a detected airflow through the aerosol generating device 18. As will be understood by one of ordinary skill in the art, an airflow through the aerosol generating device 18 is indicative of a user inhalation or 'puff'. The aerosol generating device 18 may, for example, include a puff detector, such as an airflow sensor (not shown), to detect an airflow through the aerosol generating device 18.
The controller 26 includes electronic circuitry. The power source 24 and the electronic circuitry may be configured to operate at a high frequency. For example, the power source 24 and the electronic circuitry may be configured to operate at a frequency of between approximately 80 kHz and 500 kHz, possibly between approximately 150 kHz and 250 kHz, and possibly at approximately 200 kHz. The power source 24 and the electronic circuitry could be configured to operate at a higher frequency, for example in the MHz range, if required.
The induction coil 22 may have any shape, but typically is either an axial coil (i.e. a coil helically wound around a longitudinal axis into a generally cylindrical shape) or a flat coil (i.e. a spirally wound coil, typically lying in a single plane, which may be generally circular or quadrilateral in shape). The induction coil 22 may be arranged around the susceptor 10, for example to partially surround or fully surround the susceptor 10, particularly when the induction coil 22 is substantially helical in shape. The induction coil 22 may be arranged adjacent the susceptor 10, particularly in the case of a flat coil. The induction coil 22 may comprise a Litz wire or a Litz cable. It will, however, be understood that other materials could be used. The induction coil 22 may be arranged to operate in use with a fluctuating electromagnetic field having a magnetic flux density of between approximately 20mT and approximately 2.0T at the point of highest concentration.
The induction heating assembly 14 may include one or more susceptors 10 arranged around the periphery of a heating compartment (not shown) configured for receiving an aerosol generating substrate 20. That is, one or more susceptors may be provided in the aerosol generating device 18, together with the induction coil 22. Alternatively, the susceptor 10 may instead be provided in the aerosol generating substrate 20 during manufacture, for example as part of the consumable.
Many susceptors used currently are relatively simple in geometry, being either a single strip of metal or multiple strips of metal. This leads to inefficiencies when heating a target material, (i.e. an aerosol generating substrate such as tobacco or e-liquid). In part, these inefficiencies are due to the susceptor having only a limited surface area in contact with the target material (which is typically cylindrical or in a cylindrical container, and so has poor surface contact with a planar susceptor). However, further inefficiencies are introduced by non-ideal electromagnetic coupling between the susceptor and the induction coil.
The strength and direction of a magnetic field generated by an induction coil vary with location relative to the coil. The magnetic flux density at any given location within the field impacts the strength of the eddy currents induced within a susceptor located within the field. In particular, magnetic flux density is higher closer to the coil, meaning that the closer a susceptor is located to the coil then the stronger the coupling effect between the coil and the susceptor. The stronger the coupling effect, the more current is induced in the susceptor, and so the greater the heating effect.
Figure 2 illustrates a cross-sectional view of an induction heating assembly showing, in image (a), a prior art susceptor 10 located within an alternating magnetic field 25 generated by an induction coil 22. The magnetic field has a first region of high magnetic flux density 25a and a second region of low magnetic flux density 25b. It will be appreciated that these regions 25a, 25b are illustrative only, and in reality the flux density varies continuously with distance from the coil 22 generating the field. Nevertheless, a first region 25a can be defined that is closer to the coil and thus which has a generally higher magnetic flux density than a second region 25b which is further from the coil and thus has a generally lower magnetic flux density.
The induction coil 22 in Figure 2 is an axial coil having a central longitudinal axis 28. The susceptor 10 is planar (i.e. a substantially flat plane defined by a first axis and a second axis perpendicular to that first axis) and located centrally within the coil 22, such that the longitudinal axis of the coil 28 coincides with an axis of the susceptor 10. It will be seen that a first portion 10a of the susceptor 10 falls within the high flux density region 25a, whilst a second portion 10b of the susceptor 10 falls within the low flux density region 25b. Thus, more eddy currents are induced in the first portion 10a than in the second portion 10b, meaning that the first portion 10a experiences a greater heating effect that the second portion 10b.
Image (b) of Figure 2, in contrast, shows a shaped susceptor 60 according to the present disclosure. The shaped susceptor 60 comprises a footprint 100, which is a projection of the plan outline of the shaped susceptor 60 onto a flat plane. The footprint 100 thus comprises a first (longitudinal) axis and a second axis perpendicular to that first axis. For the purposes of illustration, in the present example the footprint 100 has the same shape and surface area as the planar prior art susceptor 10 shown in image (a). Looked at another way, the footprint can be considered a maximum diameter or radius (i.e. half diameter) that would be swept out by rotation of the susceptor about its longitudinal axis.
As in the case of prior art planar susceptor 10, the three dimensional susceptor 60 is located centrally within the induction coil 22, such that the longitudinal axis 28 of the coil 22 coincides with a longitudinal axis of the susceptor 60. Similarly, a first portion 60a of the susceptor 60 falls within the high flux density region 25a, whilst a second portion 60b of the susceptor 60 falls within the low flux density region 25b.
However, unlike the planar susceptor 10, the shaped susceptor 60 is three dimensional, and comprises at least one (and in this case two) out of plane structures 64. The out of plane structures 64 give the susceptor 60 a three dimensional (i.e. non-planar) shape, which, in the example of Figure 2, has a generally S-shaped cross-section comprising a central substantially planar region connecting two oppositely curved edge regions, denoted within circles 62.
The out of plane structures 64 are shaped to place a greater surface area and/or volume of the shaped susceptor 60 in the first region 25a of high magnetic flux as compared with a planar susceptor 10 having the same footprint 100. That is, the ratio between a first portion 60a of the susceptor 60 (located in the high flux density region) and a second portion 60b of the susceptor (located in the low flux density region) is greater than the corresponding ratio for the flat susceptor 10. This means that the shaped susceptor 60 experiences an improved electromagnetic coupling with the induction coil 22 as compared to a planar susceptor 10 having the same footprint, due to the presence of the out of plane structures 64. The three dimensional susceptor 60 may thus have a more efficient heating effect than the prior art susceptor 10.
The improved coupling effect discussed above is demonstrated in Figures 3 and 4, which show the normalized surface current density for a flat susceptor 10 (Figure 3) as compared with the normalized surface current density for an S-shaped susceptor 60 of the same footprint (Figure 4). Figure 4 clearly shows that more surface current 65 is induced in the out of plane structures 64 than in the corresponding regions of the planar susceptor shown in Figure 3. In particular, the S-shaped susceptor 60 of Figure 4 experiences approximately a 20% increase in surface current as compared with the planar susceptor 10 shown in Figure 3.
Susceptor geometry is usually limited by the cost and complexity of the fabrication. Referring now to Figures 5 and 6, a method of manufacturing a susceptor of the type discussed above in connection with Figures 2 and 4 for a heating assembly of an aerosol generating system, such as that described with reference to Figure 1, is described below.
The method illustrated in Figure 5 makes use of an embossing system 30. The embossing system 30 comprises a pair of opposed rollers, namely a first (in this case upper) roller 32 and a second (in this case lower) roller 34. Each of the rollers 32, 34 comprises a pressing surface 36. One or more, and in this case a plurality of, shaping features 38 are provided on one or both of the pressing surfaces 36, such that when a starting material 40 is fed between the rollers 32, 34, the shaping features 38 are operable to make an impression into the starting material 40 to produce an embossed material 42 comprising a plurality of three dimensional structures 62. The three dimensional structures may be surface structures 44, as shown, or may be out of plane structures 64 as discussed above in connection with Figures 2 and 4. Depending on whether one or both of the rollers 32, 34 comprises shaping features 38, the three-dimensional structures may be located in a first (in this case upper) surface 46 of the embossed material 42 (produced by the first roller 32) or in a second (in this case lower) surface 48 of the embossed material (produced by the second roller 34), or in both the upper and lower surfaces 46, 48 (produced by both rollers, as shown in Figure 5). The shaping features 38 may co-operate in order to deform the planar starting material 40 into a non-planar three dimensional shape (as shown in Figures 2 and 4).
Referring now to Figure 6, a method of manufacturing a susceptor is shown. In block 50, the method begins by feeding the starting material 40 between a pair of opposing rollers, for example the rollers 32, 34 shown in Figure 5. At least one of the rollers has a shaped embossing surface, such as a surface 36 comprising shaping features 38 as shown in Figure 5.
In block 52, the starting material 40 is embossed using the rollers to produce an embossed material 42 having a plurality of three dimensional structures 62.
In block 54, the embossed starting material 42 is cut, for example using a cutter 70, to form a plurality of susceptors 60. Each of the cut susceptors 60 comprises a three dimensional structure. In one example, the susceptor material is embossed in a sheet and later cut along the width and length direction to form a susceptor. Alternatively, the starting material can be pre-cut to a desired size in one direction (e.g. the width dimension) into a flat wire and then embossed, and then cut along the length direction.
Embossing can quickly and cheaply produce a large deformation on one or both sides of a sheet. The term "three dimensional structure" as used herein refers to features at a macroscopic scale (i.e. visible to the naked eye, for example having a minimum dimension of greater than 0.1 mm (in the case of a surface structure) and a minimum dimension greater than 0.5mm (in the case of an out of plane deformation), for example between 0.5mm and 10mm out of plane deflection). Embossing can thus be used to produce a susceptor having a relatively complex surface geometry.
The starting material 40 for use in the method described herein is a thin thermally and electrically conductive material. "Thin" as used herein means the starting material has a thickness of less than 500µm and greater than 10µm. Materials that can be considered "soft" such as aluminium can have a thickness of below 500µm, below 200µm, or even below 100µm. Materials that can be considered "hard" such as stainless steel can have a thickness of below 200µm, below 100µm, or even below 50µm. Selecting a thin material can prevent wear and damage to the rollers.
A suitable electrically and thermally conducting starting material (and thus susceptor material) may be graphite, molybdenum, silicon carbide, niobium, aluminium, iron, nickel, nickel containing compounds, titanium, mild steel, stainless steel, low carbon steel and alloys thereof, e.g., nickel chromium or nickel copper, and composites of metallic materials.
Geometries that can be embossed range from simple corrugated channels structures to more complex surface structures such as pyramids, pins, chevrons, etc. Some examples of three dimensional surface structures produced by the embossing process described herein are shown in Figures 7, 8, 9 and 11-15.
As discussed above in relation to Figure 2 and 4, a planar starting material may be shaped (e.g. embossed or stamped) to place a greater amount of susceptor material in a region of high magnetic flux as compared to a planar susceptor having the same footprint. This may be achieved by bending one or more free edges of the susceptor away from the plane of the footprint 100 (which may be the plane defined by the starting material). When such a three dimensional susceptor is placed in a magnetic field a greater surface area and volume of susceptor material is located within a region of high flux density as compared with a planar susceptor of the same footprint.
Figure 7 shows examples of susceptors having out of plane structures 64 shaped so as to place a greater area/volume of susceptor material in a region of high magnetic flux. The susceptors shown are deformed along an axial dimension so as to have a constant axial cross section relative to a longitudinal axis. Ten example cross sections are shown in Figure 7, including generally S-shaped susceptors 60, generally U-shaped susceptors 60' and generally corrugated susceptors 60". Such susceptors may include greater than 20%, 25% or 30% of the susceptor material out of the plane of the original starting material, up to greater than 90% of the material out of plane. The out of plane deformation may be greater than 0.5 mm, greater than 1 mm, greater than 2 mm, greater than 3 mm or greater than 4 mm. The out of plane deformation may be for example between 0.5 mm and 5 mm, 6 mm, 7 mm, 8 mm, 9 mm or 10 mm.
In the case of the S-shaped susceptors 60, each susceptor 60 has one or more edge regions which are bent out of plane in opposing directions, such that a first edge 61 extends away from a plane 100 defining a footprint of the susceptor 60 in a first direction whilst a second edge 63 extends away from the plane in a second direction opposite to the first. As discussed above in relation to Figures 2 and 4, such S-shaped susceptors may find particular utility when located centrally in an axial coil 22, and may be included within an aerosol generating substrate for use with an aerosol generating device.
In the case of the U-shaped susceptors 60', each susceptor 60' has one or more edge regions which are bent out of plane in the same direction, such that both a first edge 61 and a second edge 63 extends away from a plane defining a footprint 100 of the susceptor 60' in the same direction. Such U shaped susceptors may find utility when located around the edges of a heating chamber of an aerosol generating device, and/or in conjunction with a flat induction coil.
In the case of the corrugated susceptors 60", a plurality of corrugations project from the plane defining a footprint 100 of the susceptor. As well as improving inductive coupling, such corrugated susceptors may improve thermal transfer (due to increased surface contact with an aerosol forming substrate) and may improve air flow within the aerosol generating system by guiding air in the direction of the corrugations.
Figures 8 and 9 illustrate susceptors 60‴ comprising out of plane structures 64 for use with flat induction coils 22'. In a similar manner to that discussed above in relation to Figure 7, the susceptors 60‴ are formed from a starting material that is shaped (e.g. embossed or stamped) to place a greater amount of susceptor material in a region of high magnetic flux as compared to a planar susceptor having the same footprint. This may be achieved by bending one or more free edges of the susceptor to curve towards the coil to form a susceptor having a generally U-shaped or cup-shaped cross section. When such a susceptor is placed in a magnetic field, a greater surface area and volume of susceptor material is located within a region of high flux density as compared with a planar susceptor of the same footprint. Put another way, in use a susceptor is typically located adjacent a flat coil 22' at a predefined spacing distance d (see Figures 10 and 11). In the case of a planar susceptor 10, the distance between the coil and the susceptor increases to d_edge> d at the edges of the susceptor, due to the dissimilarity in shape between the susceptor 10 and the coil 22'. In contrast, the shaped susceptor 60‴ mimics the shape of the coil so as to complement the three dimensional surface shape. The outcome is that d_edge is less than or equal to the pre-defined distance d, so improving electromagnetic edge coupling.
Figures 10 and 11 compare the normalized surface current density for a flat susceptor 10 adjacent a planar coil (Figure 10) with the normalized surface current density for a shaped susceptor 60‴ (Figure 11) and illustrate an average 18% increase in current density in the shaped susceptor 60‴ compared to a flat susceptor 10, thus demonstrating an increased coupling effect for the shaped susceptor.
In some examples, a surface of the starting material may additionally be embossed to comprise an increased surface area in comparison with a surface of the same dimensions absent said three dimensional surface structures. For example, Figure 12 shows a susceptor 72 having a plurality of three dimensional surface structures in the form of conical recesses 44a on both a first surface 46a and a second surface 48a. To create such structures 44a the pressing surfaces 36 of both upper and lower rollers 32, 42 comprise conical shaping features 38. The conical recesses 44a on the first surface 46a do not coincide with the conical recesses 44a on the second surface 48a, although this is not essential. Such a susceptor has an increased heat transfer efficiency in comparison to a susceptor absent any surface structures 44a, as it has a larger surface area through which heat may be transferred.
Figure 13 shows a second susceptor 74 having a plurality of three dimensional surface structures in the form of truncated pyramidal recesses 44b on both a first surface 46b and a second surface 48b. To create such structures 44b the pressing surfaces 36 of both upper and lower rollers 32, 42 comprise truncated pyramidal shaping features 38. The recesses 44b on the first surface 46b do not coincide with the conical recesses 44b on the second surface 48b, although this is not essential. Such a susceptor has an increased heat transfer efficiency in comparison to a susceptor absent any surface structures 44b, as it has a larger surface area through which heat may be transferred.
In other examples, a surface of the starting material is embossed to complement the shape of a component of the aerosol generating system, such as the induction coil 22. For example, Figure 14 shows a third susceptor 76 having a plurality of three dimensional surface structures in the form of corrugations 44c on a first surface 46c (which can also be considered an outer surface). No corrugations are provided on a second surface 48c (which can also be considered an inner surface). To create such structures 44c the pressing surfaces 36 of the upper roller 32 comprises a corrugated surface, whilst the pressing surface 36 of the lower roller 34 is substantially flat and comprises no shaping features. Such a susceptor may have improved coupling to an induction coil 22 in comparison to a susceptor absent any surface structures 44c, as it more closely conforms to the shape of the induction coil. In particular, the induction coil 22 has a pitch p, and a distance d2 from the centre of a first corrugation to a centre of an adjacent corrugation may be substantially the same as the pitch p, such that the corrugations mirror the shape of the coil windings.
It will be appreciated that a susceptor of the type shown in Figure 14 may have a different shape depending on the geometry of the induction coil included in an aerosol generating device, and the shape of the susceptor may be embossed to mirror the shape of the coil, for example in surface geometry (as shown in Figure 14) or in cross sectional shape (as discussed above in connection with Figures 2-11). Such a susceptor may also comprise surface structures on the second surface 48c, which may differ to those on the first surface 46c, and may, for example, be shaped to improve heat transfer (e.g. as shown in Figures 12 and 13).
In other examples, the starting material is embossed to comprise one or more fluid deflection features to control airflow paths around the aerosol generating material and/or to control wicking (in the case of liquid aerosol generating material). For example, Figure 15 shows a third susceptor 78 having a plurality of three dimensional surface structures in the form of channels 44d on a first surface 46d. No channels are provided on a second surface 48d. To create such structures 44d the pressing surfaces 36 of the upper roller 32 comprises a ridged surface, whilst the pressing surface 36 of the lower roller 34 is substantially flat and comprises no shaping features. Such a susceptor may have an improved ability to channel air or fluid slow within an aerosol generating device. Again, such a susceptor may also comprise surface structures on the second surface, which may differ to those on the first surface, and may, for example, be shaped to improve heat transfer (e.g. as shown in Figures 12 and 13) or coupling to an external component such as a heater (e.g. as shown in Figures 2-11 and 14).
It will be appreciated that many other three dimensional geometries may be selected to optimise the electromagnetic coupling between a shaped susceptor and an induction coil in addition to those discussed above, which constitute merely examples. The three-dimensional structures may conveniently be created by embossing or stamping, but could be created in another manner.
Figures 16 and 17 show a further example of a fifth susceptor 80 that is similar to the susceptor 60‴ shown in Figures 9 and 11. The fifth susceptor 80 is shown in perspective view in Figure 16, and is shown comprised within a consumable 90 in Figure 17. The consumable 90 is generally planar in shape. That is, the consumable is flat and rectangular in plan view, and has a thickness dimension that is substantially smaller than its width and length dimensions. In the example shown, the consumable 90 is formed from a first generally planar body 92 of solid aerosol-forming substance and a second generally planar body 94 of solid aerosol-forming substance. The fifth susceptor 80 is sandwiched between the first and second generally planar bodies 92, 94 such that a first face 82 of the fifth susceptor abuts the first body 92 of aerosol-forming substrate and a second face 84 of the fifth susceptor 80 abuts the second body 94.
Like the susceptor 60‴ shown in Figure 9, the fifth susceptor 80 includes one or more out of plane structures 64 that are shaped (e.g. embossed or stamped) to place a greater amount of susceptor material in a region of high magnetic flux as compared to a planar susceptor having the same footprint. In particular, the fifth susceptor 80 includes a pair of opposing free edges 86 which are each folded or bent to form a lip, such that the fifth susceptor 80 has a generally U-shaped cross section. When placed adjacent a transverse coil 22', as shown in Figure 17, the folded edges 86 ensure that the susceptor material at the edge region of the susceptor 80 is located closer to the coil, and thus has improved electro-magnetic coupling with the coil.
The susceptor 80 additionally includes one or more out of plane structures 64, which form airflow deflection features shaped to control an airflow path around the aerosol-forming substrate. In the particular example shown, the airflow deflection features are provided as a plurality of protrusions 88 which are embossed into the susceptor material. Like the folded edges 86, the protrusions 88 are shaped to place a greater amount of susceptor material in a region of high magnetic flux as compared to a planar susceptor having the same footprint. In addition, the protrusions operate to control airflow through the system, in particular by promoting one or more of turbulence, mixing and recirculation in the airflow as the air flows over the surface of the susceptor which comprises the deflection features. A more turbulent and/or better mixed airflow may have increased heat transfer as compared with a laminar flow.
As shown in Figure 16, the protrusions 88 are substantially identical with one another and define a periodically repeating pattern. In particular the pattern is formed from a plurality of rows of protrusions. The protrusions in each row are located one behind the other, so as to be aligned with respect to a bulk airflow direction through the system. The protrusions shown are generally circular in plan view (i.e. generally semi-circular in cross section), but it will be appreciated that other shapes may be used if required, such as chevrons, pyramids, crosses, etc. Furthermore, as discussed above, the airflow deflection features could include one or more ridges, corrugations or channels.
The consumable 90 shown in Figure 17 includes a plurality of defined airflow paths 96. A first group of the airflow paths 96 are formed in the first generally planar body 92 of aerosol-forming substance, and bounded on one wall by the first surface 82 of the susceptor. A second group of the airflow paths 96 are formed in the second generally planar body 94 of aerosol-forming substance and bounded on one wall by the second surface 84 of the susceptor. Each of the defined airflow paths 96 is aligned with the longitudinal axis 98 of the consumable. The first group of defined airflow paths is laterally offset from the second group of airflow paths, although this need not be the case. The defined airflow paths may be formed from, for example, channels pressed into the solid aerosol forming substrate during a molding or shaping operation.
The protrusions 88 each protrude into one of the defined airflow paths 96, so as to influence the airflow within that defined airflow path. In the example shown, the protrusions 88 protrude into the first group of airflow paths defined in the first body of aerosol forming substrate only. It will be appreciated however that a further group of protrusions could be shaped (e.g. embossed) into the susceptor so as to protrude into the second group of airflow paths defined in the second body of aerosol forming substrate in as well, or instead. This further group of protrusions would necessarily extend away from the plane of the susceptor in the opposite direction to the protrusions 88 (i.e. away from the transverse coil 22').
Due to the presence of the protrusions 88, air flowing through the first group of airflow paths defined in the first body 92 of aerosol forming substrate is disrupted. In particular, said airflow must flow around the protrusions and over the protrusions in order to pass through the channels defining the air flow paths, which increases mixing and turbulence within the flow. Because the susceptor 80 includes a plurality of protrusions 88 located one behind the other, this mixing effect is maintained for the duration of the flow path through the consumable.
As discussed above, typically embossed features may have a minimum dimension of 0.1 mm or greater, for example between 0.5-10 mm.
To further promote turbulence and mixing, the susceptor may further comprises a plurality of roughness enhancing microstructures (not visible in the Figures). As used herein, a microstructure refers to a structure on a scale which is not visible to the naked eye, typically as revealed by an optical microscope above 25x magnification. A microstructure typically has a largest dimension of less than 200µm, for example between 0.1µm and 100µm. Such microstructures may improve the heat transfer further by causing additional turbulence/mixing.
The roughness enhancing microstructures may comprise micro-scale protrusions, which may for example have semi-circular or triangular cross sections. The micro-scale protrusions may be provided randomly, or may be provided in a regular pattern similar to that discussed above. The plurality of roughness enhancing microstructures may be located on the entire surface of the susceptor, or may be provided in selected locations. The plurality of roughness enhancing microstructures may be located on the out of plane structures, between the out of plane structures, or both.
Figures 18 and 19 show a further susceptor 110 similar to that shown in Figures 16 and 17, and so like reference numerals are used for like features, which are not described again below for the sake of brevity.
The main difference between the system shown in Figure 19 and that shown in Figure 17 is that the system of Figure 19 includes a pair of opposing transverse induction coils 22a, 22b. The consumable 90 including the sixth susceptor 110 is located between the pair of transverse coils.
In this case, one set of out of plane features 64, namely edge portions 86, are shaped to place a greater amount of susceptor material closer to a first coil 22a, whilst another set of out of plane features 64, namely protrusions 88, are shaped to place a greater amount of susceptor material closer to a second coil 22b. In this way improved coupling may be achieved with both coils, as well as improved airflow control.
In consumables of the types shown in Figures 17 and 19, where the heat source is a susceptor and the airflow path is well defined, e.g. via channels as shown, the airflow can be manipulated in a controlled manner with the use of airflow guides or deflection features 64, 88. Many traditional consumables however, such as those using a solid aerosol-forming substrate (e.g. in the form of cut-rag or looseleaf tobacco) do not have a defined airflow path, because the air may pass through any section of the consumable, depending on packing from consumable to consumable, and so air flow is less easy to reliably manipulate. In contrast, in the embodiments discussed here, the consumable has well defined air flow path as shown in the figures. The susceptor component acts as at least one wall of the defined airflow path. This wall includes some surface structures on it which extend away from the surface of the main body of the susceptor and towards the coil, as well as protruding into the airstream. This has the effect of enhancing coupling with the generated electromagnetic field as well as influencing the airflow in a defined and beneficial manner. The airflow may be influenced by features such as pins, fins, ribs, etc., which may increase fluidic mixing downstream and generate a preferential flow regime for heat transfer/vapour extraction.
It will be appreciated that the consumable need not have the shape and dimensions shown. For example, the consumable may be a cylindrical consumable. Similarly, the defined airflow channels may differ in shape and number, and the airflow deflection features may differ in shape and number.
As described above, embossed features at the macroscopic scale can result in large deformation on both sides of a susceptor sheet, effectively generating a three dimensional component out of a two dimensional sheet geometry. This additional dimension in the susceptor allows for a few different enhancements:

A larger surface area can be generated in a smaller volume leading to enhanced heat transfer to the target material. This avoids large, localised heating of a non-optimal susceptor shape.
The susceptor can be formed to better couple to the inductor coil, which is nearly always a non-planar shape.
The 3D shape can be used to control airflow paths in and around the target material.
In cases of e-liquids the shape can be used to control wicking as well if the susceptor is at least partially perforated.

Although exemplary embodiments have been described in the preceding paragraphs, it should be understood that various modifications may be made to those embodiments without departing from the scope of the appended claims. Thus, the breadth and scope of the claims should not be limited to the above-described exemplary embodiments. Any combination of the above-described features in all possible variations thereof is encompassed by the present disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.

Claims

An aerosol generating system (16) comprising:
an aerosol generation device (18) comprising a region arranged for receiving a consumable comprising an aerosol-forming substance (20),

an induction heating assembly (14) comprising an induction coil (22) and a susceptor (60", 80, 110), said susceptor having a footprint (100), the induction heating assembly being configured to heat said aerosol-forming substance in the consumable to generate an aerosol that may be inhaled by a user,

wherein the susceptor (60", 80, 110) comprises at least one out of plane structure (64) that forms one or more airflow deflection features shaped to control an airflow path around said aerosol-forming substrate.
The aerosol generating system of claim 1, wherein the induction coil is operable to generate an alternating magnetic field having a region of high magnetic flux density (25a) and a region of low magnetic flux density (25b), and wherein the susceptor (60", 80, 110) comprises at least one out of plane structure (64) shaped to place a greater surface area and/or volume of the susceptor in the region of high magnetic flux as compared with a planar susceptor having the same footprint.
The aerosol generating system of claim 1 or claim 2, wherein the susceptor (60", 80, 110) comprises a plurality of out of plane structures.
The aerosol generating system of claim 3, wherein the susceptor (60", 80, 110) comprises a periodically repeating pattern of out of plane structures.
The aerosol generating system according to any preceding claim, wherein the at least one out of plane structure comprises one or more recesses, protrusions (88), ridges, channels or corrugations.
The aerosol generating system according to any preceding claim, wherein the susceptor comprises a longitudinal axis (98), and at least one out of plane structure (64) runs the length of the longitudinal axis such that the susceptor has a generally S or U shaped cross section.
The aerosol generating system of any preceding claim, wherein the at least one out of plane structure (64) is operable to control an airflow path around said aerosol-forming substance by increasing one or more of turbulence, mixing or recirculation in the airflow.
The aerosol generating system of any preceding claim, wherein the susceptor (60", 80, 110) further comprises a plurality of roughness enhancing microstructures.
The aerosol generating system according to any preceding claim, wherein the induction coil (22) is a transverse coil (22', 22a, 22b), and the susceptor (80, 110) is located adjacent the coil, wherein the susceptor is shaped such that a normal distance between an out of plane structure (64, 86) at an edge region of the susceptor and the coil is less than or equal to a normal distance between a planar region of the susceptor and the coil.
The aerosol generating system according to any preceding claim, wherein the at least one out of plane structure (64) is embossed into the susceptor (60", 80, 110).
The aerosol generating system according to any preceding claim, further comprising the consumable, wherein the consumable comprises a solid aerosol-forming substance and the susceptor (60", 80, 110) is positioned within the solid aerosol-forming substance.
The aerosol generating system according to claim 11, wherein the solid aerosol-forming substance includes a defined airflow path (96), and the susceptor (80, 110) acts as at least one wall of the defined airflow path.
The aerosol generating system according to claim 12, wherein the consumable is generally planar in shape, and comprises a first generally planar body (92) of aerosol-forming substance and a second generally planar body (94) of aerosol-forming substance, with the susceptor (80, 110) being sandwiched between the first and second generally planar bodies (92, 94) of aerosol forming substance.
The aerosol generating system of claim 13, wherein the solid aerosol-forming substance includes a plurality of defined airflow paths (96), a first group of which are formed in the first generally planar body (92) of aerosol-forming substance and bounded on one wall by a first surface (82) of the susceptor (80, 110), and a second group of which are formed in the second generally planar body (94) of aerosol-forming substance and bounded on one wall by a second surface (84) of the susceptor.
The aerosol generating system according to any one of claims 12 to 14, wherein at least one out of plane structure (64, 88) protrudes into the / one of the defined airflow path(s) (96).