Technical Field
[0001] 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
[0002] 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.
[0003] 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.
[0004] 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
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] 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).
[0016] 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.
[0017] 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.
[0018] 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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.
[0026] 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.
[0027] 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.
[0028] 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.
[0029] 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.
[0030] 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.
[0031] 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%.
[0032] 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.
[0033] 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.
[0034] The susceptor may be comprised in said consumable.
[0035] The susceptor may be in direct contact with said aerosol-forming substance.
[0036] 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
[0037] 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
[0038] 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.
[0039] 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.
[0040] 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.
[0041] 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.
[0042] 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.
[0043] 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.
[0044] 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.
[0045] 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.
[0046] 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.
[0047] 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.
[0048] 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.
[0049] 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.
[0050] 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.
[0051] 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.
[0052] 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.
[0053] 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.
[0054] 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.
[0055] 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.
[0056] 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).
[0057] 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.
[0058] 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.
[0059] 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.
[0060] 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.
[0061] 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.
[0062] 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.
[0063] 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.
[0064] 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.
[0065] 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.
[0066] 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.
[0067] 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.
[0068] 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.
[0069] 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.
[0070] 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.
[0071] 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.
[0072] 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.
[0073] 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.
[0074] 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).
[0075] 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).
[0076] 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.
[0077] 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.
[0078] 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.
[0079] 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.
[0080] 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.
[0081] 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.
[0082] 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').
[0083] 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.
[0084] As discussed above, typically embossed features may have a minimum dimension of 0.1
mm or greater, for example between 0.5-10 mm.
[0085] 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.
[0086] 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.
[0087] 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.
[0088] 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.
[0089] 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.
[0090] 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.
[0091] 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.
[0092] 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.
If required, macroscopic embossed features may be supplemented with microscale features,
which may also be embossed.
[0093] 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.
1. 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.
2. 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.
3. The aerosol generating system of claim 1 or claim 2, wherein the susceptor (60", 80,
110) comprises a plurality of out of plane structures.
4. The aerosol generating system of claim 3, wherein the susceptor (60", 80, 110) comprises
a periodically repeating pattern of out of plane structures.
5. 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.
6. 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.
7. 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.
8. The aerosol generating system of any preceding claim, wherein the susceptor (60",
80, 110) further comprises a plurality of roughness enhancing microstructures.
9. 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.
10. 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).
11. 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.
12. 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.
13. 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.
14. 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.
15. 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).