Aerosol generating device for inductively heating an aerosol-forming substrate - Patent Application 20070233633

Abstract

The present invention relates to an aerosol-generating device for generating an aerosol by inductively heating an aerosol-forming substrate. The present invention further relates to an aerosol-generating system comprising such a device and an aerosol-generating article, the article including an aerosol-forming substrate to be heated. The device comprises a first LC resonator circuit and a second LC resonator circuit, the first LC resonator circuit having a first resonant frequency and the second LC resonator circuit having a second resonant frequency different from the first resonant frequency. The control circuit further comprises a drive oscillator circuit comprising an oscillator coil inductively coupled to the induction coil to selectively generate an alternating magnetic oscillator field at either the first resonant frequency or the second resonant frequency, such that an alternating magnetic field is selectively generated to selectively heat a susceptor or different sections of different susceptors in different sections of the device. The present invention further relates to an aerosol-generating system comprising such a device and an aerosol-generating article, the article including an aerosol-forming substrate to be heated.

Description

[Technical field]

[0001] The present invention relates to an aerosol-generating device for generating an aerosol by inductive heating of an aerosol-forming substrate. The present invention further relates to an aerosol-generating system comprising such a device and an aerosol-generating article, the article comprising an aerosol-forming substrate to be heated. [Background technology]

[0002] Aerosol generating systems based on inductive heating of an aerosol-forming substrate capable of forming an inhalable aerosol are generally known from the prior art. Such a system may comprise an aerosol generating device having a cavity for receiving the substrate to be heated. The substrate may be an integral part of an aerosol-generating article configured for use in the device. To heat the substrate, the device may comprise an induction heater including an induction source comprising an induction coil for generating an alternating magnetic field in the cavity. The magnetic field is used to inductively heat a susceptor that is disposed in thermal proximity or in direct physical contact with the substrate, such as to heat the substrate. In general, the susceptor may be either an integral part of the device or an integral part of the article.

[0003] To separately heat different segments of the susceptor and / or substrate, the apparatus may comprise multiple induction coils for selectively generating multiple magnetic fields. Thus, the induction source may be configured such that one coil is actively driven to generate a varying magnetic field while the other coil is inactive. Typically, this is achieved by a control circuit comprising a transistor switch for each induction coil. However, the use of multiple transistor switches requires precise control of the switching operation, especially in time, to avoid serious damage to the transistors due to undesirable power overload. Furthermore, in many cases, the inactive coils are not sufficiently prevented from passing the current induced by the active coils, resulting in substantial heating, although not actually desired.

[0004] It would therefore be desirable to have an aerosol generating apparatus and system for inductively heating an aerosol-forming substrate that has the advantages of the prior art solutions but without their limitations. In particular, it would be desirable to have an inductively heated aerosol generating apparatus and system that includes control circuitry for selectively driving multiple induction coils with little complexity and high reliability. Summary of the Invention

[0005] According to the present invention, there is provided an aerosol generating device for generating an aerosol by inductive heating of an aerosol-forming substrate. The device comprises a device housing with a cavity configured for removably receiving an aerosol-forming substrate to be heated. The device further comprises at least a first induction coil and a second induction coil. The first induction coil is arranged and configured to generate an alternating magnetic field in a first section of the cavity. The second induction coil is arranged and configured to generate an alternating magnetic field in a second section of the cavity. The device further comprises a control circuit for selectively driving the first induction coil and the second induction coil to selectively generate the alternating magnetic field in the first and second sections, respectively. The control circuit comprises a first LC resonator circuit and a second LC resonator circuit, the first LC resonator circuit including a first induction coil and a first capacitor, and the second LC resonator circuit including a second induction coil and a second capacitor. The first LC resonator has a first resonant frequency and the second LC resonator circuit has a second resonant frequency different from the first resonant frequency. The control circuit further comprises a drive oscillator circuit comprising an oscillator coil for selectively generating an alternating magnetic oscillating field near or having a frequency close to or at the first resonant frequency or near or having a frequency close to or at the second resonant frequency, the oscillator coil being inductively coupled to the first induction coil and the second induction coil such that an alternating magnetic field is generated in the first section when the frequency of the oscillator field is near or at the first resonant frequency and thus near or resonating with the first LC resonator circuit, and an alternating magnetic field is generated in the second section when the frequency of the oscillator field is near or at the second resonant frequency and thus near or resonating with the second LC resonator circuit.

[0006] In accordance with the present invention, it is recognized that multiple inductive coils may be used to selectively generate multiple magnetic fields, selectively driven by making each coil portion of a respective LC resonator circuit have a distinct resonant frequency, and by inductively coupling each LC resonator circuit to a driving oscillator coil that can selectively operate at a distinct resonant frequency. Advantageously, by having different resonant frequencies, the non-active coils are sufficiently prevented from flowing current induced by the active coils, since the non-active coils are off-resonance with respect to the current operating frequency of the oscillator coil. Furthermore, the control circuitry is less complex, and in particular does not require precise control of multiple transistor switches.

[0007] The frequency difference between the first and second resonant frequencies is preferably selected to be at least as large as necessary to inductively isolate the first and second inductive coils from each other such that only one of the coils is operable at a time while the respective other coil is inactive and sufficiently blocks the flow of current induced by the active coil. In general, the frequency difference between the first and second resonant frequencies depends on several factors. As will be explained in more detail below, the frequency difference depends in particular on the quality factor of each of the first and second LC resonator circuits. The quality factor characterizes the bandwidth of each resonator circuit relative to its central resonant frequency. A high quality factor is typically associated with a small bandwidth, thereby allowing a smaller frequency difference between the first and second resonant frequencies.

[0008] The first resonant frequency is preferably within a range of 1% to 20% of the second resonant frequency. For example, when the second resonant frequency is 20 MHz (megahertz), the first resonant frequency is within a range of 200 kHz (kilohertz) to 4 MHz (megahertz). Of course, the second resonant frequency may be within a range of 1% to 20% of the first resonant frequency.

[0009] In absolute numbers, the first resonant frequency may differ from the second resonant frequency by at least 40 kHz, in particular at least 100 kHz, preferably at least 200 kHz, more preferably at least 500 kHz, or even 1 MHz. For example, the first resonant frequency differs from the second resonant frequency by 120 kHz. A frequency difference between the first and second resonant frequencies in this range is particularly suitable for sufficiently isolating the first and second induction coils from each other.

[0010] For the same reason, at least one of the first and second LC resonator circuits, preferably both LC resonator circuits, may have a quality factor in the range of 2 to 50, in particular in the range of 2 to 20, for example 10. The term "quality factor" as used herein denotes a dimensionless parameter that characterizes the bandwidth of the respective resonator circuit relative to its central resonant frequency and describes how underdamped the respective resonator circuit is. That is, the quality factor relates the maximum or peak energy stored in the circuit (reactance) to the energy dissipated during each cycle of oscillation (resistance). A higher quality factor indicates a lower rate of energy loss compared to the resonator's stored energy, and the oscillations die out more slowly. Thus, by increasing the quality factor of the first and second LC resonator circuits, the bandwidth of the first and second LC resonator circuits is reduced, which advantageously suppresses the coupling of the respective LC resonator circuits to off-resonant magnetic fields. This further prevents the respective inactive coils from conducting currents induced by the respective active coils. Furthermore, increasing the quality factors of the first LC resonator circuit and the second LC resonator circuit minimizes the energy loss of the LC resonator circuits, thus increasing the heating efficiency.

[0011] The first and second resonant frequencies are preferably selected within a range of 100 kHz to 30 MHz, particularly 5 MHz to 15 MHz, and preferably 5 MHz to 10 MHz. The first and second resonant frequencies preferably correspond to the operating frequencies of the first and second induction coils, respectively. For example, at least one of the first and second resonant frequencies may be within a range of 100 kHz to 300 kHz, particularly 150 kHz to 270 kHz.

[0012] Thus further, the respective operating frequencies correspond to the frequency of the alternating magnetic field generated by the first and second induction coils in the first and second sections of the cavity, respectively. Preferably, the respective alternating magnetic fields are high-frequency alternating magnetic fields. As referred to herein, the high-frequency magnetic field may be in the range of 100 kHz (kilohertz) to 30 MHz (megahertz), in particular 5 MHz (megahertz) to 15 MHz (megahertz), preferably 5 MHz (megahertz) to 10 MHz (megahertz). Such values ​​have been demonstrated to be advantageous for induction heating in aerosol generating devices. Thus, the first and second resonant frequencies may be in the range of 100 kHz (kilohertz) to 30 MHz (megahertz), in particular 5 MHz (megahertz) to 15 MHz (megahertz), preferably 5 MHz (megahertz) to 10 MHz (megahertz). For example, at least one of the first resonant frequency and the second resonant frequency may be in the range of 100 kHz (kilohertz) to 300 kHz (kilohertz), particularly 150 kHz (kilohertz) to 270 kHz (kilohertz).

[0013] As referred to herein, the frequency of the oscillator field is close to the first or second resonant frequency, respectively, when the difference between the frequency of the oscillator field and the first or second resonant frequency is less than 500 kHz, in particular less than 100 kHz, preferably less than 50 kHz, more preferably less than 20 kHz, even more preferably less than 10 kHz, and most preferably less than 5 kHz.

[0014] The oscillator coil is preferably arranged coaxially with at least one of the first induction coil and the second induction coil, in particular with each of them. Due to the coaxial arrangement, the magnetic field generated by the oscillator coil largely overlaps with the first induction coil and the second induction coil, respectively. Advantageously, this increases the inductive coupling between the oscillator coil and the first induction coil and the second induction coil, respectively.

[0015] Similarly, the oscillator coil may at least partially surround at least one of, and in particular each of, the first induction coil and the second induction coil, which also advantageously increases the inductive coupling between the oscillator coil and the first induction coil and the second induction coil, respectively.

[0016] Preferably, the oscillator coil is arranged at least partially coaxially around at least one of the first induction coil and at least one of the second induction coil, i.e. the oscillator coil may at least partially surround and may be arranged coaxially around at least one of the first induction coil and at least one of the second induction coil, advantageously this further increases the overlap between the magnetic fields of the different coils and thus increases the inductive coupling between the oscillator coil and the first and second induction coils.

[0017] At least one, particularly each, of the oscillator coil, the first induction coil and the second induction coil may be a helical coil. A helical coil configuration proves to be particularly advantageous for a coaxial, particularly coaxial, surrounding arrangement of the oscillator coil and each of the first and second induction coils. Furthermore, the use of a helical induction coil advantageously provides a substantially homogenous electric field configuration inside the coil. To prevent possible deposition and / or corrosion on the induction coil, at least one, particularly each, of the oscillator coil, the first induction coil and the second induction coil may be provided with a protective cover or layer.

[0018] In the case of a helical coil, in particular at least one, and in particular each, of the oscillator coil, the first induction coil and the second induction coil may have a substantially cylindrical shape, and similarly, the cross-section of at least one, and in particular each, of the oscillator coil, the first induction coil and the second induction coil may be one of a circle, an ellipse, an oval, a rectangle, a square, a triangle, a polygon when viewed along the longitudinal axis of the coil.

[0019] The aerosol generating device may further comprise a magnetic flux concentrator for inductively coupling the oscillator coil to at least one of the first induction coil and the second induction coil. Advantageously, the magnetic flux concentrator increases the inductive coupling between these coils. The term "magnetic flux concentrator" as used herein refers to an element configured to concentrate the magnetic field, i.e. to distort the magnetic field such that the density of the magnetic field increases within a certain volume range. Thus, the magnetic flux concentrator is preferably configured to distort the magnetic field of the oscillator coil towards at least one of the regions of the magnetic field of the first induction coil and the region of the magnetic field of the second induction coil. Furthermore, the magnetic flux concentrator may be used to reduce the extent to which the magnetic field propagates beyond the various coils. That is, the magnetic flux concentrator preferably acts as a magnetic shield. Advantageously, this may reduce undesired heating of adjacent sensitive parts of the device (e.g. the metallic outer housing) or adjacent sensitive items outside the device. By reducing undesired heating losses, the efficiency of the aerosol generating device may be further improved.

[0020] The magnetic flux concentrator preferably has a high relative permeability, which acts to concentrate and guide the magnetic field or attic lines of force generated by the oscillator coil. The term "high relative permeability" as used herein refers to a relative permeability of at least 100, particularly at least 1000, preferably at least 10000, even more preferably at least 50000, and most preferably at least 80000. These exemplary values ​​refer to values ​​of relative permeability at DC and at a temperature of 25 degrees Celsius. Similarly, at frequencies between 6 MHz (megahertz) and 10 MHz (megahertz), and at a temperature of 25 degrees Celsius, the relative permeability is preferably 80. The term "relative permeability" as used herein and in the art refers to the ratio of the permeability of a material or medium, such as a magnetic flux concentrator, to the permeability of free space, "μ0", where μ0 is 4π·10-7N·A-2 (4·Pi·10E-07 Newtons per square ampere). Thus, the magnetic flux concentrator preferably comprises, and in particular is made of, a material having a relative permeability of at least 100, in particular at least 1000, preferably at least 10000, even more preferably at least 50000, and most preferably at least 80000. These values ​​also refer to the values ​​of relative permeability for DC and a temperature of 25 degrees Celsius. Similarly, at frequencies between 6 MHz (megahertz) and 10 MHz (megahertz) and a temperature of 25 degrees Celsius, the relative permeability is preferably 80.

[0021] The magnetic flux concentrator preferably comprises a ferrite material, such as, for example, ferrite particles, ferrite powder held in a matrix, or any other suitable material including a ferromagnetic material, such as ferritic iron, ferromagnetic steel, or stainless steel. The matrix may include a binder, such as a polymer (such as silicon). The ferromagnetic material may include at least one metal selected from iron, nickel, copper, molybdenum, manganese, silicon, and combinations thereof.

[0022] To drive the oscillator coil at or near the first resonant frequency or at or near the second resonant frequency, the drive oscillator circuit preferably comprises a single transistor switch selectively operable at or near the first resonant frequency or at or near the second resonant frequency. Advantageously, using a single transistor switch to drive multiple induction coils reduces the complexity of the drive oscillator circuit. Furthermore, using a single transistor switch is space-saving and therefore allows for a very compact design of the aerosol generating device.

[0023] The transistor switch may be any type of transistor. For example, the transistor switch may be embodied as a bipolar junction transistor (BJT). However, more preferably, the transistor switch is embodied as a field effect transistor (FET), such as a metal oxide semiconductor field effect transistor (MOSFET) or a metal semiconductor field effect transistor (MESFET).

[0024] The different resonant frequencies of the first and second LC resonator circuits can be realized in several ways. In general, the resonant frequency of an LC circuit including an induction coil and a capacitor is given by the formula f=1 / (2·π·square root [L·C]), where f is the resonant frequency in Hertz, L is the inductance of the induction coil in Henries, and C is the capacitance of the capacitor in Farads. A particular resonant frequency can therefore be realized by appropriate selection of the capacitance of the capacitor and the inductance of the induction coil. The inductance of the induction coil depends, among other things, on the number of windings and, in the case of a helical coil, for example, on the axial length and diameter of the coil. A particular inductance of the induction coil can therefore be realized by appropriate selection of the number of windings, the axial length, and the diameter of the coil. In general, this inductance increases with an increase in the number of windings. Similarly, the inductance decreases with an increase in the length or an increase in the diameter of the coil.

[0025] Thus, different resonant frequencies of the first LC resonator circuit and the second LC resonator circuit can be achieved by having at least one of the inductances of the first induction coil being different, in particular larger or smaller, than the inductance of the second induction coil, or the capacitance of the first capacitor being different, in particular larger or smaller than the capacitance of the second capacitor.

[0026] For example, it may be preferable to make the first induction coil and the second induction coil the same, and in particular, it may be preferable for the inductance of the first induction coil to be equal to the inductance of the second induction coil. In this case, the different resonant frequencies may be realized by the capacitance of the first capacitor of the first LC resonator circuit being smaller than the capacitance of the second capacitor of the second LC resonator circuit. Thus, the inductance of the first induction coil may be equal to the inductance of the second induction coil, and the capacitance of the first capacitor may be smaller or larger than the capacitance of the second capacitor. In particular, the capacitance of the first capacitor may be 2% (percent), preferably 5% (percent), more preferably 10% (percent) smaller or larger than the capacitance of the second capacitor. In particular, the capacitance of the second capacitor may be 2% (percent), preferably 5% (percent), more preferably 10% (percent) smaller or larger than the capacitance of the first capacitor.

[0027] Alternatively, the inductance of the first induction coil may be smaller or larger than the inductance of the second induction coil, in particular, twice as large, preferably ten times larger, and the capacitance of the first capacitor may be equal to the capacitance of the second capacitor.

[0028] Similarly, the inductance of the first induction coil may be different from, and in particular larger or smaller than, the inductance of the second induction coil, and the capacitance of the first capacitor may be different from, and in particular larger or smaller than, the capacitance of the second capacitor.

[0029] In one embodiment, the first induction coil may have seven windings and the second induction coil may have nine windings, such that the inductance of the first induction coil is less than the inductance of the second induction coil.

[0030] At least one of the first induction coil and the second induction coil may have an inductance in the range of 0.1 μH (microhenry) to 2 mH (millihenry), in particular 0.1 μH (microhenry) to 1 mH (millihenry), preferably 0.3 μH (microhenry) to 1.2 μH (microhenry), more preferably 0.6 μH (microhenry) to 0.9 μH (microhenry). Depending on the frequency of the magnetic field to be achieved, the capacitance values ​​of the first capacitor and the second capacitor may be selected correspondingly. Preferably, at least one of the first capacitor and the second capacitor has a capacitance in the range of 0.1 nF (nanofarad) to 20 μF (microfarad), in particular 1 nF (nanofarad) to 5 μF (microfarad), preferably 10 nF (nanofarad) to 1 μF (microfarad).

[0031] As further described above, the alternating magnetic fields of the first and second induction coils are used to inductively heat at least one susceptor, which in turn is disposed in thermal proximity or direct physical contact with a substrate, such as to heat the substrate. Generally, at least the susceptor may be either an integral part of the apparatus or an integral part of the aerosol-generating article that includes the aerosol-forming substrate to be heated, and is configured to be removably received within a cavity of the aerosol-generating device.

[0032] As part of the device, the at least one susceptor may be disposed at least partially within the cavity. Similarly, as part of the aerosol-generating article, the at least one susceptor may be disposable within the cavity of the aerosol-generating device after insertion of the article into the cavity of the device.

[0033] In particular, the aerosol generating device may comprise at least one susceptor, in particular one (single) susceptor or two susceptors.

[0034] In the case of a single susceptor, the susceptor is preferably disposed within the cavity such that a first portion of the susceptor is at least partially, preferably entirely, disposed within a first section of the cavity and a second portion of the susceptor is at least partially, preferably entirely, disposed within the second section, such that in use of the apparatus, the first portion of the susceptor is subjected to the magnetic field of the first induction coil and the second portion of the susceptor is subjected to the magnetic field of the second induction coil.

[0035] Similarly, when the aerosol generating device comprises a plurality of susceptors, in particular two susceptors, the device may comprise a first susceptor and a second susceptor. The first susceptor and the second susceptor are preferably disposed within the cavity such that the first susceptor is at least partially, preferably entirely, disposed within a first section of the cavity, and the second susceptor is at least partially, preferably entirely, disposed within a second section of the cavity. Thus, in use of the device, the first susceptor is subjected to the magnetic field of the first induction coil, and the second susceptor is subjected to the magnetic field of the second induction coil.

[0036] Advantageously, the first and second sections of a (single) susceptor, or the first and second susceptors, may be or may be disposable apart from each other within the aerosol-forming substrate(s) so as to heat different parts of the aerosol-forming substrate, in particular the first and second parts of the aerosol-forming substrate, or to heat different aerosol-forming substrates, in particular a first and a second aerosol-forming substrate that are discharged at different locations within the article.

[0037] The first susceptor and the second susceptor may form different parts, in particular the first susceptor and the second susceptor may be disposed or disposable within the aerosol-forming substrate separately from each other.

[0038] The term "susceptor" as used herein refers to an element that has the ability to convert electromagnetic energy into heat when subjected to an alternating electromagnetic field. This can be the result of hysteresis losses and / or eddy currents induced in the susceptor, depending on the electrical properties and magnetic properties of the susceptor material. Hysteresis losses occur in ferromagnetic or ferrimagnetic susceptors due to magnetic domains in the material that are switched under the influence of the alternating electromagnetic field. Eddy currents may be induced if the susceptor is conductive. In the case of conductive ferromagnetic or ferrimagnetic susceptors, heat can be generated by both eddy currents and hysteresis losses.

[0039] Thus, the at least one susceptor may be formed from any material that can be inductively heated to a temperature sufficient to generate an aerosol from the aerosol-forming substrate. The at least one susceptor may include metal or carbon. The at least one susceptor may include a ferromagnetic material, such as ferritic iron, or ferromagnetic steel or stainless steel. A preferred susceptor may be formed from 400 series stainless steel, such as grade 410, or grade 420, or grade 430 stainless steel. Another suitable susceptor may include aluminum.

[0040] The at least one susceptor may include a variety of geometric configurations. The at least one susceptor element may include or be a susceptor pin, susceptor rod, susceptor blade, susceptor strip, or susceptor plate. If the susceptor is part of an aerosol-generating device, the susceptor pin, susceptor rod, susceptor blade, susceptor strip, or susceptor plate may preferably protrude into a cavity of the device toward an opening of the cavity for inserting an aerosol-generating article into the cavity.

[0041] The at least one susceptor may include or be a filament susceptor, a mesh susceptor, or a wick susceptor.

[0042] Similarly, the at least one susceptor may include or be a susceptor sleeve, susceptor cup, cylindrical susceptor, or tubular susceptor. Preferably, an inner cavity of the susceptor sleeve, susceptor cup, cylindrical susceptor, or tubular susceptor is configured to removably receive at least a portion of the aerosol-forming substrate to be heated.

[0043] The susceptors described above may have any cross-sectional shape, such as, for example, circular, oval, square, rectangular, triangular, or any other suitable shape.

[0044] The term "aerosol generating device" as used herein generally refers to an electrically operated device capable of interacting with at least one aerosol-forming substrate, particularly an aerosol-forming substrate provided within an aerosol-generating article, to generate an aerosol by heating the substrate. The aerosol generating device is preferably a smoke extractor for generating an aerosol that can be directly inhaled by a user through the user's mouth. In particular, the aerosol generating device is a handheld aerosol generating device.

[0045] A control circuit according to the invention may form part of, or be the overall controller of, an aerosol generating device arranged to control the operation of the device. In particular, the controller may be arranged to control the operation of the induction heating process, in particular the induction heating of the aerosol-forming substrate to a predetermined operating temperature.

[0046] The operating temperature used for heating the aerosol-forming substrate may be at least 180°C, in particular at least 300°C, preferably at least 350°C, more preferably at least 370°C, and most preferably at least 400°C. These temperatures are typical operating temperatures for heating but not burning the aerosol-forming substrate. For example, the operating temperature may be in the range of 180°C to 370°C, in particular 180°C to 240°C, or 280°C to 370°C. In general, the operating temperature may depend on at least one of the type of aerosol-forming substrate to be heated, the configuration of the susceptor, and the arrangement of the susceptor relative to the aerosol-forming substrate in use of the system. For example, if the susceptor is configured and arranged to surround the aerosol-forming substrate in use of the system, the operating temperature may be in the range of 180°C to 240°C. Similarly, if the susceptor is configured to be arranged within the aerosol-forming substrate in use of the system, the operating temperature may be in the range of 280°C to 370°C.

[0047] The controller may comprise a microprocessor, such as a programmable microprocessor, a microcontroller, or an application specific integrated circuit chip (ASIC) or other electronic circuit capable of providing control.

[0048] The controller may be configured to generate and provide an alternating drive signal to the oscillator circuit, in particular to the single transistor switch (more specifically to the gate of the single transistor switch), to operate the oscillator circuit, in particular to the single transistor switch, at either a frequency close to or equal to the first resonant frequency or a frequency close to or equal to the second resonant frequency. That is, the controller may be configured to generate and provide the alternating drive signals at different frequencies, in particular at a first frequency close to or equal to the first resonant frequency or at a second frequency close to or equal to the second resonant frequency. For example, the controller may comprise a clock, or a voltage controlled oscillator, configured to provide the respective alternating drive signals.

[0049] The aerosol generating device may comprise a power source, in particular a DC power source configured to provide a DC supply voltage and a DC supply current to the controller. In particular, the DC voltage may be applied to the drain and source inputs of a single transistor switch. The power source is preferably a battery, such as a lithium iron phosphate battery. Alternatively, the power source may be another form of charge storage device, such as a capacitor. The power source may require recharging, i.e., the power source may be rechargeable. The power source may have a capacity that allows for storage of sufficient energy for one or more user experiences. For example, the power source may have a capacity sufficient to allow continuous generation of aerosol for about six minutes, or a multiple of six minutes. In another embodiment, the power source may have a capacity sufficient to allow a predetermined number of puffs, or discontinuous activation of the induction heating device.

[0050] The aerosol generating device may comprise a body preferably including at least one of the control circuitry, in particular the first and second induction coils, the first and second capacitors, the drive oscillator circuit, the oscillator coil, a single transistor switch (if present), a magnetic flux concentrator (if present), at least one susceptor (if present), a controller, a power source, and at least a portion of the cavity.

[0051] In addition to the main body, the aerosol generating device may further comprise a mouthpiece, especially if the aerosol generating article used with the device does not include a mouthpiece. The mouthpiece may be mounted on the main body of the device. The mouthpiece may be configured to close the cavity when the mouthpiece is attached to the main body. To attach the mouthpiece to the main body, the proximal end portion of the main body may comprise a magnetic or mechanical mount, e.g. a bayonet mount or a snap-fit ​​mount, that engages with a corresponding counterpart at the distal end portion of the mouthpiece. If the device does not comprise a mouthpiece, the aerosol generating article used with the aerosol generating device may comprise a mouthpiece, e.g. a filter segment.

[0052] The aerosol generating device may comprise at least one air outlet, for example an air outlet in the mouthpiece (if present).

[0053] The aerosol generating device preferably comprises an air path extending from the at least one air inlet, through the cavity, and optionally further to an air outlet in the mouthpiece, if any. The aerosol generating device preferably comprises at least one air inlet in fluid communication with the cavity. As a result, the aerosol generating system may comprise an air path extending from the at least one air inlet into the cavity, and optionally further through an aerosol-forming substrate in the article and the mouthpiece into the mouth of the user.

[0054] The first induction coil, the second induction coil, the first capacitor, the second capacitor, the oscillator coil, and the flux concentrator (if present) may form an induction module disposed within the device housing and forming at least a portion of the cavity of the device or disposed circumferentially therearound, in particular removably disposed therearound.

[0055] According to the present invention there is also provided an aerosol generating system comprising an aerosol generating device according to the present invention and as described herein. The system further comprises an aerosol-generating article for use with the device, the article comprising an aerosol-forming substrate inductively heated by the device. The aerosol-generating article is received or receivable at least partially within a cavity of the device.

[0056] As used herein, the term "aerosol generating system" refers to the combination of an aerosol generating article as further described herein and an aerosol generating device according to the present invention as described herein, in which the article and device cooperate to generate a respirable aerosol.

[0057] The term "aerosol-generating article" as used herein refers to an article comprising at least one aerosol-forming substrate that releases a volatile compound capable of forming an aerosol when heated. The aerosol-generating article is preferably a heated aerosol-generating article, i.e. an aerosol-generating article comprising at least one aerosol-forming substrate that is intended to be heated, rather than burned, to release a volatile compound capable of forming an aerosol. The aerosol-generating article may be a consumable product, in particular a consumable product that is discarded after a single use. For example, the article may be a cartridge that comprises a liquid aerosol-forming substrate that is heated. Alternatively, the article may be a rod-shaped article (in particular a tobacco article) that resembles a conventional cigarette.

[0058] The term "aerosol-forming substrate" as used herein means a substrate formed from or including an aerosol-forming material capable of releasing a volatile compound upon heating to form an aerosol. The aerosol-forming substrate is intended to be heated, not combusted, to release the aerosol-forming volatile compound. The aerosol-forming substrate may be a solid or liquid aerosol-forming substrate or a gel-like aerosol-forming substrate, or any combination thereof. For example, the aerosol-forming substrate may include solid and liquid components, or liquid and gel-like components, or solid and gel-like components, or liquid, solid and gel-like components. The aerosol-forming substrate may include a tobacco-containing material that contains volatile tobacco flavor compounds that are released from the substrate upon heating. Alternatively, or additionally, the aerosol-forming substrate may include a non-tobacco material. The aerosol-forming substrate may further include an aerosol former. Examples of suitable aerosol formers are glycerin, triacetin (glycerol triacetate) and propylene glycol. The aerosol-forming substrate may also contain other additives and ingredients such as nicotine or flavourants. The aerosol-forming substrate may also be a paste-like material, a sachet of porous material containing the aerosol-forming substrate, or loose tobacco, for example mixed with a gelling or adhesive agent, which may contain a common aerosol former such as glycerin, which is compressed or moulded into a plug.

[0059] As mentioned above, the at least one susceptor used to inductively heat the aerosol-forming substrate may be an integral part of the aerosol-generating article rather than being part of the aerosol-generating device. Thus, the aerosol-generating article may comprise at least one susceptor positioned in thermal proximity or thermal contact with the aerosol-forming substrate such that, in use, the susceptor can be inductively heated by the inductive heating device when the article is received in the cavity of the device. In particular, the aerosol-forming substrate may comprise one (single) susceptor or two susceptors.

[0060] In the case of a single susceptor, the susceptor may be disposed within the article such that, after insertion of the article into the cavity of the apparatus, a first portion of the susceptor is at least partially, preferably entirely, disposed within a first section of the cavity and a second portion of the susceptor is at least partially, preferably entirely, disposed within the second section. Thus, in use of the system, the first portion of the susceptor is subjected to the magnetic field of the first induction coil and the second portion of the susceptor is subjected to the magnetic field of the second induction coil.

[0061] Similarly, when the aerosol-generating article comprises a plurality of susceptors, in particular two susceptors, the article may comprise a first susceptor and a second susceptor. The first susceptor and the second susceptor may be disposed within the article such that, after insertion of the article into the cavity of the device, the first susceptor is disposed at least partially, preferably entirely, within a first section of the cavity, and the second susceptor is disposed at least partially, preferably entirely, within a second section of the cavity. Thus, in use of the system, the first susceptor is subjected to the magnetic field of the first induction coil, and the second susceptor is subjected to the magnetic field of the second induction coil. The first susceptor and the second susceptor may form different parts.

[0062] Advantageously, the first and second sections of a (single) susceptor, or the first and second susceptors, may be arranged apart from each other within the aerosol-forming substrate(s) so as to heat different parts of the aerosol-forming substrate, in particular the first and second parts of the aerosol-forming substrate, or to heat different aerosol-forming substrates, in particular a first and a second aerosol-forming substrate that are discharged at different locations within the article.

[0063] Thus, an aerosol-generating article may comprise a first and a second aerosol-forming substrate disposed at different locations within the article. In particular, the first and the second aerosol-forming substrate may differ from each other in at least one of content, composition, flavour, texture or state of matter (solid, gel-like, liquid).

[0064] Further features and advantages of the aerosol generating system according to the invention have been described in relation to the aerosol generating device and will not be repeated here.

[0065] Of course, the aerosol-generating device according to the invention and described herein may be configured to heat three aerosol-forming substrates or three or more portions of an aerosol-forming substrate separately. Thus, the aerosol-generating device according to the invention and described herein may comprise a plurality of induction coils, e.g., three, four, five or more induction coils, for generating respective alternating magnetic fields in three or more sections of the cavity in three, four, five or more sections. Thus, the aerosol-generating device may comprise three or more LC resonator circuits, one for each coil, each LC resonator circuit comprising one of the coils and a respective capacitor, each having a resonant frequency different from the resonant frequency of each of the other LC resonator circuits. Similarly, the driving oscillator circuit comprising the oscillator coil may be configured to selectively generate alternating magnetic oscillator fields at or near three or more frequencies, i.e. at or near the respective resonant frequencies of the different LC resonator circuits. Thus, the aerosol-generating article according to the invention and described herein may comprise three or more portions of an aerosol-forming substrate, e.g., three, four, five or more portions. Similarly, such an article may include three or more aerosol-forming substrates, e.g., three, four, five or more aerosol-forming substrates. Thus, if the susceptor is or is part of an aerosol-generating device, the article may include a susceptor having three or more portions, e.g., three, four, five or more portions. Similarly, the device may comprise three or more susceptors, e.g., three, four, five or more susceptors. Vice versa, if the susceptor is or is part of an aerosol-generating article, the article may include a susceptor having three or more portions, e.g., three, four, five or more portions. Similarly, the article may comprise three or more susceptors, e.g., three, four, five or more susceptors.

[0066] The invention will now be further described, by way of example only, with reference to the accompanying drawings in which: [Brief description of the drawings]

[0067] [Figure 1] FIG. 1 shows a schematic cross-sectional view of an aerosol generation system according to a first embodiment of the present invention. [Diagram 2] FIG. 2 illustrates, in a schematic manner, an exemplary embodiment of a control circuit that may be used in the aerosol generation system according to FIG. [Diagram 3] FIG. 3 shows a schematic cross-sectional view of an aerosol generation system according to a second embodiment of the present invention. [Figure 4] FIG. 4 shows a schematic cross-sectional view of an aerosol generation system according to a third embodiment of the present invention. [Diagram 5] FIG. 5 shows a schematic cross-sectional view of an aerosol generation system according to a fourth embodiment of the present invention.

[0068] 1 illustrates diagrammatically a first exemplary embodiment of an aerosol-generating system 1 according to the present invention. The system 1 is configured to generate an aerosol by inductively heating an aerosol-forming substrate 91, in particular in sections or portions. The system 1 comprises two main components: an aerosol-generating article 90 comprising the aerosol-forming substrate to be heated, and an aerosol-generating device 10 for use with the article 90. The device 10 comprises a cavity 20 for receiving the article 90 and an inductive heating device 30 for heating the substrate in the article 90 when the article 90 is inserted into the cavity 20.

[0069] The article 90 has a substantially rod-shaped shape substantially similar to that of a conventional cigarette. In this embodiment, the article 90 includes four elements arranged in a coaxial alignment: a substrate segment 91, a support segment 92, an aerosol cooling segment 94, and a filter segment 95. The substrate segment is arranged at the distal end of the article 90 and includes an aerosol-forming substrate 91 that is heated. The aerosol-forming substrate may include, for example, a crimped sheet of homogenized tobacco material that includes glycerin as an aerosol former. The support segment 92 includes a hollow core that forms a central air passage 93. The aerosol cooling segment 94 is used to cool the volatile components of the aerosol-forming substrate. The filter segment 95 functions as a mouthpiece and may include, for example, cellulose acetate fibers. All four elements are substantially cylindrical elements that are arranged consecutively one after the other. The segments have substantially the same diameter and are surrounded by an outer wrapper 99 made of cigarette paper to form a cylindrical rod.

[0070] The device 10 comprises a substantially rod-shaped main body 11 formed by a substantially cylindrical device housing. The device 10 comprises within a distal portion 13 a power source 16 (e.g. a lithium ion battery) and control circuitry 17 for controlling the operation of the device 10, in particular for controlling the induction heating process.

[0071] In the proximal portion 14 opposite the distal portion 13, the device 10 comprises a cavity 20. The cavity 20 is open at the proximal end 12 of the device 10, so that an item 90 can be easily inserted into the cavity 20. A bottom portion 25 of the cavity 20 separates the distal portion 13 of the device 10 from the proximal portion 14 of the device 10, and in particular from the cavity 20. The bottom portion 25 is preferably made of a thermally insulating material, such as, for example, PEEK (polyetheretherketone). Thus, the electrical components of the control circuitry 17 in the distal portion 13 can be kept isolated from heat, aerosols, or residues generated in the cavity 20 during heating of the substrate 91.

[0072] The aerosol-generating device 10 according to this embodiment is configured to heat the aerosol-forming substrate in sections, i.e. separately, different parts of the aerosol-forming substrate within the cross-section of the substrate segment 91. In this embodiment, the device 10 is configured to separately heat a first portion 96 and a section 97 of the aerosol-forming substrate. The imaginary separation of the aerosol-forming substrate into the first portion and the section portions 96, 97 is indicated by the dotted line 98 in Figure 1.

[0073] To separately heat the first portion and section portions 96, 97, the induction heating device 30 comprises a first induction coil 31 and a second induction coil 32. The first induction coil 31 is arranged and configured to generate an alternating magnetic field in the first section 21 of the cavity 20, and the second induction coil 32 is arranged and configured to generate an alternating magnetic field in the second section of the cavity 22. The first and second sections 21, 22 of the cavity 20 are assigned to the positions of the first portion and section portions 96, 97 of the aerosol-forming substrate when the aerosol-generating article 90 is received in the cavity 20.

[0074] The induction heating apparatus 30 further includes a susceptor 60 disposed within the cavity 20 such that a first portion 61 of the susceptor 60 is affected by an electromagnetic field generated by the first induction coil 31 and a second portion 62 of the susceptor 60 is affected by an electromagnetic field generated by the second induction coil 32.

[0075] In this embodiment, the susceptor 60 is a susceptor blade attached to the bottom portion 25 of the cavity 20 with its distal end. From there, the susceptor blade extends into the inner void of the cavity 20 toward the opening of the cavity 20 at the proximal end 12 of the apparatus 10. The other end, i.e., the free distal end, of the susceptor blade 60 is tapered to allow the susceptor blade to easily penetrate the aerosol-forming substrate in the distal end portion of the article 90. As can be seen in FIG. 1, when the aerosol-generating article 90 is received in the cavity 20, the first portion 61 of the susceptor 60 is disposed within the first portion 96 of the aerosol-forming substrate and the second portion 62 of the susceptor 60 is disposed within the second portion 97 of the substrate. Instead of a blade, the susceptor may be a susceptor pin or a susceptor rod.

[0076] Thus, when the first induction coil 31 is activated, an alternating electromagnetic field is generated substantially only in the first section 21 of the cavity 20. As a result, heating that generates eddy currents and / or hysteresis losses is induced substantially only in the first portion 61 of the susceptor 60, depending on the magnetic and electrical properties of the susceptor material. Thus, when the second induction coil 32 is inactive, only the first portion 61 of the susceptor 60 is substantially heated, while the second portion 62 of the susceptor 60 remains substantially unheated. Thus, only the first portion 96 of the substrate is heated to form an aerosol that can be drawn downstream through the aerosol-generating article 90 for inhalation by a user. Similarly, when the second induction coil 32 is activated, an alternating electromagnetic field is generated substantially only in the second section 22 of the cavity 20, and only the second portion 62 of the susceptor 60 is inductively heated, while the first portion 61 of the susceptor 60 remains substantially unheated. As a result, only the second portion 97 of the substrate is heated to form an aerosol that can be drawn downstream through the aerosol-generating article 90 for inhalation by a user.

[0077] In order to be able to activate the first induction coil 31 and the second induction coil 32 independently of each other and therefore selectively generate an alternating magnetic field in either the first section 21 or the second section 22 of the cavity 20, each coil 31, 32 is part of an LC resonator circuit having a distinct resonant frequency. Each LC resonator circuit is inductively coupled to a (common) driving oscillator coil 32 that is close to or can selectively operate at a distinct resonant frequency. That is, the invention is based on inductively driving the first and second induction coils 31, 32, but at a different driving frequency, so as to inductively decouple the operation of the first and second induction coils 31, 32 from each other.

[0078] Fig. 2 is a schematic diagram of an exemplary embodiment of a control circuit 18 that may be used in the aerosol generating system according to Fig. 1. According to the basic idea described above, the control circuit 18 comprises a first LC resonator circuit 51 and a second LC resonator circuit 52, the first LC resonator circuit 51 including a first induction coil 31 and a first capacitor 41, and the second LC resonator circuit 52 including a second induction coil 32 and a second capacitor 42. The first LC resonator circuit 51 has a first resonant frequency, while the second LC resonator circuit 52 has a second resonant frequency f2 different from the first resonant frequency f1. The control circuit 18 further comprises a drive oscillator circuit 35 comprising an oscillator coil 33 (also shown in Fig. 1) for selectively generating an alternating magnetic oscillator field either close to or at the first resonant frequency f1 or close to or at the second resonant frequency f2. The oscillator coil 33 is inductively coupled to both the first induction coil 31 and the second induction coil 32. However, due to the difference between the first resonant frequency f1 and the second resonant frequency f2, the alternating magnetic oscillator field generated by the oscillator coil 33 is substantially only coupled into the first induction coil 31 or the first LC resonator circuit 51, respectively, when the frequency of the magnetic oscillator field is close to or equal to the first resonant frequency f1 of the first LC resonator circuit 51. Vice versa, the alternating magnetic oscillator field generated by the oscillator coil 33 is substantially only coupled into the second induction coil 32 or the second LC resonator circuit 52, respectively, when the frequency of the magnetic oscillator field is close to or equal to the second resonant frequency f2 of the second LC resonator circuit 52.

[0079] 1, an alternating magnetic field is generated in the first section 21 of the cavity 20 when the oscillator field is close to or at a first resonant frequency f1 and therefore close to or resonating with the first LC resonator circuit 51. Similarly, an alternating magnetic field is generated in the second section 22 of the cavity 21 when the oscillator field is close to or at a second resonant frequency f2 and therefore close to or resonating with the second LC resonator circuit.

[0080] Advantageously, because the inactive coils are sufficiently off-resonance with respect to the current operating frequency of the oscillator coil 33, the difference between the first resonant frequency f1 and the second resonant frequency f2 also prevents the current induced by the active coils from flowing in the respective inactive coils.

[0081] Preferably, the difference between the first resonant frequency f1 and the second resonant frequency f2 is at least 40 kHz, in particular at least 100 kHz, preferably at least 100 kHz, more preferably at least 500 kHz, or at least 1 MHz. For example, the first resonant frequency is different from the second resonant frequency of 120 kHz. The first resonant frequency and the second resonant frequency are preferably selected within a range of 100 kHz to 30 MHz, in particular 5 MHz to 15 MHz, preferably 5 MHz to 10 MHz. For example, the first resonant frequency may be 150 kHz and the second resonant frequency may be 270 kHz.

[0082] The first induction coil 31 and the second induction coil 32 may have an inductance, for example, in the range of 0.3 μH (microhenry) to 1.2 μH (microhenry), preferably in the range of 0.6 μH (microhenry) to 0.9 μH (microhenry). Depending on the frequency of the magnetic field to be achieved, the capacitance values ​​of the first capacitor 41 and the second capacitor 42 may be selected correspondingly. Preferably, the first capacitor 41 and the second capacitor 42 have a capacitance in the range of 1 nF (nanofarad) to 10 μF (microfarad), in particular 10 nF (nanofarad) to 2 μF (microfarad).

[0083] To drive the oscillator coil 33 at or near the first resonant frequency f1 or at or near the second resonant frequency f2, the drive oscillator circuit 35 according to the embodiment shown in FIG. 2 comprises a single transistor switch 70 selectively operable at either or near the first resonant frequency f1 or near or near the second resonant frequency f2. In this embodiment, the switch 70 is a field effect transistor (FET) having a gate input 71 for controlling the gate terminal. The source input 72 and drain output 73 of the field effect transistor are in series with the oscillator coil 33 and a power supply 16, which may correspond to the power supply 16 shown in FIG. 1. Thus, by applying an alternating drive signal to the gate input 71 having a drive frequency at or near the first or second resonant frequency f1, f2, the oscillator coil 33 is alternately switched on and off at the drive frequency. By switching on and off, oscillator coil 32 generates a magnetic oscillator field close to or at first or second resonant frequencies f1, f2 due to changes in magnetic flux in oscillator coil 33. The alternating drive signal is illustrated diagrammatically in Figure 2 by two square wave signals having frequencies f1 and f2. Preferably, the alternating drive signal is generated and provided to oscillator circuit 35 by control 17 shown in Figure 1.

[0084] As can be seen in FIG. 1, the first and second induction coils 31, 32 are helical coils that circumferentially surround the first and second sections 21, 22 of the cylindrical cavity 20, respectively. The first induction coil 31 and the second induction coil 32 are each formed from a number of wire windings that extend along the length axis of the respective coil 31. The wire may have any suitable cross-sectional shape, such as square, oval, or triangular. In this embodiment, the wire has a circular cross-section. In other embodiments, the wire may have a flat cross-sectional shape. Essentially the same shape is maintained for the oscillator coil 33.

[0085] 1, the oscillator coil 33 is disposed coaxially with and partially around each of the first and second induction coils 31, 32. Advantageously, this further increases the overlap between the magnetic fields of the different coils and therefore increases the inductive coupling between the oscillator coil and each of the first and second induction coils.

[0086] Fig. 3 shows a schematic cross-sectional view of an aerosol-generating system 101 according to a second embodiment of the invention. The system 101 according to Fig. 3 is similar to the system 1 according to Fig. 1. Therefore, identical or similar features are indicated with the same reference numerals, and even with a reference numeral increased by 100. In contrast to the aerosol-generating system 1 according to the first embodiment, the system 101 according to the second embodiment comprises an aerosol-generating article 190, comprising a first aerosol-forming substrate 196 and a second aerosol-forming substrate 197, which are in turn arranged at a distal end portion of the article 190. The first and second aerosol-forming substrates 196, 197 differ from each other with respect to their composition and ingredients in order to enrich the user experience.

[0087] Further in contrast to the system 1 according to Fig. 1, the system 101 according to Fig. 3 comprises two susceptors which are not part of the aerosol-generating device 110 but rather part of the aerosol-generating article 190. The strip-like first susceptor 161 is arranged in a first aerosol-forming substrate 196. In a similar manner, the strip-like second susceptor 162 is arranged in a second aerosol-forming substrate 197. Both susceptors 161, 162 are centrally arranged in the respective aerosol-forming substrates extending substantially along the longitudinal central axis of the aerosol-generating article 190. In particular, the susceptors 161, 162 are formed as separate parts spaced apart from each other, which makes both susceptors 161, 162 thermally isolated from each other.

[0088] After insertion of the article 190 into the cavity 120 of the apparatus 110, the first susceptor 161 and the first aerosol-forming substrate 196 are disposed in the first section 121 of the cavity 120. Similarly, the second susceptor 162 and the second aerosol-forming substrate 197 are disposed in the second section 122 of the cavity 120. Thus, in use of the system 101, the first susceptor 161 is subjected to the magnetic field of the first induction coil 131, while the second susceptor 162 is subjected to the magnetic field of the second induction coil 132, allowing the first and second aerosol-forming substrates 196, 197 to be heated separately from each other.

[0089] The aerosol generating device 110 according to the second embodiment further differs from the device 10 according to the first embodiment by a magnetic flux concentrator 180 arranged coaxially around the first induction coil 131, the second induction coil 132 and the oscillator coil 133. In this embodiment, the magnetic flux concentrator 180 is a cylindrical element made of a material with high relative magnetic permeability, for example ferromagnetic stainless steel. The magnetic flux concentrator 180 is arranged and configured to distort the magnetic field of the oscillator coil 133 towards the region of the magnetic fields of the first induction coil 131 and the second induction coil 132, thereby increasing the magnetic coupling between the oscillator coil 133 and the first and second induction coils 131, 132. Furthermore, as mentioned above, the magnetic flux concentrator acts as a magnetic shield.

[0090] Apart from that, the aerosol generating device of FIG. 3 is identical to the device according to FIG.

[0091] Figure 4 shows a schematic cross-sectional view of an aerosol generation system 201 according to a third embodiment of the present invention. The system 201 according to Figure 4 is similar to the system 101 according to Figure 3. Therefore, identical or similar features are designated with the same reference numbers, and even with reference numbers increased by 100. In contrast to the aerosol generation system 101 according to the second embodiment, the system 201 according to the third embodiment comprises a first susceptor 261 and a second susceptor 262, which are part of the aerosol generation device 210 but are not part of the article 290. In this embodiment, the first and second susceptors 261, 262 are susceptor sleeves.

[0092] The sleeve-like first susceptor 261 is disposed on the inner surface of the cavity 220 within the outer periphery of the first section 221 of the cavity 220. Thus, in use of the apparatus 210, the first susceptor 261 is substantially only subjected to the magnetic field of the first induction coil 231, and similarly, the sleeve-like second susceptor 262 is disposed on the inner surface of the cavity 220 within the outer periphery of the second section 222 of the cavity 220. Thus, in use of the apparatus 210, the second susceptor 262 is substantially only subjected to the magnetic field of the second induction coil 232. In particular, the first and second susceptors 261, 262 are formed as separate parts spaced apart from each other, which thermally isolates both susceptors 261, 262 from each other.

[0093] 3, the first and second aerosol-forming substrates 296, 297 are disposed within the article 290 such that, after insertion of the article 290 into the cavity 220 of the device 210, the first aerosol-forming substrate 296 is disposed within the first section 221 of the cavity 220 and the second aerosol-forming substrate 297 is disposed within the second section 222 of the cavity 220. Thus, the first and second aerosol-forming substrates 296, 297 may be heated separately from each other.

[0094] Fig. 5 shows a schematic cross-sectional view of an aerosol-generating system 301 according to a fourth embodiment of the present invention. The system 301 according to Fig. 5 is very similar to the system 201 according to Fig. 4. Therefore, identical or similar features are designated with the same reference numbers, or even with a reference number increased by 100. In contrast to the third embodiment, the aerosol-generating device 310 according to the fourth embodiment comprises a single sleeve-like susceptor 360. The single sleeve-like susceptor 360 is arranged on the inner surface of the cavity 320 relative to the first induction coil 331 and the second induction coil 332 such that, in use, a first portion 361 of the susceptor 360 is subjected to the electromagnetic field generated by the first induction coil 331 and a second portion 362 of the susceptor 360 is subjected to the electromagnetic field generated by the second induction coil 332. Thus, the heating device 330 of the device 310 can be used to heat different portions of the aerosol-forming substrate 391 separately. That is, when the article 390 is inserted into the cavity 320 and the first induction coil 331 is activated, the first portion 361 of the susceptor 360 heats the first portion 396 of the aerosol-forming substrate. Similarly, when the second induction coil 332 is activated, the second portion 362 of the susceptor 360 heats the second portion 397 of the aerosol-forming substrate 391.

[0095] 1, 3 and 4, the aerosol-generating article 390 according to Fig. 5 does not include a support segment. Instead, the article according to Fig. 5 comprises a substrate segment 391 including an aerosol-forming substrate to be heated, an aerosol-cooling segment 392 adjacent to the substrate segment 391 for cooling volatile components of the aerosol-forming substrate, a filter segment 394 adjacent to the aerosol-cooling segment 392 for filtering volatile components of the aerosol-forming substrate, and an oral end segment 395 adjacent to the filter segment 394 for receipt in the mouth of a user. Furthermore, the article 390 may comprise an end member (not shown) at its distal end opposite the proximal end, i.e. opposite the oral end segment 395.

[0096] For example, the substrate segment 391 may include an aerosol-forming substrate including homogenized tobacco strands and an aerosol former, such as, for example, glycerol (glycerin), propylene glycol, triacetin (glycerin triacetate), or combinations thereof.

[0097] The cooling segment 392 may comprise a hollow tube defining an air passage through which the volatile constituents of the heated aerosol-forming substrate flow and cool. The thickness of the tube wall may be, for example, 0.29 millimeters. The length of the cooling segment 392 is preferably such that when the article 390 is fully inserted into the device 310, the cooling segment 392 is partially inserted into the cavity 320. The length of the cooling segment 392 may be between 20 millimeters and 30 millimeters, in particular between 23 millimeters and 27 millimeters, preferably between 25 millimeters and 27 millimeters, for example 25 millimeters. The cooling segment 392 may be made of paper, for example a spirally wound paper tube.

[0098] The filter segment 394 may be formed of any filter material sufficient to remove one or more compounds volatilized from the aerosol-forming substrate. For example, the filter segment 394 may be made of a monoacetate material, such as cellulose acetate. One or more flavorants may be added to the filter segment 394, either by injecting a flavored liquid directly into the filter segment 394, or by embedding or disposing one or more flavored frangible capsules or other flavored carriers, for example, within the cellulose acetate tow of the filter segment 394. The length of the filter segment 394 may be between 6 millimeters and 10 millimeters, for example, 8 millimeters.

[0099] The mouth end segment 395 serves the function of preventing any liquid condensate that accumulates at the outlet of the filter segment 394 from coming into direct contact with the user. Similar to the cooling segment 392, the mouth end segment 395 may comprise a hollow tube, in particular an annular tube, that defines an air passage for the volatile components of the heated aerosol-forming substrate flowing therethrough. The length of the mouth end segment 395 may be between 6 millimeters and 10 millimeters, for example 8 millimeters. The mouth end segment 395 may be made of paper, for example a spirally wound paper tube. The tube wall thickness may be, for example, 0.29 millimeters.

[0100] Additionally, the aerosol-generating article 390 according to FIG. 5 includes a vent region that allows air to flow from the exterior of the article 390 to the interior of the article 390. For example, the vent region may take the form of one or more vent holes formed through an outer layer of the article 390. In particular, the vent region comprises one or more rows of vent holes, each row of holes being disposed circumferentially around the article 390 in a cross section substantially perpendicular to the longitudinal axis of the article 390. Each row of vent holes may have 12 to 36 vent holes. The vent holes may, for example, be 100 to 500 micrometers in diameter. The axial separation between the rows of vent holes may be 0.25 millimeters to 0.75 millimeters, for example 0.5 millimeters. In this embodiment, the vent region comprises two rows of vent holes 393, each row being disposed circumferentially around the article 390. As can be seen in FIG. 5, the vent holes 393 are located within the cooling segment 392 to aid in aerosol cooling. In particular, vent 393 is disposed such that when article 390 is received within cavity 320, vent 393 is located outside cavity 320, thereby permitting unheated air to enter article 390 from the outside through vent 393. For example, vent 393 may be located at least 11 millimeters, and particularly 17-20 millimeters from the proximal end of article 390. In any case, the location of the vent is preferably selected such that a user does not block vent 393 during use.

[0101] It will be appreciated that the above-mentioned ventilation areas, and in particular the one or more ventilation holes described above, may also be provided in the aerosol-generating articles 90, 190, and 290 shown in FIGS.

[0102] The cooling segment 392, the filter segment 394 and the mouth end segment 395 may collectively comprise a filter assembly. For example, the overall length of the filter assembly may be between 37 millimeters and 45 millimeters. Preferably, the overall length of the filter assembly is about 41 millimeters. The length of the substrate segment 391 may be between 34 millimeters and 50 millimeters, preferably between 38 millimeters and 46 millimeters, for example, 42 millimeters. The overall length of the article 390 may be between 71 millimeters and 95 millimeters, preferably between 79 millimeters and 87 millimeters, for example, about 83 millimeters.

[0103] As with the other embodiments shown in Figures 1, 3, and 4, all segments 391, 392, 394, and 395 of article 390 according to Figure 5 have substantially the same diameter and are surrounded by an outer wrapper 399 made of cigarette paper, such as to form a cylindrical rod.

Claims

1. 1. An aerosol generating apparatus for generating an aerosol by inductive heating of an aerosol-forming substrate, said apparatus comprising: a device housing having a cavity configured to removably receive the aerosol-forming substrate to be heated; at least a first induction coil and a second induction coil, the first induction coil arranged and configured to generate an alternating magnetic field in a first section of the cavity and the second induction coil arranged and configured to generate an alternating magnetic field in a second section of the cavity; a control circuit for selectively driving the first induction coil and the second induction coil to selectively generate an alternating magnetic field in the first section and the second section, respectively; the control circuit comprises a first LC resonator circuit including the first induction coil and a first capacitor, and a second LC resonator circuit including the second induction coil and a second capacitor, the first LC resonator circuit having a first resonant frequency, and the second LC resonator circuit having a second resonant frequency different from the first resonant frequency; the control circuit further comprises a drive oscillator circuit comprising a common oscillator coil for selectively generating an alternating magnetic oscillator field having a frequency either close to or at the first resonant frequency or close to or at the second resonant frequency, the common oscillator coil inductively coupled to the first induction coil and the second induction coil such that an alternating magnetic field is generated in the first section when the frequency of the oscillator field is close to or at the first resonant frequency and thus close to or in resonance with a first LC resonator circuit, and an alternating magnetic field is generated in the second section when the frequency of the oscillator field is close to or at the second resonant frequency and thus close to or in resonance with the second LC resonator circuit.

2. The apparatus of claim 1 , wherein the first resonant frequency is within 1 percent to 20 percent of the second resonant frequency.

3. 3. The apparatus of claim 1, wherein the first resonant frequency differs from the second resonant frequency by at least 40 kHz.

4. The apparatus of any one of claims 1 to 3, wherein the first resonant frequency and the second resonant frequency are in the range of 100 kHz to 30 MHz, in the range of 5 MHz to 15 MHz, or in the range of 5 MHz to 10 MHz.

5. The apparatus of any one of claims 1 to 4, wherein the common oscillator coil is disposed coaxially with each of the first induction coil and the second induction coil.

6. The apparatus of any one of claims 1 to 5, wherein the common oscillator coil, the first induction coil and the second induction coil are helical coils.

7. The apparatus of any one of claims 1 to 6, wherein the common oscillator coil at least partially surrounds each of the first induction coil and the second induction coil.

8. 8. Apparatus according to any one of claims 1 to 7, wherein the drive oscillator circuit comprises a single transistor switch selectively operable at either the first resonant frequency or the second resonant frequency to drive the common oscillator coil at either the first resonant frequency or the second resonant frequency.

9. The apparatus of any one of claims 1 to 8, wherein at least one of the first capacitor and the second capacitor has a capacitance in the range of 1 nF to 10 μF.

10. 10. The apparatus of claim 1, wherein an inductance of the first induction coil is equal to an inductance of the second induction coil, and a capacitance of the first capacitor is smaller or larger than a capacitance of the second capacitor.

11. The apparatus of any one of claims 1 to 10, wherein at least one of the first LC resonator circuit and the second LC resonator circuit has a quality factor in the range of 2 to 50.

12. The apparatus of any one of claims 1 to 11, further comprising a flux concentrator for inductively coupling the common oscillator coil to the first induction coil and the second induction coil.

13. The apparatus of any one of claims 1 to 12, further comprising at least one susceptor at least partially disposed within the cavity and surrounded by the first and second induction coils.

14. 14. An aerosol generation system comprising an aerosol generating device according to any one of claims 1 to 13 and an aerosol-generating article at least partially received or receivable in the cavity of the device, the aerosol-generating article comprising at least one aerosol-forming substrate that can be heated.

15. The system described in claim 14, which cites claim 13, wherein the aerosol-generating article comprises at least one susceptor positioned in thermal proximity or thermal contact with at least one aerosol-forming substrate such that, in use, the susceptor can be inductively heated by the aerosol-generating device when the aerosol-generating article is received in the cavity of the device.

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