Aerosol generating device with induction heater

Abstract

A method of operating an aerosol generating device is described, the device comprising a heating chamber (18) configured to receive an aerosol-generating article (100) and an induction heater comprising an induction coil (36) operable to provide an alternating magnetic field to the heating chamber (18) to induce eddy currents in a susceptor (40) located within the heating chamber (18). The method includes (a) applying an alternating current at an applied frequency to the induction coil (36), (b) measuring a characteristic indicative of the impedance of the induction coil (36) while moving the susceptor (40) located within the heating chamber (18) through a predetermined motion, (c) using the measured characteristic to determine a minimum baseline impedance of the induction coil (36) and a maximum baseline impedance of the induction coil (36), (d) measuring a characteristic indicative of the operating impedance of the induction coil (36), and (e) using the operating impedance to set a power delivered by the induction coil (36).

Description

[Technical field]

[0001] The present disclosure generally relates to an aerosol generating device for heating an aerosol-generating substrate to generate an aerosol that is inhaled by a user of the aerosol generating device. The present disclosure is particularly applicable to portable (handheld) aerosol generating devices. Such devices heat the aerosol-generating substrate, e.g., tobacco or other suitable material, by conduction, convection, and / or radiation, rather than by combustion, to generate an aerosol that is inhaled by a user of the aerosol generating device. [Background technology]

[0002] In recent years, risk-reducing or risk-modifying devices (also known as aerosol-generating or vapor-generating devices) have rapidly increased in popularity and use as alternatives to the use of traditional tobacco products. A variety of devices and systems are available that heat or warm an aerosol-generating substance to generate an aerosol that is inhaled by the user.

[0003] A commonly available risk reduction or risk modification device is the substrate heated aerosol generating device or so-called heated non-combustion device. This type of device generates an aerosol or vapour by heating an aerosol-generating substrate, typically to a temperature in the range of 150° C. to 300° C. Heating the aerosol-generating substrate to a temperature in this range, without burning or combusting the aerosol-generating substrate, generates a vapour which is typically cooled and condensed to form an aerosol which is inhaled by the user of the device.

[0004] Currently available aerosol-generating devices can provide heat to the aerosol-generating substrate using one of several different techniques. One such technique employs an induction heating system. In such devices, an induction coil is provided within the device and an inductively heatable susceptor is provided to heat the aerosol-generating substrate. When a user activates the device, electrical energy is supplied to the induction coil, which in turn generates an alternating electromagnetic field. The susceptor couples with the electromagnetic field to generate heat, which is transferred, for example by conduction, to the aerosol-generating substrate, which heats up and generates an aerosol. The susceptor may surround the aerosol-generating substrate to transfer heat to the exterior surface of the aerosol-generating substrate. Alternatively, the susceptor may be embedded in the aerosol-generating substrate.

[0005] In most such aerosol generating devices, the heater operates in a predetermined manner when commanded to start, for example, in response to a user pressing a start button or in response to the device determining via an airflow sensor that the user has inhaled a puff through the device. Some aerosol generating devices allow the user to select various power levels or heating profiles according to personal preference. Such selection is typically made via a user interface on the aerosol generating device or a connected device. Summary of the Invention [Means for solving the problem]

[0006] According to a first aspect of the present invention there is provided a method of operating an aerosol generating device, the aerosol generating device comprising: a heating chamber configured to receive an aerosol-generating article; an induction heater comprising an induction coil operable to provide an alternating magnetic field to the heating chamber to induce eddy currents in a susceptor located within the heating chamber; Equipped with The method is: (a) applying an alternating current of an applied frequency to an induction coil; (b) measuring a characteristic indicative of impedance of the induction coil while moving a susceptor located within the heating chamber in a predetermined motion; (c) determining, using the measured characteristic, a minimum reference impedance of the induction coil and a maximum reference impedance of the induction coil, the minimum reference impedance being associated with a first position within the predetermined range of motion and the maximum impedance being associated with a second position within the predetermined range of motion; (d) measuring a characteristic indicative of the operational impedance of the induction coil while a susceptor located within the heating chamber is maintained at a user-selected position within a predetermined range of motion; (e) using the operating impedance to set the power delivered by the induction coil; A method is provided, comprising:

[0007] The maximum reference impedance corresponds to a first position of the susceptor selected from a range of possible positions allowed within the predetermined range of motion. Similarly, the minimum reference impedance corresponds to a second position of the susceptor within the predetermined range of motion. In use, a user of the device can select whether to place the susceptor in the first position or the second position, or in a third position different from both the first and second positions. In accordance with the method described above, the controller sets the power delivered by the induction coil using the measured operating impedance determined by the user-selected position of the aerosol-generating article. Thus, a user can easily and intuitively set the power delivered by the induction coil by moving the aerosol-generating article in the heating chamber to a user-selected position.

[0008] The predetermined motion refers to a motion of the susceptor that can be actuated by a user in a consistent and repeatable manner. The predetermined motion can be, for example, a rotation through 360 degrees or more. Rotating the susceptor one complete revolution within the heating chamber ensures measurement of the full range of impedance values ​​of the coil. Furthermore, the rotation is an intuitive motion for the user that can be easily and consistently repeated.

[0009] The susceptor may be asymmetric under a given motion; that is, the susceptor may have a shape that is asymmetric under a given motion. Such asymmetry may result in a large change in the measured impedance. For example, the susceptor may be helical and selected to have the same pitch as the induction coil. Again, this may result in a large change in the measured impedance (note that a helix is ​​asymmetric under rotation).

[0010] The applied frequency may be greater than 1 MHz, for example in the range of 1 to 15 MHz, 1 to 12 MHz, or 1 to 10 MHz.

[0011] The method may further include providing an indication to the user indicating the power set in step (e). The indication may be provided via a user interface such as one or more LEDs or a screen of the aerosol generating device or a connected device.

[0012] Using the operating impedance to set the power delivered by the induction coil may include determining a scaling factor by comparing the operating impedance to one or both of a maximum reference impedance and a minimum reference impedance, and scaling the power delivered by the induction coil using the determined scaling factor.

[0013] The method may further include detecting insertion of the susceptor into the heating chamber, detecting movement of the susceptor in a predetermined motion, and automatically operating the method of steps (b)-(e).

[0014] A characteristic indicative of impedance may be continuously measured in step (b). The measurement may be made by comparing the impedance of the coil with a known reference impedance.

[0015] According to a second aspect of the present invention there is provided an aerosol generating device comprising: a heating chamber configured to receive an aerosol-generating article; an induction heater comprising an induction coil operable to provide an alternating magnetic field to the heating chamber to induce eddy currents in a susceptor located within the heating chamber; A controller, (a) An alternating current of an applied frequency is applied to an induction coil; (b) measuring a characteristic indicative of impedance of the induction coil while moving a susceptor located within the heating chamber in a predetermined motion; (c) using the measured characteristic to determine a minimum reference impedance of the induction coil and a maximum reference impedance of the induction coil, the minimum reference impedance being associated with a first position within the predetermined range of motion and the maximum impedance being associated with a second position within the predetermined range of motion; (d) measuring a characteristic indicative of the operational impedance of the induction coil while a susceptor located within the heating chamber is maintained at a user-selected position within a predetermined range of motion; (e) Using the operating impedance to set the power delivered by the induction coil With a controller configured like this: An aerosol generating device is provided, comprising:

[0016] The aerosol generating device of the second aspect of the invention may further comprise any of the optional features of the first aspect of the invention.

[0017] According to a third aspect of the present invention, there is provided an aerosol generation system comprising an aerosol generating device according to the second aspect of the present invention and an aerosol-generating article comprising an asymmetric susceptor.

[0018] The induction coil may be a helical coil having a coil pitch, and the asymmetric susceptor may include a helical susceptor having a susceptor pitch, the susceptor pitch being substantially the same as the coil pitch.

[0019] The asymmetric susceptor may include a first susceptor and a secondary susceptor, the secondary susceptor being smaller than the first susceptor such that the heating effect provided by the secondary susceptor is negligible compared to the heating effect provided by the primary susceptor.

[0020] The features of the above aspects of the invention may be combined with each other, as well as with selected features from the present description, unless expressly stated otherwise.

[0021] The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0022] [Figure 1] 1 is a schematic cross-sectional view of an aerosol generating system comprising an aerosol generating device and an aerosol-generating article positioned within a heating chamber of the aerosol generating device. [Diagram 2] FIG. 1 is a schematic diagram of an induction coil, a helical susceptor, and a heating controller isolated from the aerosol generating device. [Diagram 3] Cross-sectional views of a helical susceptor in an induction coil are shown when (A) it is in phase (0 degrees), (B) it is completely out of phase (180 degrees), and (C) it is partially out of phase (90 degrees). [Figure 4] 1 is a schematic diagram illustrating exemplary magnetic flux lines around an induction coil. [Figure 5A] 1 illustrates the change in magnetic flux density when a helical susceptor is (A) in phase with an induction coil, and (B) 180 degrees out of phase with the same induction coil. [Figure 5B]1 illustrates the change in magnetic flux density when a helical susceptor is (A) in phase with an induction coil, and (B) 180 degrees out of phase with the same induction coil. [Figure 6] 1 illustrates a method for calibrating an aerosol generating device. [Figure 7] 4 shows the change in impedance measured during the calibration method. [Figure 8] 1 illustrates a schematic representation of an alternative susceptor. [Figure 9] A further alternative susceptor is shown. [Figure 10] 1 is a flow chart illustrating a method of operating an aerosol generating device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] 1, there is shown a schematic diagram of an example aerosol generating system 1. The aerosol generating system 1 comprises an aerosol generating device 10 and an aerosol generating article 100 for use with the device 10. The aerosol generating device 10 can have any shape that is compatible with the components described in the various embodiments set forth herein and is sized to be held comfortably in one hand by a user without assistance.

[0024] A first end 14 of the aerosol generating device 10, shown on the bottom side of Figure 1, is for convenience described as the distal, bottom, base or lower end of the aerosol generating device 10. A second end 16 of the aerosol generating device 10, shown on the top side of Figure 1, is described as the proximal, apical or upper end of the aerosol generating device 10. During use, a user typically orients the aerosol generating device 10 with the first end 14 facing downward and / or in a distal position relative to the user's mouth and the second end 16 facing upward and / or in a proximal position relative to the user's mouth.

[0025] The aerosol generating device 10 comprises a heating chamber 18. The heating chamber 18 defines an interior volume in the form of a cavity 20 having a generally cylindrical cross-section for receiving an aerosol generating article 100. The cavity 20 of the heating chamber 18 opens towards the second end 16 of the aerosol generating device 10. The heating chamber 18 comprises an induction heater, such as an induction coil 36, for heating the aerosol generating article 100 received within the cavity 20. The heating chamber 18 has a longitudinal axis defining a length and is formed from a heat resistant plastic material, such as polyetheretherketone (PEEK).

[0026] The aerosol generating device 10 further comprises a power source 22, e.g., one or more batteries, which may be rechargeable, and a controller 24 that couples the power source to the heater. The controller 24 may also be connected to a user interface 23 that may comprise an input, such as a power button, for receiving commands from a user, and / or an output, such as an indicator light, a display screen, or an audible or vibrating alarm, for providing information to the user. The controller may also be interfaced with an antenna 25 for input and output, as well as for wireless communication with a remote device, such as a user's smartphone, that may be used to relay data between the aerosol generating device 10 and its manufacturer.

[0027] The heating chamber 18, and specifically the cavity 20, is arranged to receive a correspondingly shaped, generally cylindrical or rod-shaped aerosol-generating article 100. Typically, the aerosol-generating article 100 comprises a pre-packaged aerosol-generating substrate 102. The aerosol-generating article 100 is a disposable and replaceable article (also known as a "consumable") that may, for example, contain tobacco as the aerosol-generating substrate 102. The aerosol-generating article 100 has a proximal end 104 (or mouth end) and a distal end 106. The distal end 106 is inserted into the heating chamber 18 of the aerosol generating device 10 such that at least the aerosol-generating substrate 102 is contained within the heating chamber 18. The aerosol-generating article 100 further comprises a mouthpiece segment 108 positioned downstream of the aerosol-generating substrate 102. At least a portion of the mouthpiece segment 108 protrudes from the heating chamber 18 such that the proximal end 104 of the aerosol-generating article 100 is accessible to enter a user's mouth. When the aerosol generating device 10 applies heat to the aerosol-generating article 100, heated vapor is emitted from the aerosol-generating substrate 102. As inhalation by a user draws air towards the proximal end 104 of the aerosol-generating article 100, the vapor cools and condenses as it passes through the mouthpiece segment 108 to form an aerosol having suitable properties for inhalation. The mouthpiece segment 108 may further comprise a filter (not shown) that removes particles or droplets above a certain size from the airflow.

[0028] The aerosol-generating substrate 102 and mouthpiece segment 108 are coaxially aligned and positioned within a wrapper 110 (e.g., a paper wrapper) to hold the components in place and form the rod-shaped aerosol-generating article 100. The wrapper 110 typically does not cover the ends 104, 106 of the aerosol-generating article 100 so that air can flow through the aerosol-generating article 100 from the distal end 106 to the proximal end 104.

[0029] In the illustrated embodiment of the invention, the heating chamber 18 has an open end 26 and a closed base 32. That is, the heating chamber 18 is cup-shaped. This ensures that air drawn from the open end 26 is directed through the aerosol-generating substrate 102.

[0030] As mentioned above, in the example shown in Figure 1, an induction heater is provided for heating the aerosol-generating article 100 received within the cavity 20. An induction coil 36, specifically a helical induction coil, surrounds and is spaced from the cavity 20. A means for mounting the induction coil 36 is typically attached to the outer wall of the heating chamber 18. A heating controller 38 controls the supply of power from the power source 22 to the induction coil 36. The controller 38 includes, among other electronic components, an inverter arranged to convert direct current from the power source 22 to alternating high frequency current for the induction coil 36.

[0031] The susceptor 40 is located within the cavity 20 of the heating chamber 18. Typically, the susceptor 40 includes one or more elements disposed in contact with or in close proximity to the aerosol-generating substrate 102 of the aerosol-generating article 100 received within the cavity 20. When the heating controller 38 supplies power to the heating coil 36 at an appropriate frequency, the heating coil 36 generates an alternating magnetic field, which induces a current flow in the susceptor 40. The material and construction of the susceptor 40 are selected such that the eddy currents induced in the susceptor 40 dissipate the power as heat. The heat is transferred by conduction, convection, and / or radiation to the substrate 102 of the aerosol-generating article 100, vaporizing the volatile material in the substrate 102. The volatile material is entrained in the airflow drawn through the aerosol-generating article to form an aerosol that can be inhaled by a user as previously described.

[0032] The susceptor 40 may be formed from any suitable material, such as a ferromagnetic metal, that generates eddy currents under the influence of an alternating magnetic field to produce a heating effect sufficient to generate an aerosol from the aerosol-forming substrate. Non-limiting exemplary materials include carbon steel, stainless steel, and aluminum.

[0033] In this example, the susceptor 40 is shown included within the aerosol-generating article 100 such that it is in physical contact with the aerosol-generating substrate 102 .

[0034] As shown in Figure 2, the heating controller 38 includes a power control subsystem 42 and a measurement subsystem 44. The heating controller further includes a memory 46. The power control subsystem 42 is operable to control the operation of the induction coil to deliver an alternating magnetic field to the susceptor. The measurement subsystem 44 is operable to measure the impedance (or a characteristic representative of the impedance) of the induction coil while the coil is energized. Measurements made by the measurement subsystem 44 and / or power delivery control instructions may be stored in the memory 46.

[0035] Applicant recognizes that the impedance of an induction coil is affected not only by the coil itself, but also by the geometrical characteristics of the susceptor when it is placed in the electromagnetic (EM) field generated by the coil. In general, the magnetic flux density around the induction coil is non-uniform, as shown diagrammatically in FIG. 4. This means that the placement of the susceptor relative to the EM field will result in different coupling effects depending on where the susceptor is located in the EM field. These coupling effects include the generation of eddy currents in the susceptor, which induce their own EM fields and affect the impedance of the induction coil in the device (in addition to causing heating of the susceptor, as described above). Thus, moving the susceptor into the EM field generated by the induction coil changes the coupling effect between the susceptor and the coil. This change, in turn, changes how the eddy currents affect the impedance of the induction coil. This change in impedance can be measured, for example, by comparing the detected coil impedance to a known reference impedance.

[0036] 10, a method of operating the aerosol generating device 10 is described. In step 1010, the controller 24 (more specifically, the power control subsystem 42 of the heating controller 38) is operable to apply an alternating current of an applied frequency to the induction coil 36 of the aerosol generating device. In step 1012, the controller 24 (more specifically, the measurement subsystem 44 of the heating controller 38) is operable to measure a characteristic indicative of the impedance of the induction coil 36 while moving the susceptor 40 located in the heating chamber 18 in a predetermined motion. In step 1014, a minimum reference impedance of the induction coil 36 and a maximum reference impedance of the induction coil 36 are determined using the measured impedance (or the measured characteristic, as the case may be). Steps 1012 and 1014 may be considered a calibration phase in which the relative change in the impedance of the induction coil is measured when moving the susceptor in a predetermined motion. Some or all of the measurement data, particularly the determined maximum and minimum reference impedance values, may be stored in the memory 46.

[0037] In step 1016, the controller 24 (more specifically, the measurement subsystem 44 of the heating controller 38) measures the operating impedance (or, optionally, a characteristic indicative of said operating impedance) of the induction coil 36. Finally, in step 1018, the controller 24 (more specifically, the power control subsystem 42 of the heating controller 38) uses the measured operating impedance to set the power delivered by the induction coil 36.

[0038] Thus, the controller 24 utilizes the change in coupling effect described above to set the power delivered by the coil in response to the measured operating impedance of the susceptor. Operating impedance refers to the impedance when the susceptor is stationary in the position where the user intends to operate the aerosol generating device. The operating impedance can be compared to stored impedance information measured when the susceptor is moved in a predetermined motion, and a scaling factor can be determined that expresses the operating impedance as a percentage of the maximum measured impedance. This scaling factor is used to set the power delivered by the induction heater.

[0039] In other words, the controller uses the measured impedance to determine a first position of the susceptor within a predetermined range of movement that corresponds to a maximum base impedance, and a second position of the susceptor within a predetermined range of movement that corresponds to a minimum base impedance. The first position may correspond to, for example, 100% power delivery, and the second position may correspond to a reduced power delivery, for example, 50%, 60%, or 70%. In use, a user of the device has the option of placing the susceptor in any position. This may be the first position, the second position, or a third position that is different from both the first and second positions. In the third position, power may be delivered at a scaled percentage between 100% and a minimum value (for example, 60%) depending on a scaling factor determined by comparing the operating impedance at the third position to the maximum measured impedance. The controller 24 measures the operating impedance to identify a position selected by the user and sets the power based on the selected position.

[0040] The user interface 23 (if present) is operable to indicate to the user which power profile has been selected. For example, one or more LED indicators may increase in brightness or be selectively illuminated upon increasing power delivery. This allows the user to know whether the aerosol-generating article is in a first (maximum) position, a second (minimum) position, or an intermediate third position.

[0041] It should be noted that the changing coupling effects occurring during susceptor movement are not in themselves large enough to inherently result in the temperature change achieved by the susceptor: this must be done separately by firmware in the power control subsystem 42 as a function of the measured operating impedance relative to the maximum / minimum reference impedance.

[0042] The change in measured impedance described above may be greater if the susceptor 40 is asymmetric (e.g., asymmetric in shape under a given motion). Thus, providing an asymmetric susceptor may facilitate and / or simplify measurements in the power control methods described above.

[0043] 2 and 3 show an example of the induction coil 36 and the susceptor 40 in more detail. The induction coil 36 is a helical coil having a coil pitch p1 (see FIG. 3). The susceptor 40 is an asymmetric susceptor. Specifically, the susceptor 40 is a helical susceptor having a susceptor pitch p2. It will be understood that the pitch of a helix is ​​the height of one complete helix turn, measured parallel to the longitudinal axis of the helix. In the illustrated example, p1 is approximately equal to p2, i.e., the induction coil 36 and the susceptor 40 have the same (or approximately the same) pitch.

[0044] The induction coil also has a coil diameter (which is the diameter of the entire coil) and a wire diameter (which is the diameter of the wire that forms the windings of the coil). Similarly, the susceptor 40 has a susceptor diameter that is smaller than the coil diameter such that the susceptor 40, when incorporated into the aerosol-generating article 100, can fit comfortably within the induction coil 36 that surrounds the heating chamber 20.

[0045] The susceptor 40, in this example, is a metal tape. The height of the metal tape may be comparable to or less than the wire diameter of the induction coil 36. Such a helical or spiral susceptor shape approximates a thin-walled cylinder.

[0046] To make an aerosol-generating article 100 incorporating such a susceptor, a flat, thin metal tape, e.g., carbon steel, stainless steel, aluminum, etc., may be wrapped around a strip of reconstituted tobacco, then wrapped with another layer of tobacco and finally with wrapping paper. This places the susceptor circumferentially between two tobacco regions of approximately equal thermal mass. The flat wire of the susceptor is wound in a helical or spiral shape, which also ensures good thermal contact. This ensures more uniform heating of the tobacco, which can reduce peak temperatures at the susceptor, increase energy efficiency, and mitigate the risk of localized thermal decomposition.

[0047] In the example shown in FIG. 3, the induction coil has the following characteristics: Copper coil: 6 turns 8mm coil diameter 1mm wire diameter Relative permeability=1 Dielectric constant = 1 Conductivity=5.998e7 S / m

[0048] In the example shown in FIG. 3, the susceptor has the following characteristics: Aluminum susceptor: 6 turns 4mm susceptor diameter 0.2x0.8mm cross section Relative permeability=1 Dielectric constant = 1 Conductivity=3.77e7 S / m

[0049] It will be appreciated that the above values ​​are merely exemplary and that other values ​​are possible.

[0050] The non-uniformity of the magnetic flux density generated by the induction coil allows for specific orientation of the susceptor relative to the coil, for example using an asymmetric susceptor 40 of the type shown in FIGS.

[0051] 3 demonstrates how the phase angle between induction coil 36 and helical susceptor 40 located within the induction coil changes as the helical susceptor is rotated relative to the induction coil. The phase angle ranges from 0 degrees (in phase) as shown in image A to 180 degrees (out of phase) as shown in image B. Image C shows an intermediate position where the phase angle is 90 degrees.

[0052] Due to non-uniform magnetic flux density, the coupling effect between the coil and the susceptor changes as the phase angle changes. Image A of FIG. 5 illustrates the change in magnetic flux density between the windings of the induction coil 36 and the helical susceptor located within the coil when the coil and the susceptor are in phase. Conversely, image B of FIG. 5 illustrates the change in magnetic flux density between the windings of the induction coil 36 and the helical susceptor when the coil and the susceptor are 180 degrees out of phase.

[0053] As shown in Figures 3 and 5, a susceptor made of a thin metal tape wound in a helical shape with the same pitch as the induction coil can be oriented toward areas of high or low magnetic flux simply by rotating the susceptor within the coil. During the rotation of the susceptor, the device measures the impedance of the induction coil and records the minimum and maximum impedance values, which are stored in memory 46. A similar phase-changing effect can be produced by moving the susceptor longitudinally within the induction coil. When the susceptor is stationary, the final position of the susceptor is determined and used to set the power profile of the device.

[0054] The change in the coupling effect can be measured using the change in the impedance of the coil, as described above. For example, one way to measure the impedance of a coil is to compare it to a known impedance in a circuit. This allows the unknown impedance of the coil to be measured. The coil impedance is a function of the AC frequency applied to the coil. If the applied frequency is 1 MHz or higher, for example in the range of 1 to 10 MHz, a fairly large relative change can be measured.

[0055] It will be appreciated that the susceptor 40 may be rotated relative to the induction coil 36 by rotating the aerosol-generating article 100 in which the susceptor is contained, as shown in Figure 6. In use, a user inserts the aerosol-generating article 100 into the aerosol generating device 10. The aerosol-generating article includes an asymmetric susceptor of the type described above. The device 10 utilizes the coupling effect of the susceptor with the device's induction coil 36 to recognize the presence of the susceptor, and therefore, that the aerosol-generating article 100 has been inserted.

[0056] The user rotates the inserted aerosol-generating article 100 at least one complete revolution (360 degrees). During this initial calibration, the device 10 measures the impedance of the coil 36. The impedance may be measured incrementally (e.g., at discrete intervals close enough to each other to obtain a substantially continuous impedance profile during the revolution) and / or continuously throughout the movement. This produces a range of measured impedance 50 of the type shown in FIG. 7. The range of impedance includes a maximum measured value 52 and a minimum measured value 54, which, as described above, may be stored in memory and used as control parameters / scalars, e.g., minimum=60% power, maximum=100% power.

[0057] Thus, the methods described herein increase or decrease the power delivery depending on the measured operating impedance. Hence, the methods described herein allow a user to physically control the power delivery by simply moving (e.g., rotating) the aerosol-generating article 100 to a selected position within a range of motion defined by a predetermined motion. For example, if the predetermined motion is a rotation, 360 degree rotation, etc., of the aerosol-generating article 100, the user may rotate the aerosol-generating article 100 in a selected angular orientation to control the power delivered by the aerosol generating device.

[0058] Using the aerosol generating article 100 to set the power delivery provides an intuitive feel similar to a control knob, which may lead to an improved user experience. A user may activate the power control methods described herein by making a selection through a user interface, if present. Alternatively, a user may activate the power control methods described herein by inserting the aerosol generating article 100 into the aerosol generating device 10 and moving the aerosol generating article 100 in a predetermined motion.

[0059] As mentioned above, the predetermined motion may be a rotation, such as a rotation of more than 180 degrees, a rotation of more than 270 degrees, or a rotation of at least 360 degrees (or more). By rotating the aerosol-generating article 100 one complete rotation, the full range of impedance values ​​for that particular aerosol-generating article 100 may be recorded. However, it will be appreciated that other predetermined motions are possible, such as up and down movement within the heating chamber.

[0060] 8 and 9 show different examples of an asymmetric susceptor 40. FIG.

[0061] FIG. 8 shows a secondary control susceptor 40a that is not aligned with the central axis of the tobacco stick while the primary susceptor 40b is aligned with the central axis. The primary susceptor 40b is significantly larger than the secondary control susceptor 40a and is the main source of induction heating within the aerosol-generating article. The secondary susceptor 40a has sufficient mass to affect the coil impedance and is preferably located closer to or on the surface of the aerosol-generating article. In the example shown in FIG. 8, the secondary susceptor is located adjacent to the location where the induction coil terminates, where there is a large change in the range of impedance measured. The secondary susceptor may be made of the same or different material as the primary susceptor.

[0062] Figure 9 shows a further example including a primary spiral susceptor 40c, whose asymmetry is enhanced by the addition of a secondary linear susceptor 40d. As with the secondary control susceptor 40a shown in Figure 8, the secondary linear susceptor 40d may be located closer to, e.g., at, the surface of the aerosol-generating article compared to the primary susceptor 40c to further enhance the asymmetry. The secondary susceptor may be made of the same or a different material as the primary susceptor.

[0063] Although exemplary embodiments have been described in the preceding paragraphs, it should be understood that various modifications can 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.

[0064] Any combination of the above-described features in all possible variations thereof is encompassed by the present disclosure unless otherwise indicated herein or clearly contradicted by context.

Claims

1. 1. A method of operating an aerosol generating device, the aerosol generating device comprising: a heating chamber (18) configured to receive an aerosol-generating article (100); an induction heater comprising an induction coil (36) operable to provide an alternating magnetic field to the heating chamber (18) to induce eddy currents in a susceptor (40) located within the heating chamber (18); wherein the method comprises: (a) applying an alternating current of an applied frequency to the induction coil (36); (b) measuring a characteristic indicative of the impedance of the induction coil (36) while moving a susceptor (40) located within the heating chamber (18) through a predetermined motion; (c) using the measured characteristic to determine a minimum reference impedance of the induction coil (36) and a maximum reference impedance of the induction coil (36), the minimum reference impedance being associated with a first position within the predetermined motion and the maximum impedance being associated with a second position within the predetermined motion; (d) measuring a characteristic indicative of the operating impedance of the induction coil (36) while the susceptor located within the heating chamber is maintained at a user-selected position within the predetermined motion; (e) using the operating impedance to set the power delivered by the induction coil (36); A method comprising:

2. The method of claim 1 , wherein the predetermined motion is a rotation.

3. The method of claim 2 , wherein the rotation is 360 degrees or greater.

4. The method of any one of claims 1 to 3, wherein the susceptor is asymmetric under the predetermined movement.

5. The method according to any one of claims 1 to 3, wherein the applied frequency is in the range of 1 to 10 MHz.

6. The method of any one of claims 1 to 3, further comprising the step of providing an indication to a user indicating the power set in step (e).

7. using the operating impedance to set the power delivered by the induction coil (36); determining a scaling factor by comparing the operating impedance to one or both of the maximum reference impedance and the minimum reference impedance; scaling the power delivered by the induction coil using the determined scaling factor; The method according to any one of claims 1 to 3, comprising:

8. detecting insertion of a susceptor into the heating chamber; detecting movement of the susceptor through the predetermined motion; automatically operating the method comprising steps (b) to (e); The method of any one of claims 1 to 3, further comprising:

9. A method according to any one of claims 1 to 3, wherein the property indicative of impedance is measured continuously in step (b).

10. An aerosol generating device (10), comprising: a heating chamber (18) configured to receive an aerosol-generating article (100); an induction heater comprising an induction coil (36) operable to provide an alternating magnetic field to the heating chamber (18) to induce eddy currents in a susceptor (40) located within the heating chamber (18); a controller (24) configured to perform the method of any one of claims 1 to 3 when an aerosol-generating article (100) comprising a susceptor (40) is inserted into the heating chamber (18); An aerosol generating device (10) comprising:

11. An aerosol generating device (10) according to claim 10; an aerosol-generating article (100) comprising an asymmetric susceptor (40); An aerosol generating system comprising:

12. 12. The aerosol generation system of claim 11, wherein the induction coil (36) is a helical coil having a coil pitch (p1), and the asymmetric susceptor (40) includes a helical susceptor having a susceptor pitch (p2), the susceptor pitch being substantially the same as the coil pitch.

13. 12. The aerosol generating system of claim 11, wherein the asymmetric susceptor (40) includes a first susceptor and a secondary susceptor, the secondary susceptor being smaller than the first susceptor such that the heating effect provided by the secondary susceptor is insignificant compared to the heating effect provided by the primary susceptor.

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