WO2024179860A1

WO2024179860A1 - Aerosol generating devices

Info

Publication number: WO2024179860A1
Application number: PCT/EP2024/054062
Authority: WO
Inventors: Erik SNIJDER; Jeroen DAMMERS
Original assignee: JT International SA
Current assignee: JT International SA
Priority date: 2023-03-02
Filing date: 2024-02-16
Publication date: 2024-09-06
Anticipated expiration: 2025-09-02

Abstract

An aerosol generating device (10) comprises a heating chamber (18) configured to receive a consumable (100) comprising an aerosol generating substrate (102), a heating circuit (40) configured to supply heat to the heating chamber (18), a controller (24); and a monitoring circuit (50) having a predetermined time constant. The monitoring circuit (50) is electrically connected to the heating circuit (40), and the controller (24) is operable to use a time delay associated with the monitoring circuit (50) to determine a presence or absence of a consumable (100) within the heating chamber. The monitoring circuit may be an RC circuit. A method of operating an aerosol generating device is also described.

Description

AEROSOL GENERATING DEVICES

Technical Field

The present disclosure relates generally to an aerosol generating device for heating an aerosol generating substrate to generate an aerosol for inhalation by a user of the aerosol generating device. The present disclosure is particularly applicable to a portable (hand-held) aerosol generating device. Such devices heat, rather than burn, a solid (i.e. non-liquid) aerosol generating substrate, e.g., tobacco or other suitable materials, by conduction, convection, and/or radiation to generate an aerosol for inhalation by a user.

Technical Background

The popularity and use of reduced-risk or modified-risk devices (also known as aerosol generating devices or vapour generating devices) has grown rapidly in recent years as an alternative to the use of traditional tobacco products. Various devices and systems are available that heat or warm aerosol generating substances to generate an aerosol for inhalation by a user.

A commonly available reduced-risk or modified-risk device is the heated substrate aerosol generating device, or so-called heat-not-burn device. Devices of this type generate an aerosol or vapour by heating an aerosol generating substrate to a temperature typically in the range 150°C to 300°C. Heating the aerosol generating substrate to a temperature within this range, without burning or combusting the aerosol generating substrate, generates a vapour which typically cools and condenses to form an aerosol for inhalation by a user of the device.

Currently available aerosol generating devices can use one of a number of different approaches to provide heat to the aerosol generating substrate. One such approach is to employ an induction heating system. In such a device, an induction coil is provided in the device and an inductively heatable susceptor is provided to heat the aerosol generating substrate. Electrical energy is supplied to the induction coil when a user activates the device which in turn generates an alternating electromagnetic field. The susceptor couples with the electromagnetic field and generates heat which is transferred, for example by conduction, to the aerosol generating substrate and an aerosol is generated as the aerosol generating substrate is heated. Another heating approach is to use a resistive heating system. In such a device, a resistive heating element is provided to heat the aerosol generating substrate. Electrical energy is supplied to the resistive heating element when a user activates the device which in turn generates heat which is transferred, for example by conduction, to the aerosol generating substrate and an aerosol is generated as the aerosol generating substrate is heated.

In most such aerosol generating devices, the heater operates in a predetermined manner when commanded to start, for example in response to the user pushing a start button or in response to the device determining by means of an airflow sensor that the user has inhaled a puff through the device. In some circumstances however it may be desirable to automatically initiate heating, for example on insertion of an aerosol generating article into a heating chamber of the device. It is therefore an object of the invention to provide an aerosol generating device that is operable to detect the presence of an aerosol generating article in a heating chamber of the device.

Summary of the Invention

According to a first aspect of the invention there is provided an aerosol generating device comprising: a heating chamber configured to receive a consumable comprising a solid aerosol generating substrate; a heating circuit configured to supply heat to the heating chamber; a controller; and a monitoring circuit having a predetermined time constant; wherein the monitoring circuit is electrically connected to the heating circuit, and the controller is operable to use a time delay associated with the monitoring circuit to determine a presence or absence of a consumable within the heating chamber.

The time constant, r(tau), of a circuit is a parameter characterizing the response of the circuit to a step input. For example, in an RC circuit composed of a single resistor and capacitor, the time constant T (in seconds) = RC, where R is the resistance (in ohms) and C is the capacitance (in farads). A consumable has a non-zero capacitance, such that the introduction of a consumable into a monitoring circuit having a known time constant will change the capacitance of the circuit, and thus will change the time constant of that circuit. The inventors have noted that the consumable does not need to be in physical contact with the monitoring circuit in order to have an effect on the capacitance of the circuit. It is thus possible to determine whether or not a consumable is present in a heating chamber of an aerosol forming device using a change in the time constant of a monitoring circuit having a known time constant. The change is typically an increase in the known time constant, which can be measured as a time delay.

The change in time constant is typically small, particularly when the consumable is not in physical contact with the monitoring circuit. The inventors have found that electrically connecting the monitoring circuit to the heating circuit of the aerosol forming device increases the magnitude of the change in time constant, and thus increases the sensitivity of the detection. Since a heating circuit is necessarily provided in an aerosol forming device, this increased sensitivity does not come at the cost of increased complexity or additional manufacturing expense.

By “connected” it is meant “connected at least during monitoring”. Thus, the monitoring circuit may be electrically connectable to, and disconnectable from, the heating circuit. The option to disconnect the monitoring circuit from the heating circuit during heating may prevent the high voltage supplied during heating from damaging the components of the monitoring circuit.

The monitoring circuit may comprise an RC circuit having a predetermined resistance and capacitance. An RC circuit has a simple and low cost construction, and the time constant of such a circuit is computationally straightforward to measure. It will be appreciated that the wiring of a circuit necessarily has a certain capacitance, and thus the use of an RC circuit does not necessarily imply the presence of a capacitor.

The controller may be operable to supply a signal to an input of the monitoring circuit, and to receive an altered signal from an output of the monitoring circuit. The controller may be operable to determine the time delay from the altered signal. The time delay may comprise a rise and/or fall time associated with the signal. As used herein, the term “rise time” refers to the time (in seconds) for a signal (e.g. a voltage) to change from a specified low value to a specified high value. Similarly, the term “fall time” refers to the time taken for the signal to change from a specified high value to a specified low value. Thus, rather than monitoring the time constant itself, the controller may be operable to monitor changes in rise and/or fall time. The relative change in rise time between a state where a consumable is present in the heating chamber and a state where a consumable is absent from the heating chamber may be greater than a relative change between the known time constant of the monitoring circuit and the altered time constant due to the presence of the consumable. Thus utilising the rise and/or fall time may improve the accuracy of the determination.

The signal that is input to the monitoring circuit may comprise a voltage pulse, such as a square wave. The controller may be operable to input the signal to the monitoring circuit periodically. Use of a sharp edged signal such as a pulse may make observation of the rise and/or fall time more straightforward.

The controller may be operable to compare the time delay with a first threshold, wherein a time delay that is greater than the first threshold indicates the presence of a consumable in the heating chamber. Following a determination of a presence of a consumable within the heating chamber, the controller may be operable to automatically operate the heating circuit to initiate heating of the consumable. This may improve the convenience of the aerosol generating device for a user, by avoiding the need for the user to take action to initiate heating once a consumable is inserted into the heating chamber.

The controller may be operable to use the time delay to determine that a consumable is being inserted into the heating chamber and/or is being removed from the heating chamber. The controller may be operable to compare the time delay with a second threshold, wherein a time delay that is greater than the first threshold and greater than the second threshold indicates that a consumable is being inserted into the heating chamber.

Following a determination of that a consumable is being inserted into the heating chamber, the controller may be operable to automatically operate the heating circuit to initiate pre-heating of the heating chamber. This may improve the convenience of the aerosol generating device for a user, as preheating the heating chamber during insertion of the consumable may reduce the heating time once the consumable is inserted into the heating chamber.

The aerosol generating device may be switchable between a heating mode in which a voltage is supplied to the heating circuit and a time delay monitoring mode in which a signal is supplied to the monitoring circuit. The controller may be operable to only use the time delay associated with the monitoring circuit to determine the presence or absence of the consumable when the aerosol generating device is in the time delay monitoring mode. The aerosol generating device may comprise a switch between the monitoring circuit and the heating circuit such that the monitoring circuit may be physically disconnected from the heating circuit during heating. This may prevent the monitoring circuit being damaged when a voltage is supplied to the heating circuit in the heating mode. The aerosol generating device may comprise a first switch that may be closed in the time delay monitoring mode and open in the heating mode and a second switch that may be closed in the heating mode and open in the time delay monitoring mode.

The heating circuit may comprise a resistive heater, such as a resistive wire or a thin film heater.

The heating chamber may be substantially cup shaped, and may have an open first end operable to receive the consumable. For example, the heating chamber may comprise a substantially cylindrical side wall that is open at a first end, so defining the open first end, and closed at a second end, defining a base to the heating chamber. The resistive heater may be external to the heating chamber, and may be wrapped around the heating chamber.

According to a second aspect of the invention we provide a method of operating an aerosol generating device that comprises: a heating chamber configured to receive a consumable comprising a solid aerosol generating substrate; a heating circuit configured to supply heat to the heating chamber; a controller; and a monitoring circuit having a predetermined time constant, wherein the monitoring circuit is electrically connected to the heating circuit; wherein the method comprises: measuring a time delay associated with the monitoring circuit, and comparing the measured time delay to a first threshold to determine a presence or absence of a consumable within the heating chamber.

Following a determination of a presence of a consumable within the heating chamber, the method may further comprise automatically operating the heating circuit to initiate heating of the consumable.

The method may be implemented in the aerosol generating device of the first aspect of the invention and may further comprise any of the optional features of the first aspect of the invention.

Features of the above aspects of the invention may be combined together, as well as with features selected from the description, in any order unless expressly stated otherwise.

Brief Description of the Drawings

The present invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic cross-sectional view of an aerosol generating system comprising an aerosol generating device and a consumable positioned in a heating chamber of the aerosol generating device;

Figure 2 is a schematic illustration of a thin film heater suitable for use in the aerosol generating device of Figure 1 ;

Figure 3 shows the thin film heater of Figure 2 wrapped around a heating chamber;

Figure 4 illustrates an exemplary monitoring circuit suitable for use in the aerosol generating device of Figure 1 in a first, time delay monitoring mode, and in a second, heating mode;

Figure 5 schematically illustrates a time delay monitoring method; and

Figure 6 illustrates variations in measured rise and/or fall time before, during and after insertion of a consumable into a heating chamber. Detailed Description

Referring initially to Figure 1 , there is shown diagrammatically an example of an aerosol generating system 1. The aerosol generating system 1 comprises an aerosol generating device 10 and a consumable 100, also referred to herein as an aerosol generating article, for use with the device 10. The aerosol generating device 10 can have any shape that is sized to fit the components described in the various embodiments set out herein and to be comfortably held by a user unaided, in a single hand.

A first end 14 of the aerosol generating device 10, shown towards the bottom of Figure 1 , is described for convenience as a distal, bottom, base or lower end of the aerosol generating device 10. A second end 16 of the aerosol generating device 10, shown towards the top of Figure 1 , is described as a proximal, top or upper end of the aerosol generating device 10. During use, the user typically orients the aerosol generating device 10 with the first end 14 downwards and/or in a distal position with respect to the user’s mouth and the second end 16 upwards and/or in a proximal position with respect to the user’s mouth.

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 substantially cylindrical cross-section. The cavity 20 of the heating chamber 18 is open towards the second end 16 of the aerosol generating device 10. The heating chamber 18 has a longitudinal axis defining a longitudinal direction and is formed of a metal material, such as stainless steel.

A heating element 22 is located in proximity to the heating chamber 18 and is operable to provide heat to the heating chamber. The heating element 22 is comprised within a heating circuit 40, which is electrically connected to a controller 24.

The aerosol generating device 10 further comprises a power source 26, for example one or more batteries which may be rechargeable. The controller 24 couples the power source 26 to the heating element 22. The controller 24 may also be connected to a user interface 23 comprising inputs such as a power button for receiving commands from a user and/or outputs such as indicator lights, a display screen or an audible or vibratory alarm for providing information to the user. The controller 24 may also be interfaced with an antenna 25 for wireless communication with a remote device such as the user’s smartphone, which can be used for input and output, as well as for relaying data between the aerosol generating device 10 and its manufacturer.

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 solid (i.e. non-liquid) aerosol generating substrate 102. The aerosol generating article 100 is a disposable and replaceable article (also known as a “consumable”) which may, for example, contain tobacco as the solid 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 so 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 part of the mouthpiece segment 108 projects from the heating chamber 18 so that the proximal end 104 of the aerosol generating article 100 is accessible to be taken into the mouth of a user. When the aerosol generating device 10 applies heat to the aerosol generating article 100, heated vapour is emitted from the aerosol generating substrate 102. As inhalation by the user draws air towards the proximal end 104 of the aerosol generating article 100, the vapour cools and condenses as it passes through the mouthpiece segment 108 to form an aerosol with characteristics suitable for inhalation. The mouthpiece segment 108 may further comprise a filter (not shown) to remove particles or drops above a certain size from the airstream.

The aerosol generating substrate 102 and the mouthpiece segment 108 are arranged in coaxial alignment inside a wrapper 110 (e.g., a paper wrapper) to hold the components in position to 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 in order that air can flow through the aerosol generating article 100 from the distal end 106 to the proximal end 104. In the illustrated embodiments of the invention, the heating chamber 18 comprises an open first end 28 and a closed base 30 at a second end. That is, the heating chamber 18 is cup shaped. This can ensure that air drawn from the open end 28 is guided around the consumable towards the base 30, at which point the air is drawn through the aerosol generating substrate 102.

As noted above with regards to Figure 1 , the aerosol generating device 10 comprises a heating chamber 18 configured to receive a consumable 100 comprising an aerosol generating substrate, a heating circuit 40 configured to supply heat to the heating chamber 18, and a controller 24. The aerosol generating device 10 further comprises a monitoring circuit 50 having a predetermined time constant. The monitoring circuit 50 is electrically connected to the heating circuit 40, and the controller 24 is operable to use a time delay associated with the monitoring circuit to determine a presence or absence of a consumable within the heating chamber.

Figure 2 shows one example of a heating element 22 for use in a heating circuit of the type shown in Figure 1. The heating element 22 is a resistive heating element, specifically a thin film heater. The heating element includes a heating track 32 embedded within a thin film and a pair of contacts 34, 36 permitting connection to the controller 24.

Figure 3 shows the heating chamber 18 of an aerosol generating device 10 in more detail. The heating chamber 18 has a cylindrical side wall 38 connecting the open first end 28 and the closed base 30. The heating element 22 is wrapped around an exterior surface of the side wall 38.

Referring now to Figure 4, the monitoring circuit 50 is shown in more detail, together with the heating circuit 40. The monitoring circuit 50 includes a resistor R and an optional capacitor C, and thus constitutes an RC circuit. The monitoring circuit comprises an electrical input 52 and an electrical output 54 connected to a microcontroller pC. It will be appreciated that the microcontroller pC may be comprised within the controller 24, or may be separate from the controller 24 and under the command of the controller 24. The resistor R is connected between the input 52 and the output 54 and is connected in parallel with the capacitor C, which is connected to ground. The resister R has a value in the range 500kQ - 10MQ. The capacitor C is optional, but if present, assists in cleaning the signal.

The monitoring circuit 50 further comprises a first switch 56 connected between the monitoring circuit 50 and the heating circuit 40, and specifically between the monitoring circuit 50 and a contact 34 of the heating track 32. When the first switch 56 is in a closed position the monitoring circuit is electrically connected to the heating circuit 40. In this state, the aerosol generating device 10 can be considered to be in a time delay monitoring mode. When the first switch 56 is in an open position the monitoring circuit 50 is not electrically connected to the heating circuit 40, such that no current may flow between the monitoring circuit 50 and the heating circuit 40.

The heating circuit 40 includes a second switch 42 located between the heating element 22 and an input voltage (e.g. supplied by the power supply 26), and a third switch 44 located between the heating element 22 and ground. When the second and third switches 42, 44 are closed the heating element 22 is electrically connected to the input voltage such that a voltage may be supplied to the heating element to cause the heating element 22 to generate heat. In this state, the aerosol generating device can be considered to be in a heating mode. When the second and third switches 42, 44 are open the heating element 22 is disconnected from the input voltage, and cannot generate heat.

The aerosol generating device may be in the heating mode and the time delay monitoring mode simultaneously, such that all three switches 56, 42, 44 are closed at the same time. In the present example however, the aerosol generating device is operable to switch between the time delay monitoring mode and the heating mode, such that time delay monitoring does not occur during heating.

Referring now to Figure 5, the operation of the aerosol generating device 10 in a time delay monitoring mode will now be described. In the time delay monitoring mode, the microcontroller pC is operable to send a signal 60 to the input 52 of the monitoring circuit 50 (e.g. from a pin labelled “send”). The signal 60 is a voltage pulse, such as a square wave defined by a low value 62 and a high value 64, and may be periodically repeating.

The signal passes through the monitoring circuit 50 and also the heating circuit 40, since in the time delay monitoring mode the switch 56 is closed. The signal is received from the output 54 by the microcontroller pC (e.g. at a pin labelled “return”); however, the received signal is altered due to the capacitance in the system. This alteration is characterised by the rise time d, which constitutes the time for the signal to change from the low value 62 to the high value 64, and/or the fall time, which constitutes the time for the signal to return from the high value 64 to the low value 62. In the original signal these changes are effectively instantaneous, but in the received signal there is a delay as the signal rises from low to high, and as the signal falls from high to low. The rise time is proportional to the time constant of the circuit. Similarly, the fall time is also proportional to the time constant of the circuit.

Figure 5 includes a graph 70 which plots rise and fall time 72 against time 74, thus allowing variations in rise and fall time over time to be perceived. It can be seen that the rise time di at a first time 76 is smaller than the rise time d₂ at a second time 78. This indicates that the capacitance in the system has changed between the first time and the second time. In particular, the capacitance in the system has increased between the first time 76 and the second time 78.

Figure 6 illustrates how the variations in rise and/or fall time shown in Figure 5 can be used to determine the presence or absence of a consumable 100 within a heating chamber 18 of an aerosol generating device 10. Figure 6 includes a graph plotting measured rise and fall time 72 (in this example, the rise and fall time is represented by the transmission time of the signal from the input to the output) against time 74 between an initial time to and an end time t₅.

During a first time period 82 between time to and time ti , a reference transmission time, such as an average rise and fall time, is a first reference time ai. During this time period no consumable is present in the heating chamber. The rise and fall time experienced by a signal during this time period is thus indicative of the time constant T of the monitoring circuit absent any consumable, and can be considered to be a predetermined time constant. At time ti the measured rise and fall time increases, and averages a third reference time a₃ for a second time period 84 between time ti and time t₂. The increase in rise and fall time indicates that a capacitance of the system has increased, and thus that the time constant T of the monitoring circuit has changed, and in particular, increased. During this time period a consumable is being inserted into the heating chamber 18 (i.e. is in the process of being inserted and is not yet fully inserted but is instead partially inserted and/or in close proximity to the heating chamber). The increased capacitance during this time period is due to the presence of the consumable 100 in proximity to and/or partially within the cavity of the heating chamber, and potentially may also be influenced by contact between the consumable and the fingers of a user.

At time t₂ the measured rise and fall time decreases, and averages a second reference time a₂ for a third time period 86 between time t₂ and time t₃. The decreased rise and fall time indicates that a capacitance of the system has decreased, and thus that the time constant T of the monitoring circuit has changed, and in particular, decreased. However, it is noted that the value a₂> ai, meaning that the capacitance in the system, and so the time constant of the system, is greater than the predetermined time constant T of the monitoring circuit absent any consumable. During this time period a consumable 100 is present within the heating chamber 18 of the aerosol generating device.

At time t₃ the rise and fall time increases, and averages a further rise/fall time for a fourth time period 88 between time t₃ and time t4. The fourth time period 88 represents the reverse of the second time period 84, in that during the fourth time period a consumable is being removed from the heating chamber. The average rise and fall time during the fourth time period is thus similar to and approximately the same as the average rise and fall time a₃ during the second time period.

Similarly, the average rise and fall time in a fifth time period 90 between times t₄ and t₅ is similar to and approximately the same as the first average rise and fall time ai during the first time period, indicating that the consumable is no longer present in the heating chamber. The change in time constant of the monitoring circuit, measured, for example, using the change in time delay, such as the change in rise and/or fall time as discussed above, can thus be used to determine whether a consumable is present in the heating chamber or absent from the heating chamber. It can also be used to detect the act of inserting a consumable into the heating chamber and or removing a consumable from the heating chamber.

In one example, the controller is operable to compare the time delay detected using the monitoring circuit with a first threshold, and when the time delay is equal to and/or greater than the first threshold the controller determines that a consumable is present in the heating chamber. In the example shown in Figure 6, the first threshold may be the second rise/fall time a₂. It will be appreciated that the numerical value of the first threshold is implementation dependent, and may vary depending on the physical parameters of the aerosol generating device and consumable.

In another example, the controller is operable to compare the time delay detected using the monitoring circuit with a second threshold, and when the time delay is equal to and/or greater than the second threshold the controller determines that a consumable is being inserted into the heating chamber, and/or that a consumable is being removed from the heating chamber. For example, if no consumable was present in the heating chamber prior to the determination, the controller may conclude that a consumable is being inserted. Conversely, if a consumable was previously present in the heating chamber, the controller may conclude that the consumable is being removed from the heating chamber. In the example shown in Figure 6, the second threshold may be the third rise/fall time a₃.

Following a determination that a consumable is present in the heating chamber, the controller switches from the time delay monitoring mode to the heating mode, for example by closing second and third switches 42, 44 and by opening first switch 52. The controller is then operable to automatically initiate heating by operating the heating circuit, so avoiding the need for the user to take physical action (e.g. operate a button or draw on the mouthpiece) in order to initiate heating.

The controller may, in some examples, initiate preheating of the heating chamber following a determination that a consumable is being inserted into the heating chamber. This may reduce the heat up time of the device once the consumable is fully inserted.

Although exemplary embodiments have been described in the preceding paragraphs, it should be understood that various modifications may be made to those embodiments without departing from the scope of the appended claims. Thus, the breadth and scope of the claims should not be limited to the above-described exemplary embodiments.

Claims

1. An aerosol generating device (10) comprising: a heating chamber (18) configured to receive a consumable (100) comprising a solid aerosol generating substrate (102); a heating circuit (40) configured to supply heat to the heating chamber (18); a controller (24); and a monitoring circuit (50) having a predetermined time constant; wherein the monitoring circuit (50) is electrically connected to the heating circuit (40), and the controller (24) is operable to use a time delay associated with the monitoring circuit (50) to determine a presence or absence of a consumable (100) within the heating chamber.

2. The aerosol generating device of claim 1 , wherein the monitoring circuit (50) comprises an RC circuit having a predetermined resistance and capacitance.

3. The aerosol generating device of claim 1 or claim 2, wherein the controller (24) is operable to supply a signal to an input of the monitoring circuit (50), and to receive an altered signal from an output of the monitoring circuit, the controller being operable to determine the time delay from the altered signal.

4. The aerosol generating device of claim 3, wherein the time delay comprises a rise and/or fall time associated with the signal.

5. The aerosol generating device of claim 3 or claim 4, wherein the signal that is input to the monitoring circuit (50) comprises a voltage pulse.

6. The aerosol generating device of any one of claims 3 to 5, wherein the controller (24) is operable to input the signal to the monitoring circuit (50) periodically.

7. The aerosol generating device of any preceding claim, wherein the controller (24) is operable to compare the time delay with a first threshold, wherein a time delay that is greater than the first threshold indicates the presence of a consumable in the heating chamber.

8. The aerosol generating device of any preceding claim, wherein, following a determination of a presence of a consumable (100) within the heating chamber (18), the controller (24) is operable to automatically operate the heating circuit (40) to initiate heating of the consumable.

9. The aerosol generating device of any preceding claim, wherein the controller (24) is further operable to use the time delay to determine that a consumable is being inserted into the heating chamber and/or is being removed from the heating chamber.

10. The aerosol generating device of claim 9, wherein, following a determination of that a consumable (100) is being inserted into the heating chamber (18), the controller is operable to automatically operate the heating circuit (40) to initiate pre-heating of the heating chamber.

11. The aerosol generating device of any preceding claim, wherein the aerosol generating device (10) is switchable between a heating mode in which a voltage is supplied to the heating circuit (40) and a time delay monitoring mode in which a signal is supplied to the monitoring circuit (50) .

12. The aerosol generating device of claim 11 , further comprising a first switch (56) that is closed in the time delay monitoring mode and open in the heating mode and a second switch (42) that is closed in the heating mode and open in the time delay monitoring mode.

13. The aerosol generating device of any preceding claim, wherein the heating circuit comprises a resistive heater (22), and preferably a thin film heater.

14. A method of operating an aerosol generating device that comprises: a heating chamber (18) configured to receive a consumable comprising a solid aerosol generating substrate (102); a heating circuit (40) configured to supply heat to the heating chamber; a controller (24); and a monitoring circuit (50) having a predetermined time constant, wherein the monitoring circuit is electrically connected to the heating circuit; wherein the method comprises: measuring a time delay associated with the monitoring circuit, and comparing the measured time delay to a first threshold to determine a presence or absence of a consumable within the heating chamber.

15. The method of claim 14, wherein, following a determination of a presence of a consumable within the heating chamber, the method further comprises: automatically operating the heating circuit to initiate heating of the consumable.