EP4297598A1

EP4297598A1 - Electronic cigarette and method for controlling an electronic cigarette

Info

Publication number: EP4297598A1
Application number: EP22707748.4A
Authority: EP
Inventors: Olayiwola Olamiposi POPOOLA; Kyle ADAIR; Peter LOVEDAY
Original assignee: JT International SA
Current assignee: JT International SA
Priority date: 2021-02-25
Filing date: 2022-02-24
Publication date: 2024-01-03
Also published as: US20240122265A1; WO2022180192A1

Abstract

An electronic cigarette comprising: a vaporizing unit configured to generate a vapor from a substrate; an air flow inlet; a vapor outlet configured for a user to inhale the vapor; a main vapor flow channel extending past the vaporizing unit from the air flow inlet to the vapor outlet; a pressure sensor arranged to measure a pressure at the main vapor flow channel; and control circuitry configured to monitor user inhalation by: obtaining pressure measurements from the pressure sensor at a sampling frequency; calculating a background pressure as a moving average of the pressure measurements obtained within a moving sampling period; and calculating a current pressure difference as a difference between a current pressure measurement and the background pressure, wherein the control circuitry is configured to select an operation state in dependence upon the current pressure difference, wherein the operation state is one of a plurality of states comprising: a sleep state in which the sampling frequency is a first frequency; and an active state in which the sampling frequency is a second frequency higher than the first frequency.

Description

ELECTRONIC CIGARETTE AND METHOD FOR CONTROLLING AN ELECTRONIC CIGARETTE

TECHNICAL FIELD

The present invention relates to personal vaporizing devices, such as electronic cigarettes. For example, the invention relates to an electronic cigarette and disposable capsules therefor, or to an electronic cigarette that has an internal reservoir for a liquid substrate.

BACKGROUND

Electronic cigarettes are an alternative to conventional cigarettes. Instead of generating a combustion smoke, they generate a vapor from a substrate, which can be inhaled by a user. In many cases, the substrate is a liquid comprising an aerosol-forming substance, such as glycerin or propylene glycol that creates the vapor. Other common substances in the liquid are nicotine and various flavorings. Electronic cigarettes can comprise a pressure sensor which is used, for example, to detect a pressure drop when a user inhales vapor from the electronic cigarette. The pressure sensor can be a microphone-type sensor which can only detect discrete pressure changes (ON/OFF), or multiple pressure sensors can be used to detect spatial pressure differences. It is desirable to provide a pressure sensing technique capable of more accurately detecting how the electronic cigarette is being used. Additionally, it is desirable to minimize the required number of pressure sensors and the power consumption of the pressure sensing technique.

SUMMARY According to a first aspect, the present disclosure provides an electronic cigarette comprising: a vaporizing unit configured to generate a vapor from a substrate; an air flow inlet; an vapor outlet; a main vapor flow channel extending past the vaporizing unit from the air flow inlet to the vapor outlet; a pressure sensor arranged to measure a pressure at the main vapor flow channel; and control circuitry configured to monitor user inhalation by: obtaining pressure measurements from the pressure sensor at a sampling frequency; calculating a background pressure as a moving average of the pressure measurements obtained within a moving sampling period; and calculating a current pressure difference as a difference between a current pressure measurement and the background pressure, wherein the control circuitry is configured to select an operation state in dependence upon the current pressure difference, wherein the operation state is one of a plurality of states comprising: a sleep state in which the sampling frequency is a first frequency; and an active state in which the sampling frequency is a second frequency higher than the first frequency.

By configuring the control circuitry to compare a current measurement to a moving average, a single sensor can be used to detect both general trends and short term variations in pressure. By taking background pressure into account, accuracy of detecting intentional usage of the device can be improved. Furthermore, this can be achieved without the need for multiple sensors. Furthermore, by configuring the control circuitry with multiple states and different sampling frequencies for pressure measurements, power can be conserved by reducing the sampling frequency when the electronic cigarette is not in expected to be in use (for example when the electronic cigarette has not been recently used), while still allowing for the possibility of detecting usage of the electronic cigarette.

In some embodiments, the control circuitry is configured to switch from the sleep state to the active state in response to the current pressure difference exceeding a first threshold. This has the advantage that the electronic cigarette can automatically “wake up”, thereby simplifying user operation of the electronic cigarette, and reducing the need for an alternative user control such as a button.

In some embodiments, the electronic cigarette further comprises an accelerometer configured to measure an acceleration of the electronic cigarette, and the control circuitry is configured to switch from the sleep state to the active state in response to the acceleration exceeding a threshold. This provides an alternative way to “wake up” the electronic cigarette. Furthermore, by detecting that the electronic cigarette is accelerating, it can be inferred that the electronic cigarette is moving, and therefore the background pressure is more likely to change. By automatically increasing the sampling frequency when acceleration is detected, the electronic cigarette can more accurately track the background pressure, and thus more accurately track variations in the current pressure relative to the background pressure.

In some embodiments, the plurality of states further comprises a vaping state in which the control circuitry controls the vaporizing unit to generate the vapor. By selecting between operation states, including a vaping state, in dependence upon the current pressure difference, the pressure sensor can act as a sensor for intuitively activating the electronic cigarette.

In some embodiments, in the vaping state, the sampling frequency is a third frequency higher than the second frequency. This has the effect that, in the active state the control circuitry can obtain a reasonable resolution of pressure samples for tracking background pressure but, in the vaping state, the control circuitry can obtain even better resolution to track and count user interactions including inhalations and exhalations.

In some embodiments, the control circuitry is configured to switch from the active state to the vaping state in response to the current pressure difference exceeding a second threshold, the second threshold indicating that a user is inhaling at the vapor outlet. By using such a trigger for the vaping state, the vaping state can be restricted to only generate vapor when the user is ready to inhale, reducing the energy requirements of the device (and improving battery life where the electronic cigarette is internally powered).

In some embodiments, in the vaping state, the control circuitry is configured to calculate the background pressure by: calculating a first background pressure within a moving sampling period having a first sampling length, and calculating a second background pressure within a moving sampling period having a second sampling length.

In some embodiments, the pressure sensor is configured to measure an absolute pressure. By measuring absolute pressure, the pressure measurements incorporate any variations in background pressure as the electronic cigarette is used in different locations (such as near sea level where air pressure is generally higher and on mountains where air pressure is generally lower). This is in contrast to microphone-type pressure sensors, where relative pressure measurements may have little significance since background pressure is not monitored.

In some embodiments, the pressure sensor is a MEMS sensor. MEMS pressure sensors have the advantage of being able to record a continuous range of pressure values, rather than simple thresholds, and being able to react quickly to obtain pressure measurements in real time.

Optionally, the control circuitry is configured to estimate a temperature based on the background pressure. This has the advantage of obtaining a temperature measurement without requiring a temperature sensor separate from the pressure sensor.

According to a second aspect, the present disclosure provides a control circuit for controlling an electronic cigarette comprising: a vaporizing unit configured to generate a vapor from a substrate; an air flow inlet; a vapor outlet; a main vapor flow channel extending past the vaporizing unit from the air flow inlet to the vapor outlet; and a pressure sensor arranged to measure a pressure at the main vapor flow channel, or arranged near to the air flow inlet or the vapor outlet, wherein the control circuit is configured to: obtain pressure measurements from the pressure sensor at a sampling frequency; calculate a background pressure as a moving average of the pressure measurements obtained within a moving sampling period; and calculate a current pressure difference as a difference between a current pressure measurement and the background pressure, wherein the control circuit is configured to operate in one of a plurality of states comprising: a sleep state in which the sampling frequency is a first frequency; and an active state in which the sampling frequency is a second frequency higher than the first frequency.

According to a third aspect, the present disclosure provides a method for controlling an electronic cigarette comprising: a vaporizing unit configured to generate a vapor from a substrate; an air flow inlet; a vapor outlet; a main vapor flow channel extending past the vaporizing unit from the air flow inlet to the vapor outlet; and a pressure sensor arranged to measure a pressure at the main vapor flow channel, or arranged near to the air flow inlet or the vapor outlet, the method comprising: obtaining pressure measurements from the pressure sensor at a sampling frequency; calculating a background pressure as a moving average of the pressure measurements obtained within a moving sampling period; calculating a current pressure difference as a difference between a current pressure measurement and the background pressure; and switching between a plurality of states comprising: a sleep state in which the sampling frequency is a first frequency; and an active state in which the sampling frequency is a second frequency higher than the first frequency.

According to a fourth aspect, the present disclosure provides a non-transitory computer-readable medium storing instructions which, when executed by a processor, cause the processor to perform a method according the third aspect.

According to a fourth aspect, the present disclosure provides a signal comprising computer-readable instructions which, when executed by a processor, cause the processor to perform a method according to the third aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic perspective view of an electronic cigarette according to an embodiment;

Fig. 2 is a graph of pressure against time in an example usage of the electronic cigarette; Fig. 3 is a flow chart schematically illustrating a process of monitoring user inhalation;

Fig. 4 is a schematic block diagram of control circuitry of the embodiment.

DETAILED DESCRIPTION

Fig. 1 is a schematic perspective view of an electronic cigarette according to an exemplary embodiment of the present invention.

As illustrated in Fig. 1 , the electronic cigarette 1 comprises a main vapor flow channel 10 extending from an air flow inlet 11 to a vapor outlet 12. The electronic cigarette 1 is configured such that a user may inhale a vapor, such as a nicotine vapor, from the vapor outlet 12. When the user inhales, air is drawn into the air flow inlet 11 , along the main vapor flow channel 10 and to the vapor outlet 12.

The electronic cigarette 1 additionally comprises a vaporizing unit 20 configured to generate a vapor from a substrate. The vaporizing unit 20 may, for example, comprise a heater configured to heat and vaporize a liquid substrate or configured to heat a solid substrate and vaporize a volatile component of the solid substrate. Any other type of vaporizing unit may alternatively be used, including an atomizer, a nebulizer, etc.

The main vapor flow channel 10 extends past the vaporizing unit 20, such that vapor generated by the vaporizing unit is mixed with air flowing along the main vapor flow channel 10, and supplied to the user at the vapor outlet 12.

The main vapor flow channel 10 may further be configured to allow cooling and/or aerosol formation as the vapor is mixed with air in the main vapor flow channel 10.

The electronic cigarette of Fig. 1 may for example be implemented as a liquid vaporizing cigarette as described in WO 2020/030792 A1. The electronic cigarette 1 further comprises a pressure sensor 30 arranged to measure a gas pressure at the main vapor flow channel 10. The pressure sensor 30 may be arranged in the main vapor flow channel 10. Alternatively, the pressure sensor 30 may be arranged near to the air flow inlet 11 or the vapor outlet 12, for example being arranged on an exterior housing of the electronic cigarette.

The pressure sensor 30 may be any type of gas pressure sensor suitable for monitoring changes in gas pressure over time.

However, the pressure sensor 30 is preferably suitable for measuring an absolute gas pressure. By measuring absolute pressure, the pressure measurements incorporate any variations in background pressure as the electronic cigarette is used in different locations (such as near sea level where air pressure is generally higher and on mountains where air pressure is generally lower). This is in contrast to microphone-type pressure sensors, where relative pressure measurements may have different significance depending upon not-measured background pressure.

As one example benefit, an absolute pressure measurement can also be used to estimate a temperature based on gas laws, whereas a relative pressure measurement would not be suitable for estimating a temperature.

The pressure sensor 30 is more preferably a MEMS pressure sensor, such as a MEMS piezoresistive sensor. MEMS pressure sensors have the advantage of being able to record a continuous range of pressure values, rather than simple thresholds, and being able to react quickly to obtain pressure measurements in real time.

Pressure measurements sensed by pressure sensor 30 are communicated to control circuitry 40, which is configured to monitor user inhalation. Furthermore, the control circuitry 40 may be configured to control the vaporizing unit 20. For example, the control circuitry 40 may be configured to process pressure measurements in order to, for example, detect when a user is inhaling or exhaling at the vapor outlet 12.

The electronic cigarette 1 may further comprise an accelerometer 50. An accelerometer 50 can be used to detect motion of the electronic cigarette 1 , and thus detect when a user may imminently wish to inhale vapor from the electronic cigarette 1.

The electronic cigarette 1 may also comprise various software or hardware interfaces for controlling the electronic cigarette 1 , such as a charging interface, a user interface, or a communication interface (such as USB or Bluetooth ®).

Fig. 2 is a graph of pressure against time in an example usage of the electronic cigarette. The trace 201 illustrates raw pressure measurements obtained by a pressure sensor 30. On the other hand, trace 202 illustrates a moving average of the pressure measurements.

As shown in Fig. 2, with one particular configuration of the main vapor flow channel 10 and pressure sensor 30, user exhalation events 203 appear as upward spikes in pressure and user inhalation events 204 appear as downward spikes in pressure. Additionally, minor fluctuations 205 are present. These may, for example, be normal user breathing without inhaling or exhaling.

Throughout the trace 201 , the absolute pressure varies considerably, both in short term events and in the background pressure. The variation in background pressure may, for example, be due to a temperature rise in the electronic cigarette when the user expels warm air or when a heater in the vaporizing unit 20 is activated.

On the other hand, the moving average trace 202 does not show short term events, and only represents changes in background pressure.

As a result, by calculating a difference between a moving average of pressure measurements and a current pressure measurement, short term variations in pressure can be identified. Furthermore, by setting a minimum threshold for the magnitude of this difference, minor fluctuations 205 can be filtered out, enabling detection of the larger fluctuations associated with user exhalation events 203 and user inhalation events 204.

Figs. 3 and 4 schematically illustrate a method for monitoring user inhalation, and a control circuitry 40 configured to perform the method.

Referring to Fig. 3, at step S301, the control circuitry 40 obtains pressure measurements from the pressure sensor 30. The pressure measurements are obtained at a regular sampling frequency.

The regular sampling frequency is chosen according to the timescales of events which are to be detected using pressure measurements, such as user inhalation or user exhalation, or other variations in pressure which may occur due, for example, to the user moving a handheld electronic cigarette rapidly when moving their arm. The sampling frequency may, for example, be a relatively slow rate in the range of 0.1 Hz to 10 Hz (such as specifically 1 Hz) , a medium rate in the range 10 Hz to 100 Hz (such as specifically 50Hz), or a high rate in the range of 100 Hz to 1kHz (such as specifically 200Hz). As discussed further below, a different sampling frequency may be used at different times.

Sampling of the pressure at pressure sensor 30 may be controlled in different ways. The pressure sensor 30 may provide a continuous signal to the control circuitry 40, and the control circuitry 40 may internally store samples from the continuous signal. Alternatively, a sampling clock signal may be driven through the pressure sensor 30 in order to obtain samples at the frequency of the clock signal.

The control circuitry 40 stores the pressure measurements in a memory 41. A series of pressure measurements is stored, such as the last 10 measurements. The memory 41 may be a small RAM buffer. Alternatively, a longer history of pressure measurements may be stored. In this case, the memory 41 may be a larger general data storage memory. More generally, memory 41 may be any suitable volatile or non-volatile memory.

At step S302, a background pressure calculator 42 calculates a moving average of the pressure measurements obtained within a moving sampling period. For example, if the memory 41 stores the last 10 pressure measurements, the moving average may be calculated as the average of the last 10 pressure measurements.

The moving average may be calculated by any moving average technique. For example, each of the pressure measurements may be given equal weight in the average, or the pressure measurements may be weighted according to how recently they were obtained. Additionally, weighted measurements may be combined as a linear average or using more complex functions such as exponential or polynomial averaging.

At step S303, a current pressure difference calculator 43 calculates a current pressure difference between a current pressure measurement and the background pressure calculated in step S302. The current pressure measurement is a recent measurement, such as the latest measurement, and may be obtained from the pressure sensor 30 or the memory 41.

Referring again to Fig. 2, the current pressure difference calculated in step S303 can be understood as the difference between the traces 201 and 202. In particular, the current pressure difference may be relatively large during a user inhalation event or a user exhalation event.

At steps S304 and S305, an operation state controller 44 makes one or more decisions based on the current pressure difference calculated in step S303.

Firstly, the operation state controller 44 may, in step S304, change the sampling frequency used in step S301.

For example, if a magnitude of the current pressure difference is below a first threshold or a significant time has elapsed since a last user inhalation event or user exhalation event (monitored using a timer), then the operation state controller 44 may switch to a sleep state with a low sampling frequency (such as 1Hz). This reduces the power consumed by the control circuitry 40 when the electronic cigarette 1 is not in use. If the electronic cigarette has been in a vaping state with a high sampling frequency (such as 200 Hz), the operation state controller 44 may switch from the vaping state to an active monitoring state with a medium sampling frequency (such as 50Hz), and then only switch to the sleep state after further monitoring indicates that the electronic cigarette 1 is still not in use.

Similarly, if a magnitude of the current pressure difference is above the first threshold or the electronic cigarette has been in the sleep state for a significant time (monitored using a timer), then the operation state controller 44 may switch to the active monitoring state with the medium sampling frequency (such as 50Hz). The medium sampling frequency increases the precision of the pressure measurements and the responsiveness of the electronic cigarette, when the electronic cigarette may imminently be actively used. In an example of the significant time monitored using a timer, the electronic cigarette may be configured to wake up periodically, for example once a minute.

Alternatively, if a magnitude of the current pressure difference is above a second threshold (higher than the first threshold), then the operation state controller 44 may detect a user inhalation event or a user exhalation event, and may switch to the vaping state with the high sampling frequency (such as 200 Hz). This increases the precision of the pressure measurements and the responsiveness of the electronic cigarette, when the electronic cigarette is being actively used. In the vaping state, the operation state controller 44 may also control the vaporizing unit 20 to generate the vapor. In some cases, the operation state controller 44 may rapidly switch from the sleep state to the vaping state, or may briefly switch to the active monitoring state (e.g. for a few milliseconds) before switching to the vaping state.

As illustrated in Fig. 4, the operation state controller 44 may also obtain an acceleration measurement from accelerometer 50. If the accelerometer 50 detects acceleration, this is a likely indication that the user is moving the electronic cigarette and that the user may imminently wish to inhale vapor. Accordingly, this may be used as an alternative trigger to switch from the sleep state to the active state, if the acceleration measurement exceeds a threshold. The sampling frequency in the active state is higher than in the sleep state and thereby improves the obtaining of pressure measurements when the electronic cigarette is accelerating. Furthermore, when the electronic cigarette is accelerating, fluctuations in pressure are likely to be larger, and this is another reason to increase the sampling frequency of obtaining pressure measurements.

If the accelerometer 50 detects sustained acceleration in a specific direction, then this may further indicate that the user is travelling, such as in a car or train. For example, if the user is travelling uphill or downhill, then the travelling may further lead to changes in pressure associated with changing altitude. In some embodiments, the operation state controller may be configured to respond to sustained acceleration in a specific direction by switching to a high sampling rate for the pressure sensor 30 (such as 200 Hz), to ensure that the pressure is accurately tracked.

Similarly, if the accelerometer 50 does not detect acceleration, this may indicate that the user is not using the electronic cigarette, and a lack of acceleration 50 may be used to trigger a switch from the active state to the sleep state or from the vaping state to the active state.

The operation state controller may also control other functions of the electronic cigarette based on the selected operation state. For example, in the sleep state, the electronic cigarette 1 may disable a user interface or communication interface in order to save power.

Additionally, the electronic cigarette 1 may enable a user interface for manually activating the vaporizing unit only when the electronic cigarette is in the active monitoring state. Thus, the slow sampling frequency in the sleep state provides a way of activating the cigarette from the sleep state, while also improving safety by disabling manual activation of the vaporizing unit.

The sleep, active monitoring, and vaping states described above are one example of how the electronic cigarette may be beneficially controlled based on a current pressure difference from a background pressure. More generally, any combination of operation states may be configured and switched between as appropriate according to the specific design of the vaporizing unit and main vapor flow channel.

The background pressure calculator 42, current pressure difference calculator 43 and operation state controller 44 are functional programming units which may be implemented in any way that programming instructions can be stored, including as hard-coded instructions in one or more ASICs, as executable instructions in a memory of the control circuitry, as data in a non-transitory computer-readable medium such as a flash memory, or as signal data in an electrical or optical signal.

It should be understood that steps S301 to S305 may each be repeatedly performed, for example as a loop or as parallel processes. For example, step S301 has the effect of continuously updating the set of pressure measurements which are used to calculate a moving average in step S302.

The above-described concepts are not limited to any particular type of vapor, substrate or vaporizing unit. The vapor may be partially condensed as an aerosol. The substrate may be a liquid substrates and may also be a solid substrate (preferably a high surface area solid such as a powder or porous structure). Furthermore, “generating a vapor from a substrate” is not limited to heating the substrate, and may alternatively comprise other techniques such as nebulization.

Claims

1. An electronic cigarette comprising: a vaporizing unit configured to generate a vapor from a substrate; an airflow inlet; a vapor outlet configured for a user to inhale the vapor; a main vapor flow channel extending past the vaporizing unit from the air flow inlet to the vapor outlet; a pressure sensor arranged to measure a pressure at the main vapor flow channel; and control circuitry configured to monitor user inhalation by: obtaining pressure measurements from the pressure sensor at a sampling frequency; calculating a background pressure as a moving average of the pressure measurements obtained within a moving sampling period; and calculating a current pressure difference as a difference between a current pressure measurement and the background pressure, wherein the control circuitry is configured to select an operation state in dependence upon the current pressure difference, wherein the operation state is one of a plurality of states comprising: a sleep state in which the sampling frequency is a first frequency; and an active state in which the sampling frequency is a second frequency higher than the first frequency. the electronic cigarette further comprising an accelerometer configured to measure an acceleration of the electronic cigarette, wherein the control circuitry is configured to switch from the sleep state to the active state in response to the acceleration exceeding a threshold, and wherein the control circuitry is further configured to respond to an acceleration sustained in a specific direction for at least a threshold period of time by switching the sampling frequency to a high sampling frequency higher than the second frequency.

2. An electronic cigarette according to claim 1 , wherein the control circuitry is configured to switch from the sleep state to the active state in response to the current pressure difference exceeding a first threshold.

3. An electronic cigarette according to any preceding claim, wherein the plurality of states further comprises a vaping state in which the control circuitry controls the vaporizing unit to generate the vapor.

4. An electronic cigarette according to claim 3 wherein, in the vaping state, the sampling frequency is a third frequency higher than the second frequency.

5. An electronic cigarette according to any preceding claim, wherein the control circuitry is configured to switch to the vaping state in response to the current pressure difference exceeding a second threshold, the second threshold indicating that a user is inhaling at the vapor outlet.

6. An electronic cigarette according to any preceding claim, wherein the pressure sensor is configured to measure an absolute pressure.

7. An electronic cigarette according to claim 6, wherein the pressure sensor is a MEMS sensor.

8. An electronic cigarette according to claim 6 or claim 7, wherein the control circuitry is configured to estimate a temperature based on the background pressure.

9. A control circuit for controlling an electronic cigarette, the electronic cigarette comprising: a vaporizing unit configured to generate a vapor from a substrate; an air flow inlet; an vapor outlet; a main vapor flow channel extending past the vaporizing unit from the air flow inlet to the vapor outlet; a pressure sensor arranged to measure a pressure at the main vapor flow channel, or arranged near to the air flow inlet or the vapor outlet; and an accelerometer configured to measure an acceleration of the electronic cigarette, wherein the control circuit is configured to monitor user inhalation by: obtaining pressure measurements from the pressure sensor at a sampling frequency; calculating a background pressure as a moving average of the pressure measurements obtained within a moving sampling period; and calculating a current pressure difference as a difference between a current pressure measurement and the background pressure, wherein the control circuit is configured to select an operation state in dependence upon the current pressure difference, wherein the operation state is one of a plurality of states comprising: a sleep state in which the sampling frequency is a first frequency; and an active state in which the sampling frequency is a second frequency higher than the first frequency, wherein the control circuitry is configured to switch from the sleep state to the active state in response to the acceleration exceeding a threshold, and wherein the control circuitry is further configured to respond to an acceleration sustained in a specific direction for at least a threshold period of time by switching the sampling frequency to a high sampling frequency higher than the second frequency.

10. A method for controlling an electronic cigarette comprising: a vaporizing unit configured to generate a vapor from a substrate; an air flow inlet; an vapor outlet; a main vapor flow channel extending past the vaporizing unit from the air flow inlet to the vapor outlet; a pressure sensor arranged to measure a pressure at the main vapor flow channel, or arranged near to the air flow inlet or the vapor outlet; and an accelerometer configured to measure an acceleration of the electronic cigarette, the method comprising monitoring user inhalation by: obtaining pressure measurements from the pressure sensor at a sampling frequency; calculating a background pressure as a moving average of the pressure measurements obtained within a moving sampling period; calculating a current pressure difference as a difference between a current pressure measurement and the background pressure; and selecting an operation state in dependence upon the current pressure difference, wherein the operation state is one of a plurality of states comprising: a sleep state in which the sampling frequency is a first frequency; and an active state in which the sampling frequency is a second frequency higher than the first frequency, wherein the control circuitry is configured to switch from the sleep state to the active state in response to the acceleration exceeding a threshold, and wherein the control circuitry is further configured to respond to an acceleration sustained in a specific direction for at least a threshold period of time by switching the sampling frequency to a high sampling frequency higher than the second frequency.

11. A non-transitory computer-readable medium storing instructions which, when executed by a processor, cause the processor to perform a method according to claim 10.

12. A signal comprising computer-readable instructions which, when executed by a processor, cause the processor to perform a method according to claim 10.