Patent Publication Number: US-2023157370-A1

Title: Electronic aerosol provision system

Description:
PRIORITY CLAIM 
     The present application is a Continuation of U.S. application Ser. No. 16/619,670, filed Dec. 5, 2019, which is a National Phase entry of PCT Application No. PCT/GB2018/051540, filed Jun. 6, 2018, which claims priority from GB Patent Application No. 1709201.6, filed Jun. 9, 2017, which is hereby fully incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to electronic aerosol provision systems such as nicotine delivery systems (e.g. electronic cigarettes and the like). 
     BACKGROUND 
     Electronic aerosol provision systems such as electronic cigarettes (e-cigarettes) generally contain a reservoir of a source liquid containing a formulation, typically including nicotine, from which an aerosol is generated, e.g. through heat vaporization. An aerosol source for an aerosol provision system may thus comprise a heater having a heating element arranged to receive source liquid from the reservoir, for example through wicking/capillary action. While a user inhales on the device, electrical power is supplied to the heating element to vaporize source liquid in the vicinity of the heating element to generate an aerosol for inhalation by the user. Such devices are usually provided with one or more air inlet holes located away from a mouthpiece end of the system. When a user sucks on a mouthpiece connected to the mouthpiece end of the system, air is drawn in through the inlet holes and past the aerosol source. There is a flow path connecting between the aerosol source and an opening in the mouthpiece so that air drawn past the aerosol source continues along the flow path to the mouthpiece opening, carrying some of the aerosol from the aerosol source with it. The aerosol-carrying air exits the aerosol provision system through the mouthpiece opening for inhalation by the user. 
     Usually an electric current is supplied to the heater when a user is drawing/puffing on the device. Typically, the electric current is supplied to the heater, e.g. resistance heating element, in response to either the activation of an airflow sensor along the flow path as the user inhales/draw/puffs or in response to the activation of a button by the user. The heat generated by the heating element is used to vaporize a formulation. The released vapor mixes with air drawn through the device by the puffing consumer and forms an aerosol. When the user has finished the puff (drop of air flow/drop of pressure) the flow or pressure sensor deactivates the electric heater by cutting off the electric current. At that point of time the heater is still at an elevated temperature capable of vaporizing a certain portion of liquid. The heat for this continued vaporization originates from the heat capacity of the heater itself. Subsequently, the heater cools down. When the temperature of the heater falls below the boiling point of the higher volatile formulation components (e.g. water, propylene glycol), the vaporization process stalls. The vapor released during the continued vaporization phase after deactivation is not delivered to the consumer since there is no air flow through the device anymore. Instead the vapor condenses on internal walls of the device causing potential problems (e.g. clogging). The evaporation heat released by the heater during the continued vaporization phase can also be considered as an energy loss. The energy is lost as condensation heat which in turn is heating up structural components of the device. This issue is exacerbated in devices with larger heater elements. 
     Various approaches are described which seek to help address some of these issues. 
     SUMMARY 
     According to a first aspect of certain embodiments there is provided an electronic vapor provision system comprising a vaporizer for vaporizing liquid for inhalation by a user of the electronic vapor provision system, a power supply for supplying power to the vaporizer to vaporize the liquid in response to a user activation of the device, and a control unit configured to firstly learn a user&#39;s expected puff duration and secondly cause power to be supplied to the vaporizer for a period of time shorter than a user&#39;s expected puff duration. 
     The control unit continuously measures the puff duration of a given user, and computes an expected puff duration for that user. After activation of the device by the user, the control unit supplies an electric current to the heater for a total period slightly shorter than the expected puff duration (e.g. 0.05-0.5 seconds shorter). Hence the consumer is most likely still puffing on the device when the supply of electric current has already been cut off. As a result the vapor released during the post-deactivation continued vaporization phase (i.e. when no power is supplied to the heater but it is still of a sufficient temperature to vaporize the liquid) can be utilized to form an aerosol inhalable by the consumer. This vapor fraction and the energy used to release it cannot be considered as a loss anymore. That way the energy efficiency and the number of puffs achievable with a given battery capacity can be increased. 
     It will be appreciated that features and aspects of the disclosure described above in relation to the first and other aspects of the disclosure are equally applicable to, and may be combined with, embodiments of the disclosure according to other aspects of the disclosure as appropriate, and not just in the specific combinations described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG.  1    is a schematic (exploded) diagram of an electronic vapor provision system such as an e-cigarette in accordance with some embodiments of the disclosure. 
         FIG.  2    is a schematic diagram of the body of the e-cigarette of  FIG.  1    in accordance with some embodiments of the disclosure. 
         FIG.  3    is a schematic diagram of the vaporizer portion of the e-cigarette of  FIG.  1    in accordance with some embodiments of the disclosure. 
         FIG.  4    is a schematic diagram showing certain aspects of one end of the body portion of the e-cigarette of  FIG.  1    in accordance with some embodiments of the disclosure. 
         FIG.  5    is a schematic flowchart which illustrates certain aspects of operation of the e-cigarette of  FIG.  1    in accordance with some embodiments of the disclosure. 
         FIG.  6    is a schematic flowchart which illustrates certain aspects of operation of the e-cigarette of  FIG.  1    in accordance with some other embodiments of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Aspects and features of certain examples and embodiments are discussed/described herein. Some aspects and features of certain examples and embodiments may be implemented conventionally and these are not discussed/described in detail in the interests of brevity. It will thus be appreciated that aspects and features of apparatus and methods discussed herein which are not described in detail may be implemented in accordance with any conventional techniques for implementing such aspects and features. 
     As described above, the present disclosure relates to an aerosol provision system, such as an e-cigarette. Throughout the following description the term “e-cigarette” is sometimes used but this term may be used interchangeably with aerosol (vapor) provision system. 
       FIG.  1    is a schematic diagram of an electronic vapor provision system such as an e-cigarette  10  in accordance with some embodiments of the disclosure (not to scale). The e-cigarette has a generally cylindrical shape, extending along a longitudinal axis indicated by dashed line LA, and comprises two main components, namely a body  20  and a cartomizer  30 . The cartomizer includes an internal chamber containing a reservoir of a payload such as for example nicotine, a vaporizer (such as a heater), and a mouthpiece  35 . References to “nicotine” hereafter will be understood to be merely exemplary and can be substituted with any suitable payload. The reservoir may be a foam matrix or any other structure for retaining the nicotine until such time that it is required to be delivered to the vaporizer. The vaporizer is for vaporizing the nicotine, and the cartomizer  30  may further include a wick or similar facility to transport a small amount of nicotine from the reservoir to a vaporizing location on or adjacent the vaporizer. In the following, a heater is used as a specific example of a vaporizer. However, it will be appreciated that other forms of vaporizer (for example, those which utilize ultrasonic waves) could also be used. 
     The body  20  includes a re-chargeable cell or battery to provide power to the e-cigarette  10  and a circuit board for generally controlling the e-cigarette. When the heater receives power from the battery, as controlled by the circuit board, the heater vaporizes the nicotine and this vapor is then inhaled by a user through the mouthpiece  35 . In some specific embodiments the body is further provided with a manual activation device  265 , e.g. a button, switch, or touch sensor located on the outside of the body. 
     The body  20  and cartomizer  30  may be detachable from one another by separating in a direction parallel to the longitudinal axis LA, as shown in  FIG.  1   , but are joined together when the device  10  is in use by a connection, indicated schematically in  FIG.  1    as  25 A and  25 B, to provide mechanical and electrical connectivity between the body  20  and the cartomizer  30 . The electrical connector  25 B on the body  20  that is used to connect to the cartomizer  30  also serves as a socket for connecting a charging device (not shown) when the body  20  is detached from the cartomizer  30 . The other end of the charging device may be plugged into a USB socket to re-charge the cell in the body  20  of the e-cigarette  10 . In other implementations, a cable may be provided for direct connection between the electrical connector  25 B on the body  20  and a USB socket. 
     The e-cigarette  10  is provided with one or more holes (not shown in  FIG.  1   ) for air inlets. These holes connect to an air passage through the e-cigarette  10  to the mouthpiece  35 . When a user inhales through the mouthpiece  35 , air is drawn into this air passage through the one or more air inlet holes, which are suitably located on the outside of the e-cigarette. When the heater is activated to vaporize the nicotine from the cartridge, the airflow passes through, and combines with, the nicotine vapor, and this combination of airflow and nicotine vapor then passes out of the mouthpiece  35  to be inhaled by a user. Except in single-use devices, the cartomizer  30  may be detached from the body  20  and disposed of when the supply of nicotine is exhausted (and replaced with another cartomizer if so desired). It will be appreciated that the e-cigarette  10  shown in  FIG.  1    is presented by way of example, and various other implementations can be adopted. For example, in some embodiments, the cartomizer  30  is provided as two separable components, namely a cartridge comprising the nicotine reservoir and mouthpiece (which can be replaced when the nicotine from the reservoir is exhausted), and a vaporizer comprising a heater (which is generally retained). As another example, the charging facility may connect to an additional or alternative power source, such as a car cigarette lighter. 
       FIG.  2    is a schematic (simplified) diagram of the body  20  of the e-cigarette  10  of  FIG.  1    in accordance with some embodiments of the disclosure.  FIG.  2    can generally be regarded as a cross-section in a plane through the longitudinal axis LA of the e-cigarette  10 . Note that various components and details of the body, e.g. such as wiring and more complex shaping, have been omitted from  FIG.  2    for reasons of clarity. 
     The body  20  includes a battery or cell  210  for powering the e-cigarette  10  in response to a user activation of the device. Additionally, the body  20  includes a control unit (not shown in  FIG.  2   ), for example a chip such as an application specific integrated circuit (ASIC) or microcontroller, for controlling the e-cigarette  10 . The microcontroller or ASIC includes a CPU or micro-processor. The operations of the CPU and other electronic components are generally controlled at least in part by software programs running on the CPU (or other component). Such software programs may be stored in non-volatile memory, such as ROM, which can be integrated into the microcontroller itself, or provided as a separate component. The CPU may access the ROM to load and execute individual software programs as and when required. The microcontroller also contains appropriate communications interfaces (and control software) for communicating as appropriate with other devices in the body  10 . 
     The control unit is operable to learn a user&#39;s expected puff duration, and to cause power to be supplied to the vaporizer for a period of time shorter than the user&#39;s expected puff duration. As such, the control unit is operable to measure the length of time the user activates the device (i.e. the puff duration). Furthermore the control unit is able to store the length of time of successive puffs in the memory associated with the ASIC. The control unit may utilize the CPU to execute software programs to analyze the puff information. 
     In some embodiments the CPU analyses the puff information to learn an average puff duration for a user, by calculating the cumulative total duration of all puffs and dividing it by the total number of puffs. In one embodiment the total number of puffs may be limited to a certain number of puffs N, for example up to the last 100 puffs or up to the last 10 puffs. As such, the e-cigarette may be deemed responsive to changes in usage behavior. It will be appreciated that for ‘new’ devices the user will have taken a limited number of puffs which may be less than the total number typically used to calculate an average. For such devices the total number of puffs taken will be used to calculate an average, while this number is less than the limit. Optionally, given that the memory may be used in a first-in-first out configuration (i.e. a circular configuration) to store the last N puff durations, the memory may be provided with N instances of an average puff duration pre-loaded at manufacture so that the system does not have to operate differently during initial use. Over time, these pre-loaded values are supplanted by measured values from the user. In some other embodiments the control unit learns a user&#39;s expected puff duration by employing machine learning. The CPU may be operable to employ certain software to analyze puff information, and identify trends in the user&#39;s usage behavior. This may also be more responsive to a user&#39;s changing demands. 
     As noted above, the control unit is operable to cause power to be supplied to the vaporizer for a period of time shorter than the user&#39;s expected puff duration. Hence the user is most likely still puffing on the device when the supply of electric current has already been cut off. When the supply of electric current has been cut off, the heater remains at a sufficient temperature to continue to vaporize liquid for a short period of time. By causing the power to be cut off while the user is still puffing on the device, the vapor released during the continued vaporization phase (i.e. when no power is supplied to the heater but it is still of a sufficient temperature to vaporize the liquid) can be utilized to form an aerosol inhalable by the user. This vapor fraction and the energy used to release it cannot be considered as a loss anymore. That way the energy efficiency and the number of puffs achievable with a given battery capacity can be increased. The power to the heater is cut off after being active for a time slightly shorter than the learned user puff duration. In some embodiments, the time power is supplied to the heater is between 0.05 to 0.5 seconds shorter than the expected user puff duration. In one embodiment, the time power is supplied to the heater is 0.3 seconds shorter than the expected user puff duration. More generally, the manufacturer of a device may measure the time taken for a heating element to drop below the vaporization temperature of the payload liquid, and use this time (or a suitable approximation thereto) as the advance cut-off time. Where different available payloads have different vaporization temperatures, then optionally the lowest temperature (the longest advance time) may be chosen, or optionally the device may be adapted to recognize the payload type and select the appropriate cut-off time. 
     The body  20  further includes a cap  225  to seal and protect the far (distal) end of the e-cigarette  10 . Typically there is an air inlet hole provided in or adjacent to the cap  225  to allow air to enter the body  20  when a user inhales on the mouthpiece  35 . The control unit or ASIC may be positioned alongside or at one end of the battery  210 . In some embodiments, the ASIC is attached to a sensor unit  215  to detect an inhalation on mouthpiece  35  (or alternatively the sensor unit  215  may be provided on the ASIC itself). An air path is provided from the air inlet through the e-cigarette, past the airflow sensor  215  and the heater (in the vaporizer or cartomizer  30 ), to the mouthpiece  35 . Thus when a user inhales on the mouthpiece of the e-cigarette, the CPU detects such inhalation based on information from the airflow sensor  215 . 
     At the opposite end of the body  20  from the cap  225  is the connector  25 B for joining the body  20  to the cartomizer  30 . The connector  25 B provides mechanical and electrical connectivity between the body  20  and the cartomizer  30 . The connector  25 B includes a body connector  240 , which is metallic (silver-plated in some embodiments) to serve as one terminal for electrical connection (positive or negative) to the cartomizer  30 . The connector  25 B further includes an electrical contact  250  to provide a second terminal for electrical connection to the cartomizer  30  of opposite polarity to the first terminal, namely body connector  240 . The electrical contact  250  is mounted on a coil spring  255 . When the body  20  is attached to the cartomizer  30 , the connector  25 A on the cartomizer  30  pushes against the electrical contact  250  in such a manner as to compress the coil spring in an axial direction, i.e. in a direction parallel to (co-aligned with) the longitudinal axis LA. In view of the resilient nature of the spring  255 , this compression biases the spring  255  to expand, which has the effect of pushing the electrical contact  250  firmly against connector  25 A of the cartomizer  30 , thereby helping to ensure good electrical connectivity between the body  20  and the cartomizer  30 . The body connector  240  and the electrical contact  250  are separated by a trestle  260 , which is made of a non-conductor (such as plastic) to provide good insulation between the two electrical terminals. The trestle  260  is shaped to assist with the mutual mechanical engagement of connectors  25 A and  25 B. 
     As mentioned above, a button  265 , which represents a form of manual activation device  265 , may be located on the outer housing of the body  20 . The button  265  may be implemented using any appropriate mechanism which is operable to be manually activated by the user—for example, as a mechanical button or switch, a capacitive or resistive touch sensor, and so on. It will also be appreciated that the manual activation device  265  may be located on the outer housing of the cartomizer  30 , rather than the outer housing of the body  20 , in which case, the manual activation device  265  may be attached to the ASIC via the connections  25 A,  25 B. The button  265  might also be located at the end of the body  20 , in place of (or in addition to) cap  225 . 
       FIG.  3    is a schematic diagram of the cartomizer  30  of the e-cigarette  10  of  FIG.  1    in accordance with some embodiments of the disclosure.  FIG.  3    can generally be regarded as a cross-section in a plane through the longitudinal axis LA of the e-cigarette  10 . Note that various components and details of the cartomizer  30 , such as wiring and more complex shaping, have been omitted from  FIG.  3    for reasons of clarity. 
     The cartomizer  30  includes an air passage  355  extending along the central (longitudinal) axis of the cartomizer  30  from the mouthpiece  35  to the connector  25 A for joining the cartomizer  30  to the body  20 . A reservoir of nicotine  360  is provided around the air passage  335 . This reservoir  360  may be implemented, for example, by providing cotton or foam soaked in nicotine. The cartomizer  30  also includes a heater  365  for heating nicotine from reservoir  360  to generate nicotine vapor to flow through air passage  355  and out through mouthpiece  35  in response to a user inhaling on the e-cigarette  10 . The heater  365  is powered through lines  366  and  367 , which are in turn connected to opposing polarities (positive and negative, or vice versa) of the battery  210  of the main body  20  via connector  25 A (the details of the wiring between the power lines  366  and  367  and connector  25 A are omitted from  FIG.  3   ). 
     The connector  25 A includes an inner electrode  375 , which may be silver-plated or made of some other suitable metal or conducting material. When the cartomizer  30  is connected to the body  20 , the inner electrode  375  contacts the electrical contact  250  of the body  20  to provide a first electrical path between the cartomizer  30  and the body  20 . In particular, as the connectors  25 A and  25 B are engaged, the inner electrode  375  pushes against the electrical contact  250  so as to compress the coil spring  255 , thereby helping to ensure good electrical contact between the inner electrode  375  and the electrical contact  250 . 
     The inner electrode  375  is surrounded by an insulating ring  372 , which may be made of plastic, rubber, silicone, or any other suitable material. The insulating ring is surrounded by the cartomizer connector  370 , which may be silver-plated or made of some other suitable metal or conducting material. When the cartomizer  30  is connected to the body  20 , the cartomizer connector  370  contacts the body connector  240  of the body  20  to provide a second electrical path between the cartomizer  30  and the body  20 . In other words, the inner electrode  375  and the cartomizer connector  370  serve as positive and negative terminals (or vice versa) for supplying power from the battery  210  in the body  20  to the heater  365  in the cartomizer  30  via supply lines  366  and  367  as appropriate. 
     The cartomizer connector  370  is provided with two lugs or tabs  380 A,  380 B, which extend in opposite directions away from the longitudinal axis of the e-cigarette  10 . These tabs are used to provide a bayonet fitting in conjunction with the body connector  240  for connecting the cartomizer  30  to the body  20 . This bayonet fitting provides a secure and robust connection between the cartomizer  30  and the body  20 , so that the cartomizer and body are held in a fixed position relative to one another, with minimal wobble or flexing, and the likelihood of any accidental disconnection is very small. At the same time, the bayonet fitting provides simple and rapid connection and disconnection by an insertion followed by a rotation for connection, and a rotation (in the reverse direction) followed by withdrawal for disconnection. It will be appreciated that other embodiments may use a different form of connection between the body  20  and the cartomizer  30 , such as a snap fit or a screw connection. 
       FIG.  4    is a schematic diagram of certain details of the connector  25 B at the end of the body  20  in accordance with some embodiments of the disclosure (but omitting for clarity most of the internal structure of the connector as shown in  FIG.  2   , such as trestle  260 ). In particular,  FIG.  4    shows the external housing  201  of the body  20 , which generally has the form of a cylindrical tube. This external housing  201  may comprise, for example, an inner tube of metal with an outer covering of paper or similar. The external housing  201  may also comprise the manual activation device  265  (not shown in  FIG.  4   ) so that the manual activation device  265  is easily accessible to the user. 
     The body connector  240  extends from this external housing  201  of the body  20 . The body connector  240  as shown in  FIG.  4    comprises two main portions, a shaft portion  241  in the shape of a hollow cylindrical tube, which is sized to fit just inside the external housing  201  of the body  20 , and a lip portion  242  which is directed in a radially outward direction, away from the main longitudinal axis (LA) of the e-cigarette. Surrounding the shaft portion  241  of the body connector  240 , where the shaft portion does not overlap with the external housing  201 , is a collar or sleeve  290 , which is again in a shape of a cylindrical tube. The collar  290  is retained between the lip portion  242  of the body connector  240  and the external housing  201  of the body, which together prevent movement of the collar  290  in an axial direction (i.e. parallel to axis LA). However, collar  290  is free to rotate around the shaft portion  241  (and hence also axis LA). 
     As mentioned above, the cap  225  is provided with an air inlet hole to allow air to flow when a user inhales on the mouthpiece  35 . However, in some embodiments the majority of air that enters the device when a user inhales flows through collar  290  and body connector  240  as indicated by the two arrows in  FIG.  4   . 
       FIG.  5    shows a flow chart illustrating a process performed by the control unit for controlling operation of the electronic vapor provision system according to some embodiments of the present disclosure. 
     The process starts at  500 . At  505 , it is determined whether or not the device has been activated by the user. Activation may be by inhalation, button press or touch sensor interaction, for example. If the device has not been activated, then the process returns to the beginning of  505 . On the other hand, if the device has been activated, then the process moves onto  510 , and a timer is started to measure the total length of time the user activates the device. Immediately after, at  515 , the control unit causes power to be supplied to the vaporizer (such as heater  365 ). This activates the vaporizer and causes the liquid of the cartomizer  30  to be vaporized for inhalation by the user. 
     The process then moves onto  520 , in which it is determined whether or not the device is still being activated by the user, i.e. if the user is still inhaling, pressing the button or interacting with the touch sensor, as applicable. If it is determined at  520  that the device is still activated, then the process moves onto  525 . At  525 , the control unit compares the current time against the first period of time (i.e. the period of time shorter than the expected puff duration, that the control unit powers the vaporizer). If the current time is less than the first period of time then the system returns to  515  and continues to supply power to the vaporizer. A loop is formed by  515 ,  520 , and  525  that can only be broken by the user deactivating the device at  520  or if the period of activation exceeds the first period of time, at  525 . If the user deactivates the device, the system proceeds to  530  and immediately stops supplying power to the vaporizer. Alternatively, if the period of activation exceeds the first period of time the system proceeds to  540  and immediately stops supplying power to the vaporizer. 
     After  530  the control unit can immediately stop the timer at  535 , so that the time measured corresponds to the length of time the device has been activated. Alternatively, after  540 , power has stopped being supplied to the vaporizer but the user is still activating the device, e.g. still puffing. As such,  545  continuously queries whether the user has ceased to activate the device. Once the user has stopped, the system proceeds to  535  and the timer is stopped, so that the time measured corresponds to the length of time the device has been activated. At  550  the control unit incorporates the latest puff duration into the analysis of the expected puff duration, to estimate the user&#39;s next expected puff duration. The process ends at  560  and returns the device to  500 , ready for the next user activation. Note that although  FIG.  6    shows starting of the timer  510  and supplying power to the vaporizer  515  being performed sequentially, in practice these may be performed in parallel. 
     In an embodiment, the first period of time is 0.3 seconds shorter than the expected puff duration of the user. It is expected that 0.3 seconds represents a threshold time at which a user cannot detect the heater has switched off prematurely. As an example, for an expected puff duration of 3 seconds the first period of time would be 2.7 seconds. If the user presses an activation button for 2.9 seconds then 0.2 seconds of energy have been saved. Given the short period of time and the thermal inertia of the heater, liquid vaporized in this time is inhaled while no power is wasted. Furthermore as less liquid is vaporized as the temperature of the heater drops, once the user stops inhaling there will be less additional vaporization that subsequently condenses on the internal walls of the device. 
     Thus, it can be seen from  FIG.  5    that power is provided to the vaporizer for a period of time slightly shorter than the expected puff duration of the user, unless the user prematurely stops the puff after a time much shorter than the expected puff duration. In general terms, the vaporizer remains activated, thus vaporizing the liquid, for as long as necessary so that the user does not detect a reduction in quality. This mechanism is hidden from the user and, therefore, does not require the user to practice certain behavior in relation to the use of the device; for example releasing a button  265  early to deactivate the device prior to finishing the puff. Instead this functionality is inherent in the device, to provide a more intuitive experience. 
     However, the embodiment detailed in  FIG.  5    has the potential, in some circumstances, to provide an unsatisfactory user experience. If the actual user puff duration exceeds the estimated (expected) user puff duration greatly, then the user may detect a significant loss of performance in the final stage of the puff. To overcome this issue some embodiments of the device are further configured to resume supplying power to the vaporizer, in response to a longer than expected puff, for a second period of time. 
       FIG.  6    shows a flow chart illustrating a process performed by the control unit for controlling operation of the electronic vapor provision system according to some embodiments of the present disclosure, wherein the system is further configured to resume supplying power to the vaporizer in response to a longer than expected puff. 
     The process starts at  600 . At  605 , it is determined whether or not the device has been activated by the user (again for example by inhalation, button press or touch sensor interaction). If the device has not been activated, then the process returns to the beginning of  605 . On the other hand, if the device has been activated, then the process moves to  610 , and a timer is started to measure the total length of time the user activates the device. Immediately after, at  615 , the control unit causes power to be supplied to the vaporizer (such as heater  365 ). This activates the vaporizer and causes the liquid of the cartomizer  30  to be vaporized for inhalation by the user. 
     The process then moves onto  620 , in which it is determined whether or not the device is still being activated by the user. If it is determined at  620  that the device is still activated, then the process moves onto step  625 . At  625 , the control unit compares the current time against the first period of time (i.e. the period of time shorter than the expected puff duration that the control unit powers the vaporizer). If the current time is less than the first period of time then the system returns to  615  and continues to supply power to the vaporizer. A loop is formed by  615 ,  620 , and  625  that can only be broken by the user deactivating the device at  620  or the period of activation exceeding the first period of time, at  625 . If the user deactivates the device, the system proceeds to  630  and immediately stops supplying power to the vaporizer. Alternatively, if the period of activation exceeds the first period of time the system proceeds to  640  and immediately stops supplying power to the vaporizer. 
     After  630  the control unit can immediately stop the timer at  635 , so that the time measured corresponds to the length of time the device has been activated. Alternatively, after  640 , power has stopped being supplied to the vaporizer but the user is still activating the device, i.e. still puffing. As such,  645  queries whether the user has ceased to activate the device. If the user is not activating the device, the control unit proceeds to  635  and the timer is stopped, so that the time measured corresponds to the length of time the device has been activated. If the user is still activating the device, the control unit proceeds to  650  and the control unit queries whether the current time is greater than the expected puff duration. If the current time is not greater, the system loops back to  645 . If, however the current time is greater, the system proceeds to  655  and the control unit resumes supplying power to the vaporizer. At  660  the system continuously queries whether the user has ceased to activate the device. Once the answer is no the system proceeds to  665  and the control unit stops supplying power to the vaporizer. Next the control unit proceeds to  635  and the timer is stopped, so that the time measured corresponds to the length of time the device has been activated by the user. At  670  the control unit incorporates the latest puff duration into the analysis of the expected puff duration, to estimate the next puff duration. The process ends at  680  and returns the device to  600 , ready for the next user activation. 
     Different embodiments may adopt different approaches to the power management of the heater. The embodiment of  FIG.  6    powers the heater for a first period of time, slightly shorter than the expected puff duration, and then resumes powering the heater for a second period of time if the user activation of the device exceeds the expected puff duration. In one embodiment, it may be advantageous to resume powering the heater for the second period of time at a lower power level, thereby reducing the continued vaporization phase after the user deactivates the device. In an alternate embodiment, the power may be pulsed repeatedly during the second period while the user continues to activate the device. For an equivalent period of time, the integrated energy supplied by the pulses will be significantly less than the integrated energy supplied by the power level of the first period of time. In either of these embodiments the energy usage is reduced, enhancing the number of puffs that can be achieved per battery, whilst also ensuring that the performance of the device is not noticeably reduced. Additionally by reducing the length of the continued vaporization phase, there is less condensation of vapor on the internal walls of the device. In certain embodiments, the control unit may not completely stop powering the heater after the first period, and instead may immediately start pulsing power to the heater or may immediately power the heater at a lower power for the second period of time. The thermal inertia of the heater will be slowly reduced; however this will not occur as quickly as if the heater were powered off and therefore if the user activates the device for a larger than expected time they are less likely to notice a loss of performance. 
     As previously mentioned, some embodiments may adopt implementations of a manual activation device  265 . The manual activation device may be activated by the user to cause the control unit to supply power to the vaporizer to vaporize the liquid. In these embodiments the user activation of the manual activation device facilitates the user activation of the device, thereby starting the processes described above, for example in  FIG.  5    and  FIG.  6   . The manual activation device  265  may be, for example, a physical button or switch or may be a touch sensor (such as a resistive or capacitive touch sensor) which is activated simply by being touched by the user. In addition, the method of activating and deactivating the manual activation device  265  may also take a range of different approaches. For example, in some cases the manual activation device may be activated for a predetermined period of time after the button  265  is pressed or touched, after which the manual activation device is de-activated. Such an implementation helps to ensure that the manual activation device is de-activated by the user, although the user does not have full (direct) control over the supply of power to the vaporizer. 
     In some embodiments, the manual activation device  265  comprises a button which is activated by a first press of the button by the user, and then deactivated by a second (subsequent) press of the button by the user. In other words, alternate presses of the button activate and then deactivate the manual activation device. During the time period between the first and second press, the microcontroller regards the manual activation device  265  as activated. This method has the advantage of providing the user with direct control over the duration of activation, although the manual activation device may remain activated if the user forgets or neglects to make a second press. In another example, the manual activation device  265  is deemed activated for as long as the button is continuously pressed by the user. This method again gives the user control over how long the vaporizer is activated. Moreover, it is natural for a user to stop pressing the button  265  when they have finished using the e-cigarette, so it is unlikely that the manual activation device would remain in an activated state unintentionally. 
     Similar methods may also be adopted when the manual activation device  265  comprises a touch sensor. That is, in one example, the manual activation device  265  is deemed to be activated following a first touch of the touch sensor by the user and then deemed to be deactivated following a second touch of the touch sensor by the user. During the time period between the first and second touch, the manual activation device  265  is deemed activated. In another example, the manual activation device  265  is deemed activated for as long as the touch sensor is continuously touched by the user. 
     In another example, if the manual activation device  265  comprises a manual switch, such as a slidable or rotatable switch, then the manual activation device  265  will be activated when the switch is put into an “on” position and deactivated when the switch is put into an “off” position. In such embodiments, the switch may be biased towards the “off” position so that the user has to continually hold the switch in the “on” position in order for the manual activation device to be activated. In this case, when the user stops holding the switch in the “on” position, the switch will automatically return (under the influence of a spring or some other resilient bias mechanism, etc) to the “off” position. This not only makes it more difficult for the switch to be unintentionally retained in the “on” (activated) position, but also makes it easier for the user, since the user does not have to manually change the switch back to the “off” position after inhaling on the e-cigarette. 
     The manual activation device  265 , be it a button, touch sensor, switch or any other suitable device, is generally positioned such that it is easily accessible to the user when the user holds the e-cigarette  10  so as to inhale on it. For example, the manual activation device  265  may be located somewhat closer to the proximal (mouth) end of the e-cigarette than to the distal (cap) end of the e-cigarette, since the user is more likely to hold the e-cigarette closer at a position closer to its proximal end (as is the case for conventional combustible cigarettes). Thus in the example shown in  FIG.  1   , the button  265  is located on the body portion  25  (since the cartridge  30  is disposable), but at the end nearest to the mouthpiece. The button may be activated (pressed, moved or touched) conveniently while the e-cigarette is being held by a user. While the manual activation devices have been described in-depth with regard to the activation of the device and consequently the vaporizer, it will be appreciated that in many embodiments additional manual activation devices may serve ancillary functions, for example an on/off or lock switch. 
     In alternate embodiments, an air flow sensor may be implemented in the device so that the user may activate the device and cause the control unit to supply power to the vaporizer to vaporize the liquid by inhaling on the device. In these embodiments the user activation of the air flow sensor facilitates the user activation of the device, thereby starting the processes described above, for example in  FIG.  5    and  FIG.  6   . The body  20  includes the sensor unit  215  located in or adjacent to the air path through the body  20  from the air inlet to the air outlet (to the vaporizer). The sensor unit  215  may include a pressure drop sensor and temperature sensor (also in or adjacent to this air path). It will be appreciated, however, that the sensor unit  215  may include the pressure drop sensor without the temperature sensor or may include an airflow monitor to directly measure airflow (rather than pressure drop). Thus when a user inhales on the mouthpiece of the e-cigarette, the control unit detects such inhalation based on information from the pressure drop sensor. In response to the detection of an inhalation, the CPU supplies power to the heater, which thereby heats and vaporizes the nicotine from the wick for inhalation by the user. 
     Hence it will be appreciated that “activation” and “deactivation” may equally be considered separate actions (such as pushing a button or switch on and then off) or the commencement and cessation of a single action (such as inhalation, pressing a button or interacting with a touch sensor). 
     Advantageously, the above described embodiments act to reduce the energy supplied to the heater during each puff. As such, this may increase the number of puffs for a given battery capacity or present an opportunity to reduce the battery capacity of the device. The reduced length of the continued vaporization phase additionally reduces unwanted condensates on the internal walls of the device, improves puff count for a given volume of liquid, and may also help to alleviate carbonyl build up, which occurs when the heater is on but there is no airflow in the device. 
     Thus, there has been described an electronic vapor provision system comprising a vaporizer for vaporizing liquid for inhalation by a user of the electronic vapor provision system; a power supply for supplying power to the vaporizer to vaporize the liquid in response to a user activation of the device; and a control unit configured to: i) estimate a user&#39;s expected activation duration; ii) cause power to be supplied to the vaporizer for a period of time shorter than a user&#39;s activation duration. Variations on this system have similarly been described as outlined herein. Likewise, there has been described a method of operating an electronic vapor provision system including a vaporizer for vaporizing liquid for inhalation by a user of the electronic vapor provision system; wherein the electronic vapor provision system includes a power supply for supplying power to the vaporizer to vaporize the liquid in response to a user activation of the device, the method comprising; 
     causing a control unit to estimate a user&#39;s expected activation duration; and 
     causing a control unit to supply power to the vaporizer for a period of time shorter than a user&#39;s activation duration. Variations on this method have similarly been described as outlined herein. 
     While the above described embodiments have in some respects focused on some specific example aerosol provision systems, it will be appreciated the same principles can be applied for aerosol provision systems using other technologies. That is to say, the specific manner in which various aspects of the aerosol provision system function are not directly relevant to the principles underlying the examples described herein. 
     In order to address various issues and advance the art, this disclosure shows by way of illustration various embodiments in which the claimed invention(s) may be practiced. The advantages and features of the disclosure are of a representative sample of embodiments only, and are not exhaustive and/or exclusive. They are presented only to assist in understanding and to teach the claimed invention(s). It is to be understood that advantages, embodiments, examples, functions, features, structures, and/or other aspects of the disclosure are not to be considered limitations on the disclosure as defined by the claims or limitations on equivalents to the claims, and that other embodiments may be utilized and modifications may be made without departing from the scope of the claims. Various embodiments may suitably comprise, consist of, or consist essentially of, various combinations of the disclosed elements, components, features, parts, steps, means, etc. other than those specifically described herein, and it will thus be appreciated that features of the dependent claims may be combined with features of the independent claims in combinations other than those explicitly set out in the claims. The disclosure may include other inventions not presently claimed, but which may be claimed in future.