Patent Publication Number: US-2021169146-A1

Title: Aerosol generating material characteristic determination

Description:
PRIORITY CLAIM 
     The present application is a National Phase entry of PCT Application No. PCT/EP2019/073263, filed Aug. 30, 2019 which claims priority from GB Patent Application No. 1814197.8, filed Aug. 31, 2018, each of which is hereby fully incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to determining characteristics of an aerosol generating material, and more particularly to determining characteristics of an aerosol generating material of an aerosol generating device. 
     BACKGROUND 
     Smoking articles such as cigarettes, cigars and the like burn tobacco during use to create tobacco smoke. Attempts have been made to provide alternatives to these articles by creating products that release compounds without combusting. Examples of such products are so-called “heat not burn” products or tobacco heating devices or products, which release compounds by heating, but not burning, material. The material may be, for example, tobacco or other non-tobacco products, which may or may not contain nicotine. 
     SUMMARY 
     According to a first aspect of the present invention, there is provided apparatus for determining a characteristic of an aerosol generating material of an aerosol generating device, the aerosol generating device comprising a heater for heating of the aerosol generating material in use; the apparatus being arranged to: monitor a first property of the heating of the aerosol generating material, thereby to determine a heating profile of the aerosol generating material; analyse the heating profile to identify a feature of the heating profile corresponding to a heating of one or more constituents of the aerosol generating material; and determine, based on the identified one or more features, the characteristic of the aerosol generating material. 
     Optionally, the apparatus is arranged to analyse the heating profile to identify a feature of the heating profile corresponding to a vaporization of one or more constituents of the aerosol generating material. 
     Optionally, the first property is relatable to a temperature of the aerosol generating material. 
     Optionally, the heater is an induction heater for inductive heating of the aerosol generating material in use, and the apparatus is arranged to monitor a first property of the inductive heating of the aerosol generating material, thereby to determine the heating profile of the aerosol generating material. 
     Optionally, the first property comprises a property of the induction heater. 
     Optionally, the first property comprises a temperature of a susceptor of the induction heater. 
     Optionally, the first property comprises an electrical property of the induction heater. 
     Optionally, the electrical property comprises a property indicative of a current supplied to an inductor of the induction heater. 
     Optionally, the first property comprises a frequency characteristic of a resonance drive circuit of the induction heater. 
     Optionally, the frequency characteristic comprises a resonant frequency of the resonance drive circuit. 
     Optionally, the inductive heating has a substantially constant inductive heating power. 
     Optionally, the apparatus is arranged to: determine a rate of change of the first property; and identify the one or more features of the heating profile on the basis of the determined rate of change of the first property. 
     Optionally, the one or more features comprise a portion of the heating profile in which the first property remains substantially constant. 
     Optionally, the characteristic comprises a temperature of the aerosol generating material. 
     Optionally, the one or more features comprise a second portion of the heating profile in which the first property changes immediately following a or the first portion of the heating profile in which the first property remains substantially constant. 
     Optionally, the characteristic comprises an end point of vaporization of one or more of the constituents of the aerosol generating material. 
     Optionally, the apparatus is arranged to: control the heater based on the one or more determined characteristics. 
     Optionally, the apparatus is arranged to: determine, based on the determined characteristic, that an end point of vaporization of one or more constituents of the aerosol generating material has been reached; and responsive to the determination that an end point of vaporization of one or more constituents of the aerosol generating material has been reached, control the heater. 
     Optionally, the apparatus is arranged to: control the heater to further heat the aerosol generating material a predefined amount. 
     Optionally, the apparatus is arranged to: control the supply of a predetermined amount of energy to the aerosol generating material. 
     Optionally, the apparatus is arranged to present information to a user based on the determined characteristic. 
     Optionally, the apparatus is arranged to present information to a user relating to one or more constituents of the aerosol generating material based on the determined characteristic. 
     Optionally, the apparatus is arranged to present information to a user relating to an environment in which the device is being operated based on the determined characteristic. 
     Optionally, one of the one or more constituents of the aerosol generating material is a liquid. 
     According to a second aspect of the present invention, there is provided an aerosol generating device comprising: the apparatus according to the first aspect; and the heater. 
     Optionally, the heater is an induction heater, and the induction heater comprises: a or the inductor; and a or the susceptor arranged for inductive energy transfer with the inductor, the susceptor being arranged for heating of the aerosol generating material received in the aerosol generating device in use. 
     Optionally, the aerosol generating device comprises: the aerosol generating material. 
     Optionally, a mass of the heater is lower than a mass of the aerosol generating material. 
     According to a third aspect of the present invention, there is provided a method for determining a characteristic of an aerosol generating material of an aerosol generating device, the aerosol generating device comprising a heater for heating of the aerosol generating material in use, the method comprising: monitoring a first property of the heating of the aerosol generating material, thereby to determine a heating profile of the aerosol generating material; analysing the heating profile to identify a feature of the heating profile corresponding to a heating of one or more constituents of the aerosol generating material; and determining, based on the identified one or more features, the characteristic of the aerosol generating material. 
     According to a fourth aspect of the present invention, there is provided a program which when executed on a processor causes the processor to perform the method according to the third aspect. 
     Further features and advantages will become apparent from the following description, given by way of example only, with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates schematically an aerosol generating device according to an example; 
         FIG. 2  illustrates schematically an induction heater according to an example; 
         FIG. 3  illustrates a heating profile according to an example; 
         FIG. 4  illustrates schematically a plot of the rate of change of an induction heating property according to an example; and 
         FIG. 5  illustrates schematically a flow diagram of a method according to an example. 
     
    
    
     DETAILED DESCRIPTION 
     Induction heating is a process of heating an electrically conducting object (or susceptor) by electromagnetic induction. An induction heater may comprise an induction element, such as an electromagnet, and circuitry for passing a varying electric current, such as an alternating electric current, through the electromagnet. The varying electric current in the electromagnet produces a varying magnetic field. The varying magnetic field penetrates a susceptor suitably positioned with respect to the electromagnet, generating eddy currents inside the susceptor. The susceptor has electrical resistance to the eddy currents, and hence the flow of the eddy currents against this resistance causes the susceptor to be heated by Joule heating. In cases whether the susceptor comprises ferromagnetic material such as iron, nickel or cobalt, heat may also be generated by magnetic hysteresis losses in the susceptor, i.e. by the varying orientation of magnetic dipoles in the magnetic material as a result of their alignment with the varying magnetic field. 
     In inductive heating, as compared to heating by conduction for example, heat is generated inside the susceptor, allowing for rapid heating. Further, there need not be any physical contact between the inductive heater and the susceptor, allowing for enhanced freedom in construction and application. 
     An induction heater may comprise an RLC circuit, comprising a resistance (R) provided by a resistor, an inductance (L) provided in part by an induction element, for example the electromagnet which may be arranged to inductively heat a susceptor, and a capacitance (C) provided by a capacitor, connected in series. In some cases, resistance is provided by the ohmic resistance of parts of the circuit connecting the inductor and the capacitor, and hence the RLC circuit need not necessarily include a resistor as such. Such a circuit may be referred to, for example as an LC circuit. RLC and LC circuits may exhibit electrical resonance, which occurs at a particular resonant frequency when the imaginary parts of impedances or admittances of circuit elements cancel each other. Resonance occurs in an RLC or LC circuit because the collapsing magnetic field of the inductor generates an electric current in its windings that charges the capacitor, while the discharging capacitor provides an electric current that builds the magnetic field in the inductor. In these circuits described above, when the circuit is driven at the resonant frequency, the series impedance of the inductor and the capacitor is at a minimum, and circuit current is maximum. Driving the RLC or LC circuit at or near the resonant frequency may therefore provide for effective and/or efficient inductive heating. 
       FIG. 1  illustrates schematically an aerosol generating device  100  according to an example. The aerosol generating device  100  is hand-held. The aerosol generating device  100  comprises a battery portion  106 , an aerosol generating portion  104 , and a mouthpiece portion  102 . The aerosol generating portion  104  comprises a controller  112 , an induction heater  114 , and aerosol generating material  116 . The aerosol generating material  116  may be removable and/or replaceable in the aerosol generating device  100 , for example via a cartridge (not shown) that is removably connected to the aerosol generating device  100 . The battery portion  106  comprises a battery  110 . The battery  110  is arranged to power the induction heater  114 . The induction heater  114  is arranged to inductively heat the aerosol generating material  116  in use. The controller  112  is arranged to control the induction heating provided by the induction heater  114 . The aerosol generating device  100  is arranged to heat the aerosol generating material  116  to generate aerosol for inhalation by a user via the mouthpiece portion  102 . 
     The aerosol generating material  116  may include materials that provide volatilised components upon heating, typically in the form of vapour or an aerosol. The aerosol generating material  116  may be a non-tobacco-containing material or a tobacco-containing material. Aerosol generating material may, for example, include one or more of tobacco per se, tobacco derivatives, expanded tobacco, reconstituted tobacco, tobacco extract, homogenised tobacco or tobacco substitutes. The aerosol generating material can be in the form of ground tobacco, cut rag tobacco, extruded tobacco, reconstituted tobacco, reconstituted material, liquid, gel, gelled sheet, powder, or agglomerates, or the like. Aerosol generating material also may include other, non-tobacco, products, which, depending on the product, may or may not contain nicotine. Aerosol generating material may comprise one or more humectants, such as glycerol or propylene glycol. In some examples, the aerosol generating material  116  may comprise two or more constituents different from one another. For example, the aerosol generating material  116  may have a first constituent having a first phase, and a second constituent having a second phase. For example, the aerosol generating material  116  may comprise a constituent in solid form and a constituent in liquid form (at ambient temperatures and pressures). For example, the aerosol generating material  116  may comprise tobacco containing material comprising, for example tobacco in solid form and one or more constituents in liquid form, such as water and/or humectants or the like. The working temperature of the aerosol generating device (i.e. the temperature to which the aerosol generating material  116  is heated in use in order to generate aerosol) may be higher than a vaporization or boiling temperature of one of the one or more constituents of the aerosol generating material  116 , for example higher than a vaporization or boiling temperature of a liquid constituent of the aerosol generating material  116 , for example, higher than the boiling temperature of water. The liquid content, for example the water content, of the aerosol generating material  116 , may vary between batches, uses, and or types of aerosol generating material  116  and/or may be dependent on the external environment in which the aerosol generating material  116  is present. 
     In use, a user may activate, for example via a button (not shown) or a puff detector (not shown) which is known per se, the controller  112  to cause the induction heater  114  to heat the aerosol generating material  116 , which causes the aerosol generating material  116  to generate an aerosol. The aerosol is generated into air drawn into the device  100  from an air inlet (not shown), and is thereby carried to the mouthpiece  102 , where the aerosol exits the device  100 . 
     The induction heater  114  and/or the device  100  as a whole may be arranged to heat the aerosol generating material  116  to a range of temperatures to volatilise at least one constituent of the aerosol generating material without combusting the aerosol generating material. For example, the temperature range may be about 50° C. to about 350° C., such as between about 50° C. and about 250° C., or between about 50° C. and about 150° C. In some examples, the temperature range is between about 170° C. and about 220° C. In some examples, the temperature range may be other than this range, and the upper limit of the temperature range may be greater than 350° C. 
     Referring now to  FIG. 2 , there is illustrated an induction heater  114  that may be used in the aerosol generating device  100 , according to an example. The induction heater  114  comprises an RLC resonance circuit  200  for inductive heating of a susceptor  210 . The resonance circuit  200  comprises a resistor  204 , a capacitor  206 , and an inductor  208  connected in series. The resonance circuit  200  has a resistance R, an inductance L and a capacitance C. The inductor  208  is arranged for inductive energy transfer to the susceptor  210 . The susceptor  210  is arranged to heat the aerosol generating material  116 . In some examples, the susceptor  210  may be provided with the aerosol generating material  116 , and the susceptor  210  and aerosol generating material  116  may be provided in a cartridge (not shown) that is removably connected to the overall device  100 , for example to allow replacement of the cartridge (not shown). 
     The inductance L of the circuit  200  is provided by the inductor  208  arranged for inductive heating of the susceptor  210 . The inductive heating of the susceptor  210  is via an alternating magnetic field generated by the inductor  108 , which as mentioned above induces Joule heating and/or magnetic hysteresis losses in the susceptor  210 . A portion of the inductance L of circuit  200  may be due to the magnetic permeability of the susceptor  210 . The alternating magnetic field generated by the inductor  208  is generated by an alternating current flowing through the inductor  208 . The alternating current flowing through the inductor  208  is an alternating current flowing through the RLC resonance circuit  200 . The inductor  208  may, for example, be in the form of a coiled wire. 
     The capacitance C of the circuit  200  is provided by the capacitor  206 . The resistance R of the circuit  200  may be provided by the resistor  204 , the resistance of the wire connecting the components of the resonance circuit  200 , the resistance of the inductor  208 , and/or the resistance to current flowing in the resonance circuit  200  provided by the susceptor  210  arranged for inductive energy transfer with the inductor  108 . It will be appreciated that the circuit  200  need not necessarily comprise a resistor  204 , and that the resistance R in the circuit  200  may be provided by the resistance of the connecting wire, the inductor  208  and/or the susceptor  210 . 
     The alternating current is driven in the circuit  200  by a suitable driving circuitry  202 , for example, a H-Bridge driver  202  or another varying or alternating current source. The driving circuitry  202  is controllable by the controller  112  to provide an alternating current in the resonance circuit  200 . The driving circuitry  202  is connected to a DC voltage supply from the battery  110 . For example, the driving circuitry  202  may provide an alternating current in the circuit  100  from the DC voltage supply of the battery  110  by reversing (and then restoring) the voltage across the circuit via switching components (not shown). This may be useful as it allows the RLC resonance circuit to be powered by a DC battery, and allows the frequency of the alternating current to be controlled. 
     The driving circuitry  202  is connected to a controller  112 . The controller  112  controls the driving circuitry  202  or components thereof (not shown) to provide an alternating current I in the RLC resonance circuit  200  at a given drive frequency f. The drive frequency f may be controlled to be at or around the resonant frequency f r  of the particular RLC circuit  200 , for example. 
     It is desirable to determine characteristics of the aerosol generating material  116 , for example characteristics of the aerosol generating material  116  during inductive heating of the aerosol generating material  116 . For example, it may be useful to determine, or calibrate a determination of, the temperature of the aerosol generating material  116 , for example so as to allow for accurate control of the heating of the aerosol generating material  116 . As another example, it may be useful to determine when, during heating, water or other constituents of the aerosol generating material  116 , have been vaporized, or to determine when an end point of a vaporization of a constituent of the aerosol generating material  116  has been reached, as this may allow for improved control of further heating of the aerosol generating material up to vaporization temperatures of one or more other constituents. For example, aerosol generating material  116  may comprise varying water content which may vary greatly depending on many factors such as manufacturing processes, external environment, etc. Determining when, during heating, substantially all of the water has been vaporized from the aerosol generating material  116 , may allow for control of the further heating of the aerosol generating material independent of the initial water content, and hence allow for a more consistent aerosol deliver, as well as more efficient heating control, for example. For example, the point where water has been completed vaporized may infer that a certain amount of additional energy is then required to reach the vaporization temperature of the other constituents. 
     According to examples of the present invention, an apparatus (for example the controller  112 ), is arranged to determine a characteristic of the aerosol generating material  116  during heating of the aerosol generating material  116 . In broad overview, and as described in more detail below, the controller  112  is arranged to monitor a first property P of the inductive heating of the aerosol generating material  116 , thereby to determine a heating profile of the aerosol generating material  116 . The controller  112  is arranged to analyse the heating profile to identify a feature of the heating profile corresponding to a heating (for example a vaporization) of one or more constituents of the aerosol generating material  116 . The controller  112  is arranged to determine, based on the identified one or more features, the characteristic of the aerosol generating material. For example, the characteristic may be a temperature of the aerosol generating material  116 , and/or an end point of vaporization of a constituent (e.g. water) of the aerosol generating material  116 . As explained in more detail below, determining such characteristics may allow for an accurate determination of the temperature of the aerosol generating material, and/or for improved control of further heating of the aerosol generating material  116 , for example. 
     As mentioned above, the controller  112  is arranged to monitor a first property P of the inductive heating of the aerosol generating material  116 , thereby to determine a heating profile of the aerosol generating material  116 . 
     Referring now to  FIG. 3 , there is illustrated schematically an example heating profile  302  of the aerosol generating material  116 . The heating profile  302  corresponds to a value of the first property P of the inductive heating of the aerosol generating material  116  as a function of time t. As the induction heater  114  heats the aerosol generating material  116 , the first property P of the inductive heating changes as a function of time t. The first property P may be recorded continuously or discretely by the controller  112  as a function of time t, for example in a storage or memory (not shown). 
     In some examples, the first property P is relatable to a temperature of the aerosol generating material  116 . For example, the property P may be a measured temperature of the aerosol generating material  116 . For example, the temperature of the aerosol generating material  116  may be sensed by a separate temperature sensor (not shown) positioned at or near the aerosol generating material  116 . The controller  112  may be communicatively coupled with the temperature sensor (not shown), and may collect temperature data from the temperature sensor (not shown) so as to monitor the temperature of the aerosol generating material  116  as a function of time t. 
     In some examples, the first property P is a property of the induction heater  114 . For example, the first property P may comprise a temperature of the susceptor  210  of the induction heater  114 . For example, a temperature sensor (not shown) may be placed at or near the susceptor  210 . In this regard, it should be appreciated that the temperature of the susceptor  210  may be a function of the heating of the aerosol generating material  116 . The controller  112  may be communicatively coupled with the temperature sensor (not shown), and may collect temperature data from the temperature sensor (not shown) so as to monitor the temperature of the susceptor  210  as a function of time t. Since the susceptor  210  is arranged for heating the aerosol generating material  116 , for example it may be in thermal contact or close thermal contact with the aerosol generating material  116 , the determined temperature of the susceptor may be the same or similar to the temperature of the aerosol generating material  116 , or at least a portion of the aerosol generating material  116 . 
     The first property P need not necessarily be a direct temperature measurement of the susceptor  210  and/or the aerosol generating material  116  by a separate temperature sensor (not shown). For example, in some examples, the first property P comprises an electrical property of the induction heater  114  (or more generally the circuit  200 ), which may be indicative of the temperature of the susceptor  210  and/or the aerosol generating material  116 . 
     In one example, the first property P comprises a property indicative of the current I supplied to the inductor  208  of the induction heater  114 . As described above, the battery  110  may supply a DC voltage (and substantially DC current) to the drive circuitry  202 , which then provides an alternating current to the resonance circuit  200  comprising the inductor  208 . As the temperature of the susceptor  210  increases by inductive heating, the properties of the susceptor  210  (e.g., the ohmic resistance of the susceptor  210 ) may change. Purely by way of example only, the ohmic resistance of the susceptor  210  may increase with temperature. The increase of the ohmic resistance of the susceptor  210  may in turn increase the overall effective resistance R of the resonant circuit  200 . Hence, by Ohms law, for a given DC supply voltage, for example supplied by the battery  110 , as the effective resistance R of the resonant circuit  200  increases, the current I drawn from the battery  110  by the drive circuitry  202  will decrease, the current I flowing in the resonant circuit  200  will decrease, and hence the current I supplied to the inductor  208  will decrease. Hence the current I supplied to the inductor  208  of the induction heater  114  may be relatable to the relative temperature of the susceptor  210 , and may be used as a first property P of the inductive heating of the aerosol generating material  116 . 
     The current I drawn from the battery  110  by the drive circuitry  202  and/or the current I flowing in the resonant circuit  200  and/or the current I supplied to the inductor may be monitored by the controller  112  in a number of ways. For example, the current I may be measured passively or actively. For example, a current meter (not shown) may be applied on a supply line (not shown) between the battery  110  and the drive circuitry  202 , to measure the current drawn by the drive circuitry  202 . This measurement may be provided to the controller  112 , which may monitor the current I as the first property P, as a function of time t. As another example, a pick-up coil (not shown) may be placed in proximity with the inductor  208 , and a voltage meter (not shown) may be used to measure the voltage induced across the pick-up coil (not shown) by the inductor  208 . The induced voltage may be proportional to the current I flowing in the resonance circuit  200 , and provided to the inductor  208 . The induced voltage is therefore an example of a property indicative of the current I supplied to the inductor  208  of the induction heater  114 . The measured induced voltage may be provided to the controller  112 , which may monitor the induced voltage and/or convert the induced voltage into a measure of the current I flowing in the resonance circuit  200 , as the first property P. 
     It should be appreciated that in other implementations, an electrical property of the circuit  200  other than the current I may be measured as the first property P. 
     In some examples, the first property P comprises a frequency characteristic of the resonance circuit  200  of the induction heater  114 . 
     For example, the frequency characteristic may comprise a resonant frequency f r  of the resonance drive circuit  200 . The resonant frequency f r  of the circuit  200  may be dependent on the capacitance C and inductance L of the circuit  200 , and may be given by: 
     
       
         
           
             
               
                 
                   
                     f 
                     r 
                   
                   = 
                   
                     1 
                     
                       2 
                        
                       π 
                        
                       
                         
                           L 
                            
                           C 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     The inductance L of the inductor  208  and hence of the resonance circuit  200  is dependent on the magnetic permeability μ of the susceptor  210 . Magnetic permeability μ is a measure of the ability of a material to support the formation of a magnetic field within itself, and expresses the degree of magnetization that a material obtains in response to an applied magnetic field. The greater the magnetic permeability μ of the susceptor  210 , the greater the inductance L. The magnetic permeability μ of a material from which the susceptor  116  is comprised may change with temperature. For example, for susceptors comprising ferromagnetic and ferrimagnetic materials operating below their Curie temperature T c  for example, as the temperature of the susceptor  210  increases, the magnetic permeability μ of the susceptor  210  will decrease and hence the inductance L in the resonance circuit  200  will decrease, and hence, via equation (1), the resonant frequency f r  of the resonant circuit  200  will decrease. Hence the resonant frequency f r  of the resonant circuit  200  of the induction heater  114  may be relatable to the relative temperature of the susceptor  210 , and may be used as a first property P of the inductive heating of the aerosol generating material  116 . 
     The resonant frequency f r  of the resonance circuit  200  may be measured using any suitable means. At the resonant frequency f r , the series impedance Z of the inductor  208  and the capacitor  206  is at a minimum, and hence the circuit current I is maximum. The resonant frequency Jr of the circuit  200  may be determined by the controller  112  being arranged to measure a frequency response of the resonance circuit  200 . For example, the controller  112  may be arranged to intermittently measure the current I flowing in the RLC circuit  100  (or a parameter relatable to the current I flowing in the RLC circuit  200  as described above) as a function of the driving frequency fat which the RLC circuit is driven. For example, the controller  112  may be arranged to control the drive circuitry  202  to scan through a range of drive frequencies f. The current I flowing in the circuit  200  (or a parameter relatable thereto) may be measured during the scan of drive frequencies, and hence the frequency response of the RLC circuit  200  as a function of the driving frequency f may be determined. The resonant frequency f r  may then be determined from the frequency response as the frequency f at which the current I flowing in the circuit  200  is a maximum, for example. This process can be repeated over time to obtain a variation of frequency f (as the first property P) as a function of time t. 
     Referring again to  FIG. 3 , the first property P of the inductive heating of the aerosol generating material is monitored as a function of time t, thereby to determine the heating profile  302  of the aerosol generating material  116 . For ease of explanation, it is assumed in the following description of  FIG. 3  that the first property P is directly proportional to the temperature of the aerosol generating material, although it will be appreciated that, as described above, in other examples any first property P of the inductive heating of the aerosol generating material may be used. Further, for ease of explanation, it is assumed in the following description of  FIG. 3  that the power of the inductive heating (i.e. the rate of energy supplied to the aerosol generating material by inductive heating) remains substantially constant over the heating profile  302 , although it will be appreciated that, as described in more detail below, this need not necessarily be the case and that in other examples (not shown) the inductive heating power may vary. 
     In the example illustrated in  FIG. 3 , at time to, the first property P is at some initial value P 0 , corresponding to some initial temperature of the aerosol generating material  116 . As the inductive heating begins (in this example with a constant heating power), the first property P increases as a function of time t between t 0  and t 1 . This corresponds to the temperature of the aerosol generating material  116  increasing, as the energy applied to the aerosol generating material  116  by the susceptor  210  increases the temperature of the aerosol generating material  116 . However, at time t 1 , the first property P substantially ceases to rise (which may include increasing at a different rate/a substantially reduced rate), and instead stays substantially constant at a value of P 1  between times t 2  and t 3 . In other words, there is a portion  304  of the heating profile between t 1  and t 2  in which the first property P stays substantially constant (plateaus) as a function of time t. 
     The first property P stays constant between times t 1  and t 2  due to the latent heat of vaporization of a constituent of the aerosol generating material. This latent heat is the energy supplied to the constituent of the aerosol generating material  116  at its boiling point to change its phase (e.g. liquid to gas) without changing its temperature. In other words, the first property P stays substantially constant because, although the aerosol generating material  116  is still being inductively heated (in this example still being heated with a constant heating power), the energy supplied to the aerosol generating material is, instead of increasing the temperature of the aerosol generating material  116 , being used to vaporize a constituent of the aerosol generating material  116 . As one example, the constituent may be water, which has a known boiling point of 100° C. It may therefore be accurately determined that between times t 1  and t 2  where the first property remains substantially constant at P 1 , that the temperature of the aerosol generating material  116  is 100° C., i.e. that the value P 1  of the first property P corresponds to a temperature of the aerosol generating material  116  of 100° C. 
     At time t 2 , the first property P begins to increase again, which corresponds to an increase in the temperature of the aerosol generating material  116 . The first property P increases at t 2  due to all or substantially all of the constituent of the aerosol generating material  116  having been vaporized, and hence the inductive heating of the aerosol generating material  116  once again increasing the temperature of the aerosol generating material  116 . A portion  306  of the heating profile  302  at which the first property P beings to increase again, immediately after the portion  304  in which the first property P remains substantially constant, may correspond, for example, to the end point of vaporization of the constituent of the aerosol generating material. For example, the constituent may be water, and it may be accurately determined that at t 2  all or substantially all of the water of the aerosol generating material  116  has been vaporized, and that e.g. the water content of the aerosol generating material at time t 2  is substantially zero, for example. 
     As mentioned above, the apparatus (e.g. controller  112 ) is arranged to analyse the heating profile  302  to identify a feature of the heating profile  302  corresponding to a vaporization of one or more constituents of the aerosol generating material  116 . The apparatus (e.g. controller  112 ) is arranged to determine, based on the identified one or more features, the characteristic of the aerosol generating material  116 . For example, the controller  112  may comprise a processor (not shown) and a memory (not shown). The processor may, for example, extract heating profile data stored in the memory, and process the data so as to perform the analysis of the heating profile, and/or the determination of the characteristic. It should be appreciated that the heating profile data comprises at least two data points representing the first property P at two different times, which can then be used to calculate a change of the first property P. 
     In some examples, the feature of the heating profile  302  comprises the portion  304  of the heating profile  302  in which the first property P remains substantially constant. The controller  112  may determine, based on an identification of the feature of the first property P remaining substantially constant, a temperature of the aerosol generating material. For example, as described above, the constituent may be water, which has a known boiling point of 100° C., and hence on identification of the feature of the first property P remaining substantially constant, the controller  112  may determine that the temperature of the aerosol generating material  116  is approximately 100° C. 
     In some examples, a mass of the heater  114 , for example the mass of the susceptor  210  of the induction heater  114 , may be larger than the mass of the aerosol generating material  116 . This may help ensure that the first property P is accurately relatable to the temperature of the aerosol generating material. For example, this may help ensure that the feature of the first property P remaining substantially constant is readily identifiable, which may help improve the reliability and/or accuracy of the determination of the features of the heating profile and hence the characteristics of the aerosol generating material  116 . Further, the power of the inductive heating provided may be so as to allow the feature of the heating profile to be readily identifiable. For example, where the feature is a portion  304  where the first property P stays substantially constant, the power of the inductive heating provided may be such that the time between times t 1  and t 2  is large enough to allow the portion  304  to be readily identified. As will be appreciated, a power of inductive heating which allows the feature of the heating profile to be readily identifiable may be dependent on the mass and/or the type of aerosol generating material used and/or a mass and/or type of the susceptor used to heat the aerosol generating material. 
     The aerosol generating material  116  may comprise other known vaporizable constituents. For example, it may be known that the aerosol generating material  116  comprises a plurality of, for example two, known vaporizable constituents. It may be known, for example, that a first of the constituents has a boiling point of X° C., and that a second of the constituents has a boiling point of Y° C., where X° C. is lower than Y° C. Hence, on heating of the aerosol generating material, the controller  112  may determine that, when a first portion of the heating profile (not shown) in which the first property P remains substantially constant is reached, the temperature of the aerosol generating material is X° C., and when a second portion of the heating profile (not shown) in which the first property P remains substantially constant is reached, the temperature of the aerosol generating material is Y° C., for example. The controller  112  may therefore reliably and accurately determine the temperature of the aerosol generating material  116 . This may offer a more reliable temperature determination as compared to, for example, direct temperature measurement using a temperature sensor, as this method may be less susceptible to calibration error, for example. 
     As another example, the one or more features may comprise the second portion  306  of the heating profile  302  in which the first property P changes immediately following the first portion  304  of the heating profile  302  in which the first property P remains substantially constant. The controller  112  may determine, based on the identification of such a feature, an end point of vaporization of one or more of the constituents of the aerosol generating material  116 . For example, as described above, the constituent may be water, and it may be accurately determined that when the first property begins to rise again immediately following a portion in which the first property P remains substantially constant, that an end point of the vaporization of water has been reached, i.e. that all or substantially all of the water of the aerosol generating material  116  has been vaporized. It may therefore be determined, for example, that the water content of the aerosol generating material  112  at this point is substantially zero. This may allow for improved control of further heating of the aerosol generating material  116 , as described in more detail below. 
     In some examples, the controller  112  may be arranged to control the induction heater  114  based on the one or more determined characteristics. For example, the controller  112  may control the induction heater  114  to increase or decrease an inductive heating power, and/or to apply a different heating power, and/or to control the inductive heater  114  to cease to provide inductive heating, and/or to control the inductive heater  114  to provide inductive heating according to a predefined control pattern or sequence, and/or to provide a predefined further inductive heating and/or further predefined amount of energy to the aerosol generating material  116 . The controller  112  may control the inductive heater  114 , for example, by controlling a current supplied to the drive means  202 , or by controlling a drive frequency f of the drive circuitry  202 . 
     As described above, the determined characteristic may be a temperature of the aerosol generating material  116 . The controller  112  may control the induction heater  114  based on the determined temperature of the aerosol generating material. For example, the controller  112  may control the induction heater  114  according to a predefined control sequence or particular heating profile once a given temperature (e.g. corresponding to the boiling point of a known constituent) is determined to have been reached. This may, for example, help to prevent overheating of the aerosol generating material. 
     As another example, as described above, the determined characteristic may be an end point of vaporization of a constituent of the aerosol generating material. The controller  112  may be arranged to determine that an end point of vaporization of one or more constituents of the aerosol generating material has been reached, and responsive to the determination that an end point of vaporization of one or more constituents of the aerosol generating material has been reached, control the induction heater. For example, the controller  112  may control the induction heater  114  to further inductively heat the aerosol generating material  116  a predefined amount. For example, the controller  112  may control the supply of a predetermined amount of energy to the aerosol generating material  116 . 
     For example, different aerosol generating materials  116  that may be used with the aerosol generating device  100 , or different batches of the same aerosol generating material  116  that may be used (e.g. successively used) with the aerosol generating device  100 , may comprise varying water content (or varying content of other constituents). Determining a point, during heating, at which all of the water (or other constituent) has been vaporized from the aerosol generating material  116 , allows for control of the further heating of the aerosol generating material independent of the initial water (or other constituent) content, and hence may allow for a more consistent aerosol delivery, as well as more efficient heating control. In other words, the variation due to water is eliminated (or substantially reduced) and hence the controller  112  may supply a set amount of power to the susceptor  210 /aerosol generating material  116  from the point at which water is substantially vaporized. This means that the operational temperature can be reached with more accuracy. 
     For example, the additional energy required, after the water (or other constituent) has been vaporized, to increase the temperature of the aerosol generating material  116  to a given operating temperature (e.g. to an optimum temperature at which the aerosol generating material  116  generated aerosol) may be predetermined, and the controller  112  may control the induction heater  114  to supply that predetermined amount of energy to the aerosol generating material  116 . This may allow for simpler and/or more accurate control of the induction heating. For example, control may be made independent of an initial constituent (e.g. water) content of the aerosol generating material, which may vary between uses, batches, or types etc of the aerosol generating material. This may allow that at least a portion of the inductive heating control may be applied more accurately as compared for example to control in which these variations are not taken into account, and/or more simply as compared for example to control in which these variations are taken into account over a whole control range, for example. The controller  112  may therefore allow for improved control of inductive heating of aerosol generating material, and for an improved aerosol generating device  100 . 
     In another example, the controller  112  may be configured to present information to the user based on the determined characteristic of the aerosol generating material  116 . For example, where the determined characteristic is indicative that all of the water (or other constituent) has been vaporized from the aerosol generating material  116 , the user may be provided with information indicative of this. In another example, the information presented to the user may be indicative of a temperature of the aerosol generating material  116 . For example, the information may inform the user that the aerosol generating material  116  is at the boiling temperature of water when the determined characteristic is indicative that all of the water has been vaporized from the aerosol generating material  116 . In other examples, the user may be presented with information related to a composition of the aerosol generating material  116 . For example, information relating to the composition of the aerosol generating material  116  may be determined based on analysis of the heating profile  302 . For example, analysis of the heating profile may reveal the presence in the aerosol generating material  116  of first and second vaporizable constituents having different boiling points, as discussed above. The user may therefore be presented with information indicating that these constituents are present in the aerosol generating material  116 . The controller  112  may further, in some examples, determine if the aerosol generating material  116  is a material which is approved for use with the device  100  based on the determined information relating to the composition of the aerosol generating material  116 . In examples, the controller  112  may present such information to the user and/or the controller  112  may be configured to take an action, such as determining whether to allow operation of the device  100  to heat the aerosol generating material  116  based on if the aerosol generating material  116  is approved for use with the device  100 . In another example, the controller  112  may be configured to determine, based on the determined characteristic of the aerosol generating material  116 , a parameter relating to an environment in which the device  100  is being operated. For example, the controller  112  may determine an amount of water in the aerosol generating material  116  based on a feature of the heating profile  302 . In examples, the amount of water in the aerosol generating material  116  may be indicative of a humidity of the environment in which the device  100  is being operated. The user may therefore, for example, be presented with information relating to a humidity of the environment. 
     In some examples, the controller  112  is arranged to determine a rate of change of the first property P, for example a rate of change of the first property as a function of time. The controller  112  may be arranged to identify the one or more features of the heating profile on the basis of the determined rate of change of the first property.  FIG. 4  illustrates schematically a plot  402  of the rate of change dP/dt of the first property P as a function of time t. As with  FIG. 3 , it is assumed in  FIG. 4  that the inductive heating has a constant heating power, and that the property P is directly proportional to a temperature of the aerosol generating material  116 . At time t 0 , induction heating begins, and the rate of change dP/dt (i.e. in this example the first derivative of the first property P with respect to time t) is at a value Q 1 . This remains the case until at time t 1 , the rate of change dP/dt reduces to substantially zero, where it remains until t 2 . This indicates that, in the portion  404  of the plot  402  in the time range t 1  to t 2 , the property P does not substantially change, i.e. remains substantially constant, as a function of time t. As described above, it may be determined from this, for example, that a constituent (e.g. water) has reaches its boiling (or vaporization) point, and hence that the temperature of the aerosol generating material  116  at this point is the boiling (or vaporization) point of the constituent, for example 100° C. for water. At time t 2 , in a second portion  406  of the plot  402 , the rate of change dP/dt increases again. This indicates that the property P has begun again to increase (immediately following the portion  404  where the property P has remained substantially constant), and hence the controller  112  may determine form this, as described above, that the end point of vaporization of the constituent (e.g. water) of the aerosol generating material  116  has been reached. The controller  112  may perform the control of the induction heater  114  as described above on the basis of such a determination. Identifying the one or more features of the heating profile on the basis of a determined rate of change of the first property P may allow for sensitive identification by the controller  112  of the relevant changes in the first property P, and hence for reliable and accurate control. 
       FIG. 5  illustrates schematically a method for determining a characteristic of the aerosol generating material  116  of the aerosol generating device  100 . As mentioned above, the aerosol generating device  100  comprises an induction heater  114  for inductive heating of the aerosol generating  116  material in use. The method may be performed, for example, by an apparatus, for example the controller  112  of the aerosol generating device  100 . The controller  112  (or other apparatus) may comprise a processor (not shown) and a memory (not shown). The memory (not shown) may have instructions (e.g. a computer program) stored thereon which when executed by the processor (not shown) causes the controller  112  (or other apparatus) to perform the method. 
     In step  502 , the method comprises monitoring a first property P of the inductive heating of the aerosol generating material  116 , thereby to determine a heating profile of the aerosol generating material  116 . In some examples, the first property P may be any of the first properties P described above. The heating profile may be, for example, similar to that described above with reference to  FIG. 3 . 
     In step  504 , the method comprises analysing the heating profile to identify a feature of the heating profile corresponding to a vaporization of one or more constituents of the aerosol generating material. As described above, the feature may comprise a portion in which the first property P remains substantially constant (e.g. indicating the vaporization of a constituent), and/or a portion in which the first property P changes immediately following the portion in which the first property remains substantially constant (e.g. indicating an end point of vaporization of the constituent). 
     In step  506 , the method comprises determining, based on the identified one or more features, the characteristic of the aerosol generating material. As described above, the characteristic may be, for example, a temperature of the aerosol generating material  116  and/or an end point of the vaporization of a constituent of the aerosol generating material  116 . Although not illustrated in  FIG. 5 , the method may comprise controlling the inductive heating on the basis of the determined characteristic, for example as described above. 
     In some examples, the monitoring of the first property P of the inductive heating thereby to determine a heating profile, and the analysing the heating profile to identify a feature corresponding to the vaporization of one or more constituents of the aerosol generating material  116 , may occur substantially successively or may occur substantially concurrently (i.e. simultaneously). For example, the analysis of the heating profile may occur as the monitoring of the first property is taking place, i.e. in real time. For example, the analysis may be conducted for a present value of the first property and one or more values of the first property P determined or recorded immediately previously to the present value of the first property P. Performing the monitoring and the analysis substantially concurrently may allow for a responsive determination of the characteristic of the aerosol generating material  116 , and may allow for a responsive and hence more accurate and reliable control of the aerosol generating device  100 . 
     In some of the above examples, it was assumed that the first property P was directly proportional to a temperature of the aerosol generating material. However, it will be appreciated that this need not necessarily be the case and that in other examples the first property P may have other dependencies on the temperature of the aerosol generating material, but that nonetheless the heating profile may be analysed to identify a feature of the heating profile corresponding to a vaporization of one or more constituents of the aerosol generating material. 
     In some of the above examples, it was assumed that the inductive heating was performed with a constant inductive heating power. However, it will be appreciated that the aerosol generating material  116  need not necessarily be heated with a constant inductive heating power in order for the characteristic to be determined, and that in other examples variable inductive heating power may be used. Similarly, it will be appreciated that the first property P need not necessarily be monitored as a direct function of time tin order to determine a heating profile, i.e. it will be appreciated that the heating profile determined need not necessarily be the first property P as a direct function of time t. For example, in other examples, the first property P may be monitored as a function of an energy E supplied to the aerosol generating material  116 , and/or consumed by the inductive heater  114 , for example. The heating profile may therefore comprise the first property P as a function of the energy E supplied to the aerosol generating material  116 , and/or energy consumed by the inductive heater  114 . The energy E may be determined, for example, by multiplying the electrical power provided to (i.e. consumed by) the induction heater  114  (which may be, for example, the same or similar or proportional to the inductive heating power provided by the induction heater  104 ) by the time t that the power has been provided for. Similarly to as for the above examples, when a constituent of the aerosol generating material  116  begins to vaporize, the first property P may remain substantially constant as a function of the energy E provided because the energy E, instead of increasing the temperature of the aerosol generating material, is used to vaporize the constituent of the aerosol generating material. Hence, for example, at this point, a temperature of the aerosol generating material  116  may be accurately determined as the boiling point (or vaporization point) of the constituent. Similarly, when the first property P increases immediately after a portion where the first property has remained substantially constant, it may be determined that an end point of vaporization of the constituent has been reached. As above, control of further heating by the induction heater  114  may then be controlled on the basis of this point having been reached. 
     In some of the above examples, it is described that the apparatus for determining the characteristic of the aerosol generating material  116  is the controller  112  of the aerosol generating device  100 . However, it will be appreciated that this need not necessarily be the case, and that in other examples, the apparatus may not be an internal or integral component of an aerosol generating device  100 , and may be provided for example, as a separate apparatus. 
     In a further example, the feature of the first property P may be used to identify the aerosol generating material  116  and/or determine if the aerosol generating material  116  is intended for use with the aerosol generating device  100 . For example, the controller may determine that the aerosol generating material  116  is not to be used with the aerosol generating device  100 . This could be based on identifying the aerosol generating material explicitly (e.g., by name or constituents) or by comparing the feature of the first property P to an expected feature (e.g., stored in advance). If the measured feature of the first property P is different to the expected feature, then the controller may prevent the heating of the aerosol generating material  116  or may provide a warning to the user of the device  100 . 
     In some of the above examples, it is described that the aerosol generating device comprises an induction heater for inductive heating of the aerosol generating material in use, and that the apparatus is arranged to monitor a first property of the inductive heating of the aerosol generating material to determine a heating profile of the aerosol generating material. However, it will be appreciated that this need not necessarily be the case, and that in some examples the aerosol generating device may comprise any heater for heating of the aerosol generating material in use, and the apparatus may be arranged to monitor a first property of the heating of the aerosol generating material, thereby to determine the heating profile of the aerosol generating material. For example, in some examples, the heater may be a resistive heater and the first property may be, for example, a temperature of the aerosol generating material measured by a temperature sensor, for example as described above. 
     In some of the above examples, it is described that the apparatus analyses the heating profile to identify a feature of the heating profile corresponding to a vaporization of one or more constituents of the aerosol generating material. However, it will be appreciated that this need not necessarily be the case, and that in some examples the apparatus may analyse the heating profile to identify a feature of the heating profile corresponding (more generically) to a heating of one or more constituents of the aerosol generating material. For example, apart from a vaporization of one or more constituents of the aerosol generating material, the feature of the heating profile may be, for example, a certain heating gradient (e.g. a rate at which one or more constituents of the aerosol generating material is heating up). The identified heating gradient may then be used, for example to determine a characteristic of the aerosol generating material. For example, different constituents of the aerosol generating material may have different heat capacities, which may affect the heating gradient identified. Therefore, a characteristic of the aerosol generating material may be an identity of a constituent of the aerosol generating material and/or e.g. a type of aerosol generating material. As another example, different amounts of a certain aerosol generating material (or constituents thereof) may result in different observed heating gradients. Therefore, a characteristic of the aerosol generating material may be a (current) amount of aerosol generating material (or constituent thereof). It will be appreciated that other features of the heating profile corresponding to a heating of one or more constituents of the aerosol generating material may be identified and used to determine a characteristic of the aerosol generating material. 
     In another example, the apparatus may analyse the heating profile to identify a feature of the heating profile corresponding to a vaporization of one or more constituents of the aerosol generating material using gradients relating to different portions of the heating profile. For example, prior to a constituent, such as water, being vaporized from the aerosol generating material, the heating profile may have a first gradient M 1 . However, after all of the water in the aerosol generating material has been vaporized, the heating profile may have a second gradient M 2 . In this example, the second gradient M 2  will be larger than the first gradient M 1  since at the point in the heating profile having the gradient M 2 , the aerosol generating material  116  requires less energy to raise its temperature by a given amount since there is water no longer is being heated. A point at which tangents to the heating profile having gradients M 1  and M 2  could be determined in order to determine an inflection point in the heating profile. The feature of the heating profile corresponding to a vaporization of one or more constituents of the aerosol generating material can thereby be determined. This may be useful if the inflection point is not readily identifiable by other techniques, for example if the induction heating power is high such that the inflection point is short-lived. 
     It should be noted that it is a feature of the heating profile of the aerosol generating material itself that is identified so as to determine a characteristic of the aerosol generating material. Therefore, while in some examples a property of the (induction) heater may be monitored to determine the heating profile of the aerosol generating material, it is nonetheless a feature of the heating profile corresponding to a heating of the one or more constituents of the aerosol generating material that is identified in order to determine the characteristic of the aerosol generating material. This may be, for example, as opposed to some feature of the heater (e.g. the susceptor of an inductive heater) itself. Identifying a feature of the heating profile corresponding to a heating of the one or more constituents of the aerosol generating material in order to determine the characteristic of the aerosol generating material may allow for characteristics specific to the aerosol generating material being heated to be determined, which has benefits for example described hereinbefore, such as improved consistency and control of heating. 
     The above examples are to be understood as illustrative examples of the invention. It is to be understood that any feature described in relation to any one example may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the examples, or any combination of any other of the other examples. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.