Patent Publication Number: US-2022225685-A1

Title: Heat-not-burn (hnb) aerosol-generating devices including energy based heater control, and methods of controlling a heater

Description:
BACKGROUND 
     Field 
     The present disclosure relates to heat-not-burn (HNB) aerosol-generating devices and methods of controlling a heater in an aerosol-generating device. 
     Description of Related Art 
     Some electronic devices are configured to heat a plant material to a temperature that is sufficient to release constituents of the plant material while keeping the temperature below a combustion point of the plant material so as to avoid any substantial pyrolysis of the plant material. Such devices may be referred to as aerosol-generating devices (e.g., heat-not-burn aerosol-generating devices), and the plant material heated may be tobacco. In some instances, the plant material may be introduced directly into a heating chamber of an aerosol-generating device. In other instances, the plant material may be pre-packaged in individual containers to facilitate insertion and removal from an aerosol-generating device. 
     SUMMARY 
     At least one embodiment relates to a heat-not-burn (HNB) aerosol-generating device. 
     At least one example embodiment provides a system for controlling a heater in a non-combustible aerosol-generating device, the system comprising a memory storing computer-readable instructions and a controller configured to execute the computer-readable instructions to cause the non-combustible aerosol-generating device to apply a first power to the heater based on a first preheat temperature determine an estimated energy applied to the heater during application of the first power, and apply a second power to the heater based on the estimated energy, an energy threshold and a second preheat temperature, the second power being less than the first power. 
     In at least one example embodiment, the first power is a maximum power. 
     In at least one example embodiment, the second preheat temperature is lower than the first preheat temperature. 
     In at least one example embodiment, the first preheat temperature and the second preheat temperature are 320° C. or less. 
     In at least one example embodiment, the controller is configured to cause the non-combustible aerosol-generating device to obtain values corresponding to the first power, the first preheat temperature, the second preheat temperature and the energy threshold before the application of the first power. 
     In at least one example embodiment, the controller is configured to cause the non-combustible aerosol-generating device to obtain values for a first instance and values for a second instance, the values corresponding to the first power, the first preheat temperature, the second preheat temperature and the energy threshold being for the first instance. 
     In at least one example embodiment, the controller is configured to cause the non-combustible aerosol-generating device to output an indicator using a human machine interface upon applying the first power. 
     In at least one example embodiment, the controller is configured to cause the non-combustible aerosol-generating device to determine if the estimated energy is greater than the energy threshold, wherein the application of the second power applies the second power to the heater when the estimated energy is greater than the energy threshold. 
     In at least one example embodiment, the controller is configured to cause the non-combustible aerosol-generating device to output an indicator using a human machine interface upon the application of the second power. 
     In at least one example embodiment, the system further includes a voltage measurement circuit configured to measure a first voltage across first contact points, the first contact points connected to the heater and a compensation voltage measurement circuit configured to measure a second voltage across second contact points, wherein the controller is configured to cause the non-combustible aerosol-generating device to determine the estimated energy applied to the heater based on the first voltage and the second voltage. 
     In at least one example embodiment, the controller is configured to cause the non-combustible aerosol-generating device to adjust the first power based on the second voltage. 
     At least one example embodiment provides a method of controlling a heater in a non-combustible aerosol-generating device, the method comprising applying a first power to the heater based on a first preheat temperature, determining an estimated energy applied to the heater during the applying and applying a second power to the heater based on the estimated energy, an energy threshold and a second preheat temperature, the second power being less than the first power. 
     In at least one example embodiment, the first power is a maximum power. 
     In at least one example embodiment, the second preheat temperature is lower than the first preheat temperature. 
     In at least one example embodiment, the first preheat temperature and the second preheat temperature are 320° C. or less. 
     In at least one example embodiment, the method further includes obtaining values corresponding to the first power, the first preheat temperature, the second preheat temperature and the energy threshold before the applying. 
     In at least one example embodiment, the method obtains values for a first instance and values for a second instance, the values corresponding to the first power, the first preheat temperature, the second preheat temperature and the energy threshold being for the first instance. 
     In at least one example embodiment, the method further includes outputting an indicator using a human machine interface upon applying the first power. 
     In at least one example embodiment, the method further includes determining if the estimated energy is greater than the energy threshold, wherein the applying applies the second power to the heater when the estimated energy is greater than the energy threshold. 
     In at least one example embodiment, the method further includes outputting an indicator using a human machine interface upon applying the second power. 
     At least one example embodiment provides a non-combustible aerosol-generating device, the system including a heater and circuitry configured to cause the non-combustible aerosol-generating device to apply a first power to the heater based on a first preheat temperature, determine an estimated energy applied to the heater during application of the first power, and apply a second power to the heater based on the estimated energy, an energy threshold and a second preheat temperature, the second power being less than the first power. 
     In at least one example embodiment, the first power is a maximum power. 
     In at least one example embodiment, the second preheat temperature is lower than the first preheat temperature. 
     In at least one example embodiment, the first preheat temperature and the second preheat temperature are 320° C. or less. 
     In at least one example embodiment, the circuitry is configured to cause the non-combustible aerosol-generating device to obtain values corresponding to the first power, the first preheat temperature, the second preheat temperature and the energy threshold before the application of the first power. 
     In at least one example embodiment, the circuitry is configured to cause the non-combustible aerosol-generating device to obtain values for a first instance and values for a second instance, the values corresponding to the first power, the first preheat temperature, the second preheat temperature and the energy threshold being for the first instance. 
     In at least one example embodiment, the circuitry is configured to cause the non-combustible aerosol-generating device to output an indicator using a human machine interface upon applying the first power. 
     In at least one example embodiment, the circuitry is configured to cause the non-combustible aerosol-generating device to determine if the estimated energy is greater than the energy threshold, wherein the application of the second power applies the second power to the heater when the estimated energy is greater than the energy threshold. 
     In at least one example embodiment, the circuitry is configured to cause the non-combustible aerosol-generating device to output an indicator using a human machine interface upon the application of the second power. 
     In at least one example embodiment, the non-combustible aerosol-generating device further includes a voltage measurement circuit configured to measure a first voltage across first contact points, the first contact points connected to the heater and a compensation voltage measurement circuit configured to measure a second voltage across second contact points, wherein the circuitry is configured to cause the non-combustible aerosol-generating device to determine the estimated energy applied to the heater based on the first voltage and the second voltage. 
     In at least one example embodiment, the circuitry is configured to cause the non-combustible aerosol-generating device to adjust the first power based on the second voltage. 
     At least one example embodiment provides a system for controlling a heater in a non-combustible aerosol-generating device, the system including a memory storing computer-readable instructions and a controller configured to execute the computer-readable instructions to cause the non-combustible aerosol-generating device to apply a first power to the heater based on a first preheat temperature, determine a voltage applied to the heater and a current applied to the heater during application of the first power, the application of the first power being a period of time, and apply a second power to the heater based on the voltage applied to the heater and the current applied to the heater over the period of time, a threshold and a second preheat temperature, the second power being less than the first power. 
     In at least one example embodiment, the controller is configured to cause the non-combustible aerosol-generating device to obtain values corresponding to the first power, the first preheat temperature, the second preheat temperature and the threshold before the application of the first power. 
     In at least one example embodiment, the controller is configured to cause the non-combustible aerosol-generating device to obtain values for a first instance and values for a second instance, the values corresponding to the first power, the first preheat temperature, the second preheat temperature and the threshold being for the first instance. 
     In at least one example embodiment, the controller is configured to cause the non-combustible aerosol-generating device to determine a sum of products of the voltage applied to the heater and a current applied to the heater during application of the first power and determine if the sum is greater than the threshold, wherein the application of the second power applies the second power to the heater when the sum is greater than the threshold. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various features and advantages of the non-limiting embodiments herein may become more apparent upon review of the detailed description in conjunction with the accompanying drawings. The accompanying drawings are merely provided for illustrative purposes and should not be interpreted to limit the scope of the claims. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. For purposes of clarity, various dimensions of the drawings may have been exaggerated. 
         FIGS. 1A-1C  illustrate various perspective views of an aerosol-generating device according to one or more example embodiments. 
         FIG. 2A  illustrates the aerosol-generating device of  FIGS. 1A-1C  according to at least one example embodiment. 
         FIG. 2B  illustrates a capsule for the aerosol-generating device of  FIGS. 1A-1C  according to at least one example embodiment. 
         FIGS. 2C-2D  illustrate partially-disassembled views of the aerosol-generating device of  FIGS. 1A-1C  according to at least one example embodiment. 
         FIGS. 2E-2F  illustrate cross-sectional views of the aerosol-generating device of  FIGS. 1A-1C  according to at least one example embodiment. 
         FIG. 3  illustrates electrical systems of an aerosol-generating device and a capsule according to one or more example embodiments. 
         FIG. 4  illustrates a heater voltage measurement circuit according to one or more example embodiments. 
         FIG. 5  illustrates a heater current measurement circuit according to one or more example embodiments. 
         FIGS. 6A-6B  illustrates a compensation voltage measurement circuit and algorithm according to one or more example embodiments. 
         FIGS. 7A-7C  illustrates a circuit diagrams illustrating a heating engine control circuit according to one or more example embodiments. 
         FIGS. 8A-8B  illustrate methods of controlling a heater in a non-combustible aerosol-generating device according to one or more example embodiments. 
         FIG. 9  illustrates a block diagram illustrating a temperature heating engine control algorithm according to at least one or more example embodiments. 
         FIG. 10  illustrates a timing diagram of the methods illustrated in  FIGS. 8A-8B  one or more example embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Some detailed example embodiments are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. Example embodiments may, however, be embodied in many alternate forms and should not be construed as limited to only the example embodiments set forth herein. 
     Accordingly, while example embodiments are capable of various modifications and alternative forms, example embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit example embodiments to the particular forms disclosed, but to the contrary, example embodiments are to cover all modifications, equivalents, and alternatives thereof. Like numbers refer to like elements throughout the description of the figures. 
     It should be understood that when an element or layer is referred to as being “on,” “connected to,” “coupled to,” “attached to,” “adjacent to,” or “covering” another element or layer, it may be directly on, connected to, coupled to, attached to, adjacent to or covering the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to,” or “directly coupled to” another element or layer, there are no intervening elements or layers present. Like numbers refer to like elements throughout the specification. As used herein, the term “and/or” includes any and all combinations or sub-combinations of one or more of the associated listed items. 
     It should be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, regions, layers and/or sections, these elements, regions, layers, and/or sections should not be limited by these terms. These terms are only used to distinguish one element, region, layer, or section from another region, layer, or section. Thus, a first element, region, layer, or section discussed below could be termed a second element, region, layer, or section without departing from the teachings of example embodiments. 
     Spatially relative terms (e.g., “beneath,” “below,” “lower,” “above,” “upper,” and the like) may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It should be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the term “below” may encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     The terminology used herein is for the purpose of describing various example embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes,” “including,” “comprises,” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, and/or elements, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, and/or groups thereof. 
     When the words “about” and “substantially” are used in this specification in connection with a numerical value, it is intended that the associated numerical value include a tolerance of ±10% around the stated numerical value, unless otherwise explicitly defined. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, including those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
       FIG. 1A  is a front perspective view of an aerosol-generating device according to an example embodiment.  FIG. 1B  is a rear perspective view of the aerosol-generating device of  FIG. 1A .  FIG. 1C  is an upstream perspective view of the aerosol-generating device of  FIG. 1A . Referring to  FIGS. 1A-C , an aerosol-generating device  10  is configured to receive and heat an aerosol-forming substrate to produce an aerosol. The aerosol-generating device  10  includes, inter alia, a front housing  1202 , a rear housing  1204 , and a bottom housing  1206  coupled to a frame  1208  (e.g., chassis). A door  1210  is also pivotally connected/attached to the front housing  1202 . For instance, the door  1210  is configured to move or swing about a hinge  1212  and configured to reversibly engage/disengage with the front housing  1202  via a latch  1214  in order to transition between an open position and a closed position. The aerosol-forming substrate, which may be contained within a capsule  100  (e.g.,  FIG. 2 ), may be loaded into the aerosol-generating device  10  via the door  1210 . During an operation of the aerosol-generating device  10 , the aerosol produced may be drawn from the aerosol-generating device  10  via the aerosol outlet  1102  defined by the mouth-end segment  1104  of the mouthpiece  1100  (e.g.,  FIG. 2 ). 
     As illustrated in  FIG. 1B , the aerosol-generating device  10  includes a first button  1218  and a second button  1220 . The first button  1218  may be a pre-heat button, and the second button  1220  may be a power button (or vice versa). Additionally, one or both of the first button  1218  and the second button  1220  may include a light-emitting diode (LED) configured to emit a visible light when the first button  1218  and/or the second button  1220  is pressed. Where both of the first button  1218  and the second button  1220  includes an LED, the lights emitted may be of the same color or of different colors. The lights may also be of the same intensity or of different intensities. Furthermore, the lights may be configured as continuous lights or intermittent lights. For instance, the light in connection with the power button (e.g., second button  1220 ) may blink/flash to indicate that the power supply (e.g., battery) is low and in need charging. While the aerosol-generating device  10  is shown as having two buttons, it should be understood that more (e.g., three) or less buttons may be provided depending on the desired interface and functionalities. 
     The aerosol-generating device  10  may have a cuboid-like shape which includes a front face, a rear face opposite the front face, a first side face between the front face and the rear face, a second side face opposite the first side face, a downstream end face, and an upstream end face opposite the downstream end face. As used herein, “upstream” (and, conversely, “downstream”) is in relation to a flow of the aerosol, and “proximal” (and, conversely, “distal”) is in relation to an adult operator of the aerosol-generating device  10  during aerosol generation. Although the aerosol-generating device  10  is illustrated as having a cuboid-like shape (e.g., rounded rectangular cuboid) with a polygonal cross-section, it should be understood that example embodiments are not limited thereto. For instance, in some embodiments, the aerosol-generating device  10  may have a cylinder-like shape with a circular cross-section (e.g., for a circular cylinder) or an elliptical cross-section (e.g., for an elliptic cylinder). 
     As illustrated in  FIG. 1C , the aerosol-generating device  10  includes an inlet insert  1222  configured to permit ambient air to enter the device body  1200  (e.g.,  FIG. 2 ). In an example embodiment, the inlet insert  1222  defines an orifice as an air inlet which is in fluidic communication with the aerosol outlet  1102 . As a result, when a draw (e.g., a puff) or negative pressure is applied to the aerosol outlet  1102 , ambient air will be pulled into the device body  1200  via the orifice in the inlet insert  1222 . The size (e.g., diameter) of the orifice in the inlet insert  1222  made be adjusted, while also taking in account other variables (e.g., capsule  100 ) in the flow path, to provide the desired overall resistance-to-draw (RTD). In other embodiments, the inlet insert  1222  may be omitted altogether such that the air inlet is defined by the bottom housing  1206 . 
     The aerosol-generating device  10  may additionally include a jack  1224  and a port  1226 . In an example embodiment, the jack  1224  permits the downloading of operational information for research and development (R&amp;D) purposes (e.g., via an RS232 cable). The port  1226  is configured to receive an electric current (e.g., via a USB/mini-USB cable) from an external power supply so as to charge an internal power supply within the aerosol-generating device  10 . In addition, the port  1226  may also be configured to send data to and/or receive data (e.g., via a USB/mini-USB cable) from another aerosol-generating device or other electronic device (e.g., phone, tablet, computer). Furthermore, the aerosol-generating device  10  may be configured for wireless communication with another electronic device, such as a phone, via an application software (app) installed on that electronic device. In such an instance, an adult operator may control or otherwise interface with the aerosol-generating device  10  (e.g., locate the aerosol-generating device, check usage information, change operating parameters) through the app. 
       FIG. 2A  is the front perspective view of the aerosol-generating device of  FIGS. 1A-1C , wherein a mouthpiece  1100  and a capsule  100  are separated from the device body. Referring to  FIG. 2 , the aerosol-generating device  10  includes a device body  1200  configured to receive a capsule  100  and a mouthpiece  1100 . In an example embodiment, the device body  1200  defines a receptacle  1228  configured to receive the capsule  100 . The receptacle  1228  may be in a form of a cylindrical socket with outwardly-extending, diametrically-opposed side slots to accommodate the electrical end sections/contacts of the capsule  100 . However, it should be understood that the receptacle  1228  may be in other forms based on the shape/configuration of the capsule  100 . 
     As noted supra, the device body  1200  includes a door  1210  configured to open to permit an insertion of the capsule  100  and the mouthpiece  1100  and configured to close to retain the capsule  100  and the mouthpiece  1100 . The mouthpiece  1100  includes a mouth end (e.g., of the mouth-end segment  1104 ) and an opposing capsule end (e.g., of the capsule-end segment  1106 ). In an example embodiment, the capsule end is larger than the mouth end and configured to prevent a disengagement of the mouthpiece  1100  from the capsule  100  when the door  1210  of the device body  1200  is closed. When received/secured within the device body  1200  and ready for aerosol generation, the capsule  100  may be hidden from view while the mouth-end segment  1104  defining the aerosol outlet  1102  of the mouthpiece  1100  is visible. As illustrated in the figures, the mouth-end segment  1104  of the mouthpiece  1100  may extend from/through the downstream end face of the device body  1200 . Additionally, the mouth-end segment  1104  of the mouthpiece  1100  may be closer to the front face of the device body  1200  than the rear face. 
     In some instances, the device body  1200  of the aerosol-generating device  10  may optionally include a mouthpiece sensor and/or a door sensor. The mouthpiece sensor may be disposed on a rim of the receptacle  1228  (e.g., adjacent to the front face of the device body  1200 ). The door sensor may be disposed on a portion of the front housing  1202  adjacent to the hinge  1212  and within the swing path of the door  1210 . In an example embodiment, the mouthpiece sensor and the door sensor are spring-loaded (e.g., retractable) projections configured as safety switches. For instance, the mouthpiece sensor may be retracted/depressed (e.g., activated) when the mouthpiece  1100  is fully engaged with the capsule  100  loaded within the receptacle  1228 . Additionally, the door sensor may be retracted/depressed (e.g., activated) when the door  1210  is fully closed. In such instances, the control circuitry of the device body  1200  may permit an electric current to be supplied to the capsule  100  to heat the aerosol-forming substrate therein (e.g., pre-heat permitted when the first button  1218  is pressed). Conversely, the control circuitry (e.g., a controller  2105 ) of the device body  1200  may prevent or cease the supply of electric current when the mouthpiece sensor and/or the door sensor is not activated or deactivated (e.g., released). Thus, the heating of the aerosol-forming substrate will not be initiated if the mouthpiece  1100  is not fully inserted and/or if the door  1210  is not fully closed. Similarly, the supply of electric current to the capsule  100  will be disrupted/halted if the door  1210  is opened during the heating of the aerosol-forming substrate. 
     The capsule  100 , which will be discussed herein in more detail, generally includes a housing defining inlet openings, outlet openings, and a chamber between the inlet openings and the outlet openings. An aerosol-forming substrate is disposed within the chamber of the housing. Additionally, a heater may extend into the housing from an exterior thereof. The housing may include a body portion and an upstream portion. The body portion of the housing includes a proximal end and a distal end. The upstream portion of the housing may be configured to engage with the distal end of the body portion. 
       FIG. 2B  illustrates a capsule for the aerosol-generating device of  FIGS. 1A-1C  according to at least one example embodiment. 
     An aerosol-forming substrate contained within the capsule  100  may be in the form of a first aerosol-forming substrate  160   a  and a second aerosol-forming substrate  160   b . In an example embodiment, the first aerosol-forming substrate  160   a  and the second aerosol-forming substrate  160   b  are housed between a first cover  110  and a second cover  120 . During the operation of the aerosol-generating device  10 , the first aerosol-forming substrate  160   a  and the second aerosol-forming substrate  160   b  may be heated by a heater  336  to generate an aerosol. As will be discussed herein in more detail, the heater  336  includes a first end section  142 , an intermediate section  144 , and a second end section  146 . Additionally, prior to the assembly of the capsule  100 , the heater  336  may be mounted in the base portion  130  during a manufacturing process. 
     As illustrated, the first cover  110  of the capsule  100  defines a first upstream groove  112 , a first recess  114 , and a first downstream groove  116 . The first upstream groove  112  and the first downstream groove  116  may each be in the form of a series of grooves. Similarly, the second cover  120  of the capsule  100  defines a second upstream groove, a second recess, and a second downstream groove  126 . In an example embodiment, the second upstream groove, the second recess, and the second downstream groove  126  of the second cover  120  are the same as the first upstream groove  112 , the first recess  114 , and the first downstream groove  116 , respectively, of the first cover  110 . Specifically, in some instances, the first cover  110  and the second cover  120  are identical and complementary structures. In such instances, orienting the first cover  110  and the second cover  120  to face each other for engagement with the base portion  130  will result in a complementary arrangement. As a result, one part may be used interchangeably as the first cover  110  or the second cover  120 , thus simplifying the method of manufacturing. 
     The first recess  114  of the first cover  110  and the second recess of the second cover  120  collectively form a chamber configured to accommodate the intermediate section  144  of the heater  336  when the first cover  110  and the second cover  120  are coupled with the base portion  130 . The first aerosol-forming substrate  160   a  and the second aerosol-forming substrate  160   b  may also be accommodated within the chamber so as to be in thermal contact with the intermediate section  144  of the heater  336  when the capsule  100  is assembled. The chamber may have a longest dimension extending from at least one of the inlet openings (e.g., of the upstream passageway  162 ) to a corresponding one of the outlet openings (e.g., of the downstream passageway  166 ). In an example embodiment, the housing of the capsule  100  has a longitudinal axis, and the longest dimension of the chamber extends along the longitudinal axis of the housing. 
     The first downstream groove  116  of the first cover  110  and the second downstream groove  126  of the second cover  120  collectively form the downstream passageway  166 . Similarly, the first upstream groove  112  of the first cover  110  and the second upstream groove of the second cover  120  collectively form the upstream passageway  162 . The downstream passageway  166  and the upstream passageway  162  are dimensioned to be small or narrow enough to retain the first aerosol-forming substrate  160   a  and the second aerosol-forming substrate  160   b  within the chamber but yet large or wide enough to permit a passage of air and/or an aerosol therethrough when the first aerosol-forming substrate  160   a  and the second aerosol-forming substrate  160   b  are heated by the heater  336 . 
     In one instance, each of the first aerosol-forming substrate  160   a  and the second aerosol-forming substrate  160   b  may be in a consolidated form (e.g., sheet, pallet, tablet) that is configured to maintain its shape so as to allow the first aerosol-forming substrate  160   a  and the second aerosol-forming substrate  160   b  to be placed in a unified manner within the first recess  114  of the first cover  110  and the second recess of the second cover  120 , respectively. In such an instance, the first aerosol-forming substrate  160   a  may be disposed on one side of the intermediate section  144  of the heater  336  (e.g., side facing the first cover  110 ), while the second aerosol-forming substrate  160   b  may be disposed on the other side of the intermediate section  144  of the heater  336  (e.g., side facing the second cover  120 ) so as to substantially fill the first recess  114  of the first cover  110  and the second recess of the second cover  120 , respectively, thereby sandwiching/embedding the intermediate section  144  of the heater  336  in between. Alternatively, one or both of the first aerosol-forming substrate  160   a  and the second aerosol-forming substrate  160   b  may be in a loose form (e.g., particles, fibers, grounds, fragments, shreds) that does not have a set shape but rather is configured to take on the shape of the first recess  114  of the first cover  110  and/or the second recess of the second cover  120  when introduced. 
     As noted supra, the housing of the capsule  100  may include the first cover  110 , the second cover  120 , and the base portion  130 . When the capsule  100  is assembled, the housing may have a height (or length) of about 30 mm-40 mm (e.g., 35 mm), although example embodiments are not limited thereto. Additionally, each of the first recess  114  of the first cover  110  and the second recess of the second cover  120  may have a depth of about 1 mm-4 mm (e.g., 2 mm). In such an instance, the chamber collectively formed by the first recess  114  of the first cover  110  and the second recess of the second cover  120  may have an overall thickness of about 2 mm-8 mm (e.g., 4 mm). Along these lines, the first aerosol-forming substrate  160   a  and the second aerosol-forming substrate  160   b , if in a consolidated form, may each have a thickness of about 1 mm-4 mm (e.g., 2 mm). As a result, the first aerosol-forming substrate  160   a  and the second aerosol-forming substrate  160   b  may be heated relatively quickly and uniformly by the intermediate section  144  of the heater  336 . 
     The control circuitry may instruct a power supply to supply an electric current to the heater  336 . The supply of current from the power supply may be in response to a manual operation (e.g., button-activation) or an automatic operation (e.g., draw/puff-activation). As a result of the current, the capsule  100  may be heated to generate an aerosol. In addition, the change in resistance of the heater may be used to monitor and control the aerosolization temperature. The aerosol generated may be drawn from the aerosol-generating device  10  via the mouthpiece  1100 . In addition, the control circuitry (e.g., a controller  2105 ) may instruct a power supply to supply an electric current to the heater  336  to maintain a temperature of the capsule  100  between draws. 
     As discussed herein, an aerosol-forming substrate is a material or combination of materials that may yield an aerosol. An aerosol relates to the matter generated or output by the devices disclosed, claimed, and equivalents thereof. The material may include a compound (e.g., nicotine, cannabinoid), wherein an aerosol including the compound is produced when the material is heated. The heating may be below the combustion temperature so as to produce an aerosol without involving a substantial pyrolysis of the aerosol-forming substrate or the substantial generation of combustion byproducts (if any). Thus, in an example embodiment, pyrolysis does not occur during the heating and resulting production of aerosol. In other instances, there may be some pyrolysis and combustion byproducts, but the extent may be considered relatively minor and/or merely incidental. 
     The aerosol-forming substrate may be a fibrous material. For instance, the fibrous material may be a botanical material. The fibrous material is configured to release a compound when heated. The compound may be a naturally occurring constituent of the fibrous material. For instance, the fibrous material may be plant material such as tobacco, and the compound released may be nicotine. The term “tobacco” includes any tobacco plant material including tobacco leaf, tobacco plug, reconstituted tobacco, compressed tobacco, shaped tobacco, or powder tobacco, and combinations thereof from one or more species of tobacco plants, such as  Nicotiana rustica  and  Nicotiana tabacum.    
     In some example embodiments, the tobacco material may include material from any member of the genus  Nicotiana . In addition, the tobacco material may include a blend of two or more different tobacco varieties. Examples of suitable types of tobacco materials that may be used include, but are not limited to, flue-cured tobacco, Burley tobacco, Dark tobacco, Maryland tobacco, Oriental tobacco, rare tobacco, specialty tobacco, blends thereof, and the like. The tobacco material may be provided in any suitable form, including, but not limited to, tobacco lamina, processed tobacco materials, such as volume expanded or puffed tobacco, processed tobacco stems, such as cut-rolled or cut-puffed stems, reconstituted tobacco materials, blends thereof, and the like. In some example embodiments, the tobacco material is in the form of a substantially dry tobacco mass. Furthermore, in some instances, the tobacco material may be mixed and/or combined with at least one of propylene glycol, glycerin, sub-combinations thereof, or combinations thereof. 
     The compound may also be a naturally occurring constituent of a medicinal plant that has a medically-accepted therapeutic effect. For instance, the medicinal plant may be a  cannabis  plant, and the compound may be a cannabinoid. Cannabinoids interact with receptors in the body to produce a wide range of effects. As a result, cannabinoids have been used for a variety of medicinal purposes (e.g., treatment of pain, nausea, epilepsy, psychiatric disorders). The fibrous material may include the leaf and/or flower material from one or more species of  cannabis  plants such as  Cannabis sativa, Cannabis indica , and  Cannabis ruderalis . In some instances, the fibrous material is a mixture of 60-80% (e.g., 70%)  Cannabis sativa  and 20-40% (e.g., 30%)  Cannabis  indica. 
     Examples of cannabinoids include tetrahydrocannabinolic acid (THCA), tetrahydrocannabinol (THC), cannabidiolic acid (CBDA), cannabidiol (CBD), cannabinol (CBN), cannabicyclol (CBL), cannabichromene (CBC), and cannabigerol (CBG). Tetrahydrocannabinolic acid (THCA) is a precursor of tetrahydrocannabinol (THC), while cannabidiolic acid (CBDA) is precursor of cannabidiol (CBD). Tetrahydrocannabinolic acid (THCA) and cannabidiolic acid (CBDA) may be converted to tetrahydrocannabinol (THC) and cannabidiol (CBD), respectively, via heating. In an example embodiment, heat from a heater (e.g., heater  336  shown in  FIG. 2B ) may cause decarboxylation so as to convert the tetrahydrocannabinolic acid (THCA) in the capsule  100  to tetrahydrocannabinol (THC), and/or to convert the cannabidiolic acid (CBDA) in the capsule  100  to cannabidiol (CBD). 
     In instances where both tetrahydrocannabinolic acid (THCA) and tetrahydrocannabinol (THC) are present in the capsule  100 , the decarboxylation and resulting conversion will cause a decrease in tetrahydrocannabinolic acid (THCA) and an increase in tetrahydrocannabinol (THC). At least 50% (e.g., at least 87%) of the tetrahydrocannabinolic acid (THCA) may be converted to tetrahydrocannabinol (THC) during the heating of the capsule  100 . Similarly, in instances where both cannabidiolic acid (CBDA) and cannabidiol (CBD) are present in the capsule  100 , the decarboxylation and resulting conversion will cause a decrease in cannabidiolic acid (CBDA) and an increase in cannabidiol (CBD). At least 50% (e.g., at least 87%) of the cannabidiolic acid (CBDA) may be converted to cannabidiol (CBD) during the heating of the capsule  100 . 
     Furthermore, the compound may be or may additionally include a non-naturally occurring additive that is subsequently introduced into the fibrous material. In one instance, the fibrous material may include at least one of cotton, polyethylene, polyester, rayon, combinations thereof, or the like (e.g., in a form of a gauze). In another instance, the fibrous material may be a cellulose material (e.g., non-tobacco and/or non- cannabis  material). In either instance, the compound introduced may include nicotine, cannabinoids, and/or flavorants. The flavorants may be from natural sources, such as plant extracts (e.g., tobacco extract,  cannabis  extract), and/or artificial sources. In yet another instance, when the fibrous material includes tobacco and/or  cannabis , the compound may be or may additionally include one or more flavorants (e.g., menthol, mint, vanilla). Thus, the compound within the aerosol-forming substrate may include naturally occurring constituents and/or non-naturally occurring additives. In this regard, it should be understood that existing levels of the naturally occurring constituents of the aerosol-forming substrate may be increased through supplementation. For example, the existing levels of nicotine in a quantity of tobacco may be increased through supplementation with an extract containing nicotine. Similarly, the existing levels of one or more cannabinoids in a quantity of  cannabis  may be increased through supplementation with an extract containing such cannabinoids. 
     The first cover  110  and the second cover  120  also define a first furrow  118  and a second furrow  128 , respectively. The first furrow  118  and the second furrow  128  collectively form a downstream furrow configured to accommodate the first annular member  150   a . Similarly, the base portion  130  defines an upstream furrow  138  configured to accommodate the second annular member  150   b . As noted supra, the base portion  130  includes an engagement assembly  136  configured to facilitate a connection with the first cover  110  and the second cover  120 . The engagement assembly  136  may be an integrally formed part of the base portion  130 . In an example embodiment, the base portion  130  defines a base outlet  134  in fluidic communication with the base inlet  132 , and the engagement assembly  136  is in the form of a projecting rim/collar on each side of the base outlet  134 . Additionally, each of the first cover  110  and the second cover  120  may define a slot configured to receive a corresponding projecting rim/collar of the engagement assembly  136 . As a result, the first cover  110  and the second cover  120  (e.g., via their distal ends) may interlock with the engagement assembly  136  of the base portion  130  (while also interfacing with each other) to form the housing of the capsule  100 . 
     The first cover  110  and the second cover  120  may be made of a liquid-crystal polymer, PEEK (polyetheretherketone) or aluminum, for example. 
     A sheet material may be cut or otherwise processed (e.g., stamping, electrochemical etching, die cutting, laser cutting) to produce the heater  336 . The sheet material may be formed of one or more conductors configured to undergo Joule heating (which is also known as ohmic/resistive heating). Suitable conductors for the sheet material include an iron-based alloy (e.g., stainless steel, iron aluminides), a nickel-based alloy (e.g., nichrome), and/or a ceramic (e.g., ceramic coated with metal). For instance, the stainless steel may be a type known in the art as SS316L, although example embodiments are not limited thereto. The sheet material may have a thickness of about 0.1-0.3 mm (e.g., 0.15-0.25 mm). The heater  336  may have a resistance between 0.5-2.5 Ohms (e.g., 1-2 Ohms). 
     The heater  336  has a first end section  142 , an intermediate section  144 , and a second end section  146 . The first end section  142  and the second end section  146  are configured to receive an electric current from a power supply during an activation of the heater  336 . When the heater  336  is activated (e.g., so as to undergo Joule heating), the temperature of the first aerosol-forming substrate  160   a  and the second aerosol-forming substrate  160   b  may increase, and an aerosol may be generated and drawn or otherwise released through the downstream passageway  166  of the capsule  100 . The first end section  142  and the second end section  146  may each include a fork terminal to facilitate an electrical connection with the power supply (e.g., via a connection bolt), although example embodiments are not limited thereto. Additionally, because the heater  336  may be produced from a sheet material, the first end section  142 , the second end section  146 , and the intermediate section  144  may be coplanar. Furthermore, the intermediate section  144  of the heater  336  may have a planar and winding form resembling a compressed oscillation or zigzag with a plurality of parallel segments (e.g., eight to sixteen parallel segments). However, it should be understood that other forms for the intermediate section  144  of the heater  336  are also possible (e.g., spiral form, flower-like form). 
     In an example embodiment, the heater  336  extends through the base portion  130 . In such an instance, the terminus of each of the first end section  142  and the second end section  146  may be regarded as external segments of the heater  336  protruding from opposite sides of the base portion  130 . In particular, the intermediate section  144  of the heater  336  may be on the downstream side of the base portion  130  and aligned with the base outlet  134 . During manufacturing, the heater  336  may be embedded within the base portion  130  via injection molding (e.g., insert molding, over molding). For instance, the heater  336  may be embedded such that the intermediate section  144  is evenly spaced between the pair of projecting rims/collars of the engagement assembly  136 . 
     Although the first end section  142  and the second end section  146  of the heater  336  are shown in the drawings as projections (e.g., fins) extending from the sides of the base portion  130 , it should be understood that, in some example embodiments, the first end section  142  and the second end section  146  of the heater  336  may be configured so as to constitute parts of the side surface of the capsule  100 . For instance, the exposed portions of the first end section  142  and the second end section  146  of the heater  336  may be dimensioned and oriented so as to be situated/folded against the sides of the base portion  130  (e.g., while also following the underlying contour of the base portion  130 ). As a result, the first end section  142  and the second end section  146  may constitute a first electrical contact and a second electrical contact, respectively, as well as parts of the side surface of the capsule  100 . 
       FIG. 2C  is a partially-disassembled view of the aerosol-generating device of  FIGS. 1A-1C .  FIG. 2D  is a partially-disassembled view of the aerosol-generating device of  FIG. 2 . Referring to  FIGS. 2C-2D , the frame  1208  (e.g., metal chassis) serves as a foundation for the internal components of the aerosol-generating device  10 , which may be attached either directly or indirectly thereto. With regard to structures/components shown in the figures and already discussed above, it should be understood that such relevant teachings are also applicable to this section and may not have been repeated in the interest of brevity. In an example embodiment, the bottom housing  1206  is secured to the upstream end of the frame  1208 . Additionally, the receptacle  1228  (for receiving the capsule  100 ) may be mounted onto the front side of the frame  1208 . Between the receptacle  1228  and the bottom housing  1206  is an inlet channel  1230  configured to direct an incoming flow of ambient air to the capsule  100  in the receptacle  1228 . The inlet insert  1222  (e.g.,  FIG. 1C ), through which the incoming air may flow, may be disposed in the distal end of the inlet channel  1230 . Furthermore, the receptacle  1228  and/or the inlet channel  1230  may include a flow sensor (e.g., integrated flow sensor). 
     A covering  1232  and a power supply  1234  therein (e.g.,  FIG. 2E ) may be mounted onto the rear side of the frame  1208 . To establish an electrical connection with the capsule  100  (e.g., which is in the receptacle  1228  and covered by the capsule-end segment  1106  of the mouthpiece  1100 ), a first power terminal block  1236   a  and a second power terminal block  1236   b  may be provided to facilitate the supply of an electric current. For instance, the first power terminal block  1236   a  and the second power terminal block  1236   b  may establish the requisite electrical connection between the power supply  1234  and the capsule  100  via the first end section  142  and the second end section  146  of the heater  336 . The first power terminal block  1236   a  and/or the second power terminal block  1236   b  may be formed of brass. 
     The aerosol-generating device  10  may also include a plurality of printed circuit boards (PCBs) configured to facilitate its operation. In an example embodiment, a first printed circuit board  1238  (e.g., bridge PCB for power and I2C) is mounted onto the downstream end of the covering  1232  for the power supply  1234 . Additionally, a second printed circuit board  1240  (e.g., HMI PCB) is mounted onto the rear of the covering  1232 . In another instance, a third printed circuit board  1242  (e.g., serial port PCB) is secured to the front of the frame  1208  and situated behind the inlet channel  1230 . Furthermore, a fourth printed circuit board  1244  (e.g., USB-C PCB) is disposed between the rear of the frame  1208  and the covering  1232  for the power supply  1234 . However, it should be understood that the example embodiments herein regarding the printed circuit boards should not be interpreted as limiting since the size, shapes, and locations thereof may vary depending on the desired features of the aerosol-generating device  10 . 
       FIG. 2E  is a cross-sectional view of the aerosol-generating device of  FIGS. 1A-1C .  FIG. 2F  is another cross-sectional view of the aerosol-generating device of  FIGS. 1A-1C . With regard to structures/components shown in the figures and already discussed above, it should be understood that such relevant teachings are also applicable to this section and may not have been repeated in the interest of brevity. Referring to  FIGS. 2E-2F , the mouth-end segment  1104  of the mouthpiece  1100  is illustrated as defining an aerosol outlet  1102  in the form of a single outlet. However, it should be understood that example embodiments are not limited thereto. For instance, the aerosol outlet  102  may alternatively be in the form of a plurality of smaller outlets (e.g., two to six outlets). In one instance, the plurality of outlets may be in the form of four outlets. The outlets may be radially-arranged and/or outwardly-angled so as to release diverging streams of aerosol. 
     In an example embodiment, at least one of a filter or a flavor medium may be optionally disposed within the mouth-end segment  1104  of the mouthpiece  1100 . In such an instance, a filter and/or a flavor medium will be downstream from the chamber  164  such that the aerosol generated therein passes through at least one of the filter or the flavor medium before exiting through the at least one aerosol outlet  1102 . The filter may reduce or prevent particles from the aerosol-forming substrate (e.g., aerosol-forming substrate  160   a  and/or aerosol-forming substrate  160   b ) from being inadvertently drawn from the capsule  100 . The filter may also help reduce the temperature of the aerosol in order to provide the desired mouth feel. The flavor medium (e.g., flavor beads) may release a flavorant when the aerosol passes therethrough so as to impart the aerosol with a desired flavor. The flavorant may be the same as described above in connection with the aerosol-forming substrate. Furthermore, the filter and/or the flavor medium may have a consolidated form or a loose form as described supra in connection with the aerosol-forming substrate. 
     The aerosol-generating device  10  may also include a third annular member  150   c  seated within the receptacle  1228 . The third annular member  150   c  (e.g., resilient O-ring) is configured to establish an air seal when the base portion  130  of the capsule  100  is fully inserted into the receptacle  1228 . As a result, most if not all of the air drawn into the receptacle  1228  will pass through the capsule  100 , and any bypass flow around the capsule  100  will be minuscule if any. In an example embodiment, the first annular member  150   a , the second annular member  150   b , and/or the third annular member  150   c  may be formed of clear silicone. 
     In addition to the printed circuit boards already discussed above, the aerosol-generating device  10  may also include a fifth printed circuit board  1246  (e.g., main PCB) disposed between the frame  1208  and the power supply  1234 . The power supply  1234  may be a 900 mAh battery, although example embodiments are not limited thereto. Furthermore, a sensor  1248  may be disposed upstream from the capsule  100  to enhance an operation of the aerosol-generating device  10 . For instance, the sensor  1248  may be an air flow sensor. In view of the sensor  1248  as well as the first button  1218  and the second button  1220 , the operation of the aerosol-generating device  10  may be an automatic operation (e.g., puff-activated) or a manual operation (e.g., button-activated). In at least one example embodiment, the sensor may be a microelectromechanical system (MEMS) flow or pressure sensor or another type of sensor configured to measure air flow such as a hot-wire anemometer. 
     Upon activating the aerosol-generating device  10 , the capsule  100  within the device body  1200  may be heated to generate an aerosol. In an example embodiment, the activation of the aerosol-generating device  10  may be triggered by the detection of an air flow by the sensor  1248  and/or the generation of a signal associated with the pressing of the first button  1218  and/or the second button  1220 . With regard to the detection of an air flow, a draw or application of negative pressure on the aerosol outlet  1102  of the mouthpiece  1100  will pull ambient air into the device body  1200  via the inlet channel  1230 , wherein the air may initially pass through an inlet insert  1222  (e.g.,  FIG. 1C ). Once inside the device body  1200 , the air travels through the inlet channel  1230  to the receptacle  1228  where it is detected by the sensor  1248 . After the sensor  1248 , the air continues through the receptacle  1228  and enters the capsule  100  via the base portion  130 . Specifically, the air will flow through the base inlet  132  of the capsule  100  before passing through the upstream passageway  162  and into the chamber  164 . Moreover, the control circuitry (e.g., a controller  2105 ) may instruct a power supply to supply an electric current to the heater  336  to maintain a temperature of the capsule  100  between draws. 
     The detection of the air flow by the sensor  1248  may cause the control circuitry to the power supply  1234  to supply an electric current to the capsule  100  via the first end section  142  and the second end section  146  of the heater  336 . As a result, the temperature of the intermediate section  144  of the heater  336  will increase which, in turn, will cause the temperature of the aerosol-forming substrate (e.g., aerosol-forming substrate  160   a  and/or aerosol-forming substrate  160   b ) inside the chamber  164  to increase such that volatiles are released by the aerosol-forming substrate to produce an aerosol. The aerosol produced will be entrained by the air flowing through the chamber  164 . In particular, the aerosol produced in the chamber  164  will pass through the downstream passageway  166  of the capsule  100  before exiting the aerosol-generating device  10  from the aerosol outlet  1102  of the mouthpiece  1100 . 
     Additional details and/or alternatives for the aerosol-generating devices, capsules, and/or the aerosol-forming substrate may be found in discussed herein may also be found in U.S. application Ser. No. ______, titled “HEAT-NOT-BURN (HNB) AEROSOL-GENERATING DEVICES AND CAPSULES,” Atty. Dkt. No. 24000NV-000717-US, filed concurrently herewith; U.S. application Ser. No. ______, titled “HEAT-NOT-BURN AEROSOL GENERATING DEVICE WITH A FLIP-TOP LID,” Atty. Dkt. No. 24000NV-000719-US, filed concurrently herewith; U.S. application Ser. No. ______, titled “CAPSULES INCLUDING EMBEDDED HEATERS AND HEAT-NOT-BURN (HNB) AEROSOL-GENERATING DEVICES,” Atty. Dkt. No. 24000NV-000667-US, filed concurrently herewith; U.S. application Ser. No. ______, titled “CLOSED SYSTEM CAPSULE WITH AIRFLOW, HEAT-NOT-BURN (HNB) AEROSOL-GENERATING DEVICES, AND METHODS OF GENERATING AN AEROSOL,” Atty. Dkt. No. 24000NV-000630-US, filed concurrently herewith; U.S. application Ser. No. ______, titled “AEROSOL-GENERATING CAPSULES,” Atty. Dkt. No. 24000NV-000716-US, filed concurrently herewith; and U.S. application Ser. No. ______, titled “HEAT-NOT-BURN (HNB) AEROSOL-GENERATING DEVICES AND CAPSULES,” Atty. Dkt. No. 24000NV-000734-US, filed concurrently herewith, the disclosures of each of which are incorporated herein in their entirety by reference. 
       FIG. 3  illustrates electrical systems of an aerosol-generating device and a capsule according to one or more example embodiments. 
     Referring to  FIG. 3 , the electrical systems include an aerosol-generating device electrical system  2100  and a capsule electrical system  2200 . The aerosol-generating device electrical system  2100  may be included in the aerosol-generating device  10 , and the capsule electrical system  2200  may be included in the capsule  100 . 
     In the example embodiment shown in  FIG. 3 , the capsule electrical system  2200  includes the heater  336 . 
     The capsule electrical system  2200  may further include a body electrical/data interface (not shown) for transferring power and/or data between the aerosol-generating device  10  and the capsule  100 . According to at least one example embodiment, the electrical contacts shown in  FIG. 2B , for example, may serve as the body electrical interface, but example embodiments are not limited thereto. 
     The aerosol-generating device electrical system  2100  includes a controller  2105 , a power supply  1234 , device sensors or measurement circuits  2125 , a heating engine control circuit  2127 , aerosol indicators  2135 , on-product controls  2150  (e.g., buttons  1218  and  1220  shown in  FIG. 1B ), a memory  2130 , and a clock circuit  2128 . In some example embodiments, the controller  2105 , the power supply  1234 , device sensors or measurement circuits  2125 , the heating engine control circuit  2127 , the memory  2130 , and the clock circuit  2128  are on the same PCB (e.g., the main PCB  1246 ). The aerosol-generating device electrical system  2100  may further include a capsule electrical/data interface (not shown) for transferring power and/or data between the aerosol-generating device  10  and the capsule  100 . 
     The power supply  1234  may be an internal power supply to supply power to the aerosol-generating device  10  and the capsule  100 . The supply of power from the power supply  1234  may be controlled by the controller  2105  through power control circuitry (not shown). The power control circuitry may include one or more switches or transistors to regulate power output from the power supply  1234 . The power supply  1234  may be a Lithium-ion battery or a variant thereof (e.g., a Lithium-ion polymer battery). 
     The controller  2105  may be configured to control overall operation of the aerosol-generating device  10 . According to at least some example embodiments, the controller  2105  may include processing circuitry such as hardware including logic circuits; a hardware/software combination such as a processor executing software; or a combination thereof. For example, the processing circuitry more specifically may include, but is not limited to, a central processing unit (CPU), an arithmetic logic unit (ALU), a digital signal processor, a microcomputer, a field programmable gate array (FPGA), a System-on-Chip (SoC), a programmable logic unit, a microprocessor, application-specific integrated circuit (ASIC), etc. 
     In the example embodiment shown in  FIG. 3 , the controller  2105  is illustrated as a microcontroller including: input/output (I/O) interfaces, such as general purpose input/outputs (GPIOs), inter-integrated circuit (I 2 C) interfaces, serial peripheral interface bus (SPI) interfaces, or the like; a multichannel analog-to-digital converter (ADC); and a clock input terminal. However, example embodiments should not be limited to this example. In at least one example implementation, the controller  2105  may be a microprocessor. 
     The memory  2130  is illustrated as being external to the controller  2105 , in some example embodiments the memory  2130  may be on board the controller  2105 . 
     The controller  2105  is communicatively coupled to the device sensors  2125 , the heating engine control circuit  2127 , aerosol indicators  2135 , the memory  2130 , the on-product controls  2150 , the clock circuit  2128  and the power supply  1234 . 
     The heating engine control circuit  2127  is connected to the controller  2105  via a GPIO (General Purpose Input/Output) pin. The memory  2130  is connected to the controller  2105  via a SPI (Serial Peripheral Interface) pin. The clock circuit  2128  is connected to a clock input pin of the controller  2105 . The aerosol indicators  2135  are connected to the controller  2105  via an I 2 C (Inter-Integrated Circuit) interface pin and a SPI/GPIO pin. The device sensors  2125  are connected to the controller  2105  through respective pins of the multi-channel ADC. 
     The clock circuit  2128  may be a timing mechanism, such as an oscillator circuit, to enable the controller  2105  to track idle time, preheat length, aerosol-generating (draw) length, a combination of idle time and aerosol-generating (draw) length, a power-use time to determine a hot capsule alert (e.g., 30 s after instance has ended) or the like, of the aerosol-generating device  10 . The clock circuit  2128  may also include a dedicated external clock crystal configured to generate the system clock for the aerosol-generating device  10 . 
     The memory  2130  may be a non-volatile memory storing operational parameters and computer readable instructions for the controller  2105  to perform the algorithms described herein. In one example, the memory  2130  may be an electrically erasable programmable read-only memory (EEPROM), such as a flash memory or the like. 
     Still referring to  FIG. 3 , the device sensors  2125  may include a plurality of sensor or measurement circuits configured to provide signals indicative of sensor or measurement information to the controller  2105 . In the example shown in  FIG. 3 , the device sensors  2125  include a heater current measurement circuit  21258 , a heater voltage measurement circuit  21252 , and a compensation voltage measurement circuit  21250 . The electrical systems of  FIG. 3  may further includes the sensors discussed with reference to  FIGS. 1A-2F . 
     The heater current measurement circuit  21258  may be configured to output (e.g., voltage) signals indicative of the current through the heater  336 . An example embodiment of the heater current measurement circuit  21258  will be discussed in more detail later with regard to  FIG. 5 . 
     The heater voltage measurement circuit  21252  may be configured to output (e.g., voltage) signals indicative of the voltage across the heater  336 . An example embodiment of the heater voltage measurement circuit  21252  will be discussed in more detail later with regard to  FIG. 4 . 
     The compensation voltage measurement circuit  21250  may be configured to output (e.g., voltage) signals indicative of the resistance of electrical power interface (e.g., electrical connector) between the capsule  100  and the aerosol-generating device  10 . In some example embodiments, the compensation voltage measurement circuit  21250  may provide compensation voltage measurement signals to the controller  2105 . Example embodiments of the compensation voltage measurement circuit  21250  will be discussed in more detail later with regard to  FIGS. 6A-6B . 
     As discussed above, the compensation voltage measurement circuit  21250 , the heater current measurement circuit  21258  and the heater voltage measurement circuit  21252  are connected to the controller  2105  via pins of the multi-channel ADC. To measure characteristics and/or parameters of the aerosol-generating device  10  and the capsule  100  (e.g., voltage, current, resistance, temperature, or the like, of the heater  336 ), the multi-channel ADC at the controller  2105  may sample the output signals from the device sensors  2125  at a sampling rate appropriate for the given characteristic and/or parameter being measured by the respective device sensor. 
     The aerosol-generating device electrical system  2100  may include the sensor  1248  to measure airflow through the aerosol-generating device  10 . In at least one example embodiment, the sensor may be a microelectromechanical system (MEMS) flow or pressure sensor or another type of sensor configured to measure air flow such as a hot-wire anemometer. In an example embodiment, the output of the sensor to measure airflow to the controller  2105  is instantaneous measurement of flow (in ml/s or cm 3 /s) via a digital interface or SPI. In other example embodiments, the sensor may be a hot-wire anemometer, a digital MEMS sensor or other known sensors. The flow sensor may be operated as a puff sensor by detecting a draw when the flow value is greater than or equal to 1 mL/s, and terminating a draw when the flow value subsequently drops to 0 mL/s. In an example embodiment, the sensor  1248  may be a MEMS flow sensor based differential pressure sensor with the differential pressure (in Pascals) converted to an instantaneous flow reading (in mL/s) using a curve fitting calibration function or a Look Up Table (of flow values for each differential pressure reading). In another example embodiment, the flow sensor may be a capacitive pressure drop sensor. 
     The heating engine control circuit  2127  is connected to the controller  2105  via a GPIO pin. The heating engine control circuit  2127  is configured to control (enable and/or disable) the heater  336  of the aerosol-generating device  10  by controlling power to the heater  336 . 
     The controller  2105  may control the aerosol indicators  2135  to indicate statuses and/or operations of the aerosol-generating device  10  to an adult operator. The aerosol indicators  2135  may be at least partially implemented via a light guide and may include a power indicator (e.g., LED) that may be activated when the controller  2105  senses a button pressed by the adult operator. The aerosol indicators  2135  may also include a vibrator, speaker, or other feedback mechanisms, and may indicate a current state of an adult operator-controlled aerosol generating parameter (e.g., aerosol volume). 
     Still referring to  FIG. 3 , the controller  2105  may control power to the heater  336  to heat the aerosol-forming substrate in accordance with a heating profile (e.g., heating based on volume, temperature, flavor, or the like). The heating profile may be determined based on empirical data and may be stored in the memory  2130  of the aerosol-generating device  10 . 
       FIG. 4  illustrates an example embodiment of the heater voltage measurement circuit  21252 . 
     Referring to  FIG. 4 , the heater voltage measurement circuit  21252  includes a resistor  3702  and a resistor  3704  connected in a voltage divider configuration between a terminal configured to receive an input voltage signal COIL_OUT and ground. The resistances of the resistor  3702  and the resistor  3704  may be 8.2 kiloohms and 3.3 kiloohms, respectively. The input voltage signal COIL_OUT is the voltage input to (voltage at an input terminal of) the heater  336 . A node N 3716  between the resistor  3702  and the resistor  3704  is coupled to a positive input of an operational amplifier (Op-Amp)  3708 . A capacitor  3706  is connected between the node N 3716  and ground to form a low-pass filter circuit (an R/C filter) to stabilize the voltage input to the positive input of the Op-Amp  3708 . The capacitance of the capacitor  3706  may be 18 nanofarads, for example. The filter circuit may also reduce inaccuracy due to switching noise induced by PWM signals used to energize the heater  336 , and have the same phase response/group delay for both current and voltage. 
     The heater voltage measurement circuit  21252  further includes resistors  3710  and  3712  and a capacitor  3714 . The resistor  3712  is connected between node N 3718  and a terminal configured to receive an output voltage signal COIL_RTN and may have a resistance of 8.2 kiloohms, for example. The output voltage signal COIL_RTN is the voltage output from (voltage at an output terminal of) the heater  336 . 
     Resistor  3710  and capacitor  3714  are connected in parallel between a node N 3718  and an output of the Op-Amp  3708 . The resistor  3710  may have a resistance of 3.3 kiloohms and the capacitor  3714  may have a capacitance of 18 nanofarads, for example. A negative input of the Op-Amp  3708  is also connected to node N 3718 . The resistors  3710  and  3712  and the capacitor  3714  are connected in a low-pass filter circuit configuration. 
     The heater voltage measurement circuit  21252  utilizes the Op-Amp  3708  to measure the voltage differential between the input voltage signal COIL_OUT and the output voltage signal COIL_RTN, and output a scaled heater voltage measurement signal COIL_VOL that represents the voltage across the heater  336 . The heater voltage measurement circuit  21252  outputs the scaled heater voltage measurement signal COIL_VOL to an ADC pin of the controller  2105  for digital sampling and measurement by the controller  2105 . 
     The gain of the Op-Amp  3708  may be set based on the surrounding passive electrical elements (e.g., resistors and capacitors) to improve the dynamic range of the voltage measurement. In one example, the dynamic range of the Op-Amp  3708  may be achieved by scaling the voltage so that the maximum voltage output matches the maximum input range of the ADC (e.g., about 2.5V). In at least one example embodiment, the scaling may be about 402 mV per V, and thus, the heater voltage measurement circuit  21252  may measure up to about 2.5V/0.402V=6.22V. 
     The voltage signals COIL_OUT and COIL_RTN are clamped by diodes  3720  and  3722 , respectively, to reduce risk of damage due to electrostatic discharge (ESD) events. 
     In some example embodiments, four wire/Kelvin measurement may be used and the voltage signals COIL_OUT and COIL_RTN may be measured at measurement contact points (also referred to as voltage sensing connections (as opposed to main power contacts)) to take into account the contact and bulk resistances of an electrical power interface (e.g., electrical connector) between the heater  336  and the aerosol-generating device  10 . 
       FIG. 5  illustrates an example embodiment of the heater current measurement circuit  21258  shown in  FIG. 3 . 
     Referring to  FIG. 5 , an output current signal COIL_RTN_I is input to a four terminal (4T) measurement resistor  3802  connected to ground. The differential voltage across the four terminal measurement resistor  3802  is scaled by an Op-Amp  3806 , which outputs a heater current measurement signal COIL_CUR indicative of the current through the heater  336 . The heater current measurement signal COIL_CUR is output to an ADC pin of the controller  2105  for digital sampling and measurement of the current through the heater  336  at the controller  2105 . 
     In the example embodiment shown in  FIG. 5 , the four terminal measurement resistor  3802  may be used to reduce error in the current measurement using a four wire/Kelvin current measurement technique. In this example, separation of the current measurement path from the voltage measurement path may reduce noise on the voltage measurement path. 
     The gain of the Op-Amp  3806  may be set to improve the dynamic range of the measurement. In this example, the scaling of the Op-Amp  3806  may be about 0.820 V/A, and thus, the heater current measurement circuit  21258  may measure up to about 2.5 V/(0.820 V/A)=3.05 A. 
     Referring to  FIG. 5  in more detail, a first terminal of the four terminal measurement resistor  3802  is connected to a terminal of the heater  336  to receive the output current signal COIL_RTN_I. A second terminal of the four terminal measurement resistor  3802  is connected to ground. A third terminal of the four terminal measurement resistor  3802  is connected to a low-pass filter circuit (R/C filter) including resistor  3804 , capacitor  3808  and resistor  3810 . The resistance of the resistor  3804  may be 100 ohms, the resistance of the resistor  3810  may be 8.2 kiloohms and the capacitance of the capacitor  3808  may be 3.3. nanofarads, for example. 
     The output of the low-pass filter circuit is connected to a positive input of the Op-Amp  3806 . The low-pass filter circuit may reduce inaccuracy due to switching noise induced by the PWM signals applied to energize the heater  336 , and may also have the same phase response/group delay for both current and voltage. 
     The heater current measurement circuit  21258  further includes resistors  3812  and  3814  and a capacitor  3816 . The resistors  3812  and  3814  and the capacitor  3816  are connected to the fourth terminal of the four terminal measurement resistor  3802 , a negative input of the Op-Amp  3806  and an output of the Op-Amp  3806  in a low-pass filter circuit configuration, wherein the output of the low-pass filter circuit is connected to the negative input of the Op-Amp  3806 . The resistors  3812  and  3814  may have resistances of 100 ohms and 8.2 kiloohms, respectively, and the capacitor  3816  may have a capacitance of 3.3. nanofarads, for example. 
     The Op-Amp  3806  outputs a differential voltage as the heater current measurement signal COIL_CUR to an ADC pin of the controller  2105  for sampling and measurement of the current through the heater  336  by the controller  2105 . 
     According to at least this example embodiment, the configuration of the heater current measurement circuit  21258  is similar to the configuration of the heater voltage measurement circuit  21252 , except that the low-pass filter circuit including resistors  3804  and  3810  and the capacitor  3808  is connected to a terminal of the four terminal measurement resistor  3802  and the low-pass filter circuit including the resistors  3812  and  3814  and the capacitor  3816  is connected to another terminal of the four terminal measurement resistor  3802 . 
     The controller  2105  may average multiple samples (e.g., of voltage) over a time window (e.g., about 1 ms) corresponding to the ‘tick’ time (iteration time of a control loop) used in the aerosol-generating device  10 , and convert the average to a mathematical representation of the voltage and current across the heater  336  through application of a scaling value. The scaling value may be determined based on the gain settings implemented at the respective Op-Amps, which may be specific to the hardware of the aerosol-generating device  10 . 
     The controller  2105  may filter the converted voltage and current measurements using, for example, a three tap moving average filter to attenuate measurement noise. The controller  2105  may then use the filtered measurements to calculate: resistance R HEATER  of the heater  336  (R HEATER =COIL_VOL/COIL_CUR), power P HEATER  applied to the heater  336  (P HEATER =COIL_VOL*COIL_CUR) or the like. 
     According to one or more example embodiments, the gain settings of the passive elements of the circuits shown in  FIGS. 4 and/or 5  may be adjusted to match the output signal range to the input range of the controller  2105 . 
       FIG. 6A  illustrates electrical systems of an aerosol-generating device including a separate compensation voltage measurement circuit according to one or more example embodiments. 
     As shown in  FIG. 6A , a contact interface between the heater  336  and the aerosol-generating device electrical system  2100  includes a four wire/Kelvin arrangement having an input power contact  6100 , an input measurement contact  6200 , an output measurement contact  6300  and an output power contact  6400 . 
     A voltage measurement circuit  21252 A receives a measurement voltage COIL_OUT_MEAS at the input measurement contact  6200  and an output measurement voltage COIL_RTN_MEAS at the output measurement contact  6300 . The voltage measurement circuit  21252 A is the same circuit as the voltage measurement circuit  21252  illustrated in  FIG. 4  and outputs the scaled heater voltage measurement signal COIL_VOL. While in  FIG. 4  COIL_OUT and COIL_RTN are illustrated, it should be understood that in example embodiments without a separate compensation voltage measurement circuit, the voltage measurement circuit  21252  may receive voltages at the input and output measurement contacts  6200 ,  6300  instead of the input and output power contacts  6100 ,  6400 . 
     The systems shown in  FIG. 6A  further include the compensation voltage measurement circuit  21250 . The compensation voltage measurement circuit  21250  is the same as the voltage measurement circuit  21252 A except the compensation voltage measurement circuit  21250  receives the voltage COIL_OUT at the input power contact  6100  and receives the voltage COIL_RTN at the output power contact  6400  and outputs a compensation voltage measurement signal VCOMP. 
     The current measurement circuit  21258  receives the output current signal COIL_RTN_I at the output power contact  6400  and outputs the heater current measurement signal COIL_CUR. 
       FIG. 6B  illustrates a method of the using a compensation voltage measurement signal to adjust a target power for a heater according to example embodiments. 
     The controller  2105  may perform the method shown in  FIG. 6B . 
     At  56500 , the controller starts a power delivery loop for the heater. At  6505 , the controller pulls the operating parameters (e.g., heating engine control circuit threshold voltage, power loss threshold and wetting timer limit) from the memory. 
     At  6510 , the controller determines whether power lost at the contacts PCONTACT exceeds a loss threshold. The controller may determine the power lost at the contacts PCONTACT as follows: 
       PCONTACT=abs((VCOMP*COIL_CUR)−(COIL_VOL*COIL_CUR))
 
     The loss threshold may be an absolute value (e.g., 3 W) or a percentage of the power applied to the heater (e.g., 25%). 
     If the controller determines the power lost PCONTACT is equal to or less than the loss threshold, the controller clears a wetting flag at S 6515 . The controller monitors the compensation voltage measurement signal VCOMP at S 6520  and determines whether the compensation voltage measurement signal VCOMP exceeds a threshold voltage VMAX at S 6525 . The threshold voltage VMAX may be the rated voltage of the heating engine control circuit  2127 . 
     If the controller determines the compensation voltage measurement signal VCOMP does not exceed the threshold voltage VMAX, the controller proceeds to the next iteration (i.e., next tick time) at S 6530 . If the controller determines the compensation voltage measurement signal VCOMP exceeds the threshold voltage VMAX, the controller reduces the heater power target for the next iteration at S 6532  and proceeds to the next iteration at  6530 . 
     Thus, if the power loss PCONTACT is less than the loss threshold, the controller may reduce the applied power to reduce a contact heating effect. 
     Returning back to S 6510 , if the controller determines the power lost PCONTACT is greater than the loss threshold, the controller determines if a wetting flag is set at  6535 . If the controller determines the wetting flag is set at S 6535 , the controller terminates heating (e.g., does not supply power to the heater) at S 6550 . 
     If the controller determines the wetting flag is not set at S 6535 , the controller determines whether a wetting timer is running at S 6540 . The wetting time is used to permit an increased power loss for a desired/selected time period (e.g., 200 ms). 
     If the controller determines the wetting timer is not running, the controller starts the wetting timer at S 6545  and then proceeds to monitor the compensation voltage measurement signal VCOMP at  6520 . 
     If the controller determines the wetting timer is running at S 6540 , the controller determines whether the wetting timer has expired at S 6555 . If the controller determines the wetting timer is not expired, the controller proceeds to monitor the compensation voltage measurement signal VCOMP at S 6520 . Thus, the power loss in the contacts PCONTACT being above the power loss threshold is permitted if the wetting timer is still running. 
     If the controller determines the wetting timer is expired, the controller sets the wetting flag at  6560 . The controller then reduces a heater power target at S 6565  such that the power loss in the contacts PCONTACT falls below the loss threshold and the controller proceeds to monitor the compensation voltage measurement signal VCOMP at  6520 . More specifically, the controller sets an upper power limit that can be used by the PID controller (i.e., instead of the PID loop being able to use a full power range it is restricted to a lower range such as 6 W instead of 12 W). The controller continues to use the same temperature error input, but responds more slowly since an upper power limit is lowered. 
     In other example embodiments, a controller may change the temperature target. 
     Contact resistances change with temperature (and may alternatively go down due to “wetting current” removing an oxidation layer of the contact) and, as a result, a proportion of power lost in the power contacts may change during use. By compensating for power loss at the contacts, the electrical systems improve the delivery of power to the heater (e.g., a latency to achieve a heater temperature can be reduced by increasing power once a wetting effect has taken place). 
     On each subsequent iteration of the power delivery loop shown in  FIG. 6B , the controller  2105  may re-enter a ‘wetting’ process (e.g., to respond to a change in contact forces), however, the wetting flag is used to ensure that the controller does not continually restart the process. 
       FIGS. 7A-7C  is a circuit diagram illustrating a heating engine control circuit according to example embodiments. The heating engine control circuit shown in  FIGS. 7A-7C  is an example of the heating engine control circuit  2127  shown in  FIG. 3 . 
     The heating engine control circuit includes a boost converter circuit  7020  ( FIG. 7A ), a first stage  7040  ( FIG. 7B ) and a second stage  7060  ( FIG. 7C ). 
     The boost converter circuit  7020  is configured to create a voltage signal VGATE (e.g., 9V supply) (also referred to as a power signal or input voltage signal) from a voltage source BATT to power the first stage  7040  based on a first power enable signal PWR_EN_VGATE (also referred to as a shutdown signal). The controller may generate the first power enable signal PWR_EN_VGATE to have a logic high level when the aerosol-generating device is ready to be used. In other words, the first power enable signal PWR_EN_VGATE has a logic high level when at least the controller detects that a capsule is properly connected to the aerosol-generating device. In other example embodiments, the first power enable signal PWR_EN_VGATE has a logic high level when the controller detects that a capsule is properly connected to the aerosol-generating device and the controller detects an action such as a button being pressed. 
     The first stage  7040  utilizes the input voltage signal VGATE from the boost converter circuit  7020  to drive the heating engine control circuit  2127 . The first stage  7040  and the second stage  7060  form a buck-boost converter circuit. 
     In the example embodiment shown in  FIG. 7A , the boost converter circuit  7020  generates the input voltage signal VGATE only if the first enable signal PWR_EN_VGATE is asserted (present). The controller  2105  may VGATE to cut power to the first stage  7040  by de-asserting (stopping or terminating) the first enable signal PWR_EN_VGATE. The first enable signal PWR_EN_VGATE may serve as a device state power signal for performing an aerosol-generating-off operation at the device  1000 . In this example, the controller  2105  may perform an aerosol-generating-off operation by de-asserting the first enable signal PWR_EN_VGATE, thereby disabling power to the first stage  7040 , the second stage  7060  and the heater  336 . The controller  2105  may then enable aerosol-generating at the device  1000  by again asserting the first enable signal PWR_EN_VGATE to the boost converter circuit  7020 . 
     The controller  2105  may generate the first enable signal PWR_EN_VGATE at a logic level such that boost converter circuit  7020  outputs the input voltage signal VGATE having a high level (at or approximately 9V) to enable power to the first stage  7040  and the heater  336  in response to aerosol-generating conditions at the device  1000 . The controller  2105  may generate the first enable signal PWR_EN_VGATE at another logic level such that boost converter circuit  7020  outputs the input voltage signal VGATE having a low level (at or approximately 0 V) to disable power to the first stage  7040  and the heater  336 , thereby performing a heater-off operation. 
     Referring in more detail to the boost converter circuit  7020  in  FIG. 7A , a capacitor C 36  is connected between the voltage source BATT and ground. The capacitor C 36  may have a capacitance of 10 microfarads. 
     A first terminal of inductor L 1006  is connected to node Node 1  between the voltage source BATT and the capacitor C 36 . The inductor L 1006  serves as the main storage element of the boost converter circuit  7020 . The inductor L 1006  may have an inductance of 10 microhenrys. 
     Node  1  is connected to a voltage input pin A 1  a boost converter chip U 11 . In some example embodiments, the boost converter chip may be a TPS61046. 
     A second terminal of the inductor L 1006  is connected to a switch pin SW of the boost converter chip U 11 . An enable pin EN of the booster converter chip U 11  is configured to receive the first enable signal PWR_EN_VGATE from the controller  2105 . 
     In the example shown in  FIG. 7A , the boost converter chip U 11  serves as the main switching element of the boost converter circuit  7020 . 
     A resistor R 53  is connected between the enable pin EN of the booster converter chip U 11  and ground to act as a pull-down resistor to ensure that operation of the heater  336  is prevented when the first enable signal PWR_EN_GATE is in an indeterminate state. The resistor R 53  may have a resistance of 100 kiloohms in some example embodiments. 
     A voltage output pin VOUT of the boost converter chip U 11  is connected to a first terminal of a resistor R 49  and first terminal of a capacitor C 58 . A second terminal of the capacitor C 58  is connected to ground. A voltage output by the voltage output pin VOUT is the input voltage signal VGATE. 
     A second terminal of the resistor R 49  and a first terminal of a resistor R 51  are connected at a second node Node 2 . The second node Node 2  is connected to a feedback pin FB of the booster converter chip U 11 . The booster converter chip U 11  is configured to produce the input voltage signal VGATE at about 9 V using the ratio of the resistance of the resistor R 49  to the resistance of the resistor R 51 . In some example embodiments, the resistor R 49  may have a resistance of 680 kiloohms and the resistor R 51  may have a resistance of 66.5 kiloohms. 
     The capacitors C 36  and C 58  operate as smoothing capacitors and may have capacitances of 10 microfarads and 4.7 microfarads, respectively. The inductor L 1006  may have an inductance selected based on a desired output voltage (e.g., 9V). 
     Referring now to  FIG. 7B , the first stage  7040  receives the input voltage signal VGATE and a second enable signal COIL_Z. The second enable signal is a pulse-width-modulation (PWM) signal and is an input to the first stage  7040 . 
     The first stage  7040  includes, among other things, an integrated gate driver U 6  configured to convert low-current signal(s) from the controller  2105  to high-current signals for controlling switching of transistors of the first stage  7040 . The integrated gate driver U 6  is also configured to translate voltage levels from the controller  2105  to voltage levels required by the transistors of the first stage  7040 . In the example embodiment shown in  FIG. 7B , the integrated gate driver U 6  is a half-bridge driver. However, example embodiments should not be limited to this example. 
     In more detail, the input voltage signal VGATE from the boost converter circuit  7020  is input to the first stage  7040  through a filter circuit including a resistor R 22  and a capacitor C 32 . The resistor R 22  may have a resistance of 10 ohms and the capacitor C 32  may have a capacitance of 1 microfarad. 
     The filter circuit including the resistor R 22  and the capacitor C 32  is connected to the VCC pin (pin  4 ) of the integrated gate driver U 6  and the anode of Zener diode D 2  at node Node 3 . The second terminal of the capacitor C 32  is connected to ground. The anode of the Zener diode D 2  is connected to a first terminal of capacitor C 32  and a boost pin BST (pin  1 ) of the integrated gate driver U 6  at node Node 7 . A second terminal of the capacitor C 31  is connected to the switching node pin SWN (pin  7 ) of the integrated gate driver U 6  and between transistors Q 2  and Q 3  at node Node 8 . In the example embodiment shown in  FIG. 7B , the Zener diode D 2  and the capacitor C 31  form part of a boot-strap charge-pump circuit connected between the input voltage pin VCC and the boost pin BST of the integrated gate driver U 6 . Because the capacitor C 31  is connected to the input voltage signal VGATE from the boost converter circuit  7020 , the capacitor C 31  charges to a voltage almost equal to the input voltage signal VGATE through the diode D 2 . The capacitor C 31  may have a capacitance of 220 nanofarads. 
     Still referring to  FIG. 7B , a resistor R 25  is connected between the high side gate driver pin DRVH (pin  8 ) and the switching node pin SWN (pin  7 ). A first terminal of a resistor R 29  is connected to the low side gate driver pin DRVL at a node Node 9 . A second terminal of the resistor R 29  is connected to ground. 
     A resistor R 23  and a capacitor C 33  form a filter circuit connected to the input pin IN (pin  2 ) of the integrated gate driver U 6 . The filter circuit is configured to remove high frequency noise from the second heater enable signal COIL_Z input to the input pin IN. The second heater enable signal COIL_Z is a PWM signal from the controller  2105 . Thus, the filter circuit is designed to filter out high frequency components of a PWM square wave pulse train, slightly reduces the rise and fall times on the square wave edges so that transistors are turned on and off gradually. 
     A resistor R 24  is connected to the filter circuit and the input pin IN at node Node 10 . The resistor R 24  is used as a pull-down resistor, such that if the second heater enable signal COIL_Z is floating (or indeterminate), then the input pin IN of the integrated gate driver U 6  is held at a logic low level to prevent activation of the heater  336 . 
     A resistor R 30  and a capacitor C 37  form a filter circuit connected to a pin OD (pin  3 ) of the integrated gate driver U 6 . The filter circuit is configured to remove high frequency noise from the input voltage signal VGATE input to the pin OD. 
     A resistor R 31  is connected to the filter circuit and the pin OD at node Node 11 . The resistor R 31  is used as a pull-down resistor, such that if the input voltage signal VGATE is floating (or indeterminate), then the pin OD of the integrated gate driver U 6  is held at a logic low level to prevent activation of the heater  336 . The signal output by the filter circuit formed by the resistor R 30  and the capacitor C 37  is referred to as filtered signal GATEON. R 30  and R 31  are also a divider circuit such that the signal VGATE is divided down to ˜2.5V for a transistor driver chip input. 
     The transistors Q 2  and Q 3  field-effect transistors (FETs) connected in series between the voltage source BATT and ground. In addition, a first terminal of an inductor L 3  is connected to the voltage source BATT. A second terminal of the inductor L 3  is connected to a first terminal of a capacitor C 30  and to a drain of the transistor Q 2  at a node Node 12 . A second terminal of the capacitor C 30  is connected to ground. The inductor L 3  and the capacitor C 30  form a filter to reduce and/or prevent transient spikes from the voltage source BATT. 
     The gate of the transistor Q 3  is connected to the low side gate driver pin DRVL (pin  5 ) of the integrated gate driver U 6 , the drain of the transistor Q 3  is connected to the switching node pin SWN (pin  7 ) of the integrated gate driver U 6  at node Node 8 , and the source of the transistor Q 3  is connected to ground GND. When the low side gate drive signal output from the low side gate driver pin DRVL is high, the transistor Q 3  is in a low impedance state (ON), thereby connecting the node Node 8  to ground. 
     As mentioned above, because the capacitor C 31  is connected to the input voltage signal VGATE from the boost converter circuit  7020 , the capacitor C 31  charges to a voltage equal or substantially equal to the input voltage signal VGATE through the diode D 2 . 
     When the low side gate drive signal output from the low side gate driver pin DRVL is low, the transistor Q 3  switches to the high impedance state (OFF), and the high side gate driver pin DRVH (pin  8 ) is connected internally to the boost pin BST within the integrated gate driver U 6 . As a result, transistor Q 2  is in a low impedance state (ON), thereby connecting the switching node SWN to the voltage source BATT to pull the switching node SWN (Node  8 ) to the voltage of the voltage source BATT. 
     In this case, the node Node 7  is raised to a bootstrap voltage V(BST)≈V(VGATE)+V(BATT), which allows the gate-source voltage of the transistor Q 2  to be the same or substantially the same as the voltage of the input voltage signal VGATE (e.g., V(VGATE)) regardless (or independent) of the voltage from the voltage source BATT. The circuit arrangement ensures that the BST voltage is not changed as the voltage of the voltage source drops, i.e., the transistors are efficiently switched even as the voltage of the voltage source BATT changes. 
     As a result, the switching node SWN (Node  8 ) provides a high current switched signal that may be used to generate a voltage output to the second stage  7060  (and a voltage output to the heater  336 ) that has a maximum value equal to the battery voltage source BATT, but is otherwise substantially independent of the voltage output from the battery voltage source BATT. 
     A first terminal of a capacitor C 34  and an anode of a Zener diode D 4  are connected to an output terminal to the second stage  7060  at a node Node 13 . The capacitor C 34  and a resistor R 28  are connected in series. A second terminal of the capacitor C 34  and a first terminal of the resistor R 28  are connected. A cathode of the Zener diode D 4  and a second terminal of the resistor R 28  are connected to ground. 
     The capacitor C 34 , the Zener diode D 4  and the resistor R 28  form a back EMF (electric and magnetic fields) prevention circuit that prevents energy from an inductor L 4  (shown in  FIG. 7C ) from flowing back into the first stage  7040 . 
     The resistor R 25  is connected between the gate of the transistor Q 2  and the drain of the transistor Q 3 . The resistor R 25  serves as a pull-down resistor to ensure that the transistor Q 2  switches to a high impedance more reliably. 
     The output of the first stage  7040  is substantially independent of the voltage of the voltage source and is less than or equal to the voltage of the voltage source. When the second heater enable signal COIL_Z is at 100% PWM, the transistor Q 2  is always activated, and the output of the first stage  7040  is the voltage of the voltage source or substantially the voltage of the voltage source. 
       FIG. 7C  illustrates the second stage  7060 . The second stage  7060  boosts the voltage of the output signal from the first stage  7040 . More specifically, when the second heater enable signal COIL_Z is at a constant logic high level, a third enable signal COIL_X may be activated to boost the output of the first stage  7040 . The third enable signal COIL_X is a PWM signal from the controller  2105 . The controller  2105  controls the widths of the pulses of the third enable signal COIL_X to boost the output of the first stage  7040  and generate the input voltage signal COIL_OUT. When the third enable signal COIL_X is at a constant low logic level, the output of the second stage  7060  is the output of the first stage  7040 . 
     The second stage  7060  receives the input voltage signal VGATE, the third enable signal COIL_X and the filtered signal GATEON. 
     The second stage  7060  includes, among other things, an integrated gate driver U 7  configured to convert low-current signal(s) from the controller  2105  to high-current signals for controlling switching of transistors of the second stage  7060 . The integrated gate driver U 7  is also configured to translate voltage levels from the controller  2105  to voltage levels required by the transistors of the second stage  7060 . In the example embodiment shown in  FIG. 7B , the integrated gate driver U 7  is a half-bridge driver. However, example embodiments should not be limited to this example. 
     In more detail, the input voltage signal VGATE from the boost converter circuit  7020  is input to the second stage  7060  through a filter circuit including a resistor R 18  and a capacitor C 28 . The resistor R 18  may have a resistance of 10 ohms and the capacitor C 28  may have a capacitance of 1 microfarad. 
     The filter circuit including the resistor R 18  and the capacitor C 28  is connected to the VCC pin (pin  4 ) of the integrated gate driver U 7  and the anode of Zener diode D 1  at node Node 14 . The second terminal of the capacitor C 28  is connected to ground. The anode of the Zener diode D 2  is connected to a first terminal of capacitor C 27  and a boost pin BST (pin  1 ) of the integrated gate driver U 7  at node Node 15 . A second terminal of the capacitor C 27  is connected to the switching node pin SWN (pin  7 ) of the integrated gate driver U 7  and between transistors Q 1  and Q 4  at node Node 16 . 
     In the example embodiment shown in  FIG. 7C , the Zener diode D 1  and the capacitor C 27  form part of a boot-strap charge-pump circuit connected between the input voltage pin VCC and the boost pin BST of the integrated gate driver U 7 . Because the capacitor C 27  is connected to the input voltage signal VGATE from the boost converter circuit  7020 , the capacitor C 27  charges to a voltage almost equal to the input voltage signal VGATE through the diode D 1 . The capacitor C 31  may have a capacitance of 220 nanofarads. 
     Still referring to  FIG. 7C , a resistor R 21  is connected between the high side gate driver pin DRVH (pin  8 ) and the switching node pin SWN (pin  7 ). A gate of the transistor Q 4  is connected to the low side gate driver pin DRVL (pin  5 ) of the integrated date driver U 7 . 
     A first terminal of the inductor L 4  is connected to the output of the first stage  7040  and a second terminal of the inductor L 4  is connected to the node Node 16 . The inductor L 4  serves as the main storage element of the output of the first stage  7040 . In example operation, when the integrated gate driver U 7  outputs a low level signal from low side gate driver pin DRVL (pin  5 ), the transistor Q 4  switches to a low impedance state (ON), thereby allowing current to flow through inductor L 4  and transistor Q 4 . This stores energy in inductor L 4 , with the current increasing linearly over time. The current in the inductor is proportional to the switching frequency of the transistors (which is controlled by the third heater enable signal COIL_X). 
     A resistor R 10  and a capacitor C 29  form a filter circuit connected to the input pin IN (pin  2 ) of the integrated gate driver U 7 . The filter circuit is configured to remove high frequency noise from the third heater enable signal COIL_X input to the input pin IN. 
     A resistor R 20  is connected to the filter circuit and the input pin IN at node Node 17 . The resistor R 20  is used as a pull-down resistor, such that if the third heater enable signal COIL_X is floating (or indeterminate), then the input pin IN of the integrated gate driver U 7  is held at a logic low level to prevent activation of the heater  336 . 
     A resistor R 30  and a capacitor C 37  form a filter circuit connected to a pin OD (pin  3 ) of the integrated gate driver U 6 . The filter circuit is configured to remove high frequency noise from the input voltage signal VGATE input to the pin OD. 
     The pin OD of the integrated gate driver U 7  receives the filtered signal GATEON. 
     The transistors Q 1  and Q 4  field-effect transistors (FETs). A gate of the transistor Q 1  and a first terminal of the resistor R 21  are connected to the high side gate driver pin DRVH (pin  8 ) of the integrated gate driver U 7  at a node Node 18 . 
     A source of the transistor Q 1  is connected to a second terminal of the resistor R 21 , an anode of a Zener diode D 3 , a drain of the transistor Q 4 , a first terminal of a capacitor C 35 , a second terminal of the capacitor C 27  and the switching node pin SWN (pin  7 ) of the integrated gate driver U 7  at node Node 16 . 
     A gate of the transistor Q 4  is connected to the low side gate driver pin DRVL (pin  5 ) of the integrated gate driver U 7  and a first terminal of a resistor R 27  at a node Node 19 . A source of the transistor Q 4  and a second terminal of the resistor R 27  are connected to ground. 
     A second terminal of the capacitor C 35  is connected to a first terminal of a resistor R 29 . A second terminal of the resistor R 29  is connected to ground. 
     A drain of the transistor Q 1  is connected to a first terminal of a capacitor C 36 , a cathode of the Zener diode D 3  and a cathode of a Zener diode D 5  at a node Node 20 . A second terminal of the capacitor C 36  and an anode of the Zener diode D 5  are connected to ground. An output terminal  7065  of the second stage  7060  is connected to the node Node 20  and outputs the input voltage signal COIL_OUT. The output terminal  7065  serves as the output of the heating engine control circuit  2127 . 
     The capacitor C 35  may be a smoothing capacitor and the resistor limits in-rush current. The Zener diode D 3  is a blocking diode to stop a voltage in the node Node 20  discharging into the capacitor C 35 . The capacitor C 36  is an output capacitor charged by the second stage  7060  (and reduces ripple in COIL_OUT) and the Zener diode D 5  is an ESD (electrostatic discharge) protection diode. 
     When the low side gate drive signal output from the low side gate driver pin DRVL is high, the transistor Q 4  is in a low impedance state (ON), thereby connecting the node Node  16  to ground and increasing the energy stored in the magnetic field of the inductor L 4 . 
     As mentioned above, because the capacitor C 27  is connected to the input voltage signal VGATE from the boost converter circuit  7020 , the capacitor C 27  charges to a voltage equal or substantially equal to the input voltage signal VGATE through the diode D 1 . 
     When the low side gate drive signal output from the low side gate driver pin DRVL is low, the transistor Q 4  switches to the high impedance state (OFF), and the high side gate driver pin DRVH (pin  8 ) is connected internally to the bootstrap pin BST within the integrated gate driver U 7 . As a result, transistor Q 1  is in a low impedance state (ON), thereby connecting the switching node SWN to the inductor L 4 . 
     In this case, the node Node 15  is raised to a bootstrap voltage V(BST)≈V(VGATE)+V(INDUCTOR), which allows the gate-source voltage of the transistor Q 1  to be the same or substantially the same as the voltage of the input voltage signal VGATE (e.g., V(VGATE)) regardless (or independent) of the voltage from the inductor L 4 . As the second stage  7060  is a boost circuit, the bootstrap voltage may also be referred to as a boost voltage. 
     The switching node SWN (Node  8 ) is connected to the inductor voltage and the output capacitor C 36  is charged, generating the voltage output signal COIL_OUT (the voltage output to the heater  336 ) that is substantially independent of the voltage output from the first stage  7040 . 
       FIGS. 8A-8B  illustrate methods of controlling a heater in a non-combustible aerosol-generating device according to example embodiments. 
     Many non-combustible devices use a preheat of organic material (e.g., tobacco) prior to use. The preheat is used to elevate the temperature of the material to a point at which the compounds of interest begin to volatize such that the first negative pressure applied by an adult operator contains a suitable volume and composition of aerosol. 
     In at least some example embodiments, applied energy is used as a basis for controlling the heater during preheat. Using applied energy to control the heater improves the quality and consistency of the first negative pressure applied by the adult operator. By contrast, time and temperature are generally used as a basis for controlling the preheat. 
     The methods of  FIGS. 8A-8B  may be implemented at the controller  2105 . In one example, the methods of  FIGS. 8A-8B  may be implemented as part of a device manager Finite State Machine (FSM) software implementation executed at the controller  2105 . 
     As shown in  FIG. 8A , the method includes applying a first power based on a first target preheat temperature at S 805 . An example embodiment of S 805  is further illustrated in  FIG. 8B . 
     As shown in  FIG. 8B , the controller detects that a capsule is inserted into the aerosol-generating device. In some example embodiments, the controller obtains a signal from an opening closing switch coupled to the door, which is illustrated in  FIGS. 1A-1C . In other example embodiments, the aerosol-generating device further includes (or alternatively includes) a capsule detection switch. The capsule detection switch detects whether the capsule is properly inserted (e.g., capsule detection switch gets pushed down/closes when the capsule is properly inserted). Upon the capsule being properly inserted, the controller may generate the signal PWR_EN_VGATE (shown in  FIG. 7A ) as a logic high level. In addition, the controller may perform a heater continuity check to determine the capsule is inserted and the heater resistance is within the specified range (e.g. ±20%). 
     After a capsule has been inserted (as detected by the switch) and/or when the aerosol-generating device  10  is turned on (e.g. by operation of the button), the heater  336  may be powered with a low power signal from the heating engine control circuit (˜1 W) for a short duration (˜50 ms) and the resistance may be calculated from the measured voltage and current during this impulse of energy. If the measured resistance falls within the range specified (e.g. a nominal 2100 mΩ±20%) the capsule is considered acceptable and the system may proceed to aerosol-generation. 
     The low power and short duration is intended to provide a minimum amount of heating to the capsule (to prevent any generation of aerosol). 
     At S 825 , the controller obtains operating parameters from the memory. The operating parameters may include values identifying a maximum power level (P max ), initial preheat temperature, subsequent preheat temperature and a preheat energy threshold. For example, the operating parameters may be predetermined based on empirical data or adjusted based on obtained measurements from the capsule (e.g., voltage and current). However, example embodiments are not limited thereto. In addition to or alternatively, the operating parameters may include different initial preheat temperatures for subsequent instances for a multi-instances device. For example, the controller may obtain operating parameters for an initial instance and operating parameters for a second subsequent instance. 
     At S 830 , the controller may cause the aerosol-generating device to display an “on” state. The controller may cause the aerosol-generating device to generate a visual indicator and/or a haptic feedback to display an “on” state. 
     At S 835 , the controller determines whether a preheat has started. In some example embodiments, the controller may start the preheat upon receiving an input from the on-product controls indicating a consumer has pressed a button to initiate the preheat. In some example embodiments, the button may be separate from a button that powers on the aerosol-generating device and in other example embodiments, the button may be the same button that powers on the aerosol-generating device. In other example embodiments, the preheat may be started based on another input such as sensing an airflow above a threshold level. In other example embodiments, the on-product controls may permit an adult operator to select one or more temperature profiles (each temperature profile associated operating parameters stored in the memory). 
     If the controller determines that no preheat has started, the method proceeds to S 880  where the controller determines whether an off timer has elapsed. If the off timer has not elapsed, the method returns to S 830  and if the controller determines the off timer has elapsed, the controller causes the aerosol-generating device to display an “off” state at S 885  and power off at S 890 . The off timer starts when the detected air flow falls below a threshold level. The off timer is used to display the “off” state based on inaction for a period of time such as 15 minutes. However, example embodiments are not limited to 15 minutes. For example, the duration of the off timer may be 2 minutes or 10 minutes. 
     If the controller determines the preheat has started (e.g., detects input from the on-product controls) at S 835 , the controller obtains the operating parameters associated with the input from the on-product controls from the memory. In an example, where the aerosol-generating instance is not the initial instance for the capsule, the controller may obtain operating parameters associated with the instance number. For example, the memory may store different temperature targets based on the instance number (e.g., different temperature targets for instance numbers, respectively) and different target energy levels to use for preheating based on the instance number. 
     The initial instance occurs when the controller initiates the preheat algorithm for a first time after detecting a capsule has been removed and one has since been inserted. Additionally, the instance number increments if the instance times out (e.g. after 8 minutes) or if the consumer switches off the device during an instance. 
     Upon obtaining the operating parameters at S 5840 , the controller may cause the aerosol-generating device to display an indication that preheat has started via the aerosol indicators. 
     At S 850 , the controller ramps up to a maximum available power to the heater (through the VGATE, COIL_Z and COIL_X signals provided to the heating engine control circuit  2127 ) (e.g., the controller provides a maximum available power of 10 W within 200 ms). In more detail, the controller requests maximum power, but ramps up to the maximum power to reduce an instantaneous load on the power supply. In an example embodiment, the maximum available power is a set value based on the capability of a battery and to minimize overshoot such that the aerosol-forming substrate is not burnt by the heater (i.e., how much energy can be put into the aerosol-forming substrate without burning). The maximum available power may be set based on empirical evidence and may be between 10-15 W. The controller provides the maximum available power until the controller determines that a target initial preheat temperature of the heater (e.g., 320° C.) is approaching, at S 855 . While 320° C. is used as an example target initial preheat temperature for an aerosol-forming substrate containing tobacco, it should be understood example embodiments are not limited thereto. For example, the target initial preheat temperature for an aerosol-forming substrate containing tobacco may be less than 400° C., such as 350° C. Moreover, the target initial preheat temperature is based on the materials in the aerosol-forming substrate. The controller may determine the temperature of the heater using the measured voltages from the heater voltage measurement circuit (e.g., COIL_VOL) and the compensation voltage measurement circuit, and may determine the measured current from the heater current measurement circuit (e.g., COIL_RTN_I). The controller may determine the temperature of the heater  336  in any known manner (e.g., based on the relatively linear relationship between resistance and temperature of the heater  336 ). 
     Further, the controller may use the measured current COIL_RTN_I and the measured voltage COIL_RTN to determine the resistance of the heater  336 , heater resistance R Heater  (e.g., using Ohm&#39;s law or other known methods). For example, according to at least some example embodiments, the controller may divide the measured voltage COIL_RTN (or compensated voltage VCOMP) by the measured current COIL_RTN_I to be the heater resistance R Heater . 
     In some example embodiments, the measured voltage COIL_RTN measured at the measurement contacts for the resistance calculation may be used in temperature control. 
     For example, the controller  2105  may use the following equation to determine (i.e., estimate) the temperature: 
         R   Heater   =R   0 [1+α( T−T   0 )]
 
     where α is the temperature coefficient of resistance (TCR) value of the material of the heater, R 0  is a starting resistance and T 0  is a starting temperature, R Heater  is the current resistance determination and T is the estimated temperature. 
     The starting resistance R 0  is stored in the memory  2130  by the controller  2105  during the initial preheat. More specifically, the controller  2105  may measure the starting resistance R 0  when the power applied to the heater  336  has reached a value where a measurement error has a reduced effect on the temperature calculation. For example, the controller  2105  may measure the starting resistance R 0  when the power supplied to the heater  336  is 1 W (where resistance measurement error is approximately less than 1%). 
     The starting temperature T 0  is the ambient temperature at the time when the controller  2105  measures the starting resistance R 0 . The controller  2105  may determine the starting temperature T 0  using an onboard thermistor to measure the starting temperature T 0  or any temperature measurement device. 
     According to at least one example embodiment, a 10 ms (millisecond) measurement interval may be used for measurements taken from the heater current measurement circuit  21258  and the heater voltage measurement circuit  21252  (since this may be the maximum sample rate). In at least one other example embodiment, however, for a resistance-based heater measurement, a 1 ms measurement interval (the tick rate of the system) may be used. 
     In other example embodiments, the determining of the heater temperature value may include obtaining, from a look-up table (LUT), based on the determined resistance, a heater temperature value. In some example embodiments, a LUT indexed by the change in resistance relative to a starting resistance may be used. 
     The LUT may store a plurality of temperature values that correspond, respectively, to a plurality of heater resistances, the obtained heater temperature value may be the temperature value, from among the plurality of temperature values stored in the LUT, that corresponds to the determined resistance. 
     Additionally, the aerosol-generating device  10  may store (e.g., in the memory  2130 ) a look-up table (LUT) that stores a plurality of heater resistance values as indexes for a plurality of respectively corresponding heater temperature values also stored in the LUT. Consequently, the controller may estimate a current temperature of the heater  336  by using the previously determined heater resistance R Heater  as an index for the LUT to identify (e.g., look-up) a corresponding heater temperature T from among the heater temperatures stored in the LUT. 
     Once the controller determines the target initial preheat temperature is approaching, the controller begins to reduce the applied power to the heater to an intermediate power level to avoid a temperature overshoot at S 855 . 
     A proportional-integral-derivative (PID) controller (shown in  FIG. 9 ) applies a proportionate control based on an error signal (i.e., the target temperature minus the current determined temperature) so, as the error signal reduces towards zero, the controller  2105  starts to back off the power being applied (this is largely controlled by a proportional term (P) of the PID controller, but an integral term (I), and a derivative term also contribute). 
     The P, I and D values balance overshoot, latency and steady state error against one another and control how the PID controller adjusts its output. The P, I and D values may be derived empirically or by simulation. 
       FIG. 9  illustrates a block diagram illustrating a temperature heating engine control algorithm according to at least some example embodiments. 
     Referring to  FIG. 9 , the temperature heating engine control algorithm  900  uses a PID controller  970  to control an amount of power applied to the heating engine control circuit  2127  so as to achieve a desired temperature. For example, as is discussed in greater detail below, according to at least some example embodiments, the temperature heating engine control algorithm  900  includes obtaining a determined temperature value  974  (e.g., determined as described above); obtaining a target temperature value (e.g., target temperature  976 ) from the memory  2130 ; and controlling, by a PID controller (e.g., PID controller  970 ), a level of power provided to the heater, based on the determined heater temperature value and the target temperature value. 
     Further, according to at least some example embodiments, the target temperature  976  serves as a setpoint (i.e., a temperature setpoint) in a PID control loop controlled by the PID controller  970 . 
     Consequently, the PID controller  970  continuously corrects a level of a power control signal  972  so as to control a power waveform  930  (i.e., COIL_X and COIL_Z) output by the power level setting operation  944  to the heating engine control circuit  2127  in such a manner that a difference (e.g., a magnitude of the difference) between the target temperature  976  and the determined temperature  974  is reduced or, alternatively, minimized. The difference between the target temperature  976  and the determined temperature  974  may also be viewed as an error value which the PID controller  970  works to reduce or minimize. 
     For example, according to at least some example embodiments, the power level setting operation  944  outputs the power waveform  930  such that levels of the power waveform  930  are controlled by the power control signal  972 . The heating engine control circuit  2127  causes an amount of power provided to the heater  336  by the power supply  1234  to increase or decrease in manner that is proportional to an increase or decrease in a magnitude of the power levels of a power level waveform output to the heating engine control circuit  2127 . Consequently, by controlling the power control signal  972 , the PID controller  970  controls a level of power provided to the heater  336  (e.g., by the power supply  1234 ) such that a magnitude of the difference between a target temperature value (e.g., target temperature  976 ) and a determined temperature value (e.g., determined temperature  974 ) is reduced, or alternatively, minimized. 
     According to at least some example embodiments, the PID controller  970  may operate in accordance with known PID control methods. According to at least some example embodiments, the PID controller  970  may generate 2 or more terms from among the proportional term (P), the integral term (I), and the derivative term (D), and the PID controller  970  may use the two or more terms to adjust or correct the power control signal  972  in accordance with known methods. In some example embodiments, the same PID settings for the initial and subsequent preheat phases may be used. 
     In other example embodiments, different PID settings may be used for each phase (e.g., if the temperature targets used for the initial and subsequent preheats are substantially different). 
       FIG. 10  shows an example manner in which levels of the power waveform  930  may vary over time as the PID controller  970  continuously corrects the power control signal  972  provided to the power level setting operation  944 .  FIG. 10  shows an example manner in which levels of the power waveform  930  may vary as temperature thresholds and energy thresholds are reached. The power in  FIG. 10  is COIL_VOL*COIL_CUR. In  FIG. 10 , the PID loop will start to lower the applied power from a maximum power P max  as the temperature approaches the setpoint, which reduces overshoot of the target temperature. 
       FIG. 10  is discussed in further detail below. 
     Referring back to  FIG. 8A , the controller determines an estimated energy that has been delivered to the heater as part of applying the first power, at S 810 . 
     As shown in  FIG. 8B  and previously discussed, the controller controls power supplied to the heater at S 855 . At S 860 , the controller determines whether an estimated energy applied to the heater has reached a preheat energy threshold. More specifically, the controller integrates (or sums the samples) the power delivered to the heater since starting the preheat to estimate the energy delivered to the heater. In an example embodiment, the controller determines the power (Power=COIL_VOL*COIL_CUR) applied to the heater every millisecond and uses that determined power as part of the integration (or the sum). 
     If the controller determines the preheat energy threshold has not been met, the method proceeds to S 855  where power is supplied to the heater as part of the preheating process of the heater. 
     When the controller determines the applied energy reaches the preheat energy threshold (e.g.,  75 J), the controller causes the aerosol-generating device to output a preheat complete indication at S 865  via the aerosol indicators. 
     Referring to both  FIGS. 8A and 8B , the controller applies a second power to the heater at S 815  upon the preheat energy threshold being met. The second power may be less than the first power. 
     The controller changes the target initial preheat temperature of the heater to a subsequent preheat temperature (e.g., 300° C.) and the controller reduces input power accordingly to the second power using the temperature control algorithm described in  FIG. 9 . The subsequent preheat temperature may be based on empirical data and less than the target initial preheat temperature. In some example embodiments, the subsequent preheat temperature may be based on a number of times a negative pressure is applied to the device with the capsule in the device. 
     While  FIG. 8B  and  FIG. 10  illustrate preheating to a subsequent preheat temperature target, an adult operator may start aerosol-generation after the initial preheat temperature target is reached. More specifically, the controller  2105  may initiate aerosol-generation (i.e., supplying power to the heater such that the heater reaches a temperature sufficient to produce an aerosol) upon detecting a negative pressure being applied by the adult operator and upon the initial preheat temperature target being reached. 
     The preheat energy threshold may be determined based on empirical data and determined to be sufficient energy to produce a desired/selected amount of aerosol upon a negative pressure above a pressure threshold being applied. 
     At S 875 , the adult operator may apply a negative pressure to the aerosol-generating device. In response, the aerosol-generating device heats the pre-aerosol formulation in the capsule to generate an aerosol. 
     By using applied energy as a factor for controlling the temperature of the heater and/or during heating, sensory experience and energy efficiency are improved, resulting in conservation of battery power. 
       FIG. 10  illustrates a timing diagram of the methods illustrated in  FIGS. 8A-8B . At T 1 , the preheat commences and the controller ramps up power to apply a first power to the heater, which in this example is a maximum power P max . At T 2 , the controller determines the heater is approaching an initial preheat target temperature Temp 1  (due to reduction in error signal in the PID control loop) and begins to reduce the applied power from P max  to an intermediate power P int  to avoid a temperature overshoot. The reduction to the intermediate power P int  includes at least two intervals Int 1  and Int 2 . The controller reduces the power at a faster rate (i.e., larger slope) than during the interval Int 2 . The interval Int 2  has a smaller rate of change to allow the intermediate power Pint to be reached at substantially the same time the controller determines the initial preheat temperature Temp 1  has been reached. The PID settings used for the preheat may be the same for both intervals Int 1  and Int 2  (e.g., P=100, I=0.25 and D=0). The change in power application during intervals Int 1  and Int 2  is a result of the reduction in temperature error signal. 
     At T 3 , the controller determines the initial preheat temperature Temp 1  has been reached. At T 4 , the controller determines the applied energy reaches the preheat energy threshold and reduces the power to a second power P 2  to maintain the temperature of the heater at a subsequent preheat temperature Temp 2 . 
     The transition from the intermediate power P int  to the second power P 2  includes two intervals Int 3  and Int 4 . In the interval Int 3 , the controller decreases the power at a first slope. In the interval Int 4 , the controller increases the power at a slope whose magnitude is less than the magnitude of the first slope. The controller starts the interval Int 4 , when the power is at P dip , which is less than the second power P 2 . 
     While a number of example embodiments have been disclosed herein, it should be understood that other variations may be possible. Such variations are not to be regarded as a departure from the spirit and scope of the present disclosure, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.