Patent Publication Number: US-2022225668-A1

Title: Aerosol-generating device with heating zone insulation

Description:
The invention relates to an aerosol-generating device for heating an aerosol-forming substrate. In particular, the aerosol-generating device is configured to provide improved thermal insulation of an aerosol-forming substrate. 
     A number of prior art documents disclose aerosol-generating devices that include, for example, heated aerosol-generating systems and electrically heated aerosol-generating systems. An example of a heated aerosol-generating system is disclosed in WO2013/076098, which describes embodiments in which an aerosol-forming substrate of an aerosol-generating article is penetrated by a heating element of an aerosol-generating device in order to generate an inhalable aerosol. The heating element is in contact with the aerosol-forming substrate and raises the temperature of the substrate, thereby vaporising volatile components of the substrate. When the aerosol-forming substrate is exhausted, the aerosol-generating article containing the aerosol-forming substrate is removed from the aerosol-generating device and disposed of. The aerosol-generating article disclosed in WO2013/076098 fits snugly within a cavity of an extractor portion of an aerosol-generating device. This provides a tight fit, which holds the article in the cavity. Heat supplied to the aerosol-forming substrate swiftly raises the temperature of the substrate due to direct contact between the heating element and the substrate. Heat is also swiftly removed from the article, however, by conduction into walls of the cavity, which may act as a heat sink. 
     WO2018/050735 discloses an embodiment of an aerosol-generating device in which an aerosol-generating article cavity is provided with ribs to provide improved retention of an aerosol-generating article in the cavity. The ribs are spaced apart, defining airflow channels between neighbouring ribs and possibly also between discontinuous ribs. The ribs are preferably arranged in an oblique manner, so that a user may extract the aerosol-generating article by applying an axial force together with a torque in order to facilitate removal. However, significant contact points the aerosol-generating article and the ribs of the cavity still exist and air flow between the longitudinal ribs also contributes to cooling of the aerosol-forming substrate. 
     The disclosure herein relates to an aerosol-generating device for heating an aerosol-forming substrate. The aerosol-forming substrate may be provided in an aerosol-generating article. The aerosol-generating article may be a substantially cylindrical aerosol-generating article. The aerosol-generating device may comprise a longitudinally extending cavity for receiving a distal portion of the aerosol-generating article. The longitudinally extending cavity may have a longitudinal axis. The longitudinal cavity may be defined by a base, side walls extending from the base, and an opening at an opposite end of the cavity to the base. Internal surfaces of the side walls define a first portion of the cavity, having a first diameter. The first portion of the cavity may be a stabilising portion. A second portion of the cavity, having a second diameter, may be located between the stabilising portion and the base. The second portion may be a heating portion. The second diameter may be greater than the first diameter. 
     In a preferred embodiment, there is provided an aerosol-generating device for heating an aerosol-forming substrate provided in a substantially cylindrical aerosol-generating article. The aerosol-generating device comprises a longitudinally extending cavity for receiving a distal portion of the aerosol-generating article. The longitudinally extending cavity has a longitudinal axis and is defined by a base, side walls extending from the base, and an opening at an opposite end of the cavity to the base. Internal surfaces of the side walls define a stabilising portion of the cavity having a first diameter. A heating portion of the cavity is located between the stabilising portion and the base. The heating portion has a second diameter that is greater than the first diameter. 
     The diameter of the stabilizing portion is such that the distal portion of the aerosol-generating article can be inserted therethrough. When the distal portion of the aerosol-generating article is inserted through the stabilising portion, preferably, there is minimal space between an outer surface of the aerosol-generating article and an inner surface of the stabilizing portion. Preferably, there is a close or snug fit between the aerosol-generating article and the stabilising portion. Preferably, there is no gap between the outer surface of the aerosol-generating article and the inner surface of the stabilizing portion when the aerosol-generating article is received in the cavity. The outer surface of the aerosol-generating article may contact the inner surface of the stabilizing portion when the article is inserted into or received within the cavity. Thus, it is preferable that the inner diameter of the stabilizing portion is substantially the same dimension as the outer diameter of the aerosol-generating article. For example, the inner diameter of the stabilizing portion may be the same diameter as the outer diameter of the aerosol-generating article, plus or minus 10%, or plus or minus 5%. In some embodiments, the inner diameter of the stabilizing portion may be between 0% and 5% greater than the outer diameter of the aerosol-generating article, for example between 1% and 4% greater, or between 2% and 3% greater. Preferably, the dimensions are such that the article can be inserted into, and removed from, the cavity, while maintaining an interference, for example contact or a loose seal, between the article and the inner diameter of the stabilizing portion when inserted. Preferably, the dimensions are such that the article can be inserted into, and removed from, the cavity without damage to the article. Preferably, the dimensions are such that the article is supported within the cavity without allowing any substantial movement in a radial direction. 
     When the aerosol-generating article is fully inserted into the cavity, a distal end of the article preferably abuts the base of the cavity. When the aerosol-generating article is fully inserted into the cavity, a distal end of the aerosol-generating article may abut an optional stop or an end-point at, or adjacent to, the base of the cavity. Preferably, when the aerosol-generating article is fully inserted into the cavity, at least a portion of the aerosol-generating article is located within the heating portion of the cavity. Preferably, the aerosol-generating article is configured so that an aerosol-forming substrate of the aerosol-generating article is received within the heating portion of the cavity when the aerosol-generating article is fully inserted into the cavity. A diameter of the inner surface of the heating portion is greater than a diameter of the stabilizing portion. Thus, a gap exists between the outer surface of the aerosol-generating article and the inner surface of the heating portion. Preferably, an air-gap is present entirely, or substantially entirely, around the outer surface of the portion of aerosol-generating article located within the heating portion of the cavity. Preferably, an air-gap provides an air insulation layer between a portion of the aerosol-generating article and the inner surface of the heating portion. 
     A transverse cross-section of the cavity at the stabilising portion is preferably of substantially the same shape as a transverse cross-section of the cavity at the heating portion. Preferably the cross-sectional shape is circular, or oval. Preferably the stabilising portion of the cavity and the heating portion of the cavity are co-axial. 
     In some embodiments, the diameter of the stabilizing portion may change to the diameter of the heating portion at a step in the internal wall of the cavity. In some embodiments, the diameter of the stabilizing portion may change to the diameter of the heating portion by means of a series of steps. In some embodiments, the diameter of the stabilizing portion may change to the diameter of the heating portion by means of a sloped internal portion of the cavity wall. 
     The aerosol-generating article comprises an aerosol-forming substrate that can be heated to generate an aerosol. Preferably, the aerosol-forming substrate is located at, or near to, the distal end of the aerosol-generating article. Thus, at least a portion of the aerosol-forming substrate is positioned within the heating portion when the aerosol-generating article is fully inserted into the cavity of the device. A heating means for heating the aerosol-forming substrate is positioned to heat a portion of an aerosol-forming substrate of an aerosol-generating article that is positioned within the heating portion. The heating means may comprise a heating element. In some embodiments, the heating element may comprise a resistive heating element. In some embodiments, the resistive heating element may comprise one or more electrically conductive tracks on an electrically insulating substrate. 
     In some embodiments, the heating means may comprise a susceptor and inductor. The heating means preferably comprises a heating element or susceptor arranged to penetrate a distal end of the aerosol-generating article and contact the aerosol-forming substrate when the aerosol-generating article is fully inserted into the cavity of the aerosol-generating device. In some embodiments, the susceptor may be provided as part of the aerosol-generating article. In some embodiments, the susceptor may be provided as part of the aerosol-generating device and as a part of the aerosol-generating article. 
     In some embodiments, the heating element may be provided as part of the aerosol-generating device. The heating element may be arranged to at least partially penetrate a portion of an aerosol-forming substrate when the aerosol-forming substrate is received within the heating portion. The heating element may be an elongate heating element. The heating element may comprise a pointed or tapered end. A pointed or tapered end advantageously facilitates penetration of the aerosol-forming substrate by the heating element. The heating element may be a blade shaped heating element. The heating element may be a pin shaped heating element. The heating element may comprise only one heating element. The heating element may be provided along a central longitudinal axis of the heating portion. The heating element may comprise multiple heating elements. The multiple heating elements may have the same properties. One or more of the multiple heating elements may have one or more different properties compared to the remainder of the multiple heating elements. Said property may be, for example, size, shape, dimension, operating temperature. 
     In some embodiments, the heating element may be provided as part of the aerosol-generating article and may be operable in combination with one or more features of the device. The heating element may be a susceptor provided as part of the aerosol-generating article. The heating element may be a susceptor provided in the region of the aerosol-forming substrate. The heating element may be a susceptor element having any of a variety of shapes. The susceptor element may be a rod shape, a cube shape, a cuboid shape, or any other shape, incorporated into the aerosol-generating article. The susceptor element may be provided centrally along a central longitudinal axis of the aerosol-generating article. The heating element may be a susceptor material incorporated into the aerosol-forming substrate portion of the aerosol-generating article. The susceptor material may be provided in the form of, for example, any of: particles, strips, shreds, powder, sheets or a mesh. 
     As used herein, the term ‘susceptor’ refers to a material that can convert electromagnetic energy into heat. When located within a fluctuating electromagnetic field, eddy currents induced in the susceptor cause heating of the susceptor. As the susceptor is located in thermal contact with or at least proximal to the aerosol-forming substrate, the aerosol-forming substrate is heated by the susceptor. 
     As used herein, the term inductor refers to a component which can generate a fluctuating electromagnetic field for heating a susceptor located within the fluctuating electromagnetic field. In use, the aerosol-generating article may engage with the aerosol-generating device such that the susceptor is located within the fluctuating electromagnetic field generated by the inductor. 
     As used herein, an ‘aerosol-generating device’ relates to a device that interacts with an aerosol-forming substrate to generate an aerosol. The aerosol-forming substrate may be a component part of an aerosol-generating article. An aerosol-generating device may comprise one or more components for supplying energy from a power supply to an aerosol-forming substrate to generate an aerosol. For example, an aerosol-generating device may be a heated aerosol-generating device. An aerosol-generating device may be an electrically heated aerosol-generating device or a gas-heated aerosol-generating device. An aerosol-generating device may be an aerosol-generating device that interacts with an aerosol-forming substrate of an aerosol-generating article to generate an aerosol that is directly inhalable into a user&#39;s lungs thorough the user&#39;s mouth. 
     As used herein, the term ‘aerosol-forming substrate’ relates to a substrate capable of releasing volatile compounds that are able to form an aerosol. Such volatile compounds may be released by heating the aerosol-forming substrate. An aerosol-forming substrate may conveniently be used as a component part of an aerosol-generating article. An aerosol-forming substrate may be described as being located in a heating zone of an aerosol-generating article. An aerosol-generating article may be an elongate aerosol-generating article. An aerosol-generating article may be substantially rod shaped. An aerosol-generating article may have a substantially constant diameter along the length of the entire aerosol-generating article. 
     As used herein, the term ‘aerosol-generating article’ refers to an article comprising an aerosol-forming substrate that is capable of releasing volatile compounds, which compounds are able to form an aerosol. For example, an aerosol-generating article may be able to generate an aerosol that is directly inhalable into a user&#39;s lungs through the user&#39;s mouth. An aerosol-generating article may be disposable. The aerosol-generating article is a heatable aerosol-generating article which is intended to be heated rather than combusted in order to release volatile compounds that are able to form an aerosol. The aerosol formed by heating the aerosol-forming substrate may contain fewer known harmful constituents than would be produced by combustion or pyrolytic degradation of the aerosol-forming substrate. In some embodiments, an aerosol-generating article may comprise an aerosol-forming substrate. In some embodiments, the aerosol-forming substrate may be formed from, or may comprise, processed tobacco, for example homogenised tobacco or cast leaf tobacco. 
     As used herein, the term “aerosol-generating system” refers to an aerosol-generating device and at least one aerosol-generating article configured to be used with the device. 
     As used herein, the terms “upstream”, “downstream”, “proximal” and “distal” are used to describe the relative positions of elements, or portions of elements, of aerosol-generating articles, aerosol-generating devices and aerosol-generating systems according to the invention. 
     Aerosol-generating articles as described herein comprise a proximal end through which, in use, an aerosol exits the aerosol-generating article. The proximal end may also be referred to as the mouth end. In use, a user draws on the proximal or mouth end of the aerosol-generating article in order to inhale an aerosol generated by the aerosol-generating article. In some embodiments, the aerosol-generating device and the aerosol-generating article are configured so that at least a portion of the mouth end is not received within the longitudinally extending cavity of the device when the article is fully inserted in the cavity. That is, at least a portion of the mouth end extends outwardly, beyond the opening of the cavity of the aerosol-generating device. In this way, a user may puff on the mouth end of the aerosol-generating article. In some embodiments, the aerosol-generating device and the aerosol-generating article are configured so that the entire length of the aerosol-generating article is received within the longitudinally extending cavity of the device when the article is fully inserted in the cavity. In some embodiments a mouthpiece element comprising an airflow channel alignable with the mouth end of the aerosol-generating article may be provided. In this way, the user may instead puff on the mouthpiece. In some embodiments, the mouthpiece element may be a separate mouthpiece element. The separate mouthpiece may be engageable with one or both of the aerosol-generating device and the aerosol-generating article. In some embodiments, instead of a separate mouthpiece element, the mouthpiece element may be provided as part of the aerosol-generating device. 
     The aerosol-generating article comprises a distal end opposed to the proximal or mouth end. The proximal or mouth end of the aerosol-generating article may also be referred to as the downstream end and the distal end of the aerosol-generating article may also be referred to as the upstream end. Components, or portions of components, of the aerosol-generating article may be described as being upstream or downstream of one another based on their relative positions between the proximal or downstream end and the distal or upstream end of the aerosol-generating article. 
     As used herein the term “diameter” is used to refer to the maximum transverse dimension of elements, or portions of elements, of aerosol-generating articles, aerosol-generating devices and aerosol-generating systems according to the invention. For the avoidance of doubt, as used herein the term “diameter” may refer to the “width” of elements, or portions of elements, of aerosol-generating articles, aerosol-generating devices and aerosol-generating systems, of non-circular transverse cross-section. 
     As used herein the term “longitudinal” is used to describe the direction between the downstream or proximal end and opposed upstream or distal end of aerosol-generating articles, aerosol-generating devices and aerosol-generating systems according to the invention and the term “transverse” is used to describe the direction perpendicular to the longitudinal direction. 
     For the avoidance of doubt, in this description the term “heating element” may mean one or more heating elements. 
     Prior art aerosol-generating systems exist in which a cylindrical aerosol-generating article arranged to be inserted into a cavity of an aerosol-generating device to be penetrated by a heating means, for example as disclosed in WO2013/076098. The heating means in WO2013/076098 is a heating element that penetrates an aerosol-forming substrate to heat the substrate sufficiently to form an aerosol. Efficiency of the device may be affected, however, by contact between walls of the cavity and the article inserted into the cavity. Use of the aerosol-generating device disclosed herein provides a number of advantages compared to this prior art. 
     A heating element that is arranged to be inserted into at least a portion of the aerosol-forming substrate of an aerosol-generating article can deliver heat immediately to that portion of aerosol-forming substrate that it is in contact with. In some embodiments, it is preferable to heat the aerosol-forming substrate to a temperature of between 150° C. and 450° C., for example between 200° C. and 400° C., or between 250° C. and 350° C., or between 300° C. and 350° C. Thermal transfer within the aerosol-forming substrate results in the entire aerosol-forming substrate being heated, although there may be a time lag for the temperature towards an outer portion of the aerosol-forming substrate to reach the temperatures required to form an aerosol. The present aerosol-generating device minimises, or avoids, contact between an outer surface of the aerosol-generating article, at least in the heating portion of the aerosol-generating article, and internal walls of an article receiving cavity of the aerosol-generating device. This helps prevent thermal transfer between the aerosol-generating article and the walls of the cavity. Dissipation of thermal energy within a heated aerosol-forming substrate may be minimised as a result of reduced contact between an outer surface of an aerosol-generating article comprising the aerosol-forming substrate, at least in the heating portion of the aerosol-generating article, and internal walls of an article receiving cavity of the aerosol-generating device. As a result, a greater proportion of heat from the heating means may be retained within the aerosol-forming substrate and the entire substrate may be brought to an operating temperature more rapidly. Air between the outer walls of the cavity in the heating portion and the aerosol-generating article may provide thermal insulation of the aerosol-generating article as a thermal barrier 
     The present invention may reduce the time lag between initiating operation of the heating element and the aerosol-forming substrate coming to an operating temperature. An operating temperature may be a temperature at or above which one or more volatile compounds are released from the aerosol-forming substrate. Advantageously, a time between a user initiating operation of the aerosol-generating system and the aerosol-generating device being ready for a user to take a first puff, also referred to as TT1P may be reduced. Advantageously, the initial aerosol delivery provided by the aerosol-generating device described herein may be improved. The user experience in the first few puffs may therefore be improved. 
     In a further advantage, the reduced thermal transfer between the outer surface of the aerosol-generating article and the walls of the cavity of the aerosol-generating device means that less thermal energy is dissipated away from the aerosol-generating article on heating. Thus, the aerosol-forming substrate may remain at operating temperature for longer, for example between puffs. Once at operating temperature, it may be that a lower energy input is required to maintain the aerosol-forming substrate at that operating temperature. This helps provide a consistent user experience during consumption of the article. This may also mean that less overall energy needed for consumption of an aerosol-generating article is lower. Thus, the device may be operational with smaller power source, for example a smaller battery, than would otherwise be required. The device may be able to perform a greater number of operational cycles without the need to provide a larger battery. 
     In a further advantage, the reduction, or elimination, of contact points between the aerosol-generating article and the walls of the cavity may help prevent the formation of cold spots in the aerosol-forming substrate. Cold spots are regions of aerosol forming substrate that do not reach optimal operating temperature during consumption of the device due to localised dissipation of heat. If cold spots occur, the aerosol-forming substrate may not be completely consumed during use. Thus, by minimising or preventing cold spots in the aerosol-forming substrate, the total amount of substrate required for a satisfactory user experience may be lower. 
     In a further advantage, reduction of heat dissipated from the aerosol-generating article may lower the maximum temperature that the heating element needs to achieve for a satisfactory user experience. In addition to lower energy requirements, this may also reduce the chance of heating the portions of the aerosol-forming substrate in regions contacting the heating element to a high degree, which may cause unpleasant flavours and smells. 
     The substantially cylindrical aerosol-generating article to be heated with the device may have a longitudinal axis and an article diameter. The first diameter is preferably substantially equal to the article diameter such that the distal portion of the substantially cylindrical aerosol-generating article can be inserted through the stabilising portion of the cavity. Preferably, the transverse cross-sectional shape of the aerosol-generating article is substantially the same as the transverse cross-sectional shape of the stabilising portion of the cavity. 
     The diameter of the cavity in the heating portion may be between 105% and 170% greater than a diameter of the cavity in the stabilising portion, for example between 110% and 150% greater. Preferably, the diameter of the cavity in the heating portion may be between 120% and 140% greater than a diameter of the cavity in the stabilising portion, for example between 125% and 130% greater. 
     A transverse cross sectional area of the cavity in the heating portion may be between 110% and 300% greater than a transverse cross-sectional area of the cavity in the stabilising portion. For example, a transverse cross sectional area of the cavity in the heating portion may be between 115% and 280% greater than a transverse cross-sectional area of the cavity in the stabilising portion, for example between 130% and 200% greater, preferably between 140% and 160% greater. 
     Preferably, the difference in diameter between the first diameter at the stabilising portion and the second diameter at the heating portion is referred to as the gap diameter. Preferably, the gap diameter may be between 0.5 mm and 5 mm, for example between 1 mm and 4 mm. In other words, the aerosol-generating device is configured such that there is an air-gap equal to half of the gap diameter, for example of between 0.25 mm and 2.5 mm, between an outer surface of the aerosol-generating article and an inner surface of the heating portion of the cavity, when the aerosol-generating article is fully inserted into the cavity. Preferably, the air-gap is between 0.25 mm and 2.5 mm, for example between 0.3 mm and 2 mm, or between 0.5 mm and 1 mm. The air-gap provides an air insulation layer between the outer surface of the aerosol-generating article and the inner surface of the heating portion of the cavity. 
     Preferably, the difference in diameter between the stabilising portion and the heating portion provides one or more insulating air pockets surrounding an external surface of an aerosol-generating article that has its distal portion fully inserted into the longitudinally extending cavity. Where there is more than one air pocket, preferably there is no through-flow of air between the air pockets. In some embodiments, the air pocket is preferably annular, extending around an aerosol-generating when the aerosol-generating article is received in the cavity. Two or more semi-annular air pockets may be defined. Where more than one air pocket is defined, in some embodiments, the air pockets are separated by a rib, such as a longitudinal rib, or an annular rib. Flow of air within the air pocket or air pockets may contribute to thermal dissipation from the aerosol-generating article. Thus, it is highly preferable that there are no air inlets or air outlets defined in the device in the heating portion which might otherwise allow air to flow into or out of the air pocket or pockets defined by the gap between the aerosol-generating article and the inner walls of the heating portion, when the article is inserted into the cavity. In particular, it is preferable that there are no air inlets or air outlets defined through the side wall of the cavity extending into the heating portion. 
     It may be advantageous that an air inlet is defined through the base of the cavity. Such an inlet may provide a source of air to allow air to be drawn into the distal end of the aerosol-generating article, along the length of the article, and into the user&#39;s mouth through the proximal end, or mouth end, of the aerosol-generating article. Such an air inlet through the base of the cavity may be provided by a single hole at a central point of the base, or within a small radius of this central point. Such an inlet may be positioned so that when an aerosol-generating article is inserted into the cavity of the aerosol-generating device, the air inlet is aligned with an end face of the aerosol-generating article. That is, the air inlet is not positioned in a region of the gap diameter. 
     In preferred embodiments, the internal walls of the cavity may further define a locating portion disposed at a distal end of the cavity. The heating portion may be disposed between the stabilising portion and the locating portion. The locating portion of the cavity may have a third diameter that is substantially equal to the first diameter of the stabilising portion. The locating portion is preferably co-axially aligned with the stabilisation portion. In this way, a cylindrical article may be able pass through the stabilisation portion, and a distal end of the article may be able to lodge in the locating portion. The distal end of the article may be, thereby, radially constrained. Preferably, when the article is fully inserted into the cavity, the article is retained by contact with inner walls of both the stabilisation portion and inner walls of the locating portion. Preferably, the dimensions of the locating portion and the aerosol-generating article are such that the article can be inserted into, and removed from, the cavity, while maintaining an interference, for example contact or a loose seal, between the article and the inner diameter of the locating portion when inserted in the cavity. Advantageously, in such a configuration, one or more closed air pockets may be defined by a gap between the outer surface of the aerosol-generating article and an inner surface of the cavity. Thus, outer boundaries of a circumferential or annular air pocket, when an aerosol-generating article is fully inserted into the cavity, may be formed by (1) an outer surface of the aerosol-generating article, (2) an inner surface of the heating portion of the cavity, (3) a radially extending step or slope extending between the inner surface of the heating portion and the inner surface of the stabilising portion, and (4) a radially extending step or slope extending between the inner surface of the heating portion and the inner surface of the locating portion. 
     In some embodiments, the diameter of the heating portion may change to the diameter of the locating portion at a step in the internal wall of the cavity. Alternatively, in some embodiments, the diameter of the heating portion may change to the diameter of the locating portion by means of a series of steps. In some embodiments, the diameter of the heating portion may change to the diameter of the locating portion by means of a sloped internal portion of the cavity wall. In some embodiments, the internal walls of the cavity may define a tapered region in which the diameter of the cavity changes between the second diameter and the third diameter. Advantageously, a taper may assist in alignment of the aerosol-generating article when the aerosol-generating article is inserted into the cavity. A tapered region may act as a funnel to guide the distal end of the aerosol-generating article into the locating portion of the cavity. 
     It is preferable that there is minimal contact between the article and the cavity wall in the heating portion. It may be preferable, for example, for there to be a circumferential air-gap defined around an article inserted into the cavity. However, it may be desirable to include one or more ribs. The one or more ribs may help guide and stabilise an aerosol-generating article inserted into the cavity. In some embodiments, only one rib is provided. In some embodiments, multiple ribs are provided. In some embodiments, 3 ribs are provided. In some embodiments, 6 ribs are provided. Where more than one rib is provided, preferably, the ribs are substantially evenly spaced about the circumference of the cavity. The one or more ribs may be longitudinally extending ribs. Such ribs may extend radially into the cavity from the inner wall of the heating portion of the cavity. Preferably, any such ribs extend radially by a distance substantially equal to the air gap. The internal side walls of the cavity may define one or more ribs extending longitudinally in the heating portion. The ribs may have a radial dimension equal to half of the gap diameter. Multiple individual partially annular air pockets may be formed by such ribs. For example, two longitudinally extending ribs may divide the heating portion of the cavity to allow two semi-annular air pockets to be defined when an article is inserted into the cavity. In some embodiments, the ribs may be annular. In some embodiments, the ribs may be a combination of longitudinal and annular ribs. A combination of longitudinal and annular ribs may define a plurality of air cavities. 
     In some embodiments, an aerosol-generating device may comprise a first body portion and a second body portion that is movable relative to the first body portion. The first body portion may house a power source, control electronics and at least part of a heating means of the aerosol-generating device. The longitudinally extending cavity may be defined in the second body portion. The second body portion may be able to function, as an extractor. In some embodiments, the extractor may facilitate at least partial separation of the aerosol-forming substrate from a heating element. In some embodiments, the extractor may facilitate full separation of the aerosol-forming substrate from a heating element. In some embodiments, the extractor may facilitate unsticking of the aerosol-forming substrate from a heating element. In some embodiments, the extractor may facilitate removal of an aerosol-generating article after the article has been consumed. For example, the aerosol-generating device may comprise a heating means that is attached to, integrated in or part of the first body portion. The movement of the second body portion relative to the first body portion may act to separate an aerosol-forming substrate of an aerosol-generating article received in the cavity of the second body portion of the aerosol-generating device, from the heating means. The first body portion and the second body portion may be removably coupleable with each other. Thus, the second body portion may be easily removed from the first body portion to facilitate, for example, cleaning. 
     In some embodiments, the second body portion may be movable between a first position and a second position. The first position may be an operating position defined by a heating means, such as a heating element, or an inductor, being engageable with the aerosol-forming substrate of the aerosol-generating article. The first position may be an operating position defined by a heating element being inserted into and in contact with the aerosol-forming substrate of the aerosol-generating article. The first position may be an operating position defined by the aerosol-forming substrate of the aerosol-generating article being located within an alternating magnetic field generated by an inductor. The second position may be an extraction position defined by the aerosol-forming substrate being at least partially disengaged or separated from the heating means. At least partially separated may include physically separated, or simply separated insofar as a bond or interface between the heating means and the aerosol-forming substrate is broken. For example, during and after heating, the aerosol-forming substrate may stick to the heating means. The second, extraction, position may be a position in which the aerosol-forming substrate is unstuck from the heating means. The second, extraction, position may be a position in which the aerosol-forming substrate is moved out of an alternating magnetic field generated by an inductor. Advantageously, such an extractor helps to facilitate removal of the aerosol-generating article from the aerosol-generating device. Thus, the extractor may be movably-coupled to an aerosol-generating device, and may be movable between a first position in which the aerosol-forming substrate is in contact with a heating element of the aerosol-generating device, and a second position in which the aerosol-forming substrate is at least partially separated from the heating element. Preferably the extractor remains coupled to the aerosol-generating device when in the first position. Preferably, the extractor remains coupled to the aerosol-generating device in the second position. In some embodiments, the extractor remains coupled to the aerosol-generating device in any intermediate point between the first position and second position. The extractor may be removably coupleable to the aerosol-generating device. 
     The extractor may comprise a sliding receptacle. The sliding receptacle may define the cavity for receiving an aerosol-generating article. The sliding receptacle is preferably slidable between the first position and the second position. In some embodiments, the entire extractor including the sliding receptacle may move to translate the sliding receptacle between the first position and the second position. Alternatively, only the sliding receptacle of the extractor may be slidable between the first position and the second position. 
     In preferred embodiments, a heating element may extend into the heating portion of the cavity of the aerosol-generating device. The heating element may be substantially blade-shaped for insertion into the aerosol-forming substrate of the aerosol-forming article. The heating element may have a length of between 10 mm and 60 mm. The heating element may have a width of between 2 mm and 10 mm. The heating element may have a thickness of between 0.2 mm and 1 mm. A preferred length may be between 15 mm and 50 mm, for example between 18 mm and 30 mm. A preferred length may be about 19 mm or about 20 mm. A preferred width may be between 3 mm and 7 mm, for example between 4 mm and 6 mm. A preferred width may be about 5 mm. A preferred thickness may be between 0.25 mm and 0.5 mm. A preferred thickness may be about 0.4 mm. The heating element may comprise an electrically-insulating substrate and an electrically-resistive heating element. In some embodiments, the electrically-resistive heating element comprises one or more tracks. In some embodiments, the electrically-resistive heating element is provided on the electrically insulating substrate or is embedded in the electrically insulating substrate. The electrically-resistive heating element may be supported by the electrically insulating substrate. Alternatively or in addition, a heating element may surround the heating portion of the cavity. 
     The invention may provide an aerosol-generating system comprising an aerosol-generating article and an aerosol-generating device configured to heat an aerosol-forming substrate of the aerosol-generating article. The aerosol-generating device may be any device as described herein. 
     The aerosol-generating article may be any article suitable for consumption using such a device. For example, the aerosol-generating article may be any article described herein. For example, in some embodiments, the aerosol-generating article may comprise a plurality of co-axially aligned components. The plurality of coaxially aligned may include an aerosol-forming substrate, assembled within a wrapper to form a substantially cylindrical article. The aerosol-generating article may have a longitudinal axis and an article diameter. The aerosol-generating article may have a proximal portion terminating in a proximal end and a distal portion terminating in a distal end. The aerosol-forming substrate is preferably located at or near the distal portion of the article. In some embodiments, the aerosol-forming substrate may be a tobacco plug, such as a cylindrical tobacco plug. 
     The aerosol-generating article may have a total length between approximately 30 mm and approximately 100 mm, preferably between 40 mm and 60 mm, or 42 mm and 52 mm, for example about 45 mm. The aerosol-generating article may have an external diameter between approximately 5 mm and approximately 12 mm, for example between 6 mm and 9 mm, or between 7 mm and 8 mm. 
     The aerosol-generating article may comprise a filter element. The filter element may comprise a filter plug. The filter element may be located at a downstream end of the aerosol-generating article. The filter element may be a cellulose acetate filter plug. In some embodiments, the filter element is approximately 7 mm in length. The filter element may have a length of between approximately 5 mm to approximately 10 mm. 
     In some embodiments, the aerosol-generating article has a total length of approximately 45 mm. The aerosol-generating article may have an external diameter of approximately 7 mm, for example between 6.8 mm and 7.2 mm. The aerosol-forming substrate may have a length of between approximately 8 mm and 14 mm, for example 10 mm, or 11 mm, or 12 mm. 
     The diameter of the aerosol-forming substrate may be between approximately 5 mm and approximately 12 mm. The aerosol-generating article may comprise an outer paper wrapper. The aerosol-generating article may comprise a separation between the aerosol-forming substrate and the filter plug. The separation may be in the range of approximately 5 mm to approximately 25 mm. Preferably, the separation is approximately 18 mm. The separation may comprise one or more spacer components. 
     In some embodiments, the aerosol-forming substrate is a solid aerosol-forming substrate. In some embodiments, the aerosol-forming substrate is a liquid aerosol-forming substrate. In some embodiments the aerosol-forming substrate is a gel aerosol-forming substrate. In some embodiments, the aerosol-forming substrate comprises both a solid and a liquid component. In some embodiments, the aerosol-forming substrate comprises both a solid and a gel component. In some embodiments, the aerosol-forming substrate comprises both a liquid and a gel component. 
     The aerosol-forming substrate is preferably a solid aerosol-forming substrate. The aerosol-forming substrate may comprise a tobacco-containing material comprising volatile compounds which are released from the substrate upon heating. The volatile compounds may comprise volatile tobacco flavour compounds. The aerosol-forming substrate may comprise an aerosol former that facilitates the formation of a dense and stable aerosol. Examples of suitable aerosol formers are glycerine and propylene glycol. In some embodiments, the aerosol-forming substrate may comprise a non-tobacco material. In some embodiments, the aerosol-forming substrate may comprise a tobacco material and additionally a non-tobacco material. 
     If the aerosol-forming substrate is a solid aerosol-forming substrate, in some embodiments, the solid aerosol-forming substrate may comprise, for example, one or more of: powder, granules, pellets, shreds, spaghettis, strips or sheets. In some embodiments the aerosol-forming substrate comprises one or more of: herb leaf, tobacco leaf, fragments of tobacco ribs, reconstituted tobacco, homogenised tobacco, extruded tobacco, cast leaf tobacco and expanded tobacco. In some embodiments, the solid aerosol-forming substrate may be in loose form. In some embodiments, the aerosol-forming substrate may be provided in a suitable container or cartridge. Optionally, the solid aerosol-forming substrate may comprise additional tobacco or non-tobacco volatile compounds, such as volatile flavour compounds, to be released upon heating of the substrate. The solid aerosol-forming substrate may comprise capsules that, for example, include the additional tobacco or non-tobacco volatile compounds. In some embodiments, such capsules may melt during heating of the solid aerosol-forming substrate. In some embodiments, such capsules may comprise a frangible membrane. The frangible membrane may be crushed, for example by a user, prior to or during use to release the volatile compounds. 
     As used herein, homogenised tobacco refers to material formed by agglomerating particulate tobacco. Homogenised tobacco may be in the form of a sheet. Homogenised tobacco material may have an aerosol-former content of greater than 5% on a dry weight basis. Homogenised tobacco material may alternatively have an aerosol former content of between 5% and 30% by weight on a dry weight basis. Sheets of homogenised tobacco material may be formed by agglomerating particulate tobacco obtained by grinding or otherwise combining one or both of tobacco leaf lamina and tobacco leaf stems. Alternatively, or in addition, sheets of homogenised tobacco material may comprise one or more of tobacco dust, tobacco fines and other particulate tobacco by-products formed during, for example, the treating, handling and shipping of tobacco. Sheets of homogenised tobacco material may comprise one or more intrinsic binders, that is tobacco endogenous binders, one or more extrinsic binders, that is tobacco exogenous binders, or a combination thereof to help agglomerate the particulate tobacco; alternatively, or in addition, sheets of homogenised tobacco material may comprise other additives including, but not limited to, tobacco and non-tobacco fibres, aerosol-formers, humectants, plasticisers, flavourants, fillers, aqueous and non-aqueous solvents and combinations thereof. 
     In a particularly preferred embodiment, the aerosol-forming substrate comprises a gathered crimpled sheet of homogenised tobacco material. As used herein, the term ‘crimped sheet’ denotes a sheet having a plurality of substantially parallel ridges or corrugations. Preferably, when the aerosol-generating article has been assembled, the substantially parallel ridges or corrugations extend along or parallel to the longitudinal axis of the aerosol-generating article. This advantageously facilitates gathering of the crimped sheet of homogenised tobacco material to form the aerosol-forming substrate. However, it will be appreciated that crimped sheets of homogenised tobacco material for inclusion in the aerosol-generating article may alternatively or in addition have a plurality of substantially parallel ridges or corrugations that are disposed at an acute or obtuse angle to the longitudinal axis of the aerosol-generating article when the aerosol-generating article has been assembled. In certain embodiments, the aerosol-forming substrate may comprise a gathered sheet of homogenised tobacco material that is substantially evenly textured over substantially its entire surface. For example, the aerosol-forming substrate may comprise a gathered crimped sheet of homogenised tobacco material comprising a plurality of substantially parallel ridges or corrugations that are substantially evenly spaced-apart across the width of the sheet. 
     Optionally, the solid aerosol-forming substrate may be provided on or embedded in a thermally stable carrier. The carrier may take the form of powder, granules, pellets, shreds, spaghettis, strips or sheets. Alternatively, the carrier may be a tubular carrier having a thin layer of the solid substrate deposited on its inner surface, or on its outer surface, or on both its inner and outer surfaces. Such a tubular carrier may be formed of, for example, a paper, or paper like material, a non-woven carbon fibre mat, a low mass open mesh metallic screen, or a perforated metallic foil or any other thermally stable polymer matrix. 
     The solid aerosol-forming substrate may be deposited on the surface of the carrier in the form of, for example, a sheet, foam, gel or slurry. The solid aerosol-forming substrate may be deposited on the entire surface of the carrier, or alternatively, may be deposited in a pattern in order to provide a non-uniform flavour delivery during use. 
     The aerosol-generating system is a combination of an aerosol-generating device and one or more aerosol-generating articles for use with the device. However, aerosol-generating system may include additional components, such as for example a charging unit for recharging an on-board electric power supply in an electrically operated or electric aerosol-generating device 
    
    
     
       Specific embodiments of the invention will now be described with reference to figures, in which: 
         FIG. 1  is a schematic illustration of an aerosol-generating article suitable for use with an aerosol-generating device according to the invention; 
         FIG. 2  is a schematic illustration of a cavity of an aerosol-generating device according to an aspect of the invention, the cavity defining an article receiving cavity for receiving a suitable aerosol-generating article; 
         FIG. 3  is a schematic illustration showing the aerosol-generating article of  FIG. 1  when inserted into the article receiving cavity of  FIG. 2 ; 
         FIG. 4  is a schematic transverse cross section of  FIG. 3 , showing the aerosol-generating article positioned within a heating portion of the cavity; 
         FIG. 5  is a schematic illustration showing an extractor comprising the cavity of  FIG. 2  coupled to a main body portion of an aerosol-generating device according to the invention; 
         FIG. 6  is a schematic illustration showing the aerosol-generating article of  FIG. 1  when fully inserted into the cavity of the aerosol-generating device of  FIG. 5 ; 
         FIG. 7  is a schematic illustration of a cavity of a control aerosol-generating device not according to an aspect of the invention, the cavity defining an article receiving cavity for receiving a suitable aerosol-generating article; 
         FIG. 8  is a schematic illustration showing the aerosol-generating article of  FIG. 1  when fully inserted into the cavity of the aerosol-generating device of  FIG. 7 ; 
         FIG. 9  is a graph comparing nicotine delivery per puff between an aerosol-generating device according to the invention and a control device; 
         FIG. 10  is a graph comparing glycerol delivery per puff between an aerosol-generating device according to the invention and a control device; 
         FIG. 11  is a schematic illustration of a further embodiment of a cavity of an aerosol-generating device according to an aspect of the invention, the cavity comprising ribs extending longitudinally along the heating portion; 
         FIG. 12  is a schematic transverse cross-sectional view of a heating portion of a cavity showing two ribs; 
         FIG. 13  is a schematic transverse cross-sectional view of a heating portion of a cavity showing three ribs; 
         FIG. 14  is a schematic transverse cross-sectional view of a heating portion of a cavity showing six ribs; 
         FIG. 15  is a schematic longitudinal cross-sectional view of an extractor showing some of its six ribs; and 
         FIG. 16  is a schematic illustration of a further embodiment of an aerosol-generating device according to an aspect of the invention, the aerosol-generating device comprising an inductor and an aerosol-generating article suitable for use with the device comprising a susceptor. 
     
    
    
       FIG. 1  illustrates an aerosol-generating article  10  suitable for use with an aerosol-generating device according to an embodiment of the invention. The aerosol-generating article  10  comprises four elements arranged in coaxial alignment: an aerosol-forming substrate  20 , a support element  30 , a transfer section  40 , and a mouthpiece  50 . These four elements are arranged sequentially and are circumscribed by an outer wrapper  60  to form the aerosol-generating article  10 . The aerosol-generating article  10  has a mouth end  70 , which a user inserts into his or her mouth during use, and a distal end  80  located at the opposite end of the aerosol-generating article  10  to the mouth end  70 . 
     In use air is drawn through the aerosol-generating article by a user from the distal end  80  to the mouth end  70 . The distal end  80  of the aerosol-generating article may thus also be described as the upstream end of the aerosol-generating article  10  and the mouth end  70  of the aerosol-generating article  10  may also be described as the downstream end of the aerosol-generating article  10 . Elements of the aerosol-generating article  10  located between the mouth end  70  and the distal end  80  can be described as being upstream of the mouth end  70  or, alternatively, downstream of the distal end  80 . 
     The aerosol-forming substrate  20  is located at the extreme distal or upstream end of the aerosol-generating article  10 . In the embodiment illustrated in  FIG. 1 , aerosol-forming substrate  20  comprises a gathered sheet of crimped homogenised tobacco material circumscribed by a wrapper. The crimped sheet of homogenised tobacco material comprises glycerine as an aerosol-former. 
     The support element  30  is located immediately downstream of the aerosol-forming substrate  20  and abuts the aerosol-forming substrate  20 . 
     In the embodiment shown in  FIG. 1 , the support element is a hollow cellulose acetate tube. The support element  30  locates the aerosol-forming substrate  20  at the extreme distal end  80  of the aerosol-generating article  10  so that it can be contacted with a heating element of an aerosol-generating device. The support element  30  acts to prevent the aerosol-forming substrate  20  from being forced downstream within the aerosol-generating article  10  towards the transfer element  40  when an internal heating element of an aerosol-generating device is inserted into the aerosol-forming substrate  20 . The support element  30  also acts as a spacer to space the transfer element  40  of the aerosol-generating article from the aerosol-forming substrate  20 . 
     The transfer element  40  is located immediately downstream of support element  30  and abuts the support element  30 . In use, volatile substances released from the aerosol-forming substrate  20  pass along the transfer section  40  towards the mouth end  70  of the aerosol-generating article  10 . The volatile substances may cool within the transfer section  40  to form an aerosol that is inhaled by the user. In the embodiment illustrated in  FIG. 1 , the transfer element  40  is an aerosol-cooling element. The aerosol-cooling element comprises a crimped and gathered sheet of polylactic acid circumscribed by a wrapper  90 . The crimped and gathered sheet of polylactic acid defines a plurality of longitudinal channels that extend along the length of the aerosol-cooling element  40 . 
     The mouthpiece  50  is located immediately downstream of the transfer section  40  and abuts the transfer section  40 . In the embodiment illustrated in  FIG. 1 , the mouthpiece  50  comprises a conventional cellulose acetate tow filter of low filtration efficiency. 
     To assemble the aerosol-generating article  10 , the four elements described above are aligned and tightly wrapped within the outer wrapper  60 . In the embodiment illustrated in  FIG. 1 , the outer wrapper is a conventional cigarette paper. 
     The aerosol-generating article illustrated in  FIG. 1  is designed to engage with an aerosol-generating device comprising an internal heating element in order to be consumed by a user. In use, the internal heating element of the aerosol-generating device heats the aerosol-forming substrate  20  of the aerosol-generating article  10  to a sufficient temperature to form an aerosol. The aerosol is drawn downstream through the aerosol-generating article  10  and inhaled by the user. The aerosol-generating article illustrated in  FIG. 1  is substantially cylindrical and has a diameter of about 7 mm and a total length of about 45 mm. 
       FIG. 2  shows a longitudinally extending cavity  110 . In the embodiment illustrated in  FIG. 2 , the cavity  110  is provided in an extractor  100  of an aerosol-generating device according to an aspect of the invention. The extractor  100  is a component that is removably couplable to a main device portion to form the aerosol-generating device. The longitudinally extending cavity  110  of the extractor  100  is arranged for receiving a distal end and distal portion of an aerosol-generating article, for example the aerosol-generating article  10  as described in relation to  FIG. 1 . 
     The extractor  100  has a base  102  and side walls  103  that extend from the base  102 . The longitudinally extending cavity  110  is defined by internal surfaces of the base  102  and the side walls  103  and has an opening  111  at an opposite end of the cavity  110  to the base  102 . The cavity is circular in transverse cross-section and has three separate longitudinally separated portions, the diameter of the cavity varying between adjacent portions. 
     A first portion, or stabilizing portion  120 , of the cavity  110  has a first diameter. This diameter is dimensioned to closely match the outer diameter of an aerosol-generating article for use with the aerosol-generating device. Thus, if the aerosol-generating article of  FIG. 1  is to be used with the device, the first diameter may be approximately the same as the outer diameter of the aerosol-generating article, or of slightly greater diameter than the outer diameter of the aerosol-generating article. Thus, in a specific embodiment the first diameter may be about 7.2 mm. 
     A second portion, or heating portion  130 , has a second diameter. This second diameter is greater than the first diameter to help minimise or prevent contact between an outer surface of an aerosol-generating article received in the cavity and an inner surface  131  of the cavity in the heating portion  130 . For example, if the first diameter is approximately 7.2 mm, the second diameter may be between approximately 8.8 mm and approximately 9.2 mm. This would provide an air-gap of approximately 1 mm between an outer surface of an article fully inserted into the cavity and the inner surface  131  of the cavity walls in the heating portion  130  of the cavity. The second portion extends longitudinally for about 12 mm. 
     A first flared or sloped portion  135  of the inner surface of the cavity provides a transition between the stabilization portion  120  and the heating portion  130 . 
     A third portion, or locating portion  140 , has a third diameter. The third diameter is preferably substantially the same as, or identical to, the first diameter. Thus, in the present example, the third diameter may be 7.2 mm. A second flared or sloped portion  145  of the inner surface of the cavity provides a transition between the heating portion  120  and the locating portion  130 . This second sloped portion is a region in which the diameter of the cavity decreases from the second diameter to the third diameter. The slope may act to guide the distal end of an aerosol-generating article into the locating portion  140 . 
     A hole or slot  150  is defined through a radially central portion of the base  102 . This hole  150  allows a heating element attached to the main portion of the aerosol-generating device to be inserted into the cavity  110  when the extractor  100  is coupled to the main portion of the device. The hole  150  also allows inflow of air into the cavity  110 . 
     The external surfaces of the walls of the extractor may comprise features designed to assist coupling with a main portion of an aerosol-generating device. Such features may include, for example, grooves, slots, ridges, and snaps. The extractor is designed to have a sliding engagement with a main portion of an aerosol-generating device. A portion of the extractor may slide into a corresponding sheath on the main portion of the aerosol-generating device. 
     The extractor  100  is formed from injection moulded polyether ether ketone (PEEK). The extractor  100  may be formed from any suitable material, however, for example other polymeric materials such as polyethylene or polypropylene. 
       FIG. 3  illustrates the aerosol-generating article  10 , as described in relation to  FIG. 1 , when fully inserted into the cavity  110  of the extractor  100  as described in relation to  FIG. 2 . The distal end of the aerosol-generating article has been inserted through the opening  111  and pushed through the stabilising portion  120 , and the heating portion  130 , to lodge within the locating portion  140 . The distal end  80  of the article  10  rests against an inner surface of the base  102 . As the outer diameter of the article  10  is substantially the same as the first diameter of the cavity in the stabilising portion  120  and the third diameter of the cavity at the locating portion  140 , there is a close contact between the article and the cavity walls at these points. The diameter of the cavity at the heating portion  130  is greater than at the stabilising portion and the locating portion, however. As the aerosol-generating article  10  is substantially cylindrical, there is an air-gap  160  formed between an outer surface  61  of the aerosol generating article and an inner surface of the cavity in the heating portion. The width of this gap may be determined by subtracting the first diameter of the stabilising portion (and the aerosol-generating article) from the second diameter of the heating portion and dividing by two. The longitudinal dimension of the heating portion is similar to the longitudinal dimension of the aerosol-forming substrate of the article. The aerosol-forming substrate of the article is substantially within the heating portion when the article is fully inserted into the cavity of the extractor. 
     There are no inlets defined through the side walls of the cavity. Thus, when an article is located within the cavity, the air gap  160  forms an annular pocket of air. This pocket of air helps to insulate the aerosol-forming substrate during use of the aerosol-generating device. 
     The ability to thermally insulate an aerosol-generating article is a result of the difference in thermal conductivity between air and the material forming the side walls of the cavity, for example PEEK. At preferred operating temperatures (for example between 300 and 600 Kelvin) the thermal conductivity of air ranges between 0.0262 Watts per metre Kelvin (W·m −1 ·K −1 ) and 0.0457 W·m −1 ·K −1 . By contrast, the thermal conductivity of PEEK at 300 Kelvin is about 0.25 W·m −1 ·K −1 . Thus, air is about ten times less conductive than PEEK. If, as is preferable, through-flow of air within the air gap is prevented, the air gap  160  may function to help prevent dissipation of heat from the aerosol-forming substrate of the aerosol-generating article. 
       FIG. 4  shows a transverse cross-section of the heating portion of an extractor with an aerosol-generating article inserted. The side walls  103  can be seen to be circular in transverse cross-section. The cavity  110  is defined by an internal surface  131  of the side walls  103 . The aerosol-generating article  10  extends through the heating portion. In cross-section, the aerosol-forming substrate  20  of the aerosol-generating article fills a central portion of the cavity. The air-gap  160  can be seen to be an annular gap, extending completely around the aerosol-generating article. The air-gap forms a pocket of air when the article is inserted. 
     The extractor  100  is a component part of an aerosol-generating device  500 . The extractor is removably couplable to a main portion to form the aerosol-generating device. Thus, the main portion, which may be termed a first body portion  501 , comprises a power supply, control electronics, and a heating element. The extractor, which may be termed a second body portion  100  comprises the article receiving cavity  110 . 
     As can be seen in  FIG. 5 , in a specific embodiment the main portion/second body portion  501  comprises a sheath  510  for coupling with the extractor/second body portion  100  and a heating element  520  for insertion into the cavity  110  of the extractor  100 . The extractor  100  and the main portion  501  couple together by relative longitudinal movement. The heating element  520  extends into the cavity  110  through the opening  150  defined through the base  102 . Thus, the opening  150  also permits movement of the extractor relative to the heating element  520 . 
       FIG. 6  shows the aerosol-generating article  10  operationally coupled to the aerosol-generating device  500 . The heating element  520  penetrates the distal end of the aerosol-generating article  10  and contacts the aerosol-forming substrate  20 . 
     In use, operation of the heating element is initiated and raises the temperature of the aerosol-generating forming substrate to an operating temperature, for example between 300° C. and 350° C. This causes volatilisation of substances within the aerosol-forming substrate. When a user inhales on the proximal end of the aerosol-generating article  10 , an aerosol that is formed from those volatile components can be inhaled. The presence of the air-gap  160 , helps to minimise loss of heat through outer walls of the aerosol-generating article. In tests on aerosol-generating articles comprising homogenised tobacco as an aerosol-forming substrate, the delivery of nicotine and other aerosol-formers was greater in initial puffs compared to a control device in which there was no air-gap. 
     Experiments have been carried out to compare aerosol delivery from an aerosol-generating article as described in relation to  FIG. 1  when (a) heated in a device having an extractor as described in relation to  FIGS. 2 to 6 , and (b) heated in a control device having an extractor with no air gap. 
       FIGS. 7 and 8  are provided to illustrate the control extractor  700  and the control device  800  comprising that extractor. It is noted that  FIGS. 7 and 8  are provided for comparison only and do not illustrate embodiments of the invention. 
     The control extractor  700  differs from the extractor  100  of  FIG. 2  in that a cavity  710  of the control extractor  700  does not define separate stabilising, heating, and locating portions. Rather the cavity  710  is defined by inner walls  760  that extend uniformly between a cavity opening  711  and a cavity base  702 . The diameter of the cavity  710  is substantially uniform along the length of the cavity at about 7.2 mm. That is, the diameter of the entire cavity of the control extractor is about the same as the diameter of the stabilising portion of the extractor of  FIG. 2 . In other regards the control extractor and the extractor of  FIG. 2  are the same. 
       FIG. 8  illustrates an aerosol-generating article operationally coupled to an extractor  700  of a control device  800 . The aerosol-generating article fits snugly into the cavity  710  of the extractor  700 , thereby providing significant contact between an outer surface of the aerosol-generating article and an inner surface  760  of the cavity  710 . 
     Identical aerosol-generating articles were tested under identical conditions. The only difference being that one set of articles were tested using the extractor and device described in relation to  FIGS. 2 to 6 , and a control set of articles were tested using the control extractor and control device described in relation to  FIGS. 7 and 8 . Fourier Transform Infrared (FTIR) Spectroscopy was performed on aerosols generated by these experiments. 
       FIG. 9  is a graph plotting nicotine delivery (measured in milligrams on the y-axis) versus number of puffs on an aerosol-generating article (x-axis). Results generated using the extractor of  FIGS. 2 to 6 , comprising an air-gap surrounding a portion of the article are shown with a solid line (a). Results generated using the control extractor of  FIGS. 7 and 8 , without an air-gap surrounding a portion of the article, are shown with a dotted line (b). It can be seen that nicotine delivery is approximately the same for the first two puffs, but thereafter nicotine delivery is significantly improved using the extractor of  FIG. 2  compared to the control extractor. It may be surmised that the air-gap  160  does provide an insulating effect and reduce thermal dissipation from the aerosol-forming substrate of the article, thereby improving nicotine delivery. 
       FIG. 10  is a graph plotting glycerol delivery (measured in milligrams on the y-axis) versus number of puffs on an aerosol-generating article (x-axis). Results generated using the extractor of  FIGS. 2 to 6 , comprising an air-gap surrounding a portion of the article are shown with a solid line (a). Results generated using the control extractor of  FIGS. 7 and 8 , without an air-gap surrounding a portion of the article, are shown with a dotted line (b). It can be seen that glycerol delivery is approximately the same for the first two or three puffs, but thereafter glycerol delivery is significantly improved using the extractor of  FIG. 2  compared to the control extractor. This result mirrors the nicotine delivery results plotted in  FIG. 9 . 
     While it is preferable that the extractor  100  is configured to provide a fully annular air-gap between the aerosol-generating article and the heating portion of the cavity, there may be circumstances in which one or more ribs are required. Such ribs may help to stabilise the aerosol-generating article within the longitudinally extending cavity  110 . Such ribs may provide a strengthening effect for the extractor. Such ribs may help guide a distal end of an aerosol-generating article towards the locating portion when inserted into the cavity. Such ribs may help prevent radial deformation of an aerosol-generating article if a heating element is inserted into an aerosol-forming substrate of the aerosol-generating article. 
     For example, turning now to  FIG. 11 , the extractor  100  may comprise one or more ribs  790 . The one or more ribs preferably extend along the heating portion  130 . Preferably, the one or more ribs extending along the heating portion  130  extend from a start, or downstream end  736  of a transition  735  between the stabilising portion  120  and the heating portion  130 , along to the end, or upstream end  746  of the transition  745  from the heating portion  130  to the locating portion  140 . Such ribs  790  should not project into the cavity any further than the walls of the stabilising portion, such that passage of an aerosol-generating article is not prevented. Although continuous ribs extending along the entire length of the heating portion  130  are illustrated, it will be appreciated that other designs which still function to stabilise the aerosol-generating article  10  within the chamber with minimal contact may be used. It is preferred that any ribs have a relatively small width dimension, for example a width of between 0.5 mm and 1.5 mm in the dimension that may contact an aerosol-forming article. 
       FIG. 12  shows a transverse cross-sectional view of an extractor  800  having two longitudinally extending ribs  890  extending along a heating portion, between a stabilising portion and a locating portion. The cross-sectional view is taken through the heating portion. When an aerosol-generating article  10  is inserted into the cavity, the ribs  890  help define a first air-pocket  860 A and a second air-pocket  860 B. There is very little contact between the article  10  and the ribs  890 , and only negligible heat is lost at these contact points. Insulation of the aerosol-forming substrate is provided by the two semi-annular air-pockets  890 A,  890 B. 
       FIG. 13  shows a transverse cross-sectional view of an extractor  900  having three longitudinally extending ribs  990  extending along a heating portion between a stabilising portion and a locating portion. The cross-sectional view is taken through the heating portion. When an aerosol-generating article  10  is inserted into the cavity, the ribs help define a first air-pocket  960 A, a second air-pocket  960 B, and a third air-pocket  960 C. There is very little contact between the article  10  and the ribs  990 , and only negligible heat is lost at these contact points. Insulation of the aerosol-forming substrate is provides by the three partially-annular air-pockets  960 A,  960 B,  960 C. 
       FIG. 14  shows a transverse cross-sectional view of an extractor  1400  having six longitudinally extending ribs  1490  extending along a heating portion between a stabilising portion and a locating portion. The cross-sectional view is taken through the heating portion. When an aerosol-generating article  10  is inserted into the cavity, the ribs help define a first air-pocket  1460 A, a second air-pocket  1460 B, a third air-pocket  1460 C, a fourth air-pocket  1460 D, a fifth air-pocket  1460 E, and a sixth air-pocket  1460 F. There is very little contact between the article  10  and the ribs  1490 , and only negligible heat is lost at these contact points. Insulation of the aerosol-forming substrate is provides by the six partially-annular air-pockets  1460 A,  1460 B,  1460 C,  1460 D,  1460 E, and  1460 F. 
       FIG. 15  shows a longitudinal cross-sectional view of an extractor  1400  having six longitudinally extending ribs  1490  extending along a heating portion  1430  between a stabilising portion  1420  and a locating portion  1440 . Such longitudinally extending ribs  1490  may provide a strengthening effect for the extractor. Such longitudinally extending ribs  1490  may help guide a distal end of an aerosol-generating article towards the locating portion when inserted into the cavity. Such longitudinally extending ribs  1490  may help prevent radial deformation of an aerosol-generating article if a heating element is inserted into an aerosol-forming substrate of the aerosol-generating article. 
     Embodiments above describe an aerosol-generating system comprising an aerosol-generating article  10  and an aerosol-generating device  500 , comprising an extractor for receiving the aerosol-generating article  10 . The heating element disclosed is a resistive heating element. Alternative embodiments of the invention may exist, however. For example, the heating means may comprise an induction heating means. The heating element may comprise a susceptor in the form of a blade and an inductor, such as an inductor coil may be disposed about the cavity  110 . Alternatively, the aerosol-generating article  110  may comprise a susceptor and the aerosol-generating device may comprise an inductor arranged to heat the susceptor. 
       FIG. 16  schematically illustrates such an induction actuated aerosol-generating system. In this system, an aerosol-generating article  1000  is similar to the article  10  described in relation to  FIG. 1 . One difference in the system of  FIG. 16  compared with systems described above, for example in relation to  FIGS. 2 to 6 , is that the aerosol forming substrate  1025  of the article  1000  incorporates, or is associated with, a susceptor  1020 . The susceptor in this example is a longitudinal strip of stainless steel. This strip acts as a susceptor  1020  which can be heated to heat the aerosol-forming substrate. In one specific embodiment, the susceptor  1020  may be in the form of a strip of grade 430 stainless steel having dimensions of 12 mm by 4 mm by 35 micrometres. 
     The aerosol-generating device  1500  is similar to the device described in relation to  FIGS. 2 to 6 . There is no heating element associated with the device, however. Instead, the susceptor  1020  is located in thermal communication with the aerosol-forming substrate of the aerosol-generating article, and heat may be generated in the susceptor by inductive heating when the susceptor is placed within a fluctuating magnetic field generated by the aerosol-generating device. Thus, the aerosol-generating device  1500  comprises an inductor in the form of an induction coil  1600 , as well as a power supply, such as a battery, and control electronics. The induction coil  1600  is capable of generating a fluctuating magnetic field within the cavity of the extractor. The susceptor and the induction coil may in combination form a heating means for the aerosol-forming substrate. 
     Inductive heating is a known phenomenon described by Faraday&#39;s law of induction and Ohm&#39;s law. More specifically, Faraday&#39;s law of induction states that if the magnetic induction in a conductor is changing, a changing electric field is produced in the conductor. Since this electric field is produced in a conductor, a current, known as an eddy current, will flow in the conductor according to Ohm&#39;s law. The eddy current will generate heat proportional to the current density and the conductor resistivity. A conductor which is capable of being inductively heated is known as a susceptor. The aerosol-generating device is an inductive heating device equipped with an inductive heating source, such as, e.g., an induction coil  1600 , which is capable of generating an alternating electromagnetic field from an AC source such as an LC circuit. Heat generating eddy currents are produced in the susceptor  1020  thereby raising the temperature of the susceptor such that it can function as a heating element. 
     The aerosol-generating device  1500  comprises a battery and electronics (not illustrated) that allow the inductor  1600  to be actuated. Such actuation may be manually operated or may occur automatically in response to a user drawing on an aerosol-generating article  1000  inserted into the substrate receiving cavity of the aerosol-generating device  1500 . The battery supplies a DC current. The electronics include a DC/AC inverter for supplying the inductor with a high frequency AC current. 
     When the device is actuated, a high-frequency alternating current is passed through coils of wire that form part of the induction coil  1600 . This causes the induction coil  1600  to generate a fluctuating electromagnetic field within a portion of the substrate receiving cavity of the device. The electromagnetic field preferably fluctuates with a frequency of between 1 and 30 MHz, preferably between 2 and 10 MHz, for example between 5 and 7 MHz. When an aerosol-generating article  1000  is correctly located in the substrate receiving cavity, as illustrated in  FIG. 16 , the susceptor  1020  of the article  1000  is located within this fluctuating electromagnetic field. The fluctuating field generates eddy currents within the susceptor, which is heated as a result. Further heating is provided by magnetic hysteresis losses within the susceptor. The heated susceptor heats the aerosol-forming substrate  1020  of the aerosol-generating article  1000  to a sufficient temperature to form an aerosol. The aerosol is drawn downstream through the aerosol-generating article  1000  and inhaled by the user. Dissipation of heat from the aerosol-forming substrate  1025  is minimised by the air gap  160  provided at a heating portion of the cavity. As a result, aerosol deliveries to a user may be improved.