WO2024141331A1

WO2024141331A1 - Heater assembly with measurement contacts

Info

Publication number: WO2024141331A1
Application number: PCT/EP2023/086609
Authority: WO
Inventors: Kyle Robert Adair; Andrew Robert John ROGAN
Original assignee: Philip Morris Products SA
Current assignee: Philip Morris Products SA
Priority date: 2022-12-29
Filing date: 2023-12-19
Publication date: 2024-07-04
Anticipated expiration: 2025-06-29
Also published as: KR20250132513A; CN120390594A; EP4642269A1

Abstract

A heater assembly for an aerosol-generating system, comprising an electrical heating element for heating a liquid aerosol-forming substrate to form an aerosol; a porous body for supplying the liquid aerosol-forming substrate to the electrical heating element, the electrical heating element being arranged along a porous outer surface of the porous body; a protection layer arranged to extend across at least a portion of the electrical heating element to protect the electrical heating element; and measurement contacts arranged to permit measurement of an electrical parameter of the heater assembly to detect whether a sufficient amount of liquid aerosol-forming substrate is supplied to the electrical heating element.

Description

HEATER ASSEMBLY WITH MEASUREMENT CONTACTS

The present disclosure relates to a heater assembly for an aerosol-generating system. In particular, but not exclusively, the present disclosure relates to a heater assembly for a handheld electrically operated aerosol-generating system for heating an aerosol-forming substrate to generate an aerosol and for delivering the aerosol into the mouth of a user. The present disclosure further relates to a cartridge and an aerosol-generating system comprising the heater assembly and also to a method of operation of a heater assembly.

Aerosol-generating systems that heat a liquid aerosol-forming substrate in order to generate an aerosol for delivery to a user are generally known in the prior art. These systems typically comprise an aerosol-generating device and a replaceable cartridge. The cartridge includes a liquid aerosol-forming substrate that is capable of releasing volatile compounds when heated. The cartridge typically also includes a heater for heating the liquid aerosol-forming substrate. In known aerosol-generating systems, the heater comprises a resistive heating element wound around a wick that supplies liquid aerosol-forming substrate to the heating element. The aerosolgenerating device or cartridge also comprises a mouthpiece. When a negative pressure is applied at the mouthpiece, an electric current is passed through the heating element causing it to be heated by resistive or Joule heating, which, in turn, heats the liquid aerosol-forming substrate supplied by the wick. This causes volatile compounds to be released from the liquid aerosolforming substrate that cool to form an aerosol. The aerosol is then drawn into a user’s mouth via the mouthpiece.

Such known aerosol-generating systems have a number of drawbacks. For example, they can be difficult to manufacture with consistent manufacturing tolerances which can result in inconsistent vapour production and flavour generation. Inconsistent manufacturing tolerances can also affect the transfer of heat from the heating element to the wick reducing the energy efficiencies of such devices. A further problem encountered by such known aerosol-generating systems is “dry heating” or a “dry puff”, which arises when the heating element is heated with insufficient liquid aerosol-forming substrate being supplied to the heating element. This can occur, for example, when a user has consumed all of the liquid aerosol-forming substrate in the cartridge such that the cartridge is depleted of liquid aerosol-forming substrate and needs replacing. During operation, it is preferable to maintain a supply of liquid aerosol-forming substrate to the heating element such that the heating element is maintained in a wet state because this helps to ensure that a satisfactory aerosol is produced when a negative pressure is applied at the mouthpiece. Dry heating can result in overheating of the heating element and, potentially, thermal decomposition of the liquid aerosol-forming substrate, which can produce undesirable by-products and an unsatisfactory aerosol. Allowing the aerosol-generating system to continue to operate when liquid aerosol-forming substrate is not being supplied to the heating element can result in a poor user experience.

One known aerosol-generating system has a ceramic body and a heating element, to which power is supplied through electrical contacts. The ceramic body has a coating or protective layer on a single face. Liquid is supplied from a liquid reservoir to the heating element via pores within the ceramic body. This known aerosol-generating system may also experience a “dry heating” or “dry puff” situation, and as such has the associated disadvantages, namely undesirable byproducts, an unsatisfactory aerosol, and a poor user experience.

It would be desirable to provide a more energy efficient heater assembly capable of generating a more consistent aerosol. It would be desirable to provide a heater assembly that reduces the likelihood of a user experiencing dry heating or a dry puff and that restricts a user from being able to continue to use an aerosol-generating system when liquid aerosol-forming substrate is not being supplied to the heating element.

According to an example of the present disclosure, there is provided a heater assembly for an aerosol-generating system. The heater assembly may comprise an electrical heating element for heating a liquid aerosol-forming substrate to form an aerosol. The heater assembly may comprise a porous body for supplying the liquid aerosol-forming substrate to the electrical heating element. The heater assembly may comprise an electrical heating element. The electrical heating element may be arranged along a porous outer surface of the porous body. The porous outer surface on which the electrical heating element is disposed may be substantially flat. The electrical heating element may at least partially extend into pores of the porous outer surface. The heater assembly may comprise a protection layer. The protection layer may be arranged to extend across at least a portion of the electrical heating element to protect the electrical heating element. The heater assembly may comprise measurement contacts arranged to permit measurement of an electrical parameter of the heater assembly to detect whether a sufficient amount of liquid aerosol-forming substrate is supplied to the electrical heating element.

According to an example of the present disclosure, there is provided a heater assembly for an aerosol-generating system. The heater assembly comprises an electrical heating element for heating a liquid aerosol-forming substrate to form an aerosol. The heater assembly comprises a porous body for supplying the liquid aerosol-forming substrate to the electrical heating element. The heater assembly comprises an electrical heating element being arranged along a porous outer surface of the porous body. The heater assembly comprises a protection layer arranged to extend across at least a portion of the electrical heating element to protect the electrical heating element. The heater assembly comprises measurement contacts arranged to permit measurement of an electrical parameter of the heater assembly to detect whether a sufficient amount of liquid aerosol-forming substrate is supplied to the electrical heating element. With this arrangement, the presence of, absence of, or amount of liquid is accurately measured, despite the protection layer being present. This reduces the likelihood of a dry heating event. It is unexpectedly difficult to measure the resistance change of the electrical heating element when a protection layer is present. An advantage of the claimed arrangement is that the resistance across the heating assembly can be accurately measured as it is heated, to detect the presence of, absence of, or amount of liquid and control the temperature of the electrical heating element to avoid a dry heat situation.

Advantageously, the heater assembly allows the aerosol-generating system to detect and control the occurrence of an overheating or dry heating situation. By measuring an electrical parameter using measurement contacts, an overheating or drying heating situation can be detected, which if prevented can reduce the likelihood of unwanted by-products being produced and the user receiving a poor user experience. By measuring an electrical parameter using measurement contacts, it can be determined when a level of liquid is below a predetermined value, and as such is approaching an overheating or drying heating situation.

As used herein, the term “aerosol-generating device” relates to a device that interacts with a liquid aerosol-forming substrate to generate an aerosol.

As used herein, the term “aerosol-generating cartridge” relates to a component that interacts with a liquid aerosol-forming device to generate an aerosol. An aerosol-generating cartridge contains, or is configured to contain, a liquid aerosol-generating substrate.

As used herein, the term “liquid aerosol-generating substrate” relates to a liquid substrate capable of releasing volatile compounds that can form an aerosol. Such volatile compounds can be released by heating the aerosol-forming substrate.

As used herein, the term “electrical heating element” refers to a component which transfers heat energy to the liquid aerosol-generating substrate. It will be appreciated that the electrical heating element may be deposited directly on the porous body.

As used herein, the term “electrical parameter” refers to an electrical property or characteristic, including but not being limited to, a voltage or potential difference, an electric current or an electrical resistance. The electrical parameter can be monitored by measuring the parameter directly such as a voltage or can be determined indirectly from another electrical parameter or parameters. For example, an electrical resistance can be determined using Ohm’s Law by firstly determining a voltage across a component and an electric current through the component and dividing the voltage by the current.

As used herein, the term “porous body” refers to a component which has a plurality of pores, at least some of which are interconnected. The porous body is configured to contain liquid within the plurality of pores. As used herein, the term “protection layer” refers to a component which is configured to protect the electrical heating element. Specifically, the protection layer is configured to extend the life of the electrical heating element.

As used herein, the term “sufficient” when used in the phrase “sufficient amount of liquid aerosol-forming substrate” refers to an amount of aerosol-forming substrate which, when present at the electrical heating element, prevents a dry heating or a dry puff situation.

The liquid aerosol-forming substrate may be liquid at room temperature. The liquid aerosol-forming substrate may comprise both liquid and solid components. The liquid aerosolforming substrate may comprise nicotine. The nicotine containing liquid aerosol-forming substrate may be a nicotine salt matrix. The liquid aerosol-forming substrate may comprise plantbased material. The liquid aerosol-forming substrate may comprise tobacco. The liquid aerosolforming substrate may comprise a tobacco-containing material containing volatile tobacco flavour compounds, which are released from the aerosol-forming substrate upon heating. The liquid aerosol-forming substrate may comprise homogenised tobacco material. The liquid aerosolforming substrate may comprise a non-tobacco-containing material. The liquid aerosol-forming substrate may comprise homogenised plant-based material.

The liquid aerosol-forming substrate may comprise one or more aerosol-formers. An aerosol-former is any suitable known compound or mixture of compounds that, in use, facilitates formation of a dense and stable aerosol and that is substantially resistant to thermal degradation at the temperature of operation of the system. Examples of suitable aerosol formers include glycerine and propylene glycol. Suitable aerosol-formers are well known in the art and include, but are not limited to: polyhydric alcohols, such as triethylene glycol, 1 ,3-butanediol and glycerine; esters of polyhydric alcohols, such as glycerol mono-, di- or triacetate; and aliphatic esters of mono-, di- or polycarboxylic acids, such as dimethyl dodecanedioate and dimethyl tetradecanedioate. The liquid aerosol-forming substrate may comprise water, solvents, ethanol, plant extracts and natural or artificial flavours.

The liquid aerosol-forming substrate may comprise nicotine and at least one aerosolformer. The aerosol-former may be glycerine or propylene glycol. The aerosol former may comprise both glycerine and propylene glycol. The liquid aerosol-forming substrate may have a nicotine concentration of between about 0.5% and about 10%, for example about 2%.

The electrical parameter may be an electrical parameter of the protection layer. The measurement contacts may be disposed on a surface of the protection layer at opposite sides of the surface of the protection layer. The measurement contacts may be disposed at opposite sides of the surface of the protection layer such that the measurement contacts can measure the electrical parameter across the protection layer. The protection layer has a thickness, a width and a length. The thickness may be smaller than the width or the length. The measurement contacts may be spaced apart from each other in a direction orthogonal to the thickness. This has the advantage of accurately allowing determination of whether liquid is present or absent at the protection layer.

The electrical parameter may be an electrical parameter of the porous body. The measurement contacts may be disposed on opposing surfaces of the porous body. This is a particularly advantageous arrangement in which the likelihood of a dry heating event is reduced. The heater assembly may be configured for liquid aerosol-forming substrate to travel from a nonheated surface of the porous body to a heated surface of the porous body. There may be instances in which liquid aerosol-forming substrate is present at the heated surface of the porous body, but is not present within the porous body. In such an instance, measurement of an electrical parameter of the porous body can be used to identify and pre-empt a dry heating event. By measuring an electrical parameter of the porous body the likelihood of a dry heating event is reduced.

The measurement contacts may be disposed on opposing surfaces of the porous body such that the measurement contacts can measure the electrical parameter across the porous body. The measurement contacts may be disposed on a surface of the porous body. The measurement contacts may be disposed on opposing sides of the surface of the porous body such that the measurement contacts can measure the electrical parameter across the porous body.

The measurement contacts may be spaced apart from each other in a direction aligned to or parallel to the porous outer surface. The porous body may have a liquid absorption side and an aerosolization side. The measurement contacts may be arranged on the aerosolization side of the porous body.

The electrical parameter may be indicative of an electrical resistance.

The electrical parameter may be used to determined whether the porous body or the protection layer is being supplied with sufficient liquid aerosol-forming substrate. Values for the electrical parameter may be stored in a memory of an aerosol-generating system. By comparing the electrical parameter to one or more values stored in the memory, an aerosol-generating system may determine whether the electrical heating element is being supplied with sufficient liquid aerosol-forming substrate.

The electrical heating element may be electrically connected to electrical contacts. The electrical heating element may be configured to heat the liquid aerosol-forming substrate upon application of an electrical potential difference to the electrical contacts. The electrical heating element may be one or more of: a curvilinear or a serpentine shape. The electrical heating element may comprise an electrically resistive heating element. The electrical heating element may be made from any suitable electrically conductive material. Suitable materials include but are not limited to: semiconductors such as doped ceramics, electrically “conductive” ceramics (such as, for example, molybdenum disilicide), carbon, graphite, metals, metal alloys and composite materials made of a ceramic material and a metallic material. Such composite materials may comprise doped or undoped ceramics. Examples of suitable doped ceramics include doped silicon carbides. Examples of suitable metals include titanium, zirconium, tantalum and metals from the platinum group. Examples of suitable metal alloys include stainless steel, constantan, nickel-, cobalt-, chromium-, aluminum-, titanium-, zirconium-, hafnium-, niobium-, molybdenum-, tantalum-, tungsten-, tin-, gallium-, manganese- and iron-containing alloys, and super-alloys based on nickel, iron, cobalt, stainless steel, Timetai®, iron-aluminum based alloys and iron-manganese-aluminum based alloys. Timetai® is a registered trade mark of Titanium Metals Corporation. The electrical heating element may be made from stainless steel, for example, a 300 series stainless steel such as AISI 304, 316, 304L, 316L.

Additionally, the electrical heating element may comprise combinations of the above materials. A combination of materials may be used to improve the control of the resistance of the electrical heating element. For example, materials with a high intrinsic resistance may be combined with materials with a low intrinsic resistance. This may be advantageous if one of the materials is more beneficial from other perspectives, for example price, machinability or other physical and chemical parameters. Advantageously, high resistivity heating allow more efficient use of battery energy.

According to an example of the present disclosure, there is provided a cartridge for an aerosol-generating system. The cartridge may comprise the heater assembly. The cartridge may comprise a liquid storage portion configured to hold a liquid aerosol-forming substrate. The liquid storage portion may be arranged at an opposite side of the heater assembly to the porous outer surface.

According to an example of the present disclosure, there is provided a cartridge for an aerosol-generating system. The cartridge comprises a heater assembly. The cartridge comprises a liquid storage portion configured to hold a liquid aerosol-forming substrate. The liquid storage portion is arranged at an opposite side of the heater assembly to the porous outer surface.

According to an example of the present disclosure, there is provided an aerosolgenerating system. The aerosol-generating system may comprise a cartridge. The aerosolgenerating system may comprise a power supply for supplying electrical power to the electrical heating element. The aerosol-generating system may comprise control circuitry configured to control a supply of power from the power supply to the electrical heating element. The control circuitry may further be configured to receive a signal from the measurement contacts and, based on the signal, to determine whether liquid aerosol-forming substrate is supplied to the electrical heating element. According to an example of the present disclosure, there is provided an aerosolgenerating system. The aerosol-generating system comprises a cartridge. The aerosolgenerating system comprises a power supply for supplying electrical power to the electrical heating element. The aerosol-generating system comprises control circuitry configured to control a supply of power from the power supply to the electrical heating element. The control circuitry is further configured to receive a signal from the measurement contacts and, based on the signal, to determine whether liquid aerosol-forming substrate is supplied to the electrical heating element.

The electrical parameter may be greater than a maximum threshold value or less than a minimum threshold value indicating that liquid aerosol-forming substrate supplied to the electrical heating element is below a threshold amount. The maximum threshold value may be a maximum threshold value indicative of resistance. The maximum threshold value may relate to a maximum threshold resistance value of 7 x 10⁷ Ohms, based on a glycerol aerosol-forming substrate and a distance between the measurement contacts of 7 mm. The maximum threshold value may be a maximum threshold resistance value of 7 x 10⁷ Ohms, based on a glycerol aerosol-forming substrate and a distance between the measurement contacts of 7 mm. The minimum threshold value may be a minimum threshold value indicative of conductance. The minimum threshold value may relate to a minimum threshold conductance value of (1/7) x 10'⁷ Siemens. The minimum threshold value may be a minimum threshold conductance value of (1/7) x 10'⁷ Siemens Ohms.

The controller may be configured to prevent power being supplied to the electrical heating element if liquid aerosol-forming substrate is not supplied to the electrical heating element or if liquid aerosol-forming substrate in the electrical heating element is below a threshold amount.

According to an example of the present disclosure, there is provided a method of controlling heating in an aerosol-generating system comprising a heater assembly. The heater assembly may comprise an electrical heating element for heating a liquid aerosol-forming substrate to form an aerosol. The heater assembly may comprise a porous body for supplying the liquid aerosol-forming substrate to the electrical heating element. The electrical heating element may be arranged along a porous outer surface of the porous body. The protection layer may be arranged to extend across at least a portion of the electrical heating element to protect the electrical heating element. The heater assembly may comprise measurement contacts arranged to permit measurement of an electrical parameter of the heater assembly to detect whether a sufficient amount of liquid aerosol-forming substrate is supplied to the electrical heating element. The method may comprise measuring the electrical parameter of the heater assembly between the measurement contacts, to detect whether liquid aerosol-forming substrate is supplied to the electrical heating element.

According to an example of the present disclosure, there is provided a method of controlling heating in an aerosol-generating system comprising a heater assembly. The heater assembly comprises an electrical heating element for heating a liquid aerosol-forming substrate to form an aerosol. The heater assembly comprises a porous body for supplying the liquid aerosolforming substrate to the electrical heating element. The electrical heating element is arranged along a porous outer surface of the porous body. The protection layer is arranged to extend across at least a portion of the electrical heating element to protect the electrical heating element. The heater assembly comprises measurement contacts arranged to permit measurement of an electrical parameter of the heater assembly to detect whether a sufficient amount of liquid aerosolforming substrate is supplied to the electrical heating element. The method comprises measuring the electrical parameter of the heater assembly between the measurement contacts, to detect whether liquid aerosol-forming substrate is supplied to the electrical heating element.

A sufficient amount of liquid aerosol-forming substrate may be an amount which provides an electrical connection between the measurement contacts. This electrical connection may be made without a short-circuit, i.e. , the aerosol-forming substrate may form a pathway for current between the measurement contacts. A sufficient amount of liquid aerosol-forming substrate in the porous body may be an amount which produces enough aerosol to allow a user to inhale at least once. Preferably, a sufficient amount of liquid aerosol-forming substrate in the porous body is an amount which produces enough aerosol to allow a user to inhale at least at least five times. A sufficient amount of liquid aerosol-forming substrate in the porous body may be between 0.3 mg and 32.5 mg, preferably between 1.5 mg and 32.5 mg. A sufficient amount of liquid aerosolforming substrate in the porous body may be at least 20 mg, preferably at least 30 mg. A sufficient amount of liquid aerosol-forming substrate in the porous body may be 32.5 mg. A sufficient amount of liquid aerosol-forming substrate on the protection layer may be an amount which produces enough aerosol to allow a user to inhale once. A sufficient amount of liquid aerosolforming substrate on the protection layer may be between 0.3 mg and 15 mg, preferably between 10 mg and 15 mg. A sufficient amount of liquid aerosol-forming substrate on the protection layer may be at least 1 mg, preferably at least 5 mg, more preferably at least 10 mg.

The method may comprise determining, based on the electrical parameter measurement, an indication of one or more of: the absence of liquid aerosol-forming substrate, the presence of liquid aerosol-forming substrate, an amount of liquid aerosol-forming substrate.

The method may comprise, upon determining a low amount of liquid aerosol-forming substrate in the porous body, preventing power from being supplied to the electrical heating element.

The method may comprise, upon detection of an absence of liquid aerosol-forming substrate in the porous body, preventing power from being supplied to the electrical heating element. The porous body may have a very high electrical resistance when dry. The porous body may have a liquid absorption side and an aerosolization side. The electrical heating element may be disposed along the aerosolization side of the porous body. The porous body may be configured to supply liquid aerosol-forming substrate from the liquid absorption side to the aerosolization side of the porous body. The porous body may be a ceramic body. The porous body may be an open- porous body, i.e. may comprise a plurality of interconnected open cell pores. The porous body may define a series of capillaries. The porous body may have been manufactured by sintering. The porous body may have been manufactured by directly sintering a ceramic powder, to form a porous body having pores between interconnected powder particles. The porous body may have been manufactured by using a sacrificial material within a ceramic powder, the sacrificial material being used as a spacer to form pores. The sacrificial material may have been burnt off during sintering.

The protection layer may have a very high electrical resistance when dry. The protection layer may comprise or consist of an inorganic material. The protection layer may be arranged to substantially cover the porous body. The protection layer may have an electrical conductivity of at most 1 x 10'¹¹ Siemens per cm. The protection layer may have an electrical conductivity of at most 1 x 10'¹⁴ Siemens per cm. The protection layer may have an electrical conductivity of 1 x 10' ¹⁴ Siemens per cm. The protection layer may have an electrical conductivity of at most 1 x 10'¹² Siemens per cm. The protection layer may have an electrical conductivity of 1 x 10'¹² Siemens per cm.

The aerosol-generating system may be portable. The aerosol-generating system may have a size comparable to a conventional cigar or cigarette.

The aerosol-generating device may contain control circuitry. The control circuitry may comprise any suitable controller or electrical components. The controller may comprise a memory. Information for performing the above-described method may be stored in the memory. The control circuitry may comprise a microprocessor. The microprocessor may be a programmable microprocessor, a microcontroller, or an application specific integrated chip (ASIC) or other electronic circuitry capable of providing control. The control circuitry may be configured to supply power to the electrical heating element continuously following activation of the device, or may be configured to supply power intermittently, such as on a puff-by-puff basis. The power may be supplied to the electrical heating element in the form of pulses of electrical current, for example, by means of pulse width modulation (PWM). The control circuitry may comprise further electronic components. For example, in some embodiments, the control circuitry may comprise any of: sensors, switches, display elements.

The aerosol-generating device may contain a power supply in the form of a battery. The battery may be rechargeable. The battery may be a Lithium based battery, for example a Lithium- Cobalt, a Lithium-lron-Phosphate, a Lithium Titanate or a Lithium-Polymer battery. The battery may be a Nickel-metal hydride battery or a Nickel cadmium battery. The power supply may be another form of charge storage device such as a capacitor. The power supply may be rechargeable and be configured for many cycles of charge and discharge. The power supply may have a capacity that allows for the storage of enough energy for one or more user experiences of the aerosol-generating system; for example, the power supply may have sufficient capacity to allow for the continuous generation of aerosol for a period of around six minutes, corresponding to the typical time taken to smoke a conventional cigarette, or for a period that is a multiple of six minutes. In another example, the power supply may have sufficient capacity to allow for a predetermined number of puffs or discrete activations of the aerosol-generating system.

The aerosol-generating device may comprise a housing. The housing may be elongate. The housing may comprise any suitable material or combination of materials. Examples of suitable materials include metals, alloys, plastics or composite materials containing one or more of those materials, or thermoplastics that are suitable for food or pharmaceutical applications, for example polypropylene, polyetheretherketone (PEEK) and polyethylene. The material is preferably light and non-brittle.

The cartridge may be releasably couplable to the aerosol-generating device.

The cartridge of the aerosol-generating system may have a connection end. At the connection end, the cartridge may be connected to or connectable to the aerosol-generating device. The connection end of the cartridge may have electrical contacts which are electrically connectable to electrical contacts on the aerosol-generating device. The cartridge may comprise one or more of: a mouthpiece, a cartridge body, an external air inlet, an internal air passage and an aerosol outlet.

The mouthpiece may be connected to or connectable to the cartridge body. The mouthpiece may be connected to or connectable to the cartridge body so as to define one or more external air inlets between the mouthpiece and the cartridge body. The mouthpiece may be arranged at an end of the cartridge body. The mouthpiece may be arranged at an end of the cartridge body opposite to the connection end. The mouthpiece may comprise the aerosol outlet.

The cartridge body may comprise the heater assembly. The cartridge body may comprise the liquid storage portion. The heater assembly may be disposed proximate to or at the connection end. The liquid storage portion may be disposed between the heater assembly and the mouthpiece.

The liquid storage portion may be disposed at a first side of the heater assembly. An airflow channel may be disposed at an opposite side of the heater assembly to the first side. The airflow channel may be adjacent to the electrical heating element. An airflow path may extend past the electrical heating element. The airflow path may be configured to convey the aerosol. The cartridge body may be configured such that air flow past the heater assembly entrains vapourised aerosol-forming substrate. The cartridge may be configured such that air can flow from external to the system, through external air inlets and within the cartridge body. The cartridge may be configured so that air can then flow towards the connection end. At the connection end, air may be guided to turn back on itself to flow through a centre of the cartridge. In doing this, airflow may pass the heater assembly. At the heater assembly, air may be combined with aerosol. The cartridge may be configured such that after being combined with aerosol, airflow passes through the centre of the cartridge to the mouthpiece. Airflow may then pass out of the aerosol outlet aperture.

The mouthpiece may include internal baffles. The internal baffles may be integrally moulded with the external walls of the mouthpiece portion. The baffles may ensure that, as air is drawn from inlets to the aerosol outlet aperture, it flows over the heater assembly on the cartridge where aerosol-forming substrate is being vapourised. As the air passes the heater assembly, vapourised substrate may be entrained in the airflow, and may cool to form an aerosol before exiting the aerosol outlet aperture.

Features described in relation to one of the above examples may equally be applied to other examples of the present disclosure.

The invention is defined in the claims. However, below there is provided a non-exhaustive list of non-limiting examples. Any one or more of the features of these examples may be combined with any one or more features of another example, embodiment, or aspect described herein.

Example Ex1 : A heater assembly for an aerosol-generating system, comprising: an electrical heating element for heating a liquid aerosol-forming substrate to form an aerosol; a porous body for supplying the liquid aerosol-forming substrate to the electrical heating element, the electrical heating element being arranged along a porous outer surface of the porous body; and a protection layer arranged to extend across at least a portion of the electrical heating element to protect the electrical heating element.

Example Ex2: A heater assembly according to Example Ex1 , further comprising measurement contacts arranged to permit measurement of an electrical parameter of the heater assembly to detect whether a sufficient amount of liquid aerosol-forming substrate is supplied to the electrical heating element.

Example Ex3: A heater assembly according to Example Ex1 or Ex2, wherein the protection layer comprises an inorganic material.

Example Ex4: A heater assembly according to any of Examples Ex1 to Ex3, wherein the protection layer has an electrical conductivity of at most 1 x 10'¹¹ Siemens per cm. Example Ex5: A heater assembly according to any of Examples Ex1 to Ex4, wherein the protection layer has an electrical conductivity of at most 1 x 10'¹² Siemens per cm.

Example Ex6: A heater assembly according to any of Examples Ex2 to Ex5, wherein the electrical parameter is an electrical parameter of the protection layer.

Example Ex7: A heater assembly according to any of Examples Ex2 to Ex6, wherein the measurement contacts are disposed on a surface of the protection layer at opposite sides of the surface of the protection layer such that the measurement contacts can measure the electrical parameter across the protection layer.

Example Ex8: A heater assembly according to any of Examples Ex2 to Ex7, wherein the electrical parameter is an electrical parameter of the porous body.

Example Ex9: A heater assembly according to any of Examples Ex1 to Ex8, wherein the protection layer has an electrical conductivity of at most 1 x 10'¹² Siemens per cm.

Example Ex10: A heater assembly according to any of Examples Ex1 to Ex9, wherein the protection layer has an electrical conductivity of at most 1 x 10'¹⁴ Siemens per cm.

Example Ex11 : A heater assembly according to any of Examples Ex1 to Ex10, wherein the porous body comprises a sintered ceramic material.

Example Ex12: A heater assembly according to any of Examples Ex2 to Ex11 , wherein the measurement contacts are disposed on opposing surfaces of the porous body such that the measurement contacts can measure the electrical parameter across the porous body.

Example Ex13: A heater assembly according to any of Examples Ex2 to Ex12, wherein the electrical parameter is indicative of an electrical resistance.

Example Ex14: A heater assembly according to any of Examples Ex1 to Ex13, wherein the electrical heating element is electrically connected to electrical contacts.

Example Ex15: A heater assembly according to any of Examples Ex14, wherein the electrical heating element is configured to heat the liquid aerosol-forming substrate upon application of an electrical potential difference to the electrical contacts.

Example Ex16: A cartridge for an aerosol-generating system, comprising: the heater assembly of any of Examples Ex1 to Ex15; and a liquid storage portion configured to hold a liquid aerosol-forming substrate; wherein the liquid storage portion is arranged at an opposite side of the heater assembly to the porous outer surface.

Example Ex17: An aerosol-generating system, comprising: the cartridge of Example Ex16; a power supply for supplying electrical power to the electrical heating element; control circuitry configured to control a supply of power from the power supply to the electrical heating element, wherein the control circuitry is further configured to receive a signal from the measurement contacts and, based on the signal, to determine whether liquid aerosolforming substrate is supplied to the electrical heating element.

Example Ex18: The aerosol-generating system of Example Ex17, wherein the electrical parameter is greater than a maximum threshold value or less than a minimum threshold value indicating that liquid aerosol-forming substrate supplied to the electrical heating element is below a threshold amount.

Example Ex19: The aerosol-generating system of Example Ex18, wherein the maximum threshold value or minimum threshold value is related to a minimum conductivity of at least 1x1 O’ ¹⁰ Siemens per cm measured across the measurement contacts.

Example Ex20: The aerosol-generating system of Example Ex19, wherein the maximum threshold value or minimum threshold value is related to a minimum conductivity of at least 1x1 O’ ⁹ Siemens per cm measured across the measurement contacts.

Example Ex21 : The aerosol-generating system of Example Ex20, wherein the maximum threshold value or minimum threshold value is related to a minimum conductivity of at least 1x1 O’ ⁸ Siemens per cm measured across the measurement contacts.

Example Ex22: The aerosol-generating system of Example Ex21 , wherein the maximum threshold value or minimum threshold value is related to a minimum conductivity of at least 1x1 O’ ⁷ Siemens per cm measured across the measurement contacts.

Example Ex23: The aerosol-generating system according to any of Examples Ex17 to Ex22, wherein the controller is configured to prevent power being supplied to the electrical heating element if liquid aerosol-forming substrate is not supplied to the electrical heating element.

Example Ex24: The aerosol-generating system according to any of Examples Ex17 to Ex23, wherein the controller is configured to prevent power being supplied to the electrical heating element if liquid aerosol-forming substrate in the porous body is below a threshold amount.

Example Ex25: A method of controlling heating in an aerosol-generating system comprising a heater assembly; the heater assembly comprising: an electrical heating element for heating a liquid aerosol-forming substrate to form an aerosol; a porous body for supplying the liquid aerosol-forming substrate to the electrical heating element, the electrical heating element being arranged along a porous outer surface of the porous body; a protection layer arranged to extend across at least a portion of the electrical heating element to protect the electrical heating element; and measurement contacts arranged to permit measurement of an electrical parameter of the heater assembly to detect whether a sufficient amount of liquid aerosol-forming substrate is supplied to the electrical heating element, the method comprising: measuring the electrical parameter of the heater assembly between the measurement contacts, to detect whether liquid aerosol-forming substrate is supplied to the electrical heating element.

Example Ex26: The method of Example Ex25, comprising: determining, based on the electrical parameter measurement, an indication of one or more of: the absence of liquid aerosol-forming substrate, the presence of liquid aerosol-forming substrate, an amount of liquid aerosol-forming substrate.

Example Ex27: The method of Example Ex26: wherein determining an indication of one or more of: the absence of liquid aerosol-forming substrate, the presence of liquid aerosol-forming substrate, an amount of liquid aerosol-forming substrate, involves comparing a measured electrical parameter to one or more predetermined reference parameters.

Example Ex28: The method of Examples Ex26 or Ex27, wherein the one or more predetermined reference parameters are resistance or conductance values indicative of the absence of liquid aerosol-forming substrate, the presence of liquid aerosol-forming substrate, an amount of liquid aerosol-forming substrate.

Example Ex29: The method of any of Examples Ex26 to Ex28, comprising: upon determining a low amount of liquid aerosol-forming substrate in the porous body, preventing power from being supplied to the electrical heating element.

Example Ex30: The method of any of Examples Ex26 to Ex29, comprising: upon determining a low amount of liquid aerosol-forming substrate on the protection layer, preventing power from being supplied to the electrical heating element.

Example Ex31 : The method of any of Example Ex30, wherein a low amount of liquid aerosol-forming substrate is determined by measurement of the electrical parameter indicating an electrical conductivity of less than 1x1 O'⁸ Siemens per cm across the measurement contacts.

Example Ex32: The method of any of Examples Ex26 to Ex31 , comprising: upon detection of an absence of liquid aerosol-forming substrate in the porous body, preventing power from being supplied to the electrical heating element.

Example Ex33: The method of any of Examples Ex26 to Ex32, comprising: upon detection of an absence of liquid aerosol-forming substrate on the protection layer, preventing power from being supplied to the electrical heating element.

Example Ex34: The method of any of Examples Ex26 to Ex33, comprising: wherein an absence of liquid aerosol-forming substrate is determined by a measurement indicating an electrical conductivity of less than 1x10^-11 Siemens per cm across the measurement contacts.

Examples will now be further described with reference to the figures in which:

Figure 1 is a schematic illustration of a heater assembly in accordance with an example of the present disclosure, in which measurement contacts are disposed on the protection layer;

Figure 2 is a schematic illustration of a heater assembly in accordance with an example of the present disclosure, in which measurement contacts are disposed on the porous body;

Figure 3 is a schematic illustration of a cartridge having a heater assembly in accordance with an example of the present disclosure;

Figure 4 is a schematic illustration of an aerosol-generating system in accordance with an example of the present disclosure;

Figure 5 is a flowchart showing a method of controlling heating in an aerosol-generating system in accordance with an example of the present disclosure; and

Figure 6 is an electrical circuit showing the conversion of electrical resistance measurement to electrical signal.

The above and other features and advantages of example embodiments will become more apparent by describing in detail, example embodiments with reference to the attached drawings. 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 embodiments set forth herein.

Accordingly, while example embodiments are capable of various modifications and alternative forms, 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 falling within the scope of example embodiments. Like numbers refer to like elements throughout the description of the figures.

Spatially relative terms (for example, "below") may be used herein for ease of description to describe one element or feature's relationship to another element or feature 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" other elements or features would then be oriented "above" the other elements or features. Therefore, 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.

It should be understood that when an element or layer is referred to as being “disposed on”, another element or layer, it may be directly on, connected to, coupled 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 disposed on" another element or layer, there are no intervening elements or layers present.

The terminology used herein is for the purpose of describing various 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 "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations or elements, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements or groups thereof.

Example embodiments are described herein with reference to cross-sectional illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of example embodiments. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques or tolerances, are to be expected. Therefore, example embodiments should not be construed as limited to the shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. Therefore, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of example embodiments. The same reference numerals represent the same elements throughout the drawings. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. It will be appreciated that the figures in the application are schematic, and that some features have been omitted for the sake of clarity.

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.

The accompanying drawings are intended to depict example embodiments and should not be interpreted to limit the intended scope of the claims.

Referring to figure 1 , there is shown a schematic illustration of a heater assembly 100 for an aerosol-generating system, in accordance with an example of the present disclosure. The heater assembly 100 comprises: an electrical heating element 120, a porous body 110, a protection layer 140, and measurement contacts 150, an electrical circuit 160, an electrical parameter measurement apparatus 170, and control circuitry (not shown for clarity).

The porous body 110 is configured to supply liquid aerosol-forming substrate to the electrical heating element 120. Specifically, the porous body 110 is configured to transmit liquid aerosol-forming substrate from a liquid reservoir (not shown in figure 1 for clarity) to the electrical heating element 120. The porous body 110 is configured to store some liquid aerosol-forming substrate until it is aerosolized by the electrical heating element 120.

The porous body 110 is a rectangular block. The porous body 110 comprises a plurality open-cell pores. The plurality of open-cell pores are interconnected to provide a fluid pathway for aerosol-generating liquid through the porous body 110. The porous body 110 comprises a material which does not chemically interact with the liquid aerosol-forming substrate. The porous body 110 comprises ceramic. The porous body 110 comprises Ca2SiOs or SiCh (orCa2SiC>3 and SiCh). It will be appreciated that the porous body 110 may have a different shape or comprise a different material.

The electrical heating element 120 is configured to heat a liquid aerosol-forming substrate to form an aerosol. The electrical heating element 120 is configured to convert electrical energy into heat energy by material resistance of the electrical heating element 120 to an electrical current.

The electrical heating element 120 is elongate. The electrical heating element 120 comprises NiCr or TiZr (or NiCr and TiZr). It will be appreciated that the electrical heating element 120 may have a different shape or comprise a different material.

The electrical heating element 120 is arranged along a porous outer surface of the porous body 110. The electrical heating element 120 is in direct contact with the porous body 110. The electrical heating element 120 is disposed on a single surface of the porous body 110.

The electrical heating element 120 is electrically connected to electrical contacts 130. The electrical heating element 120 is configured to heat the liquid aerosol-forming substrate upon application of an electrical potential difference to the electrical contacts 130. The electrical contacts 130 are disposed at each end of the elongate electrical heating element 120. The electrical contacts 130 are directly disposed on the same surface of the porous body 110 as the electrical heating element 120. The electrical contacts 130 comprise CuZnAu. The electrical contacts 130 are disposed at opposite edges of the porous outer surface of the porous body 110. The electrical contacts 130 are aligned with opposite edges of the porous outer surface of the porous body 110.

The protection layer 140 is arranged to extend across at least a portion of the electrical heating element 120 to protect the electrical heating element 120. The protection layer 140 is configured to protect the electrical heating element 120 extend the life of the electrical heating element 120. The protection layer 140 is configured to prevent the electrical heating element 120 from oxidising.

The protection layer 140 is planar. The protection layer 140 has a size and a shape configured to cover the electrical heating element 120. The protection layer 140 is configured to entirely cover a surface of the electrical heating element 120. The protection layer 140 is configured to substantially cover the porous body 110 below the electrical heating element 120. The protection layer 140 comprises an inorganic material such as AI2O3, SiC>2, MgO, BaO, CaO, ZrC>2, or ZnO. It will be appreciated that the protection layer 140 may have a different shape or comprise a different material.

The protection layer 140 is arranged along the electrical heating element 120. The protection layer 140 is in direct contact with the electrical heating element 120. The protection layer 140, the electrical heating element 120 and the porous body 110 are arranged such that the electrical heating element 120 is between the protection layer 140 and the porous body 110.

The measurement contacts 150 are directly disposed on a surface of the protection layer 140 at opposite sides of the surface of the protection layer 140 such that the measurement contacts 150 can measure the electrical parameter across the protection layer 140. The measurement contacts 150 are arranged to permit measurement of an electrical parameter of the heater assembly 100 to detect whether a sufficient amount of liquid aerosol-forming substrate is supplied to the electrical heating element 120.

Two measurement contacts 150 are provided. The measurement contacts 150 are the same as one another in terms of material, shape and size. The measurement contacts 150 are attached to the protection layer 140. The measurement contacts 150 extend from the inorganic protection layer 140.

An electrical circuit 160 is provided to connect the measurement contacts 150 to each other via an electrical parameter measurement apparatus 170, which in this example is an apparatus configured to measure electrical resistance between the measurement contacts 150. The electrical circuit 160 is capable of measurements up to 0.1 x 10⁷ Ohms.

In this example, the electrical parameter measured across the measurement contacts 150 is an electrical parameter of the protection layer 140. In this example, the electrical parameter is indicative of electrical resistance across the protection layer 140. The protection layer 140 is configured to have a very low conductivity, so that resistance measurement across the measurement contacts 150 when no liquid is present will be high, corresponding to an open circuit measurement. As noted above, the porous body 110 may comprise SiC>2, which can have an electrical conductivity of 1 x 10'¹². Resistance measurement across the measurement contacts 150 when a liquid film is present on the protection layer measurably decreases, due to the higher conductivity of the liquid. The liquid may comprise propylene glycol, for example, which can have an electrical conductivity of 0.1 x 10'⁶. The liquid may comprise glycerol, which can have an electrical conductivity of 0.06 x 10'⁶. As such, electrical resistance measured across the protection layer 140 is indicative of whether liquid is present on, at or within the protection layer 140. Electrical resistance measured across the protection layer 140 may decrease as an amount of liquid on, at or within the protection layer increases.

Control circuitry (not shown in figure 1 for clarity) is configured to only permit electrical power to the electrical heating element 120 when the resistance measurement indicates that there is liquid present on at or within the inorganic protection layer 140. This has the advantage of reducing the likelihood of a user experiencing dry heating or a dry puff when using the aerosolgenerating device.

Referring to figure 2, there is shown a heater assembly 100 for an aerosol-generating system, in accordance with a second example of the present disclosure. The heater assembly 100 comprises: an electrical heating element 120, a porous body 110, a protection layer 140, and measurement contacts 150, an electrical circuit 160, an electrical parameter measurement apparatus 170, and control circuitry (not shown for clarity).

The electrical heating element 120, the porous body 110, and the protection layer 140 are as described in relation to the example shown in figure 1.

The measurement contacts 150 of the second example are directly disposed on opposing surfaces of the porous body 110 such that the measurement contacts 150 can measure the electrical parameter across the porous body 110.

Two measurement contacts 150 are provided. The measurement contacts 150 are the same as one another in terms of material, shape and size. The measurement contacts 150 are attached to the porous body 110. Each measurement contact 150 extends along the side of the porous body 110 on which they are disposed.

An electrical circuit 160 is provided to connect the measurement contacts 150 to each other via an electrical parameter measurement apparatus 170, which in this example is an apparatus configured to measure electrical resistance between the measurement contacts 150.

In this example, the electrical parameter measured across the measurement contacts 150 is an electrical parameter of the porous body 110. In this example, the electrical parameter is indicative of electrical resistance across the porous body 110. Electrical resistance across the porous body 110 is indicative of whether liquid is present on or within the porous body 110. When liquid is present on or within the porous body 110, electrical resistance measured across the porous body 110 is significantly lower than when liquid is not present. Electrical resistance measured across the porous body 110 may decrease as an amount of liquid within the porous body 110 increases. Referring to figures 3 and 4, there is shown a schematic illustration of an example aerosolgenerating cartridge 400 and a schematic illustration of an example aerosol-generating system 600. The aerosol-generating system 600 comprises two main components, a cartridge 400 and a main body part or aerosol-generating device 500.

The aerosol-generating cartridge 400 comprises: a heater assembly 100, and a liquid storage portion 430, 435 configured to hold a liquid aerosol-forming substrate. The liquid storage portion 430, 435 is arranged at an opposite side of the heater assembly to the porous outer surface.

The aerosol-generating system 600 comprises: a cartridge 400; a power supply 510 for supplying electrical power to the heating element; control circuitry 520 configured to control a supply of power from the power supply 510 to the heating element, wherein the control circuitry 520 is further configured to receive a signal from the measurement contacts and, based on the signal, to determine whether liquid aerosol-forming substrate is supplied to the porous body. An electrical parameter measured by the measurement contacts is greater than a maximum threshold value or less than a minimum threshold value indicating that liquid aerosol-forming substrate supplied to the porous body is below a threshold amount.

A connection end 415 of the cartridge 400 is removably connected to a corresponding connection end 505 of the aerosol-generating device 500. The connection end 415 of the cartridge 400 and connection end 505 of the aerosol-generating device 500 each have electrical contacts or connections (not shown) which are arranged to cooperate to provide an electrical connection between the cartridge 400 and the aerosol-generating device 500. The aerosol-generating device 500 contains a power source in the form of a battery 510, which in this example is a rechargeable lithium ion battery, and control circuitry 520. The aerosol-generating system is portable and has a size comparable to a conventional cigar or cigarette. A mouthpiece 425 is arranged at the end of the cartridge 400 opposite the connection end 415.

The cartridge 400 comprises a housing 405 containing the heater assembly 100 of figure 1 or figure 2 and a liquid storage compartment or portion having a first storage portion 430 and a second storage portion 435. A liquid aerosol-forming substrate is held in the liquid storage compartment. Although not illustrated in figures 3 or 4, the first storage portion 430 of the liquid storage compartment is connected to the second storage portion 435 of the liquid storage compartment so that liquid in the first storage portion 430 can pass to the second storage portion 435. The heater assembly 100 receives liquid from the second storage portion 435 of the liquid storage compartment. At least a portion of the porous body of the heater assembly 100 extends into the second storage portion 435 of the liquid storage compartment to contact the liquid aerosol-forming substrate therein. An air flow passage 440, 445 extends through the cartridge 400 from an air inlet 450 formed in a side of the housing 405 past the electrical heating element of the heater assembly 100 and from the heater assembly 100 to a mouthpiece opening 410 formed in the housing 405 at an end of the cartridge 400 opposite to the connection end 415.

The components of the cartridge 400 are arranged so that the first storage portion 430 of the liquid storage compartment is between the heater assembly 100 and the mouthpiece opening 410, and the second storage portion 435 of the liquid storage compartment is positioned on an opposite side of the heater assembly 100 to the mouthpiece opening 410. In other words, the heater assembly 100 lies between the two portions 430, 435 of the liquid storage compartment and receives liquid from the second storage portion 435. The first storage portion 430 of the liquid storage compartment is closer to the mouthpiece opening 410 than the second storage portion 435 of the liquid storage compartment. The air flow passage 440, 445 extends past the electrical heating element of the heater assembly 100 and between the first 430 and second 435 portions of the liquid storage compartment.

The aerosol-generating system is configured so that a negative pressure can be applied at the mouthpiece 425 of the cartridge to draw aerosol out of the mouthpiece opening 410. In operation, when a negative pressure is applied to the mouthpiece 425, air is drawn through the airflow passage 440, 445 from the air inlet 450, past the heater assembly 100, to the mouthpiece opening 410. The control circuitry 520 controls the supply of electrical power from the battery 510 to the cartridge 400 when the system is activated. This in turn controls the amount and properties of the vapour produced by the heater assembly 100. The control circuitry 520 may include an airflow sensor (not shown) and the control circuitry 520 may supply electrical power to the heater assembly 100 when user puffs are detected by the airflow sensor. This type of control arrangement is well established in aerosol-generating systems such as inhalers and e-cigarettes. When a negative pressure is applied to the mouthpiece opening 410 of the cartridge 400, the heater assembly 100 is activated and generates a vapour that is entrained in the air flow passing through the air flow passage 440. The vapour cools within the airflow in passage 445 to form an aerosol, which is then drawn into the user’s mouth through the mouthpiece opening 410.

In operation, the mouthpiece opening 410 is typically the highest point of the system. The construction of the cartridge 400, and, in particular, the arrangement of the heater assembly 100 between first and second storage portions 430, 435 of the liquid storage compartment, is advantageous because it exploits gravity to ensure that the liquid substrate is delivered to the heater assembly 100 even as the liquid storage compartment is becoming empty, but prevents an oversupply of liquid to the heater assembly 100 which might lead to leakage of liquid into the air flow passage 440. A method of controlling heating in an aerosol-generating system is shown in the flow chart of figure 5. The heater assembly controlled by the method comprises: an electrical heating element for heating a liquid aerosol-forming substrate to form an aerosol; a porous body for supplying the liquid aerosol-forming substrate to the electrical heating element, the electrical heating element being arranged along a porous outer surface of the porous body; a protection layer arranged to extend across at least a portion of the electrical heating element to protect the electrical heating element; and measurement contacts arranged to permit measurement of an electrical parameter of the heater assembly to detect whether a sufficient amount of liquid aerosol-forming substrate is supplied to the electrical heating element.

In a first step 61 , the method comprises measuring the electrical parameter of the heater assembly between the measurement contacts, to detect whether liquid aerosol-forming substrate is supplied to the electrical heating element.

In a second step 62, the method comprises determining, based on the electrical parameter measurement, an indication of one or more of: the absence of liquid aerosol-forming substrate, the presence of liquid aerosol-forming substrate, an amount of liquid aerosol-forming substrate.

In a third step 63, the method comprises: upon determining a low amount of liquid aerosolforming substrate in the porous body, preventing power from being supplied to the electrical heating element.

In a fourth step 64, the method comprises: upon detection of an absence of liquid aerosolforming substrate in the porous body, preventing power from being supplied to the electrical heating element.

The third step 63 may be performed without the fourth step 64. Equally, the fourth step 64 may be performed without the third step 63. It will be appreciated that the method does not have to be performed in the order of steps shown in Figure 5.

Figure 6 shows a schematic circuit diagram of part of the control circuitry 520 of the aerosol-generating system of figure 4 in more detail. The circuit 200 of Figure 6 is used for determining one or more electrical parameters of a the heater assembly.

The circuit 200 includes a resistance Rz corresponding, or equivalent to, a resistance of the protection layer or porous body between two measurement contacts 210, 211 , which is connected to an electric power supply via connection 202. The power supply provides a voltage Vin. An additional resistor R having a known value is inserted in series with the heater Rz. Resistance Rz and known resistor R form a potential divider. There is a voltage Vz at the point Z in the circuit 200 between the heater Rz and the additional resistor R. The voltage Vz is intermediate between ground and voltage Vin.

The circuit 200 determines an electrical parameter of the resistance Rz, in this example, the electrical resistance of the resistance Rz. An analogue input 204 on a microcontroller MCU is used to monitor the voltage Vin provided by connection 202. An analogue input 206 on the microcontroller MCU is used to monitor the voltage Vz at point Z. The analogue input 206 is connected to an analogue-to-digital converter (ADC) input of the microcontroller MCU. In order for the microprocessor MCU to measure the resistance of resistance Rz, the current through the resistance Rz and the voltage across resistance Rz are determined. Ohm’s law is then used to determine the resistance Rz.

The voltage across the resistance Rz is Vz and the current through the resistance Rz is I. Thus, the resistance of the resistance Rz can be determine by equation 1 :

Rz = V_z / l (1)

The current through the known resistor R is the same as the current through the resistance Rz because they are connected in series. That is, the current through resistor R and the current through the resistance Rz is current I. As mentioned above, resistor R has a known value. The voltage across the resistor R is Vin - Vz. By applying Ohm’s law, the current through resistor R can be determined by equation 2:

I = Vin - V_z / R (2)

So, combining (1) and (2) gives:

Rz = (V_z I (Vin - V_z)) x R (3)

Thus, the microprocessor MCU can measure Vin and Vz, as the aerosol generating system is being used and, knowing the value of resistor R, can determine the resistance of the resistance Rz.

The microprocessor MCU is configured to prevent power being supplied to the electrical heating element if liquid aerosol-forming substrate is not supplied to the porous body or if liquid aerosol-forming substrate in the porous body is below a threshold amount.

The microprocessor can determine, by determining an inverse of the resistance measured RH, electrical conductance. For the purpose of the present description and of the appended claims, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term "about". Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein. In this context, therefore, a number A is understood as A ± 10 percent (10%) of A. Within this context, a number A may be considered to include numerical values that are within general standard error for the measurement of the property that the number A modifies. The number A, in some instances as used in the appended claims, may deviate by the percentages enumerated above provided that the amount by which A deviates does not materially affect the basic and novel characteristic(s) of the claimed invention.

Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein.

Claims

1 . A heater assembly for an aerosol-generating system, comprising: an electrical heating element for heating a liquid aerosol-forming substrate to form an aerosol; a porous body for supplying the liquid aerosol-forming substrate to the electrical heating element, the electrical heating element being arranged along a porous outer surface of the porous body; a protection layer arranged to extend across at least a portion of the electrical heating element to protect the electrical heating element; and measurement contacts arranged to permit measurement of an electrical parameter of the heater assembly to detect whether a sufficient amount of liquid aerosol-forming substrate is supplied to the electrical heating element.

2. The heater assembly of claim 1 , wherein the electrical parameter is an electrical parameter of the protection layer.

3. The heater assembly of claim 1 or claim 2, wherein the measurement contacts are disposed on a surface of the protection layer at opposite sides of the surface of the protection layer such that the measurement contacts can measure the electrical parameter across the protection layer.

4. The heater assembly of claim 1 , wherein the electrical parameter is an electrical parameter of the porous body.

5. The heater assembly of claim 1 or claim 4, wherein the measurement contacts are disposed on opposing surfaces of the porous body such that the measurement contacts can measure the electrical parameter across the porous body.

6. The heater assembly of any of the preceding claims, wherein the electrical parameter is indicative of an electrical resistance.

7. The heater assembly of any of the preceding claims, wherein the electrical heating element is electrically connected to electrical contacts, and the electrical heating element is configured to heat the liquid aerosol-forming substrate upon application of an electrical potential difference to the electrical contacts.

8. A cartridge for an aerosol-generating system, comprising: the heater assembly of any of claims 1 to 7; and a liquid storage portion configured to hold a liquid aerosol-forming substrate; wherein the liquid storage portion is arranged at an opposite side of the heater assembly to the porous outer surface.

9. An aerosol-generating system, comprising: the cartridge of claim 8; and an aerosol-generating device comprising: a power supply for supplying electrical power to the electrical heating element; and control circuitry configured to control a supply of power from the power supply to the electrical heating element, wherein the control circuitry is further configured to receive a signal from the measurement contacts and, based on the signal, to determine whether liquid aerosol-forming substrate is supplied to the electrical heating element.

10. The aerosol-generating system of claim 9, wherein the electrical parameter is greater than a maximum threshold value or less than a minimum threshold value indicating that liquid aerosolforming substrate supplied to the porous body is below a threshold amount.

11 . The aerosol-generating system of claim 9 or claim 10, wherein the controller is configured to prevent power being supplied to the electrical heating element if liquid aerosol-forming substrate is not supplied to the porous body or if liquid aerosol-forming substrate in the porous body is below a threshold amount.

12. A method of controlling heating in an aerosol-generating system comprising a heater assembly; the heater assembly comprising: an electrical heating element for heating a liquid aerosol-forming substrate to form an aerosol; a porous body for supplying the liquid aerosol-forming substrate to the electrical heating element, the electrical heating element being arranged along a porous outer surface of the porous body; a protection layer arranged to extend across at least a portion of the electrical heating element to protect the electrical heating element; and measurement contacts arranged to permit measurement of an electrical parameter of the heater assembly to detect whether a sufficient amount of liquid aerosol-forming substrate is supplied to the electrical heating element, the method comprising: measuring the electrical parameter of the heater assembly between the measurement contacts, to detect whether liquid aerosol-forming substrate is supplied to the electrical heating element.

13. The method of claim 12, comprising: determining, based on the electrical parameter measurement, an indication of one or more of: the absence of liquid aerosol-forming substrate, the presence of liquid aerosol-forming substrate, an amount of liquid aerosol-forming substrate.

14. The method of claim 13, comprising: upon determining a low amount of liquid aerosol-forming substrate in the porous body, preventing power from being supplied to the electrical heating element.

15. The method of claim 13 or claim 14, comprising: upon detection of an absence of liquid aerosol-forming substrate in the porous body, preventing power from being supplied to the electrical heating element.