Wearable air purifier

Abstract

A wearable air purifier comprising headgear 102 for wearing on a wearer’s head, wherein the headgear comprises: a first housing to be supported over a wearer’s ear, a second housing to be supported ov

Description

BACKGROUND Exposure to air pollution such as pollutant gases or airborne particulates presents a risk of harm to human health. An approach to reducing a person’s exposure to air pollution is to use a wearable air purifier to discharge filtered air towards a wearer’s face. SUMMARY According to a first aspect of the invention, there is provided a wearable air purifier, comprising: headgear for wearing on a wearer’s head, a power source located in the headgear, a fan assembly operable to generate a filtered airflow, wherein the fan assembly is releasably attachable to the headgear, and a wireless power transfer assembly, wherein the headgear comprises a first wireless coupling device of the wireless power transfer assembly, the first coupling device being connected to the power source, herein the fan assembly comprises a second wireless coupling device of the wireless power transfer assembly, and wherein, when the fan assembly is attached to the headgear, the wireless power transfer assembly is configured to wirelessly transfer energy stored in the power source to the fan assembly via the first and second wireless coupling devices. The fan assembly is reversibly attachable and detachable by the wearer from the headgear. The wearer may attach the fan assembly to the headgear when the provision of filtered airflow by the fan assembly is desired, and detach the fan assembly from the headgear when the airflow is not desired. The headgear may thus be worn without the fan assembly attached, and thus without the additional mass and bulk of the fan assembly. This may be useful as the wearer may desire to wear the headgear, which may in some cases be headphones, without the fan assembly in scenarios where the filtered airflow is not desired, such as in environments with low levels of air pollution. Whereas in environments with high levels of air pollution the wearer may desire to also receive the filtered airflow to reduce their exposure to the air pollution. The headgear and components thereof may thus have dual functionality, which may desirably reduce a perceived need for the wearer to have separate air purifying and non-air purifying headgears, e.g., separate air purifying and non-air purifying headphones. By providing a wireless power transfer assembly between the headgear and the fan assembly, the process of attaching the fan assembly to the headgear is greatly simplified for the wearer. For example, the fan assembly simply needs to be releasably attached the headgear in order to establish a powered connection between the headgear and the fan assembly and is not required to align points electrical contact on the headgear and the fan assembly separately. Similarly, when detaching the fan assembly from the headgear, the wearer may simply remove the fan assembly from the headgear in order to disengage the powered connection and is not required to disconnect any electrical connection between the headgear and the fan assembly separately. The power source may be a battery, such as a rechargeable battery. The fan assembly is operable to generate filtered airflow to be discharged from the wearable air purifier for inhalation by the wearer. The fan assembly may comprise an outlet for discharging the filtered airflow directly out of the wearable air purifier for inhalation by the wearer. The filtered airflow directly discharged from the fan assembly may be directed towards the wearer’s face, past the wearer’s face and / or generally towards the vicinity of the wearer's face. When the fan assembly is attached to the headgear, the fan assembly may be rotatably connected to the headgear at one of a plurality of rotational positions, and wherein the wireless power transfer assembly is configured to wirelessly transfer energy stored in the power source to the fan assembly via the first and second wireless coupling devices when the fan assembly is connected to the headgear at any of the plurality of rotational positions. In other words, the fan assembly may attach to the headgear in a variety of different orientations without impacting the wireless power transfer from the headgear to the fan assembly. This further simplifies the process of attaching the fan assembly to the headgear for the wearer as the fan assembly simply needs to be releasably attached the headgear in one of a number of orientations in order to establish a powered connection between the headgear and the fan assembly and is not required to align the fan assembly to a single orientation. Further, as the fan assembly may attach to the headgear in a variety of different orientations without impacting the wireless power transfer from the headgear to the fan assembly, multiple different attachment positions are available for greater user adjustability, for example, to accommodate different nozzle positions (if attached) for different head sizes. The first coupling device of the wireless power transfer assembly may comprise a first electromagnetic coil, and wherein the second coupling device of the wireless power transfer assembly comprises a second electromagnetic coil such that the wireless power transfer assembly is configured to wirelessly transfer the energy stored in the power source to the fan assembly via inductive coupling. In other words, the wireless transfer of power from the headgear to the fan assembly may be implemented by providing a first electromagnetic coil, or solenoid, in the headgear that is driven to generate an alternating magnetic field, which causes a current to be generated in a second electromagnetic coil, or solenoid, provided in the fan assembly by way of electromagnetic induction. The first electromagnetic coil and the second electromagnetic coil may by the same or similar sizes, in terms of coil diameter, or may be different. The first electromagnetic coil and the second electromagnetic coil may comprise the same number of coils or a different number of coils. The electromagnetic coils may be made from any suitable conductive material. When the fan assembly is attached to the headgear, the first wireless coupling device and the second wireless coupling device may be concentrically aligned. In other words, the first wireless coupling device and the second wireless coupling device may be arranged so as to align when the fan assembly is attached to the headgear, thereby improving the efficiency of the wireless power transfer assembly. For example, where the first coupling device comprises a first electromagnetic coil and the second coupling device comprises a second electromagnetic coil, the coils may be concentrically aligned with each other. When the fan assembly is attached to the headgear, the first wireless coupling device may be spaced from second wireless coupling device by less than 1cm. In other words, the first wireless coupling device and the second wireless coupling device may be arranged so as to be brought within a predetermined distance, such as 1cm, when the fan assembly is attached to the headgear, thereby improving the efficiency of the wireless power transfer assembly. The first wireless coupling device and the second wireless coupling device may be axially spaced from each other. For example, where the first coupling device comprises a first electromagnetic coil and the second coupling device comprises a second electromagnetic coil concentrically aligned with each other, the first and second electromagnetic coils may be spaced apart from each other along their shared central axis by less than 1 cm. The headgear may comprise a protruding portion and the fan assembly comprises an intruding portion to accommodate the protruding portion of the headgear when the fan assembly is attached to the headgear. The protruding portion of the speaker housing cooperates with the intruding portion of the fan assembly to function as a locating feature. This may desirably aid correct positioning of the fan assembly relative to the headgear during attachment of the fan assembly by the wearer. Correct positioning of the fan assembly relative to the headgear during attachment may be particularly complicated in a scenario where the wearer attaches the fan assembly to the headgear in use, whilst the headgear is worn on the wearer’s head, in which case the speaker housing may be outside of the wearer’s field of view. The protruding and intruding portions of the headgear and the fan assembly, respectively, may prevent the fan assembly from sheering away from the headgear, thereby improving the robustness of the attachment of the fan assembly to the speaker housing. The protruding and intruding portions of the headgear and the fan assembly, respectively, may also serve to align the first coupling device and the second coupling device during the attachment of the fan assembly to the headgear, thereby improving the efficiency of the wireless power transfer assembly. The first wireless coupling device may be concentrically aligned with a central axis of the protruding portion and the second wireless coupling device is concentrically aligned with a central axis of the intruding portion. The protruding and intruding portions of the headgear and the fan assembly, respectively, may serve to concentrically align the first coupling device and the second coupling device during the attachment of the fan assembly to the headgear, thereby improving the efficiency of the wireless power transfer assembly. The first wireless coupling device may be provided radially outward of an outer circumference of the protruding portion and the second wireless coupling device is provided radially outward of an outer circumference of the intruding portion. In other words, when the wireless coupling devices are both provided radially outwards of the protruding and intruding portions, the protruding and intruding portions may serve to align the first coupling device and the second coupling device during the attachment of the fan assembly to the headgear, thereby improving the efficiency of the wireless power transfer assembly. The first wireless coupling device may be provided radially inward of an outer circumference of the protruding portion and the second wireless coupling device is provided radially inward of an outer circumference of the intruding portion. In other words, when the wireless coupling devices are both provided radially inwards of the protruding and intruding portions, the protruding and intruding portions may serve to align the first wireless coupling device and the second wireless coupling device during the attachment of the fan assembly to the headgear, thereby improving the efficiency of the wireless power transfer assembly. The protruding portion may contact the intruding portion when the fan assembly is attached to the headgear. The contact between the protruding portion and the intruding portion may desirably provide support to the fan assembly, to thereby reduce unwanted movement of the fan assembly relative to the headgear in use. In particular, the contact may act to retain the fan assembly to the headgear, and so inhibit inadvertent detachment of the fan assembly from the headgear in use. Further, by inhibiting the movement of the fan assembly relative to the headgear, the alignment of the first and second wireless coupling devices may be maintained more securely and act to prevent the coupling devices from becoming unaligned or misaligned over time or during use. The protruding portion may contact the intruding portion about a full circumference of the protruding portion when the fan assembly is attached to the speaker housing. The contact between the full circumference of the protruding portion and the intruding portion may desirably provide support to the fan assembly in all the directions of the plane through the circumference of the protruding portion. Thus, unwanted movement of the fan assembly relative to the headgear, and so unwanted movement of the first coupling device relative to the second coupling device, in use may desirably be reduced. In particular, the contact may act to retain the fan assembly to the headgear, and so inhibit inadvertent decoupling of the first and second wireless coupling devices in use. The protruding portion may narrow progressively with protrusion. Put another way, a width of the protruding portion may decrease with distance from the headgear, i.e., distance from the point of attachment between the protruding portion and the headgear. This narrowing of the protruding portion may desirably ease its location in the intruding portion during attachment of the fan assembly to the headgear. Thus, attachment of the fan assembly to the headgear by the wearer may be simplified. The protruding portion could, for example, be convex in shape. The intruding portion may narrow progressively with intrusion. Put another way, a width of the intruding portion may decrease with distance into the fan assembly, i.e., distance from the point of attachment between the fan assembly and the headgear. This narrowing of the intruding portion may desirably ease locating of the protruding portion therein during attachment of the fan assembly to the headgear. Thus, attachment of the fan assembly to the headgear by the wearer may be simplified. The intruding portion could, for example, be concave in shape. The headgear and the fan assembly may define respective mating surfaces, the mating surfaces being configured to contact when the fan assembly is attached to the headgear, wherein the first wireless coupling device is provided on an inner surface of the headgear opposing the mating surface of the headgear, and wherein the second wireless coupling device is provided on an inner surface of the fan assembly opposing the mating surface of the fan. This contact between the cooperating mating surfaces may desirably provide support to the fan assembly, to thereby reduce unwanted movement of the fan assembly relative to the headgear in use. In particular, the contact may act to retain the fan assembly to the headgear, and so inhibit inadvertent decoupling of the first and second wireless coupling devices in use. For example, the mating surfaces could extend about at least part of the circumference of the protruding portion and the intruding portion respectively, e.g., about at least half of the circumference thereof. The headgear further comprises a controller connected to the first wireless coupling device and the power source, and wherein the controller is adapted to generate an alternating signal from a power output from the power source and transmit the alternating signal to the first wireless coupling device, wherein a frequency of the alternating signal is at least 1MHz. In other words, the headgear may comprise circuitry to control the frequency of the wireless power transfer assembly, thereby optimizing the wireless power transfer between the headgear and the fan assembly. The fan assembly may be releasably attachable to the headgear by way of a magnet coupling. By providing a magnet coupling as the means of releasably attaching the fan assembly to the headgear, the process of attaching the fan assembly to the headgear is greatly simplified for the wearer. For example, to attach the fan assembly to the headgear, the wearer may simply bring the fan assembly into close proximity with the headgear in order to engage the magnet coupling and is not required to rotate or actuate a locking mechanism separately. Similarly, to detach the fan assembly from the headgear, the wearer may simply pull the fan assembly away from the headgear in order to disengage the magnet coupling and is not required to rotate or actuate a locking mechanism separately. Further, as magnet couplings do not require direct contact in order to attach to each other, the fan assembly may attach to the headgear in a variety of different orientations without reducing the attachment strength of the magnet coupling. The magnet coupling may comprise: a first attachment feature provided in and / or on the headgear; and a second attachment feature provided in and / or on the fan assembly. In other words, the magnet coupling may comprise a plurality of attachment features distributed across both the fan assembly and the headgear. The attachments features may be realised in a number of way, which are discussed in further detail below. Due to the magnetic nature of the magnet coupling, the first and second attachment features do not require direct contact in order to attach to each other. Accordingly, the first and second attachment features may be provided within the headgear and the fan assembly, respectively. Alternatively, the first and second attachment features may be provided on the headgear and the fan assembly, respectively, for example on a surface of the headgear and the fan assembly. The first attachment feature may comprise a headgear magnet. In other words, the headgear may comprise a magnet forming part of the magnet coupling between the headgear and the fan assembly. The headgear magnet may comprise a plurality of headgear magnets. In other words, the headgear may comprise a plurality of magnets forming part of the magnet coupling between the speaker housing and the fan assembly. The provision of a plurality of magnets in the headgear may improve the strength of the magnet coupling between the headgear and the fan assembly. Further, the provision of a plurality of magnets in the headgear may provide multiple different attachment points and / or orientations between the headgear and the fan assembly. In addition, the plurality of magnets may comprise a plurality of the same type of magnets or a plurality of different types of magnets. The plurality of headgear magnets may be arranged in an annular array, and optionally wherein the headgear magnets are spaced from each other uniformly within the annular array. In other words, the plurality of magnets in the headgear may be arranged in an annular array within, or on, the headgear. The annular array may be a complete annulus or a partial annulus. The annular array may be substantially annular and may comprise one or more concentric annular arrangements of magnets. The annular array may enable the airflow generating assembly to be indexed in a plurality of positions about a centre of the annular array. This may increase flexibility for a wearer by allowing the airflow generating assembly to be rotated to a number of different rotational positions relative to the headgear. The headgear magnet may comprise one or more ring-shaped magnets. In other words, the magnet in the headgear may be provided in the shape of a ring. In this way, the magnet may be arranged concentrically with substantially circular features or components of the headgear, such as the protruding portion. The second attachment feature may comprise a fan assembly ferromagnetic element. In other words, the fan assembly may include an element that a magnet provided in the headgear may attract. Thus, the magnet coupling may comprise a magnet-ferromagnetic element coupling. The first attachment feature may comprise a headgear assembly ferromagnetic element. In other words, the headgear may include an element that a magnet in the fan assembly may attract. Thus, the magnet coupling may comprise a magnet-ferromagnetic element coupling. The second attachment feature may comprise a fan assembly magnet. In other words, the fan assembly may comprise a magnet forming part of the magnet coupling between the headgear and the fan assembly. The fan assembly magnet may comprise a plurality of fan assembly magnets. In other words, the fan assembly may comprise a plurality of magnets forming part of the magnet coupling between the headgear and the fan assembly. The provision of a plurality of magnets in the fan assembly may improve the strength of the magnet coupling between the headgear and the fan assembly. Further, the provision of a plurality of magnets in the fan assembly may provide multiple different attachment points and / or orientations between the headgear and the fan assembly. The plurality of fan assembly magnets may be arranged in an annular array, and optionally wherein the fan assembly magnets are spaced from each other uniformly about the annular array. In other words, the plurality of magnets in the fan assembly may be arranged in an annular array within, or on, the fan assembly. The annular array may be a complete annulus or a partial annulus. The annular array may be substantially annular and may comprise one or more concentric annular arrangements of magnets. The annular array may enable the airflow generating assembly to be indexed in a plurality of positions about a centre of the annular array. This may increase flexibility for a wearer by allowing the airflow generating assembly to be rotated to a number of different rotational positions relative to the headgear. The fan assembly magnet may comprise one or more ring-shaped magnets. In other words, the magnet in the fan assembly may be provided in the shape of a ring. In this way, the magnet may be arranged concentrically with substantially circular features or components of the fan assembly, such as the protruding portion. The magnet coupling may comprise a magnet-magnet coupling where both the speaker housing and the fan assembly comprise a magnet. The magnet coupling may comprise a magnet-ferromagnetic coupling where one of the headgear and the fan assembly comprises a magnet and the other comprises a ferromagnetic element. The magnet coupling may comprise a mixed magnet coupling, where both the fan assembly and the headgear comprise both magnets and ferromagnetic elements. The magnet coupling may comprise a partially mixed magnet coupling, where one of the headgear and the fan assembly comprises a magnet and the other comprises both magnets and ferromagnetic elements. The headgear may comprise: a speaker housing to be supported over a wearer’s ear in use, and a speaker located in the speaker housing, and wherein the fan assembly is releasably attachable to the speaker housing. The headgear thus forms headphones, which may be used for audio playback. The fan assembly is reversibly attachable and detachable by the wearer from the headphones. The wearer may attach the fan assembly to the headgear when the provision of filtered airflow by the fan assembly is desired, and detach the fan assembly from the headgear when the airflow is not desired. The headgear may thus be used without the fan assembly attached, and thus without the additional mass and bulk of the fan assembly. This may be useful as the wearer may desire to wear the headgear, i.e., the headphones, without the fan assembly in scenarios where the filtered airflow is not desired, such as in environments with low levels of air pollution. Whereas in environments with high levels of air pollution the wearer may desire to also receive the filtered airflow to reduce their exposure to the air pollution. The headgear and components thereof may thus have dual functionality, which may desirably reduce a perceived need for the wearer to have separate air purifying and non-air purifying headgears, i.e., separate air purifying and non-air purifying headphones. The wearable air purifier may comprise a nozzle attachable to the fan assembly to receive the filtered airflow generated by the fan assembly and discharge the filtered airflow towards the wearer’s face. The nozzle may thus function to carry airflow from the fan assembly closer to the wearer’s face, e.g., closer to the nose / mouth region of the wearer’s face. Thus, the fan assembly may be attached to the headgear at a location relatively remote from the wearer’s face, for example, at the side, top, or rear of the wearer’s head, thereby avoiding obstructing the wearer’s face, e.g., obstructing the wearer’s vision. Whereas, notwithstanding that the fan assembly may be relatively remote from the wearer’s face, the filtered airflow may still be provided relatively directly to the wearer’s nose and / or mouth via the nozzle, thereby reducing dilution of the filtered airflow by unfiltered ambient air prior to inhalation. The nozzle may, for example, be arranged to extend from the fan assembly in front of the wearer’s face, to thereby duct airflow from the fan assembly to the front of the wearer’s face, e.g., to the wearer’s lower nasal and mouth region. The fan assembly may comprise a fan operable to generate the filtered airflow, wherein the fan is arranged concentrically with the second wireless coupling device. In other words, other components of the wearable air purifier that operate by way of electromagnetic coupling may be provided concentrically with the first and second coupling devices so as to minimize interference between components. According to a second aspect of the invention, there is provided headgear for a wearable air purifier comprising a wireless power transfer assembly, the headgear being adapted to releasably connect to a fan assembly comprising a second wireless coupling device, the headgear comprising: a power source, and a first wireless coupling device connected to the power source, wherein, when the fan assembly is attached to the headgear, the wireless power transfer assembly is configured to wirelessly transfer energy stored in the power source to the fan assembly via the first and second wireless coupling devices. The headgear of the second aspect is thus provided without the fan assembly. The further features and advantages of the headgear of the first aspect are equally applicable to and are hereby restated in respect of the headgear of the second aspect. According to a third aspect of the invention, there is provided a fan assembly for a wearable air purifier comprising a wireless power transfer assembly, the fan assembly being adapted to releasably connect to headgear comprising a first wireless coupling device connected to a power source, the fan assembly comprising: a fan operable to generate a filtered airflow, and a second wireless coupling device connected to the fan, wherein, when the fan assembly is attached to the headgear, the wireless power transfer assembly is configured to wirelessly transfer energy stored in the power source to the fan assembly via the first and second wireless coupling devices. The further features and advantages of the fan assembly of the first aspect are equally applicable to and are hereby restated in respect of the fan assembly of the third aspect. According to a fourth aspect of the invention, there is provided a wearable air purifier, comprising: headgear for wearing on a wearer’s head, a left housing to be supported by the headgear at a left side of the wearer’s head, a right housing to be supported by the headgear at a right side of the wearer’s head, a speaker located in one of the left and right housings, a left assembly releasably attachable to the left housing by way of a first mechanical coupling by rotating the left assembly with respect to the left housing in a first direction, a right assembly releasably attachable to the right housing by way of a second mechanical coupling by rotating the right assembly with respect to the right housing in a second direction opposite the first direction, and a fan operable to generate a filtered airflow provided in one of the left and right assemblies. The headgear thus forms headphones, which may be used for audio playback. The assemblies are reversibly attachable and detachable by the wearer from the headphones. The wearer may attach the assemblies to the headgear when the provision of filtered airflow by the fan is desired, and detach the assemblies from the headgear when the airflow is not desired. The headgear may thus be used without the assemblies attached, and thus without the additional mass and bulk of the assemblies. This may be useful as the wearer may desire to wear the headgear, i.e., the headphones, without the assemblies in scenarios where the filtered airflow is not desired, such as in environments with low levels of air pollution. Whereas in environments with high levels of air pollution the wearer may desire to also receive the filtered airflow to reduce their exposure to the air pollution. The headgear and components thereof may thus have dual functionality, which may desirably reduce a perceived need for the wearer to have separate air purifying and non-air purifying headgears, i.e., separate air purifying and non-air purifying headphones. The mechanical couplings are provided on opposite sides of the headgear, i.e., the first mechanical coupling being provided on the left housing and left assembly and the second mechanical coupling being provided of the right housing and the right assembly. By providing mechanical couplings that engage by rotating the assemblies in opposite directions relative to the respective housings, the user may attach both assemblies by performing the same rotating action. Put another way, by providing mechanical couplings that are engaged through opposing rotations, the left and right assemblies are given a handedness in the way they releasable attach to the left and right housings. For example, the left and right assemblies may both be attached by rotating both of them forwards (from the wearer’s perspective) and may both be detached by rotating both of them backwards (from the wearer’s perspective). In another embodiment, attachment may be via backwards rotation and detachment may be via forwards rotation. The fan is operable to generate filtered airflow to be discharged from the wearable air purifier for inhalation by the wearer. The assemblies may comprise an outlet for discharging the filtered airflow directly out of the wearable air purifier for inhalation by the wearer. The filtered airflow directly discharged from the assemblies may be directed towards the wearer’s face, past the wearer’s face and / or generally towards the vicinity of the wearer's face. The first direction may be clockwise and the second direction may be anti-clockwise. In other words, when wearing the headgear, the wearer may releasably attach the assemblies to the housings by rotating the assemblies in a direction that travels from the bottom of the wearer’s face to the top of the wearer's face. The first mechanical coupling may comprise a first rotational locking mechanism, such as a first threaded assembly or a first bayonet assembly. In other words, the first mechanical coupling may comprise an assembly that inhibits the axial movement of the left assembly relative to the left housing. In this way, the left assembly may be securely held to the left housing. The first bayonet assembly may comprise: a bayonet projection provided on the left assembly; and a cavity provided on the left housing adapted to receive the bayonet projection, the cavity having an opening and a securing end at an end of the cavity opposite the opening, wherein the cavity is adapted to receive the bayonet projection at the opening, and wherein the bayonet projection is moved from the opening to the securing end by the rotation of the left assembly with respect to the left housing in the first direction in order to attach the left assembly to the left housing. In other words, the first bayonet assembly may comprise a cavity adapted to receive the bayonet projection at one end and releasably secure it at another end after the wearer has rotated the left assembly in the first direction. Accordingly, the process of attaching the left assembly to the left housing is greatly simplified for the wearer. For example, to attach the left assembly to the left housing, the wearer may simply bring the left assembly to the left housing such that the bayonet projection of the first bayonet assembly is received in the cavity and rotate the left assembly in the first direction in order to releasably attach the left assembly to the left housing. Accordingly, the wearer is not required to actuate a locking mechanism separately. Similarly, to detach the left assembly from the left housing, the wearer may simply rotate the left assembly in the second direction and pull the left assembly away from the left housing in order to disengage the mechanical coupling and is not required to actuate a locking mechanism separately. Alternatively, the bayonet projection may be provided on the left housing and the cavity may be provided on the left assembly. The first mechanical coupling may comprise a plurality of first bayonet assemblies, and optionally wherein the plurality of first bayonet assemblies comprises two first bayonet assemblies arranged at least 90° (for example, arranged at 180°) from each other about an axis of rotation of the left assembly. In other words, the mechanical coupling of the left assembly to the left housing may be made more secure by providing multiple attachment points around the connection between the left assembly and the left housing. The first mechanical coupling may further comprise a sloped portion adapted to contact the first bayonet as it is received in the cavity. In other words, the first mechanical coupling may comprise a means of aligning the depth of the bayonet within the cavity, thereby ensuring that the first bayonet engages correctly with the securing end of the cavity. The first mechanical coupling may comprise a first locking assembly. In other words, the first mechanical coupling may comprise a means of releasably rotationally locking the left assembly to the left housing when attached. Accordingly, the mechanical coupling of the left assembly to the left housing may be made more secure by preventing unintended rotation of the left assembly in the second direction, which would otherwise release the left assembly from the left housing. The first locking assembly may comprise: a first resilient arm provided on the left assembly comprising a first projection; and a first receiving portion provided on the left housing, the first receiving portion comprising a first track having a first ridge section connected to a first seat section, wherein relative rotation of the left assembly and the left housing (i) forces the first resilient arm to deflect so that the first projection passes over the first ridge section and (ii) permits the first resilient arm to return towards a rest state as the first projection enters the first seat section so as to releasably rotationally inhibit rotation of the left assembly and the left housing together. In other words, the resilient arm may have a strength sufficiently high enough to prevent unwanted rotation of the left assembly with respect to the left housing; whilst still allowing the wearer to overcome the retaining force of the resilient arm and rotate the left assembly to release the first mechanical coupling and detach the left assembly from the left housing, without requiring the user to perform any additional actions. The first track may further comprise a stop section connected to the first seat section, wherein the first stop section is adapted to engage with the projection when the first projection is in the first seat section to inhibit rotation of the left assembly relative to the left housing in the first direction. In other words, the wearer may be prevented from over-rotating the left assembly with respect to the left housing, which may otherwise release the locking mechanism or damage the first mechanical coupling. The first locking assembly may further comprise a sloped portion adapted to contact the first resilient arm as it is received in the cavity. In other words, the first locking assembly may comprise a means of aligning the first resilient arm along the track, thereby ensuring that the first projection engages correctly with the seat. The first mechanical coupling may comprise a plurality of first locking assemblies, and optionally wherein the plurality of first locking assemblies comprises two first locking assemblies arranged at least 90° (for example, arranged at 180°) from each other about an axis of rotation of the left assembly. In other words, the mechanical coupling of the left assembly to the left housing may be made more secure by providing multiple locking assembly around the connection between the left assembly and the left housing. The plurality of first bayonet assemblies and the plurality of first locking assemblies may be arranged in an alternating order about an axis of rotation of the left assembly. In other words, the components of the first mechanical coupling may be distributed about the left assembly and the left housing in order to prevent excess mechanical stress being applied to a specific portion of the first mechanical coupling. The second mechanical coupling may comprise a second rotational locking mechanism, such as a second threaded assembly or a second bayonet assembly. In other words, the second mechanical coupling may comprise an assembly that inhibits the axial movement of the right assembly relative to the right housing. In this way, the right assembly may be securely held to the right housing. The second bayonet assembly may comprise: a bayonet projection provided on the right assembly; and a cavity provided on the right housing adapted to receive the bayonet projection, the cavity having an opening and a securing end at an end of the cavity opposite the opening, wherein the cavity is adapted to receive the bayonet projection at the opening, and wherein the bayonet projection is moved from the opening to the securing end by the rotation of the right assembly with respect to the right housing in the second direction in order to attach the right assembly to the right housing. Accordingly, the process of attaching the right assembly to the right housing is greatly simplified for the wearer. For example, to attach the right assembly to the right housing, the wearer may simply bring the right assembly to the right housing such that the bayonet projection of the second bayonet assembly is received in the cavity and rotate the right assembly in the second direction in order to releasably attach the right assembly to the right housing. Accordingly, the wearer is not required to actuate a locking mechanism separately. Similarly, to detach the right assembly from the right housing, the wearer may simply rotate the left assembly in the first direction and pull the right assembly away from the right housing in order to disengage the mechanical coupling and is not required to actuate a locking mechanism separately. Alternatively, the bayonet projection may be provided on the right housing and the cavity may be provided on the right assembly. The second mechanical coupling may comprise a plurality of second bayonet assemblies, and optionally wherein the plurality of second bayonet assemblies comprises two second bayonet assemblies arranged at least 90° (for example, arranged at 180°) from each other about an axis of rotation of the right assembly. In other words, the mechanical coupling of the right assembly to the right housing may be made more secure by providing multiple attachment points around the connection between the right assembly and the right housing. The second mechanical coupling may further comprise a sloped portion adapted to contact the second bayonet as it is received in the cavity. In other words, the second mechanical coupling may comprise a means of aligning the depth of the bayonet within the cavity, thereby ensuring that the second bayonet engages correctly with the securing end of the cavity. The second mechanical coupling may comprise a second locking assembly. In other words, the second mechanical coupling may comprise a means of releasably rotationally locking the right assembly to the right housing when attached. Accordingly, the mechanical coupling of the right assembly to the right housing may be made more secure by preventing unintended rotation of the right assembly in the first direction, which would otherwise release the right assembly from the right housing. The second locking assembly may comprise: a second resilient arm provided on the right assembly comprising a second projection; and a second receiving portion provided on the right housing, the second receiving portion comprising a second track having a second ridge section connected to a second seat section, wherein relative rotation of the right assembly and the right housing (i) forces the second resilient arm to deflect so that the second projection passes over the second ridge section and (ii) permits the second resilient arm to return towards a rest state as the second projection enters the second seat section so as to releasably rotationally inhibit rotation of the right assembly and the right housing together: In other words, the resilient arm may have a strength sufficiently high enough to prevent unwanted rotation of the right assembly with respect to the right housing; whilst still allowing the wearer to overcome the retaining force of the resilient arm and rotate the right assembly to release the second mechanical coupling and detach the right assembly from the right housing, without requiring the user to perform any additional actions. The second track may further comprise a second stop section connected to the second seat section, wherein the second stop section is adapted to engage with the projection when the second projection is in the second seat section to inhibit rotation of the right assembly relative to the right housing in the second direction. In other words, the wearer may be prevented from over-rotating the right assembly with respect to the right housing, which may otherwise release the locking mechanism or damage the second mechanical coupling. The second locking assembly may further comprise a sloped portion adapted to contact the second resilient arm as it is received in the cavity. In other words, the second locking assembly may comprise a means of aligning the second resilient arm along the track, thereby ensuring that the second projection engages correctly with the seat. The second mechanical coupling may comprise a plurality of second locking assemblies, and optionally wherein the plurality of second locking assemblies comprises two second locking assemblies arranged at least 90° (for example, arranged at 180°) from each other about an axis of rotation of the right assembly. In other words, the mechanical coupling of the right assembly to the right housing may be made more secure by providing multiple locking assembly around the connection between the right assembly and the right housing. The plurality of second bayonet assemblies and the plurality of second locking assemblies are arranged in an alternating order about an axis of rotation of the right assembly. In other words, the components of the second mechanical coupling may be distributed about the right assembly and the right housing in order to prevent excess mechanical stress being applied to a specific portion of the second mechanical coupling. The first mechanical coupling may be provided adjacent an outer perimeter of the left housing and the left assembly and the second mechanical coupling is provided adjacent an outer perimeter of the right housing and the right assembly. In other words, the assemblies and the housings may be secured to each other towards their outer edges, thereby improving the strength of the coupling between the assemblies and the housings. The left and right housings may comprise protruding portions and the left and right assemblies may comprise intruding portions to accommodate the protruding portions of the left and right housings when the left and right assemblies are releasably attached to the left and right housings. The protruding portions of the housings cooperates with the intruding portions of the assemblies to function as a locating feature. This may desirably aid correct positioning of the assemblies relative to the housings during attachment of the assemblies by the wearer. Correct positioning of the assemblies relative to the housings during attachment may be particularly complicated in a scenario where the wearer attaches the assemblies to the housings in use, whilst the headgear is worn on the wearer’s head, in which case the housings may be outside of the wearer’s field of view. Forming the male locating feature of the housings by the protruding portion has the advantage that the protruding portion is dual functional. In addition to acting as a male locating feature, the protruding portion is usable to accommodate at least a part of the speaker. Thus, the volume of the protruding portion is efficiently used, which may thereby desirably allow a reduction in overall size of the headgear compared, for example, to an alternative scenario in which the male locating feature does not accommodate the speaker. The wearable air purifier may comprise a power source mounted in the headgear and a power transfer assembly to transfer energy stored in the power source to the left and right assemblies. In other words, the power source for powering the fan may be mounted directly to the headgear instead of being integrated with the left or right assemblies, and a breakable electrical coupling is provided to the assembly, the breakable coupling allowing the releasable attachment of the assembly to the headgear. Mounting the power source to the headgear, instead of to the assemblies, may desirably result in the mass of the power source being brought closer to a centre of gravity of the wearer’s head. Thereby wearer comfort may be improved. The power source may be a battery, such as a rechargeable battery. The power transfer assembly comprises a wireless power transfer assembly. The features and advantages of the wireless power transfer arrangement of the first aspect are equally applicable to and are hereby restated in respect of the wireless power transfer arrangement of the fourth aspect. The power transfer may comprise a left releasable conductive coupler to facilitate releasable conductive coupling of the left assembly to the power source and a right releasable conductive coupler to facilitate releasable conductive coupling of the right assembly to the power source, and wherein the left and right releasable conductive couplers comprise cooperating conductive contacts provided on the left and right housings and the left and right assemblies. In other words, the releasable conductive couplers accommodate the releasable attachment of the fan assembly to the headgear. The conductor assembly could directly conductively couple the power source to the assembly, or could conductively couple the power source indirectly to the assembly, for example, via a fan controller mounted to the headgear. When the left and right assemblies are rotated for attachment to the respective left and right housings, the cooperating conductive contacts may be brought into contact for at least part of the rotation for cleaning the cooperating conductive contacts. Bringing the cooperating conductive contacts in contact in this way may help to avoid and / or overcome ingress buildup. In other words, the rotation of the left and right assemblies required to releasably engage the assemblies with the left and right housings may serve a dual purpose of cleaning the electrical contacts brought into contact with each other during the rotation. Accordingly, a good electrical connection may be maintained between the housings and the assemblies without requiring additional user intervention. The wearable air purifier may comprise a nozzle attached, for example releasably attached, to the left and right assemblies to receive airflow generated by the fan and discharge the filtered airflow towards the wearer’s face. The nozzle may thus function to carry airflow from the fan closer to the wearer’s face, e.g., closer to the nose / mouth region of the wearer’s face. Thus, the assemblies may be attached to the headgear at a location relatively remote from the wearer’s face, for example, at the side, top, or rear of the wearer’s head, thereby avoiding obstructing the wearer’s face, e.g., obstructing the wearer’s vision. Whereas, notwithstanding that the assembly may be relatively remote from the wearer’s face, the filtered airflow may still be provided relatively directly to the wearer’s nose and / or mouth via the nozzle, thereby reducing dilution of the filtered airflow by unfiltered ambient air prior to inhalation. The nozzle may, for example, be arranged to extend from the assembly in front of the wearer’s face, to thereby duct airflow from the fan assembly to the front of the wearer’s face, e.g., to the wearer’s lower nasal and mouth region. According to a fifth of the invention, there is provided a fan assembly for a wearable air purifier, the fan assembly being adapted to releasably connect to headgear of the wearable air purifier, the fan assembly comprising: a left assembly releasably attachable to the headgear by way of a first mechanical coupling by rotating the left assembly with respect to the headgear in a first direction, a right assembly releasably attachable to the headgear by way of a second mechanical coupling by rotating the right assembly with respect to the headgear in a second direction opposite the first direction, and a fan operable to generate a filtered airflow provided in one of the left and right assemblies. The further features and advantages of the fan assembly of the fifth aspect are equally applicable to and are hereby restated in respect of the fan assembly of the fourth aspect. According to a sixth aspect of the invention, there is provided a head support for wearing a wearable air purifier on a wearer’s head, the support comprising: headgear for wearing on a wearer’s head, left housing supported by the headgear at a left side of the wearer’s head, a right housing by the headgear at a right side of the wearer’s head, a speaker located in one of the left and right housings, wherein, the left housing is releasably attachable to a left fan assembly by way of a first mechanical coupling by rotating the left fan assembly with respect to the left housing in a first direction, wherein, the right housing is releasably attachable to a right fan assembly by way of a second mechanical coupling by rotating the right fan assembly with respect to the right housing in a second direction opposite the first direction. The further features and advantages of the fan assembly of the sixth aspect are equally applicable to and are hereby restated in respect of the fan assembly of the fourth aspect. According to a seventh aspect of the invention, there is provided a wearable air purifier, comprising: headgear for wearing on a wearer’s head, wherein the headgear comprises: a first housing to be supported over a wearer’s ear, a second housing to be supported over a wearer’s ear, a speaker located in one of the first and second housings, a first assembly releasably attachable to the first housing by way of a first releasable coupling, and a second assembly releasably attachable to the second housing by way of a second releasable coupling, a fan operable to generate a filtered airflow provided in one of the first and second assemblies, and wherein the first and second assemblies are releasably attachable to each other by way of the first and second releasable couplings. The headgear thus forms headphones, which may be used for audio playback. The assemblies are reversibly attachable and detachable by the wearer from the headphones. The wearer may attach the assemblies to the headgear when the provision of filtered airflow by the fan is desired, and detach the assemblies from the headgear when the airflow is not desired. The headgear may thus be used without the assemblies attached, and thus without the additional mass and bulk of the assemblies. This may be useful as the wearer may desire to wear the headgear, i.e., the headphones, without the assemblies in scenarios where the filtered airflow is not desired, such as in environments with low levels of air pollution. Whereas in environments with high levels of air pollution the wearer may desire to also receive the filtered airflow to reduce their exposure to the air pollution. The headgear and components thereof may thus have dual functionality, which may desirably reduce a perceived need for the wearer to have separate air purifying and non-air purifying headgears, i.e., separate air purifying and non-air purifying headphones. The first and second assemblies being releasably attachable to each other by way of the first and second releasable couplings means that the first and second releasable couplings may perform the dual purpose of attaching the assemblies to the housings and the assemblies to each other for convenient storage. The fan is operable to generate filtered airflow to be discharged from the wearable air purifier for inhalation by the wearer. The assemblies may comprise an outlet for discharging the filtered airflow directly out of the wearable air purifier for inhalation by the wearer. The filtered airflow directly discharged from the assemblies may be directed towards the wearer’s face, past the wearer’s face and / or generally towards the vicinity of the wearer's face. The headgear may further comprise an additional speaker located in the other of the first and second housings to the speaker. In other words, speakers may be provided in both housings, thereby improving the quality of the audio playback. The wearable air purifier may comprise an additional fan operable to generate a filtered airflow provided in the other of the first and second assemblies to the fan. In other words, both assemblies may be provided with fans, thereby improving the filtered air flow capabilities of the wearable air purifier. The first assembly may be releasably attachable to the second housing by way of at least part of the first releasable coupling and at least part of the second releasable coupling, and wherein the second assembly is releasably attachable to the first housing by way of at least part of the second releasable coupling and at least part of the first releasable coupling. In other words, the first and second assemblies may be interchangeably connected to the housings using the same releasable couplings, thereby further reducing the burden of the wearer when attaching the assemblies to the headgear. The first housing may be a right housing to be supported over a wearer’s right ear and the first assembly is a right assembly, and wherein the second housing may be a left housing to be supported over a wearer’s left ear and the second assembly is a left assembly, In other words, the housings may be adapted to be supported over the wearer’s ears when the headgear is worn. The first releasable coupling may comprise a first attachment feature provided on or in one of the first housing and the first assembly, and a second attachment feature provided on or in the other of the first housing and the first assembly. In other words, the attachment features may be provided on the surfaces of the housings and the assemblies and / or within the housings and assemblies. Both the first and second attachment features may comprise a magnet. By providing a magnet as the means of releasably attaching the first assembly to the first housing, the process of attaching the assembly to the housing is greatly simplified for the wearer. For example, to attach the assembly to the housing, the wearer may simply bring the assembly into close proximity with the housing in order to engage the first releasable coupling and is not required to rotate or actuate a locking mechanism separately. Similarly, to detach the assembly from the housing, the wearer may simply pull the assembly away from the housing in order to disengage the first releasable coupling and is not required to rotate or actuate a locking mechanism separately. Further, as magnets do not require direct contact in order to attach to each other, the assembly may attach to the housing in a variety of different orientations without reducing the attachment strength of the first releasable coupling. One of the first attachment feature and the second attachment feature may comprise a magnet and the other of the first attachment feature and the second attachment feature may comprise a ferromagnetic element. In other words, the assembly and / or the housing may include an element that a magnet may attract. Thus, the first releasable coupling may comprise a magnet-ferromagnetic element coupling. The magnet may comprise a ring magnet. In other words, the magnet may be provided in the shape of a ring. In this way, the magnet may be arranged concentrically with substantially circular features or components of the housing, such as the protruding portion. The second releasable coupling may comprise a third attachment feature provided on or in one of the second housing and the second assembly, and a fourth attachment feature provided on or in the other of the second housing and the second assembly. In other words, the attachment features may be provided on the surfaces of the housings and the assemblies and / or within the housings and assemblies. Both the third and fourth attachment features may comprise a magnet. By providing a magnet as the means of releasably attaching the second assembly to the second housing, the process of attaching the assembly to the housing is greatly simplified for the wearer. For example, to attach the assembly to the housing, the wearer may simply bring the assembly into close proximity with the housing in order to engage the first releasable coupling and is not required to rotate or actuate a locking mechanism separately. Similarly, to detach the assembly from the housing, the wearer may simply pull the assembly away from the housing in order to disengage the first releasable coupling and is not required to rotate or actuate a locking mechanism separately. Further, as magnets do not require direct contact in order to attach to each other, the assembly may attach to the housing in a variety of different orientations without reducing the attachment strength of the first releasable coupling. One of the third attachment feature and the fourth attachment feature may comprise a magnet and the other of the third attachment feature and the fourth attachment feature may comprise a ferromagnetic element. In other words, the assembly and / or the housing may include an element that a magnet may attract. Thus, the first releasable coupling may comprise a magnet-ferromagnetic element coupling. The magnet may comprise a ring magnet. In other words, the magnet may be provided in the shape of a ring. In this way, the magnet may be arranged concentrically with substantially circular features or components of the housing, such as the protruding portion. The first, second, third and fourth attachment features may each comprise a plurality of magnets arranged in arrays having complimentary polarities. In other words, the magnets of the attachment features across the first and second assemblies and housings may be arranged in arrays having complimentary polarities. For example, where a magnet of a first attachment feature on a first assembly has a North pole, a corresponding magnet of the second attachment feature on the first housing and a magnet of the third attachment feature on the second assembly may have a South pole. In this case, the corresponding magnet of the fourth attachment feature on the second housing may have a North pole. The magnets in the arrays may have alternating polarities. In other words, the first, second, third and fourth attachment features may be releasably attached to any of the other attachment features simply by rotating the given assemblies and / or housings to offset the magnets arrays by one magnet. The arrays may further comprise one or more ferromagnetic elements. In other words, the assembly and / or the housing may include an element that a magnet may attract. Thus, the first releasable coupling may comprise a magnet-ferromagnetic element coupling. The first, second, third and fourth attachment features may comprise a mechanical coupling. The further features and advantages of the mechanical coupling of the fourth aspect are equally applicable to and are hereby restated in respect of the first and second assemblies of the seventh aspect. The wearable air purifier may further comprise an outlet provided on the one of the first and second assemblies comprising the fan, wherein the outlet is adapted to discharge the filtered airflow from the wearable air purifier for inhalation by the wearer. In other words, the first and second assemblies comprise an outlet for discharging the filtered airflow from the wearable air purifier for inhalation by the wearer. The filtered airflow discharged from the fan assembly may be directed towards the wearer’s face, past the wearer’s face and / or generally towards the vicinity of the wearer's face. When the assemblies are attached to the housings, the assemblies may be rotatably connected to the housings at one of a plurality of rotational positions for varying a position of the outlet relative to the headgear. In other words, the assemblies, and so the outlet, may be rotatable relative to the headgear. Rotation of the outlet relative to the headgear may be desirable as it allows the position of the outlet relative to the wearer’s face to be varied, and so adjustment of the trajectory of airflow discharged by the fan assembly, for example, to accommodate for different sizes of different wearer’s heads. In particular, rotation of the fan housing complete with the outlet allows rotation of the outlet relative to the headgear without rotation relative to the housing, thereby avoiding a requirement for a rotatable fluid coupling. The first and second housing may comprise a protruding portion and the first and second assembly may comprise an intruding portion to accommodate the protruding portion of the housings when the assemblies are attached to the housings, and optionally wherein the releasable coupling is provided radially outward of an outer circumference of the protruding and intruding portions. The protruding portion of the speaker housing cooperates with the intruding portion of the fan assembly to function as a locating feature. This may desirably aid correct positioning of the assembly relative to the housing during attachment of the assembly by the wearer. Correct positioning of the assembly relative to the housing during attachment may be particularly complicated in a scenario where the wearer attaches the assembly to the headgear in use, whilst the headgear is worn on the wearer’s head, in which case the housing may be outside of the wearer’s field of view. Forming the male locating feature of the headgear by the protruding portion of the housing has the advantage that the protruding portion is dual functional. In addition to acting as a male locating feature, the protruding portion is usable to accommodate at least a part of the speaker. Thus, the volume of the protruding portion is efficiently used, which may thereby desirably allow a reduction in overall size of the headgear compared, for example, to an alternative scenario in which the male locating feature does not accommodate the speaker. The wearable air purifier may comprise a power source mounted in the headgear and a power transfer assembly to transfer energy stored in the power source to the first and second assemblies. In other words, the power source for powering the fan may be mounted directly to the headgear instead of being integrated with the first and second assemblies, and a breakable electrical coupling is provided to the assembly, the breakable coupling allowing the releasable attachment of the assembly to the headgear. Mounting the power source to the headgear, instead of to the first and second assemblies, may desirably result in the mass of the power source being brought closer to a centre of gravity of the wearer’s head. Thereby wearer comfort may be improved. The wearable air purifier may comprise a nozzle attachable to the first and second assemblies to receive airflow generated by the first and second assemblies and discharge the airflow towards the wearer’s face and optionally wherein the nozzle is releasably attachable to the first and second assemblies. The nozzle may thus function to carry airflow from the first and second assemblies closer to the wearer’s face, e.g., closer to the nose / mouth region of the wearer’s face. Thus, the first and second assemblies may be attached to the headgear at a location relatively remote from the wearer’s face, for example, at the side, top, or rear of the wearer’s head, thereby avoiding obstructing the wearer’s face, e.g., obstructing the wearer’s vision. Whereas, notwithstanding that the first and second assemblies may be relatively remote from the wearer’s face, the filtered airflow may still be provided relatively directly to the wearer’s nose and / or mouth via the nozzle, thereby reducing dilution of the filtered airflow by unfiltered ambient air prior to inhalation. The nozzle may, for example, be arranged to extend from the fan assembly in front of the wearer’s face, to thereby duct airflow from the first and second assemblies to the front of the wearer’s face, e.g., to the wearer’s lower nasal and mouth region. The nozzle may comprise a flexible portion adapted to deform when then nozzle is attached to the first and second assemblies and the first and second assemblies are releasably attached to each other by way of the releasable coupling. In other words, the nozzle may flex to allow the assemblies to move towards and away from each other without becoming damaged or decoupling. When the first and second assemblies are attached to each other, a height of the first and second assemblies may be less than a distance between the first and second housings. According to a eighth aspect of the invention, there is provided a fan arrangement for a wearable air purifier comprising first and second housing, the fan arrangement comprising: a first assembly releasably attachable to the first housing by way of a first releasable coupling; a second assembly releasably attachable to the second housing by way of a second releasable coupling; and a fan operable to generate a filtered airflow to the wearer provided in one of the first and second assemblies; wherein the first and second assemblies are releasably attachable to each other by way of the first and second releasable couplings. The further features and advantages of the first and second assemblies of the seventh aspect are equally applicable to and are hereby restated in respect of the fan arrangement of the eighth aspect. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a perspective view of a wearable air purifier according to an aspect of the invention. Figure 2 shows a perspective view of a wearable air purifier with the fan assemblies detached according to an aspect of the invention. Figure 3 shows a cross sectional view of a wearable air purifier according to an aspect of the invention. Figure 4 shows a cross sectional view of a connected fan assembly and speaker housing according to an aspect of the invention. Figure 5 shows a cross sectional view of a connected fan assembly and speaker housing according to an aspect of the invention. Figure 6 shows a perspective view of a portion of a mechanical coupling on a speaker housing according to an aspect of the invention. Figure 7 shows a perspective view of a portion of a mechanical coupling on a fan assembly according to an aspect of the invention. Figure 8 shows an elevation view of a fan assembly and a speaker housing partially attached by way of a mechanical coupling. Figure 9 shows a left side view of a wearable air purifier according to an aspect of the invention. Figure 10 shows a right side view of a wearable air purifier according to an aspect of the invention. Figure 11 shows a perspective view of two fan assemblies according to an aspect of the invention. Figure 12 shows a perspective view of a speaker housing according to an aspect of the invention. Figure 13 shows a schematic representation of a wearable air purifier arranged for storage. DETAILED DESCRIPTION A wearable air purifier 101, embodying aspects of the present disclosure, is shown schematically in Figure 1. As will be described in further detail herein, the wearable air purifier 101 is configured to be worn on a wearer’s head and deliver a filtered airflow towards a lower nasal and mouth region of a wearer’s face. Consequently, the wearer’s exposure to ambient air pollution may desirably be reduced. The wearable air purifier 101 comprises headgear 102 for mounting on a wearer’s head, a pair of left and right fan assemblies 103, 104, such as fan assemblies for generating filtered airflows, and a detachable nozzle 105 for directing the airflows from the fan assemblies 103, 104 towards the lower nasal and mouth region of the wearer’s face. In some examples, the nozzle may be removed from the wearable air purifier and the filtered airflows discharged directly from the fan assemblies for inhalation by the user. The headgear 102 has the form of over-the-ear headphones, and comprises a headband 106 and left and right ear cups 107, 108 connected to respective ends of the headband 106. The headband 106 is arcuate, and is configured to overlie a top and sides of the wearer’s head in use, to thereby support the earcups 107,108 over the wearer’s left and right ears respectively. The headband 106 is formed to resiliently hold the earcups 107, 108 against opposite sides, i.e., left and right sides respectively, of the wearer’s head, to thereby firmly retain the headgear 102 mounted on the wearer’s head. The headband 106 is resiliently flexible to accommodate differing distances between the ear cups, and so differing head widths. The earcups 107, 108 are pivotally mounted to the ends of headband 106, to facilitate pivoting of the ear cups 107, 108 to accommodate different head shapes. The left and right earcups 107, 108 comprise respective housings for housing components, such as respective speakers. The speakers in the earcups 107, 108 may thus be supported by the headgear 102 over the wearer’s ears, e.g., to facilitate use of the headgear 102 as headphones. The earcups 107, 108 comprise respective annular cushions 109, 110 for cushioning against the wearer’s head. The fan assemblies 103, 104 are releasably attachable to a respective one of the earcups 107, 108, such that the headgear 102 may releasably support the fan assemblies 103, 104 at left and right sides respectively of the wearer’s head. The releasable attachment of the fan assemblies 103,104 to the ear cups 107, 108 will be described in further detail with reference to later Figures; however, the releasable attachment may be realised through a mechanical couple or a magnet coupling. The nozzle 105 is attachable at left and right ends 111, 112 to a respective one of the fan assemblies 103, 104 of the headgear 102. The nozzle 105 defines air inlets at the left and right ends 111, 112, to mate with respective air outlets of the fan assemblies 103, 104, to thereby receive filtered airflow from the fan assemblies 103, 104 when so attached. The nozzle 105 is configured to extend from the left and right ends 111, 112 width-wise across the wearer’s face. The nozzle 105 comprises an air outlet at a central region approximately mid-way between the left and right ends 111, 112, to be positioned approximately directly in front of and facing the wearer’s lower nasal and mouth region, in use. The nozzle 105 thus functions to duct filtered airflows from the fan assemblies 103, 104, supported at the sides of the wearer’s head, to the central outlet of the nozzle 105, and for discharging the airflows therefrom towards the lower nasal and mouth region of the wearer’s face. In use, when the fan assemblies 103, 104 are attached to the earcups 107, 108 respectively, and the nozzle 105 is attached to the fan assemblies, the headgear 102 thereby supports the nozzle 105 in front of the wearer’s face. In particular, in result of the nozzle 105 being attached to the headgear 102, via the fan assemblies 103, 104, on opposite, left and right, sides of the wearer’s head, the nozzle 105 is well supported and less prone to unintended movement, e.g., vibration of the nozzle 105 in use. In comparison, coupling of the nozzle 105 to the headgear 102 at only one side of the wearer’s head, for example, at the left end 111 only, may result in a torque being exerted on the single coupling by the mass of the nozzle, and may result in excessive undesired movement of the nozzle in use. Like the headband 102, the nozzle 105 is configured to be flexible in a width dimension, i.e., parallel to the width dimension of the wearer’s head, so as to allow a distance between the point of coupling of the nozzle 105 to the headgear 102 to be varied. This flexibility advantageously allows the nozzle 105 also to accommodate differing distances between the fan assemblies 103, 104. This may advantageously accommodate differing distances between the ear cups 107, 108, and thus differing widths of wearers’ heads. Additionally, the flexibility of the nozzle 105 may desirably aid attachment and detachment of the fan assemblies 103, 104 to the ear cups 107, 108 respectively, as will be described in further detail with reference to later Figures. In examples, the nozzle 105 is configured to not contact the wearer’s face, such that it is supported by the headgear 102 a short distance in front of the wearer’s face. This non-contact configuration may advantageously improve wearer comfort, inasmuch that the potential for skin irritation or other discomfort caused by contact of the nozzle 105 with the wearer’s face is reduced. Referring next in particular to Figure 2, because the fan assemblies 103, 104 are releasably attachable to a respective one of the earcups 107, 108 of the headgear 102, the fan assemblies 103, 104, and the nozzle 105 releasably attached thereto, may be releasably attached and detached from the headgear 102 by the wearer. In examples, the fan assemblies 103, 104 and the nozzle 105 are configured to be attachable to and detachable from the headgear as an assembly, in which the nozzle 105 remains attached to the fan assemblies 103, 104 during attachment / detachment of the fan assemblies 103, 104 to / from the headgear 102. Thus the wearer may attach the fan assemblies 103, 104 to the headgear 102 when the wearer desires the provision of filtered airflow, such as when the wearer is in an environment with relatively high levels of environmental air pollution, and the wearer may detach the fan assemblies 103, 104 from the headgear 102 when the filtered airflow is not desired, such as when the wearer is in an environment with relatively low levels of environmental air pollution. The headgear 102 may thus be used in the latter scenario without the fan assemblies 103, 104 attached, and thus without the additional mass and bulk of the fan assemblies 103, 104. For example, the headgear may be used by the wearer simply as headphones for audio playback. The headgear 102 and components thereof, to be described in further detail with reference to later figures, may thus have dual functionality, which may desirably reduce a perceived need for the wearer to have separate air purifying and non-air purifying headphones. Because the nozzle 105 attaches directly to the fan assemblies 103, 104, the fan assemblies 103, 104 and the nozzle 105 may be attached to and detached from the headgear 102 as an assembly, which may allow convenient attachment and detachment of the fan assemblies 103, 104 and nozzle 105 with respect to the headgear 102. In comparison, if the nozzle 105 were to attach to the headgear 102, for example to the earcups 107, 108, instead of directly to the fan assemblies 103, 104, the wearer may be required to separately attach and detach both the nozzle 105 and the fan assemblies 103, 104 from the headgear 102, which may be relatively inconvenient for the wearer. Additionally, because the nozzle 105 attaches directly to the fan assemblies 103, 104, rather than, for example, attaching to the ear cups 107, 108 or the headgear 102 more generally, the fan assemblies 103, 104 are not required to releasably fluidly couple to the ear cups 107, 108 or the headgear 102 more generally to deliver filtered airflow to flow to the nozzle 105. Indeed, in this configuration, the nozzle 105 is not required to fluidly couple to the headgear 102 to receive the filtered airflows, and thus a risk of airflow leakage between the fan assembles 103, 104 and the nozzle 105 may be reduced. The nozzle 105 could be releasably attached to the fan assemblies 103, 104, for example, by magnet couplings, clips, or releasable catches. Thus, the nozzle 105 may be detachable by the wearer from the fan assemblies 103, 104, for example, to facilitate ex-situ cleaning of the nozzle 105. Further, the fan assembles 103, 104 may be utilized without the nozzle to discharge the filtered airflow directly from the fan assemblies for inhalation by the user. In other examples, nozzle 105 could be non-releasably attached to the fan assemblies 103, 104. For example, the nozzle 105 could be structurally integral with housings of the fan assemblies 103, 104. To assist the wearer with the releasable attachment of the fan assemblies 103, 104 to the ear cups 107, 108 respectively, each of the ear cups 103, 104 is provided with a male locating feature, in the form of a protruding portion 301, and each of the ear cups is provided with a corresponding female locating feature, in the form of intruding portion 302. The protruding portion 301 of each earcup 107, 108 cooperates with the intruding portion 302 of the respective fan assembly 103, 104 to function as a locating feature. This may desirably aid correct positioning of the fan assembly 103, 104 relative to the headgear 102 during attachment of the fan assemblies 103, 104 by the wearer. Each of the ear cups 107, 108 defines a mating surface 304, that is flat and generally annular and extends around the circumference of the protruding portion 301. The fan assemblies 103, 104 each similarly define a flat and generally annular mating surface 303 extending around the circumference of the intruding portion x. The mating surfaces 303, 304 of the fan assemblies 103, 104 and the ear cups 107, 108 are arranged to contact when the fan assemblies 103, 104 are attached to the respective ear cups 107, 108, to thereby stably support the fan assemblies 103, 104 relative to the headgear 102. Referring next in particular to Figure 3, in examples the fan assemblies 103, 104 are substantially alike, as are the earcups 107, 108, and also the mechanism of attachment of the fan assemblies 103, 104 to the earcups 107, 108. Thus, for brevity, only fan assembly 104 and right ear cup 108 will be described in detail herein, on the understanding that substantially the same teachings apply to fan assembly 103 and left ear cup 107. Headgear 102 comprises batteries 501, 502 located in cushions 109, 110 of the headband 106, and conductor assembly 503 for electrically coupling the batteries 501, 502 and for electrically coupling the batteries 501, 502 to components of the ear cup 104 and the fan assembly 108. The batteries 501, 502 each comprise two cells. The ear cup 104 comprises speaker housing 504 attached to an end of the headband 106. The speaker housing 504 is substantially hollow, and defines the protruding portion 302 and the mating surface 303. The protruding portion 301 is generally frustoconical in shape, and narrows progressively in area in the direction of protrusion. The mating surface 303 is flat and generally annular, and extends around the circumference of the protruding portion 301. A speaker 505 is located in the speaker housing 504, and is supplied with electrical power by the batteries 501, 502 via the conductor assembly 503. A rear part of the speaker 505 is located within the part of the volume of the speaker housing 504 defined by the protruding portion 301. The fan assembly 104 comprises fan housing 506. The fan housing 506 defines intruding portion 302. The intruding portion 302 defines a generally frustoconical intrusion into the fan assembly 104, that narrows in area progressively in the direction of intrusion. Mating surface 303 that is flat and generally annular, and extends around the circumference of the intruding portion 302. The fan housing 506 is hollow, and a motor driven fan 508, fan controller, and an air filter are located therein (an example fan filter 510 is shown in Figure 3 in only one ear cup 107). The motor driven fan 508 is supplied with electrical power by the batteries 501, 502 via a wireless power transfer assembly, described in further detail below, and the fan controller. The fan housing 506 comprises inlet aperture(s) 511 and an outlet aperture, from which the filtered air may be discharged. The outlet aperture 512 may also fluidly couple with an inlet at the right end 112 of the nozzle 105 when the nozzle 105 is attached to the fan housing 506. Fan 508 is thus controllable by the fan controller to draw air in through inlets 511, via a filter when present, and discharge the filtered airflow via the outlet, as described previously with reference to earlier Figures. When the fan assembly 104 is attached to the ear cup 108, the protruding portion 301 of the ear cup 108 is accommodated in the intruding portion 302 of the fan assembly 104, such that the protruding portion 301 fills substantially the whole volume of the intruding portion 302, and the surface of the protruding portion 301 contacts the surface of the intruding portion 302. In this attached condition, the mating surface 303 of the fan assembly 104 is in contact with the mating surface 304 of the ear cup 108. Figures 4 and 5 show a cross sectional view of an ear cup 108 of a wearable air purifier according to an aspect of the invention, such as those shown in Figures 1 to 3. Features in common with those shown in previous Figures are labelled using the same reference numerals. In the examples shown in Figures 4 and 5, the wearable air purifier comprises a wireless power transfer assembly in the form of a first wireless coupling device 601, and specifically an electromagnetic coil, provided in the speaker housing and a second wireless coupling device 602, and specifically an electromagnetic coil, provided in the fan assembly. The wireless power transfer assembly is configured to wirelessly transfer energy stored in the battery to the fan assembly via the first and second wireless coupling devices. In particular, as both the first and second wireless coupling devices are electromagnetic coils, the wireless power transfer assembly is configured to wirelessly transfer the energy stored in the battery to the fan assembly via inductive coupling between the two coils. In the specific example shown in Figure 4, the first wireless coupling device 601 is provided radially inward of an outer circumference of the protruding portion 301 of the speaker housing and the second wireless coupling device 602 is provided radially inward of an outer circumference of the intruding portion 302 of the fan assembly. In the specific example shown in Figure 5, the first wireless coupling device 601 is provided radially outward of an outer circumference of the protruding portion 301 of the speaker housing and the second wireless coupling device 602 is provided radially outward of an outer circumference of the intruding portion 302 of the fan assembly. In both cases, the when the fan assembly is attached to the speaker housing, the first wireless coupling device 601 and the second wireless coupling device 602 are concentrically aligned due to the contact of the protruding portion 301 with the intruding portion 302. The alignment of the first wireless coupling device 601 and the second wireless coupling device 602 is a key factor in the strength and efficiency of the wireless transfer of power across an inductive coupling. Another factor that affects the strength and efficiency of the wireless transfer of power across an inductive coupling is the space between the coupling devices. Accordingly, the first coupling device 601 and the second coupling device may be arranged such that, when the fan assembly is attached to the speaker housing, the first wireless coupling device is spaced from second wireless coupling device by less than 1cm. For example, this may be achieved by reducing the wall thickness of the mating surfaces 303, 304 and / or the intruding portion 302 and the protruding portion 301. As the power transfer between the headgear and the fan assembly is performed wirelessly between the first coupling device 601 and the second coupling device 602, the fan assembly may be connected to the headgear at one of a plurality of rotational positions whilst still maintaining the inductive coupling between the coupling devices. Indeed, the fan assembly may be rotated through a full 360° rotation without decoupling the wireless power transfer assembly. If the fan assembly is releasably attachable to the headgear by way of a magnet coupling, the fan assembly could connect to the speaker housing in any rotational position as there are no physical connections to limit the rotational positioning of the fan assembly relative to the speaker housing. In the examples shown in Figures 4 and 5, the speaker housing further comprises a controller 603 connected, as illustrated by dotted line 604, to the first coupling device 601 and the battery 501, 502. The controller 603 is adapted to generate an alternating signal from a power output from the battery and transmit the alternating signal to the first coupling device 601 at a frequency of at least 1MHz. In the examples shown in Figures 4 and 5, the fan 508, the second coupling device 602, the first coupling device 601 and the speaker 505 are all substantially concentrically aligned along a single axis. Each of these components utilise an oscillating magnetic field in order to function and by aligning them concentrically along a single axis the interference between the different components may be reduced. Figures 6 and 7 show an example of a first mechanical coupling for releasably attaching a left assembly 701, such as a fan assembly, to a left housing 702, such as a speaker housing. Figure 8 shows an example of the first mechanical coupling when the left assembly 701 is partially attached to the left housing 702. As shown in the examples above, a wearable air purifier according to the invention may include left and right housings, to be supported at either side of the wearer’s head by the headgear, and left and right assemblies to releasably attached thereto. Other than the handiness of the mechanical couplings described below, the left and right fan assemblies are substantially alike, as are the left and right housings. Thus, for brevity, only the first mechanical coupling of the left assembly 701 and the left housing 702 will be described in detail herein, on the understanding that substantially the same teachings apply to the second mechanical coupling of the right fan assembly and the right housing. In the examples shown in Figures 6, 7 and 8, the first mechanical coupling comprises two first bayonet assemblies provided 180° about a central axis of the left assembly and housing and two first locking assemblies provided 180° about a central axis of the left assembly and housing. The first bayonet assemblies and the first locking assemblies are arranged in an alternating order about an axis of rotation of the left assembly 701. Further, the first mechanical coupling is provided adjacent an outer perimeter of the left housing 702 and the left assembly 701. Looking first to one of the first bayonet assemblies, the first bayonet assembly comprises a bayonet projection 703 provided on the left assembly 701. On the left housing 702, the first bayonet assembly comprises a cavity 704 adapted to receive the bayonet projection. The cavity 704 comprises an opening 705 and a securing end 706 at an end of the cavity opposite the opening. The cavity receives the bayonet projection 703 at the opening 705 and the bayonet projection is moved from the opening 705 to the securing end 706 by the rotation of the left assembly 701 with respect to the left housing 702 in the first direction 707 in order to attach the left assembly to the left housing. The first locking assembly comprises a first resilient arm 708 provided on the left assembly 701 comprising a first projection 709. On the left housing 702, the first locking assembly comprises a first receiving portion having a first track 710 having a first ridge section 711 connected to a first seat section 712. Rotation of the left assembly in the first direction 707 relative to the left housing 702 forces the first resilient arm 708 to deflect so that the first projection 709 passes over the first ridge section 711. Once the first projection 709 passes over the first ridge section 711, the first resilient arm 708 to return towards a rest state as the first projection 709 enters the first seat section 712 so as to releasably rotationally inhibit rotation of the left assembly and the left housing. The first track 710 further comprises a stop section 713 connected to the first seat section 712 adapted to engage with the projection 709 when the first projection is in the first seat section to inhibit rotation of the left assembly relative to the left housing in the first direction 707. The left housing 702 also comprises sloping portions 714a and 714b to contact bayonet projection 703 and resilient arm 708, respectively, which act to guide these features to the correct location for releasably coupling the left assembly to the left housing. Further, when rotating the left assembly in the second direction, the slopes 714a, 714b act to effectively eject the left assembly from the left housing attachment features, thereby facilitating the removal of the left assembly form the left housing by the wearer. The left assembly and the left housing may include a wireless power transfer assembly as described above. However, in the examples shown in Figures 6, 7 and 8, there are cooperating conductive contacts 715a, 715b provided on the provided on the left housing and the left assembly, respectively, for transferring power from the battery to the left assembly, via the left housing. The cooperating conductive contacts are brought into contact for at least part of the rotation for attaching the left housing and the left assembly, which cleans the cooperating conductive contacts through friction. Figures 9 and 10 illustrate a left side view 720 and a right side view 721 of the left 701 and right 722 assemblies and the nozzle 105 being attached to the headgear 102. As the left assembly 701 and the right assembly 722 are mirrored with respect to each other either side of the sagittal plane of the wearer’s head, the engagement rotation of the left assembly in the first direction 707 and the rotation of the right assembly in the second direction 727, which is opposite the first, means that the wearer can attach the assemblies to the headgear by performing the same motion with each hand. As the assemblies are attached to the headgear, the nozzle is raised from a first nozzle position 105a to a second nozzle position 105b. Figure 11 shows a perspective view of a left fan assembly 801 and a right fan assembly 802 that are releasably attachable to each other by way of first and second releasable couplings. In the particular example shown in Figure 11, the first and second releasable couplings comprise attachment features in the form of a plurality of magnets. The left fan assembly 801 includes a plurality of magnets 803 as a first attachment feature and the left fan assembly 802 includes a plurality of magnets 804 as a third attachment feature. In this example the first and second housings of the headgear comprise the second and fourth attachment features, which may also include a similarly arranged plurality of magnets. The magnets of the first and third attachment features have complimentary polarities, such that the first and second assemblies may releasably attach to each other. Figure 12 shows a perspective view of a left speaker housing 805 including a plurality of magnets 806 as a second attachment feature. The magnets 803 of the first attachment feature shown in Figure 11 and the magnets 806 of the second attachment feature shown in Figure 12 have complimentary polarities, such that the left fan assembly 801 and the left speaker housing 805 may releasably attach to each other. Figure 13 shows a schematic representation of a storage arrangement of the wearable air purifier, such that the headgear 102 is separate from the left and right fan assemblies 801, 802 and the nozzle 105. The left and right fan assemblies 801, 802 are releasably attached to each other as described above. In addition, the nozzle 105 is releasably attached the left and right fan assemblies 801, 802. The nozzle 105 comprises a flexible portion 903 adapted to deform when then nozzle is attached to the left and right fan assemblies 801, 802 and the left and right fan assemblies 801, 802 are releasably attached as shown in Figure 13. The folded nozzle 105 fits mostly within the space between the headgear, which may aid storage. As shown in Figure 13, when the first and second assemblies are attached to each other, the height 901 of the first and second assemblies is less than a distance 902 between the first and second housings of the headgear to allow for an efficient storage arrangement.

Claims

1. A wearable air purifier, comprising:headgear for wearing on a wearer’s head, wherein the headgear comprises: a first housing to be supported over a wearer’s ear, a second housing to be supported over a wearer’s ear, a speaker located in one of the first and second housings,a first assembly releasably attachable to the first housing by way of a first releasable coupling, anda second assembly releasably attachable to the second housing by way of a second releasable coupling,a fan operable to generate a filtered airflow provided in one of the first and second assemblies,and wherein the first and second assemblies are releasably attachable to each other by way of the first and second releasable couplings.

2. The wearable air purifier of claim 1, wherein the headgear further comprises an additional speaker located in the other of the first and second housings to the speaker.

3. The wearable air purifier of any preceding claim, wherein the wearable air purifier comprises an additional fan operable to generate a filtered airflow provided in the other of the first and second assemblies to the fan.

4. The wearable air purifier of any preceding claim, wherein the first assembly is releasably attachable to the second housing by way of at least part of the first releasable coupling and at least part of the second releasable coupling, and wherein the second assembly is releasably attachable to the first housing by way of at least part of the second releasable coupling and at least part of the first releasable coupling.

5. The wearable air purifier of any of claims 1 to 3, wherein the first housing is a right housing to be supported over a wearer’s right ear and the first assembly is a right assembly,and wherein the second housing is a left housing to be supported over a wearer’s left ear and the second assembly is a left assembly,6. The wearable air purifier of any preceding claim, wherein the first releasable coupling comprises a first attachment feature provided on or in one of the first housing and the first assembly, and a second attachment feature provided on or in the other of the first housing and the first assembly.

7. The wearable air purifier of claim 6, wherein both the first and second attachment features comprises a magnet.

8. The wearable air purifier of claim 6, wherein one of the first attachment feature and the second attachment feature comprises a magnet and the other of the first attachment feature and the second attachment feature comprises a ferromagnetic element.

9. The wearable air purifier of claim 7 or 8, wherein the magnet comprises a ring magnet.

10. The wearable air purifier of any preceding claim, wherein the second releasable coupling comprises a third attachment feature provided on or in one of the second housing and the second assembly, and a fourth attachment feature provided on or in the other of the second housing and the second assembly.

11. The wearable air purifier of claim 10, wherein both the third and fourth attachment features comprises a magnet.

12. The wearable air purifier of claim 10, wherein one of the third attachment feature and the fourth attachment feature comprises a magnet and the other of the third attachment feature and the fourth attachment feature comprises a ferromagnetic element.

13. The wearable air purifier of claim 11 or 12, wherein the magnet comprises a ring magnet.

14. The wearable air purifier of claims 7 and 11, wherein the first, second, third and fourth attachment features each comprise a plurality of magnets arranged in arrays having complimentary polarities.

15. The wearable air purifier of claim 14, wherein the magnets in the arrays have alternating polarities.

16. The wearable air purifier of any of claims 14 to 15, wherein the arrays further comprise one or more ferromagnetic elements.

17. The wearable air purifier of claims 6 and 10, wherein the first, second, third and fourth attachment features comprise a mechanical coupling.

18. The wearable air purifier of any preceding claim, wherein the wearable air purifier further comprises an outlet provided on the one of the first and second assemblies comprising the fan, wherein the outlet is adapted to discharge the filtered airflow from the wearable air purifier for inhalation by the wearer.

19. The wearable air purifier claimed in claim 18, wherein, when the assemblies are attached to the housings, the assemblies are rotatably connected to the housings at one of a plurality of rotational positions for varying a position of the outlet relative to the headgear.

20. The wearable air purifier of preceding claim, wherein the first and second housing comprises a protruding portion and the first and second assembly comprises an intruding portion to accommodate the protruding portion of the housings when the assemblies are attached to the housings, and optionally wherein the releasable coupling is provided radially outward of an outer circumference of the protruding and intruding portions.

21. The wearable air purifier of any one of the preceding claims, comprising a power source mounted to the headgear and a power transfer assembly to transfer energy stored in the power source to the first and second assemblies.

22. The wearable air purifier of any one of the preceding claims, comprising a nozzle attachable to the first and second assemblies to receive airflow generated by the first and second assemblies and discharge the airflow towards the wearer’s face and optionally wherein the nozzle is releasably attachable to the first and second assemblies.

23. The wearable air purifier of claim 22, wherein the nozzle comprises a flexible portion adapted to deform when then nozzle is attached to the first and second assemblies and the first and second assemblies are releasably attached to each other by way of the releasable coupling.

24. The wearable air purifier of any one of the preceding claims, wherein, when the first and second assemblies are attached to each other, a height of the first and second assemblies is less than a distance between the first and second housings.

25. A fan arrangement for a wearable air purifier comprising first and second housings, the fan arrangement comprising:a first assembly releasably attachable to the first housing by way of a first releasable coupling;a second assembly releasably attachable to the second housing by way of a second releasable coupling; anda fan operable to generate a filtered airflow to the wearer provided in one of the first and second assemblies;wherein the first and second assemblies are releasably attachable to each other by way of the first and second releasable couplings.

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