Hair care device

Abstract

A hair care device is described. The device includes a housing 12, and a resonator element 14. The resonator element has an active region 22 that extends along at least a portion of the housing that is configured to contact a user’s hair in use, and the active region is vibratable relative to the housing. The device also includes an exciter assembly 26 which is configured to vibrate the active region of the resonator element to cause the resonator element to resonate as a standing wave. The resonant vibrations of the resonator assembly urge portions of the hair towards one or more nodes of the standing wave, thereby controlling the location of the hair. The resonator element may be applied to hair care attachments such as a hair curler or hair straighteners.

Description

BACKGROUND It is known to provide a hair care device (e.g. a brush or electric hair styling appliance) having bristles. The bristles may be distributed along the device, to be moved against hair for removing knots from hair or applying tension to hair during heat styling. Different configurations of bristles (e.g. different materials, thicknesses, or separations) may be suitable for different hair types and / or applications. SUMMARY The present disclosure provides a hair care device comprising: a housing; a resonator element having an active region extending along at least a portion of the housing configured to contact a user’s hair in use, the active region being vibratable relative to the housing; and an exciter assembly configured to vibrate the active region of the resonator element to cause the resonator element to resonate as a standing wave for urging portions of the hair toward one or more nodes of the standing wave via resonant vibrations. As used herein, the term “standing wave” takes its normal meaning in the art, referring to a wave that oscillates in time but whose peak amplitude profile does not move in space. By resonating (vibrating) as a standing wave, the resonator element will form one or more antinodes (“peaks” and “troughs”) and nodes. This resonating vibration creates local areas of movement, which can be used to control hair. Each antinode may effectively be considered to provide a “virtual bristle”, in that hair will preferentially move towards a vibrational node rather than an antinode. Accordingly, by vibrating the resonator element to cause the resonator element to resonate as a standing wave, the present device can bias (encourage, urge, agitate, displace, push) hair towards a particular zone of the device, without requiring physical means (e.g. bristles) which can damage the hair. The device can therefore be more compact, and can guide hair towards a particular position in a gentle manner, thereby mitigating hair damage or over-stretching. The standing wave may be described herein in terms of its frequency, amplitude, phase, or wavelength. The frequency affects the spacing between nodes, which can be considered as analogous to the spacing of bristles along a hairbrush. Increasing the frequency may be considered analogous to increasing the number of bristles, thereby dividing the hair into smaller tresses which are strongly gripped between adjacent bristles (nodes) in use. The amplitude affects the size (height) of antinodes, which can be considered as analogous to the length or stiffness of bristles on a hairbrush. Increasing the amplitude can therefore be considered analogous to providing a longer / stiffer bristle. The phase affects the location of nodes / antinodes along the resonator element, and so varying the phase can be considered as analogous to varying the position of bristles along a hairbrush. The exciter assembly may be configured to vibrate the resonator element in a direction which is substantially normal to a resting plane of the resonator element. For example, the exciter assembly may be configured to vibrate the resonator element primarily (or only) in a direction which is normal to the resting plane of the resonator element. Vibrations in this direction may be particularly effective for displacing hair along the standing wave, by agitating hair toward one or more nodes of the standing wave. The active region (or “active surface”, “resonator surface”, “diaphragm”) is a region of the resonator element that is configured to vibrate as the standing wave to influence the position of hair in use. The active region may be exposed from the portion of the housing. Optionally the resonator may also have one or more inactive regions (or “fixed sections”) which are not vibratable relative to the housing. For example, the inactive region(s) may be hidden inside the housing, for mounting the resonator element to the housing. As used herein, a “resting plane” (or “resting axis”) of the resonator element may refer to a plane (or axis) which at least a portion of the resonator element (e.g. of the active region) lies along / intersects when it is not being vibrated by the exciter assembly. During resonant vibrations, nodes of the standing wave may be aligned with the resting plane, whereas antinodes of the standing wave may be offset from the resting plane. In some examples, the resonator element may be planar and may therefore lie entirely along the resting plane when it is not being vibrated. In other examples, the resonator element may be non-planar (e.g. curved) and may therefore only partially lie along or intersect the resting plane when it is not being vibrated. The resting plane (or resting axis) may be a central plane (or axis) of the resonator element when the resonator element is not being vibrated. As noted above, the exciter assembly is configured to apply vibrations to the active region of the resonator element to cause resonance. The exciter assembly may have one or more exciters configured to vibrate the active region of the resonator element. The (or each) exciter may be configured in any suitable manner. For example, an exciter may be electromechanical, pneumatic, or hydraulic in nature. For example, the exciter may comprise a speaker driver, piezoelectrics, airflow means, or any other means for vibrating the resonator. In some examples, the exciter may be directly connected to (attached to) the active region. In other examples, the exciter may not be directly connected to the active region (e.g. may be spaced from the active region). Accordingly, the exciter assembly may apply vibrations to the active region directly or indirectly. Optionally, the device further comprises means for supplying heat to the hair. For example, the means for supplying heat may comprise a structure for conveying thermal energy between a heat source (located in an appliance separate from the device) and the hair (e.g. an airflow conduit, a heat pipe, etc.). Alternatively, the means for supplying heat may comprise a heat source (e.g. airflow source, hot plate, etc) integrated into the device itself. This allows the device to be used for heat styling (e.g. as a hair dryer, straightener, curler, etc). The resonator element (e.g. active region) may be aligned with the means for supplying heat. The resonator element (together with the exciter assembly) may therefore be configured to bias hair to lie along a region to be heated by the means for supplying heat. This may help to provide effective heat styling while mitigating damage from overheating or overstretching of hair. For example, the resonator element may be aligned with a hot plate of a hair straightener. Alternatively, the resonator element may be aligned with a Coanda surface for aligning hair with an airflow pathway along the Coanda surface. Alternatively, the resonator element may be aligned along or around barrel or wand (e.g. a hair curling barrel / wand), to help align hair around the barrel / wand. As used herein, a “Coanda surface” may refer to a curved surface (e.g. convex surface) along which airflow is provided via the Coanda effect in use. For example, a suitable device having a Coanda surface is described in GB2613800A. Other example devices having Coanda surfaces are also possible. In variant embodiments, the device may not comprise means for supplying heat. For example, the device may be configured as a heatless brush, which utilises the standing wave at the resonator element for brushing hair. Optionally, the brush may lack conventional (mechanical / physical) bristles and may therefore be especially compact compared to standard brushes. The resonator element may have any suitable configuration. For example, the resonator element may be an elongate strip, e.g. rectangular strip or oblong strip. An elongate resonator element may be particularly convenient in combination with an exciter assembly arranged to vibrate the resonator element as a one-dimensional (ID) standing wave, e.g. to bias / distribute hair along a linear direction. Alternatively, in some embodiments the exciter assembly may have a planar shape and may be configured to vibrate the resonator element as a two-dimensional (2D) standing wave. This may distribute hair in any desired 2D pattern, e.g. to distribute hair in waves (having peaks and troughs along a 2D section of hair). Means for supplying heat may be provided for setting the hair in the 2D pattern. The resonator element may be configured to directly contact the user’s hair in use (e.g. at the active region). Alternatively, the resonator element (e.g. active region) may not directly contact the user’s hair. For example, another element may be provided between the resonator element and the hair which still enables the resonator element to influence the position of the hair in use via resonant vibrations. The resonator element may be formed of any suitable material(s), e.g. as a plastic or metal sheet. The configuration (shape, dimensions, materials, etc) of the resonator element (e.g. its active region) will affect its resonant frequency. Further, in use, the presence of hair against or near the resonator element (e.g. its active region) may affect the frequency or amplitude at which resonant vibrations will occur. Further, different hair types (having different thicknesses, flexibilities, etc) may affect the standing wave to different extents. Accordingly, in some embodiments, it may be desirable to configure the resonator element (e.g. the active region) and / or exciter assembly to offset or account for deviations in frequency / amplitude that could occur due to the presence of hair. For example, in some embodiments, the resonator element (e.g. active region) may be preformed to help achieve a particular standing wave pattern. Optionally, the resonator element (e.g. active region) comprises one or more variations in stiffness along its length. This may help to provide a desired standing wave pattern and / or amplitude to the standing wave in use. For example, variations in stiffness may be configured to provide a desired spacing (e.g. a desired minimum or maximum spacing) between nodes or to provide a desired amplitude (e.g. a desired minimum or maximum) at the antinodes, e.g. by configuring the resonator element to be stiffer in regions where less vibration (e.g. nodes) are desired, and to be more flexible in regions where more vibration (e.g. antinodes) are desired. Optionally, the one or more variations in stiffness may each be formed by a variation in material, dimension (e.g. width, thickness, or length), or surface pattern (e.g. surface structures such as ribs / bracing) along the resonator element (e.g. active surface). Optionally, a variation in stiffness may be formed by a plurality of these characteristics, in any combination. Optionally, the resonator element may comprise one or more fixed sections (or “inactive regions”, “secured regions”) which are fixed / secured relative to the housing during resonant vibrations (e.g. via mounting plates, brackets, adhesives, solder, or other means). The fixed section therefore defines a predetermined location for a node. Because it is fixed relative to the housing, the node will remain present across all resonant frequencies. In contrast, the number and position of other types of nodes (that are not defined by a fixed section) may be adjusted by varying the harmonic. Optionally, the location of a fixed section may be permanent (e.g. using solder or adhesive). Alternatively, the location of the fixed section may be adjustable, e.g. relative to another section of the resonator element. This allows the resonator element to have an adjustable tension, which in turn facilitates adjustment of the resonant properties (e.g. resonant frequency / harmonics) of the resonator element. For example, the fixed section (e.g. an end) of the resonator element may be (indirectly) attached / secured to the housing via an intermediary assembly, which may be referred to as a “tension adjuster”. The tension adjuster may be configured to vary a position of the fixed section along the housing and thus relative to another section (e.g. another end) of the resonator element. This adjusts the tension of the resonator element, e.g. by stretching the resonator element, thereby affecting the resonant properties thereof. Optionally, the other section of the resonator element (e.g. the other end of the resonator element) may be permanently attached to the housing (e.g. via adhesive or solder). Alternatively, it may also be adjustably attached to the housing via a further tension adjuster. The tension adjusters) may be configured in any suitable manner. For example, a tension adjuster may comprise two interengaging members (e.g. a threaded rod and threaded nut), with one member being (translatably) fixed relative to the fixed section of the resonator element and the other member being (translatably) fixed relative to the housing of the device. The two interengaging members may be translatable relative to each other (e.g. via rotation of the threaded rod through the threaded nut) to vary a position of the fixed section. In variant embodiments, the tension adjuster may be configured in other manners, e.g. by using a ratchet mechanism to adjust the position of the fixed section. The tension adjuster may be manually adjustable, e.g. using a control knob which is moveable (e.g. rotatable) by a user to cause the relative movement of the interengaging members. Alternatively, the tension adjuster may be automatically adjustable, using a controller of the device. The fixed section may be positioned in various manners to provide different predetermined properties to the hair care device. For example, optionally, the resonator element comprises a fixed section that is fixed relative to the housing, wherein the fixed section is located at a first end zone of the resonator element, and wherein the exciter assembly is configured to excite the active region at a second end zone of the resonator element opposite the first end zone to cause the resonator element to resonate. The standing wave may therefore have an amplitude that increases from the first end zone to the second end zone. Since hair will be agitated by the vibrations towards the node at the fixed section in use, this arrangement may be used to keep hair away from the second end zone of the resonator element. For example, such an arrangement may be used to retain hair within a heat styling region of the hair device. The active region may therefore be located along the second end zone Optionally the active region may also extend e.g. across a central zone of the resonator element. As used herein, the term “end zone” may refer to a section at or near an end of the resonator element, e.g. an end region of the resonator element that comprises up to 30% of the length of the resonator element, e.g. up to 20%, e.g. up to 10%, e.g. up to 5%, as measured from an end point of the resonator element. The active region may comprise one or more vibratable sections (or “excitable sections”), which are configured to be vibrated by a respective one or more exciters of an exciter assembly (e.g. with each exciter being aligned with a respective vibratable section). In some examples, the exciter assembly comprises a plurality of exciters, each configured to vibrate a respective section (vibratable section) of the resonator element. Optionally, these may be separated by a respective one or more “fixed sections”, thereby forming independent standing waves that terminate at the fixed section(s). Alternatively, the vibratable sections / exciters may not be separated by a fixed section, and thus the vibrations from each exciter may constructively or destructively interfere with each other to provide a desired wave pattern. For example, optionally, the exciter assembly comprises a first exciter configured to vibrate a first vibratable section of the resonator element (e.g. of the active region); and a second exciter configured to vibrate a second vibratable section of the resonator element (e.g. of the active region); wherein the first vibratable section is located at an opposite end zone of the resonator element from the second vibratable section. Thus, both end zones of the resonator element may be vibratable. This can provide multiple benefits, as follows. Firstly, providing exciters / vibratable sections at both end zones (e.g. both ends) can allow the phase of the standing wave to be adjusted while retaining a constant frequency, compared to arrangements in which one or both end zones are fixed. Adjustments in phase can be used to provide desired hair styles (e.g. wavy hair styles), as will be discussed in further detail herein. Secondly, providing exciters / vibratable sections at both end zones means that relatively large amplitudes can be provided at both end zones, which in turn forces hair away from the end zones of the resonator element. Optionally, the resonator element further comprises a fixed section (inactive region) interposed between the first and second vibratable sections, the fixed section being fixed relative to the housing. The resonant vibrations will move the hair towards the location of the fixed section, as this section will correspond to a node in use. The fixed section may be located at a central zone of the resonator element (e.g. a region in the centralmost 70% of the resonator element, e.g. centralmost 60%, e.g. centralmost 50%, e.g. centralmost 40%, e.g. centralmost 30%, e.g. centralmost 20%, e.g. centralmost 10%, e.g. centralmost 5%, e.g. exact centre). Optionally, the resonator element may not comprise a fixed section. This enables greater customisation on the location of the nodes, by varying the properties (e.g. frequency, phase) of the standing wave via the exciter assembly, rather than by specifically fixing sections of the resonator element relative to the housing. Alternatively, optionally, the resonator element comprises a first fixed section and a second fixed section, the first fixed section and the second fixed section each being fixed relative to the housing; wherein the first fixed section is located at an opposite end zone of the resonator element from the second fixed section; and wherein the exciter assembly is configured to excite the active region between the first fixed section and the second fixed section to cause the resonator element to resonate. This arrangement may provide one or more antinodes within a central zone of the resonator element. This can be used to evenly spread hair across the resonator element e.g. away from the centre of the resonator element and towards the end zones of the resonator element. Optionally, the housing comprises a pair of arms configured to grip hair therebetween, each arm extending from a proximal end to a distal end, the arms being movably connected together at their proximal ends, wherein the resonator element extends longitudinally along one of the arms between the proximal end and distal end thereof. The device may therefore clamp hair between the arms (e.g. as a hair straightener or a curling wand with a clamp). Optionally, the exciter assembly is configured to vibrate a distal end zone of the resonator element. This helps to prevent hair from falling out the end of the device. Optionally, a proximal end zone of the resonator element is fixed relative to the housing. By fixing the proximal end zone and providing an exciter at a distal end zone, the standing wave may increase in amplitude from the proximal to distal end zones. This may help to bias hair to remain within the arms of the housing. Optionally, one or more of the arms may comprise means for supplying heat (e.g. a heat source such as a hot plate), and the resonator assembly may be aligned with the means for supplying heat. Thus, by vibrating a distal end zone of the resonator element (and optionally vibrating a proximal end zone of the resonator element), hair can be influenced by the standing wave to remain within the same zone as the means for supplying heat. Optionally, the device further comprises a plurality of bristles located along a first arm of the housing; wherein the resonator element is located along a second arm of the housing opposite the first arm for moving hair toward the plurality of bristles via resonant vibrations. Whereas the antinodes of the standing wave may be considered to act as “virtual bristles”, the plurality of bristles may be physical / mechanical bristles that protrude from the housing to engage against hair. By providing mechanical bristles on one arm and a resonator element on the opposite arm, this arrangement allows the resonator element to align / push hairs into the bristles while maintaining low friction. Thus, this arrangement can provide good distribution of hairs into a bristle bed for better detangling and convenient hair styling, while providing relative low damage / overstretching to hair. The first and second arm may together form the “pair of arms” discussed above. Optionally, the hair care device may comprise a single resonator element as described above. Alternatively, optionally, the device comprises a plurality of said resonator elements, the exciter assembly being configured to vibrate the active regions of the plurality of resonator elements to cause each resonator element to resonate as a standing wave for urging portions of the hair toward one or more nodes of the respective standing wave via resonant vibrations. A plurality of resonator elements may further improve the detangling and / or styling ability of the hair care device. The resonator elements may be configured in the same / corresponding manners to each other (e.g. each having the same arrangement of fixed / vibratable sections, or the same variations in stiffness), or may be configured differently from one another. Each resonator element may be vibratable by at least one exciter of the exciter assembly. Optionally, the exciter assembly is configured to vibrate each resonator element (each active region) independently at different frequencies, wavelengths, amplitudes, and / or phases. For example, the exciter assembly may comprise a plurality of exciters configured to independently excite the active regions of the resonator elements. Optionally, the plurality of resonator elements comprises a first resonator element located along a first arm of the housing, and a second resonator element located along a second arm of the housing opposing the first arm, for distributing hair between the first and second resonator elements via resonant vibrations. The first arm and the second arm may form a “pair of arms” as discussed above. This allows opposing arms of a hair care device to each operate to bias hair in a particular direction via resonant vibrations. Optionally, the hair care device comprises a controller in communication with the exciter assembly for adjusting a vibration characteristic of the exciter assembly, the vibration characteristic comprising at least one of frequency, amplitude, phase, or wavelength. This arrangement allows customisability of the vibration characteristics, and thus the effect of the standing wave on hair. This can enable adjustment for a variety of different applications / styling techniques and / or hair types (e.g. fine vs thick hair; straight hair vs type 4 curly hair, etc). As discussed above, the amplitude affects the size of the antinodes (peaks), analogously to the size of bristles on a hairbrush. The amplitude may therefore be adjusted to provide improved strength to the bristles, e.g. for improved detangling. The phase affects the location of nodes / antinodes, and thus the alignment of hair along the device. Adjustments in phase may therefore provide control over the location of hair, e.g. to retain hair near the device (e.g. near means for supplying heat to the hair) or to provide a particular hair style (as will be discussed further herein). The frequency / wavelength affects the spacing between nodes (or antinodes). Adjusting the frequency / wavelength has an effect analogous to adjusting the spacing between bristles of a hairbrush. A higher frequency (analogous to denser / tightly-packed bristles) may assist with detangling. A lower frequency (analogous to fewer bristles) may enable gentler styling. Optionally, the controller may be configured to adjust the frequency in an incremental manner, to enable discrete adjustment (rather than continuous adjustment) through a number of harmonics of a starting (resonant) frequency. This enables the frequency to be adjusted in a convenient manner through frequencies that will result in resonance of the standing wave at the resonator element(s), and disregarding non-resonant frequencies. In variant embodiments, the controller may adjust the frequency in a continuous manner until a resonant harmonic is reached. In embodiments having a plurality of resonator elements, the controller may control the exciter assembly to excite the plurality of resonator elements with the same or different vibration characteristics. The controller may be configured to adjust the vibration characteristic in response to a manual input from a user (e.g. via a button or other user interface). Alternatively or additionally, the controller may be configured to adjust the vibration characteristic automatically, e.g. in response to a detection by the device itself. For example, optionally, the device comprises means for detecting non-resonance of the or each resonator element, and the controller is configured to adjust a frequency of the vibration in response to the detected non-resonance. The device can therefore provide active calibration, to ensure that the exciter assembly is vibrating the resonator element(s) at a frequency that will result in resonant vibrations (i.e. a “resonant frequency”). Since the absence or presence of hair against the device can affect the resonant frequency, and since the properties of hair (e.g. density, amount, hair type, stiffness, etc) can also affect the resonant frequency, providing means for detecting non-resonance and a controller for adjusting the frequency in response to non-resonance allows the controller to calibrate the device substantially in real-time to provide optimised functionality in a wide variety of applications. The means for detecting non-resonance (also referred to as “detecting means”) could be configured in any suitable manner. In some embodiments, the exciter assembly may comprise the detecting means. Alternatively, the detecting means may form a separate / distinct component from the exciter assembly. Optionally, the detecting means may comprise a sensor / detector (e.g. microphone transceiver or proximity sensor) for detecting resonance or non-resonance based on the vibrations of the resonator element. The detecting means may detect non-resonance either directly or indirectly. For example, the detecting means may be configured to (directly) detect resonance and thus may (indirectly) detect non-resonance due to the absence of resonance being detected. Alternatively, the detecting means may be configured to directly detect non-resonance. For example, the detecting means may comprise electronics that enable the power usage of the exciter assembly to be measured in real time. During a calibration stage, the exciter assembly may be configured to perform a sweep of frequencies for vibrating the one or more resonant elements, and the means for detecting may identify the resonant frequency based on the sweep of frequencies. For example, the resonant frequency may be identified based on measurements of wave amplitude across the frequencies. For example, the resonant frequency may be identified by measuring peak wave amplitude across the frequency sweep (with the resonant frequency corresponding to the frequency at which peak wave amplitude is maximized). Alternatively, the resonant frequency may be identified by checking for the presence of nodes that remain in the same position over a period of time (with the resonant frequency corresponding to the frequency at which nodes will remain in the same position over time). Either of these techniques may employ detecting means that comprise a sensor (e.g. proximity sensor, microphone transceiver, etc) directed toward the resonator element for measuring vibrations of the resonator element. In other examples, the detecting means may identify the resonant frequency based on the power usage of the device across the sweep of frequencies. In such examples, the detecting means may identify the frequency at which a maximum amount of power is being consumed (compared to other frequencies) as being the resonant frequency. Optionally, these electronics may be integrated into the exciter assembly itself. In such examples, the resonant frequency can be identified without an additional sensor. Alternatively, the device may not comprise detecting means. For example, optionally, the device may be factory calibrated to operate at a particular resonant frequency, which may be selected for use with a particular hair type / density. Optionally, the device comprises a memory for storing a user preference for the vibration characteristic or wherein the device comprises a communications interface for receiving a user preference for the vibration characteristic from a remote device; and wherein the controller is configured to adjust the vibration characteristic of the exciter assembly based on the stored or received user preference. This helps provide customisability in view of user preferences. Optionally, the device (or remote device) may be configured to learn the user preferences over time e.g. using artificial intelligence (AI). For example, the communications interface may be a wireless communications interface. The wireless communication interface may be capable of communicating via one or more different protocols , such as , 3G, 4G, 5G, GSM, WiFi , Bluetooth® and / or CDMA. The wireless communication interface may include communication hardware for the transmission and reception of data signals, such as, a transmitter and a receiver (or a transceiver). Also, the communication hardware may include an antenna and an RF processor which provides an RF signal to the antenna for the transmission of data signals, and the receipt therefrom. The wireless communication interface may also include a baseband processor, which provides data signals to and receives data signals from the RF Processor. The precise construction of the wireless communication interface may vary between embodiments, as would be understood by the skilled person. Optionally, the device further comprises a positional sensor for detecting a change in position of the hair care device along a length of the user’s hair; wherein the controller is configured to determine an adjusted vibration characteristic based on the change in position of the hair care device along the length of the user’s hair; and wherein the controller is configured to control the exciter assembly to vibrate according to the adjusted vibration characteristic in response to the detected change in position of the hair care device along the length of the user’s hair. By adjusting the vibration characteristic in response to movement of the device relative to the hair, the device can provide different effects on different portions of hair. For example, stronger virtual bristles may be provided near the roots of the hair, with gentler effects on the hair nearer the ends, by decreasing the amplitude over the length of the hair. Optionally, this arrangement may be provided in combination with a heat source. The controller may be configured to control the exciter assembly to vibrate (e.g. independently vibrate) one or more resonant elements with a phase that varies in response to the position of the hair care device along the length of hair. This may allow a wavy hair style to be produced in a manner which is extremely convenient to the user, who needs only move the hair care device along the length of their hair in a simple manner. The positional sensor may be configured in any suitable manner. For example, the positional sensor may comprise an optical sensor (e.g. optical flow sensor), a mechanical sensor (e.g. roller sensor), or an accelerometer. Optionally, the device comprises a hair sensor for measuring an amount of hair covering the resonator element; wherein the controller is configured to adjust a vibration characteristic of the exciter assembly in response to the measured amount of hair. This allows active adjustment of the standing wave (virtual bristles) based on the amount of hair at the device. For example, the amplitude / frequency may be increased to provide improved strength / detangling when needed due to large amounts of hair, or can be decreased to avoid excess forces on the hair when not required due to small amounts of hair. The controller may adjust the phase to deliberately eject hair from the device if an amount of hair exceeds a threshold, to prevent a user from overloading the appliance (e.g. hair straightener), and thereby ensure proper operation of the appliance for optimised hair styling. The hair sensor may measure the amount of hair, for example, by measuring a thickness of hair (e.g. between two arms of the device) or detecting a weight / pressure of hair against the sensor. Alternatively, the hair sensor may measure the amount of hair using optical means. Optionally, the device is configured as an attachment for mounting to a hair care appliance. Examples of hair care appliances include, for example, hair dryers, straighteners, curlers. The hair care appliance may comprise a power source (e.g. battery or mains-operated). The device (attachment) may comprise means for supplying heat to the hair. Optionally, the means for supplying heat may comprise a heat source integrated into the attachment. Alternatively, the hair care appliance may comprise a heat source, and the means for supplying heat (of the attachment) may comprise a structure for conveying thermal energy between the heat source (of the appliance) and the hair. For example, the structure for conveying thermal energy may comprise an inlet and an outlet defined by the housing of the hair care device, the inlet for receiving an airflow from the hair care appliance when mounted thereto and the outlet fluidly connected to the inlet for discharging the airflow to the hair. Such a hair care device may be used, for example, as an attachment for a hair dryer. Alternatively, optionally, the device is configured as a standalone hair appliance. Thus, the means for supplying heat (if present) may comprise a heat source integrated into the device itself. Alternatively, optionally, the device may not comprise a heat source. For example, such a device may provide the utility of a “bristleless brush”. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an isometric view showing a module having a resonator element that can be incorporated in a hair care device. Figure 2 is a side cross-sectional view of the module of Figure 1, showing an exciter assembly. Figure 3 is an isometric view of a resonator element during vibration by a plurality of exciters of an exciter assembly. Figures 4A to 4E are schematic drawings showing the influence of resonant vibrations on a portion of hair. Figure 5 is an isometric view of a smoothing attachment for mounting to a hair care appliance, incorporating a plurality of resonator elements and respective exciters. Figure 6 is an isometric view of a barrel attachment for mounting to a hair care appliance, incorporating a plurality of resonator elements and respective exciters. Figure 7 is an isometric view of a smoothing attachment for mounting to a hair care appliance, which incorporates a resonator element that transverses a Coanda surface of the attachment. Figures 8 to 10 are a schematic drawings showing different standing wave patterns that can be generated as a result of different configurations of an exciter assembly and resonator element. Figure 11 is an isometric view of a standalone hair straightener appliance having resonator elements and an integrated heat source. Figure 12 is a schematic drawing showing hair being influenced by a hair care device which has a resonator element that is configured to vibrate as a standing wave that increases in amplitude from a proximal end to a distal end. Figure 13 is an isometric view of a hair care appliance having a positional sensor. Figure 14 is a cross-sectional axial view of a hair care appliance having a pair of arms, showing a positional sensor and other components inside the device. Figure 15 is a cross-sectional axial view of a hair care appliance similar to that of Figure 14, but having different means for receiving user input. Figure 16 is a schematic drawing useful for demonstrating the manner in which the phase of resonant vibrations can be controlled to produce a desired hair style such as waves. Figure 17 is a schematic drawing showing a pair of resonator elements and respective exciters which can be implemented on opposing arms of a hair care device for brushing and detangling hair. Figure 18 is a schematic drawing showing a resonator element having a pair of exciters that can be implemented on one arm of a hair care device, and a set of bristles that can be implemented on an opposing arm of the hair care device for brushing and detangling hair. Figures 19A to 19E are upper and side views showing different types of resonator elements that have variations in stiffness along their lengths. Figure 20 is a side view of a resonator module having a tension adjuster. DETAILED DESCRIPTION Figures 1 and 2 show a module 10 that can be incorporated in a hair care device to control the location of hair via resonant vibrations. The module 10 comprises a housing or enclosure 12 and a resonator element 14 extending along the enclosure. The resonator element 14 is formed as an elongate strip of flexible material (e.g. thin metal or plastic). The resonator element 14 has a first end 16 and a second end 18, each of which is attached to the enclosure 12 via a set of mounting plates 20A-B. An active region 22 (active surface, exposed surface) of the resonator element 14 extends between the mounting plates 20A - B and along an opening defined by the enclosure 12. In this example, the active region 22 protrudes very slightly from the enclosure 12 when not being vibrated. An exciter assembly 24 is configured to vibrate the active region 22 of the resonator element 12 to cause resonant vibrations. The exciter assembly 24 is positioned within the enclosure 12 and below the active region 22, spacing the active region 22 from a base of the enclosure 12. In this embodiment, the exciter assembly 24 comprises a single exciter 26 aligned with a centre of the active region. In this embodiment, no fixed sections are provided along the active region 22. In this example, the module 10 is configured to be incorporated within a hair care device by inserting the module within a recess of the device. In other examples, the module may be incorporated within a hair care device in other manners, e.g. by integrally forming the enclosure of the module together with a housing of the hair care device. Examples of hair care devices incorporating the module will be discussed further herein. In some embodiments, the module 10 may comprise additional components e.g. within the enclosure 12. For example, in some embodiments a controller may be provided within the enclosure 12, in communication with the exciter assembly for adjusting a vibration characteristic of the exciter assembly. Alternatively, such additional components may be provided as part of the hair care device, outside of the enclosure. In use, the exciter assembly 24 will vibrate the active region 22 of the resonator element 14 to cause the (active region of the) resonator element 14 to resonate as a standing wave that terminates in nodes at the ends 16,18 that are fixed to the enclosure 12. In variant examples, one or both ends may be flexibly / movably attached to the housing (or not attached at all), to permit maxima at the ends of the standing wave. Figure 3 shows an instantaneous view of an exciter assembly 24 and resonator element 14 during vibrations of the resonator element 14 by a plurality of exciters 26A-C of the exciter assembly 24. The vibrations cause the active region 22 of the resonator element 14 to resiliently deform so that it no longer extends along a resting axis 28, but rather undulates to follow a wave pattern about the resting axis 28. It will be understood that the shape of the resonator element 14 will oscillate in time when vibrated by the exciter assembly 24, and that the wave pattern shown in Figure 3 is solely an instantaneous snapshot of the varying shape of the resonator element. Figures 4A to 4E are schematic diagrams useful for understanding the present disclosure, by showing how resonant vibrations of a resonator element 14 can influence the distribution of a plurality of hairs 30 in use. Figure 4A shows the resonator element 14 at rest, when it is not being vibrated to resonate as a standing wave. Therefore, the resonator element 14 does not controllably move the hairs 30 towards any particular position. In this configuration, the resonator element 14 is lying flat along a resting plane 32. The ends 16, 18 of the resonator element 14 are fixed relative to the resting plane 32. Figure 4B shows the resonator element 14 being vibrated to resonate as a standing wave at a first harmonic (also referred to as the fundamental frequency). The resonator element 14 oscillates in a direction normal to the resting plane 32, between first and second maximum displacements (shown by the solid and dashed curves) which define the standing wave pattern. In use, this movement divides the plurality of hairs 30, which are forced towards nodes of the standing wave pattern that is defined by the oscillations of the resonator element 14. In this example, because both ends 16, 18 of the resonator element 14 are fixed, the resonant pattern at the first harmonic has two nodes (one at each end 16, 18). In other examples, the resonator element 14 may be configured differently (e.g. with one vibratable end and one fixed end, or both ends being vibratable), in which case the nodes may be positioned differently (e.g. with a first harmonic pattern that has only one node rather than two). Figures 4C, 4D, and 4E show the resonator element 14 being vibrated at different frequencies, corresponding to resonance at the second, third, and fourth harmonics respectively. Each incremental increase in the harmonic results in an additional node 34 being provided in the standing wave pattern, thereby further dividing and distributing the hairs 30 across the active region 22 of the resonator element 14. Since the additional nodes 34 are the consequence of increasing frequency (rather than being created by fixing a section of the resonator element 14 to prevent vibration, like at the first and second ends 16, 18), the locations of the additional nodes 34 can be adjusted by controlling the frequency at the exciter assembly. Figures 5 to 7 show hair care devices that incorporate at least one resonator element and respective exciter assembly for styling hair using a standing wave. The devices of Figures 5 to 7 are each configured as different types of attachments for mounting to a hair care appliance. Figure 5 shows a device in the form of an attachment 36 for mounting to a hair care appliance such as an air styler. The attachment comprises a housing 38 that contains a pair of modules 10A-B. Each module 10A-B may be similar to that shown in Figures 1-2, although further modifications may also be provided e.g. to vary the location and / or number of exciters. The attachment 36 includes means for supplying heat to the hair, in the form of a structure for conveying thermal energy between a heat source of the air styler and the hair. The structure comprises an inlet 40 for receiving airflow from the air styler when mounted thereto and an outlet 42 fluidically connected to the inlet 40 for discharging the airflow to hair in use. The outlet 42 is elongate and extends longitudinally along a surface of the housing 38 between the resonator elements 14A-B of the modules 10A-B, which also extend along the surface of the housing 38, facing in substantially the same direction as the outlet 42 (e.g. within 15° of the outlet 42). This attachment 36 may be used for drying / smoothing hair, for straight hair styling. In use, a user can glide the attachment 36 (mounted to a hair care appliance) against their hair. The exciter assembly within each module 10A-B is configured to vibrate its resonator element 14A-B as a standing wave, thereby aligning and distributing hairs across the airflow outlet 42 to provide even heating and styling. The attachment 36 of Figure 5 may also be referred to as a smoothing attachment. Figure 6 shows a device in the form of a barrel attachment 44 for mounting to a hair care appliance such as an air styler. The barrel attachment 44 is used for styling hair to provide a curl, by wrapping hair around the barrel-shaped housing 38. A plurality of airflow outlets 42 extend along a length of the barrel, from a proximal end to a distal end. Each outlet 42 is located between a respective pair of resonator modules 10A-C which also extend longitudinally along a length of the barrel. In use, the resonator elements 14A-C can vibrate according to a standing wave, e.g. to help evenly distribute hair along the length of the barrel and / or to prevent hair from falling off the end of the barrel in use. Each resonator element 14A-C may be independently controllable (via independent exciters and one or more controllers) to provide precise control of the distribution of hair across the barrel. Figure 7 shows a device in the form of a Coanda attachment 46 for mounting to a hair care appliance such as a hair dryer. The Coanda attachment 46 has a housing 38 that defines an airflow inlet 40 and outlet 42 for supplying airflow to hair along a Coanda surface 48. A module 10 having a resonator element 14 and associated exciter assembly is located along the Coanda surface 48, with the resonator element 14 being aligned with the outlet 42 and angularly displaced from the outlet 42 about the Coanda surface 48. In this example, the resonator element 14 is angular displaced from the outlet 42 by approximately 90 degrees. In variant embodiments, the resonator element may have a different angular displacement from the outlet 42, e.g. between 45-135 degrees, optionally, between 75-105 degrees. In some examples, a plurality of resonator elements may be located at different angular positions along the Coanda surface. Optionally, the device 46 further includes a hair sensor 50 for measuring an amount of hair at or near the resonator element 14. The hair sensor 50 is configured to communicate with a controller (not shown) of the exciter assembly, which is configured to adjust a vibration characteristic of the exciter assembly in response to the measured amount of hair. In other examples, the hair sensor 50 may be integrated into the resonator module, e.g. at a surface of the resonator element 14. In use, vibration of the resonator element 14 by the exciter assembly can help the device to attract hair toward the Coanda surface 48, thereby helping provide effective styling. Figures 8 to 10 show schematic diagrams of exciter assemblies 24 having exciters 26 at different positions relative to a resonator element 14, to provide different types of standing waves. The exciter assemblies 24 and resonator elements 14 discussed herein may be mutually configured in various manners to provide different functionalities to the hair styling attachments. Accordingly, these configurations can be implemented in any of the examples discussed herein. In Figure 8, the resonator element 14 comprises a fixed (non-vibratable, inactive, dampened, grounded) section 52 which is fixed relative to the housing (e.g. any of the housings 38 of Figures 5 to 7). The remainder of the resonator element 14 is vibratable relative to the housing and thus constitutes an active region 22 of the resonator element 14. In this example, the fixed section 52 is located at a first end zone 58 of the resonator element 14. The exciter assembly 24 has an exciter 26 which is configured to excite the active region 22 at a second end zone 60 of the resonator element 14 opposite the first end zone 58. In this example, the exciter 26 is spaced slightly from the exact end of the resonator element 14 to accommodate (flexible) attachment to the housing. In this example, the resonator element 14 varies in stiffness along its length, with an increase in stiffness nearer the first end zone 58. This change in stiffness may be caused, for example, by variations in the material, dimension, or surface pattern of the resonator element itself, and / or by the manner in which the fixed section 52 attaches (adheres, fastens) the resonator element 14 to the housing. The increase in stiffness from the second end zone 60 to the first end zone 58 results in a dampening effect on the standing wave. Thus, when vibrating the resonator element 14 at a resonant frequency, this arrangement will cause the resonator element 14 to resonate according to a standing wave pattern 62 that increases in amplitude from the first end zone 58 to the second end zone 60. In some examples, a decreasing amplitude / dampening effect of the waveform as it propagates from the exciter (e.g. from the second end zone 60 to the first end zone 58) may be caused in other manners, e.g. as a consequence of some energy being converted to heat rather than motion along the waveform. In Figure 9, the resonator element 14 is vibratable at both end zones, with a first vibratable section 54A being located at the first end zone 58, and a second vibratable section 54B being located at the second end zone 60 opposite the first end zone 58. The exciter assembly comprises a first exciter 26A configured to vibrate the first vibratable section 54A of the resonator element 14 and a second exciter 26B configured to vibrate the second vibratable section 54B of the resonator element 14. This arrangement results in maxima at the end zones of the resonator element 14, for forcing hair from the end zones 58, 60 in use. In this example, the resonator element 14 further comprises a fixed section 52 interposed between the first and second vibratable sections 54A, 54B, at a central zone (e.g. in the centre) of the resonator element 14. Similarly to the arrangement of Figure 8, the resonator element 14 decreases in flexibility (increases in stiffness) in the vicinity of the fixed section 52. This provides a standing wave pattern 62 that has a centralised dampened region comprising a node corresponding to the fixed section 52. The dampened region helps to attract hair away from the end zones of the resonator element 14. In variant examples, the fixed section 52 may be omitted to enable greater adjustability of the location of nodes in the standing wave (by varying the frequency), without any dampened region along the standing wave (see e.g. FIGs 4A to 4E). In Figure 10, the resonator element 14 has a first fixed section 52A and a second fixed section 52B. The first fixed section 52A is located at the first end zone 58, while the second fixed section 52B is located at the second end zone 60 opposite the first end zone 58. The exciter assembly 24 has an exciter 26 configured to excite a vibratable section of the resonator element 14 between the fixed sections 52A-B to cause the resonator element 14 to resonate, as shown by the standing wave pattern 62. This arrangement results in maxima within a central zone of the standing wave, with minima toward the end zones 58, 60 Figure 11 shows a device configured as a standalone hair care appliance 64 rather than as an attachment. The standalone hair appliance 64 has a housing 38 comprising a pair of arms including a first arm 66 and second arm 68 configured to grip hair therebetween. Each arm 66, 68 extends from a proximal end 70 to a distal end 72. The arms are movably (e.g. pivotably) connected via a hinge 74 at their proximal ends 70. The first arm 66 includes means for supplying heat to hair 76 (e.g. one or more airflow orifices or conductive plates, facing toward the second arm 68). The first arm 66 further includes one or more (e.g. two) resonator modules 10 each having a respective resonator element 14 aligned with the means for supplying heat 76 and facing toward the second arm 68. In this example, two resonator modules 10 are provided on opposing sides of the means for supplying heat 76. Each resonator element 14 extends longitudinally along the arm 66 between the proximal end 70 and the distal end 72. In this example, both resonator modules 10 have the same configuration, with their respective exciter assemblies (not shown here - see Figures 1-3) being positioned in the same manner with respect to their resonator elements 14. In variant examples, the resonator modules 10 may each have different configurations. In this example, the second arm 68 has the same arrangement of resonator modules and heating means as the first arm 66. In other examples, the two arms may be configured differently. Figure 12 is a schematic diagram showing an example configuration for an appliance 64 similar to that of Figure 11, in that it has a pair of arms 66, 68 configured to grip hair between. A resonator element 14A-B extends along each arm 66,68. An exciter 26A-B is configured to vibrate a distal end zone (e.g. a distal end) of the active region 22 of each resonator element 14, to provide maxima in the standing wave 62 at the location of the exciter 26A-B. A proximal end zone of each resonator element 14A-B is fixed relative to its respective arm 66, 68 and is configured to provide a dampened / decaying effect to the standing wave 62, so that the standing wave decreases in amplitude as it approaches each fixed section 52. In use, strands of hair 30 between the arms 66, 68 will be agitated away from the vibrational peaks of the resonator element 14A - B towards the nodes (which are denoted by vertical dashed lines in Figure 12). These forces will be greatest at the regions of the standing wave that have the largest amplitude (as indicated by the different lengths of the arrows near the hairs 30 in Figure 12). Figure 13 shows another standalone hair appliance 78 in which the housing 38 has a pair of arms 66,68. The first arm 66 includes one or more (e.g. two) resonator modules 10A-B comprising respective resonator elements 14A-B that extend longitudinally along the arm 66 between its proximal end 70 and distal end 72. An exciter assembly (not shown) is configured to vibrate the resonator modules 10A-B. The exciter assembly is configured to vibrate each resonator element 14A-B independently with different vibrational characteristics (e.g. frequency, wavelength, amplitude, and / or phase). The appliance 78 further includes a positional sensor 80 for detecting a change in position of the appliance 78 along a length of hair in use. In this example, the positional sensor 80 is located along the first arm 66, between the two resonator modules 10A-B. The appliance further includes a controller (not shown) within the housing 38. The controller is in communication with the exciter assembly and positional sensor 80. In use, as a user moves the appliance 78 along hair, the positional sensor 80 will detect a change in the position of the appliance 78 relative to the hair. The controller, which is in communication with the positional sensor 80, will receive this data. Based on the change in position, the controller is configured to calculate an adjusted vibration characteristic (e.g. phase, frequency, amplitude) and control the exciter assembly to vibrate according to this adjusted vibration characteristic. The vibration characteristic can therefore be updated substantially in real time, in order to align the hair in a desired direction in dependence of the position along a length of hair. In this example, the second arm 68 has means for supplying heat (not shown) to the hair, such as an airflow orifice or heated conduction plate, facing toward the first arm 66. Figures 14 and 15 show cross-sectional views of different hair care devices 82, 84 that each have a pair of arms 66,68. Each device includes a pair of resonator modules 10 (located on opposing arms 66,68), a position sensor 80, and means for supplying heat 76. In Figure 14, the means for supplying heat 76 comprises an air source which provides an airflow 86 across the device. In Figure 15, the means for supplying heat 76 comprises a pair of hot plates, one on each arm 66, 68 of the device 84. The cross-sectional views also show various circuitry components including a controller 88, which is present in both devices 82,84. The controller 88 is in communication with the positional sensor 80 and the exciter assemblies of the resonator modules 10. In use, movement of hair (e.g. along the direction indicated by arrow 90) will be detected by the positional sensor 80 and evaluated by the controller 88 to adjust the vibrational characteristics substantially in real time. The device 82 of Figure 14 further includes a communications interface 92 for receiving a user preference for a vibrational characteristic from a remote device (e.g. via Bluetooth). The device further includes an optional memory 94 for storing a user preference, which may be learned from previous usage of the device. In contrast, the device 84 of Figure 15 is configured to receive user preferences in a different manner, via a user interface 96 (e.g. buttons or touch screen) directly on the device itself. In both devices, the controller 88 is configured to adjust the vibration characteristic based on the user preferences and / or the data from the positional sensor 80. Figure 16 is a schematic diagram showing how positional sensing can be utilised to provide a desired hair style such as waves. A pair of resonator elements 14A-B are laterally offset along a device (e.g. implemented in the device of Figures 14 or 15) such that, in use, the resonator elements 14A-B will simultaneously control different sections along the length of an individual hair strand. Therefore, as the device (and thus resonator elements 14A-B) is moved along hairs 30 in a longitudinal direction 90, the first resonator element 14A will act on a given section of hair before the second resonator element 14B. A positional sensor 80 is provided to detect movement of the device relative to the hair 30 in use. This detection is fed back to a controller (e.g. the controller 88) which uses the positional data to determine, substantially in real time, an adjusted vibration characteristic for the resonator elements 14A-B. In this example, the resonator elements 14A-B are vibrated at offset phases from each other, and the controller is configured to adjust the phases as the device is moved along the hair. For example, in the instant shown in Figure 16, the first resonator element 14A is at a first position and vibrating with a first phase, while the second resonator element 14B is at a second position and vibrating with a second phase that is offset from the first phase. When the second resonator element 14B is moved to reach the first position, the controller may adjust its phase to match the first phase. Additionally, the controller can make a corresponding adjustment to the phase of the first resonator element 14A. By adjusting the phase, the device can cause the hair to move in a wave pattern as the device is moved (linearly / longitudinally) along the hair. Heating means (e.g. the heating means 65 of Figures 14 or 15) can be used to set the wavy hair style, e.g. as a wet-to-dry styler. Figure 17 shows a schematic example of another type of device that uses a set of resonator elements 14A-B to align and detangle hair 30 without a need for physical bristles or a heat source. In this example, the resonator elements 14A-B are located on opposing arms of a device. Each resonator element has a fixed section 52 at its end zones. An exciter 26A-B is provided at the centre of each resonator element 14A-B, respectively, and is configured to vibrate the respective resonator element 14A-B to provide a standing wave pattern 62A-B. The standing wave patterns 62A-B provide a series of peaks which influence the position of the hairs 30 toward nodes of the wave (which are indicated by dashed vertical lines in the drawing). Each peak therefore effectively acts as a “virtual bristle” in a bristleless brush. Figure 18 shows a schematic example of another type of device. This device includes a plurality of bristles 98 located along a first arm 66, and a resonator element 14 having an active region 22 located along a second arm 68 opposing the first arm 66. Accordingly, in this example, the first arm 66 does not have a resonator element that opposes the resonator element 14 of the second arm 68, but instead has a plurality of bristles 98 opposing the resonator element 14. An exciter assembly is configured to vibrate the resonator element 14 as a standing wave. The resulting resonant vibrations at the second arm 68 urge hair 30 toward nodes of the standing wave (shown by vertical dashed lines in Figure 18) as well as towards the first arm 66 (i.e. towards the bristles 98 thereof). Accordingly, the one-sided resonator arrangement helps to distribute the hair in two directions, both in a direction parallel to and normal to the resting plane of the resonator element 14. In this example, the exciter assembly comprises a pair of exciters 26A-B located at opposite end zones of the resonator element 14 to vibrate respective vibratable sections 54A-B of the active surface 22. The resonator element 14 does not include any fixed / dampened / inactive regions in this arrangement, thereby helping ensure that the hairs will be pushed away from the resonator element 14 and toward the bristles 98, thereby further helping to align hairs into the bristles with relatively low friction. Figures 19A to 19E are examples of resonator elements that have one or more variations in stiffness along their length. These variations in stiffness help provide a desired resonant pattern and / or amplitude to the standing wave in use. The variations in stiffness may be formed by a variation in material, dimension, or surface pattern. Figures 19A to 19D are viewed from a side of the resonator element, whereas Figure 20E is a view from the top-down of the resonator element. Figure 19A shows a resonator element 14 that is formed of a first material 100 in its central zone, and a second material 102 at its end zones. The first material 100 has a different stiffness from the second material 102. Figure 19B shows a resonator element 14 which has a first material 100 in its central zone, a second material 102 at one end zone, and a third material 104 at another end zone. The first, second, and third materials 100,102, 104 all differ in stiffnesses. Figure 19C shows a resonator element 14 that comprises two regions each having different materials 100, 102. In this example, the regions of different materials 100, 102 taper into each other, to provide a smoother variation in stiffness along its length rather than providing a step-wise variation at an end zone. Figure 19D shows a resonator element 14 which has a variation in thickness (height) along its length. The variation in thickness is achieved by providing a groove or cut-out 106 in a central zone of the resonator element 14. In other examples, a variation in thickness may be achieved in other manners, e.g. by providing a rib or other surface structure on or under the resonator element 14. Figure 19E shows a top-down view of a resonator element 14 that has a variation in width along its length, as defined by a pair of cut outs 106A-B on opposing edges of the resonator element 14. These arrangements can be implemented in any of the examples discussed herein. Figure 20 shows an example of a resonator module 10’ which is comparable to the resonator module 10 of Figures 1 and 2, which further includes a tension adjuster 108 for adjusting the tension of the resonating element 14. In Figure 20, the resonating element 14 includes a first end 16 and a second end 18. The second end 18 is fixed relative to a housing 12 in a non-adjustable manner (e.g. using adhesive or solder). The first end 16 is indirectly attached to the housing 12 via the tension adjuster 108. The first end 16 is configured to be movable along the tension adjuster 108 in order to increase / decrease the distance between the first end 16 and the second end 18, thereby adjusting the tension of the resonating element 14. More specifically, in this example, the tension adjuster 108 includes a threaded nut 110 that is fixed to the first end 16, and a captive threaded rod 112 that extends through the threaded nut 110. The threaded rod 112 is secured relative to the housing 12 (e.g. within sockets at each end) to inhibit translation of the threaded rod 112 while permitting rotation of the threaded rod 112. The threaded rod 112 is attached to a control knob 114 that is rotatable to rotate the threaded rod 112 relative to the threaded nut 110. This rotation causes the threaded nut 110 to move (translate) along the threaded rod 112, in turn changing the position of the first end 16 relative to the second end 18 to thereby adjust the tension of the resonating element 14. The adjusted tension affects the resonant vibration of the resonant frequency. The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof. While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention. For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations. Any section headings used herein are for organizational purposes only and are not to be 5 construed as limiting the subject matter described. Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer 10 or step or group of integers or steps. It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and / or to “about” another particular value. When such a range is expressed, another embodiment 15 includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means for example + / -10%. Reference numerals: 36, 44, 46, 64, 78, 82, 84 Device 38 Housing 40 Inlet 42 Outlet 48 Coanda surface 66, 68 First arm, second arm 70 Proximal end 74 Hinge 72 Distal end 10 Module 12 Enclosure 20 Mounting plates 14 Resonator element 16 First end 18 Second end 22 Active region / active surface 52 Fixed section 54 Vibratable section 58 First end zone 60 Second end zone 62 Standing wave pattern 34 Node 100, 102, 104 First, second, third materials 106 Cut-out 28 Resting axis 32 Resting plane 24 Exciter assembly 26 Exciter 108 Tension adjuster 110 Nut 112 Rod 114 Control knob 50 76 5 80 88 92 94 96 10 98 Hair sensor Means for supplying heat 86 Airflow Positional sensor Controller Communications interface Memory User interface Bristles 3 0 Plurality of hairs 90 Hair movement direction

Claims

1. A hair care device comprising:a housing;a resonator element having an active region extending along at least a portion of the housing configured to contact a user’s hair in use, the active region being vibratable relative to the housing; andan exciter assembly configured to vibrate the active region of the resonator element to cause the resonator element to resonate as a standing wave for urging portions of the hair toward one or more nodes of the standing wave via resonant vibrations.

2. The hair care device of claim 1, further comprising means for supplying heat to the hair.

3. The hair care device of any preceding claim, wherein the resonator element comprises one or more variations in stiffness along its length for providing a desired resonant pattern and / or amplitude to the standing wave.

4. The hair care device of claim 3, wherein the one or more variations in stiffness are each formed by a variation in material, dimension, or surface pattern along the resonator element.

5. The hair care device of any preceding claim, wherein the resonator element comprises a fixed section that is fixed relative to the housing;wherein the fixed section is located at a first end zone of the resonator element, and wherein the exciter assembly is configured to excite the active region at a second end zone of the resonator element opposite the first end zone to cause the resonator element to resonate.

6. The hair care device of any one of claims 1 to 4, wherein the exciter assembly comprises:a first exciter configured to vibrate a first vibratable section of the resonator element; anda second exciter configured to vibrate a second vibratable section of the resonator element;wherein the first vibratable section is located at an opposite end zone of the resonator element from the second vibratable section;optionally wherein the resonator element further comprises a fixed section interposed between the first and second vibratable sections, the fixed section being fixed relative to the housing.

7. The hair care device of any one of claims 1 to 4, wherein the resonator element comprises a first fixed section and a second fixed section, the first fixed section and the second fixed section each being fixed relative to the housing;wherein the first fixed section is located at an opposite end zone of the resonator element from the second fixed section; andwherein the exciter assembly is configured to excite the active region between the first fixed section and the second fixed section to cause the resonator element to resonate.

8. The hair care device of any one of claims 1 to 6, wherein the housing comprises a pair of arms configured to grip hair therebetween, each arm extending from a proximal end to a distal end, the arms being movably connected together at their proximal ends;wherein the resonator element extends longitudinally along one of the arms between the proximal end and distal end thereof;wherein the exciter assembly is configured to vibrate a distal end zone of the resonator element; andoptionally wherein a proximal end zone of the resonator element is fixed relative to the housing.

9. The hair care device of any preceding claim, wherein the device further comprises a plurality of bristles located along a first arm of the housing;wherein the resonator element is located along a second arm of the housing opposite the first arm for moving hair toward the plurality of bristles via resonant vibrations.

10. The hair care device of any preceding claim, comprising a plurality of said resonator elements, the exciter assembly being configured to vibrate the active regions of the plurality of resonator elements to cause each resonator element to resonate as a standing wave for urging portions of the hair toward one or more nodes of the respective standing wave via resonant vibrations.

11. The hair care device of claim 10, wherein the exciter assembly is configured to vibrate the active region of each resonator element independently at different frequencies, wavelengths, amplitudes, and / or phases.

12. The hair care device of claim 10 or 11, wherein the plurality of resonator elements comprises a first resonator element located along a first arm of the housing, and a second resonator element located along a second arm of the housing opposing the first arm, for distributing hair between the first and second resonator elements via resonant vibrations.

13. The hair care device of any preceding claim, comprising a controller in communication with the exciter assembly for adjusting a vibration characteristic of the exciter assembly, the vibration characteristic comprising at least one of frequency, amplitude, phase, or wavelength.

14. The hair care device of claim 13, comprising means for detecting non-resonance of the or each resonator element; wherein the controller is configured to adjust a frequency of the vibration in response to the detected non-resonance.

15. The hair care device of claim 13 or 14, wherein the device comprises a memory for storing a user preference for the vibration characteristic and / or wherein the device comprises a communications interface for receiving a user preference for the vibration characteristic from a remote device; andwherein the controller is configured to adjust the vibration characteristic of the exciter assembly based on the stored and / or received user preference.

16. The hair care device of any one of claims 13 to 15, further comprising:a positional sensor for detecting a change in position of the hair care device along a length of the user’s hair;wherein the controller is configured to determine an adjusted vibration characteristic based on the change in position of the hair care device along the length of the user’s hair; andwherein the controller is configured to control the exciter assembly to vibrate according to the adjusted vibration characteristic in response to the detected change in position of the hair care device along the length of the user’s hair.

17. The hair care device of any one of claims 13 to 16, further comprising:a hair sensor for measuring an amount of hair covering the resonator element;wherein the controller is configured to adjust the vibration characteristic of the exciter assembly in response to the measured amount of hair.

18. The hair care device of any preceding claim, configured as an attachment for mounting to a hair care appliance.

19. The hair care device of any one of claims 1 to 17, configured as a standalone hair appliance.34

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