Patent Publication Number: US-2023149078-A1

Title: Improved cooling for a personal care device

Description:
FIELD OF THE INVENTION 
     The present disclosure relates to personal care devices, and is particularly, although not exclusively, concerned with a skin care device configured to perform an energy-based treatment on a body of a subject. 
     BACKGROUND OF THE INVENTION 
     Many types of personal care device exist that can be used to perform an energy-based treatment on a subject, for example on the hair and/or skin of the subject. 
     Light-based hair removal is a treatment used to inhibit the growth of hair by exposing the skin to bright flashes or pulses of light, which can be referred to as IPL (Intense Pulsed Light) where the light pulse is generated by a lamp or light bulb. Alternatively the flash or pulse can be generated using a laser or one or more light emitting diodes (LEDs). The light penetrates the skin and is absorbed - among other places - in the root of the hair. The temperature of the root of the hair will rise and subsequently the temperature of the surrounding tissue will also rise. The growth of the hair is inhibited if the temperature rise is sufficient. This process is known as photothermolysis. 
     A personal care device may include one or more sensors for monitoring one or more parameters before or during a personal care operation. For example, contact with skin is required for successful photoepilation treatment and to prevent a light pulse being directed into other body parts such as eyes, which can result in injury. Therefore the personal care device may include a skin contact sensor for measuring or detecting contact with the skin. Another type of sensor used in personal care devices is a skin tone sensor that measures the tone of the skin to which an energy-based treatment (e.g. photoepilation) is to be applied. 
     Personal care devices performing an energy-based treatment may heat up during use, especially during prolonged periods of use. Increasingly stringent safety standards (e.g. IEC 60601) describe maximum temperature limits for parts of personal care devices having contact with the body of a subject. 
     To ensure compliance with such safety standards, a temperature sensor is often provided on a part of a personal care device having contact with the body of a subject. If the temperature of a part of the device rises above a temperature limit, the device may ‘time-out’ to allow cooling. 
     EP1058569 A1 (WO 99/34867) discloses a device which comprises a housing  32 , the housing  32  comprising a flash lamp  14  and an air cavity  11 . The air cavity has a primary opening which is placed against the body and directs the lamp energy to the hair. In  FIG.  5 A , the housing  32  further includes an opening which allows the air to be pumped out of the cavity via an air pump. 
     SUMMARY OF THE INVENTION 
     It is desirable that external components of a personal care device remain within temperature ranges that are comfortable for users. The present inventors have determined that the air contained within a personal care device’s treatment cavity may be incidentally heated by the treatment energy as it passes through the treatment cavity, causing a rise in temperature and pressure of this confined air. The heated air may leave from the treatment cavity via the opening in contact with the body of the subject, the heated air thus passing across the body of the subject and heating up external surfaces of the device. This may negatively affect user experience. Improved cooling arrangements may thus be desirable. Further, it would be advantageous to perform cooling whilst the device is performing the energy-based treatment. 
     According to a first specific aspect, there is provided a personal care device configured to perform an energy-based treatment on a portion of a body of a subject, the personal care device comprising: an energy source; and a cavity having a primary opening, the cavity being configured to transmit treatment energy from the energy source to the primary opening, wherein the primary opening is configured to be placed against the body during use of the personal care device to define the portion of the body being treated by means of the treatment energy, and to define a volume of air within the cavity, wherein the cavity comprises a secondary opening arranged at a distance from the primary opening and at a distance from the body when the primary opening is placed against the body and configured to permit a flow of air via the secondary opening and, thereby, a flow of air out of the cavity whilst treatment energy is transmitted from the energy source to the primary opening. 
     The secondary opening may be configured to permit a flow of air via the secondary opening into the cavity and via the primary opening out of the cavity. The secondary opening may be configured such that, during use, the cavity is in fluidic communication with an internal air flow within the personal care device via the secondary opening. The secondary opening may be configured to be permanently open. The secondary opening may be provided along an axis tilting away from a direction of propagation of treatment energy generated by the energy source. The secondary opening may be provided along an axis tilting away from a direction of propagation of treatment energy incident upon the secondary opening during use. The secondary opening may be provided along an axis passing through the primary opening of the cavity. The secondary opening may be provided along an axis configured to restrict a loss of treatment energy, generated by the energy source, from the cavity via the secondary opening. 
     The cavity may comprise at least one reflector wall configured to reflect and thereby direct treatment energy from the energy source towards the primary opening of the cavity. The secondary opening may be provided in the reflector wall. The cavity may comprise a plurality of secondary openings. 
     The secondary opening may comprise a leading edge and a trailing edge, the leading edge being configured to extend beyond the trailing edge with respect to a direction of propagation of treatment energy incident upon the secondary opening, the secondary opening thereby being configured to restrict a loss of treatment energy from the cavity via the secondary opening. 
     The personal care device may comprise an auxiliary reflector provided externally of the cavity and in alignment with the secondary opening, the auxiliary reflector being configured to reflect treatment energy propagating from the cavity into the secondary opening back into the cavity via the secondary opening. The personal care device may comprise a reflective surface provided within the secondary opening, the reflective surface being configured to restrict a loss of treatment energy from the cavity via the secondary opening. 
     The personal care device may further comprise a supporting surface surrounding the primary opening and arranged to contact and support the portion of the body during use. The supporting surface may comprise at least one groove configured to be in fluidic communication with the cavity and with ambient air when the supporting surface is in contact with the portion of the body. At least one protrusion may be provided on the supporting surface. 
     The personal care device may be a skin care device. The energy source may comprise a light source. The treatment energy may comprise intense pulsed light. The personal care device may comprise a detachable portion configured to be detachable from a main body portion of the personal care device, the detachable portion comprising the cavity, the primary opening and the secondary opening. The main body portion may comprise the energy source. 
     These and other aspects will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments will now be described, by way of example only, with reference to the following drawings, in which: 
         FIG.  1    is a perspective view of a personal care device; 
         FIG.  2    is a front view of a detachable portion of the personal care device 
         FIG.  3    is a schematic section through the detachable portion of  FIG.  2    along the line III-III; 
         FIG.  4    is a schematic section through the cavity of the personal care device; 
         FIG.  5    is a schematic section through the personal care device when the detachable portion is attached to the main body portion 
         FIG.  6 A ,  FIG.  6 B  and  FIG.  6 C  show schematic sections through example reflector walls; 
         FIG.  7    is a front view of the detachable portion of the personal care device comprising surface features; and 
         FIG.  8 A  to  FIG.  8 D  show schematic sections through the line VIII-VIII of the detachable portion of  FIG.  7   . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     With reference to  FIG.  1   , a personal care device  10  is configured to perform an energy-based treatment on a portion of a body of a subject. In particular, the personal care device  10  depicted in  FIG.  1    is a skin care device configured to perform an intense pulsed light (IPL)-based treatment on a portion of a body of a subject, for the purposes of hair removal and/or hair growth inhibition, i.e. a photoepilator configured to perform photoepilation. However, it should be understood that the personal care device  10  depicted in  FIG.  1    is merely presented as an example of a personal care device  10  to which the present invention may be applied. For example, the personal care device  10  may be configured to perform an alternative energy-based treatment, relating to heat, and/or light and/or to apply another form of treatment energy to the body, such as a dermatological treatment, including hair growth reduction, treating acne, a phototherapy treatment, skin rejuvenation, skin tightening, port-wine stain treatment; and pain relief. 
     As described herein, the term ‘user’ refers to the person controlling the device, and the term ‘subject’ refers to the recipient of the treatment (e.g. a person or an animal). The user of the personal care device  10  may be the subject, or alternatively the personal care device  10  may be used by a user on a subject wherein the user and the subject are not the same. 
     The personal care device  10  comprises a main body portion  12  having a handle  14  and a user control  16 . The handle  14  is shaped and sized such that the personal care device  10  can be grasped in one or both hands of a user. The user control  16  can be operated by the user (e.g. a user’s digit from a hand grasping the handle  14 ) to activate the personal care device  10  so that the energy-based treatment is performed on the body of the subject. The user control  16  may be in the form of a switch, a button, a touch pad, etc. 
     The personal care device  10  comprises a detachable portion  20  configured to be detachable from, and re-attachable to, the main body portion  12 . As will be described below, the detachable portion  20  is configured to interact and communicate with features of the main body portion  12 . 
     For ease of reference, components of the personal care device  10  may be described in relation to the orientation shown in  FIG.  1    - the end of the personal care device  10 , including the detachable portion  20 , nearest the left hand side of the page, will be described as the ‘front’; the end nearest the right hand side of the page will be described as the ‘back’; the part of the device  10  nearest the top of the page as the ‘top’; the end nearest the bottom of the page as the ‘bottom’; the side of the device  10  into the page as ‘left’; and the side of the device coming out of the page as ‘right’. The top, bottom, left and right directions may be indicated in reference numerals with the letters ‘T’, ‘B’, ‘L’ and ‘R’ respectively. 
       FIG.  2    shows a front view of the detachable portion  20  of the personal care device  10 . A schematic representation of a vertical section through the detachable portion  20  along the line III-III is shown in  FIG.  3   . 
     With reference to  FIG.  1   ,  FIG.  2    and  FIG.  3   , the detachable portion  20  comprises a housing  21  having a face  22  which is configured to be placed, in use, against a body of a subject. The face  22  comprises a skin tone sensor  24  which may be used to determine the skin tone of the portion of the body on which the personal care device  10  is used, such that a suitable dose of energy-based treatment may be administered to the portion of the body of the subject. The face  22  additionally comprises two skin contact sensors  26 , which may be provided on or in the face  22 , and configured to determine whether the face  22  is in contact with the body of the subject. The skin contact sensors  26  may measure a parameter that is indicative of whether the face  22  is in contact with skin, and generate respective measurement signals (referred to as ‘skin contact measurement signals’). Typically a skin contact sensor  26  is used in a personal care device  10 , particularly a photoepilator, to make sure that the personal care device  10  is correctly in contact with skin before a light pulse is generated to avoid the light pulse being directed into the eyes of the user or subject. 
     The parameter can be capacitance, and so the skin contact sensors  26  can measure capacitance via a respective pair of electrical contacts or electrodes on the surface of the face  22 , with the measured capacitance being indicative of whether there is skin contact. Alternatively, the parameter can be an intensity or level of light, and so the skin contact sensors  26  can be light sensors that measure an intensity or level of light incident on the light sensor, with the measured intensity or level being indicative of whether there is skin contact (e.g. less/no light could indicate skin contact as the skin obscures the light sensors  26 , and vice versa). In other alternatives, the parameter can be a measure of contact pressure, and so the skin contact sensors  26  can measure contact pressure via respective pressure sensors or mechanical switches, with the measured contact pressure being indicative of whether there is skin contact. 
     The detachable portion  20  comprises an engagement portion  40 ,which may, for example, comprise barbed flanges or tabs, configured to engage a corresponding portion (not shown) of the main body portion  12 . Detachment of the detachable portion  20  from the main body portion  12  may require a threshold force in order to disengage the corresponding engagement portions  40 . 
     The face  22  comprises a primary opening  30  formed where a cavity  32  of the detachable portion  20  intersects the face  22 . A supporting surface  28  is provided about the primary opening  30 , the supporting surface  28  being configured, in use, to be placed against the body of the subject being treated. 
     The cavity  32  is configured to transmit energy from an energy source  58  ( FIG.  5   ) to the primary opening  30 . For example, an energy source  58  may be provided outside of the cavity  32  and treatment energy may be transmitted into the cavity, e.g. by an energy window  56  ( FIG.  5   ). A reflector (not shown) may be provided about the energy source  58  to direct treatment energy into the cavity  32 . The cavity  32  may be configured to transmit treatment energy from an internal end  34  of the cavity  32  towards the primary opening  30 . Additionally or alternatively, an energy source  58  may be provided within the cavity  32 , and the cavity  32  may be configured to transmit treatment energy from an energy source  58  disposed part way along, i.e. within, the cavity  32 , towards the primary opening  30 . 
     The cavity  32  comprises at least one reflector wall  36 T,  36 B,  36 L,  36 R (collectively  36 ) configured to reflect, and thereby direct, treatment energy towards the primary opening  30 . The at least one reflector wall  36  is opaque to the treatment energy emitted by the energy source  58 . In the example shown in  FIG.  2    and  FIG.  3   , the top, bottom, left and right reflector walls  36 T,  36 B,  36 L,  36 R each comprise a respective reflective surface  37 T,  37 B,  37 L,  37 R (collectively  37 ) within the cavity  32 . It will be understood by the skilled person that alternative reflector wall  36  configurations may be suitable, for example a reflector wall of circular cross section rather than rectangular. Additionally or alternatively, not every reflector wall  36  may require or comprise a reflective surface  37 . 
     A secondary opening  38 T,  38 B,  38 L,  38 R (collectively  38 ) is provided in at least one of the reflectors walls  36 . In the example shown in  FIG.  2    and  FIG.  3   , a respective secondary opening  38 T,  38 B,  38 L,  38 R is provided in each of the top, bottom, left and right reflector walls  36 T,  36 B,  36 L,  36 R. The secondary opening  38  is arranged at a distance from the primary opening  30 , such that in use, the secondary opening  38  is provided at a distance from the body of the subject. The secondary opening  38  is configured to permit a flow of air via the secondary opening  38  and, thereby, a flow of air out of the cavity  32  whilst treatment energy is transmitted from the energy source  58  to the primary opening  30 . The secondary opening  38  may be configured to be permanently open. For example, the secondary opening  38  may be configured to permit a flow of air, via the secondary opening  38 , into the cavity  32  and, via the primary opening  30 , out of the cavity  32 , whilst treatment energy is transmitted from the energy source  58  to the primary opening  30 . The secondary opening  38  may be configured to permit a flow of air into and/or out of the cavity whilst treatment energy is not being transmitted from the energy source  58  to the primary opening  30  (e.g. immediately after the transmission of treatment energy). 
     Each secondary opening  38  may comprise a cross section of any suitable shape, including but not limited to a circle, an ellipse, a square, a rectangle, or an annulus. In the example shown in  FIG.  2    and  FIG.  3   , each secondary opening  38  has a circular cross section. 
     The secondary opening  38  may be configured to restrict a loss of treatment energy from the cavity  32  via the secondary opening  38  (e.g. for a photoepilator, to minimise a loss in optical efficiency).  FIG.  4    shows a schematic section through a cavity  32  comprising a secondary opening  38  configured to restrict a loss of treatment energy via secondary opening  38 . The secondary opening  38  shown in  FIG.  4    is provided along an axis  31  which is offset or tilted away from a direction of propagation  33  of treatment energy, and offset or tilted away from a direction  35  of treatment energy incident upon the secondary opening  38 B. Additionally or alternatively, the secondary opening  38  may be provided along an axis  31  tilting away from a longitudinal axis of the cavity  32 ; and/or provided along an axis  31  passing through the primary opening  30  (e.g. a centre point of the primary opening  30 ). 
     The illustrated axis  31  of the secondary opening  38  gives rise, with respect to a direction of propagation  33  of treatment energy being incident upon the secondary opening  38 , to a leading edge  39  of the reflector wall  36  and a trailing edge 41of the reflector wall  36 . The leading edge  39  may overlap and/or extend beyond the trailing edge  41  with respect to a direction of propagation  33  of treatment energy within the cavity  32 . The leading edge  39  may be at an angle β to the reflective surface  37 B of the reflector wall  36 B. The trailing edge  41  may be at an angle α to an external surface of the reflector wall  36 B. Angle α may be less than or equal to angle β. Angle α may be less than 60°, preferably less than 45°. The difference between angle α and angle β may be less than 90°. 
     Additionally or alternatively, the secondary opening  38  may be provided along an axis  31  which is perpendicular to a direction of propagation  33  of treatment energy towards the primary opening  30 . The secondary opening  38  may be provided along an axis  31  which is perpendicular to a longitudinal axis of the cavity  32 . 
     The secondary opening  38  may comprise a reflective surface  37 H provided on an interior surface of the secondary opening  38 , the reflective surface  37 H being configured to restrict a loss of treatment energy from the cavity  32  via the secondary opening  38 . 
     The secondary opening  38  may be configured to restrict a loss of treatment energy from the cavity  32  by limiting the cross sectional area (or, if a plurality of secondary openings  38 , the total cross sectional area of the secondary openings  38 ). For example, if the treatment energy comprises light, then a reduced diameter of the secondary opening  38  will reduce optical losses from the cavity. 
     It would be advantageous if the cross sectional area of the secondary opening  38  (or, if a plurality of secondary openings  38 , the total cross sectional area of the secondary openings  38 ) were large enough to allow sufficient air flow, and thus sufficient cooling, of the cavity  32  (e.g. sufficient cooling for the cavity  32  to remain below certain threshold temperatures). Preferably, the total area of the secondary openings  38  is more than 0.1 mm 2 , more preferably more than 1 mm 2 , most preferably 10 mm 2 . 
     It would be advantageous if the hydraulic diameter of the secondary opening  38  (or, if a plurality of secondary openings  38 , the total hydraulic diameter of the secondary openings  38 ) were small enough to reduce drag of air passing through the secondary openings  38  to negligible levels. The hydraulic diameter of each secondary opening  38  is preferably less than 10 mm, more preferably less than 0.5 mm. Accordingly, multiple secondary openings  38  may be required to meet both the area requirement and hydraulic diameter requirement. 
     The secondary openings  38  may be evenly and/or uniformly distributed throughout the reflector walls  36 . In the example shown in  FIG.  2    and  FIG.  3   , one secondary opening  38  is provided in the centre of each reflector wall  36 . In alternative arrangements (not shown), multiple secondary openings  38  may be provided in each reflector wall  36  and/or at least one reflector wall  36  may comprise no secondary openings  38 . 
     The skilled person will be able to determine the appropriate number of secondary openings  38  according to the parameters of the personal care device  10 , including the rate of heat generation, and a balancing of the competing factors of cross sectional area, hydraulic diameter and energy loss from the cavity  32 . 
     In one example not shown, the reflector wall  36  may comprise a plurality of louvres or slats arranged in parallel, having secondary openings  38  in the form of slits provided therebetween. A reflective surface  37  provided on each louvre may direct treatment energy towards the primary opening  30 , whilst the slits therebetween permit a flow of air through the secondary openings  38 . A leading edge  39  and trailing edge  41  configuration may then be achieved in a similar manner to  FIG.  4   . 
       FIG.  5    shows a schematic vertical section through the personal care device  10  when the detachable portion  20  is attached to the main body portion  12  by means of the engagement portion  40  and corresponding portion (not shown) of the main body portion  12 . For simplicity, the handle  14  and user control  16  of the main body portion  12  have been omitted from  FIG.  5   . 
     The main body portion  12  comprises a housing  50  having an inlet vent  52  which may be configured to permit a flow of air into the main body portion  12 , for example as a result of a suction created by a fan (not shown) provided within the main body portion  12 . An outlet vent  54  may be provided on an opposite side of the main body portion  12  to the inlet vent  52 , such that the flow of air within the main body portion  12  may be directed through and/or past the components of the main body portion  12 , including an energy window  56  and an energy source  58 , in order to perform cooling. It will be understood that additional components (not shown) may be present within the main body portion  12 , for example components configured to direct the flow of air, and/or components towards which the flow of air may be directed for the purpose of cooling (e.g. a PCB). 
     The energy window  56  may be provided in the housing  50  at a front end of the main body portion  12 , such that when the detachable portion  20  is attached to the main body portion  12 , the internal end  34  of the cavity  32  may align with the energy window  56 . Adjacent the energy window  56 , an energy source  58  is provided within the main body portion  12 . The energy source  58  may be any energy source  58  suitable for performing an energy-based treatment on the body of a subject. For example, in a skin care device configured to perform photoepilation, the energy source may comprise a lamp, LED, laser or other light source, configured to emit intense pulsed light of a required frequency. 
     The energy window  56  is configured to be substantially transparent to the treatment energy emitted by the energy source  58 , and configured to transmit treatment energy from the energy source  58  provided inside the main body portion  12  to outside the main body portion  12 . In particular, the energy window  56  is configured to transmit treatment energy from the energy source  58  into the cavity  32  of the detachable portion  20  in a direction having at least a component towards the primary opening  30 . 
     The main body portion  12  further comprises at least one communication vent  60 L,  60 T (collectively,  60 ) configured to permit fluidic communication between the main body portion  12  and an internal space  23  of the detachable portion  20 . In the example shown in  FIG.  5   , the main body portion  12  comprises two communication vents  60 L,  60 T at a front end of the housing  50  of main body portion  12 , the communication vents  60 L,  60 T configured to ensure fluidic communicaton between the internal space  23  of the detachable portion  20  and the space within the housing  50  of the main body portion  12 . 
     In effect, upon attachment of the detachable portion  20  to the main body portion  12 , the primary opening  30  may be in (indirect) fluidic communication, via the internal space  23  of the detachable portion  20  and the communication vents  60  of the main body portion  12 , with the inlet vent  52  and outlet vent  54  of the main body portion  12 . A flow of air may thereby be permitted between the inlet vent  52  of the main body portion  12  and the primary opening  30  of the cavity  32 . 
     In use, the detachable portion  20  is attached to the main body portion  12 . The face  22  of the personal care device  10  is placed against the body of the subject, the body of the subject defining a volume of air within the cavity  32 , and the primary opening  30  defining the portion of the body of the subject being treated. The user may then trigger activation of the energy source  58  by means of the user control  16 . If the skin contact sensors  26  determine that the face  22  is in contact with the body of the subject, then the energy source  58  is activated with a dose of treatment energy according to the skin tone of the subject as detected by the skin tone sensor  24 . The energy window  56  transmits the treatment energy from the energy source  58 , provided inside the main body portion  12 , to the cavity  32 , and the reflector walls  36  reflect, and thereby direct, the treatment energy towards the primary opening  30  of the personal care device  10 . Administering the treatment energy to the body of the subject performs the energy-based treatment on the portion of the body of the subject defined by the primary opening  30 . The energy source  58  may be controlled by a controller to ensure a sufficient dose is administered, and/or to prevent an excessive dose being administered. 
     In placing the face  22  of the personal care device  10  against the body of the subject during use, an air flow into and/or out of the cavity  32  (e.g. via primary opening  30 ) may ordinarily be reduced. However, the secondary openings  38  of the present invention permit a flow of air out of the cavity  32 , whilst the treatment energy is transmitted towards the primary opening  30 . For example, air may be permitted to flow out of the cavity  32  via the primary opening  30  and/or any one or combination of the secondary openings  38 T,  38 B,  38 L,  38 R. Air may enter the cavity  32  via one or any combination of secondary openings  38 . Air may enter the cavity  32  via primary opening  30 . Air may leave the cavity  32  via one, or any combination of, the secondary openings  38 . Air may leave the cavity  32  via primary opening  30 . 
     It will be understood by the skilled person that a number of different air flow routes may be permitted by the arrangement of the primary opening  30 , the secondary openings  38 T,  38 B,  38 L,  38 R, the communication vents  60 L,  60 T, the inlet vent  52  and the outlet vent  54 . The nature and direction of each air flow route may depend, inter alia, upon the dimensions of each opening  30 ,  38  and vent  52 ,  54 ,  60 , as well as the temperature reached within the cavity  32 , relative pressures in different parts of the personal care device  10 , the internal air flow rate of the main body portion  12 , and the degree of reduction in air flow through the primary opening  30 . 
     In one example air flow path, air may enter the main body portion  12  via inlet vent  52 , and may pass clockwise with respect to  FIG.  5   . Air may enter detachable portion  20  via communication vent  60 B. Air may enter into the cavity  32  via the secondary opening  38 B. Air may leave the cavity  32  via primary opening  30 . Air may leave the cavity  32  via secondary opening  38 T. 
     In another example air flow path, air may enter the main body portion  12  via inlet vent  52 , and may pass clockwise with respect to  FIG.  5   . Air may enter the detachable portion  20  via communication vent  60 B. Air may enter cavity  32  via secondary opening  38 B. Air may leave via secondary opening  38 T, and may re-enter the main body portion  12  via communication vent  60 T. Air may leave main body portion  12  via outlet vent  54 . Air flow from secondary opening  38 B to secondary opening  38 T may draw air into the cavity  32  via primary opening  30 , which may then leave cavity  32  via secondary opening  38 T. 
     In a further example air flow path, air passing through the main body portion  12  from the inlet vent  52  to the outlet vent  54  may draw air into the main body portion  12  from the internal space of the detachable portion  20 , which may in turn draw air into the internal space of the detachable portion  20  from the cavity  32  via secondary openings  38 T,  38 B,  38 L,  38 R, which may in turn draw air into the cavity  32  via primary opening  30 . In effect, the air flow within the main body portion  12  may draw air into the cavity  32  via primary opening  30  as a result of fluidic communication between the cavity  32  and the main body portion  12 . 
     It should be understood that the above example air flow paths are not necessarily exclusive. For example, each example air flow path may occur during a typical use cycle of the personal care device  10 , in which the device  10  is placed against the body, the energy source  58  activated, then the personal care device  10  is moved away from the body, before being again placed against the body in a different location and the cycle repeated. In any case, the flow of air into and/or out of and/or through cavity  32  performs a cooling function in the cavity  32 , such that air within the cavity  32  is cooled and/or such that the components of the cavity and adjoining the cavity  32 , including the reflector walls  36 , the face  22  and supporting surface  28 , are cooled. 
       FIG.  6 A ,  FIG.  6 B  and  FIG.  6 C , collectively  FIG.  6   , show a schematic section through a single reflector wall  36 B of a cavity  32 . An auxiliary reflector  36 A may be provided externally to the cavity  32  and in alignment with the secondary opening  38  (e.g. in the internal space  23 ). The auxiliary reflector  36 A may restrict and/or prevent a loss of treatment energy from the cavity  32  via the secondary opening  38 . The auxiliary reflector  36 A may be configured to reflect treatment energy propagating from the cavity  32  into the secondary opening  38  back into the cavity  32  via a secondary opening  38  (e.g. the same secondary opening  38  and/or a different secondary opening  38 ). 
     As shown in  FIG.  6 A , the auxiliary reflector  36 A may comprise a reflective surface  37 A (e.g. a planar reflective surface) substantially parallel to the reflector wall  36  of the cavity  32 . The auxiliary reflector  36 A may be configured (e.g. arranged sufficiently proximate to the secondary opening  38  and reflector wall  36 ) to reflect treatment energy propagating from the cavity  32  into the secondary opening  38 B back into the cavity  32  via the same secondary opening  38 B through which the energy left the cavity  32 . The auxiliary reflector  36 A may reflect the treatment energy  59  back into the cavity  32  in a direction having a component towards the primary opening  30 , such that the treatment energy  59  may continue towards the body of the subject. The auxiliary reflector  36 A may be disposed on or against the housing  21  of the detachable portion  20 . 
     As shown in  FIG.  6 B , the auxiliary reflector  36 A may comprise a parabolic reflective surface  37 P, the auxiliary reflector  36 A being configured to reflect treatment energy propagating from the cavity  32  into the secondary opening  38 B back into the cavity  32  via the same secondary opening  38 B through which the energy left the cavity  32 . The parabolic reflective surface  37 P may be configured such that its focus is located at a centrepoint of the secondary opening  38 B. 
     As shown in  FIG.  6 C , the auxiliary reflector  36 A may comprise a planar reflective surface  37 A disposed substantially parallel to the reflector wall  36  of the cavity  32 , and running the length of the plurality of secondary openings  38  provided in the reflector wall  36 . The reflector wall  36  may comprise a reflective surface  37 E on its exterior, such that treatment energy may be reflected repeatedly between the reflective surface  37 A of the auxiliary reflector  36 A and the exterior reflective surface  37 E of the reflector wall  36 B. The auxiliary reflector may thereby be configured reflect treatment energy backing into the cavity  32  via a different secondary opening  38  from the secondary opening  38  through which the treatment energy left the cavity  32 . 
     In an example not shown, the reflector wall  36  may comprise a one-way reflector, such that treatment energy being reflected from an auxiliary reflector  36 A and incident upon an exterior surface of the reflector wall  36  may be transmitted into the cavity  32 , but treatment energy incident upon the reflective surface  37  of the reflector wall  36  may be reflected so as to remain within the cavity  32 . The secondary opening  38  may comprise a reflective surface  37  along its interior. 
       FIG.  7    shows a front view of the detachable portion  20  comprising at least one surface feature  64  and/or conduit  62  configured to permit fluidic communication between the cavity  32  and ambient air when the supporting surface  28  is in contact with the body of the subject.  FIG.  8    shows a schematic section through the detachable portion of  FIG.  7    along the line VIII-VIII. 
     With reference to  FIG.  7    and  FIG.  8   , the supporting surface  28  may comprise at least one surface feature  64  and/or conduit  62  configured to permit fluidic communication between the cavity  32  and ambient air when the supporting surface  28  is in contact with the body  66  of the subject. 
     The surface feature  64  and/or conduit  62  may be of any suitable shape for permitting a flow of air through the primary opening  30 . For example, the surface feature  64  and/or conduit  62  may be linear, or comprise a bend or kink along its length. The surface feature  64  and/or conduit  62  may be contiguous with the supporting surface  28 . 
     The surface feature  64  and/or conduit  62  may comprise a C-shaped groove  62 A or channel as shown in  FIG.  8 A , or alternatively a straight-sided groove  62 B or channel as shown in  FIG.  8 B . 
     Additionally or alternatively, the surface feature  64  and/or conduit  62  may comprise at least one protrusion  64  (e.g. a plurality of bumps) as shown in  FIG.  8 C . The protrusion may be configured to ensure an imperfect contact between the supporting surface  28  and the body  66  of the user. 
     Additionally or alternatively further still, the surface feature  64  and/or conduit  62  may comprise at least one conduit  62 D provided beneath the supporting surface  28 , as shown in  FIG.  8 D . 
     One end of each conduit surface feature  64  and/or conduit  62  may terminate within the cavity  32 , proximate to the primary opening  30 . Another end of each conduit may terminate on an exterior surface of the housing  21  of the detachable portion  20 , in communication with ambient air. In use, the supporting surface  28  is placed against the body  66  of the subject. The surface feature  64  and/or conduit  62  is configured to permit a flow of air through (e.g. into and/or out of) the primary opening  30  when the personal care device  10  is placed against the body  66  of the subject. In combination with the secondary openings  38 , the groove may permit a flow of air into and/or out of (e.g. through) the cavity  32  during operation of the personal care device  10 . For example, the groove may permit air entering the cavity  32  via the secondary opening  38  to exit the cavity  32  via the primary opening, whilst the personal care device is used and thus the supporting surface  28  is placed against the body/skin of the subject. 
     Preferably, a width dimension of each surface feature  64  and/or conduit  62  may be between 0.1 mm and 20 mm, more preferably between 0.5 mm and 10 mm. Preferably, a height or depth of each surface feature  64  and/or conduit  62  may be greater than 0.1 mm, more preferably between 0.5 mm and 10 mm. Nevertheless, the skilled person will be able to determine the number, shape and dimensions of the surface feature  64  and/or conduit  62  according to the parameters of the personal care device  10  and the nature of the application. 
     Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the principles and techniques described herein, from a study of the drawings, the disclosure and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single processor or other unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. A computer program may be stored or distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope.