Patent Publication Number: US-2022233400-A1

Title: Mask, and skin care apparatus comprising same

Description:
TECHNICAL FIELD 
     An embodiment relates to a mask and a skin care apparatus. 
     BACKGROUND ART 
     Human skin may be damaged or contaminated depending on external factors such as environmental pollution, ultraviolet rays, stress, and the like, and wrinkles may occur due to internal factors such as aging, hormonal changes, and the like. Recently, as interest in the skin has increased, various apparatuses for skin treatment, beauty, and anti-aging have been developed. 
     In detail, an apparatus has been developed, which is capable of applying thermal energy to the skin, for example, an apparatus capable of improving skin elasticity by applying infrared energy. In addition, an apparatus using sound waves or light rays has been developed in order to effectively inject cosmetics or drugs into the skin. For example, an apparatus has been developed, which is capable of forming a path through which cosmetics or drugs are injected into the skin using sonophoresis and laserporation. In addition, an apparatus using electric propulsion force has been developed in order to effectively inject cosmetics or drugs into the skin. For example, an apparatus has been developed, which is capable of effectively injecting ionic substances contained in cosmetics or drugs into the skin using iontophoresis, electroporation, and electroosmosis. That is, various apparatuses have been developed, which is capable of caring or treating a user&#39;s skin by providing light energy, microcurrent, vibration, or the like to the skin. 
     In general, the above-described apparatuses may be provided in a form of a patch detachable to the skin, and the apparatuses are attached to a specific skin region to care or treat the skin of the attached region. In addition, the above-described apparatuses are provided in a form of a mask pack disposed to cover the entire user&#39;s face to care or treat the facial skin. 
     However, the apparatuses have a problem that it is difficult to effectively adhere to curved skin surfaces such as both cheeks, nose, and the like. In detail, it may be difficult to effectively adhere to the user&#39;s skin due to materials and variable characteristics of the apparatus. Accordingly, the apparatus may be operated in a state in which the apparatus is not completely adhered to the user&#39;s skin, and the apparatus may be separated from the user&#39;s skin due to the user&#39;s movement or vibration of the apparatus during the operation thereof. 
     Accordingly, the apparatus may be operated in a state in which it is not completely adhered to the user&#39;s skin and may be spaced apart from the user&#39;s skin by the user&#39;s movement and vibration of the apparatus during operation. Thus, there is a problem that it is difficult to effectively obtain a care or treatment effect through the apparatus. 
     Therefore, a new mask capable of solving the above-described problem is required. 
     DISCLOSURE 
     Technical Problem 
     An embodiment is to provide a mask and a skin care apparatus that have variability and improved reliability. 
     In addition, an embodiment is to provide a mask and a skin care apparatus capable of effectively adhering to a user&#39;s skin. 
     In addition, an embodiment is to provide a mask and a skin care apparatus capable of providing uniform ultrasonic energy to a user&#39;s skin. 
     In addition, an embodiment is to provide a mask and skin care apparatus capable of reducing the overall thickness and weight. 
     In addition, an embodiment is to provide a mask and a skin care apparatus capable of minimizing the loss of ultrasonic energy generated during operation. 
     Technical Solution 
     A mask according to an embodiment includes a first substrate disposed on a first base layer, a first wire disposed on the first substrate, a piezoelectric element disposed on the first wire, a second wire disposed on the piezoelectric element, a second substrate disposed on the second wire, a second base layer disposed on the second substrate, and a cavity disposed between the first base layer and the piezoelectric element, wherein the cavity is disposed in a region overlapping the piezoelectric element in a vertical direction. 
     In addition, a skin care apparatus according to an embodiment includes a main body in which one side thereof is open and an accommodation space is formed inside the open region and the mask disposed in the open region and connected to the main body. 
     Advantageous Effects 
     A mask according to an embodiment may be varied according to a shape of a curved skin of a user by a substrate having a variable material, a first base layer, a second base layer, or the like. Accordingly, the mask can effectively adhere to the skin of the user. 
     In addition, the mask according to the embodiment may include a plurality of piezoelectric elements, and the piezoelectric elements may generate ultrasonic energy in the entire region of the mask. Accordingly, it is possible to provide ultrasonic energy having uniform intensity to a user wearing the mask. 
     In addition, the piezoelectric elements according to the embodiment may be disposed at different intervals according to a face shape of the user. For example, the piezoelectric elements disposed in a relatively curved region such as nose, cheeks, and the like and a planar region such as forehead of the user are disposed at different intervals from each other, and accordingly, it is possible to provide the ultrasonic energy having uniform intensity to the curved region of the user&#39;s face. 
     In addition, the mask according to the embodiment may include a cavity and may effectively reflect the ultrasonic energy by the cavity. Accordingly, it is possible to minimize the loss of ultrasonic energy generated during operation of the piezoelectric element. In addition, since a required thickness of the first base layer can be reduced, the overall thickness and weight of the mask can be reduced. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a front view of a mask according to an embodiment. 
         FIG. 2  is an exploded perspective view of region A 1  in  FIG. 1 . 
         FIG. 3  is a top view of the region A 1  in  FIG. 1 . 
         FIG. 4  is another top view of the region A 1  in  FIG. 1 . 
         FIG. 5  is a cross-sectional view taken along line A-A′ of  FIG. 4 . 
         FIG. 6  is an enlarged view of region A 2  in  FIG. 5 . 
         FIGS. 7 to 9  are views for describing an arrangement position of a cavity in the mask according to the embodiment. 
         FIG. 10  is another enlarged view of the region A 2  of  FIG. 5 . 
         FIG. 11  is another cross-sectional view taken along line A-A′ of  FIG. 4 . 
         FIG. 12  is an enlarged view of region A 3  in  FIG. 11 . 
         FIG. 13  is another enlarged view of region A 3  in  FIG. 11 . 
         FIGS. 14 to 16  are views illustrating an example in which an indicator and a protrusion are provided on the mask according to the embodiment. 
         FIG. 17  is a view illustrating a user wearing the mask according to the embodiment. 
         FIG. 18  is a view illustrating a skin care apparatus to which the mask according to the embodiment is applied. 
     
    
    
     MODES OF THE INVENTION 
     Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
     However, the spirit and scope of the present invention is not limited to a part of the embodiments described, and may be implemented in various other forms, and within the spirit and scope of the present invention, one or more of the elements of the embodiments may be selectively combined and replaced. 
     In addition, unless expressly otherwise defined and described, the terms used in the embodiments of the present invention (including technical and scientific terms may be construed the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, and the terms such as those defined in commonly used dictionaries may be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art. 
     In addition, the terms used in the embodiments of the present invention are for describing the embodiments and are not intended to limit the present invention. In this specification, the singular forms may also include the plural forms unless specifically stated in the phrase, and may include at least one of all combinations that may be combined in A, B, and C when described in “at least one (or more) of A (and), B, and C”. 
     In addition, in describing the elements of the embodiments of the present invention, the terms such as first, second, A, B, (A, and (b) may be used. These terms are only used to distinguish the elements from other elements, and the terms are not limited to the essence, order, or order of the elements. Further, when an element is described as being “connected”, “coupled”, or “connected” to another element, it may include not only when the element is directly “connected” to, “coupled” to, or “connected” to other elements, but also when the element is “connected”, “coupled”, or “connected” by another element between the element and other elements. 
     Further, when described as being formed or disposed “on (over)” or “under (below)” of each element, the “on (over)” or “under (below)” may include not only when two elements are directly connected to each other, but also when one or more other elements are formed or disposed between two elements. Furthermore, when expressed as “on (over)” or “under (below)”, it may include not only the upper direction but also the lower direction based on one element. 
     In addition, before describing the embodiments of the present invention, a first direction may refer to an x-axis direction shown in the drawings, and a second direction may be a different direction from the first direction. As an example, the second direction may refer to a y-axis direction shown in the drawing in a direction perpendicular to the first direction. In addition, a horizontal direction may refer to the first and second directions, and a vertical direction may refer to a direction perpendicular to at least one of the first and second directions. For example, the horizontal direction may refer to the x-axis and y-axis directions of the drawing, and the vertical direction may be a z-axis direction of the drawing and a direction perpendicular to the x-axis and y-axis directions. 
       FIG. 1  is a front view of a mask according to an embodiment, and  FIG. 2  is an exploded perspective view of region A 1  in  FIG. 1 . In addition,  FIG. 3  is a top view of the region A 1  in  FIG. 1 , and  FIG. 4  is another top view of the region A 1  in  FIG. 1 . In addition,  FIG. 5  is a cross-sectional view taken along line A-A′ of  FIG. 4 , and  FIG. 6  is an enlarged view of region A 2  in  FIG. 5 . 
     Referring to  FIGS. 1 to 6 , a mask  1000  according to the embodiment may be provided in a predetermined size to cover a user&#39;s face and have a predetermined elasticity in order to be closely adhered to the user&#39;s face. The mask  1000  may include one surface in contact with the user&#39;s skin and the other surface opposite to the one surface, and the one surface of the mask  1000  may be made of a material that is harmless to the human body, so that it is harmless despite being in contact with the user&#39;s skin for a long time. 
     The mask  1000  may include at least one of an opening  1010  and a cutout portion  1020 . In detail, the opening  1010  may be formed in a portion corresponding to the user&#39;s eyes or mouth. The opening  1010  is a region penetrating through one surface and the other surface of the mask  1000  facing the user&#39;s skin, and when the user wears the mask  1000 , the user&#39;s eyes and mouth may be inserted into the opening  1010 , and a region excluding the opening  1010  may be closely adhered to the user&#39;s face. In addition, the cutout portion  1020  may be formed in a portion corresponding to both cheek lines, chin, and the like, which are relatively curved in order to improve adhesion between the mask  1000  and the skin. The cutout portion  1020  may have a form in which one surface and the other surface of the mask  1000  are partially cut. 
     The region excluding the opening  1010  in the mask  1000  according to the embodiment may include a first substrate  110 , a first wire  210 , a piezoelectric element  300 , a second wire  220 , a second substrate  120 , a first base layer  510 , a second base layer  520 , and a cavity  410 . 
     The first substrate  110  may be transparent and include a material in consideration of moisture barrier properties, thermal stability, and the like. In addition, the first substrate  110  may include a material that has flexibility and varies according to a shape of the user&#39;s curved skin. As an example, the first substrate  110  may include a resin material such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polyimide (PI). The first substrate  110  may be provided in a form of a film. 
     The first substrate  110  may have a thickness of about 0.5 μm to about 5 μm or less. When the thickness of the first substrate  110  is less than about 0.5 μm, there may be a problem that a region of the first substrate  110  overlapping the components is struck by a weight of the components disposed on the first substrate  110 , for example, the piezoelectric element  300 . Accordingly, reliability of the first substrate  110  may be deteriorated, and a problem of alignment of the components disposed on the first substrate  110  may occur. In addition, when the thickness of the first substrate  110  exceeds about 5 μm, the overall thickness of the mask  1000  may be increased. Accordingly, there is a problem that the mask  1000  may not be efficiently varied according to the shape of the user&#39;s skin, and thus the mask  1000  does not effectively adhere to the user&#39;s skin. Preferably, the first substrate  110  may have a thickness of about 0.5 μm to about 3 μm. When the thickness of the first substrate  110  satisfies the above-described range, the first substrate  110  may be efficiently varied in a form corresponding to the user&#39;s skin and the overall thickness and weight of the mask  1000  may be reduced while maintaining reliability and alignment characteristics. 
     The first wire  210  may be disposed on the first substrate  110 . The first wire  210  may be electrically connected to the piezoelectric element  300 . The first wire  210  may include a conductive material. As an example, the first wire  210  may include at least one metal of aluminum (Al), copper (Cu), silver (Ag), gold (Au), chromium (Cr), nickel (Ni), molybdenum (Mo), titanium (Ti), and alloys thereof. In addition, the first wire  210  may include a non-metal such as carbon, and the like. 
     The first wire  210  may be disposed on one surface of the first substrate  110  facing the piezoelectric element  300 . The first wire  210  may be in direct contact with one surface of the first substrate  110  and extend in the first direction. The first wire  210  may be formed on one surface of the first substrate  110  by a process such as deposition or printing. 
     The first wire  210  may include a plurality of first sub-wires  211  disposed on the first substrate  110 . The plurality of first sub-wires  211  may extend in the first direction and may be disposed to be spaced apart from each other in the second direction different from the first direction. The plurality of first sub-wires  211  may be electrically connected to each other. Here, the second direction may be a direction different from the first direction and may be the vertical direction, for example, but the embodiment is not limited thereto. 
     A thickness of the first sub-wire  211  may be about 2 μm to about 50 μm. In detail, the thickness of the first sub-wire  211  may be about 2 μm to about 40 μm. When the thickness of the first sub-wire  211  is less than about 2 μm , electrical characteristics may be deteriorated, and it may be difficult to form uniformly. In addition, when the thickness of the first sub-wire  211  exceeds about 50 μm, the overall thickness of the mask  1000  may increase, and a manufacturing time of the first wire  210  may increase. In addition, the thickness of the first sub-wire  211  is too thick, and thus the stretchable characteristics may be deteriorated. Preferably, the thickness of the first sub-wire  211  may be about 5 μm to about 35 μm or less in consideration of stretchable characteristics in the horizontal direction, reliability, and process efficiency. 
     In addition, a line width of the first sub-wire  211  may be greater than the thickness of the first sub-wire  211 . The line width of the first sub-wire  211  may be about 50 μm to about 500 μm. In detail, the line width of the first sub-wire  211  may be about 100 μm to about 450 μm. When the line width of the first sub-wire  211  is less than about 50 μm, reliability may be deteriorated, and when the line width of the first sub-wire  211  exceeds about 500 μm, an elongation may decrease and the stretchable characteristics may be deteriorated. Preferably, the line width of the first sub-wire  211  may be about 100 μm to about 400 μm in consideration of the stretchable characteristics. 
     The first wire  210  may have various shapes. For example, when viewed in a plane, each of the plurality of first sub-wires  211  may have a shape extending in the first direction as shown in  FIG. 3 . In detail, the plurality of first sub-wires  211  may have equivalent intervals from the adjacent first sub-wires  211  and may have a linear shape extending in the first direction. 
     Alternatively, when viewed in a plane, each of the plurality of first sub-wires  211  may have a curved shape extending in the first direction. For example, each of the plurality of first sub-wires  211  may be provided in a form in which a wavy pattern is repeated. In this case, the first sub-wire  211  may have a curvature pattern of about 3 R to about 20 R (mm). Accordingly, when the mask  1000  is stretched or contracted in one direction, the first wire  210  may have the stretchable characteristics and may not be cut. Preferably, the first sub-wire  211  may have a curvature pattern of about 5 R to about 15 R (mm). In addition, the first sub-wire  211  may have an elongation of about 10% to about 50%. Accordingly, the first wire  210  may have more improved stretchable characteristics, thereby improving reliability and improving adhesion to the user&#39;s skin. 
     Still alternatively, although not shown in the drawing, when viewed in a plane, each of the plurality of first sub-wires  211  may have a shape in which a pattern in which a straight line and a curve extending in the first direction are mixed is repeated. For example, when viewed from a plane, the first sub-wire  211  positioned in a region overlapping a relatively curved region (nose, cheeks, etc.) of the user&#39;s face may be provided in a curved shape, and the first sub-wire  211  positioned in a region overlapping a relatively planar region (forehead, etc.) may be provided in a straight line. Accordingly, when the mask  1000  is attached to the user&#39;s face, it is possible to solve a problem that the first wire  210  is damaged due to deformation of the mask  1000 . In addition, the first sub-wire  211  may be provided in a form in which straight lines and curves are mixed to maintain electrical characteristics and at the same time reduce the ratio occupied by the first wire  210 , thereby reducing overall manufacturing costs. 
     The piezoelectric element  300  may be disposed on the first substrate  110 . In detail, the piezoelectric element  300  may be disposed on the first wire  210  and electrically connected to the first wire  210 . The piezoelectric element  300  may include a ceramic material. As an example, the piezoelectric element  300  may include at least one of ZnO, AN, LiNbO 4 , lead antimony stannate, lead magnesium tantalate, lead nickel tantalate, titanates, tungstates, zirconates, or lead including lead zirconate titanate [Pb(Zr x Ti 1−x )O 3 (PZT)], lead lanthanum zirconate titanate (PLZT), lead niobium Zirconate titanate (PNZT), BaTiO 3 , SrTiO 3 , lead magnesium niobate, lead nickel niobate, lead manganese niobate, lead zinc niobate, lead including lead titanate, barium, bismuth, or niobates of strontium. 
     The piezoelectric element  300  may be disposed on the first wire  210  in plural. In detail, a plurality of piezoelectric elements  300  may be disposed to be spaced apart from each other on the first sub-wire  211 . For example, the plurality of piezoelectric elements  300  may be disposed on one first sub-wire  211 , and the plurality of piezoelectric elements  300  may be spaced apart at equivalent intervals on the first sub-wire  211 . In addition, a piezoelectric element  300  disposed on one first sub-wire  211  may or may not overlap a piezoelectric element  300  disposed on the first sub-wire  211  closest to the one first sub-wire  211  in the second direction. 
     In addition, some of the piezoelectric elements  300  may be spaced apart at equivalent intervals, and the remaining piezoelectric elements  300  may not be disposed at equivalent intervals. For example, a space between the piezoelectric elements  300  may be disposed at equivalent intervals in a region overlapping a relatively planar region of the user&#39;s face surface. However, the space between the piezoelectric elements  300  may not be disposed at equivalent intervals in a region overlapping a relatively curved skin region. That is, the space between the piezoelectric elements  300  may be relatively narrow or large depending on the degree of curvature of the skin surface. As an example, the space between the piezoelectric elements  300  disposed in the region overlapping the curved region such as a user&#39;s nose and cheeks, may be relatively narrow. Accordingly, the mask  1000  according to the embodiment may effectively provide ultrasonic energy even to the curved skin. 
     The piezoelectric element  300  according to the embodiment may be disposed on the entire region of the mask  1000  at predetermined intervals and may generate evenly the ultrasonic energy in the entire region of the mask  1000 . 
     The piezoelectric element  300  may overlap the first sub-wire  211 . In detail, a lower surface of the piezoelectric element  300  may overlap the first sub-wire  211  in the vertical direction. 
     The piezoelectric element  300  may generate wave energy by an applied current. For example, the piezoelectric element  300  may generate ultrasonic energy by the applied current. In detail, the piezoelectric element  300  may generate ultrasonic energy of about 1 MHz or less. In more detail, the piezoelectric element  300  may generate ultrasonic energy of about 10 KHz to about 1 MHz. In more detail, the piezoelectric element  300  may generate ultrasonic energy of about 100 KHz to about 800 KHz. The ultrasonic energy generated by the piezoelectric element  300  may move in a direction of one surface of the mask  1000 , and may be transmitted to the user&#39;s skin to massage the user&#39;s skin. 
     A thickness of the piezoelectric element  300  may be about 1500 μm or less. In detail, the thickness of the piezoelectric element  300  may be about 1200 μm or less. Preferably, the thickness of the piezoelectric element  300  may be about 1000 μm or less. It is preferable that the thickness of the piezoelectric element  300  satisfies the above-described range in consideration of the overall thickness and variable characteristics of the mask  1000 . 
     The piezoelectric element  300  may have various shapes. For example, the piezoelectric element  300  may have a polygonal column shape in which lower and upper surfaces are polygonal, and the lower and upper surfaces may have a circular column shape. In addition, one surface of the lower and upper surfaces of the piezoelectric member  300  may be a polygon and the other surface may have a pillar shape. As an example, an area of at least one of the lower surface and the upper surface of the piezoelectric element  300  may be about 100 mm 2  or less. 
     As described above, the piezoelectric element  300  may have various pillar shapes, and intensity and an oscillation direction of ultrasonic energy generated according to the pillar shape may be controlled. In addition, the intensity of ultrasonic energy transmitted to the user&#39;s skin may be adjusted according to a size, arrangement interval, arrangement density, and the like of the piezoelectric element  300 . 
     The piezoelectric element  300  may generate various waves. As an example, the piezoelectric element  300  may generate at least one wave of a transverse wave in which a traveling direction of wave and a vibration direction of medium are perpendicular, and a longitudinal wave in which the traveling direction of wave and the vibration direction of medium are the same. In addition, the piezoelectric element  300  may multiple-resonate. For example, the piezoelectric element  300  may include at least one via hole and may multiple-resonate by the formed via holes. In this case, an upper area of the via holes may be about 10% to about 45% of an area of the upper surface of the piezoelectric element  300  for multiple resonance. In addition, when the piezoelectric element  300  multiple-resonates by the via holes, the number of multiple resonance frequency regions may correspond to the number of the via holes. That is, the piezoelectric element  300  may emit wavelengths of various frequency ranges, for example, ultrasonic energy, as the number of the via holes increases in a set number range of via holes. 
     The embodiment may include a first metal layer  350  disposed on the piezoelectric element  300 . In detail, the embodiment may further include the first metal layer  350  disposed on an upper surface of the piezoelectric element  300  in order to improve vibration characteristics of the piezoelectric element  300 . That is, the first metal layer  350  may be a vibration plate. 
     The first metal layer  350  may include a metal material and may be electrically connected to the piezoelectric element  300 . As an example, the first metal layer  350  may include at least one metal of aluminum (Al), copper (Cu), zinc (Zn), iron (Fe), nickel (Ni), chromium (Cr), silver (Ag), gold (Pt), stainless steel (SUS), and alloys thereof. 
     The first metal layer  350  may have a shape corresponding to the piezoelectric element  300 . For example, the first metal layer  350  may have a planar shape corresponding to the upper surface of the piezoelectric element  300 . In addition, the first metal layer  350  may have a width in a horizontal direction corresponding to the upper surface of the piezoelectric element  300 . 
     A thickness of the first metal layer  350  may be about 1500 μm or less. In detail, the thickness of the first metal layer  350  may be about 1200 μm or less. Preferably, the thickness of the first metal layer  350  may be about 1000 μm or less. It is preferable that the thickness of the first metal layer  350  satisfies the above-described range in consideration of the variable characteristics of the mask  1000  and the vibration characteristics of the piezoelectric element  300 . 
     The second substrate  120  may be disposed on the piezoelectric element  300 . The second substrate  120  may be disposed on the first metal layer  350 . The second substrate  120  may be transparent and include a material in consideration of moisture barrier properties, thermal stability, and the like. In addition, the second substrate  120  may include a material that has flexibility and varies according to a shape of the user&#39;s curved skin. As an example, the second substrate  120  may include a resin material such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polyimide (PI). The second substrate  120  may be provided in a form of a film. The second substrate  120  may have the same material and the same shape as the first substrate  110 , but the embodiment is not limited thereto. 
     The second substrate  120  may have a thickness of about 0.5 μm to about 5 μm. When the thickness of the second substrate  120  is less than about 0.5 μm, there may be a problem that a region of the second substrate  120  overlapping the components is struck by a weight of the components disposed on the second substrate  120 , for example, the piezoelectric element  300 . Accordingly, reliability of the second substrate  120  may be deteriorated, and a problem of alignment of the components disposed on the second substrate  120  may occur. In addition, when the thickness of the second substrate  120  exceeds about 5 μm, the overall thickness of the mask  1000  may be increased. Accordingly, there is a problem that the mask  1000  may not be efficiently varied according to the shape of the user&#39;s skin, and thus the mask  1000  does not effectively adhere to the user&#39;s skin. Preferably, the second substrate  120  may have a thickness of about 0.5 μm to about 3 μm. When the thickness of the second substrate  120  satisfies the above-described range, the second substrate  120  may be efficiently varied in a form corresponding to the user&#39;s skin and the overall thickness and weight of the mask  1000  may be reduced while maintaining reliability and alignment characteristics. The second substrate  120  may have the same thickness as the first substrate  110 , but the embodiment is not limited thereto. 
     The second wire  220  may be disposed under the second substrate  120 . The second wire  220  may be electrically connected to the piezoelectric element  300 . The second wire  220  may be electrically connected to the first metal layer  350 . The second wire  220  may include a conductive material. As an example, the second wire  220  may include at least one metal of aluminum (Al), copper (Cu), silver (Ag), gold (Au), chromium (Cr), nickel (Ni), molybdenum (Mo), titanium (Ti), and alloys thereof. In addition, the second wire  220  may include a non-metal such as carbon, and the like. The second wire  220  may include the same material as the first wire  210 . 
     The second wire  220  may be disposed on one surface of the second substrate  120  facing the piezoelectric element  300 . That is, the second wire  220  may be disposed on one surface opposite to the other surface of the second substrate  120  facing the user&#39;s skin. The second wire  220  may be in direct contact with one surface of the second substrate  120  and may extend in a different direction from the first wire  210 . For example, the second wire  220  may extend in the second direction perpendicular to the first direction in which the first wire  210  extends. The second wire  220  may be formed on one surface of the second substrate  120  by a process such as deposition or printing. 
     The second wire  220  may include a plurality of second sub-wires  221  disposed on the second substrate  120 . The plurality of second sub-wires  221  may extend in the second direction and may be spaced apart from each other in the first direction. The plurality of second sub-wires  221  may be electrically connected to each other. 
     The second sub-wire  221  may overlap the piezoelectric element  300 . In detail, the second sub-wire  221  may overlap the upper surface of the piezoelectric element  300  in the vertical direction. 
     The first wire  210  and the second wire  220  may be disposed to cross each other. In detail, when viewed in a plane as shown in  FIG. 3 , the first sub-wire  211  and the second sub-wire  221  may be disposed to cross each other in a mesh shape, and an open region OA in which the electrodes  210  and  220  are not disposed may be formed between the sub-wires  211  and  221 . 
     A thickness of the second sub-wire  221  may be about 2 μm to about 50 μm. In detail, the thickness of the second sub-wire  221  may be about 2 μm to about 40 μm. When the thickness of the second sub-wire  221  is less than about 2 μm , electrical characteristics may be deteriorated, and it may be difficult to form uniformly. In addition, when the thickness of the second sub-wire  221  exceeds about 50 μm, the overall thickness of the mask  1000  may increase, and a manufacturing time of the second wire  220  may increase. In addition, the thickness of the second sub-wire  221  is too thick, and thus stretchable characteristics may be deteriorated. Preferably, the thickness of the second sub-wire  221  may be about 30 μm or less in consideration of stretchable characteristics in the horizontal direction, reliability, and process efficiency. The thickness of the second sub-wire  221  is provided equal to the thickness of the first sub-wire  211 , so that process efficiency may be improved. 
     In addition, a line width of the second sub-wire  221  may be greater than the thickness of the second sub-wire  221 . For example, the line width of the second sub-wire  221  may be about 50 μm to about 500 μm. In detail, the line width of the second sub-wire  221  may be about 100 μm to about 450 μm. When the line width of the second sub-wire  221  is less than about 50 μm, reliability may be deteriorated, and when the line width of the second sub-wire  221  exceeds about 500 μm, an elongation may decrease and the stretchable characteristics may be deteriorated. Preferably, the line width of the second sub-wire  221  may be about 100 μm to about 400 μm in consideration of the stretchable characteristics. The line width of the second sub-wire  221  is provided equal to the line width of the first sub-wire  211 , so that process efficiency may be improved. 
     The second wire  220  may have various shapes. For example, when viewed in a plane, each of the plurality of second sub-wires  221  may have a shape extending in the second direction as shown in  FIG. 3 . In detail, the plurality of second sub-wires  221  may have equivalent intervals from the adjacent second sub-wires  221  and may have a linear shape extending in the second direction. 
     Alternatively, when viewed in a plane, each of the plurality of second sub-wires  221  may have a curved shape extending in the second direction. For example, each of the plurality of second sub-wires  221  may be provided in a form in which a wavy pattern is repeated. In this case, the second sub-wire  221  may have a curvature pattern of about 3 R to about 20 R (mm). Accordingly, when the mask  1000  is stretched or contracted in one direction, the second wire  220  may have the stretchable characteristics and may not be cut. Preferably, the second sub-wire  221  may have a curvature pattern of about 5 R to about 15 R (mm). In addition, the second sub-wire  221  may have an elongation of about 10% to about 50%. Accordingly, the second wire  220  may have more improved stretchable characteristics, thereby improving reliability and improving adhesion to the user&#39;s skin. 
     Still alternatively, although not shown in the drawing, when viewed in a plane, each of the plurality of second sub-wires  221  may have a shape in which a pattern in which a straight line and a curve extending in the second direction are mixed is repeated. For example, when viewed in a plane, the second sub-wire  221  positioned in a region overlapping a relatively curved region (nose, cheeks, etc.) of the user&#39;s face may be provided in a curved shape, and the second sub-wire  221  positioned in a region overlapping a relatively planar region (forehead, etc.) may be provided in a straight line. Accordingly, when the mask  1000  is attached to the user&#39;s face, it is possible to solve a problem that the second wire  220  is damaged due to deformation of the mask  1000 . In addition, the second sub-wire  221  may be provided in a form in which straight lines and curves are mixed to maintain electrical characteristics and at the same time reduce the ratio occupied by the second wire  220 , thereby reducing overall manufacturing costs. 
     It is preferable that the second wire  220  has the same shape as the first wire  210  in consideration of the stretchable characteristic of the mask  1000 . That is, it is preferable that the first wire  210  and the second wire  220  disposed in the same region have the same shape as each other. 
     In addition, although not shown in the drawings, the second wire  220  may extend on the second substrate  120  in the same direction as the first wire  210 . That is, the second wire  220  may extend in the same first direction as the first wire  210 . 
     The mask  1000  according to the embodiment may include the first base layer  510 . The first base layer  510  may be disposed under the first substrate  110 . The first base layer  510  may be disposed on the other surface opposite to one surface of the first substrate  110 . The first base layer  510  may be disposed in direct contact with the other surface of the first substrate  110 . 
     The first base layer  510  may include a material harmless to the human body. In addition, the first base layer  510  may include a soft and elastic material. For example, the first base layer  510  may include at least one material of silicone, a thermoplastic resin, a thermoplastic silicone resin, a thermoplastic elastomer, a polyurethane elastomer, an ethylene vinyl acetate (EVA), a polyvinyl chloride (PVC) in which a harmless plasticizer and a stabilizer are added. Preferably, the first base layer  510  may include a silicone elastomer among them that is relatively light, can minimize irritation upon contact with the user&#39;s skin, and has a predetermined elasticity. 
     The first base layer  510  may be disposed to cover the entire region of the other surface of the first substrate  110 . That is, when viewed in a plane, a plan area of the first base layer  510  may correspond to an area of the other surface of the first substrate  110 . In addition, the plan area of the first base layer  510  may be greater than the area of the other surface of the first substrate  110 . Accordingly, the first base layer  510  may be disposed surrounding a side surface of the first substrate  110 . The first base layer  510  may prevent the other surface of the first substrate  110  from being exposed to the outside. 
     In addition, the first base layer  510  may reflect wavelengths emitted from the piezoelectric element  300  in a direction of one surface of the mask  1000 . That is, the first base layer  510  may be a reflective layer. To this end, a thickness of the first base layer  510  may be equal to or smaller than a thickness of the second base layer  520  to be described later. In detail, the thickness of the first base layer  510  may be equal to or smaller than the thickness of the second base layer  520  in order to reflect the wavelengths emitted from the piezoelectric element  300  toward the first substrate  110  to the first base layer  510 . 
     The thickness of the first base layer  510  may be about 50 μm to about 1 mm. When the thickness of the first base layer  510  is less than about 50 μm, the thickness of the first base layer  510  is relatively small, so that the first substrate  110  may not be effectively protected. In addition, when the thickness of the first base layer  510  exceeds about 1 mm, the thickness of the entire mask  1000  may be increased, and most of the wavelengths emitted from the piezoelectric element  300  in a direction of the first substrate  110  pass through the first base layer  510  and are reflected by the first base layer  510 , so that the amount of reflection in the direction of one surface of the mask  1000  may be small. In addition, the thickness of the second base layer  520  may be increased for reflection in the direction of one surface of the mask  1000 , and a region of the wavelengths generated from the piezoelectric element  300  is high for reflection, and thus it may not be suitable for use in the mask  1000 . Therefore, it is preferable that the thickness of the first base layer  510  satisfies the above-described range in order to prevent the above problems. More preferably, the thickness of the first base layer  510  may be about 100 μm to about 700 μm. That is, it is preferable that the first base layer  510  has a thickness range of about 100 μm to about 700 μm in consideration of reliability, reflective properties, and the thickness and weight of the mask  1000  to be manufactured. 
     In addition, the first base layer  510  may have pores or the like formed therein in order to effectively reflect the wavelengths generated from the piezoelectric element  300 , but the embodiment is not limited thereto. 
     The mask  1000  according to the embodiment may include the second base layer  520 . The second base layer  520  may be disposed on the second substrate  120 . The second base layer  520  may be disposed on the other surface opposite to the one surface of the second substrate  120 . The second base layer  520  may be disposed in direct contact with the other surface of the second substrate  120 . 
     The second base layer  520  is a portion that may be in contact with the skin while facing the user&#39;s skin, and may include a material harmless to the human body. In addition, the second base layer  520  may include a soft and elastic material. For example, the second base layer  520  may include at least one material of silicone, a thermoplastic resin, a thermoplastic silicone resin, a thermoplastic elastomer, a polyurethane elastomer, an ethylene vinyl acetate (EVA), a polyvinyl chloride (PVC) in which a harmless plasticizer and a stabilizer are added. Preferably, the second base layer  520  may include a silicone elastomer among them that is relatively light, can minimize irritation upon contact with the user&#39;s skin, and has a predetermined elasticity. That is, the first base layer  510  may be provided with the same material as the second base layer  520 . 
     The second base layer  520  may be disposed to cover the entire region of the other surface of the second substrate  120 . That is, when viewed in a plane, a plan area of the second base layer  520  may correspond to an area of the other surface of the second substrate  120 . In addition, the plan area of the second base layer  520  may be greater than the area of the other surface of the second substrate  120 . Accordingly, the second base layer  520  may be disposed surrounding a side surface of the second substrate  120 . The second base layer  520  may prevent the other surface of the second substrate  120  from being exposed to the outside. 
     In addition, the second base layer  520  may pass through the wavelengths emitted from the piezoelectric element  300  in the direction of one surface of the mask  1000  to transmit the wavelengths to the user&#39;s skin. That is, the second base layer  520  is transmission layer and may be a matching layer. To this end, the thickness of the second base layer  520  may vary depending on an impedance of the second base layer  520  and a driving frequency of the piezoelectric element  300 . In addition, the thickness of the second base layer  520  may be equal to or greater than the thickness of the first base layer  510 . 
     As an example, when the driving frequency of the piezoelectric element  300  is about 1 MHz or less, the thickness of the second base layer  520  may be about 50 μm to about 1 mm. When the thickness of the second base layer  520  is less than about 50 μm, the thickness of the second base layer  520  is relatively small, so that the second substrate  120  may not be effectively protected. In addition, when the thickness of the second base layer  520  exceeds about 1 mm, the thickness of the entire mask  1000  may be increased. It is preferable that the thickness of the second base layer  520  satisfies the above-described range in order to effectively pass through the wavelengths emitted from the piezoelectric element  300 . Preferably, the thickness of the second base layer  520  may have a thickness range of 100 μm to about 700 μm in consideration of reliability, transmission characteristics, and the thickness and weight of the mask  1000  to be manufactured. 
     Accordingly, the wave energy emitted from the piezoelectric element  300  may be reflected by the first base layer  510  to move toward the second base layer  520 , and the wave energy may be effectively transmitted to the user&#39;s skin through the second substrate  120  and the second base layer  520 . 
     The mask  1000  according to the embodiment may include the first protective layer  551 . The first protective layer  551  may be disposed between the first substrate  110  and the second substrate  120 . The first protective layer  551  may be disposed in direct contact with one surface of the first substrate  110  and one surface of the second substrate  120 . 
     The first protective layer  551  may include a material having softness and elasticity. For example, the first protective layer  551  may include at least one material of silicone, a thermoplastic resin, a thermoplastic silicone resin, a thermoplastic elastomer, a polyurethane elastomer, an ethylene vinyl acetate (EVA), a polyvinyl chloride (PVC) in which a harmless plasticizer and a stabilizer are added. The first protective layer  551  may be preferable to include a silicone elastomer among them that is relatively light, can minimize irritation upon contact with the user&#39;s skin, and has a predetermined elasticity. 
     The first protective layer  551  may be disposed between the first substrate  110  and the second substrate  120  to protect the piezoelectric element  300 . In detail, the first protective layer  551  may be disposed between the substrates  110  and  120  to surround the piezoelectric element  300  and the wires  210  and  220  to protect the components. In addition, the first protective layer  551  may be connected to the first base layer  510  and the second base layer  520 . For example, the first passivation layer  551  may be connected to the first base layer  510  and the second base layer  520  in an end region of the mask  1000 . That is, the first base layer  510 , the second base layer  520 , and the first protective layer  551  may be integrally formed to be physically connected and support a component disposed therein. The first protective layer  551  may include the same materials as the first base layer  510  and the second base layer  520 . That is, since the first base layer  510 , the second base layer  520 , and the first passivation layer  551  include the same kind of materials, they may have an improved bonding force. 
     In addition, referring to  FIG. 6 , the piezoelectric element  300  may include a first electrode  310  disposed on a lower surface thereof. The first electrode  310  may be disposed in an area of about 80% or more of the entire area of the lower surface of the piezoelectric element  300  in consideration of electrical characteristics. The first electrode  310  may be disposed in an area of about 90% of the entire area of the lower surface of the piezoelectric element  300 . In addition, the first electrode  310  may be disposed on the entire region of the lower surface of the piezoelectric element  300 . 
     The first electrode  310  may include a conductive material. As an example, the first electrode  310  may include a metal material. In detail, the first electrode  310  may include at least one metal of aluminum (Al), copper (Cu), silver (Ag), gold (Au), chromium (Cr), nickel (Ni), molybdenum (Mo), titanium (Ti), and alloys thereof. 
     The first electrode  310  may be disposed facing the first wire  210  and may be electrically connected to the first wire  210 . In detail, a first bonding layer  251  may be disposed between the first electrode  310  and the first wire  210 , and the first electrode  310  and the first wire  210  may be physically and electrically connected by the first bonding layer  251 . In this case, an overlapping ratio between the first bonding layer  251  and the first wire  210  may be about 20% or more in consideration of physical and electrical connection characteristics. 
     The first bonding layer  251  may include at least one metal of aluminum (Al), copper (Cu), silver (Ag), gold (Au), chromium (Cr), nickel (Ni), molybdenum (Mo), titanium (Ti), and alloys thereof. 
     A thickness of the first bonding layer  251  may be about 100 μm or less. In detail, the thickness of the first bonding layer  251  may be about 20 μm to about 80 μm. Preferably, the thickness of the first bonding layer  251  may be about 30 μm to about 60 μm. 
     The first bonding layer  251  may be disposed between the first electrode  310  and the first wire  210  to serve as a conductive adhesive. As an example, the first bonding layer  251  may be applied in a form of a paste on the first wire  210 , and the piezoelectric element  300  including the first electrode  310  may be disposed on the first bonding layer  251 . Accordingly, the piezoelectric element  300  may be physically and electrically connected to the first wire  210 . 
     In addition, the piezoelectric element  300  may include a second electrode  320  disposed on an upper surface thereof. The second electrode  320  may be disposed in an area of about 80% or more of the entire area of the upper surface of the piezoelectric element  300  in consideration of electrical characteristics. In detail, the second electrode  320  may be disposed in an area of about 90% of the entire area of the upper surface of the piezoelectric element  300 . In addition, the second electrode  320  may be disposed on the entire region of the lower surface of the piezoelectric element  300 . 
     The second electrode  320  may include a conductive material. As an example, the second electrode  320  may include a metal material. In detail, the second electrode  320  may include at least one metal of aluminum (Al), copper (Cu), silver (Ag), gold (Au), chromium (Cr), nickel (Ni), molybdenum (Mo), titanium (Ti), and alloys thereof. 
     The second electrode  320  may be disposed facing the second wire  220  and may be electrically connected to the second wire  220 . In detail, the first metal layer  350  electrically connected to the second electrode  320  may be disposed on the second electrode  320 . A second bonding layer  252  may be disposed between the first metal layer  350  and the second wire  220 , and the second electrode  320  and the second wire  220  may be electrically connected by the second bonding layer  252 . An overlapping ratio between the second bonding layer  252  and the second wire  220  may be about 20% or more in consideration of physical and electrical connection characteristics. 
     The second bonding layer  252  may include at least one metal of aluminum (Al), copper (Cu), silver (Ag), gold (Au), chromium (Cr), nickel (Ni), molybdenum (Mo), titanium (Ti), and alloys thereof. 
     A thickness of the second bonding layer  252  may be about 100 μm or less. In detail, the thickness of the second bonding layer  252  may be about 20 μm to about 80 μm. Preferably, the thickness of the second bonding layer  252  may be about 30 μm to about 60 μm. 
     The second bonding layer  252  may be disposed between the second electrode  320  and the second wire  220  to serve as a conductive adhesive. In detail, the second bonding layer  252  may be disposed between the first metal layer  350  and the second wire  220  to serve as a conductive adhesive. As an example, the second bonding layer  252  may be applied in the form of the paste on the second wire  220 , and the piezoelectric element  300  in which the first metal layer  350  is disposed may be disposed on the second bonding layer  252 . Accordingly, the piezoelectric element  300  may be electrically connected to the second wire  220 , and the first substrate  110  and the second substrate  120  may be spaced apart from each other at a predetermined interval. 
     In this case, the first bonding layer  251  may be provided with the same thickness as the second bonding layer  252  to improve the variability of the mask  1000 . In addition, the thickness of the first bonding layer  251  may be different from the thickness of the second bonding layer  252 . In detail, the thickness of the first bonding layer  251  may be greater than the thickness of the second bonding layer  252 . Accordingly, the wavelengths emitted from the piezoelectric element  300  toward the first substrate  110  may be reflected by the first bonding layer  251  to move toward the second substrate  120 . 
     Thereafter, as described above, the first protective layer  551  may be filled in a space between the first substrate  110  and the second substrate  120 . The first protective layer  551  may be disposed to surround the piezoelectric element  300 , the first wire  210 , the second wire  220 , the first bonding layer  251 , the second bonding layer  252 , the first electrode  310 , and the second electrode  320 , and it is possible to prevent the components from being exposed to the outside. 
     The mask  1000  according to the embodiment may include the cavity  410 . The cavity  410  may be disposed in a region corresponding to the piezoelectric element  300 . In detail, the cavity  410  may be disposed in a region overlapping the piezoelectric element  300  in the vertical direction. 
     The cavity  410  may be an air gap made of air. The cavity  410  may reflect the ultrasonic energy emitted from the piezoelectric element  300  toward the first base layer  510  toward the second base layer  520 . 
     The cavity  410  may have various shapes. For example, a planar shape of the cavity  410  may have a circular shape or a polygonal shape, but the embodiment is not limited thereto. In addition, the cavity  410  may have a planar shape corresponding to the piezoelectric element  300 , but the embodiment is not limited thereto. 
     The cavity  410  may be disposed between the first base layer  510  and the piezoelectric element  300 . The cavity  410  may be disposed between the first substrate  110  and the piezoelectric element  300 . In detail, the cavity  410  may be disposed between the first electrode  310  and the first substrate  110 . The cavity  410  may be disposed in a region overlapping the first wire  210 . For example, the cavity  410  may be disposed in a region overlapping a part of the first sub-wire  211  and the first bonding layer  251 . In addition, the first protective layer  551  may be disposed around the cavity  410 . 
     A thickness of the cavity  410  may be about 200 μm or less. In detail, the thickness of the cavity  410  may be about 150 μm or less. For example, the thickness of the cavity  410  may correspond to the sum of thicknesses of the first bonding layer  251  and the first wire  210 . A shape of the cavity  410  will be described in more detail with reference to drawings to be described later. 
       FIGS. 7 to 9  are views for describing an arrangement position of a cavity in the mask according to the embodiment. The arrangement relationship, shape, etc. of the cavity  410  according to the embodiment will be described in more detail with reference to  FIGS. 7 to 9 . 
     First, referring to  FIG. 7 , the cavity  410  may be disposed in a region overlapping the first wire  210 . In detail, the cavity  410  may be disposed in a region overlapping the first wire  210  in the vertical direction. In detail, the cavity  410  may be disposed in a region overlapping a part of the first sub-wire  211  overlapping the piezoelectric element  300 . 
     The cavity  410  may be disposed in a region where a center of the cavity  410  overlaps a center of the piezoelectric element  300 . The cavity  410  may be disposed in the central region of the piezoelectric element  300  to effectively reflect the wave energy emitted from the piezoelectric element  300 . 
     A width of the cavity  410  in the horizontal direction may be different from a width of the piezoelectric element  300  in the horizontal direction. For example, when the planar shape of each of the piezoelectric element  300  and the cavity  410  is circular, a radius d 1  of the cavity  410  may be smaller than a radius d 2  of the piezoelectric element  300 . In detail, the radius d 1  of the cavity  410  may be smaller than the radius d 2  of the piezoelectric element  300  within a range of about 40% or more of the radius d 2  of the piezoelectric element  300 . In more detail, the radius d 1  of the cavity  410  may be smaller than the radius d 2  of the piezoelectric element  300  within a range of about 45% or more of the radius d 2  of the piezoelectric element  300 . When the radius d 1  of the cavity  410  is less than about 40% of the radius d 2  of the piezoelectric element  300 , a reflectance of waves reflected in the air gap may decrease. Therefore, it may be desirable that the radius d 1  of the cavity  410  satisfies the above-described range. In addition, it may be preferable that the radius d 1  of the cavity  410  is about 50% or more of the radius d 2  of the piezoelectric element  300  in order to minimize the loss and effectively reflect. 
     In addition, referring to  FIG. 8 , the cavity  410  may overlap the piezoelectric element  300  in the vertical direction and may not overlap the first wire  210  in the vertical direction. That is, the cavity  410  may be spaced apart from the first wire  210 . 
     In addition, referring to  FIG. 9 , at least one cavity  410  may be formed between the first substrate  110  and the piezoelectric element  300 . As an example, when there are a plurality of cavities  410 , the plurality of cavities  410  may be spaced apart in the horizontal direction. Some of the plurality of cavities  410  may overlap the first wire  210  in the vertical direction, and the others may not overlap the first wire  210  in the vertical direction. In this case, each of the plurality of cavities  410  may have a diameter smaller than that of the piezoelectric element  300 . In addition, the plurality of cavities  410  may have the same diameter as each other. Alternatively, the plurality of cavities  410  may have different diameters in consideration of reflectance. As an example, a diameter of the cavity  410  overlapping the center of the piezoelectric element  300  may be larger than a diameter of the cavity  410  overlapping an edge of the piezoelectric element  300 . 
     That is, the mask  1000  according to the embodiment may effectively reflect the wave energy emitted from the piezoelectric element  300  by the cavity  410  upward. In addition, since the mask  1000  includes the cavity  410 , the thickness of the first base layer  510  may be reduced. Accordingly, the mask  1000  according to the embodiment may have a slimmer shape and may be implemented with a lighter weight. 
       FIG. 10  is another enlarged view of the region A 2  of  FIG. 5 . Referring to  FIG. 10 , the mask  1000  according to the embodiment may include a third substrate  421 . The third substrate  421  may be disposed between the first substrate  110  and the piezoelectric element  300 . In detail, the third substrate  421  may be disposed between the piezoelectric element  300  and the cavity  410 . In more detail, the third substrate  421  may be in direct contact with the first electrode  310  facing the cavity  410 , and may cover the first electrode  310 . 
     The third substrate  421  may include a silicone-based material and a polymer-based material. In addition, the third substrate  421  may have a shape corresponding to the cavity  410 . As an example, a planar shape of the third substrate  421  may be the same as the planar shape of the cavity  410 . Accordingly, the third substrate  421  may protect the piezoelectric element  300 . In detail, the third substrate  421  may be disposed to cover the first electrode  310 , and may prevent the first electrode  310  from being exposed by the cavity  410 . 
     The third substrate  421  may be smaller than the thickness of the cavity  410 . For example, the third substrate  421  may have a thickness of about 150 μm or less. In detail, the third substrate  421  may have a thickness of about 120 μm or less. In more detail, the third substrate  421  may have a thickness of about 100 μm or less. It is preferable that the thickness of the third substrate  421  satisfies the above-described range in order to effectively reflect the wave energy through the cavity  410 . 
       FIG. 11  is another cross-sectional view taken along line A-A′ of  FIG. 4 , and  FIG. 12  is an enlarged view of region A 3  in  FIG. 11 . In addition,  FIG. 13  is another enlarged view of region A 3  in  FIG. 11 . In the description of  FIGS. 11 to 13 , descriptions of configurations the same as or similar to those of the above-described mask are omitted, and the same reference numerals are assigned to the same as or similar to the configurations. 
     Referring to  FIGS. 11 and 12 , the cavity  410  according to the embodiment may be disposed between the first base layer  510  and the first substrate  110 . The cavity  410  may be disposed on one surface of the first base layer  510  facing the piezoelectric element  300 . In detail, the cavity  410  may have a concave shape from one surface of the first base layer  510  toward the other surface opposite to the one surface. 
     The cavity  410  may be disposed in a region corresponding to the piezoelectric element  300 . The cavity  410  may overlap the piezoelectric element  300  in the vertical direction. In detail, the center of the cavity  410  may overlap the center of the piezoelectric element  300 . 
     The thickness of the cavity  410  may be about 200 μm or less. In detail, the thickness of the cavity  410  may be about 150 μm or less. In addition, the width of the cavity  410  in the horizontal direction may be different from or equal to the width of the piezoelectric element  300  in the horizontal direction. For example, when the planar shape of each of the piezoelectric element  300  and the cavity  410  is circular, a diameter d 3  of the cavity  410  may be about 40% to about 160% of a diameter of the piezoelectric element  300 . In detail, the diameter d 3  of the cavity  410  may be about 50% to about 150% of the diameter of the piezoelectric element. As the diameter d 3  of the cavity  410  satisfies the above-described range, the wave energy of the piezoelectric element  300  may be effectively reflected upward, for example, toward the second substrate  120 . In addition, the thickness of the first base layer  510  may be reduced by the cavity  410 . Therefore, the mask  1000  according to the embodiment may have a slimmer shape. 
     In addition, referring to  FIG. 13 , the mask  1000  according to the embodiment may include a fourth substrate  422 . The fourth substrate  422  may be disposed between the first substrate  110  and the cavity  410 . In detail, the fourth substrate  422  may be disposed on one surface of the first substrate  110  facing the cavity  410 . The fourth substrate  422  may be disposed in direct contact with one surface of the first substrate  110 . 
     The fourth substrate  422  may include a silicone-based material and a polymer-based material. In addition, the fourth substrate  422  may have a shape corresponding to the cavity  410 . As an example, a planar shape of the fourth substrate  422  may be the same as the planar shape of the cavity  410 . In addition, the fourth substrate  422  may be smaller than the thickness of the cavity  410 . For example, the fourth substrate  422  may have a thickness of about 150 μm or less. In detail, the fourth substrate  422  may have a thickness of about 120 μm or less. In more detail, the fourth substrate  422  may have a thickness of about 100 μm or less. It is preferable that the thickness of the fourth substrate  422  satisfies the above-described range in order to effectively reflect the wave energy through the cavity  410 . 
       FIGS. 14 to 16  are views illustrating an example in which an indicator and a protrusion are provided on the mask according to the embodiment. 
     Referring to  FIG. 14 , the mask  1000  may include an indicator  610 . The indicator  610  may include at least one of members such as an LED, a display, a buzzer, and the like that may transmit visual or auditory information to a user. 
     The indicator  610  may be disposed outside the mask  1000  to display an operation state of the mask  1000 . As an example, the indicator  610  may provide information about the start of the operation of the mask  1000 , information notifying that the operation is in progress, and information about the completion of the operation through the auditory information generated from the buzzer. In addition, the indicator  610  may display the operation state according to the light emission color of the LED. In addition, the indicator may display information on an operating frequency domain through the display. 
     In addition, referring to  FIGS. 15 and 16 , the mask  1000  may include a protrusion  620  disposed on an outer surface thereof. In detail, the protrusion  620  may be disposed on one surface of the second base layer  520  facing the user&#39;s skin. 
     The protrusion  620  may include a material harmless to the human body and may be disposed to protrude from one surface of the second base layer  520  toward the user&#39;s skin. The protrusions  620  may be disposed in a form of a plurality of points spaced apart from each other on one surface of the second base layer  520 . In addition, the protrusions  620  may be disposed in a form of a plurality of straight lines or curves spaced apart from each other on one surface of the second base layer  520 . In addition, the protrusion  620  may be disposed in a single spiral shape on one surface of the second base layer  520 . 
     When the user wears the mask  1000 , the protrusion  620  may form a predetermined space between the mask  1000  and the user&#39;s skin. Accordingly, it is possible to prevent cosmetics or drugs between the mask  1000  and the skin from being pushed out to an edge region of the mask  1000  by the pressure generated when the mask  1000  are worn and/or the ultrasonic energy generated from the piezoelectric element  300 . That is, the protrusion  620  may serve as a partition wall preventing cosmetics or drugs from getting out of the mask  1000 . Therefore, the user may effectively inject cosmetics or drugs into the skin using the mask  1000 . 
       FIG. 17  is a view illustrating a user wearing the mask according to the embodiment, and  FIG. 18  is a view illustrating a skin care apparatus to which the mask according to the embodiment is applied. 
     Referring to  FIG. 17 , a user  50  may wear the mask  1000 . The mask  1000  may include the above-described opening  1010 , and the user  50  may secure a view through the opening  1010 . In addition, the mask  1000  may include the above-described cutout portion  1020 , and the mask  1000  may be effectively close-adhered to the curved skin by the cutout portion  1020 . In this case, one surface of the second base layer  520  may be in direct contact with skin of the user  50 . In addition, drugs or cosmetics may be disposed between the second bath layer  520  and the skin of the user  50 , so that the base layer  520  may be in direct or indirect contact with the skin of the user  50 . 
     The mask  1000  may be operated by receiving power through an external power connected to the mask  1000 . In addition, the mask  1000  may be operated by receiving power through a power supply unit (not shown) disposed outside the mask  1000 , for example, on a lower surface of the first base layer  510 . 
     In addition, referring to  FIG. 18 , the mask  1000  may be applied to a skin care apparatus  1  to operate. In detail, referring to  FIG. 18 , the skin care apparatus  1  may include a main body  10  in which one side thereof is open and including an accommodation space  11  therein. 
     The main body  10  may include a material that may be light and prevent damage from external impact or contact. As an example, the main body  10  may include a plastic or ceramic material, may have improved reliability from an external environment, and may protect the mask  1000  disposed inside the accommodation space  11 . In addition, the main body  10  may include a viewing part  13  formed at a position corresponding to the user&#39;s eyes. The viewing part  13  is formed in a region corresponding to the opening  1010  of the mask  1000 , and the user may secure an external view through the viewing part  13 . 
     The mask  1000  may be disposed in the accommodation space  11  of the main body  10 . The mask  1000  may be disposed between the main body  10  and the user&#39;s skin. In detail, the first base layer  510  of the mask  1000  may be disposed to face the accommodation space  11  of the main body  10 , and the second base layer  520  of the mask  1000  may be disposed to face the user&#39;s skin. 
     The mask  1000  may be coupled to the main body  10 . For example, the mask  1000  may be fixed to a set position in the accommodation space  11  by a fastening member (not shown) and may have a structure that is detachable from the main body  10 . 
     The mask  1000  may be supplied with power through the power supply unit (not shown) disposed outside the mask  1000 , for example, on the lower surface of the first base layer  510 . Alternatively, the mask  1000  may be connected to the main body  10  to be supplied with power through the power supply unit (not shown) disposed on the main body  10 . 
     The mask  1000  may include a deformable member (not shown) disposed on the lower surface of the first base layer  510 . The deformable member may be in direct contact with the first base layer  510  and may be disposed facing the accommodation space  11  of the main body  10 . That is, the deformable member may be disposed between the main body  10  and the first base layer  510  of the mask  1000 . 
     The deformable member may include a material of which shape is changed by external pressure. For example, the deformable member may include a material such as an air gap or a sponge, but the embodiment is not limited thereto, and may include various materials of which shape is changed by external pressure. Accordingly, when the user puts on the skin care apparatus  1 , the deformable member may be deformed into a shape corresponding to the shape of the user&#39;s face. Therefore, the ultrasonic mask  1000  and the user&#39;s skin may be effectively close-adhered to each other. In addition, when a plurality of users put on the skin care apparatus  1 , the deformable member is deformed to correspond to each face shape, so that the user&#39;s skin and the mask  1000  may be effectively close-adhered to each other. 
     The characteristics, structures, effects, and the like described in the above-described embodiments are included in at least one embodiment of the present invention, but are not limited to only one embodiment. Furthermore, the characteristic, structure, and effect illustrated in each embodiment may be combined or modified for other embodiments by a person skilled in the art. Thus, it should be construed that the contents related to such combination and modification are included in the scope of the present invention. 
     In addition, the above description has been focused on the embodiments, but it is merely illustrative and does not limit the present invention. Those skilled in the art to which the embodiments pertain may appreciate that various modifications and applications not illustrated above are possible without departing from the essential features of the embodiment. For example, each component particularly represented in the embodiments may be modified and realized. In addition, it should be construed that differences related to such a modification and an application are included in the scope of the present invention defined in the appended claims.