Patent Publication Number: US-2019181327-A1

Title: Electrostatic transducer

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of International Application number PCT/JP2017/034129, filed on Sep. 21, 2017, which claims the priority benefit of Japan Patent Application No. 2016-213852, filed on Oct. 31, 2016. The entirety of each of the above-mentioned patent applications is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND 
     Technical Field 
     The disclosure relates to an electrostatic transducer. 
     Description of Related Art 
     An electrostatic transducer utilizes a change in electrostatic capacitance and is an actuator that generates vibration, sound, etc. or a sensor that detects vibration, sound, etc. Japanese Laid-open No. 2014-150600 describes an actuator in which a plurality of electrode covered bodies are alternately shifted layer by layer and laminated, which prevents creeping discharge between the electrodes. Besides, the electrode layer constituting each electrode covered body is connected to the power supply electrode. 
     Furthermore, Japanese Laid-open No. S63-10594 and Japanese Laid-open No. 2005-312230 describe devices that use piezoelectric elements. In the device described in Japanese Laid-open No. S63-10594, a large number of piezoelectric elements that have electrode thin films formed on the upper and lower surfaces are laminated with the upper and lower surfaces reversed alternately, and a side electrode is formed to commonly connect the electrode thin films. As to the device described in Japanese Laid-open No. 2005-312230, a configuration is described in which connection electrodes are disposed on both end surfaces of a roll body. 
     An electrostatic transducer that is small in size and has a large electrostatic capacitance is desirable. When a large number of electrode layers and dielectric layers are laminated to secure a large electrostatic capacitance, it is possible to form a transducer that has a small size and a large electrostatic capacitance by reducing the thickness of the electrode layer. However, for the electrostatic actuator described in Japanese Laid-open No. 2014-150600, it is difficult to make the electrode covered body having the electrode layer thinner, and when a large number of electrode covered bodies are laminated, the size of the whole actuator increases. 
     In addition, when the thickness of the electrode layer is reduced, how to configure the terminal to extract electricity from each electrode layer also becomes a problem. Particularly, because the electrode layer is thin, if the terminal is formed by extending the electrode layer, the durability of the electrode layer will be a problem. Particularly, since the dielectric of the electrostatic transducer is deformed, the portion of the electrode layer, which serves as the terminal, needs to be able to follow the deformation of the dielectric. 
     SUMMARY 
     The disclosure provides an electrostatic transducer that is small in size and has a large electrostatic capacitance and can have a durable constituent part of a conduction path, which is connected to an electrode. 
     An electrostatic transducer according to the disclosure includes a plurality of first electrode sheets formed of an elastic deformable material in a sheet shape, a plurality of second electrode sheets formed of an elastic deformable material in a sheet shape, and a plurality of dielectric sheets formed of an elastic deformable material in a sheet shape. 
     Each of the first electrode sheets includes a first counter electrode part and a first terminal electrode part extending from the first counter electrode part. Each of the second electrode sheets includes a second counter electrode part facing the first counter electrode part, and a second terminal electrode part extending from the second counter electrode part. 
     Each of the dielectric sheets includes a dielectric main body interposed between the first counter electrode part and the second counter electrode part, a first extending part extending from the dielectric main body and interposed between the first terminal electrode parts, and a second extending part extending from the dielectric main body and interposed between the second terminal electrode parts. 
     That is, the first counter electrode part and the first terminal electrode part are the same first electrode sheet. Likewise, the second counter electrode part and the second terminal electrode part are the same second electrode sheet. The first electrode sheet and the second electrode sheet can be formed very thin. In other words, an electrostatic laminate composed of the first counter electrode part, the second counter electrode part, and the dielectric main body is small in size and has a large electrostatic capacitance. 
     Here, the first electrode sheet includes the first counter electrode part and the first terminal electrode part. For example, it is conceivable to put only the first terminal electrode part outside the electrostatic laminate as the configuration of the conduction path connected to the first counter electrode part. However, the first terminal electrode part is much thinner than the electrostatic laminate. Therefore, if only the first terminal electrode part is present outside the electrostatic laminate as the portion for extracting electricity from the first counter electrode part, it may receive a large deformation force near the boundary between the first terminal electrode part and the first counter electrode part. 
     According to the disclosure, instead of putting only the first terminal electrode part outside the electrostatic laminate, the first extending part, which is a part of the dielectric sheet, is present outside the electrostatic laminate, and the first terminal electrode part and the first extending part are laminated. Accordingly, the total thickness of the first terminal electrode part and the first extending part is smaller than that of the electrostatic laminate only by the thickness of the second electrode sheet. Therefore, it is possible to suppress generation of a large deformation force near the boundary between the first terminal electrode part and the first counter electrode part. As a result, the constituent part of the conduction path connected to the first counter electrode part can be highly durable. The same applies to the second terminal electrode part. 
     As described above, the dielectric sheet is disposed not only between the first counter electrode part and the second counter electrode part but also between the first terminal electrode parts and between the second terminal electrode parts. For the value of the electrostatic capacitance of the electrostatic transducer, the first extending part of the dielectric sheet that is present between the first terminal electrode parts, and the second extending part that is present between the second terminal electrode parts are unnecessary parts. However, by disposing the first extending part and the second extending part which are parts that do not contribute to the value of the electrostatic capacitance, as described above, the durability of the first terminal electrode part and the second terminal electrode part can be improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of the electrostatic transducer  1  of the first embodiment. 
         FIG. 2  is a cross-sectional view taken along the line II-II of  FIG. 1 . 
         FIG. 3  is an exploded perspective view of three electrostatic units  10   a,    10   b,  and  10   c.    
         FIG. 4  is an exploded perspective view of individual electrostatic units  10   a,    10   b , and  10   c.    
         FIG. 5  is a diagram showing an electrical connection state of the electrostatic laminate  16 . 
         FIG. 6  is a cross-sectional view of the electrostatic transducer  1  of the third embodiment. 
         FIG. 7  is a cross-sectional view taken along the line VII-VII of  FIG. 6 . 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     1. First Embodiment 
     (1-1. Outline of the Electrostatic Transducer  1 ) 
     An electrostatic transducer  1  utilizes a change in electrostatic capacitance and is an actuator that generates vibration, sound, etc. or a sensor that detects vibration, sound, etc. The electrostatic transducer  1 , which serves as an actuator, generates vibration by applying a voltage to an electrode. The electrostatic transducer  1 , which serves as a sensor, generates a voltage at an electrode when the sensor vibrates due to input of vibration or sound. 
     The electrostatic transducer  1 , which serves as a vibration actuator, is, for example, a device for presenting tactile vibration to a human being, a device for generating vibration in an opposite phase to a structure for damping the structure, or the like. The electrostatic transducer  1 , which serves as an actuator for generating sound, is a speaker for generating sound waves to be sensed by hearing of a human being, a sound masking for cancelling noise, or the like. 
     The vibration generated by the vibration actuator is vibration at a relatively low frequency, and the sound generated by the actuator for generating sound is vibration at a relatively high frequency. Since the electrostatic transducer  1 , which serves as an actuator, in the present embodiment utilizes vibration of a spring mass system, it is suitable for a low frequency vibrator and a low frequency sound generator. 
     In the present embodiment, the electrostatic transducer  1  is, for example, a vibration actuator for presenting tactile vibration to a human being. For example, the electrostatic transducer  1  is applied to an actuator that is mounted on a portable terminal for vibrating the portable terminal. The electrostatic transducer  1 , which serves as a sensor, has substantially the same configuration. 
     (1-2. Configuration of the Electrostatic Transducer  1 ) 
     A configuration of the electrostatic transducer  1  will be described with reference to  FIG. 1  to  FIG. 4 . Here, in  FIG. 1  to  FIG. 3 , the thickness of each member is exaggerated for the sake of clarity. Therefore, in practice, the thickness of the electrostatic transducer  1  in the vertical direction of  FIG. 1  is formed to be very small. 
     As shown in  FIG. 1  and  FIG. 2 , the electrostatic transducer  1  includes an electrostatic unit  10  ( 10   a,    10   b,  and  10   c ), a first conductive part  20 , a second conductive part  30 , a first elastic body  40 , a second elastic body  50 , a control substrate  60 , and a cover  70 . 
     The electrostatic unit  10  includes a plurality of electrodes and a plurality of dielectrics that are laminated. The electrostatic transducer  1  may include one electrostatic unit  10  or include a plurality of electrostatic units  10 . In the present embodiment, as shown in  FIG. 3 , the electrostatic transducer  1  includes three electrostatic units  10   a,    10   b,  and  10   c  and is formed by laminating the three electrostatic units  10   a,    10   b,  and  10   c.    
     Each of the electrostatic units  10   a,    10   b,  and  10   c  is formed in a substantially planar shape (corresponding to a flat shape). The outer shape of each of the electrostatic units  10   a,    10   b,  and  10   c  is formed rectangular in the top view (when viewed from the surface normal direction) of  FIG. 3 . Each of the electrostatic units  10   a,    10   b , and  10   c  is formed of an elastomer. 
     As shown in  FIG. 4 , each of the electrostatic units  10   a,    10   b,  and  10   c  includes a plurality of first electrode sheets  11 , a plurality of second electrode sheets  12 , a plurality of dielectric sheets  13 , a front insulating sheet  14 , and a back insulating sheet  15 , and these are integral members. The electrostatic units  10   a,    10   b,  and  10   c  are separate members. 
     First, the constituent members  11  to  15  of each of the electrostatic units  10   a ,  10   b,  and  10   c  will be described with reference to  FIG. 4 . The first electrode sheet  11  and the second electrode sheet  12  are formed of an elastic deformable material such as an elastomer in a sheet shape. The first electrode sheet  11  and the second electrode sheet  12  are formed in the same shape and formed of the same material. The first electrode sheet  11  and the second electrode sheet  12  are formed in the shape of a rectangular thin film. 
     The first electrode sheet  11  and the second electrode sheet  12  are formed by blending conductive fillers into the elastomer. Therefore, the first electrode sheet  11  and the second electrode sheet  12  have flexibility and stretchability. The elastomer constituting the first electrode sheet  11  and the second electrode sheet  12  may be silicone rubber, ethylene-propylene copolymer rubber, natural rubber, styrene-butadiene copolymer rubber, acrylonitrile-butadiene copolymer rubber, acrylic rubber, epichlorohydrin rubber, chlorosulfonated polyethylene, chlorinated polyethylene, urethane rubber, or the like, for example. In addition, the conductive fillers blended into the first electrode sheet  11  and the second electrode sheet  12  are particles having conductivity. For example, fine particles of a carbon material, metal, or the like may be used. 
     The dielectric sheet  13  is formed of an elastic deformable material such as an elastomer in a sheet shape. The dielectric sheet  13  is formed in the shape of a rectangular thin film. The width of the dielectric sheet  13  in the transverse direction is formed to be substantially equal to the widths of the first electrode sheet  11  and the second electrode sheet  12  in the transverse direction. In addition, the length of the dielectric sheet  13  in the longitudinal direction is formed to be larger than the lengths of the first electrode sheet  11  and the second electrode sheet  12  in the longitudinal direction. Moreover, the thickness of the dielectric sheet  13  is formed to be larger than the thicknesses of the first electrode sheet  11  and the second electrode sheet  12 . 
     The dielectric sheet  13  is formed of an elastomer. Therefore, the dielectric sheet  13  has flexibility and stretchability. A material that functions as a dielectric of the electrostatic transducer  1  is applied as the dielectric sheet  13 . Particularly, the dielectric sheet  13  stretches in the thickness direction and is stretchable in the flat plane direction along with its stretch in the thickness direction. The elastomer constituting the dielectric sheet  13  may be silicone rubber, acrylonitrile-butadiene copolymer rubber, acrylic rubber, epichlorohydrin rubber, chlorosulfonated polyethylene, chlorinated polyethylene, urethane rubber, or the like, for example. 
     An insulating material is applied as the front insulating sheet  14  and the back insulating sheet  15 . In the present embodiment, the front insulating sheet  14  and the back insulating sheet  15  are formed of the same material in the same shape as the dielectric sheet  13 . That is, the front insulating sheet  14  and the back insulating sheet  15  are formed of an elastomer and are rectangular. 
     As shown in  FIG. 4 , the first electrode sheet  11 , the dielectric sheet  13 , the second electrode sheet  12 , the dielectric sheet  13 , and the first electrode sheet  11  are laminated in this order. At this time, the first electrode sheet  11  and the second electrode sheet  12  are offset in the left-right direction (longitudinal direction) of  FIG. 4 . Specifically, a part of the first electrode sheet  11  and a part of the second electrode sheet  12  are disposed to face each other. Then, the remaining parts of the first electrode sheet  11  and the second electrode sheet  12 , which do not face each other, are positioned on opposite sides with respect to the parts that face each other. 
     That is, in  FIG. 4 , in the center portion in the left-right direction, the first electrode sheet  11  and the second electrode sheet  12  face each other; in the left portion, the first electrode sheet  11  is present whereas the second electrode sheet  12  is not; and in the right portion, the second electrode sheet  12  is present whereas the first electrode sheet  11  is not. 
     The length of the dielectric sheet  13  in the longitudinal direction (width in the left-right direction of  FIG. 4 ) is formed to cover all the range where the first electrode sheet  11  and the second electrode sheet  12  face each other, the range where only the first electrode sheet  11  is present, and the range where only the second electrode sheet  12  is present. 
     The front insulating sheet  14  covers the entire surface of one outermost layer (the uppermost layer in  FIG. 4 ) of the first electrode sheets  11  and the second electrode sheets  12 . The back insulating sheet  15  covers the entire surface of the other outermost layer (the lowermost layer in  FIG. 4 ) of the first electrode sheets  11  and the second electrode sheets  12 . 
     Next, each of the electrostatic units  10   a,    10   b,  and  10   c  will be described with reference to  FIG. 3 . Each of the electrostatic units  10   a,    10   b,  and  10   c  includes an electrostatic laminate  16  positioned in the center portion in the left-right direction of FIG. 
       3 , a first terminal  17  positioned on the left side of  FIG. 3 , and a second terminal  18  positioned on the right side of  FIG. 3 . The first terminal  17  is a ground potential terminal of the electrostatic laminate  16  and the second terminal  18  is a positive electrode potential terminal of the electrostatic laminate  16 . Here, the first terminal  17  and the second terminal  18  extend to opposite sides with respect to the electrostatic laminate  16 . 
     Here, the first electrode sheet  11  includes a first counter electrode part  11   a  positioned in the center portion in the left-right direction, and a first terminal electrode part  11   b  extending from the first counter electrode part  11   a . The second electrode sheet  12  includes a second counter electrode part  12   a  positioned in the center portion in the left-right direction, and a second terminal electrode part  12   b  extending from the second counter electrode part  12   a.  The first counter electrode part  11   a  and the second counter electrode part  12   a  face each other. A direction in which the first terminal electrode part  11   b  extends from the first counter electrode part  11   a  and a direction in which the second terminal electrode part  12   b  extends from the second counter electrode part  12   a  are opposite directions. 
     The dielectric sheet  13  includes a dielectric main body  13   a,  a first extending part  13   b,  and a second extending part  13   c.  The dielectric main body  13   a  is interposed between the first counter electrode part  11   a  and the second counter electrode part  12   a . The first extending part  13   b  extends from the dielectric main body  13   a  and is interposed between the first terminal electrode parts  11   b . The second extending part  13   c  extends from the dielectric main body  13   a  and is interposed between the second terminal electrode parts  12   b.    
     In addition, the front insulating sheet  14  includes a front insulating main body  14   a,  a first front terminal insulating part  14   b,  and a second front terminal insulating part  14   c.  The front insulating main body  14   a  covers the first counter electrode part  11   a  positioned in one outermost layer (the upper side in  FIG. 3 ). The first front terminal insulating part  14   b  covers the first terminal electrode part  11   b  positioned in one outermost layer. The second front terminal insulating part  14   c  covers the second terminal electrode part  12   b  positioned in one outermost layer. 
     The back insulating sheet  15  includes a back insulating main body  15   a,  a first back terminal insulating part  15   b,  and a second back terminal insulating part  15   c.  The back insulating main body  15   a  covers the first counter electrode part  11   a  positioned in the other outermost layer (the lower side in  FIG. 3 ). The first back terminal insulating part  15   b  covers the first terminal electrode part  11   b  positioned in the other outermost layer. The second back terminal insulating part  15   c  covers the second terminal electrode part  12   b  positioned in the other outermost layer. 
     In other words, the electrostatic laminate  16  is formed in a planar shape by a plurality of first counter electrode parts  11  a, a plurality of second counter electrode parts  12   a,  a plurality of dielectric main bodies  13   a,  the front insulating main body  14   a,  and the back insulating main body  15   a.  The first terminal  17  is formed in a planar shape by a plurality of first terminal electrode parts  11   b , a plurality of first extending parts  13   b,  the first front terminal insulating part  14   b,  and the first back terminal insulating part  15   b . The first terminal  17  extends in the plane direction of the planar shape of the electrostatic laminate  16 . The second terminal  18  is formed in a planar shape by a plurality of second terminal electrode parts  12   b,  a plurality of second extending parts  13   c,  the second front terminal insulating part  14   c,  and the second back terminal insulating part  15   c.  The second terminal  18  extends in the plane direction of the planar shape of the electrostatic laminate  16 . 
     Here, the electrostatic laminate  16  includes all the constituent members, whereas the first terminal  17  does not include the second electrode sheet  12  and the second terminal  18  does not include the first electrode sheet  11 . Therefore, the first terminal  17  and the second terminal  18  are thinner than the electrostatic laminate  16 . However, the first electrode sheet  11  and the second electrode sheet  12  are very thin. Particularly, the first electrode sheet  11  and the second electrode sheet  12  are much thinner than the dielectric sheet  13 . Therefore, the difference between the thickness of the electrostatic laminate  16  and the thickness of the first terminal  17  and the difference between the thickness of the electrostatic laminate  16  and the thickness of the second terminal  18  are not so large. 
     Therefore, the bending of the first electrode sheet  11  in the boundary portion between the first counter electrode part  11   a  and the first terminal electrode part  11   b  is small. Likewise, the bending in the boundary portion between the second counter electrode part  12   a  and the second terminal electrode part  12   b  is small. 
     Furthermore, since each of the electrostatic units  10   a,    10   b,  and  10   c  is formed independently in the present embodiment, in each of the electrostatic units  10   a,    10   b,  and  10   c,  the difference between the thickness of the electrostatic laminate  16  and the thickness of the first terminal  17  and the difference between the thickness of the electrostatic laminate  16  and the thickness of the second terminal  18  are not so large. Therefore, the bending of the first electrode sheet  11  in the boundary portion between the first counter electrode part  11   a  and the first terminal electrode part  11   b  is small. Further, the bending in the boundary portion between the second counter electrode part  12   a  and the second terminal electrode part  12   b  is small. 
     Description regarding the configuration of the electrostatic transducer  1  will be continued by reverting to  FIG. 1  and  FIG. 2 . The first conductive part  20  is formed of an elastic deformable material (for example, an elastomer) in a sheet shape and bent in an L shape. Like the first electrode sheet  11 , the first conductive part  20  is formed by blending conductive fillers into the elastomer. However, the first conductive part  20  is formed thicker than the first electrode sheet  11 . 
     One side of the L shape of the first conductive part  20  is formed in a direction that intersects (is orthogonal to) the plane of the planar shape of the electrostatic laminate  16 . Then, one side of the L shape of the first conductive part  20  is in contact with an end surface of the first terminal  17 . Specifically, one side of the L shape of the first conductive part  20  is in contact with an end of the first terminal electrode part  11   b  and an end of the first extending part  13   b.  Therefore, the first conductive part  20  is electrically connected to the ends of the first terminal electrode parts  11   b.    
     The other side of the L shape of the first conductive part  20  extends in a direction away from the electrostatic laminate  16  and is formed in parallel to the plane direction of the planar shape of the electrostatic laminate  16 . The other side of the L shape of the first conductive part  20  is electrically connected to the control substrate  60  which will be described later. 
     Like the first conductive part  20 , the second conductive part  30  is formed of an elastic deformable material (for example, an elastomer) in a sheet shape and bent in an L shape. The second conductive part  30  is formed by blending conductive fillers into the elastomer. 
     One side of the L shape of the second conductive part  30  is formed in a direction that intersects (is orthogonal to) the plane of the planar shape of the electrostatic laminate  16 . Then, one side of the L shape of the second conductive part  30  is in contact with an end surface of the second terminal  18 . Specifically, one side of the L shape of the second conductive part  30  is in contact with an end of the second terminal electrode part  12   b  and an end of the second extending part  13   c.  Therefore, the second conductive part  30  is electrically connected to the ends of the second terminal electrode parts  12   b.    
     The other side of the L shape of the second conductive part  30  extends in a direction away from the electrostatic laminate  16  and is formed in parallel to the plane direction of the planar shape of the electrostatic laminate  16 . The other side of the L shape of the second conductive part  30  is electrically connected to the control substrate  60  which will be described later. 
     The first elastic body  40  is disposed in contact with one surface of the planar shape of the electrostatic laminate  16 . The second elastic body  50  is disposed in contact with the other surface of the planar shape of the electrostatic laminate  16 . That is, the first elastic body  40  and the second elastic body  50  are respectively disposed on two end surfaces (the upper and lower surfaces in  FIG. 1 ) that face away from each other in a direction orthogonal to the plane of the planar shape of the electrostatic laminate  16 . 
     In addition, as shown in  FIG. 2 , the first elastic body  40  is disposed in contact with two end surfaces (the surfaces where the first terminal  17  and the second terminal  18  are not present (the left and right surfaces in  FIG. 2 )) that face away from each other in the plane direction of the planar shape of the electrostatic laminate  16 . Furthermore, as shown in  FIG. 1 , the first elastic body  40  is disposed in contact with one surface (the upper surface in  FIG. 1 ) of the planar shape of the first terminal  17  and one surface (the upper surface in  FIG. 1 ) of the planar shape of the second terminal  18 . The second elastic body  50  is disposed in contact with the other surface (the lower surface in  FIG. 1 ) of the planar shape of the first terminal  17  and the other surface (the lower surface in  FIG. 1 ) of the planar shape of the second terminal  18 . 
     Moreover, the first elastic body  40  is disposed in contact with the entire outer surface of the L shape of the first conductive part  20  and the entire outer surface of the L shape of the second conductive part  30 . The surface of the second elastic body  50  on the side opposite to the electrostatic laminate  16  is formed to be substantially flush with the other surfaces of the L shapes of the first conductive part  20  and the second conductive part  30 . 
     For the first elastic body  40  and the second elastic body  50 , materials having small elastic moduli E (40)  and E (50)  and small loss factors tanδ (40)  and tanδ (50)  are used. 
     In other words, materials that are soft and have low attenuation characteristics are suitable for the first elastic body  40  and the second elastic body  50 . Particularly, the first elastic body  40  and the second elastic body  50  have elastic moduli E (40)  and E (50)  that are smaller than the elastic modulus E 1   (16)  in the lamination direction (the direction orthogonal to the plane of the planar shape) of the electrostatic laminate  16 . In addition, the elastic modulus E (40)  of the first elastic body  40  is smaller than the elastic modulus E 2   (16)  in the plane direction of the electrostatic laminate  16 . 
     Specifically, the ratio of the elastic modulus E (40)  of the first elastic body  40  to the elastic modulus E 1   (16)  in the lamination direction of the electrostatic laminate  16  is 15% or less. Further, the ratio of the elastic modulus E (50)  of the second elastic body  50  to the elastic modulus E 1   (16)  in the lamination direction of the electrostatic laminate  16  is 15% or less. These ratios are preferably 10% or less. Likewise, the ratio of the elastic modulus E (40)  of the first elastic body  40  to the elastic modulus E 2   (16)  in the plane direction of the electrostatic laminate  16  is 15% or less. Further, the ratio of the elastic modulus E (50)  of the second elastic body  50  to the elastic modulus E 2   (16)  in the plane direction of the electrostatic laminate  16  is 15% or less. These ratios are preferably 10% or less. 
     Besides, the first elastic body  40  and the second elastic body  50  have loss factors tanδ (40)  and tanδ (50)  equal to or smaller than the loss factor tanδ (16)  of the electrostatic laminate  16  under a predetermined condition. The predetermined condition means an environment of use where the temperature is set to −10° C. to 50° C. and the vibration frequency is set to 300 Hz or less. 
     As a material that satisfies the above, silicone rubber, for example, is suitable for the first elastic body  40  and the second elastic body  50 . Urethane rubber, for example, has better attenuation characteristics than silicone rubber. Therefore, urethane rubber is less suitable for the first elastic body  40  and the second elastic body  50  than silicone rubber. However, it is also possible to use urethane rubber for the first elastic body  40  and the second elastic body  50  depending on the desired characteristics. 
     The control substrate  60  is disposed parallel to the electrostatic laminate  16  and is disposed in contact with the surface of the second elastic body  50  on the side opposite to the electrostatic laminate  16 . Furthermore, the control substrate  60  is in contact with the other surfaces of the L shapes of the first conductive part  20  and the second conductive part  30 . 
     The cover  70  surrounds the electrostatic units  10 , the first conductive part  20 , the second conductive part  30 , the first elastic body  40 , the second elastic body  50 , and the control substrate  60 . Various materials such as metal and resin are suitable for the cover  70 . The cover  70  includes a planar first cover  71  for fixing the control substrate  60 , and a second cover  72  attached to the first cover  71 . 
     The first cover  71  and the second cover  72  hold the electrostatic laminate  16 , the first elastic body  40 , and the second elastic body  50  in a state of compressing them in the lamination direction of the electrostatic laminate  16 . In this state, according to the relationship between the elastic moduli E of the members, the first elastic body  40  and the second elastic body  50  are compressed to a greater extent than the electrostatic laminate  16  in the lamination direction of the electrostatic laminate  16 . 
     Furthermore, the first cover  71  holds the electrostatic laminate  16  and the first elastic body  40  in a state of compressing them in the plane direction of the electrostatic laminate  16 . In this state, according to the relationship between the elastic moduli E of the members, the first elastic body  40  is compressed to a greater extent than the electrostatic laminate  16  in the plane direction of the electrostatic laminate  16 . 
     (1-3. Electrical Connection State of the Electrostatic Laminate  16 ) 
     An electrical connection state of the electrostatic laminate  16  will be described with reference to  FIG. 5 . Here, the vertical direction of  FIG. 5  and the vertical direction of  FIG. 1  coincide with each other. However,  FIG. 5  shows one electrostatic cell that constitutes the electrostatic laminate  16 . The electrostatic cell is one first counter electrode part  11   a , one second counter electrode part  12   a,  and one dielectric main body  13   a.    
     As shown in  FIG. 5 , the first counter electrode part  11  a and the second counter electrode part  12   a  are disposed to face each other at a distance in the lamination direction of the electrostatic laminate  16 . The other terminal that supplies a periodic voltage is electrically connected to the first counter electrode part  11   a  by a driving circuit in the control substrate  60 . One terminal that supplies a periodic voltage is electrically connected to the second counter electrode part  12   a.  In the present embodiment, the first counter electrode part  11   a  is connected to the ground potential. The second counter electrode part  12   a  is connected to the output terminal of the control substrate  60 . 
     (1-4. Operation of the Electrostatic Transducer  1 ) 
     An operation of the electrostatic transducer  1  will be described. A periodic voltage is applied to the first counter electrode part  11   a  and the second counter electrode part  12   a  via the first terminal electrode part  11   b  and the second terminal electrode part  12   b.  Here, the periodic voltage may be an alternating voltage (a periodic voltage including positive and negative) or a periodic voltage offset to a positive value. 
     As the electric charge accumulated in the first counter electrode part  11   a  and the second counter electrode part  12   a  increases, the dielectric main body  13   a  is compressed and deformed. That is, as shown in  FIG. 5 , the thickness of the electrostatic laminate  16  decreases and the size (width and depth) in the plane direction of the electrostatic laminate  16  increases. Conversely, as the electric charge accumulated in the first counter electrode part  11   a  and the second counter electrode part  12   a  decreases, the dielectric main body  13   a  returns to the original thickness. That is, the thickness of the electrostatic laminate  16  increases and the size in the plane direction of the electrostatic laminate  16  decreases. In this way, the electrostatic laminate  16  stretches in the lamination direction and stretches in the plane direction. 
     When the electrostatic laminate  16  stretches, the electrostatic transducer  1  operates as follows. The electrostatic transducer  1  sets the state where the first elastic body  40  and the second elastic body  50  are compressed, as shown in  FIG. 1 , as the initial state. Therefore, when the thickness of the electrostatic laminate  16  decreases due to the increase in electric charge, the first elastic body  40  and the second elastic body  50  are deformed so that the compression amount is smaller than that in the initial state. Conversely, when the thickness of the electrostatic laminate  16  increases due to the decrease in electric charge, the first elastic body  40  and the second elastic body  50  operate so as to return to the initial state. That is, the first elastic body  40  and the second elastic body  50  are deformed so that the compression amount is larger than in the case where the electric charge increases. 
     Since the applied voltage changes periodically, the above operation is repeated. Then, the state where the center of the electrostatic laminate  16  is recessed toward the side of the second elastic body  50  and the state where the center of the electrostatic laminate  16  protrudes toward the side of the second elastic body  50  are repeated. Since the electrostatic laminate  16  is restricted by the cover  70  via the first elastic body  40  and the second elastic body  50 , the above operation is performed. 
     Along with the above deformation of the electrostatic laminate  16 , the displacement in the lamination direction (d 33  direction: direction the same as the electric field) of the electrostatic laminate  16  is transmitted to the cover  70  via the first elastic body  40 . In addition, the elastic deformation force of the first elastic body  40  is changed by the stretch of the electrostatic laminate  16 . The change in the elastic deformation force of the first elastic body  40  is transmitted to the cover  70 . Accordingly, as the initial state, since the first elastic body  40  and the second elastic body  50  are compressed, vibration in the lamination direction (d 33  direction) of the electrostatic laminate  16  can be efficiently transferred to the cover  70 . That is, even though the electrostatic laminate  16  alone generates small vibration, the cover  70  can have tactile vibration. 
     Further, along with the above deformation of the electrostatic laminate  16 , the displacement in the plane direction (d 31  direction: direction orthogonal to the electric field) of the electrostatic laminate  16  is transmitted to the cover  70  via the first elastic body  40 . As a result, the vibration in the plane direction (d 31  direction) of the electrostatic laminate  16  is transferred to the cover  70 . Here, the vibration in the plane direction (d 31  direction) of the electrostatic laminate  16  is smaller than the vibration in the lamination direction (d 33  direction). However, the vibration in the plane direction (d 31  direction) is added to the vibration in the lamination direction (d 33  direction) of the electrostatic laminate  16 , by which the whole cover  70  can have large tactile vibration. 
     Here, assuming that the loss factors tanδ (40)  and tanδ (50)  of the first elastic body  40  and the second elastic body  50  are very large, the vibration may be absorbed by the first elastic body  40  and the second elastic body  50  even if the electrostatic laminate  16  stretches. In such a case, even if the electrostatic laminate  16  stretches, the vibration is not transmitted to the cover  70 . 
     However, in the present embodiment, the first elastic body  40  and the second elastic body  50  use materials that have small loss factors tanδ (40)  and tanδ (50) . Therefore, the vibration generated by the stretch of the electrostatic laminate  16  is hardly absorbed by the first elastic body  40  and the second elastic body  50  and is transmitted to the cover  70 . 
     Furthermore, the elastic moduli E (40)  and E (50)  of the first elastic body  40  and the second elastic body  50  are smaller than the elastic modulus E 1   (16)  in the lamination direction of the electrostatic laminate  16 . Therefore, in the initial state where no voltage is applied to the first counter electrode part  11   a  and the second counter electrode part  12   a , the electrostatic laminate  16  is barely compressed. Accordingly, even if the cover  70  presses the electrostatic laminate  16  in the lamination direction, it does not affect the stretch of the electrostatic laminate  16  in the lamination direction. In other words, the electrostatic laminate  16  can stretch reliably. 
     In addition, the elastic modulus E (40)  of the first elastic body  40  is smaller than the elastic modulus E 2   (16)  in the plane direction of the electrostatic laminate  16 . Therefore, in the initial state where no voltage is applied to the first counter electrode part  11   a  and the second counter electrode part  12   a,  the electrostatic laminate  16  is barely compressed. Accordingly, even if the cover  70  presses the electrostatic laminate  16  in the plane direction, it does not affect the stretch of the electrostatic laminate  16  in the plane direction. In other words, the electrostatic laminate  16  can stretch reliably. 
     In the embodiment described above, the first elastic body  40  may be disposed only on the end surfaces in the direction orthogonal to the plane of the electrostatic laminate  16 . In such a case, the first elastic body  40  is not disposed on the end surfaces in the plane direction of the electrostatic laminate  16 . Therefore, the electrostatic transducer  1  does not transfer vibration in the plane direction (d 31  direction) of the electrostatic laminate  16  to the cover  70 . 
     2. Second Embodiment 
     In the second embodiment, the outermost layer of the electrostatic laminate  16  is formed with an elastic modulus in the lamination direction larger than those of the other layers. The outermost layer of the electrostatic laminate  16  is the uppermost layer of the electrostatic unit  10   a  in  FIG. 3  and the lowermost layer of the electrostatic unit  10   c  in  FIG. 3 . For example, by applying UV irradiation to surface-modify the uppermost layer of the electrostatic unit  10   a,  a nano-order cured layer is formed. Likewise, by applying 
     UV irradiation to surface-modify the lowermost layer of the electrostatic unit  10   c,  a nano-order cured layer is formed. A sheet having a desired elastic modulus may be disposed instead of applying UV irradiation. Therefore, when the vibration in the lamination direction of the electrostatic laminate  16  is transmitted to the cover  70 , the transmission sensitivity of the vibration is improved. 
     3. Third Embodiment 
     An electrostatic transducer  100  of the third embodiment will be described with reference to  FIG. 6  and  FIG. 7 . In the electrostatic transducer  100 , components the same as those of the electrostatic transducer  1  of the first embodiment are denoted by the same reference numerals, and description thereof is omitted. 
     The electrostatic transducer  100  includes an electrostatic unit  110 , a first conductive part  120 , a second conductive part  130 , a first elastic body  140 , a second elastic body  150 , a control substrate  60 , and a cover  70 . 
     The electrostatic unit  110  includes an electrostatic laminate  16 , a first terminal  117 , and a second terminal  118 . The electrostatic laminate  16  is formed in a planar shape. The electrostatic laminate  16  is formed by a first counter electrode part  11   a , a second counter electrode part  12   a,  and a dielectric main body  13   a.  In other words, the first counter electrode part  11   a , the second counter electrode part  12   a,  and the dielectric main body  13   a  are formed in a planar shape. 
     The first terminal  117  is bent in a curved shape from a plane direction of the planar shape of the electrostatic laminate  16 . The first terminal  117  is formed in an arc shape of about 90 degrees. Here, the first terminal  117  is formed by a first terminal electrode part  11   b  and a first extending part  13   b.  In other words, the first terminal electrode part  11   b  and the first extending part  13   b  are bent in a curved shape. 
     The second terminal  118  is bent in a curved shape from the plane direction of the planar shape of the electrostatic laminate  16 . The second terminal  118  is formed in an arc shape of about 90 degrees. Here, the second terminal  118  is formed by a second terminal electrode part  12   b  and a second extending part  13   c.  In other words, the second terminal electrode part  12   b  and the second extending part  13   c  are bent in a curved shape. 
     The first conductive part  120  and the second conductive part  130  are formed in a planar sheet shape. The first conductive part  120  and the second conductive part  130  are in contact with the ends of the first terminal  117  and the second terminal  118  respectively. In addition, the first conductive part  120  and the second conductive part  130  are formed in parallel to the plane direction of the planar shape of the electrostatic laminate  16 . The first conductive part  120  and the second conductive part  130  are electrically connected to the control substrate  60 . 
     As shown in  FIG. 6  and  FIG. 7 , the first elastic body  140  is disposed in contact with one surface (the upper surface in  FIG. 6  and  FIG. 7 ) of the planar shape of the electrostatic laminate  16 . Further, as shown in  FIG. 7 , the first elastic body  140  is disposed in contact with two end surfaces (the left and right surfaces in  FIG. 7 ) that face away from each other in the plane direction of the planar shape of the electrostatic laminate  16 . Also, as shown in  FIG. 6 , the first elastic body  140  is disposed in contact with the curved convex surface of the first terminal  117  and the curved convex surface of the second terminal  118 . Although not shown, the first elastic body  140  may be disposed in contact with the side surfaces (the front and rear surfaces in  FIG. 6 ) of the first terminal  117  and the side surfaces (the front and rear surfaces in  FIG. 6 ) of the second terminal  118 . 
     In addition, as shown in  FIG. 6  and  FIG. 7 , the second elastic body  150  is disposed in contact with the other surface (the lower surface in  FIG. 6  and  FIG. 7 ) of the planar shape of the electrostatic laminate  16 . In  FIG. 6 , the second elastic body  150  is not in contact with the curved concave surface of the first terminal  117  and the curved concave surface of the second terminal  118 , but it may be disposed in contact with the curved concave surfaces. 
     &lt;4. Effect&gt; 
     The electrostatic transducer  1 , 100 of the first, second, and third embodiments includes a plurality of first electrode sheets  11  formed of an elastic deformable material in a sheet shape, a plurality of second electrode sheets  12  formed of an elastic deformable material in a sheet shape, and a plurality of dielectric sheets  13  formed of an elastic deformable material in a sheet shape. 
     Each of the first electrode sheets  11  includes the first counter electrode part  11   a  and the first terminal electrode part  11   b  extending from the first counter electrode part  11   a . Each of the second electrode sheets  12  includes the second counter electrode part  12   a  facing the first counter electrode part  11   a , and the second terminal electrode part  12   b  extending from the second counter electrode part  12   a.    
     Each of the dielectric sheets  13  includes the dielectric main body  13   a  interposed between the first counter electrode part  11   a  and the second counter electrode part  12   a,  the first extending part  13   b  extending from the dielectric main body  13   a  and interposed between the first terminal electrode parts  11   b,  and the second extending part  13   c  extending from the dielectric main body  13   a  and interposed between the second terminal electrode parts  12   b.    
     In other words, the first counter electrode part  11  a and the first terminal electrode part  11   b  are the same first electrode sheet  11 . Likewise, the second counter electrode part  12   a  and the second terminal electrode part  12   b  are the same second electrode sheet  12 . The first electrode sheet  11  and the second electrode sheet  12  can be formed very thin. That is, the electrostatic laminate  16  composed of the first counter electrode part  11   a , the second counter electrode part  12   a,  and the dielectric main body  13   a  is small in size and has a large electrostatic capacitance. 
     Here, the first electrode sheet  11  includes the first counter electrode part  11   a  and the first terminal electrode part  11   b . For example, it is conceivable to put only the first terminal electrode part  11   b  outside the electrostatic laminate  16  as the configuration of the conduction path connected to the first counter electrode part  11   a . However, the first terminal electrode part  11   b  is much thinner than the electrostatic laminate  16 . Therefore, if only the first terminal electrode part  11   b  is present outside the electrostatic laminate  16  as the portion for extracting electricity from the first counter electrode part  11   a,  it may receive a large deformation force near the boundary between the first terminal electrode part  11   b  and the first counter electrode part  11   a.    
     However, according to the first, second, and third embodiments, instead of putting only the first terminal electrode part  11   b  outside the electrostatic laminate  16 , the first extending part  13   b,  which is a part of the dielectric sheet  13 , is present outside the electrostatic laminate  16 , and the first terminal electrode part  11   b  and the first extending part  13   b  are laminated. Accordingly, the total thickness of the first terminal electrode part  11   b  and the first extending part  13   b  is smaller than that of the electrostatic laminate  16  only by the thickness of the second electrode sheet  12 . Therefore, it is possible to suppress generation of a large deformation force near the boundary between the first terminal electrode part  11   b  and the first counter electrode part  11   a . As a result, the constituent part of the conduction path connected to the first counter electrode part  11   a  can be highly durable. The same applies to the second terminal electrode part  12   b.    
     As described above, the dielectric sheet  13  is disposed not only between the first counter electrode part  11   a  and the second counter electrode part  12   a  but also between the first terminal electrode parts  11   b  and between the second terminal electrode parts  12   b.  For the value of the electrostatic capacitance of the electrostatic transducer  1 , the first extending part  13   b  of the dielectric sheet  13  that is present between the first terminal electrode parts  11   b , and the second extending part  13   c  that is present between the second terminal electrode parts  12   b  are unnecessary parts. However, by disposing the first extending part  13   b  and the second extending part  13   c  which are parts that do not contribute to the value of the electrostatic capacitance, as described above, the durability of the first terminal electrode part  11   b  and the second terminal electrode part  12   b  can be improved. 
     Furthermore, in the first, second, and third embodiments, the direction in which the first terminal electrode part  11   b  extends from the first counter electrode part  11   a,  and the direction in which the second terminal electrode part  12   b  extends from the second counter electrode part  12   a  are opposite directions. That is, the first terminal  17  formed by the first terminal electrode part  11   b  and the first extending part  13   b,  and the second terminal  18  formed by the second terminal electrode part  12   b  and the second extending part  13   c  face away from each other. Therefore, among the peripheral surfaces (the peripheral surfaces around the surface normal) of the electrostatic laminate  16 , the surfaces (the left and right surfaces in  FIG. 2  and  FIG. 7 ) adjacent to the first terminal  17  and the second terminal  18  face away from each other. Accordingly, it is possible to convert deformation of the electrostatic laminate  16  and electricity on the adjacent surfaces. 
     In addition, in the first, second, and third embodiments, the electrostatic transducer  1  includes the first conductive part  20  and the second conductive part  30 . The first conductive part  20  is formed of an elastic deformable material, and is in contact with the end of the first terminal electrode part  11   b  and the end of the first extending part  13   b  and is electrically connected to the ends of the first terminal electrode parts  11   b.    
     The second conductive part  30  is formed of an elastic deformable material, and is in contact with the end of the second terminal electrode part  12   b  and the end of the second extending part  13   c  and is electrically connected to the ends of the second terminal electrode parts  12   b.    
     With the first conductive part  20 , it is possible to easily form the conduction path between the first terminal electrode parts  11   b.  Likewise, with the second conductive part  30 , it is possible to easily form the conduction path between the second terminal electrode parts  12   b.  In addition, since the first conductive part  20  and the second conductive part  30  are elastic and deformable, they can follow the deformation of the first terminal  17  and the second terminal  18 . Therefore, even if the first terminal  17  and the second terminal  18  are deformed, the conduction path can be easily formed between the first terminal electrode part  11   b  and the second terminal electrode part  12   b.    
     Moreover, in the first and second embodiments, the electrostatic laminate  16  composed of the first counter electrode part  11   a , the second counter electrode part  12   a , and the dielectric main body  13   a  is formed in a planar shape. Then, the first terminal electrode part  11   b , the second terminal electrode part  12   b,  the first extending part  13   b , and the second extending part  13   c  extend in the plane direction of the planar shape of the electrostatic laminate  16 . Therefore, it is possible to suppress generation of a large deformation force near the boundary between the first terminal electrode part  11   b  and the first counter electrode part  11   a . As a result, the constituent part for extracting electricity from the first counter electrode part  11   a  can be highly durable. The same applies to the second terminal electrode part  12   b.    
     Further, in the first and second embodiments, the electrostatic laminate  16  composed of the first counter electrode part  11   a , the second counter electrode part  12   a , and the dielectric main body  13   a  is formed in a planar shape. Then, the first terminal electrode part  11   b , the second terminal electrode part  12   b,  the first extending part  13   b , and the second extending part  13   c  extend in the plane direction of the planar shape of the electrostatic laminate  16 . Furthermore, the first conductive part  20  and the second conductive part  30  are formed in the direction that intersects the plane of the planar shape. Therefore, it is possible to suppress generation of a large deformation force near the boundary between the first terminal electrode part  11   b  and the first counter electrode part  11   a , and the conduction path of the first conductive part  20  can also be set freely. The same applies to the second terminal electrode part  12   b.    
     Particularly, the electrostatic transducer  1  includes a plurality of electrostatic units  10   a,    10   b,  and  10   c  that are laminated. Each of the electrostatic units  10   a,    10   b,  and  10   c  is formed by integrally forming the first electrode sheet  11 , the second electrode sheet  12 , and the dielectric sheet  13 . Then, the first conductive part  20  is electrically connected to the first terminal electrode parts  11   b  in the electrostatic units  10   a,    10   b,  and  10   c.  The second conductive part  30  is electrically connected to the second terminal electrode parts  12   b  in the electrostatic units  10   a,    10   b,  and  10   c.    
     Therefore, it is possible to laminate a large number of first electrode sheets  11 , a large number of second electrode sheets  12 , and a large number of dielectric sheets  13 . At this time, in each of the electrostatic units  10   a,    10   b,  and  10   c,  it is possible to suppress generation of a large deformation force near the boundary between the first terminal electrode part  11   b  and the first counter electrode part  11   a . The same applies to the second terminal electrode part  12   b.    
     Furthermore, in the third embodiment, the electrostatic laminate  16  composed of the first counter electrode part  11   a,  the second counter electrode part  12   a,  and the dielectric main body  13   a  is formed in a planar shape. The first terminal electrode part  11   b  and the first extending part  13   b  are bent in a curved shape from the plane direction of the planar shape of the electrostatic laminate  16 . Moreover, the second terminal electrode part  12   b  and the second extending part  13   c  are bent in a curved shape from the plane direction of the planar shape. 
     Thus, in the case where the direction of the end surface of the first terminal  17  is changed, by bending the first terminal  17  in a curved shape, it is possible to suppress generation of a large deformation force near the boundary between the first terminal electrode part  11   b  and the first counter electrode part  11   a . The same applies to the second terminal  18 . 
     Particularly, the electrostatic laminate  16  composed of the first counter electrode part  11   a , the second counter electrode part  12   a,  and the dielectric main body  13   a  is formed in a planar shape. The first terminal electrode part  11   b  and the first extending part  13   b  are bent in a curved shape from the plane direction of the planar shape of the electrostatic laminate  16 . In addition, the second terminal electrode part  12   b  and the second extending part  13   c  are bent in a curved shape from the plane direction of the planar shape of the electrostatic laminate  16 . Then, the first conductive part  20  and the second conductive part  30  are formed in parallel to the plane direction of the planar shape of the electrostatic laminate  16 . Therefore, it is easy to form the electrostatic transducer  1  in a flat shape as a whole. 
     Also, in the first, second, and third embodiments, the electrostatic transducer  1  further includes the insulating sheets  14  and  15  covering the entire surfaces of the outermost layers of the first electrode sheets  11  and the second electrode sheets  12 . Thus, the insulating coating of the electrostatic laminate  16 , the insulating coating of the first terminal  17 , and the insulating coating of the second terminal  18  can be made very simply. 
     Besides, in the first, second, and third embodiments, the electrostatic laminate  16  composed of the first counter electrode part  11   a , the second counter electrode part  12   a , and the dielectric main body  13   a  is formed in a planar shape. Then, the electrostatic transducer  1  includes the elastic bodies  40  and  50  which are respectively disposed on two end surfaces (the upper and lower surfaces in  FIG. 1 ) that face away from each other in the direction (surface normal direction) orthogonal to the plane of the planar shape of the electrostatic laminate  16 . In addition, the electrostatic transducer  1  includes the cover  70  that presses the electrostatic laminate  16  in the lamination direction and holds the elastic bodies  40  and  50  in a state of compressing them to a greater extent than the electrostatic laminate  16 . Thus, even though the electrostatic laminate  16  alone generates small vibration, the cover  70  can have large vibration in the lamination direction of the electrostatic laminate  16 . 
     In addition, in the first, second, and third embodiments, the elastic body  40  is disposed on two end surfaces (the upper and lower surfaces in  FIG. 1 ) that face away from each other in the direction (surface normal direction) orthogonal to the plane of the planar shape of the electrostatic laminate  16 , and on two end surfaces (the left and right surfaces in  FIG. 1 ) that face away from each other in the plane direction of the planar shape of the electrostatic laminate  16 . Further, the cover  70  presses in the plane direction of the electrostatic laminate  16  and holds the elastic body  40  in a state of compressing it to a greater extent than the electrostatic laminate  16 . Thus, vibration in the plane direction of the electrostatic laminate  16  can be utilized. Then, even though the electrostatic laminate  16  alone generates small vibration, the cover  70  can have large vibration in both the lamination direction and the plane direction. 
     The elastic moduli E (40)  and E (50)  of the elastic bodies  40  and  50  are smaller than the elastic moduli E 1   (16)  and E 2   (16)  of the electrostatic laminate  16 . That is, in the initial state, in the state where the electrostatic laminate  16  and the elastic bodies  40  and  50  are pressed by the cover  70 , the compression amount of the electrostatic laminate  16  is small. Therefore, even if the electrostatic laminate  16  is pressed by the cover  70 , it does not significantly affect the stretch of the electrostatic laminate  16 . 
     Then, when a voltage is applied to the first counter electrode part  11  a and the second counter electrode part  12   a  of the electrostatic laminate  16 , the electrostatic laminate  16  stretches in the lamination direction and the plane direction. The displacement of the plane of the electrostatic laminate  16  caused by the stretch of the electrostatic laminate  16  is transmitted to the cover  70  via the elastic bodies  40  and  50 . In addition, the elastic deformation force of the elastic bodies  40  and  50  changes due to the stretch of the electrostatic laminate  16 , and the change of the elastic deformation force of the elastic bodies  40  and  50  is transmitted to the cover  70 . Accordingly, as the initial state, since the elastic bodies  40  and  50  are compressed, the vibration can be efficiently transferred to the cover  70 . That is, even though the electrostatic laminate  16  alone generates small vibration, the cover  70  can have tactile vibration. 
     Furthermore, the elastic bodies  40  and  50  use materials having small loss factors tanδ (40)  and tanδ (50) . Thus, the elastic bodies  40  and  50  can transmit the vibration generated by the stretch of the electrostatic laminate  16  to the cover  70  without absorbing it. Particularly, the above operation can be realized reliably by using silicone rubber to form the elastic bodies  40  and  50 . 
     In addition, the loss factors tanδ (40)  and tanδ (50)  of the elastic bodies  40  and  50  are set to be equal to or smaller than the loss factor tanδ (16)  of the electrostatic laminate  16  under the predetermined condition. As described above, the predetermined condition refers to an environment of use where the temperature is set to −10° C. to 50° C. and the vibration frequency is set to 300 Hz or less. Thus, the elastic bodies  40  and  50  can reliably transmit the vibration generated by the stretch of the electrostatic laminate  16  to the cover  70  without absorbing it. 
     Also, in the second embodiment, the outermost layer of the electrostatic laminate  16  composed of the first counter electrode part  11   a,  the second counter electrode part  12   a,  and the dielectric main body  13   a  is formed with an elastic modulus in the lamination direction larger than those of the other layers. Thus, the vibration generated by the stretch of the electrostatic laminate  16  is more efficiently transmitted to the cover  70 . 
     Particularly, the outermost layer of the electrostatic laminate  16  is preferably a layer surface-modified by UV irradiation. Therefore, the outermost layer can be very thin and have a nano-order thickness. Thus, the transmission efficiency of the vibration generated by the stretch can be improved without hindering the stretch itself of the electrostatic laminate  16 .