Patent Description:
In the acoustic field, a dynamic speaker configured by a coil is generally used. Although a dynamic speaker can generate sufficient sound pressure even in the low audio frequency range, the application is limited since the weight, the volume and the power consumption of the dynamic speaker are large. On the other hand, the application of the piezoelectric speaker using the piezoelectric element has been advanced (e.g., see Patent Document <NUM>). Since the volume, the weight and the power consumption of a piezoelectric speaker are small, the piezoelectric speaker can also be used in applications difficult to apply dynamic speakers.

Patent Document <NUM> describes a piezoelectric oscillation unit including a rectangular first conductor plate; a support portion for supporting the opposite ends of the first conductor plate in the longitudinal direction; a planar piezoelectric element fixed to at least one principal surface of the first conductor plate; a first coupling portion formed on at least a part of one side face of the first conductor plate parallel with the longitudinal direction; a second coupling portion formed on at least a part of the other side face of the first conductor plate parallel with the longitudinal direction; a first weight connecting with the first coupling portion; and a second weight connecting with the second coupling portion. Further, Patent Document <NUM> describes a small-size thin piezoelectric actuator mountable on a mobile electronic device to give a contact feeling of a three dimensional movement to a user's hand palm. The piezoelectric actuator comprises a piezoelectric ceramic oscillator having a piezoelectric ceramic thin plate bonded to at least one surface of a shim member, at least one holder for holding the shim member, and a sheet-shaped elastic body.

However, in the piezoelectric speaker, it is difficult to obtain a sufficient sound pressure in the low and middle audio frequency range. As a result, the sound pressure as a whole is often reduced. If the demerit is overcome, the piezoelectric module can be applied not only to speakers for watching television programs, movies, music, and the like, but also to various applications. A piezoelectric module that can obtain sufficient sound pressure in the low and middle audio frequency range is available for a loudspeaker and noise canceller, even if it does not have an acoustic structure such as a hole and cavity, as long as it has a vibration plate.

Such a piezoelectric module has the potential to be quite different from a conventional piezoelectric module and should be referred to as a SoT (Sound of Things) module (hereinafter, piezoelectric modules that can improve sound pressure in a particular audio frequency range are referred to as a SoT module).

From the above circumstances, the inventors of the present invention have continued trial and error in the development of a piezoelectric module by which sufficient sound pressure is obtained even in the low and middle audio frequency range. For example, in the piezoelectric module <NUM> shown in <FIG>, on the vibration plate <NUM>, the piezoelectric element <NUM> is provided with a central portion supported by the elastic body <NUM>. As the material of the elastic body <NUM> and the vibration plate <NUM> of such piezoelectric module <NUM>, various materials have been tried.

Also, an attempt to increase the sound pressure by providing a plurality of piezoelectric elements has been made. In the piezoelectric module <NUM> shown in <FIG>, the sound pressure is increased by providing two piezoelectric elements 3110a and 3110b in parallel supported at the centers by elastic bodies 3120a and 3120b. However, even in such improved piezoelectric module <NUM>, sufficient sound pressure has not been obtained in the low and middle audio frequency range.

The present invention has been made in view of such circumstances, a SoT module that generates sufficient sound pressure in the low and middle audio frequency range and can be applied to a variety of applications is provided.

To achieve the above object, a piezoelectric module according to claim <NUM> comprises a plate-shaped piezoelectric composite for generating bending vibration by the impression of an AC voltage, a plurality of elastic bodies, one ends of which are bonded to a main surface of the piezoelectric composite, the elastic bodies transmitting vibration of the piezoelectric composite, and a vibration plate having a main surface which is bonded to other ends of the elastic bodies, wherein the piezoelectric composite comprises a piezoelectric element formed in a rectangular plate, there is a position of a centroid of the piezoelectric composite between the plurality of elastic bodies, and the piezoelectric composite comprises a plurality of piezoelectric elements, each of which is identical to the piezoelectric element, and each of the piezoelectric elements is partially connected to each other.

The above object is alternatively also achieved by providing a piezoelectric module according to claim <NUM>.

Thus, the stiffness of the entire module can be reduced, and the displacement amplitude of the vibration plate can be increased. As a result, sufficient sound pressure is obtained in the low and middle audio frequency range, and it can be applied to various applications.

Next, embodiments of the present invention are described with reference to the drawings.

<FIG> is a perspective view showing a SoT module <NUM>. The SoT module <NUM> comprises piezoelectric elements 110a and 110b, elastic bodies 120a and 120b and a vibration plate <NUM>. Each of the piezoelectric elements 110a and 110b is formed bending-type in a rectangular plate and generates flexural vibration by impression of an AC voltage.

The piezoelectric elements 110a and 110b are arranged in parallel and are not connected to each other. Between the elastic bodies 120a and 120b is the position of the centroid of each of the piezoelectric elements 110a and 110b. As a result, sufficient sound pressure is obtained in the low and middle audio frequency range, SoT module <NUM> can be applied to a variety of applications. Each of the piezoelectric elements 110a and 110b configures a piezoelectric composite.

<FIG> is a cross-sectional view showing an example of the configuration and operation of the piezoelectric element <NUM>. The piezoelectric element <NUM> is an example of the configuration of the piezoelectric elements 110a and 110b. The piezoelectric element <NUM> comprises piezoelectric bodies <NUM> and <NUM>, electrodes <NUM> and <NUM> and shim plate <NUM>. The shim plate <NUM> is made of metal and also has the function of an electrode.

The piezoelectric bodies <NUM> and <NUM> are preferably formed of a piezoelectric ceramic material. As the piezoelectric material, for example, zirconate titanate (Pb(Ti, Zr)O<NUM>, so-called PZT) or barium titanate (BaTiO<NUM>) is used. Both are ferroelectrics, and PZT is preferable from the viewpoint of efficiency, but barium titanate is preferable from the viewpoint of lead-free. The piezoelectric bodies <NUM> and <NUM> may be formed of a piezoelectric polymer. Piezoelectric polymers comprise polyvinylidene fluoride and copolymers thereof, polylactic acid, polyvinylidene cyanide, polyurea and odd nylon.

Piezoelectric body <NUM> is polarized in the direction of the shim plate <NUM> from the electrode <NUM>, the piezoelectric body <NUM> is polarized in the direction of the electrode <NUM> from the shim plate <NUM>. One electrode is connected to the electrodes <NUM> and <NUM>, and the other electrode is connected to the shim plate <NUM>. In this configuration, when an AC voltage is impressed to the piezoelectric bodies <NUM> and <NUM> by the power supply P1, one contracts and the other extends along a direction parallel to the surface by the reverse piezoelectric effect, and then the bending vibration occurs by repeating the movement shown as the arrow S1 and S2 in <FIG>.

The above-described piezoelectric element <NUM> has a parallel bimorph structure in which the polarization directions of the piezoelectric bodies <NUM> and <NUM> are the same but may have a series bimorph structure in which the polarization directions are different. Further, an insulator may be used for the central shim plate. The piezoelectric element <NUM> preferably has a bimorph structure but may have a unimorph structure. Further, for the piezoelectric element <NUM>, a piezoelectric multilayer body may be used in place of the piezoelectric body of a single plate. In this case, an external electrode may be used, or an electrode may be formed by a via structure. Further, the piezoelectric element <NUM> is formed by the piezoelectric layer and the electrode being stacked, it may be a stretching-type piezoelectric element which expands and contracts in the stacking direction.

The elastic body 120a has one end bonded to the main surface of the piezoelectric element 110a and the other end bonded to the main surface of the vibration plate <NUM>, and the elastic body120b has one end bonded to the main surface of the piezoelectric element 110b and the other end bonded to the main surface of the vibration plate <NUM>. For example, an epoxy-based, acrylic-based, or urethane-based adhesive can be used for bonding (hereinafter, for any bonding is the same). The elastic bodies 120a and 120b are preferably formed of a resin such as urethane. The elastic modulus of the elastic bodies 120a and 120b is preferably 70MPa or more and 690MPa or less. The elastic bodies 120a and 120b transmit the displacement of the piezoelectric elements 110a and 110b to the vibration plate <NUM>.

Between the elastic bodies 120a and 120b, the position of the centroid for each of the piezoelectric elements 110a and 110b is preferably located. Thus, the stiffness of the entire SoT module <NUM> can be reduced, and the peak dip in the middle audio frequency range occurred for the piezoelectric elements 110a and 110b in which the natural frequency is set to be small can be eliminated. It is particularly preferable that the elastic bodies 120a and 120b are bonded to respective ends of the piezoelectric elements 110a and 110b. For each of the piezoelectric elements 110a and 110b, the region can be divided into a central portion, two intermediate portions, and two end portions.

Each of the elastic bodies 120a and 120b is preferably formed in a rectangular shape as shown in <FIG> but may be formed in a cylindrical shape or an elliptical cylindrical shape. The elastic bodies 120a, 120b are preferably symmetrical in shape and arrangement with respect to the piezoelectric elements 110a, 110b to be bonded.

The vibration plate <NUM> is formed in a plate shape and bonded to the elastic bodies 120a and 120b. The material of the vibration plate <NUM> varies depending on the application. For example, a styrene board can be used as the vibration plate <NUM>. Further, it is possible to use a OLED panel as the vibration plate <NUM> of the TV speaker. Although the vibration plate <NUM> made of resin is easily used, a vibration plate with inelasticity enhanced using wood or fiber structure may be used.

The vibration plate <NUM> vibrates in the thickness direction by the displacement force transmitted through the elastic bodies 120a and 120b, vibrates air and generates sound waves. Depending on the frequency of the signal and the intensity of the current applied to the piezoelectric elements 110a and 110b, the pitch and the sound pressure of the sound generated from the vibration plate <NUM> appear differently for magnitude. In order to generate a large sound pressure, it is effective to improve the efficiency of vibration which is connected to the vibration plate.

The operation of the SoT module <NUM> is described below. By the electrical signal for the sound amplified by the amplifier being input to the SoT module <NUM>, the piezoelectric composite <NUM> vibrates. Then, the displacement due to the vibration is transmitted to the vibration plate <NUM> via the elastic bodies 120a and 120b, and the vibration plate <NUM> vibrates to generate a sound corresponding to the electric signal.

The unconnected piezoelectric elements 110a and 110b are preferably driven in anti-phase or in-phase. The stiffness of the whole path transmitted by vibration and a combination of the phase driving each piezoelectric element is determined according to the required characteristics such as the sound pressure in the low audio frequency range. The stiffness of the whole path is determined by each element. For example, even when the stiffness of the piezoelectric elements 110a and 110b and the vibration plate <NUM> is large, when the stiffness of the elastic bodies 120a and 120b is small, the stiffness of the whole path may be small.

Although the independent two piezoelectric elements are arranged in parallel in the above embodiment, the piezoelectric elements installed in parallel may be connected by connecting members. <FIG> is a perspective view showing the SoT module <NUM>.

The SoT module <NUM> comprises piezoelectric elements 210a and 210b, elastic bodies 220a and 220b, connecting members 240a and 240b and a vibration plate <NUM>. The piezoelectric elements 210a and 210b have the same configuration as the piezoelectric elements 110a and 110b, respectively. However, the piezoelectric elements 210a and 210b are provided in parallel with each other on the vibration plate <NUM>, and a part of each other is connected to configure a plate-shaped piezoelectric composite <NUM>. Thus, the vibration is amplified through the connecting portion, the displacement amplitude of the vibration plate <NUM> can be increased. Each of the elastic bodies 220a and 220b is formed of the same material in a rectangular plate shape and arranged as each of the elastic bodies 120a and 120b.

Each of the two connecting members 240a and 240b is formed of resin such as PET in a flat plate shape and connects the end of the piezoelectric element 210a and the end of the piezoelectric element 210b. The connecting is performed by bonding the back surfaces of the connecting members 240a and 240b and the surfaces of the piezoelectric elements 210a and 210b to each other. The connecting members 240a and 240b are arranged so that their longitudinal directions do not intersect each other and are preferably parallel to each other. The thickness of the connecting members 240a and 240b is designed according to the overall configuration, for example, <NUM> or more and <NUM> or less. The piezoelectric elements 210a and 210b and the connecting members 240a and 240b configure the piezoelectric composite <NUM>. In the cross-sectional view, the electrodes of the piezoelectric elements 210a and 210b are omitted.

It is preferable that the piezoelectric elements 210a and 210b are wired so as to be driven in in-phase or anti-phase to each other. That is, the piezoelectric elements 210a and 210b are wired so as to be driven in in-phase or anti-phase, and electric signals are input thereto. Thus, vibration of the piezoelectric elements 210a and 210b can be amplified via the connecting members 240a and 240b, and the sound pressure in the low audio frequency range to the middle audio frequency range can be improved. Either in-phase or anti-phase may be selected depending on the combination of the required characteristics and the stiffness of the whole path transmitted by the vibration.

For example, the piezoelectric elements 210a and 210b are wired so as to be driven in anti-phase to each other, and electric signals can be input. The respective piezoelectric elements 210a and 210b are driven in anti-phases with respect to the SoT module <NUM> in which the piezoelectric composite <NUM> is located on the upper side and the vibration plate <NUM> is located on the lower side. In this case, when the central portion of the piezoelectric element 210a is displaced downward, the central portion of the piezoelectric element 210b is displaced upward.

The piezoelectric elements 210a and 210b may be wired so as to be driven in phase with each other, and electric signals may be input. In the case that each piezoelectric element is driven in phase, when the center portion of the piezoelectric element 210a is displaced downward, the center portion of the piezoelectric element 210b is also displaced downward. When the central portion of the piezoelectric element 210a is displaced upward, the central portion of the piezoelectric element 210b is also displaced upward.

The SoT module <NUM> is preferably driven by a drive method for increasing the sound pressure of the low audio frequency range. When the displacement of the piezoelectric composite <NUM> with respect to the position is represented by a curve and the curve is overlapped with the one in anti-phase, there is a position where the curves intersect. This position would be called a displacement point, and the displacement point can be changed closer to or farther from the elastic bodies 220a and 220b by adjusting the drive signals (the anti-phase or in-phase). This adjustment allows amplification of sound pressure at a specific frequency. In this way, a sufficient sound pressure can be obtained even in the low audio frequency range, for example.

In the second embodiment, although the rectangular plate-shaped elastic body is provided only at the positions of both end portions of the piezoelectric element, the elastic body may be provided over the entire vibration plate. The elastic body may have a uniform plate shape or may be formed in a predetermined pattern as described later.

<FIG> are plan and cross-sectional views showing the SoT module <NUM>, respectively. The cross-sectional view of the <FIG> represents the cross-section 4b shown in <FIG>. The SoT module <NUM> is configured in the same manner as the SoT module <NUM> except for the elastic body <NUM>.

On the other hand, the elastic body <NUM> is formed in a uniform plate shape over the entire vibration plate <NUM>. Thus, since the elastic body <NUM> is easily arranged, the stiffness of the SoT module <NUM> can be reduced by the elastic body <NUM> while the manufacturing load is reduced. The operation of the SoT module <NUM> is the same as that of the SoT module <NUM>.

<FIG> are plan and cross-sectional views showing the SoT module <NUM>, respectively. The cross-sectional view of <FIG> represents the cross-section 5b shown in <FIG>. The SoT module <NUM> is configured in the same manner as the SoT module <NUM> except for the elastic body <NUM>.

The elastic body <NUM> has a constant pattern shape over a cross section perpendicular to the thickness direction over the entire vibration plate <NUM>. The constant pattern shape is preferably a shape in which a plurality of cylindrical holes are arranged periodically. Further, it is more preferable that a plurality of types of cylindrical holes having different diameters are provided. Thus, the constraint to the piezoelectric composite <NUM> becomes loose, and the displacement is not hindered. As a result, the stiffness S value of the whole system can be lowered, and the damping ratio of the vibration transmission path can be optimized.

<FIG> are a plan view and a cross-sectional view showing the SoT module <NUM> according to a fifth embodiment, respectively. The cross-sectional view of <FIG> represents the cross-section 6b shown in <FIG>. The SoT module <NUM> is configured in the same manner as the SoT module <NUM> except for the elastic body <NUM>.

The elastic body <NUM> has a constant pattern shape on a cross section perpendicular to the thickness direction over the entire vibration plate <NUM>. The constant pattern shape is preferably a shape in which a plurality of spherical projections or cylinders are arranged periodically. Thus, the constraint to the piezoelectric composite <NUM> becomes loose, and the displacement is not hindered. As a result, the stiffness S value of the whole system can be lowered, and the damping ratio of the vibration transmission path can be optimized.

Although two piezoelectric elements are used in the above embodiment, three piezoelectric elements may be connected for the SoT module. In that case, the central portion of the SoT module installed in parallel can be connected by a piezoelectric element.

<FIG> and <FIG> are schematic diagrams showing a configuration of the SoT module <NUM>. Each of arrows in the figure shows the displacement of each piezoelectric element in accordance with the type of arrow (hereinafter the same). The SoT module <NUM> comprises piezoelectric elements 610a to 610c, elastic bodies 620a and 620b, and a vibration plate <NUM>. Three piezoelectric elements 610a to 610c are connected in an H-shape to form a piezoelectric composite <NUM>.

The piezoelectric elements 610a and 610b are configured in the same manner as the piezoelectric elements 210a and 210b, respectively. The elastic bodies 620a and 620b are formed of the same material and are arranged in the same manner as the elastic bodies 120a and 120b. The elastic bodies 620a and 620b support the piezoelectric elements 610a and 610b on the vibration plate <NUM>, respectively, and transmit vibrations of the piezoelectric elements 610a and 610b to the vibration plate <NUM>.

The piezoelectric element 610c has the same configuration as the piezoelectric element 610a and connects the center portions of the piezoelectric elements 610a and 610b. The connection is made by bonding the back surface of ends of the piezoelectric element 610c and the surface of the center portion of the piezoelectric elements 610a and 610b.

<FIG> is a schematic diagram showing an example of the operation of the SoT module <NUM>. Electrical signals are input to the wiring configured so that the piezoelectric elements 610a to 610c are all driven in phase in the SoT module <NUM> in which the piezoelectric composite <NUM> is located on the upper side and the vibration plate <NUM> is located on the lower side. In the case, displacement occurs as indicated by the arrow shown in <FIG>, it is possible to obtain a large displacement of the entire piezoelectric composite <NUM>. In the case that the piezoelectric elements are driven in phase with each other, when the center portions of the piezoelectric elements 610a and 610b are displaced upward, both ends of the piezoelectric element 610c are displaced downward, and the center portion is displaced upward.

The wiring may be configured so that the piezoelectric elements 610a and 610b can be driven in anti-phases to the piezoelectric element 610c each other, and an electric signal may be input. <FIG> is a schematic diagram showing an operation example of the SoT module <NUM>. In this case, a displacement occurs as indicated by an arrow in <FIG>, and a large displacement can be obtained in the entire piezoelectric composite <NUM>. When the center portions of the piezoelectric elements 610a and 610b are displaced upward, both ends of the piezoelectric element 610c are displaced upward, and the center portion is displaced downward.

when the curves of the displacements of the piezoelectric composite <NUM> in anti-phases are overlapped and the position where the curves intersect is called a displacement point, the displacement point can be changed closer to or farther from the elastic bodies 620a and 620b by adjusting the drive signal (anti-phase or in-phase). This adjustment allows amplification of sound pressure at a specific frequency. By thus amplifying the displacement of the piezoelectric composite <NUM> and transmitting vibration to the vibration plate <NUM>, it is possible to improve the sound pressure of the low audio frequency range.

In the above embodiments, there is a termination in the amplification path of the displacement of the piezoelectric element, but the SoT module may have a structure for amplifying the displacement in a loop. In the following example, four piezoelectric elements are used from the viewpoint of efficiency, but other numbers of piezoelectric elements such as three or five may be used.

<FIG> are a perspective view, a schematic view, a side view showing an operation of the SoT module <NUM>, respectively. The SoT module <NUM> comprises piezoelectric elements 710a to 710d, elastic bodies 720a to 720d, and a vibration plate <NUM>. Each of the piezoelectric elements 710a to 710d has the same element structure as that of the piezoelectric element 110a. Four piezoelectric elements 710a to 710d are connected in a loop structure to form a piezoelectric composite <NUM>.

The connection is performed, for example, by bonding the back surface of one end of the piezoelectric element 710a and the front surface of the center portion of the piezoelectric element 710b. A region surrounded by a dotted line in <FIG> is a bonding region. Such connections are performed between the piezoelectric elements 710b and 710c, the piezoelectric elements 710c and 710d, and the piezoelectric elements 710d and 710a, thereby forming the loop structure. Thus, the vibration of the piezoelectric element can be amplified in a loop through the connected members until saturated, the sound pressure can be improved in the low audio frequency range. The positions at which the ends of each of the plurality of piezoelectric elements 710a to 710d are connected are the centers of the other piezoelectric elements. Thus, the characteristics of the low audio frequency range can be improved.

The elastic bodies 720a to 720d are made of the same material as that of the elastic body 120a. As described above, one end of the piezoelectric element 710a is connected to the center portion of the other piezoelectric element 710b, and the other end is supported by the elastic body 720a. In this manner, the elastic bodies 720a to 720d support the ends of the piezoelectric elements 710a to 710d on the vibration plate <NUM>, respectively and transmit the vibrations of the piezoelectric elements 710a to 710d to the vibration plate <NUM>. The piezoelectric elements 710a to 710d are driven in in-phase or anti-phase, and the driving method thereof is set according to the stiffness of the entire path through which the vibrations are transmitted. The sound pressure can be amplified at a specific frequency by adjusting the drive signal (anti-phase or in-phase) to change the displacement point closer to or farther away from the elastic bodies 720a to 720d.

In the seventh embodiment, the connecting destination of one end of the piezoelectric element is a central portion of the other piezoelectric element, but an intermediate portion between the central portion and the end portion may be the destination. <FIG> is a perspective view of the SoT module <NUM>. The connection is performed by bonding one's back surface to the other's surface. A region surrounded by a dotted line in <FIG> is a bonding region. The SoT module <NUM> is configured in the same manner as the SoT module <NUM> except for the connecting places of the piezoelectric elements 810a to 810d. The piezoelectric elements 810a to 810d are driven in in-phase or anti-phase, and the driving method thereof is set according to the stiffness of the entire path through which the vibrations are transmitted. Thus, the characteristics of the middle audio frequency range can be improved. The sound pressure can be amplified at a specific frequency by adjusting the drive signal (anti-phase or in-phase) to change the displacement point closer to or farther away from the elastic bodies 820a to 820d.

In the seventh embodiment, the connecting destination of one end of the piezoelectric element is a central portion of the other piezoelectric element, an end portion may be the destination. <FIG> is a perspective view of the SoT module <NUM>. The connection is performed by bonding one's back surface to the other's surface. A region surrounded by a dotted line in <FIG> is a bonding region. The SoT module <NUM> is configured in the same manner as the SoT module <NUM> except for the connecting places of the piezoelectric elements 910a to 910d. The piezoelectric elements 910a to 910d are driven in in-phase or anti-phase, and the driving method thereof is set according to the stiffness of the entire path through which the vibrations are transmitted. Thus, the characteristics of the high audio frequency range can be improved. The sound pressure to be amplified at a specific frequency by adjusting the drive signal (anti-phase or in-phase) to change the displacement point closer to or farther away from the elastic bodies 920a to 920d.

The piezoelectric elements may be connected so as to cross each other in the longitudinal direction to configure a piezoelectric composite. For example, the piezoelectric elements are arranged to intersect each other in the longitudinal direction and overlap the central portions. Then, the back surface of the central portion of the one piezoelectric element is bonded to the surface of the central portion of the other piezoelectric element. Thus, the displacement of the vibration plate can be amplified, and especially, the sound pressure in the middle audio frequency range from the low audio frequency range can be improved. It is preferable that the crossing is made at an orthogonal angle or an angle at which an effect equivalent thereto can be obtained.

In the above embodiment, the bending-type piezoelectric element is used, but a stretching-type piezoelectric element may be used. As the stretching-type piezoelectric element, it is preferable to use a piezoelectric element obtained by stacking a piezoelectric body and an electrode in the expansion direction. <FIG> are a perspective view and a cross-sectional view showing the SoT module <NUM>, respectively. The cross-sectional view of <FIG> represents a cross-sectional view 11b shown in <FIG>.

The SoT module <NUM> is configured of piezoelectric elements <NUM>, <NUM>, an elastic body <NUM> and a vibration plate <NUM>. Each of the piezoelectric elements <NUM> and <NUM> is a stretching-type piezoelectric element. The piezoelectric elements <NUM> and <NUM> are preferably formed by electrodes and piezoelectric bodies which are formed of piezoelectric ceramics polarized being stacked. The piezoelectric elements <NUM> and <NUM> generate stretching vibration by the impression of an AC voltage.

The piezoelectric elements <NUM> and <NUM> are alternately arranged in a single row along the longitudinal direction, by their end portions being connected to each other, to form steps of up and down. Specifically, the back surface of the piezoelectric element <NUM> is bonded to the surface of the piezoelectric element <NUM> at each of the ends. The piezoelectric elements <NUM> are located in a state where a portion overlaps with the piezoelectric element <NUM> each other on both sides of the piezoelectric element <NUM> located in the center. The piezoelectric elements <NUM> and <NUM> configure the symmetrical piezoelectric composite <NUM>.

The plurality of piezoelectric elements <NUM> and <NUM> may be driven by an input of a single signal (in-phase drive) or may be driven by different signals by shifting the phase for a central piezoelectric element <NUM> relative to the phase of the piezoelectric elements <NUM> on both sides. The displacement of the piezoelectric composite <NUM> with respect to the position is represented by a curve and the curve is overlapped with the one in anti-phase, there is a position where the curves intersect. The sound pressure can be amplified at a specific frequency by adjusting the drive signal (anti-phase or in-phase) to change the displacement point closer to or farther away from the elastic bodies <NUM>. In this manner, the amount of displacement can be amplified through the connecting portion. When only piezoelectric element <NUM> is driven in a shifting the phase, it is preferably driven in anti-phase with the piezoelectric element <NUM> on both sides.

<FIG> is a perspective view of the SoT module <NUM>. The SoT module <NUM> comprises piezoelectric composites 1105a and 1105b, elastic bodies 1120a and 1120b, and a vibration plate <NUM>. The piezoelectric composite 1105a is configured in the same manner as the piezoelectric composite <NUM>, has piezoelectric elements 1110a and 1180a and is formed by connecting respective ends thereof in a row. The piezoelectric composite 1105b is also formed by connecting ends of the piezoelectric elements 1110b and 1180b and is configured in the same manner as the piezoelectric composite <NUM>. The sound pressure can be amplified at a specific frequency by adjusting the drive signal (anti-phase or in-phase) to change the displacement point closer to or farther away from the elastic bodies 1120a and 1120b. Since the piezoelectric composites 1105a and 1105b are arranged in parallel, the amount of displacement can be amplified. The driving of the piezoelectric composites 1105a and 1105b can be performed in the same manner as the driving of the piezoelectric composite <NUM>.

<FIG> is a perspective view of the SoT module <NUM>. The SoT module <NUM> comprises a piezoelectric composite <NUM>, elastic bodies 1220a to 1220d, and a vibration plate <NUM>. The piezoelectric composite <NUM> comprises a central piezoelectric element <NUM> and peripheral piezoelectric elements 1210a to 1210d connected at their ends to the edges of the central piezoelectric element <NUM>. The central piezoelectric element <NUM> is larger than each of the peripheral piezoelectric elements 1210a to 1210d. The connection direction of the piezoelectric elements 1210a, <NUM>, and 1210c connected in one row intersects the connection direction of the piezoelectric elements 1210b, <NUM>, and 1210d connected in another row at perpendicular angle at the center.

The plurality of piezoelectric elements <NUM> and 1210a to 1210d may be driven with a single signal input (in-phase drive) or may be driven with different signals in which the phase for the center piezoelectric element <NUM> is out of the phase for the peripheral piezoelectric elements 1210a to 1210d. When only the piezoelectric element <NUM> is driven in a shifted phase, it is preferably driven in anti-phase with the peripheral piezoelectric elements 1210a to 1210d. The sound pressure can be amplified at a specific frequency by adjusting the drive signal (anti-phase or in-phase) to change the displacement point closer to or farther away from the elastic bodies 1220a to 1220d.

The central piezoelectric element may be connected to the vibration plate side of the peripheral piezoelectric elements. Further, each of the connecting portions may be shifted to one side from the plane passing through the center of the central piezoelectric element. <FIG> are plan and cross-sectional views showing the SoT module <NUM>. The cross-sectional view of <FIG> represents a cross-section 13b shown in <FIG>.

The SoT module <NUM> comprises a piezoelectric composite <NUM>, elastic bodies 2220a to 2220d, and a vibration plate <NUM>. The piezoelectric composite <NUM> comprises a central piezoelectric element <NUM> and peripheral piezoelectric elements 2210a-2210d whose ends are connected to the edges of the central piezoelectric element <NUM>. The width of the central piezoelectric element <NUM> is larger than the width of the peripheral piezoelectric elements 2210a to 2210d. The central piezoelectric element <NUM> is connected to the vibration plate <NUM> side of the peripheral piezoelectric elements 2210a to 2210d. The connection direction of the piezoelectric elements 2210a, <NUM>, and 2210c connected in one row intersects the connection direction of the piezoelectric elements 2210b, <NUM>, and 2210d connected in another row at perpendicular angle at the center.

Each of the connecting portion is shifted to one side from the plane passing through the center of the central piezoelectric element <NUM>. For example, the connecting position of the piezoelectric element 2210d with respect to the plane P1 is shifted toward the piezoelectric element 2210a, and the connecting position of the piezoelectric element 2210b is shifted toward the piezoelectric element 2210c. In this way, the SoT module <NUM> is formed in a windmill-like shape.

The plane P1 is a bisecting plane that evenly divides the piezoelectric composite <NUM>, and the piezoelectric composite <NUM> is formed such that the shapes of both sides divided by the plane P1 are point symmetric with respect to one point on the plane P1. That is, the piezoelectric composite <NUM> has a shape which looks inverted vertically and horizontally when viewed from one side to the other side divided by the plane P1. The piezoelectric composite <NUM> has the same symmetry not only with respect to the plane P1 but also with respect to a bisecting plane (e.g., the plane P2) that divides evenly regardless of the angle.

The plurality of piezoelectric elements <NUM> and 2210a to 2210d may be driven with a single signal input (in-phase drive) or may be driven with different signals in which the phase for the center piezoelectric element <NUM> is out of the phase for the peripheral piezoelectric elements 2210a to 2210d. When only piezoelectric element <NUM> is driven by shifting the phase, it is preferable to drive the piezoelectric elements 2210a to 2210d on peripheral region in anti-phase. The sound pressure to be amplified at a specific frequency by adjusting the drive signal (anti-phase or in-phase) to change the displacement point closer to or farther away from the elastic bodies 2220a to 2220d. Such adjustment is facilitated by the symmetry described above.

In the tenth to twelfth embodiments, the ends of the stretching-type piezoelectric elements are connected by bonding, but they may be connected via a base plate. <FIG> are a perspective view and a cross-sectional view showing the SoT module <NUM>, respectively. The cross-sectional view of <FIG> represents the cross-sectional view 13b shown in <FIG>.

The SoT module <NUM> comprises a piezoelectric element <NUM> and <NUM>, elastic bodies <NUM>, a base plate <NUM> and a vibration plate <NUM>. Each of the piezoelectric elements <NUM> and <NUM> is a stretching-type piezoelectric element. The piezoelectric elements <NUM> and <NUM> are preferably formed by electrodes and piezoelectric bodies which are formed of piezoelectric ceramics polarized being stacked. The piezoelectric elements <NUM> and <NUM> generate stretching vibration by the impression of an AC voltage.

The piezoelectric elements <NUM> and <NUM> are provided in a row along the longitudinal direction on a rectangular base plate <NUM>. The piezoelectric elements <NUM> and <NUM> are alternately arranged at uniform intervals, and the piezoelectric composite <NUM> is symmetrically formed. The piezoelectric elements <NUM> and <NUM> configure a symmetrical piezoelectric composite <NUM>.

The plurality of piezoelectric elements <NUM> and <NUM> may be driven by an input of a single signal (in-phase drive) or may be driven by different signals by shifting the phase for a central piezoelectric element <NUM> relative to the phase of the piezoelectric elements <NUM> on both sides. The displacement of the piezoelectric composite <NUM> with respect to the position is represented by a curve and the curve is overlapped with the one in anti-phase, there is a position where the curves intersect. The sound pressure can be amplified at a specific frequency by adjusting the drive signal (anti-phase or in-phase) to change the displacement point closer to or farther away from the elastic bodies <NUM>. In this manner, the amount of displacement can be amplified through the connecting portion. The same effect can be obtained even when the elastic bodies <NUM> and the vibration plate <NUM> are omitted and the base plate <NUM> is used as the vibration plate.

<FIG> is a perspective view of the SoT module <NUM>. The SoT module <NUM> comprises piezoelectric composites 1405a and 1405b, elastic bodies 1420a and 1420b, and a vibration plate <NUM>. The piezoelectric composite 1405a comprises piezoelectric elements 1410a and 1490a and a base plate 1460a and is configured in the same manner as the piezoelectric composite <NUM>. The piezoelectric composite 1405b also comprises piezoelectric elements 1410b and 1490b and a base plate 1460b and is configured in the same manner as the piezoelectric composite <NUM>.

The sound pressure can be amplified at a specific frequency by adjusting the drive signal (anti-phase or in-phase) to change the displacement point closer to or farther away from the elastic bodies <NUM>. Further, since the piezoelectric composites 1405a and 1405b are arranged in parallel, the amount of displacement can be amplified. The driving of the piezoelectric composites 1405a and 1405b can be performed in the same manner as the driving of the piezoelectric composite <NUM>.

<FIG> is a perspective view of the SoT module <NUM>. The SoT module <NUM> comprises a piezoelectric composite <NUM>, elastic bodies 1520a to 1520d and a vibration plate <NUM>. The piezoelectric composite <NUM> comprises piezoelectric elements 1510a to 1510d and <NUM> and a base plate <NUM>. The piezoelectric elements 1510a to 1510d and <NUM> are bonded onto a base plate <NUM>.

In the piezoelectric composite <NUM>, a central piezoelectric element <NUM> and peripheral piezoelectric elements 1510a to 1510d are located on a cross-shaped base plate <NUM>. The peripheral piezoelectric elements 1510a to 1510d are all formed in the same size. In an example shown in <FIG>, the size of the central piezoelectric element <NUM> is the same as the size of each of the peripheral piezoelectric elements 1510a to 1510d but may be different.

The plurality of piezoelectric elements 1510a to 1510d and <NUM> may be driven by an input of a single signal (in-phase drive) or may be driven by different signals by shifting the phase for a central piezoelectric element <NUM> relative to the phase of the peripheral piezoelectric elements 1510a to 1510d. When only the piezoelectric element <NUM> is driven in a shifted phase, it is preferably driven in anti-phase with the peripheral piezoelectric elements 1510a to 1510d. The sound pressure can be amplified at a specific frequency by adjusting the drive signal (anti-phase or in-phase) to change the displacement point closer to or farther away from the elastic bodies 1520a to 1520d.

The SoT module may be configured of a structure having a high thermal conductivity. <FIG> is a cross-sectional view showing the SoT module <NUM>.

The SoT module <NUM> comprises piezoelectric elements 1610a and 1610b, a base plate <NUM>, elastic bodies <NUM>, and a vibration plate <NUM>. The two piezoelectric elements 1610a and 1610b and the base plate <NUM> bonded thereto configure a piezoelectric composite <NUM>. The base plate <NUM> is preferably formed of metal.

Each of the piezoelectric elements 1610a and 1610b has an element structure similar to that of the piezoelectric element 110a. The elastic bodies <NUM> supports the base plate <NUM> on the vibration plate <NUM> in the same material and arrangement as the elastic bodies <NUM> and transmits the vibration of the piezoelectric composite <NUM> to the vibration plate <NUM>. Since one end of the elastic body <NUM> is bonded to the base plate <NUM>, heat accumulated in the piezoelectric elements 1610a and 1610b can be discharged.

The elastic body <NUM> is preferably formed of an elastomer. Further, the elastic body preferably has a thermal coefficient of <NUM>×<NUM>-<NUM>cal ▪ s-<NUM>cm-<NUM> or more. Thus, the elastic body <NUM> can discharge heat with high thermal conductivity.

The SoT module of the sixteenth embodiment is configured of piezoelectric elements, a base plate, elastic bodies and a vibration plate, but it may further have a partition. <FIG> is a cross-sectional view showing the SoT module <NUM>. <FIG> shows a cross-section of the elastic bodies <NUM> cut in a plane parallel to the vibration plate <NUM>.

The SoT module <NUM> comprises a piezoelectric element, an elastic body <NUM>, a vibration plate <NUM> and a partition <NUM>. The piezoelectric element has the same element structure as the piezoelectric element <NUM>. The piezoelectric elements are preferably connected to each other. The plurality of piezoelectric elements are separated to the left and right to form the piezoelectric composites.

The elastic body <NUM> has one end bonded to the piezoelectric composite and the other end bonded to the vibration plate <NUM>, and an assembly of the elastic bodies <NUM> is formed for each of the two piezoelectric composites. Between them, the partition <NUM> is provided. By the partition <NUM>, the acoustic interference in the left and right speakers can be suppressed.

The partition may have a structure surrounding the assembly of the elastic bodies. <FIG> is a cross-sectional view showing the SoT module <NUM>. <FIG> shows a cross section when the elastic bodies <NUM> are cut in a plane parallel to the vibration plate <NUM>.

The SoT module <NUM> is configured in the same manner as the SoT module <NUM> except that partitions 1870a and 1870b are provided instead of the partition <NUM>.

The partitions 1870a and 1870b surround assemblies of left and right elastic bodies <NUM>, respectively. The partitions 1870a and 1870b are configured of inner partitions 1871a and 1871b and outer partitions 1872a and 1872b, respectively. Since the partitions 1870a and 1870b have double structures surrounding the elastic bodies <NUM>, the sound is hardly transmitted to the outside of each of the partitions. Thus, it is possible to effectively suppress the acoustic interference occurring inside the left and right respective speakers.

The partition may have an air flow path. <FIG> is a plan view showing the SoT module <NUM>. <FIG> shows a cross section when the elastic bodies <NUM> are cut in a plane parallel to the vibration plate <NUM>.

The SoT module <NUM> is configured in the same manner as the SoT module <NUM> except that the partitions 1870a and 1870b are replaced with partitions 1970a and 1970b.

The partitions 1970a and 1970b are provided so as to surround respective assemblies of the left and right elastic bodies <NUM>. The partitions 1970a and 1970b are configured of inner partitions 1971a and 1971b and outer partitions 1972a and 1972b, respectively. The partitions 1970a and 1970b have double structures surrounding the elastic bodies <NUM>.

The inner partitions 1971a and 1971b have openings 1973a and 1973b and walls 1974a and 1974b, respectively. The outer partitions 1972a and 1972b also have walls 1975a and 1975b and openings 1976a and 1976b, respectively. Thus, a continuous air flow path is formed from the elastic body <NUM> to the outside of the partitions 1970a and 1970b. As a result, the SoT module <NUM> can improve the cooling efficiency while suppressing acoustic interference.

The SoT module configured as described above can be used in various applications. The applications can be roughly classified into acoustic and noise cancellation. Noise cancellation is a technique that uses sounds with anti-phases and is particularly effective for removing regular noise such as motor sounds. Though it is said to be difficult to cancel the noise of <NUM> or less, the SoT module can also sufficiently work for the noise cancellation of <NUM> or less.

If there is a plate which functions as a vibration plate, the SoT module can be configured by installing the piezoelectric elements and the elastic bodies there. For example, parts of plastic panels of automobile doors, ceilings, trunks, headrests, and dashboards can be utilized as vibration plates to configure the SoT modules.

In the case that the internal space is limited as in an automobile, sounds generated by placing the SoT module at various positions are audible to the listener as spatially balanced sounds rather than sounds spreading from one position. For example, sound can be generated at a small volume from the back portion of the front seat or behind the seat.

Not only for such acoustic applications, but also the SoT module can be used for a noise canceller in an automobile. Specifically, the SoT module is formed under the sheet, and the noise can be canceled with the sound in anti-phase to the engine sound.

If the above-described configuration would be realized with a speaker using a coil, it is difficult to secure the space in the automobile. Further, in terms of securing the power supply and reducing the weight, it is difficult to use a speaker using a coil. In contrast, as long as the SoT module using the piezoelectric element, a limited space, allowable weight and power source can be sufficiently utilized.

Electrical products are suitable for applications of SoT modules because power supply can be easily secured, and the housing can be utilized as a vibration plate. For example, the SoT module can be used for noise cancellation of a washing machine. In this case, the SoT module can be installed in the washing machine itself or can be installed in attachments of the washing machine. For example, it is preferable to install the SoT module on the pan of the washing machine as a noise canceller to form a mechanism that does not transmit sound. The sound leaked from the washing machine is a low sound of <NUM> or less passing through the soundproofing material, and this sound can not be cancelled by the usual piezoelectric module, but it can be cancelled by the SoT module.

Typical applications of the SoT module comprise Cinematic Sound OLDE (CSO). CSO is a technique in which acoustic techniques are added to the self-emitting OLED to match the sound positions of the screens with the actual sound generating positions. With using an OLED panel as a vibration plate, the user can hear sound according to the image by directly transmitting sound from OLED screen, rather than from a separate speaker installed in the TV. That is, the user can hear the sound of talking with each other from the mouth of the performers of movies and dramas and can also hear the sound of the rain falling from the sky touching the ground from the position where the rain hits the ground on the actual screen. In this way, the user gets more immersion feeling. This application is not limited to TV, and the SoT module can be similarly applied to signage.

The SoT module is also applicable to furniture and architectural components. For example, the piezoelectric elements and the elastic bodies can be installed in the box-shaped drawer used in the rack frame are assembled to form a SoT module. In this way, the inside of the desk drawer can be sounded, and the inside of the box can be used as a speaker. Even if the drawer is filled with objects, a desired sound can be generated.

Piezoelectric elements and elastic bodies can also be installed on the iron plates behind LED projectors installed on roads, and iron plates can be used with vibration plates to configure SoT modules. An audible alarm can be generated directly from the LED projector, for example. It is also possible to configure a SoT module using a ceiling, wall or partition as a vibration plate. In that case, it can be used for both acoustic and noise cancellation. Such a configuration is also possible with a speaker by a coil in terms of sound pressure in the low audio frequency range, it is impossible to secure the space in the building. Further, a loudspeaker with a coil requires a strong power source, which may be subject to legal restrictions. SoT modules can be installed in small spaces, and they can be retrofitted by domestic power source for general use.

Formula (<NUM>) is a mathematical expression representing a natural frequency fs of a piezoelectric module. M and S represent the mass and stiffness of the piezoelectric module, respectively. In the case of a plate type piezoelectric module, the overall stiffness value mainly depends on the stiffness of the elastic body. [Formula <NUM>] <MAT>.

Therefore, by reducing the stiffness of the elastic body, the natural frequency of the entire system can be reduced. Further, since the stiffness of the entire system is also dependent on the tensile strength of the vibration plate, it is also possible to improve the sound pressure of low audio frequency sound according to the selection of the material of the vibration plate.

However, on the other hand, the transmissibility is lowered by the weight of the vibration plate, and there is also a possibility that the sound pressure characteristics deteriorate. In order to solve this problem, if the bonding strength between the piezoelectric composite and the vibration plate is increased to increase the transfer coefficient, the piezoelectric composite must receive all the weight of the panel, and the amplitude cannot be maintained. In consideration of such circumstances, sound pressure can be improved not only by adding an elastic body to the vibration path but also by adjusting the damping ratio of the vibration transmission path.

Piezoelectric modules for testing were prepared by varying the arrangement of elastic bodies, and the frequency characteristics of sound pressure were measured. <FIG> is a side view showing the piezoelectric modules t1 to t3 for testing in which the positions of the elastic bodies differ from each other. As shown in <FIG>, the piezoelectric module t1 for testing is configured of the piezoelectric element v1, the elastic body u1, and the vibration plate w1. The piezoelectric element v1 is a bending-type piezoelectric element using PZT. The elastic body u1 has a length of <NUM> in the longitudinal direction of the piezoelectric element v1 and is formed of urethane, one surface is bonded to the central portion in the longitudinal direction of the piezoelectric element v1. The vibration plate w1 is a OLED panel and is bonded to the other surface of the elastic body u1.

The piezoelectric module t2 for testing is configured of the piezoelectric element v1, the elastic bodies u2, the vibration plate w2. The two elastic bodies u2 respectively have the length of <NUM> in the longitudinal direction of the piezoelectric element v1 and is formed of urethane in the same manner as the elastic body u1, but they are respectively located at intermediate positions between the central portion and both end portions in the longitudinal direction of the element v1.

The piezoelectric module t3 for testing is configured of the piezoelectric element v1, the elastic bodies u3, the vibration plate w1. The two elastic bodies u3 respectively have the length of <NUM> in the longitudinal direction of the piezoelectric element v1 and is formed of urethane in the same manner as the elastic body u1, but they are respectively located at both ends in the longitudinal direction of the piezoelectric element v1.

<FIG> is a graph showing the frequency characteristics of the sound pressure of the piezoelectric modules t1 to t3 for testing. As shown in <FIG>, the peak dip in the middle audio frequency region occurring with the piezoelectric modules t1 and t2 for testing does not occur with the piezoelectric module t1 for testing.

The piezoelectric modules for testing were prepared by varying the shapes of the elastic bodies, and the frequency characteristics of sound pressure were measured. <FIG> is a side view showing the piezoelectric modules t4 and t5 for testing in which the shapes of the elastic bodies differ.

As shown in <FIG>, the piezoelectric module t4 for testing is configured of the piezoelectric element v1, the elastic bodies u4, and the vibration plate w1. Each of the two elastic bodies u4 is formed of urethane in a cylindrical shape having a diameter of <NUM> at both ends in the longitudinal direction of the piezoelectric element v1. Further, the piezoelectric module t5 for testing is configured of the piezoelectric element v1, the elastic bodies u5, the vibration plate w5. Each of the two elastic body u5 is formed of urethane in a rectangular body shape having a length of <NUM> at both ends in the longitudinal direction of the piezoelectric element v1.

<FIG> is a graph showing the frequency characteristics of the sound pressure of the piezoelectric modules t4 and t5 for testing. As shown in <FIG>, the sound pressure of the piezoelectric module t5 for testing is slightly large in the low audio frequency range, the sound pressure of the piezoelectric module t4 for testing is large in the middle audio frequency range. However, there was no significant difference in the frequency characteristics of the sound pressure depending on the shape of the elastic bodies.

The frequency characteristics of the sound pressure was measured for SoT module <NUM> of the first embodiment (example E1 (parallel type)). <FIG> is a graph showing the frequency characteristics of the sound pressure of the piezoelectric module of example E1 and the piezoelectric module t5. As shown in <FIG>, although the sound pressure drops around <NUM>, the sound pressure is obtained in the low and middle audio frequency range from <NUM> to <NUM> equivalent to that in the high audio frequency range. Note that a drop in sound pressure is observed in the vicinity of <NUM>.

The SoT module <NUM> of the second embodiment (example E2 (end connection type)) was prepared to measure the frequency characteristics of the sound pressure. <FIG> is a graph showing the frequency characteristics of the sound pressure of the SoT modules for each of the examples E1 and E2. In the example E1, there is a region in which the sound pressure is small in the low audio frequency range of <NUM> to <NUM>. However, in the region of the middle audio frequency range of around <NUM>, the example E2 has the flatter characteristic of sound pressure than the example E1, and the drop in sound pressure of the example E1 does not exist in the example E2. Further, the flat characteristics are obtained in the example E2 even in the high audio frequency range of <NUM> or more.

The SoT module <NUM> of the seventh embodiment (example E7 (central connection loop type)) was prepared to measure the frequency characteristics of the sound pressure. <FIG> is a graph showing the frequency characteristics of the sound pressure of the SoT module for each of the examples E1 and E7. As shown in <FIG>, in the low audio frequency range, the example E7 provides a larger and more flat sound pressure than the example E1. In the middle and high audio frequency range, the example E1 provides a larger and more flat sound pressure than the example E7. It has been found that the example E7 (a central connection loop type) greatly improves the sound pressure in the low audio frequency range.

The SoT module <NUM> of the seventh embodiment (example E7 (central connection loop type)), the SoT module <NUM> of the eighth embodiment (example E8 (intermediate connection loop type)), and the SoT module <NUM> of the ninth embodiment (example E9 (end connection loop type)) were prepared, and the frequency characteristics of the respective sound pressures were measured. <FIG> is a graph showing the frequency characteristics of the sound pressure of the SoT module for each of the examples E7-E9. As shown in <FIG>, in the low audio frequency range, the largest sound pressure was obtained in the example E7. In the middle audio frequency region, the largest sound pressure was obtained in the example E8. In the high audio frequency range, the largest sound pressure was obtained in the example E9. Thus, the SoT modules <NUM>, <NUM>, and <NUM> have been found to be suitable for applications in low, middle and high audio frequency range, respectively.

Claim 1:
A piezoelectric module comprising:
a plate-shaped piezoelectric composite for generating bending vibration by the impression of an AC voltage,
a plurality of elastic bodies, one ends of which are bonded to a main surface of the piezoelectric composite, the elastic bodies transmitting vibration of the piezoelectric composite, and
a vibration plate having a main surface which is bonded to other ends of the elastic bodies,
wherein there is a position of a centroid of the piezoelectric composite between the plurality of elastic bodies, and
the piezoelectric composite comprises a plurality of piezoelectric elements, each of which is identical and formed in a rectangular plate, and each of the piezoelectric elements is partially connected to each other piezoelectric element.