JP2011135693A - Piezoelectric bimorph element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric bimorph element in which its bending vibration is not impeded and its degradation in characteristics prevented. <P>SOLUTION: In the piezoelectric bimorph element, a support member is installed at both ends of either main surface. The support members are fixed on a fixing support surface having a voltage line. A driven body in contact with a coupling member installed in the center of the other main surface is moved by bending vibration. Voltage is applied by the support members formed of an elastic material containing a conductive rubber. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a piezoelectric bimorph element that vibrates a vibrating body such as a panel used in a display device, an electronic device or a PDA, a personal computer, a mobile phone, a portable game machine, an information terminal and the like.

  In recent years, a product that vibrates a driven body using a piezoelectric bimorph element has a tactile sensation that stimulates the tactile sensation of the user's fingertip by vibrating the touch panel of the touching user's fingertip. There is a touch panel using a feedback (haptics) method.

  A piezoelectric bimorph element is an element in which an elastic body (metal plate) is sandwiched between two piezoelectric elements polarized in the thickness direction. When a voltage is applied to the piezoelectric element, one piezoelectric element expands due to the piezoelectric lateral effect, and the other piezoelectric element. The element shrinks, which causes the piezoelectric bimorph element to bend in one direction. By utilizing this fact, bending vibration is performed by switching between positive and negative voltages applied to the piezoelectric bimorph element. FIG. 1 shows a conventional method for fixing a piezoelectric bimorph element. Here, the piezoelectric element 2 and the piezoelectric element 3 sandwich an elastic body 4 therebetween, and the piezoelectric element 2 and the piezoelectric element 3 and the elastic body 4 are bonded. The combination of the piezoelectric element 2, the piezoelectric element 3, and the elastic body (metal plate) 4 is a piezoelectric bimorph element, and is supported on both ends of the piezoelectric bimorph element opposite to the surface bonded to the elastic body 4 of the piezoelectric element 3. Members 6 and 7 are installed. The support members 6 and 7 are assembled and fixed to a fixed support surface 8 for fixing and supporting the piezoelectric bimorph element, or are fixed to the fixed support surface 8 by applying an adhesive. And the connection member 5 is installed in the center part of the surface opposite to the surface adhere | attached with the elastic body (plate) 4 of the piezoelectric element 2 in a piezoelectric bimorph element. The distal end portion of the connecting member 5 is in contact with the driven body 1, and the driven body 1 is moved by applying a voltage to the piezoelectric bimorph element and causing the piezoelectric bimorph element to bend and vibrate.

  FIG. 2 shows a conventional method for fixing a piezoelectric bimorph element, and particularly shows a portion where the largest stress load is generated in the piezoelectric bimorph element. FIG. 2A shows an overall view, and FIG. 2B is an enlarged view showing a portion where the largest stress load is generated. As shown in FIG. 2, if the fixed support surface 8 and the support members 6 and 7 for fixing and supporting the piezoelectric bimorph element are firmly fixed, the bending vibration of the piezoelectric bimorph element is hindered by the fixing portion. End up. Further, when the piezoelectric bimorph element is flexibly vibrated, the largest stress load is generated at two stress load generation points 9 corresponding to the end portions of the bonded portions of the piezoelectric element 3 and the support members 6 and 7, and the piezoelectric bimorph element When a local load is applied, a failure occurs at the stress load occurrence point 9 or the life of the piezoelectric bimorph element is shortened.

  In contrast to such a conventional method for fixing a piezoelectric bimorph element, in Patent Document 1, one end of a piezoelectric element is bonded with a rectangular planar holder having a twisted elastic deformation structure, and the other end of the piezoelectric element is attached. Similarly, they are bonded by a rectangular planar holder having a torsional elastic deformation structure. The two planar holders are supported by a pivot shaft at the center, and the pivot shaft has a structure that can swing the planar holder like a seesaw. The rotating shaft also has a torsion elastic deformation structure, and can be twisted in accordance with the deformation of the piezoelectric element. Therefore, even in the conventional method for fixing a piezoelectric bimorph element, if the support member is a torsional elastic deformation structure, the cause of stress load is greatly reduced.

JP 2005-92537 A

  However, if the support member is made to have an elastic structure such as a torsion elastic deformation structure, the driven body cannot be moved due to the bending vibration of the piezoelectric bimorph element depending on the elastic modulus of the support member. Further, in the cited document 1, the electrode of the piezoelectric bimorph element and the flexible wiring board are soldered, and it is highly possible that the characteristics of the piezoelectric element are deteriorated in this structure. The reason why the characteristics of the piezoelectric element are deteriorated in the structure in which the electrode of the piezoelectric bimorph element and the lead wire or the flexible wiring board are soldered will be described below.

  FIG. 3 shows a soldering method between the electrodes of the piezoelectric bimorph element and various electric materials. FIG. 3A shows a soldering method for a piezoelectric bimorph element and a lead wire. FIG. 3B shows a soldering method for the piezoelectric bimorph element and the flexible printed wiring board. FIG. 4 shows a method of fixing the piezoelectric bimorph element including soldering of the lead wire 10 and the electrode of the piezoelectric bimorph element. Since the piezoelectric bimorph element 11 has a structure in which a metal plate is sandwiched between two piezoelectric elements as an elastic body, the electrodes and lead wires of the piezoelectric bimorph element are formed as shown in FIG. These lead wires are soldered, and then the piezoelectric bimorph element is fixed as shown in FIG. Further, as shown in FIG. 3B, the electrodes of the piezoelectric bimorph element and the flexible printed wiring board 12 are soldered or thermocompression bonded with an anisotropic conductive film (ACF).

In the soldering with the electrodes of such a piezoelectric element, it is necessary to apply a high temperature in order to melt the solder at the soldered portion 13 in a short time. In particular, due to environmental considerations, eutectic solder may have changed from lead-free solder, and eutectic solder has a melting point of about 183 ° C, whereas tin, silver, and copper due to solder components The melting point of lead-free solder whose main component is about 220 ° C. Therefore, the temperature during soldering becomes as high as about 250 ° C. to about 300 ° C.
Although not shown, even when an anisotropic conductive film (ACF) is used, it is necessary to apply a temperature of about 80 ° C. for several seconds by temporary pressure bonding and about 200 ° C. for about 15 seconds for main pressure bonding.
Therefore, a part of the remanent polarization of the polarized piezoelectric element disappears, and there is a problem that the characteristics of the piezoelectric element are deteriorated locally.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a piezoelectric bimorph element that does not hinder bending vibration of the piezoelectric bimorph element and prevents deterioration of characteristics. .

  In order to achieve the above object, according to the present invention, support members are installed at both ends of one main surface, the support members are fixed to a fixed support surface having a voltage line, and the other main surface has a central portion. A piezoelectric bimorph element for moving a driven body in contact with an installed connecting member by bending vibration, wherein a voltage is applied by the support member made of an elastic material including conductive rubber.

  Preferably, at least one of the support members is configured to sandwich an end portion of one main surface and an end portion of the other main surface of the piezoelectric bimorph element, and is made of an elastic material including conductive rubber, The two main surfaces of the piezoelectric bimorph element are electrically connected to the fixed support surface.

  Preferably, at least one of the support member and the connecting member are made of an elastic material including conductive rubber, and a surface of the driven body that has a voltage line is in contact with the connecting member, the connecting member, and a piezoelectric bimorph element. It is characterized in that one main surface is conductive.

  Preferably, the fixed support surface has a voltage line and a ground line, and the elastic body between the two piezoelectric elements in the ground line of the fixed support surface and the piezoelectric bimorph element is made of an elastic material including conductive rubber. It is characterized by conducting with a member interposed therebetween.

  According to the present invention, it is possible to prevent the deterioration of the characteristics of the piezoelectric bimorph element by eliminating the need for soldering between the electrode of the piezoelectric bimorph element and the electric material, and eliminating the need for pressure bonding using an anisotropic conductive film (ACF). it can. Since there is no need to use a lead wire or flexible printed circuit board (FPC) to supply power to the piezoelectric bimorph element, the degree of freedom in arranging the piezoelectric bimorph element increases, and the lead wire to the piezoelectric bimorph element, soldering of the flexible board, etc. Work can be eliminated and processing costs can be reduced. In addition, it is possible to hold the piezoelectric bimorph element supported at two points without suppressing the vibration and to apply a voltage from the support member.

It is sectional drawing which shows the fixing method of the conventional piezoelectric bimorph element. It is sectional drawing which shows the fixing method of the conventional piezoelectric bimorph element. It is a perspective view which shows the soldering method of the electrode and electrical material of a piezoelectric bimorph element. It is sectional drawing which shows the fixing method of a piezoelectric bimorph element. It is sectional drawing which shows the fixing method of the piezoelectric bimorph element of this invention. It is sectional drawing which shows the supporting member which laminated | stacked conductive rubber and insulating rubber alternately.

  Next, the best mode for carrying out the present invention will be described with reference to the drawings. In order to facilitate understanding of the description, the same reference numerals are given to the same components in the respective drawings, and duplicate descriptions are omitted. FIG. 5 is a cross-sectional view showing a method for fixing a piezoelectric bimorph element of the present invention. FIG. 5A is a cross-sectional view showing the first embodiment. In FIG. 5A, the piezoelectric bimorph element has an elastic body (plate) 4 sandwiched between the piezoelectric element 2 and the piezoelectric element 3 and is bonded to each other. In the piezoelectric element 2 and the piezoelectric element 3, conductive silver paste or the like is screen-printed on the electrode, and the piezoelectric bimorph element is polarized. A connecting member 5 is installed at the center of the upper surface of the piezoelectric bimorph element (the upper surface of the piezoelectric element 2). The connecting member 5 and the piezoelectric element 2 are bonded with an adhesive. The surface of the connecting member 5 opposite to the surface bonded to the piezoelectric element 2 is in contact with the driven body 1, and the driven body 1 moves when a voltage is applied to the piezoelectric bimorph element and the piezoelectric bimorph element bends and vibrates. . Both ends of the lower surface of the piezoelectric bimorph element (the lower surface of the piezoelectric element 3) are in contact with different support members, and the two support members are connected to the signal pattern 17 on the fixed support surface 8 by bonding or fitting means. Has been. Here, the fixing support surface 8 may be any surface as long as it is a surface for fixing and supporting the piezoelectric bimorph element. A signal pattern 17 is formed on the fixed support surface 8, and the signal pattern 17 is further divided into two patterns: a voltage line to which a constant voltage is applied and a ground line corresponding to Gnd. Here, the voltage of the voltage line of the fixed support surface 8 is supplied from an external power source (power supply device, battery, battery, etc.) not shown. The supporting member 6 that supports the piezoelectric bimorph element sandwiches the widthwise end of the piezoelectric bimorph element from the upper surface to the lower surface (the surface opposite to the surface in contact with the elastic body (plate) 4 of the piezoelectric element 2 and the piezoelectric element 3). The elastic body (plate) 4 is in contact with the surface opposite to the surface in contact with the elastic body (plate) 4, and is also in contact with the signal pattern 17 on the fixed support surface 8. The support member has a conductive rubber 16 such as conductive silicone rubber embedded therein, and the periphery of the conductive rubber 16 is covered with an insulating rubber 15 such as an insulating silicone rubber. A conductive rubber 16 is embedded from one end surface of the support member 6 to the middle of the support member 6, and the conductive rubber 16 is an upper surface electrode and a lower surface electrode of the piezoelectric bimorph element in the width direction, and the fixed support surface 8. The conductive pattern is in contact with the upper signal pattern 17. And a voltage is applied to the piezoelectric element 2 and the piezoelectric element 3 by this, and a piezoelectric bimorph element drives.

  The support member 7 that supports the piezoelectric bimorph element in FIG. 5A is in contact with any of the electrodes of the piezoelectric element 3 of the piezoelectric bimorph element, the elastic body (plate) 4, and the signal pattern 17 on the fixed support surface 8. Yes. The support member 7 is embedded with a conductive rubber 16 such as conductive silicone rubber in the same manner as the other support member described above, and the periphery of the conductive rubber 16 is an insulating rubber such as an insulating silicone rubber. 15 is covered. The conductive rubber 16 of the support member 7 is in contact with the elastic body (plate) 4 of the piezoelectric bimorph element and the signal pattern 17 on the fixed support surface 8 and is in a conductive state. Among the divided signal patterns 17 on the fixed support surface 8, the signal pattern 17 connected to the ground line corresponding to Gnd is a piezoelectric bimorph element sandwiched between conductive rubbers 16 embedded in the support member 7. In contact with the elastic body (plate) 4, the elastic body (plate) 4 of the piezoelectric bimorph element is in a grounded state.

  The connection between the support member and the piezoelectric bimorph element in FIG. 5A is not limited to using an adhesive, but a protrusion is formed on the elastic body (plate) 4 of the piezoelectric bimorph element, and the support member and the protrusion are connected to each other. There is also a method of holding and fixing in combination. Similarly, for the connection between the support member and the signal pattern 17, it is appropriate to form a projection on the signal pattern 17 other than the adhesion, and hold and fix the support member and the projection in combination. In this way, by holding and fixing by a method other than bonding, it is possible to hold without suppressing the vibration of the piezoelectric bi-full element. Therefore, with the above configuration, there is no need to solder using lead wires or flexible printed circuit boards (FPC), so voltage can be supplied to the piezoelectric element while preventing deterioration of the piezoelectric bimorph element, and vibration of the piezoelectric bimorph element can be further reduced. It can be held without being suppressed. The holding and fixing method described above is not limited to FIG. 5 (a), but a second embodiment shown in FIG. 5 (b) and a third embodiment shown in FIG. 5 (c) described below. But the same is true.

  FIG. 5B is a sectional view showing the second embodiment. The difference from the first embodiment shown in FIG. 5A described above is that the supporting member is in contact with both ends of the lower surface of the piezoelectric bimorph element (the lower surface of the piezoelectric element 3), and the upper surface of the piezoelectric bimorph element ( This is a configuration of the connecting member 5 in the central portion of the upper surface of the piezoelectric element 2. Other portions are the same as those of the first embodiment shown in FIG. 5A, and the description thereof is omitted for the sake of explanation. In FIG. 5B, the support member 6 is in contact with one end of the lower surface of the piezoelectric bimorph element (the lower surface of the piezoelectric element 3), and this support member is connected to the fixed support surface 8 by adhesion or fitting means. ing.

  The other support member 7 that supports the piezoelectric bimorph element in FIG. 5B is provided on any of the electrodes of the piezoelectric element 3 of the piezoelectric bimorph element, the elastic body (plate) 4, and the signal pattern 17 on the fixed support surface 8. It touches. The support member 7 is embedded with a conductive rubber 16 such as conductive silicone rubber in the same manner as the other support member described above, and the periphery of the conductive rubber 16 is an insulating rubber such as an insulating silicone rubber. 15 is covered. Two or more conductive rubbers 16 are embedded from one end surface of the support member 7 to the other end surface, and at least one conductive rubber 16 is an electrode on one surface of the piezoelectric bimorph element (of the piezoelectric element 3). The electrode on one side) is in contact with the signal pattern 17 on the fixed support surface 8 and is in a conductive state. Further, at least one conductive rubber 16 is in contact with the elastic body (plate) 4 of the piezoelectric bimorph element and the signal pattern 17 on the fixed support surface 8 and is in a conductive state. Among the divided signal patterns 17 on the fixed support surface 8, the signal pattern 17 connected to the voltage line to which a constant voltage is applied is sandwiched between the conductive rubber 16 embedded in the support member 7. The piezoelectric bimorph element is in contact with an electrode on one surface (an electrode on one surface of the piezoelectric element 3), whereby a voltage is applied to the piezoelectric element 3. Of the divided signal patterns 17 on the fixed support surface 8, the signal pattern 17 connected to the ground line corresponding to Gnd is a piezoelectric bimorph sandwiched between conductive rubbers 16 embedded in the support member 7. The elastic body (plate) 4 of the piezoelectric bimorph element comes into contact with the elastic body (plate) 4 of the element.

  The driven body 1 in FIG. 5B has a voltage line to which a constant voltage is fed on the surface in contact with the connecting member 5. A constant voltage is supplied to the voltage line from an external power source (power supply device, battery, battery, etc.) not shown. A signal pattern 17 is formed on the driven body 1, and the signal pattern 17 is electrically connected to the voltage line. The connecting member 5 has a conductive rubber 16 such as conductive silicone rubber embedded therein, and the periphery of the conductive rubber 16 is covered with an insulating rubber 15 such as an insulating silicone rubber. A conductive rubber 16 is embedded from one end surface of the connecting member 5 to the other end surface, and an electrode on one surface of the piezoelectric bimorph element (one surface of the piezoelectric element 2) is sandwiched between the conductive rubbers 16. Electrode) and the signal pattern 17 of the driven body 1 become conductive, and a voltage is applied to the piezoelectric element 2. Accordingly, voltage is applied to the piezoelectric element 2 and the piezoelectric element 3 with the above configuration, and the piezoelectric bimorph element is driven.

  FIG. 5C is a cross-sectional view showing a third embodiment. The difference from the first embodiment shown in FIG. 5A described above is that the supporting member is in contact with both ends of the lower surface of the piezoelectric bimorph element (the lower surface of the piezoelectric element 3), and the upper surface of the piezoelectric bimorph element ( This is a configuration of the connecting member 5 in the central portion of the upper surface of the piezoelectric element 2. Other portions are the same as those of the first embodiment shown in FIG. 5A, and the description thereof is omitted for the sake of explanation. In FIG. 5C, the support member 6 is in contact with one end of the lower surface of the piezoelectric bimorph element (the lower surface of the piezoelectric element 3), and this support member is connected to the fixed support surface 8 by adhesion or fitting means. ing. The support member 6 has a conductive rubber 16 such as conductive silicone rubber embedded therein, and the periphery of the conductive rubber 16 is covered with an insulating rubber 15 such as an insulating silicone rubber. A conductive rubber 16 is embedded from one end surface of the support member 6 to the other end surface, and an electrode on one surface of the piezoelectric bimorph element (one surface of the piezoelectric element 3) is sandwiched between the conductive rubber 16. Electrode) and a signal line 17 that is in conduction with a voltage line to which a fixed voltage is applied to the fixed support surface 8 is brought into conduction, and a voltage is applied to the piezoelectric element 3.

  The other support member 7 that supports the piezoelectric bimorph element in FIG. 5C is in contact with any of the piezoelectric element 3 of the piezoelectric bimorph element, the elastic body (plate) 4, and the signal pattern 17 on the fixed support surface 8. Yes. This support member is embedded with a conductive rubber 16 such as conductive silicone rubber in the same manner as the other support member described above, and the periphery of the conductive rubber 16 is an insulating rubber 15 such as an insulating silicone rubber. It is covered with. The conductive rubber 16 of the support member 7 is in contact with the elastic body (plate) 4 of the piezoelectric bimorph element and the signal pattern 17 on the fixed support surface 8 and is in a conductive state. Among the divided signal patterns 17 on the fixed support surface 8, the signal pattern 17 connected to the ground line corresponding to Gnd is the elasticity of the piezoelectric bimorph element with the conductive rubber 16 embedded in the support member interposed therebetween. In contact with the body (plate) 4, the elastic body (plate) 4 of the piezoelectric bimorph element is in a grounded state.

  The driven body 1 in FIG. 5C has a voltage line to which a constant voltage is fed on the surface in contact with the connecting member 5. A constant voltage is supplied to the voltage line from an external power source (power supply device, battery, battery, etc.) not shown. A signal pattern 17 is formed on the driven body 1, and the signal pattern 17 is electrically connected to the voltage line. The connecting member 5 has a conductive rubber 16 such as conductive silicone rubber embedded therein, and the periphery of the conductive rubber 16 is covered with an insulating rubber 15 such as an insulating silicone rubber. A conductive rubber 16 is embedded from one end surface of the connecting member 5 to the other end surface, and one surface of the piezoelectric bimorph element (one surface of the piezoelectric element 2) is sandwiched between the conductive rubber 16 and the other surface. The signal pattern 17 of the driven body 1 becomes conductive, and a voltage is applied to the piezoelectric element 2. Accordingly, voltage is applied to the piezoelectric element 2 and the piezoelectric element 3 with the above configuration, and the piezoelectric bimorph element is driven.

  If only one signal is transmitted to the piezoelectric bimorph element, it is only necessary to coat a thin insulating layer around the low-resistance conductive silicone rubber. On the other hand, two or more conductive rubbers 16 are embedded inside from one end surface to the other end surface as in the support member shown in FIG. 5B, and the periphery of the conductive rubber 16 is insulated. Different signals can be applied to the piezoelectric element and the metal plate, which is an elastic body, by the structure covered with the insulating rubber 15 such as the conductive silicone rubber.

  An example of the support member shown in FIG. 5B is shown in FIG. FIG. 6 is a cross-sectional view showing a support member in which conductive rubber and insulating rubber are alternately laminated. The conductive rubber 16 in FIG. 6 is a low resistance conductive silicone rubber filled with silver-based fine powder. The conductive rubber 16 and the insulating rubber 15 are alternately laminated, and a side support portion 19 made of insulating silicone rubber is formed so as to sandwich the laminated silicone rubber. A thin insulating layer 18 is coated around the side support portion 19.

  Low resistance conductive silicone rubber filled with silver fine powder has a volume resistivity of about 1 × 10 −4 cm. When such a conductive silicone rubber is used and a voltage signal is applied to the electrodes of the piezoelectric bimorph element, for example, the resistance is fixed when the width of the conductive silicone rubber is 5 mm and the height is 1 mm. Although it depends on the width of the signal pattern 17 formed on 8, it can be designed to be about 0.2Ω.

  The drive voltage of a piezoelectric bimorph element made of a single-plate piezoelectric element is about 100 to 150 V, and the drive current is normally about several tens of mA. Even if the inrush current is taken into account, it is about 100 mA. Therefore, even if the signal pattern 17 on the fixed support surface 8 is connected via the low-resistance conductive silicone, the voltage drop level does not affect the driving of the piezoelectric bimorph element. It will be small. Considering the driving of the piezoelectric bimorph element, even if the resistance of the conductive rubber is about 1Ω, there is no problem.

  Also, when low voltage drive is performed using a laminated piezoelectric element as a piezoelectric bimorph element, and the resistance of the conductive rubber of the support member must be kept low, the metal thin wires are arranged at a low pitch instead of the conductive rubber In addition, the connection resistance can be suppressed to 0.1Ω or less by using conductive rubber whose periphery is supported by insulating silicone rubber.

  It should be noted that the elastic modulus of the conductive rubber can be adjusted by the insulating silicone rubber alternately laminated in FIG. 6 or the silicone rubber of the side support portion arranged around the insulating silicone rubber.

  As described above, by using a support member embedded with conductive rubber and insulating rubber, it can be held without suppressing vibration of the piezoelectric bi-moful element, and can be used with electric materials such as flexible printed circuit boards (FPC). A voltage can be applied to the piezoelectric bimorph element with a configuration that does not require soldering.

DESCRIPTION OF SYMBOLS 1 Driven body 2 Piezoelectric element 3 Piezoelectric element 4 Elastic body (metal plate)
DESCRIPTION OF SYMBOLS 5 Connection member 6 Support member 7 Support member 8 Fixed support surface 9 Stress load generation | occurrence | production location 10 Lead wire 11 Piezoelectric bimorph element 12 Flexible printed wiring board 13 Solder location 14 Print pattern 15 Insulation rubber 16 Conductive rubber 17 Signal pattern 18 Insulation layer 19 Side support

Claims (4)

  Support members are installed at both ends of one main surface, the support members are fixed to a fixed support surface having a voltage line, and the driven body that contacts the connecting member installed at the center of the other main surface is bent and vibrated. The piezoelectric bimorph element is a piezoelectric bimorph element that is moved by a voltage applied by the support member made of an elastic material including a conductive rubber.   At least one of the support members is configured to sandwich an end portion of one main surface of the piezoelectric bimorph element and an end portion of the other main surface, and is made of an elastic material including conductive rubber, and the piezoelectric bimorph element 2. The piezoelectric bimorph element according to claim 1, wherein the two main surfaces are electrically connected to the fixed support surface.   At least one of the support member and the connecting member are made of an elastic material including conductive rubber, and a surface of the driven body that has a voltage line is in contact with the connecting member, the connecting member, and one main of the piezoelectric bimorph element. 3. The piezoelectric bimorph element according to claim 1, wherein the surface is conductive.   The fixed support surface has a voltage line and a ground line, and the elastic body between the two piezoelectric elements in the ground line of the fixed support surface and the piezoelectric bimorph element has the support member made of an elastic material including conductive rubber interposed therebetween. The piezoelectric bimorph element according to any one of claims 1 to 3, wherein the piezoelectric bimorph element is electrically connected between the two.

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