Piezoelectric sensor and musical instrument

Abstract

Provided is a piezoelectric sensor comprising: a housing having an opening; a substrate which covers the opening part and is opposite to the frame body; a sheet-like first piezoelectric element positioned within the housing and disposed such that a first surface faces the substrate; a weight disposed so as to face a second surface of the first piezoelectric element; the first piezoelectric element has a stretchable porous layer, and the weight is displaceable with respect to the substrate in accordance with the stretching of the porous layer.

Description

Technical Field

[0001] The present disclosure relates to a piezoelectric sensor and a musical instrument including the piezoelectric sensor. Background Art

[0002] In order to convert the sound emitted from a musical instrument such as a wind instrument into an electrical signal, a microphone is generally used in the vicinity of the musical instrument. The microphone captures the air vibration that spreads outside the musical instrument as the sound of the musical instrument. Techniques for capturing the air vibration generated inside the musical instrument as the sound of the musical instrument have also been developed. For example, according to Patent Document 1, a technique is disclosed in which a piezoelectric element is buried inside the mouthpiece of a wind instrument, and the piezoelectric element converts the air vibration inside the mouthpiece into an electrical signal.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: US Patent No. 3543629 Specification Summary of the Invention

[0006] Technical Problem to be Solved by the Invention

[0007] When a piezoelectric element that converts air vibration into an electrical signal is used to detect the vibration of a vibrating body, there is a problem that an unexpected vibration such as air vibration is detected simultaneously.

[0008] In view of such problems, one object of the present disclosure is to provide a piezoelectric sensor capable of suppressing the influence of air vibration. Another object of the present disclosure is to provide a musical instrument including a piezoelectric sensor capable of suppressing the influence of air vibration.

[0009] Technical Solution for Solving the Technical Problem

[0010] According to one embodiment, there is provided a piezoelectric sensor having: a housing having an opening; a substrate covering the opening and facing the housing; a sheet-like first piezoelectric element located inside the housing and arranged such that a first surface faces the substrate; a weight arranged to face a second surface of the first piezoelectric element; the first piezoelectric element having a porous layer capable of expanding and contracting, and the weight being displaceable relative to the substrate following the expansion and contraction of the porous layer.

[0011] According to one embodiment, there is provided a musical instrument including: the above piezoelectric sensor; a vibration surface on which the piezoelectric sensor is arranged and vibrates during sound production.

[0012] Advantages of the Invention

[0013] According to the present disclosure, a piezoelectric sensor capable of preventing the occurrence of howling and a musical instrument including the piezoelectric sensor can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 FIG. is a view showing the appearance of a piezoelectric sensor according to an embodiment.

[0015] Figure 2 is along Figure 1 A cross-sectional view taken along line A1-A2 of the piezoelectric sensor shown.

[0016] Figure 3 is Figure 1 A plan view of the housing shown as viewed from the first surface side.

[0017] Figure 4 is a plan view of the substrate shown as viewed from the side facing the housing Figure 1 shown.

[0018] Figure 5 is Figure 2 An enlarged view of the piezoelectric element shown.

[0019] Figure 6 FIG. is a view for explaining the electrical connection between the piezoelectric element and the substrate according to an embodiment.

[0020] Figure 7 FIG. is a view showing a state where a piezoelectric sensor according to an embodiment is mounted on a vibration surface of an object.

[0021] Figure 8 FIG. is a view for explaining the circuit configuration of a piezoelectric sensor according to an embodiment.

[0022] Figure 9 FIG. is a view showing the appearance of a piezoelectric sensor according to an embodiment.

[0023] Figure 10 is along Figure 9 A cross-sectional view taken along line B1-B2 of the piezoelectric sensor shown.

[0024] Figure 11 FIG. is a view showing the appearance of a piezoelectric sensor according to an embodiment.

[0025] Figure 12 is showing Figure 11 A view of the upper surface of the substrate of the piezoelectric sensor shown.

[0026] Figure 13 is along Figure 11 A cross-sectional view taken along line C1-C2 of the piezoelectric sensor shown. DETAILED DESCRIPTION

[0027] Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the accompanying drawings. The embodiments shown below are examples, and the present disclosure should not be construed as being limited to these embodiments. In the accompanying drawings referred to in the present embodiment, the same parts or parts having the same function are denoted by the same reference numerals or similar reference numerals (reference numerals with A, B, etc. appended after the numbers), and repeated descriptions thereof are sometimes omitted. In the drawings, for the sake of clarity of explanation, there are cases where the dimensional ratios are different from the actual ratios and a part of the structure is omitted from the drawings and illustrated schematically.

[0028] A piezoelectric sensor according to an embodiment has a function of converting the vibration of a vibrating body of a musical instrument into an electric signal. Such a function is realized by a piezoelectric element that generates a voltage corresponding to the compressive deformation of a porous layer included in the piezoelectric element. As the vibrating body, for example, structures such as the frame and soundboard of a musical instrument that vibrate during the performance of the musical instrument can be cited, but are not limited thereto.

[0029] [First Embodiment]

[0030] Figure 1 is a view showing the appearance of the piezoelectric sensor according to the first embodiment. Figure 2 is along Figure 1 A cross-sectional view of the piezoelectric sensor according to the first embodiment taken along line A1 - A2 in Figure 1 and Figure 2 As shown, the piezoelectric sensor 10 includes a housing 100, a substrate 200, a piezoelectric element 300, and a counterweight 400.

[0031] The housing 100 includes a first surface 101a opposite to the substrate 200 and a second surface 101b on the side opposite to the first surface 101a. The housing 100 has an opening 103 on the first surface 101a. The housing 100 is formed of a conductive material such as metal. By including a conductive material, the housing 100 can prevent external noise such as hum noise from entering the internal sensor. In addition, the housing 100 may be formed of an insulating material such as plastic. In the case of being formed of an insulating material, the housing 100 may form a conductive film on at least one of its outer surface and inner surface, or a conductive film may be attached.

[0032] Figure 3 is a plan view seen from the side of the first surface 101a of the housing 100. As Figure 2 and Figure 3As shown, the opening 103 provided on the first surface 101a of the housing 100 includes a first opening 103a and a second opening 103b. The first opening 103a is provided inside the second opening 103b, and the second opening 103b is provided so as to surround the periphery of the first opening 103a. The depth of the first opening 103a in the opening 103 is deeper than the depth of the second opening 103b. Here, the depth of the first opening 103a refers to the vertical distance from the position corresponding to the bottom surface of the second opening 103b to the bottom surface of the first opening 103a. The depth of the second opening 103b refers to the vertical distance from the position corresponding to the first surface 101a of the housing 100 to the bottom surface of the second opening 103b. The second opening 103b of the opening 103 is covered and blocked by the substrate 200 in contact with the housing 100. The side surface of the second opening 103b covered by the substrate 200 has a shape along the outer side surface shape of the substrate 200.

[0033] As Figures 1 to 3 shown, the housing 100 includes a wiring opening 109 for leading out the wiring 111 to the outside. The wiring opening 109 is provided on the first surface 101a side of the housing 100. When the piezoelectric sensor 10 is mounted on an object, the first opening 103a of the opening 103 and the wiring opening 109 are separated from each other by a clamping member 500 described later. The wiring 111 is electrically connected to the electrodes of the substrate 200 described later. The wiring 111 is a multi-core cable and includes at least two wires insulated from each other.

[0034] The substrate 200 is a printed wiring board provided with a plurality of electrodes and wirings. The substrate 200 faces the housing 100 and is in contact with the housing 100. Specifically, the substrate 200 covers the second opening 103b of the opening 103 provided on the first surface 101a of the housing 100. The shape of the outer side surface of the substrate 200 has a shape along the side surface of the second opening 103b of the housing 100. A space 104 is formed between the substrate 200 covering the second opening 103b and the first opening 103a. In other words, the space 104 is surrounded by the housing 100 and the substrate 200. When the piezoelectric sensor 10 is mounted on an object, the space 104 and the wiring opening 109 are separated from each other by a clamping member 500 described later.

[0035] Figure 4It is a plan view of the substrate 200 as viewed from the side facing the housing 100. The plurality of electrodes provided on the substrate 200 include a first electrode 201, a second electrode 203, and two connection electrodes 205a and 205b. The first electrode 201 is disposed inside the second electrode 203, and the second electrode 203 is disposed so as to surround the periphery of the first electrode 201. The first electrode 201 and the second electrode 203 are separated from each other. The connection electrodes 205a and 205b are disposed adjacent to the second electrode 203. The first electrode 201 is electrically connected to the connection electrode 205a. The second electrode 203 is electrically connected to the connection electrode 205b via a wiring provided on the substrate 200. Two wirings included in a multi-core cable, i.e., the wiring 111, are electrically connected to the connection electrodes 205a and 205b, respectively.

[0036] As Figure 2 shown, a piezoelectric element 300 is disposed on one surface of the substrate 200 facing the space 104. The piezoelectric element 300 may be a flexible sheet. The piezoelectric element 300 is located inside the housing 100 and is disposed in the first opening 103a of the opening 103 provided in the housing 100.

[0037] Figure 5 is Figure 2 an enlarged view of the piezoelectric element 300 shown. The piezoelectric element 300 includes an electrode 301, an electrode 303, and a porous layer 305. The piezoelectric element 300 has a first surface 302a facing the substrate 200 and a second surface 302b on the opposite side of the first surface 302a. The electrode 301 may be disposed on the first surface 302a side of the piezoelectric element 300, and the electrode 303 may be disposed on the second surface 302b side of the piezoelectric element 300. In the present embodiment, the piezoelectric element 300 is disposed on the substrate 100 such that the electrode 301 is disposed on the first electrode 201 of the substrate 200.

[0038] The porous layer 305 is sandwiched between the two electrodes 301 and the electrode 303. The porous layer 305 is, for example, an electret layer in which a large number of fine pores 307 are formed in an insulating resin such as polypropylene, and charges are held inside. These charges are, for example, pre-injected by corona discharge. By the voltage applied to the electrodes 301 and 303 and the injected charges, polarization is generated in each of the fine pores 307.

[0039] The porous layer 305 may use, for example, the electret material disclosed in International Publication No. 2018 / 101359. The electrodes 301 and 303 may be the electrode layers disclosed in this document. The proportion of the volume of the fine pores 307 in the porous layer 305 is preferably 20% or more and 80% or less. This proportion corresponds to the porosity disclosed in International Publication No. 2018 / 101359. As the lower limit of the density of the porous layer 305, it is preferably 0.2 g / cm 3, more preferably 0.4 g / cm 3 . On the other hand, as the upper limit of the density of the porous layer 305, it is preferably 0.8 g / cm 3 , more preferably 0.6 g / cm 3 . As the lower limit of the elastic modulus in the thickness direction of the porous layer 305, it is preferably 0.1 MPa, more preferably 0.3 MPa. As the upper limit of the elastic modulus in the thickness direction, it is preferably 10 MPa, more preferably 2 MPa. These elastic moduli are values measured according to JIS-K7161 (2014).

[0040] When the porous layer 305 expands and contracts in the thickness direction, the micropores 307 deform and the polarization amount changes, and the potential difference between the electrode 301 and the electrode 303 fluctuates. Thus, in the piezoelectric element 300, an electric signal corresponding to the compressive deformation of the porous layer 305 is generated. In this example, when observing the piezoelectric sensor 10 from the second surface 101b side of the housing 100, the piezoelectric element 300 and the porous layer 305 are substantially the same shape.

[0041] The electrode 301 and the electrode 303 are electrically connected to the first electrode 201 and the second electrode 203 provided on the substrate 200, respectively. In the present embodiment, the electrode 301 is electrically connected to the first electrode 201 of the substrate 200, and the electrode 303 is electrically connected to the second electrode 203 of the substrate 200. The structure for electrically connecting the electrode 301 and the electrode 303 to the first electrode 201 and the second electrode 203 provided on the substrate 200 is not particularly limited. In the present embodiment, the electrode 301 is in direct contact with the first electrode 201 of the substrate 200. However, the electrode 301 may also be electrically connected to the first electrode 201 via a conductive member such as solder. As Figure 2 shown, the electrode 303 is connected to the second electrode 203 through the conductive film 310. The piezoelectric element 300 may also be referred to as a region where the porous layer 305, the electrode 301, and the electrode 303 overlap.

[0042] Figure 6 is a diagram for explaining the case where the electrode 303 provided on the second surface 302b of the piezoelectric element 300 is electrically connected to the second electrode 203 provided on the substrate 200 through the conductive film 310. As Figure 5 and Figure 6As shown, the electrode 303 is electrically connected to the second electrode 203 through the conductive film 310, and the clamping member 500 is disposed on the second electrode 203. By disposing the clamping member 500 on the second electrode 203, when the piezoelectric sensor 10 is mounted on the vibration surface of an object (the object 20 described later), the clamping member 500 is deformed while being clamped between the housing 100 and the substrate 200. Due to the elastic force of the deformed clamping member 500, the conductive film 310 is pressed against the second electrode 203, and the reliability of the electrical connection between the second electrode 203 and the electrode 303 of the piezoelectric element 300 is improved.

[0043] The electrical signal generated by the piezoelectric element 300 is output via the first electrode 201 and the second electrode 203 provided on the substrate 200, which are electrically connected to the electrode 301 and the electrode 303. The electrical signal output from the first electrode 201 and the second electrode 203 is transmitted from Figure 2 the first electrode 201 and the second electrode 203 shown via the wiring to the connection electrodes 205a and 205b. The connection electrodes 205a and 205b are electrically connected to the wiring 111, and the electrical signal is output from the connection electrodes 205a and 205b to the outside via the wiring 111.

[0044] Refer to Figure 2 the counterweight 400 will be described. As Figure 2 shown, the counterweight 400 is disposed on the second surface 302b of the piezoelectric element 300 with the conductive film 310 interposed therebetween. The counterweight 400 is made of a metal material such as stainless steel, for example. However, the material of the counterweight 400 is not limited to metal. The counterweight 400 is separated from the housing 100 and can be displaced relative to the substrate 200. If the object on which the piezoelectric sensor 10 is mounted vibrates, due to the inertial force, the counterweight 400 vibrates up and down relative to the substrate 200. Due to the vibration of the counterweight 400, the porous layer 305 of the piezoelectric element 300 expands and contracts in its thickness direction. As described above, the piezoelectric element 300 outputs an electrical signal corresponding to the expansion and contraction of the porous layer 305.

[0045] The clamping member 500 is disposed on one surface of the substrate 200 on which the piezoelectric element 300 is disposed. The clamping member 500 is clamped between the housing 100 and the substrate 200 in the space 104. The clamping member 500 may be an elastomer. When observing the piezoelectric sensor 10 from the second surface 101b side of the housing 100, the clamping member 500 has a shape along the inner peripheral shape of the space 104. As Figure 1 shown, when observing the piezoelectric sensor 10 from the second surface 101b side of the housing 100 and the shape of the space 104 is substantially circular, as Figure 4 shown, the clamping member 500 is an annular elastomer such as an O-ring. In the present embodiment, the case where the clamping member 500 is an O-ring will be described as an example.

[0046] As shown Figure 1 in the figure, the housing 100 is provided with a hole 115 for mounting the piezoelectric sensor 10 to an object. The hole 115 may be a threaded hole. In Figure 1 the figure, as an example, a case where the housing 100 is provided with four holes 115 is shown. However, the number of holes 115 is not limited to four, and may be one or more.

[0047] Figure 7 FIG. is a view showing a case where the piezoelectric sensor 10 is mounted on the vibration surface 20a of the object 20. In the present embodiment, an example will be described in which the object 20 on which the piezoelectric sensor 10 is mounted is a part of the structure of a musical instrument 70 having a vibration surface 20a that vibrates during sound production. In Figure 7 the figure shows a cross-sectional view corresponding to a cross-section along the line A1 - A2 in Figure 1 . The object 20 is a part of the structure of the musical instrument 70 that vibrates by the operation of a player in the musical instrument 70.

[0048] When the piezoelectric sensor 10 is mounted and fixed to the vibration surface of the object 20 by a joining member such as a screw 117, the other surface side of the substrate 200 is pressed by the object 20, the substrate 200 moves toward the housing 100 side, and the housing 100 and the substrate 200 are closely attached and joined. That is, the substrate 200 closes the second opening 103b provided on the first surface 101a side of the housing 100, and one surface of the substrate 100 contacts the bottom surface of the second opening 103b. At this time, the sandwiching member 500 interposed between the housing 100 and the substrate 200 elastically deforms in the space 104 formed by one surface of the substrate 200 and the first opening 103a. Therefore, the airtightness of the space 104 is higher than in the case where the sandwiching member 500 is not used. The sandwiching member 500 that has undergone elastic deformation does not contact the conductive film 310 except on the second electrode 203. The space 104 and the wiring opening 109 are separated from each other by the sandwiching member 500.

[0049] Figure 8 FIG. is a view for explaining the circuit structure of the piezoelectric sensor 10. As described above, the electric signal generated in the piezoelectric element 300 can be output from the piezoelectric sensor 10 to the outside via the wiring provided on the substrate 200, the connection electrodes 205a, 205b, and the wiring 111. The electric signal output from the piezoelectric sensor 10 is supplied to the preamplifier 800, amplified by the preamplifier 800 at a predetermined magnification, and supplied to the output terminals T1, T2. The amplified electric signal may also be output from the output terminals T1, T2 to an external speaker device. The preamplifier 800 may be built in the piezoelectric sensor 10 as an IC chip, or may be provided outside.

[0050] In the piezoelectric sensor 10 of the present embodiment, a space 104 is formed by a housing 100 and a substrate 200. A piezoelectric element 300 and a counterweight 400 are disposed within this space 104. Accordingly, in the piezoelectric element 300 and the counterweight 400, it is possible to prevent detection of vibrations other than those of the vibrating body, such as unintended vibrations like air vibrations. Further, when the piezoelectric sensor 10 is attached to the object 20, a clamping member 500 is used to further improve the airtightness of the space 104. As a result, it is possible to significantly suppress the expansion and contraction of the porous layer 305 of the piezoelectric element 300 due to air pressure changes caused by vibrations other than the vibrations transmitted from the object (20), such as air vibrations. As a result, the piezoelectric sensor 10 can suppress detection of noise caused by external air vibrations.

[0051] [Second Embodiment]

[0052] In the piezoelectric sensor 10 of the first embodiment described above, in the housing 100 having the opening 103, a side surface of a part (second opening 103b) of the opening 103 has a shape along the outer side surface shape of the substrate 200, and the space 104 is formed by the housing 100 and the substrate 200. However, the piezoelectric sensor of the present disclosure is not limited thereto.

[0053] Figure 9 FIG. is a view showing the appearance of the piezoelectric sensor of the second embodiment. Figure 10 is along Figure 9 A cross-sectional view of the piezoelectric sensor of the second embodiment taken along line B1 - B2 in. In Figure 9 and Figure 10 , structures that are the same as or similar to those of the piezoelectric sensor 10 of the first embodiment described with reference to Figures 1 to 8 are denoted by the same reference numerals.

[0054] As Figure 9 and Figure 10 show, in the piezoelectric sensor 10A of the present embodiment, the housing has a dome shape. Hereinafter, the housing having a dome shape is referred to as a cover. In the following description of the piezoelectric sensor 10A, mainly the structures different from those of the piezoelectric sensor 10 of the first embodiment will be described, and repeated descriptions of structures that are the same as or similar to those of the piezoelectric sensor 10 will be omitted.

[0055] As Figure 9 and Figure 10 show, the piezoelectric sensor 10A includes a cover 900, a substrate 200A, a piezoelectric element 300, and a counterweight 400.

[0056] The cover 900 has a dome portion 901 and an edge portion 902. The dome portion 901 has a dome shape. Here, the dome shape means that its outer shape is a part of a sphere cut by a plane (i.e., a spherical segment). The dome portion 901 has an opening portion 903 on the side opposite to the substrate 200A. The opening portion 903 has a shape along the shape of the dome portion 901. The depth d2 of the deepest part of the opening portion 903 has a depth to the extent that the dome portion 901 does not contact the piezoelectric element 300 and the counterweight 400. For example, the depth d2 can be less than 1 / 2 of the diameter d1 of the opening portion 903. The edge portion 902 extends from the edge of the dome portion 901 along the surface of the substrate 200A on which the piezoelectric element 300 is arranged. The cover 900 can be formed of an insulating plastic material such as PET (polyethylene terephthalate) and acrylic. In addition, the material forming the cover 900 is not limited to an insulating material, and may be formed of a conductive material such as aluminum, copper, or other metals.

[0057] The substrate 200A is a printed wiring substrate provided with a plurality of electrodes and wirings. The shape of the substrate 200A is different from the shape of the substrate 200 of the piezoelectric sensor 10 of the first embodiment. The substrate 200A has a first portion 210 whose outer side surface has a shape along the shape of the edge portion 902 of the cover 900, and a second portion 212 extending from a portion of the first portion 210.

[0058] The first portion 210 of the substrate 200A is opposite to the cover 900 and contacts the edge portion 902 of the cover 900 via the clamping member 500A. A space 904 is formed between the opening 903 of the cover 900 and the substrate 200A. In other words, the space 904 is surrounded by the dome portion 901 and the substrate 200A. The clamping member 500A bonds the cover 900 to the substrate 200A. The airtightness of the space 904 is improved by being surrounded by the clamping member 500A arranged along the edge portion 902. The details of the clamping member 500A will be described later.

[0059] The plurality of electrodes provided on the substrate 200A include a first electrode 201, a second electrode 203, and two connecting electrodes 215a, 215b. The first electrode 201 and the second electrode 203 are the same as the first electrode 201 and the second electrode 203 provided on the substrate 200 of the first embodiment. The connecting electrodes 215a, 215b are arranged adjacent to the second electrode 203, as are the connecting electrodes 205a, 205b in the first embodiment. The first electrode 201 is electrically connected to the connecting electrode 215a. The second electrode 203 is electrically connected to the connecting electrode 215b via wiring provided on the substrate 200A.

[0060] Unlike the connection electrodes 205a and 205b in the first embodiment, in this embodiment, the connection electrodes 215a and 215b extend from the first part 210 to the second part 212 of the substrate 200A. That is, at least a part of the connection electrodes 215a and 215b extends to the outside of the cover 900 in contact with the substrate 200A. Two wires included in a multi-core cable, i.e., the wiring 111, are electrically connected to the connection electrodes 215a and 215b that extend to the outside of the cover 900, respectively. Although not shown, the connection electrodes 215a and 215b that extend to the outside of the cover 900 may also be covered with an insulating film together with the second part 212 of the substrate 200A, and the outer surface of the insulating film is covered with a conductive film.

[0061] A shielding electrode 220 may be provided on the substrate 200A. The shielding electrode 220 is arranged in a shape along the first part 210 of the substrate 200A. The shielding electrode 220 is separated from the first electrode 201, the second electrode 203, and the connection electrodes 215a and 215b. By providing the shielding electrode 220, it is possible to prevent external noise such as hum from entering the internal sensor.

[0062] The clamping member 500A is arranged so as to be clamped between the edge portion 902 of the cover 900 and the first part 210 of the substrate 200A. The clamping member 500A is an adhesive member that bonds the cover 900 and the substrate 200A. The clamping member 500A may also be an adhesive, a double-sided tape, etc. The clamping member 500A is arranged on at least a part of the shielding electrode 220 provided on the substrate 200A and at least a part of the connection electrodes 215a and 215b.

[0063] In the piezoelectric sensor 10A of this embodiment, the piezoelectric element 300 arranged on the substrate 200A is covered with a dome-shaped cover 900. The dome shape can achieve higher strength compared to other shapes. Therefore, in this embodiment, by using the dome-shaped cover 900, the strength of the cover 900 can be maintained and the thickness of the appearance of the cover 900 can be thinned.

[0064] [Third Embodiment]

[0065] In the piezoelectric sensor 10A of the second embodiment described above, the piezoelectric element 300 is arranged overlapping the first electrode 201, and the second electrode 203 is arranged around it. However, the arrangement of the first electrode 201 and the second electrode 203 is not limited to this.

[0066] Figure 11 It is a view showing the appearance of the piezoelectric sensor of the third embodiment. Figure 12 It is a view showing the upper surface of the substrate of the piezoelectric sensor of the third embodiment. Figure 13is a cross-sectional view of the piezoelectric sensor of the third embodiment taken along line C1-C2 in FIG. 22. In Figures 11 to 13 , structures that are the same as or similar to those of the piezoelectric sensor 10A of the second embodiment described with reference to Figure 9 and Figure 10 are labeled with the same reference numerals.

[0067] As Figures 11 to 13 shown, the piezoelectric sensor 10B of the present embodiment includes a cover 900, a substrate 200B, a first piezoelectric element 300-1, a second piezoelectric element 300-2, a conductive film 311, a weight 400B, and a clamping member 500A.

[0068] The structure of the cover 900 is the same as that of the cover 900 of the second embodiment. The substrate 200B is a printed wiring board provided with a plurality of electrodes and wirings. The shape of the substrate 200B is the same as the shape of the substrate 200A of the second embodiment. The plurality of electrodes provided on the substrate 200B include a first electrode 201B, a second electrode 203B, and two connection electrodes 215a, 215b.

[0069] As Figure 12 shown, in the present embodiment, the first electrode 201B and the second electrode 203B each have a semicircular shape and are arranged separately from each other. The first electrode 201B corresponds to the first electrode 201 in the first and second embodiments. The second electrode 203B corresponds to the second electrode 203 in the first and second embodiments.

[0070] The connection electrode 215a is electrically connected to the first electrode 201B, and the connection electrode 215b is electrically connected to the second electrode 203. Similar to the second embodiment, in the present embodiment, the connection electrodes 215a, 215b also extend from the first portion 210 of the substrate 200B to the second portion 212. Two wirings included in a multi-core cable, i.e., a wiring 111, are electrically connected to the connection electrodes 215a, 215b that extend outside the cover 900, respectively. Although not shown, the connection electrodes 215a, 215b that extend outside the cover 900 may also be covered with an insulating film together with the second portion 212 of the substrate 200B, and the outer side surface of the insulating film is covered with a conductive film.

[0071] As Figure 12As shown, a shielding electrode 220 may be provided on the substrate 200B. The shielding electrode 220 is arranged in a shape along the first part 210 of the substrate 200B. The shielding electrode 220 is separated from the first electrode 201B, the second electrode 203B, and the connection electrodes 215a and 215b, and is patterned in a way to surround the peripheries of the first electrode 201B and the second electrode 203B. The shielding electrode 220 includes a discontinuous part 222 for connecting the first electrode 201B to the connection electrode 215a and the second electrode 203B to the connection electrode 215b, while the other parts are continuous. It should be noted that, as Figure 12 shown, in the present embodiment, in order to obtain symmetry in appearance, the part 223 of the shielding electrode 220 on the opposite side of the discontinuous part 222 is covered with solder resist, but is actually continuous. The part on the opposite side of the discontinuous part 222 may not be covered with solder resist either.

[0072] As Figure 13 shown, a first piezoelectric element 300-1 is arranged on the first electrode 201B, and a second piezoelectric element 300-2 is arranged on the second electrode 203B. The shapes of the first piezoelectric element 300-1 and the second piezoelectric element 300-2 are the same as those of the first electrode 201B and the second electrode 203B, both being semi-circular. The structures of the first piezoelectric element 300-1 and the second piezoelectric element 300-2 are the same as those of the piezoelectric element 300 in the first embodiment. That is, as Figure 5 shown, the first piezoelectric element 300-1 and the second piezoelectric element 300-2 respectively have an electrode 301 arranged on the first surface 302a side, an electrode 303 arranged on the second surface 302b side, and a porous layer 305 sandwiched therebetween. In the present embodiment, the electrode 301 (refer to Figure 5 ) of the first piezoelectric element 300-1 is arranged on the first electrode 201B to be connected to the first electrode 201B. On the other hand, the electrode 303 (refer to Figure 5 ) of the second piezoelectric element 300-2 is arranged on the second electrode 203B to be connected to the second electrode 203B.

[0073] On the first piezoelectric element 300-1 and the second piezoelectric element 300-2, a counterweight 400B is arranged via a conductive film 311 having adhesiveness on both sides. Specifically, the electrode 303 (refer to Figure 5 ) arranged on the second surface 302b side of the first piezoelectric element 300-1 and the electrode 301 (refer to Figure 5 ) arranged on the first surface 302a side of the second piezoelectric element 300-2 are adhered to the conductive film 311. That is, the first piezoelectric element 300-1 and the second piezoelectric element 300-2 are electrically connected to each other at least via the conductive film 311.

[0074] The counterweight 400B is common to the first piezoelectric element 300-1 and the second piezoelectric element 300-2. As Figure 13 shown, the counterweight 400B has a first portion P1 that overlaps with the first piezoelectric element 300-1, a second portion P2 that overlaps with the second piezoelectric element 300-2, and a third portion P3 that connects the first portion P1 and the second portion P2. The counterweight 400B can displace relative to the substrate 200B following the expansion and contraction of the porous layer 305 of the first piezoelectric element 300-1 and the porous layer 305 of the second piezoelectric element 300-2. That is, the counterweight 400B displaces relative to the substrate 200B in such a manner that the porous layer 305 of the first piezoelectric element 300-1 and the porous layer 305 of the second piezoelectric element 300-2 expand or contract simultaneously.

[0075] As described above, in the piezoelectric sensor 10B, two piezoelectric elements (the first piezoelectric element 300-1 and the second piezoelectric element 300-2) are arranged on the substrate 200B. That is, the piezoelectric sensor 10B has a structure in which two piezoelectric elements are connected in series on a plane. Therefore, the thickness of the appearance of the cover 900 can be made thinner, and the output from the piezoelectric sensor 10B can be increased.

[0076] [Modification Example]

[0077] Above, one embodiment of the present disclosure has been described, but the present invention can be implemented in various ways as follows.

[0078] (1)In the above-described embodiment, the electrode 303 provided on the second surface 302b of the piezoelectric element 300 is electrically connected to the second electrode 203 of the substrate 200 through the conductive film 310. However, the electrode 303 of the piezoelectric element 300 may also be connected to the second electrode 203 of the substrate 200 through a wire.

[0079] (2)The elasticity of the piezoelectric element 300 can also be adjusted by changing the weight of the counterweight 400 provided on the second surface 302b of the piezoelectric element 300 or by changing the thickness of the piezoelectric element 300 (especially the porous layer 305), thereby adjusting the sensitivity and resonance frequency of the piezoelectric sensor 10. Thereby, vibrations to be detected as desired, such as vibrations of a specific frequency, can be detected with high precision. In addition, according to the unevenness of the vibration mode of the object (20), a plurality of piezoelectric sensors 10 having different weights of the counterweight 400 or different thicknesses of the piezoelectric element 300 can be installed at a plurality of positions on the vibration surface of the object (20). By combining a plurality of piezoelectric sensors 10 having different weights of the counterweight 400 or different thicknesses of the piezoelectric element 300, vibrations can be detected with high precision over a wide frequency range.

[0080] (3) The clamping member 500 disposed between the housing 100 and the substrate 200 is not limited to an elastomer such as an O-ring. The shape of the clamping member 500 is not limited to a ring shape. In addition, the clamping member 500 may also be an adhesive for bonding the housing 100 and the substrate 200. When the clamping member 500 is an adhesive, the clamping member 500 is disposed on the surface where the housing 100 and the substrate 200 contact. When the housing 100 and the substrate 200 contact, the housing 100 and the substrate 200 are bonded through the clamping member 500. In this case, when the housing 100 and the substrate 200 contact, the space 104 formed by the housing 100 and the substrate 200 is sealed and in an airtight state.

[0081] (4) In the above-described embodiment, the case where the object (20) to which the piezoelectric sensor 10 is mounted is a part of the structure of a musical instrument having a vibrating surface that vibrates during sound production has been described. As the musical instrument, for example, it may also be a percussion instrument such as a drum having a striking surface, a keyboard instrument such as a piano, or a string instrument such as a guitar or a violin. When the piezoelectric sensor 10 is mounted on a drum, for example, the piezoelectric sensor 10 can be mounted on the striking surface of the drum. When the piezoelectric sensor 10 is mounted on a piano or a guitar, for example, the piezoelectric sensor 10 can be mounted on the bridge that transmits the vibration of the strings. In addition, when the piezoelectric sensor 10 is mounted on a violin or the like, for example, the piezoelectric sensor 10 can be mounted on the bridge or the sound post that transmits the vibration of the strings.

[0082] (5) The piezoelectric sensor 10 may include a shielding film that covers the other surface on the opposite side of the surface of the substrate 200 on which the piezoelectric element 300 is disposed. The shielding film may be a metal foil such as copper foil. The shielding film has an electromagnetic shielding effect with respect to the substrate 200 and can further improve the electrical characteristics of the piezoelectric sensor 10. The shielding film may also cover not only the other surface of the substrate 200 but also the first surface 101a and the second surface 102b of the housing 100. In other words, the shielding film may be provided so as to cover substantially the entire piezoelectric sensor 10.

[0083] (6) An IC chip on which a preamplifier for amplifying the electrical signal output from the piezoelectric element 300 is mounted may also be disposed on the piezoelectric element 300 as a counterweight 400.

[0084] (7) In the above embodiment, the case where the piezoelectric sensor 10 is mounted on the vibrating surface of a musical instrument has been described. However, the object to which the piezoelectric sensor 10 is mounted is not limited to musical instruments.

[0085] As an embodiment of the present disclosure, the above embodiments and variations can be appropriately combined and implemented as long as they do not conflict with each other. In addition, based on the solutions shown in the embodiments, solutions in which those skilled in the art have appropriately added, deleted, or changed the design of components, or solutions in which processes have been added, omitted, or conditions have been changed, as long as they have the gist of the present invention, are also included in the scope of the invention.

[0086] Description of Reference Numerals

[0087] 10, 10A, 10B: Piezoelectric sensors;

[0088] 70: Musical instrument;

[0089] 100: Housing;

[0090] 101a: First surface;

[0091] 101b: Second surface;

[0092] 103, 903: Openings;

[0093] 103a: First opening;

[0094] 103b: Second opening;

[0095] 104, 904: Spaces;

[0096] 109: Wiring opening;

[0097] 111: Wiring;

[0098] 200, 200A, 200B: Substrates;

[0099] 201, 201B: First electrodes;

[0100] 203, 203B: Second electrodes;

[0101] 205a, 205b, 215a, 215b: Connecting electrodes;

[0102] 220: Shielding electrode;

[0103] 300: Piezoelectric element;

[0104] 300-1: First piezoelectric element;

[0105] 300-2: Second piezoelectric element;

[0106] 301: Electrode;

[0107] 303: Electrode;

[0108] 305: Porous layer;

[0109] 307: Microscopic pore;

[0110] 310: Conductive film;

[0111] 311: Conductive film;

[0112] 400, 400B: Counterweight;

[0113] 500, 500A: Clamping component;

[0114] 800: Preamplifier;

[0115] 900: Cover;

[0116] 901: Round top;

[0117] 902: Edge part.

Claims

1. A piezoelectric sensor, characterized in that, it has: a housing having an opening; a substrate that covers the opening and faces the housing; a sheet-like first piezoelectric element located within the housing and arranged with a first surface facing the substrate; a counterweight arranged to face a second surface of the first piezoelectric element; the first piezoelectric element has a porous layer capable of expansion and contraction, and the counterweight can displace relative to the substrate following the expansion and contraction of the porous layer.

2. The piezoelectric sensor according to claim 1, characterized in that, it further has a clamping member sandwiched between the substrate and the housing.

3. The piezoelectric sensor according to claim 2, characterized in that, the clamping member is an annular elastic body.

4. The piezoelectric sensor according to claim 3, characterized in that, the substrate can move relative to the housing in a direction that deforms the elastic body.

5. The piezoelectric sensor according to claim 1, characterized in that, the substrate has a plurality of electrodes, the first piezoelectric element has a first electrode provided on the first surface and a second electrode provided on the second surface, the second electrode is covered by a conductive film and is electrically connected to at least one of the plurality of electrodes of the substrate via the conductive film.

6. The piezoelectric sensor according to claim 5, characterized in that, the clamping member is arranged on the at least one electrode and on the conductive film.

7. The piezoelectric sensor according to claim 1, characterized in that, it further includes: a sheet-like second piezoelectric element located within the housing, having a third surface and a fourth surface located at a position opposite to the third surface, and the fourth surface is arranged to face the substrate; a conductive film that electrically connects the second surface and the third surface; the substrate has a third electrode and a fourth electrode arranged separately from the third electrode, the third electrode is electrically connected to the first surface, and the fourth electrode is electrically connected to the fourth surface.

8. The piezoelectric sensor according to claim 7, characterized in that, the conductive film is arranged between the second surface and the counterweight and between the third surface and the counterweight.

9. The piezoelectric sensor according to claim 7, characterized in that, the counterweight has a first portion overlapping the first piezoelectric element, a second portion overlapping the second piezoelectric element, and a third portion connecting the first portion and the second portion.

10. An instrument, characterized in that, it includes: the piezoelectric sensor according to any one of claims 1 to 9; a vibrating surface on which the piezoelectric sensor is arranged and vibrates during sound production.

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