JP2014239386A - Piezoelectric type electroacoustic transducer and electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small piezoelectric type electroacoustic transducer which achieves high sound quality and has an impact stability, and to provide an electronic apparatus.SOLUTION: A piezoelectric type electroacoustic transducer includes: a metal plate 12 having a groove part 12a on a main surface; a first elastic member 13 buried in the groove part; a piezoelectric film 14 joined to the metal plate and the first elastic member on the main surface of the metal plate; a frame 10 having a through slot 10a; and a second elastic member 11 which is joined to the metal plate and a wall surface of the through slot. The first elastic member is disposed at a position that is overlapped with at least an end part of the piezoelectric film when viewed from the upper side of the main surface of the metal plate.

Description

  The present invention relates to a piezoelectric electroacoustic transducer and an electronic apparatus using the same.

  In portable electronic devices such as mobile phones and smartphones, electrodynamic electroacoustic transducers are used as acoustic components. The electrodynamic electroacoustic transducer is composed of a permanent magnet, a voice coil, and a diaphragm. The principle of operation of the electrodynamic electroacoustic transducer is that a vibration film (for example, an organic film) fixed to a voice coil vibrates by the action of a magnetic circuit of a stator using a permanent magnet to generate sound waves. .

  Incidentally, in recent years, demand for portable electronic devices such as mobile phones and laptop personal computers has increased, and there has been an increasing demand for miniaturization of electroacoustic transducers. However, the sound pressure level, which is an important indication in the acoustic performance of the conductive electroacoustic transducer, is determined by the volume exclusion of the diaphragm against air. Therefore, when the conductive electroacoustic transducer is downsized, there is a problem that the sound pressure level is lowered because the radiation surface area of the diaphragm is reduced.

  On the other hand, in the electroconductive electroacoustic transducer, as means for improving the sound pressure level, there is means for increasing the magnetism of the magnetic circuit and increasing the amplitude of the diaphragm. However, this means requires an increase in magnetic flux density and an increase in drive current, and there is a problem in that the thickness of the magnetic circuit increases due to the increase in the volume of the permanent magnet and the thickening of the voice coil, making it difficult to reduce the size. . In addition, the conductive electroacoustic transducer also has problems such as an increase in power consumption accompanying an increase in the amount of current.

  On the other hand, as means for realizing a small and thin electroacoustic transducer, there is a piezoelectric electroacoustic transducer using a piezoelectric actuator (see, for example, Patent Document 1). This piezoelectric electroacoustic transducer uses a piezoelectric effect of a piezoelectric actuator to generate a vibration amplitude by an electrostrictive action by inputting an electric signal. In the piezoelectric actuator, for example, a sheet-like piezoelectric ceramic itself having upper and lower layers sandwiched between electrode materials vibrates, and the piezoelectric ceramic functions as a drive source. Therefore, the piezoelectric electroacoustic transducer has a smaller number of members and is superior in thinning compared to a conductive electroacoustic transducer having a magnetic circuit composed of a large number of members such as permanent magnets and voice coils.

JP 2000-23286 A

  The following analysis is given by the inventor.

  However, since the piezoelectric electroacoustic transducer uses piezoelectric ceramics having a low internal loss as a vibration source, the mechanical quality factor Q tends to be higher than that of an electrodynamic electroacoustic transducer that generates amplitude through an organic film. . For example, the mechanical quality factor Q of the electrodynamic electroacoustic transducer is about 3 to 5, whereas the mechanical quality factor Q of the piezoelectric electroacoustic transducer is about 50.

  Since the mechanical quality factor Q indicates sharpness at the time of resonance, the piezoelectric electroacoustic transducer has a characteristic that the sound pressure is high near the fundamental resonance frequency and the sound pressure is attenuated in a band other than the fundamental resonance frequency. In other words, in the piezoelectric electroacoustic transducer, in the sound pressure level frequency characteristics, peaks and valleys in the acoustic characteristics occur, and the sound of a specific frequency is emphasized or lost, so that sufficient sound quality for music reproduction and the like is obtained. There is a problem that can not be.

  In addition, since piezoelectric electroacoustic transducers use ceramics, which are brittle materials, impact stability when dropped is weak, and there is a problem in securing reliability when mounted on portable electronic devices such as cellular phones.

  A main object of the present invention is to provide a piezoelectric electroacoustic transducer and an electronic device that are small in size, have high sound quality, and have impact stability.

  In a first aspect of the present invention, in the piezoelectric electroacoustic transducer, a metal plate having a groove on a main surface, a first elastic member embedded in the groove, and the main surface of the metal plate A piezoelectric film bonded to the metal plate and the first elastic member; a frame having a through hole; and a second elastic member bonded to the metal plate and to the wall surface of the through hole; The first elastic member is disposed at a position overlapping at least an end portion of the piezoelectric film as viewed from above the main surface of the metal plate.

  In a second aspect of the present invention, the electronic electroacoustic transducer is mounted in an electronic device.

  According to the present invention, it is possible to provide a piezoelectric electroacoustic transducer and an electronic device that are small, have high sound quality, and have impact stability.

It is sectional drawing which showed typically the structure of the piezoelectric type electroacoustic transducer which concerns on one Embodiment of this invention. It is the expansion | deployment perspective view which showed typically the structure of the piezoelectric type electroacoustic transducer which concerns on one Embodiment of this invention. It is sectional drawing which showed typically the structure of the modification of the piezoelectric electroacoustic transducer which concerns on one Embodiment of this invention. It is sectional drawing which showed typically the structure of the piezoelectric type electroacoustic transducer which concerns on a comparative example. It is the figure which showed typically the frequency sound pressure characteristic of the piezoelectric electroacoustic transducer which concerns on one Embodiment of this invention.

[Embodiment]
A piezoelectric electroacoustic transducer according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing a configuration of a piezoelectric electroacoustic transducer according to an embodiment of the present invention. FIG. 2 is a developed perspective view schematically showing the configuration of the piezoelectric electroacoustic transducer according to one embodiment of the present invention. FIG. 3 is a cross-sectional view schematically showing a configuration of a modified example of the piezoelectric electroacoustic transducer according to the embodiment of the present invention.

  The piezoelectric electroacoustic transducer 1 is a piezoelectric electroacoustic transducer that generates vibration amplitude using the electrostrictive effect of the piezoelectric actuator 2 (see FIGS. 1 and 2). The piezoelectric electroacoustic transducer 1 is mounted on, for example, a portable electronic device such as a mobile phone or a smartphone. In the piezoelectric electroacoustic transducer 1, a metal plate 12 is mounted in a through-hole 10 a of a frame 10 via an annular elastic member 11, and an electrode 15 is disposed on the metal plate 12 via a piezoelectric film 14. ing. The piezoelectric electroacoustic transducer 1 includes, as main components, a frame 10, an elastic member 11, a metal plate 12, an elastic member 13, a piezoelectric film 14, an electrode 15, and lead wires 16 and 17. Have.

  The frame 10 is a member that supports (or holds) the piezoelectric actuator 2 that is assembled from the elastic member 11, the metal plate 12, the piezoelectric film 14, and the electrode 15. The frame 10 supports the metal plate 12 via the elastic member 11. The frame 10 is formed in an annular shape when viewed from the upper side (the upper side in FIG. 1), and has a through-hole 10a penetrating the center. The through-hole 10a is formed in a circular shape (may be elliptical or rectangular) when viewed from above. The frame 10 is joined (adhered, press-fitted, or the like) over the entire outer periphery of the annular elastic member 11 on the inner wall surface in the through-hole 10a. For the frame 10, for example, a resin material, brass, stainless steel, or the like can be used.

  The elastic member 11 is a member for elastically attaching the metal plate 12 to the frame 10 and is a constituent member of the piezoelectric actuator 2. The elastic member 11 has a circular opening 11a at the center. The elastic member 11 is formed in an annular shape when viewed from the upper side (the upper side in FIG. 1). The elastic member 11 is joined to the peripheral edge on the lower surface (lower side in FIG. 1) of the circular metal plate 12 at the inner peripheral edge on the upper surface (upper in FIG. 1). The elastic member 11 is joined (adhered or the like) to the inner wall surface of the through hole 10a of the frame 10 at the outer peripheral end. The vibration of the metal plate 12 propagates to the elastic member 11 and generates an amplitude by buckling. For the elastic member 11, for example, a porous material, a urethane-based material (for example, urethane foam), a resin material with a high internal loss, a carbon-based material, or the like can be used.

  The metal plate 12 is a plate-like member made of metal and is a constituent member of the piezoelectric actuator 2. The metal plate 12 is formed in a circular shape (may be an elliptical shape) when viewed from the upper side (the upper side in FIG. 1). The metal plate 12 is separated from the inner wall surface of the through-hole 10a of the frame 10, and is an annular elastic member at the outer peripheral side peripheral portion (or the outer peripheral end portion is acceptable) on the lower (lower side in FIG. 1) surface. 11 (bonding, bonding, etc. are also possible). The metal plate 12 has a larger outer diameter than the piezoelectric film 14 and the electrode 15. The metal plate 12 is joined (adhered or the like) to the piezoelectric film 14 at the center of the upper surface (upper side in FIG. 1). The metal plate 12 is a support member that supports the piezoelectric film 14 and the electrode 15, and at the same time can conduct electricity, and therefore can be used as an electrode of the piezoelectric film 14. In the metal plate 12, a groove 12a having a predetermined depth is formed at a portion overlapping the outer peripheral end surface of the piezoelectric film 14 on the upper surface (upper side in FIG. 1, the piezoelectric film 14 side). The groove 12 a is formed in an annular shape along the end (end surface) of the piezoelectric film 14. The side wall surface on the outer side of the groove portion 12 a is disposed on the radially outer side than the end portion (end surface) of the piezoelectric film 14. The side wall surface on the inner side of the groove portion 12 a is disposed on the radially inner side with respect to the end portion (end surface) of the piezoelectric film 14. An elastic member 13 is embedded in the groove 12a. The metal plate 12 is electrically connected to the lead wire 17 and has a role of applying an electric signal from the lead wire 17 to the piezoelectric film 14. The metal plate 12 is made of a metal material (including a metal material such as an alloy) that has conductivity and functions as a vibration plate. For example, phosphor bronze, a stainless material, or the like can be used.

  The elastic member 13 is a member made of an elastic material embedded in the groove 12 a in the metal plate 12 and is a constituent member of the piezoelectric actuator 2. The elastic member 13 is joined to the metal plate 12 in the groove 12a. The elastic member 13 is formed in an annular shape along the groove 12a when viewed from the upper side (the upper side in FIG. 1). The elastic member 13 is disposed at a position that overlaps at least the end portion (end surface) of the piezoelectric film 14 when viewed from the upper side (the upper side in FIG. 1). The elastic member 13 is disposed along the end portion of the piezoelectric film 14, and the lower surface of the piezoelectric film 14 (lower side in FIG. 1) at the inner peripheral edge of the upper surface (upper side in FIG. 1) of the elastic member 13. Side main surface). For the elastic member 13, for example, a porous material, a urethane-based material (for example, urethane foam), a resin material with a high internal loss, a carbon-based material, or the like can be used.

The piezoelectric film 14 is a film-like (sheet-like, film-like) member having piezoelectricity interposed between the metal plate 12 and the electrode 15, and is a constituent member of the piezoelectric actuator 2. The piezoelectric film 14 is joined (adhered or bonded, etc.) to the electrode 15 on the upper surface (upper main surface in FIG. 1), and the metal plate 12 on the lower surface (lower main surface in FIG. 1). Bonding (adhesion, bonding, etc. is also possible). The outer peripheral end of the piezoelectric film 14 is disposed so as to overlap the elastic member 13 embedded in the groove 12 a of the metal plate 12. The piezoelectric film 14 is bonded to the elastic member 13 (adhesion, bonding, or the like is possible) at the peripheral edge on the lower surface (lower side in FIG. 1). That is, the peripheral portion of the piezoelectric film 14 is joined to the elastic member 13, so that the acoustic characteristics and stability at the time of drop impact can be improved. The piezoelectric film 14 is formed in a circular shape (may be an elliptical shape) when viewed from the upper side (the upper side in FIG. 1). The piezoelectric film 14 is disposed so as to be concentric with the frame 10, the elastic member 11, the metal plate 12, the elastic member 13, and the electrode 15. The piezoelectric film 14 is separated from the inner wall surface of the through hole 10 a of the frame 10. A piezoelectric material is used for the piezoelectric film 14, for example, piezoelectric ceramics such as PZT (Pb (Zr _x , Ti _1-x ) O ₃ ; lead zirconate titanate), polyvinylidene fluoride, vinylidene fluoride, and three Piezoelectric organic materials such as copolymers of fluorinated ethylene can be used. If a piezoelectric organic material is used for the piezoelectric film 14, it has impact stability when dropped. When the piezoelectric film 14 is a unit with a metal film (similar to the electrode 15), there may be a metal film between the piezoelectric film 14 and the metal plate 12.

  The electrode 15 is a film-like member made of a conductor formed on the piezoelectric film 14. The electrode 15 is bonded to the piezoelectric film 14 (adhesion, bonding, or the like is also possible). The electrode 15 is formed in a circular shape (may be an elliptical shape) when viewed from the upper side (the upper side in FIG. 1). The electrode 15 is disposed away from the elastic members 11 and 13. The electrode 15 is separated from the inner wall surface of the through hole 10 a of the frame 10. The electrode 15 is electrically connected to the lead wire 16 and serves to apply an electric signal from the lead wire 16 to the piezoelectric film 14. For the electrode 15, a conductive material (including metal materials such as metals and alloys) is used. For example, silver foil can be used, and phosphor bronze, stainless material, etc. similar to the material of the metal plate 12 can be used. it can.

  In FIG. 1, the single-layer piezoelectric actuator 2 having the piezoelectric film 14 and the electrode 15 on the metal plate 12 is used. However, as shown in FIG. 3, the piezoelectric film 14, the electrode 15, A stacked piezoelectric actuator 2 in which the piezoelectric film 18, the electrode 19, the piezoelectric film 20, and the electrode 21 are stacked may be used. In the case of the multilayer piezoelectric actuator 2, the electrode 15 and the electrode 21 are electrically connected by the wiring 22 or the like, and the electrode 15 and the metal plate 12 are electrically connected by the wiring 23 or the like, and the electrode 21 is the lead The metal plate 12 is electrically connected to the lead wire 17. By using the laminated piezoelectric actuator 2, the electric field strength can be improved, the voltage application amount can be reduced, and the vibration amplitude can be increased.

  The lead wires 16 and 17 are wirings for supplying electric signals to the corresponding electrodes 15 and the metal plate 12. The lead wires 16 and 17 are electrically connected to a controller, an amplifier circuit, and the like. For the lead wires 16 and 17, not only a conductive wire (for example, copper wire) but also a metal foil (for example, copper foil) may be used.

  The piezoelectric electroacoustic transducer 1 described above can be manufactured as follows. First, the groove part 12a is formed in the predetermined position of the upper surface (upper side of FIG. 1) of the metal plate 12, and the elastic member 13 is embedded in the groove part 12a. Thereafter, the elastic member 11, the metal plate 12 (including the elastic member 13), the piezoelectric film 14, and the electrode 15 are bonded together to produce the piezoelectric actuator 2, and the piezoelectric actuator 2 is mounted in the through-hole 10 a of the frame 10.

  The piezoelectric electroacoustic transducer 1 operates as follows. The piezoelectric film 14 generates vibration due to an electrostrictive effect by applying an electric signal to the metal plate 12 and the electrode 15, generates an amplitude motion, and emits a sound wave. That is, when a voltage is applied to the piezoelectric film 14, a diameter spreading motion is generated with respect to the main surface of the piezoelectric film 14. As the expansion and contraction motion grows, lateral vibration is propagated to the metal plate 12 that restrains the piezoelectric film 14 and the elastic member 11. Due to the buckling movement caused by the restraint of the frame 10, an amplitude is generated in a direction perpendicular to the main surface of the piezoelectric film 14, and this is converted into a sound wave. In this vibration mechanism, the end portion of the piezoelectric film 14 serving as a driving force becomes a stress concentration location. By constraining this stress concentration location with the elastic member 13 having a large internal loss, the sharpness of vibration can be reduced and the mechanical quality factor Q of the piezoelectric electroacoustic transducer 1 can be reduced. Further, by constraining the end portion of the piezoelectric film 14 that is a stress concentration location with the elastic member 13 rich in elasticity, the vibration movable range of the end portion of the piezoelectric film 14 can be expanded and the vibration amplitude can be increased. it can. Furthermore, the rigidity of the metal plate 12 can be reduced by the interposition of the elastic member 13, and the fundamental resonance frequency of the piezoelectric electroacoustic transducer 1 itself can be reduced. In addition, the vibration at the end of the piezoelectric film 14 that is a stress concentration portion at the time of dropping is absorbed by the elastic member 13, so that the impact stability at the time of dropping is also improved.

  Next, the frequency sound pressure characteristics of the piezoelectric electroacoustic transducer according to one embodiment of the present invention will be described with reference to the drawings while comparing comparative examples. FIG. 4 is a cross-sectional view schematically showing a configuration of a piezoelectric electroacoustic transducer according to a comparative example. FIG. 5 is a diagram schematically showing the frequency sound pressure characteristics of the piezoelectric electroacoustic transducer according to one embodiment of the present invention.

  In addition, the piezoelectric electroacoustic transducer 101 according to the comparative example of FIG. 4 eliminates the groove 12a and the elastic members 11 and 13 in the metal plate 12 according to the embodiment of FIG. The frames 25 and 26 are sandwiched and joined. Other configurations are the same as in the embodiment.

  Referring to the frequency sound pressure characteristic of FIG. 5, the piezoelectric electroacoustic transducer according to the comparative example (101 in FIG. 4) has a plurality of peaks in the frequency sound pressure characteristic, whereas the piezoelectric according to the present embodiment. In the type electroacoustic transducer (1 in FIG. 1), the frequency sound pressure characteristics are relatively flat.

  According to the present embodiment, the metal plate 12 is supported by the frame 10 via the elastic member 11, and the piezoelectric film 14 that becomes a stress concentration location by the elastic member 13 embedded in the groove 12 a formed in the metal plate 12. Since the vibration movable range of the end portion of the piezoelectric film 14 can be expanded and the vibration amplitude can be expanded with the end portion of the piezoelectric film 14 being small, Flattening and high sound quality can be obtained. In addition, when the actuator is dropped, the vibration of the piezoelectric actuator 2 is absorbed by the elastic member 11, and the vibration of the end portion of the piezoelectric film 14 that is a stress concentration portion is absorbed by the elastic member 13, thereby stabilizing the impact at the time of dropping. Can be improved. As described above, the piezoelectric electroacoustic transducer 1 according to the present embodiment is suitable as an electroacoustic transducer for a portable electronic device such as a cellular phone because of its high strength when dropped. Industrial value is great as a thin acoustic device.

  Note that, in the present application, where reference numerals are attached to the drawings, these are only for the purpose of helping understanding, and are not intended to be limited to the illustrated embodiments.

(Appendix)
In a first aspect of the present invention, in the piezoelectric electroacoustic transducer, a metal plate having a groove on a main surface, a first elastic member embedded in the groove, and the main surface of the metal plate A piezoelectric film bonded to the metal plate and the first elastic member; a frame having a through hole; and a second elastic member bonded to the metal plate and to the wall surface of the through hole; The first elastic member is disposed at a position overlapping at least an end portion of the piezoelectric film as viewed from above the main surface of the metal plate.

  In the piezoelectric electroacoustic transducer of the present invention, the first elastic member is disposed along an end portion of the piezoelectric film, and the piezoelectric body is disposed at an inner peripheral edge of the first elastic member. It is preferable to join with the peripheral edge of the film.

  In the piezoelectric electroacoustic transducer of the present invention, the piezoelectric film is formed in a circular shape when viewed from the upper side of the main surface of the metal plate, and the first elastic member is the metal plate of the metal plate. It is preferable that it is formed in an annular shape when viewed from the upper side of the main surface.

  In the piezoelectric electroacoustic transducer according to the present invention, the metal plate is formed in a circular shape when viewed from above the main surface of the metal plate, and the second elastic member is the main plate of the metal plate. The frame is preferably formed in an annular shape when viewed from above the surface, and the frame is formed in an annular shape when viewed from above the main surface of the metal plate.

  In the piezoelectric electroacoustic transducer according to the present invention, it is preferable that the second elastic member is joined to a peripheral portion of the metal plate at an inner peripheral portion of the second elastic member.

  In the piezoelectric electroacoustic transducer of the present invention, the piezoelectric film is arranged so as to be concentric with each of the frame, the first elastic member, the metal plate, the second elastic member, and the electrode. It is preferable that

  In the piezoelectric electroacoustic transducer of the present invention, it is preferable that the piezoelectric film is made of a piezoelectric organic material.

  In the piezoelectric electroacoustic transducer according to the aspect of the invention, it is preferable that the frame is bonded to the end of the second elastic member over the entire circumference in the through hole.

  In the piezoelectric electroacoustic transducer of the present invention, it is preferable that electrodes and other piezoelectric films are alternately stacked on the piezoelectric film.

  In a second aspect of the present invention, the electronic electroacoustic transducer is mounted in an electronic device.

  It should be noted that the embodiments and examples may be changed and adjusted within the scope of the entire disclosure (including claims and drawings) of the present invention and based on the basic technical concept. Various combinations or selections of various disclosed elements (including each element of each claim, each element of each embodiment or example, each element of each drawing, etc.) are included within the scope of the claims of the present invention. Is possible. That is, the present invention naturally includes various variations and modifications that could be made by those skilled in the art according to the entire disclosure including the claims and the drawings, and the technical idea.

DESCRIPTION OF SYMBOLS 1,101 Piezoelectric electroacoustic transducer 2 Piezoelectric actuator 10, 25, 26 Frame 10a Through-hole 11 Elastic member (2nd elastic member)
11a Opening 12 Metal plate 12a Groove 13 Elastic member (first elastic member)
14 Piezoelectric film 15 Electrode 16, 17 Lead wire 18 Piezoelectric film 19 Electrode 20 Piezoelectric film 21 Electrode 22, 23 Wiring

Claims (10)

A metal plate having a groove on the main surface;
A first elastic member embedded in the groove,
A piezoelectric film bonded to the metal plate and the first elastic member on the main surface of the metal plate;
A frame having a through hole;
A second elastic member joined to the metal plate and joined to the wall surface of the through hole;
With
The piezoelectric electroacoustic transducer, wherein the first elastic member is disposed at a position overlapping at least an end portion of the piezoelectric film as viewed from above the main surface of the metal plate.   The first elastic member is disposed along an end portion of the piezoelectric film, and is joined to a peripheral portion of the piezoelectric film at an inner peripheral portion of the first elastic member. The piezoelectric electroacoustic transducer according to claim 1. The piezoelectric film is formed in a circular shape when viewed from above the main surface of the metal plate,
3. The piezoelectric electroacoustic transducer according to claim 1, wherein the first elastic member is formed in an annular shape when viewed from the upper side of the main surface of the metal plate. The metal plate is formed in a circular shape when viewed from the upper side of the main surface of the metal plate,
The second elastic member is formed in an annular shape when viewed from above the main surface of the metal plate,
The piezoelectric electroacoustic transducer according to any one of claims 1 to 3, wherein the frame is formed in an annular shape when viewed from above the main surface of the metal plate.   5. The piezoelectric electroacoustic conversion according to claim 1, wherein the second elastic member is joined to a peripheral portion of the metal plate at an inner peripheral portion of the second elastic member. vessel.   The piezoelectric film is disposed so as to be concentric with each of the frame, the first elastic member, the metal plate, the second elastic member, and the electrode. 5. The piezoelectric electroacoustic transducer according to claim 5.   The piezoelectric electroacoustic transducer according to any one of claims 1 to 6, wherein the piezoelectric film is made of a piezoelectric organic material.   The piezoelectric electroacoustic transducer according to any one of claims 1 to 7, wherein the frame is joined to the end of the second elastic member over the entire circumference in the through hole.   9. The piezoelectric electroacoustic transducer according to claim 1, wherein electrodes and other piezoelectric films are alternately stacked on the piezoelectric film.   10. An electronic apparatus on which the piezoelectric electroacoustic transducer according to any one of claims 1 to 9 is mounted.

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