JP2014160915A - Piezoelectric type electroacoustic transducer and electronic apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve an epoch-making technology for providing a piezoelectric type electroacoustic transducer capable of a compact size and reproduction of high sound quality, which is an alternative to an electrodynamic electroacoustic transducer.SOLUTION: The piezoelectric type electroacoustic transducer includes: a plurality of piezoelectric devices: a diaphragm that vibrates along with electrostrictive actions of the plurality of piezoelectric devices; a frame that supports the diaphragm; and a plurality of coupling members that connect directly or indirectly between one end of each of the plurality of piezoelectric devices and an edge of the diaphragm.

Description

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

  An electrodynamic electroacoustic transducer is used as an acoustic component of an electronic device such as a mobile phone. This electrodynamic electroacoustic transducer is composed of a permanent magnet, a voice coil, and a diaphragm. The principle of operation is that a vibration film such as an organic film fixed to a voice coil vibrates due to the action of a magnetic circuit of a stator using a magnet to generate sound waves.

  By the way, in recent years, demand for portable terminals such as mobile phones and laptop personal computers has increased, and thus there has been an increasing demand for miniaturization of electroacoustic transducers. In the acoustic performance of the electroacoustic transducer, the sound pressure level, which is an important enhancement amount, is determined by the volume exclusion of the diaphragm against air. Therefore, when the 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.

  As a means for improving the sound pressure level, there is a method of increasing the generating force 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 driving current, and there is a problem that the thickness of the magnetic circuit increases due to an increase in the volume of the permanent magnet and a thickening of the voice coil. Furthermore, there is a problem such as an increase in power consumption accompanying an increase in current amount.

  On the other hand, as a means for realizing a small and thin electroacoustic transducer, there is a piezoelectric electroacoustic transducer using a piezoelectric effect by piezoelectric ceramics. This piezoelectric method uses a piezoelectric effect of a ceramic material to generate a vibration amplitude by an electrostrictive action by inputting an electric signal. In a piezoelectric electroacoustic transducer, the ceramic itself, whose upper and lower layers are constrained by electrode materials, vibrates and functions as a drive source. Compared to a type electroacoustic transducer, the number of members is reduced, which is advantageous in terms of thickness reduction.

  Patent Document 1 discloses a speaker in which a plurality of piezoelectric elements are arranged at a side portion or a central portion of a diaphragm, and the plurality of piezoelectric elements are joined to the diaphragm over the entire main surface thereof.

Japanese Patent Publication No. 58-56319 (see FIG. 1 (a))

  The following analysis is given by the present invention.

  Since the piezoelectric electroacoustic transducer uses a ceramic material 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 an amplitude through an organic film. For example, the electrodynamic type is about 3 to 5 and the piezoelectric type is about 50. Since the mechanical quality factor Q indicates the sharpness at the time of resonance, in summary, in the piezoelectric electroacoustic transducer, it means that the sound pressure is high in the vicinity of the fundamental resonance frequency and the sound pressure is attenuated in other bands. That is, in the sound pressure level frequency characteristic, there is a problem that the sound characteristic level peaks and valleys occur, and the sound of a specific frequency is emphasized or lost, so that sufficient sound quality for music reproduction or the like cannot be obtained. In addition, since ceramic, which is a brittle material, is used, the impact stability when dropped is weak, and there is a problem in securing reliability when mounted on a small electronic device such as a mobile phone.

  Moreover, in the speaker of patent document 1, all the several piezoelectric elements are arrange | positioned at the side part or center part of the diaphragm, and the whole main surface of several piezoelectric elements is joined to the diaphragm. Therefore, there is a problem that the amplitude of the diaphragm is small and the sound pressure is small.

  For this reason, an epoch-making technique for providing a piezoelectric electroacoustic transducer that is small and can reproduce with high sound quality, which is an alternative to an electrodynamic electroacoustic transducer, is required.

  A piezoelectric electroacoustic transducer according to a first aspect includes a plurality of piezoelectric elements, a diaphragm that vibrates in accordance with an electrostrictive action of the plurality of piezoelectric elements, a frame that supports the diaphragm, and the plurality of piezoelectric elements. A plurality of connecting members for directly or indirectly connecting one end of the element and the edge of the diaphragm.

  The electronic device of the second viewpoint uses the piezoelectric electroacoustic transducer of the first viewpoint as a speaker.

  The first viewpoint contributes to the provision of a piezoelectric electroacoustic transducer that can be played back with small size and high sound quality, which is an alternative to the electrodynamic electroacoustic transducer, and the second viewpoint is small size and high sound quality playback. Contribute to the provision of electronic devices that can

1 is an exploded view of a piezoelectric electroacoustic transducer according to Embodiment 1. FIG. 6 is a cross-sectional view of a piezoelectric electroacoustic transducer according to Embodiment 2. FIG. It is sectional drawing of the piezoelectric type electroacoustic transducer which concerns on a comparative example. 6 is a graph showing frequency characteristics of sound pressure levels of the piezoelectric electroacoustic transducer of Embodiment 1 and the piezoelectric electroacoustic transducer according to the comparative example.

  Preferably, the piezoelectric element is cantilevered with respect to the diaphragm.

  Preferably, the plurality of piezoelectric elements are arranged along the edge of the diaphragm.

  Preferably, the diaphragm has a plurality of corners, and each piezoelectric element is connected to the corners via a connecting member.

  Preferably, the joints (one end) of the plurality of piezoelectric elements to the diaphragm are arranged symmetrically or diagonally with respect to the center of the diaphragm.

  Preferably, the other end of the piezoelectric element is connected to the frame via at least a support.

  Preferably, the edge of the piezoelectric element and the diaphragm are connected via a metal plate that constrains the main surface of the piezoelectric element and a connecting member.

  Preferably, the diaphragm includes a first diaphragm made of metal and a second diaphragm made of resin, and more preferably, the first diaphragm is connected to a plurality of connecting members, and the second diaphragm Is connected between one connecting member and the frame.

  An outline of an embodiment of the present invention will be described with reference to the drawings. Note that the reference numerals of the drawings attached to this summary are attached to the respective elements for convenience as an example for facilitating understanding, and are not intended to limit the present invention to the illustrated embodiment.

  Referring to FIG. 1, a piezoelectric electroacoustic transducer 1 supports a plurality of piezoelectric elements (actuators) 2, a diaphragm 3 that vibrates with the electrostrictive action of the plurality of piezoelectric elements 2, and the diaphragm 3. A plurality of frames 4, one end of a plurality of piezoelectric elements 2, and edges (3 a-3 a to 3 a-3 a) of the diaphragm 3, preferably a plurality of corners 3 a are connected directly or indirectly to each other. And a connecting member 5.

  The ends of the plurality of piezoelectric elements 2 having large or maximum vibration displacement are joined to the edges (3a-3a-3a-3a) of the diaphragm 3, preferably the corners 3a, in a cantilevered manner. Therefore, the diaphragm 3 vibrates greatly over the entire surface. Further, in the diaphragm 3, the bending vibration peculiar to the piezoelectric element 2 is attenuated or canceled, and piston vibration that is vibration in the normal direction of the diaphragm 3 is promoted. By these actions, even if the piezoelectric electroacoustic transducer 1 is downsized, the amplitude of the diaphragm 3 can be sufficiently increased, and reproduction with high sound pressure is possible.

  Further, the sound quality can be improved by optimizing the connecting member 5 or the like. For example, when the connecting member 5 is formed from a resin material, the basic resonance frequency of the piezoelectric element 2 can be reduced, and the low-frequency sound pressure can be increased. On the other hand, when the connecting member 5 is formed of a metal material, the vibration propagation efficiency is increased and the displacement at a desired frequency can be increased.

  Since the piezoelectric electroacoustic transducer 1 has a structure that absorbs an impact when dropped due to the piezoelectric element 2 being cantilevered by the diaphragm 3, a portable electronic device such as a cellular phone is used. It is suitable as a speaker.

  Therefore, the piezoelectric electroacoustic transducer 1 has a high industrial value as an acoustic device for electronic equipment that is small and thin, and capable of reproducing with high sound pressure and high sound quality.

  The piezoelectric electroacoustic transducer according to the embodiment is suitably applied to all portable electronic devices such as portable terminals. For example, a cellular phone, a smartphone, a game machine, a tablet PC (Personal Computer), a notebook PC, and a PDA (Personal Data Assistants). : Mobile information terminal), digital camera, etc.

  When the diaphragm is rectangular, the plurality of piezoelectric elements are arranged in a rectangular shape along the edge or outer periphery of the diaphragm. When the diaphragm is circular or annular, the plurality of piezoelectric elements are arranged circumferentially along the edge or outer periphery of the diaphragm.

  The diaphragm is preferably formed in a rectangular shape, for example, a quadrangle, in some cases, a triangle, or a polygon that is a pentagon or more, and a vibration element is connected to each corner.

  The piezoelectric element can be composed of ceramics and a pair of electrodes. Various types of piezoelectric elements can be used as the piezoelectric element. For example, a structure in which two piezoelectric elements are constrained by a metal material, that is, a so-called bimorph piezoelectric element can be used. As the piezoelectric ceramic of the piezoelectric element, PZT (lead titanium zirconate) or the like can be used.

  The diaphragm or the connecting member can be formed from various materials such as metal and resin. Examples of the metal material include phosphor bronze, stainless steel, magnesium, aluminum, titanium, beryllium, and alloys thereof. Examples of the resin material include urethane, polypropylene, polyethylene, polystyrene, and polyamide.

  Next, an embodiment of the present invention will be described in detail with reference to the drawings. In the following description, many specific items are made for the purpose of explanation and to help understanding of the present invention.

Embodiment 1

  FIG. 1 is an exploded view of the piezoelectric electroacoustic transducer according to the first embodiment. Referring to FIG. 1, a piezoelectric electroacoustic transducer 1 includes four piezoelectric elements 2, a rectangular diaphragm 3 having four corners 3 a, a frame 4 that supports the diaphragm 3, and four pieces. And four connecting members 5 for connecting the one end of the piezoelectric element 2 and the four corners 3a, respectively.

  Specifically, one end at which the vibration displacement of each piezoelectric element 2 is maximized is connected to the corner 3 a via the connecting member 5, and the other end of the piezoelectric element 2 is connected to the frame 4 via the support 6. Yes. In the illustrated form, each piezoelectric element 2 extends along the edge (3a-3a-3a-3a) of the diaphragm 3. The frame 4 has a flat plate shape, and the plurality of supports 6 are joined on one surface of the frame 4. In addition, the support body 6 can be formed from various materials, such as a metal and resin, and it is preferable to form elastically.

  Since the four piezoelectric elements 2 are joined to the four corners 3a of the diaphragm 3 in a cantilevered manner, the amplitude of the diaphragm 3 is enlarged, and the entire surface of the diaphragm 3 vibrates greatly. Moreover, the diaphragm 3 can largely vibrate the piston. Further, the joint portions (one end) of the two sets of piezoelectric elements 2 and 2 with respect to the diaphragm 3 are arranged symmetrically with respect to the center of the diaphragm 3, in other words, arranged on the diagonal of the diaphragm 3. . Accordingly, the four connecting members 5 are arranged at an equal distance with respect to the center of the diaphragm 3.

  When the piezoelectric electroacoustic transducer 1 is mounted on an electronic device, the frame 4 may be attached to the frame of the electronic device, or the frame 4 of the piezoelectric electroacoustic transducer 1 and the frame of the electronic device may be integrated. Good.

Embodiment 2

  FIG. 2 is a cross-sectional view of the piezoelectric electroacoustic transducer according to the second embodiment. In the second embodiment, differences from the first embodiment will be mainly described, and the description of the first embodiment will be referred to as appropriate for the common points of the two embodiments.

  Similarly to the piezoelectric electroacoustic transducer 1 of the first embodiment, the piezoelectric electroacoustic transducer 11 of the second embodiment also includes four piezoelectric elements 2 that are cantilevered by the diaphragm 3. Since this has already been described in the first embodiment, in the second embodiment, the configuration of the diaphragm will be described in detail.

  Referring to FIG. 2, the piezoelectric element 2 includes a piezoelectric ceramic 2a and a pair of electrodes 2b and 2c that sandwich the piezoelectric ceramic 2a. The piezoelectric element 2 may be a so-called bimorph type piezoelectric element having a structure in which two piezoelectric ceramics or piezoelectric elements are constrained by a metal material. A metal plate 7 that restrains the main surface is joined to the main surface on the front side (electrode 2b side) of the piezoelectric element 2. The piezoelectric element 2 is connected to the corner 3a shown in FIG. 1 through the metal plate 7 and the connecting member 5 described above.

  The diaphragm 3 includes a first diaphragm 3b made of metal and a second diaphragm 3c made of resin. The first diaphragm 3 b connects the plurality of connecting members 5, that is, the two connecting members 5 and 5 for different piezoelectric elements 2. The second diaphragm 3 c connects between one connecting member 5 and the frame 4. In the illustrated form, the frame 4 has a bottomed frame shape, and one end of the second diaphragm 3 c is joined to the frame end surface of the frame 4 with an adhesive or the like.

  In this way, the diaphragm 3 is formed from a resin material and a metal material, and in particular, an end portion of the diaphragm 3, that is, a portion that propagates vibration to the frame 4 is formed from the second diaphragm 3c made of resin. By forming the central portion of the metal plate 3 from the first diaphragm 3b made of metal, the above-described piston motion is promoted and the impact at the time of dropping is further alleviated.

  Next, the frequency characteristics of the sound pressure level of the piezoelectric electroacoustic transducers according to Embodiments 1 to 3 shown in FIG. 1 and the piezoelectric electroacoustic transducer according to the comparative example shown in FIG. 3 were verified. The diaphragm 3 was made of phosphor bronze, the connecting member 5 was made of urethane rubber, and the piezoelectric ceramic of the piezoelectric element 2 was made of PZT (lead zirconate titanium).

  Referring to FIG. 3, a piezoelectric electroacoustic transducer 31 of a comparative example includes a piezoelectric element 32 including a piezoelectric ceramic 32a and a pair of electrodes 32b and 32c sandwiching the piezoelectric ceramic 32a, and one main surface of the piezoelectric element 32 as a whole. The metal diaphragm 33 is joined and connected between the piezoelectric element 32 and the inner wall of the frame 34. The entire surface of the metal diaphragm 33 is bonded to the entire main surface of one of the piezoelectric elements 32 to restrain it.

  FIG. 4 is a graph illustrating frequency characteristics of sound pressure levels of the piezoelectric electroacoustic transducer according to the first embodiment and the piezoelectric electroacoustic transducer according to the comparative example. Referring to FIG. 4, it can be seen that the first embodiment has a generally higher sound pressure level and no sharp peaks. Therefore, it can be seen that the piezoelectric electroacoustic transducer according to the first embodiment can reproduce sound with high sound pressure at a high sound pressure without having a small peak and valley of acoustic characteristics and excessively emphasizing the sound of a specific frequency.

  Although one embodiment of the present invention has been described above, the present invention is not limited to the above-described one embodiment and the like, and further modifications, within the scope not departing from the basic technical idea of the present invention, Substitutions or adjustments can be made.

  The disclosure of the above patent document is incorporated herein by reference. Within the scope of the entire disclosure (including claims) of the present invention, the embodiments and examples can be changed and adjusted based on the basic technical concept. Further, 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.) within the scope of the claims of the present invention. Is possible. That is, the present invention of course 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 technical idea.

1,11 Piezoelectric electroacoustic transducer 2 Piezoelectric element (piezoelectric actuator)
2a Piezoelectric ceramics 2b, 2c Electrode 3 Diaphragm 3a Corner 3a-3a-3a-3a Edge 3b First diaphragm made of metal 3c Second diaphragm made of resin 4 Frame 5 Connecting member 6 Support body 7 Metal Board

Claims (10)

A plurality of piezoelectric elements;
A diaphragm that vibrates with the electrostrictive action of the plurality of piezoelectric elements;
A frame that supports the diaphragm;
A plurality of connecting members for directly or indirectly connecting one end of the plurality of piezoelectric elements and an edge of the diaphragm;
A piezoelectric electroacoustic transducer characterized by comprising:   The piezoelectric electroacoustic transducer according to claim 1, wherein the piezoelectric element is cantilevered with respect to the diaphragm.   3. The piezoelectric electroacoustic transducer according to claim 1, wherein the plurality of piezoelectric elements are arranged along an edge of the diaphragm. The diaphragm has a plurality of corners;
The piezoelectric electroacoustic transducer according to any one of claims 1 to 3, wherein the plurality of piezoelectric elements are respectively connected to the plurality of corners through at least the plurality of connecting members. .   The piezoelectric electroacoustic transducer according to claim 1, wherein joint portions of the plurality of piezoelectric elements to the diaphragm are arranged symmetrically with respect to a center of the diaphragm.   6. The piezoelectric electroacoustic transducer according to claim 1, wherein the other ends of the plurality of piezoelectric elements are respectively connected to the frame via at least a plurality of supports. A plurality of metal plates that respectively restrain the principal surfaces of the piezoelectric elements;
The piezoelectric electroacoustic transducer according to claim 1, wherein the plurality of piezoelectric elements and the edge portion are connected to each other via the plurality of metal plates and the connecting member.   The piezoelectric electroacoustic transducer according to claim 1, wherein the diaphragm includes a first diaphragm made of metal and a second diaphragm made of resin. The first diaphragm is connected to a plurality of the connecting members,
The second diaphragm is connected between one of the connecting members and the frame.
The piezoelectric electroacoustic transducer according to any one of claims 1 to 8,   An electronic apparatus using the piezoelectric electroacoustic transducer according to claim 1 as a speaker.

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