JP2014160914A - 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 piezoelectric device; a frame that supports or stores the piezoelectric device; a high-rigidity section that is a diaphragm supported on the frame and connected directly or indirectly with the piezoelectric device and that is formed to traverse the diaphragm; and a low-rigidity section formed between the high-rigidity section and the frame.

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 including a piezoelectric element and a diaphragm made entirely of resin.

JP 2011-249990 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 frequency characteristics of the sound pressure level, there is a problem that the sound characteristics have a peak and valley, 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.

  Moreover, in the speaker of patent document 1, the rigidity of the diaphragm made of resin as a whole is low, and there is a problem that split vibration is likely to occur.

  On the other hand, a diaphragm made entirely of metal has a problem that since the internal loss is small, the vibration continues for a long period of time and the timbre tends to be disturbed.

  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 piezoelectric element, a frame that supports or accommodates the piezoelectric element, and a diaphragm that is supported by the frame and that is directly or indirectly connected to the piezoelectric element. And a diaphragm having a high rigidity portion formed so as to cross the diaphragm and a low rigidity portion formed between the high rigidity portion and the frame.

  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

(A) is a top view of the piezoelectric electroacoustic transducer according to Embodiment 1, and (B) is a sectional view of the same. 6 is an exploded 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 highly rigid portion of the diaphragm is formed on a diagonal line of the diaphragm and has an X shape.

  Preferably, the low rigidity portion of the diaphragm is formed between the edge portion of the high rigidity portion and the inner edge of the frame.

  Preferably, the central portion of one surface of the piezoelectric element is coupled to the diaphragm or the central portion of the highly rigid portion via a coupling member. More preferably, the center of one surface of the piezoelectric element is connected to the center of the diaphragm or its high-rigidity portion via a connecting member.

  Preferably, the other surface of the piezoelectric element is supported by the frame via at least an elastic member.

  Preferably, the highly rigid portion of the diaphragm gradually becomes wider from the center to the end of the diaphragm.

  Preferably, the high rigidity portion of the diaphragm is made of metal, and the low rigidity portion of the diaphragm is made of resin.

  Preferably, the piezoelectric electroacoustic transducer of the embodiment is used as a parametric speaker.

  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 includes a piezoelectric element 2, a frame 4 that supports or accommodates the piezoelectric element 2, and is supported by the frame 4 and is directly or indirectly connected to the piezoelectric element 2. The diaphragm 3 is provided. The vibration plate 3 includes a high rigidity portion 3 a formed so as to cross the vibration plate 3 and a low rigidity portion 3 b formed between the high rigidity portion 3 a and the frame 4.

  The high rigidity portion 3a increases the rigidity of the diaphragm 3, prevents divided vibration of the diaphragm 3, and increases the sound pressure level. Further, the high-rigidity portion 3a itself is also deformed by vibration, thereby assisting the entire vibration plate 3 to perform a piston motion. By these actions, the sound pressure level is increased and high-efficiency reproduction is possible. Since the low rigidity portion 3b has a large internal loss, the vibration of the diaphragm 3 is attenuated and the sound quality is improved.

  Moreover, the piezoelectric element 1 is restrained by the high rigidity part (metal plate) 3a of the diaphragm 3, and the high rigidity part 3a is joined to the frame 4 via the low rigidity part 3b such as a resin film. Thereby, the rigidity of the end portion where the stress of the diaphragm 3 is concentrated is reduced, and the vibration movable range is expanded. In addition, vibration is attenuated by the low rigidity portion 3b, and the mechanical quality factor Q is reduced.

  Since an ordinary piezoelectric electroacoustic transducer has a plurality of vibration modes, the frequency sound pressure characteristics with peaks and valleys are obtained by the generation of divided vibrations. According to the piezoelectric electroacoustic transducer 1 of the embodiment, the vibration 3 is controlled by the vibration plate 3 composed of a plurality of portions having different rigidity, thereby suppressing divided vibrations and obtaining good acoustic characteristics. it can.

  Preferably, as shown in FIG. 1, the piezoelectric electroacoustic transducer 1 includes a piezoelectric element 2, a diaphragm 3 supported by the frame 4, and a connecting member 5 that connects one surface of the piezoelectric element 2 and the diaphragm 3. And a metal plate 6 bonded to the other surface of the piezoelectric element 2 and restraining the other surface, and an elastic member 7 connecting the metal plate 6 to the frame 4. The diaphragm 3 includes a high rigidity portion 3a made of metal and a low rigidity portion 3b made of resin. The high rigidity portion 3a is disposed on the diagonal line of the diaphragm 3 or the vibration surface. The low-rigidity part 3b is joined to the outer edge of the high-rigidity part 3a.

  The high rigidity portion is preferably formed from a metal thin film having a thickness of 100 μm or less.

  Preferably, a connecting member is interposed between the piezoelectric element and the diaphragm. By causing the vibration from the piezoelectric element (piezoelectric actuator) to propagate to the diaphragm via the connecting member, stress can be concentrated on the diaphragm and the vibration displacement can be expanded. Further, there is an advantage that the resonance frequency can be easily controlled by adjusting the shape of the vibrating body.

  The piezoelectric electroacoustic transducer of the embodiment is small and highly efficient, and is useful as an electroacoustic transducer for a portable terminal. Further, by using this as a sound source of a parametric speaker, high-quality sound reproduction is possible. Note that the piezoelectric electroacoustic transducer of the embodiment can also reproduce ultrasonic waves of 20 kHz or higher. In this way, by setting the oscillation frequency to the ultrasonic band, the piezoelectric element or the piezoelectric electroacoustic transducer can be reduced in size, and directivity can be controlled by utilizing the straightness of the ultrasonic wave. Therefore, it is possible to realize a privacy sound source limited to the vicinity of the position. Therefore, the piezoelectric electroacoustic transducer of the embodiment can be suitably used as a parametric speaker that conveys an audio signal to an ultrasonic wave and demodulates it in the air.

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

  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.

  Preferably, the upper and lower main surfaces of the piezoelectric ceramic are constrained by electrodes to form a piezoelectric element. Preferably, the piezoelectric element is constrained by a metal plate and joined to the frame via the metal plate. The resonance frequency of the piezoelectric element can be easily controlled by adjusting the rigidity by changing the thickness or material of the metal plate. The metal plate may be formed from a composite material with resin or a laminated material instead of a single metal material.

  Note that the resonance frequency of the piezoelectric element (mechanical vibrator) is governed by the shape, weight and rigidity thereof. Since a normal piezoelectric element is difficult to process into an arbitrary shape because piezoelectric ceramic is a brittle material, the resonance frequency is adjusted by a technique such as adding a weight. In such a method, although the resonance frequency can be reduced by adding weight, there is a problem that the vibration amplitude is attenuated because the amplitude portion is constrained by a weight.

  In the diaphragm, the ratio of the specific elastic modulus of the high-rigidity part to the low-rigidity part (= specific elastic modulus of the high-rigidity part / specific elastic modulus of the low-rigidity part) is, for example, several times to several thousand times, several times It is adjusted to be in the range of several hundred times or in the range of several times to several tens of times.

In the diaphragm, the specific elastic modulus of the high-rigidity part is set to an order of 10 ⁷ (E / ρ) m ² / s ² or more, for example, and the specific elastic modulus of the low-rigidity part is set to an order of less than that. The Preferably, the high-rigidity part is formed from a metal material such as stainless steel, phosphor bronze, magnesium, aluminum, titanium, beryllium or an alloy thereof, and the low-rigidity part is polyethylene-based, polypropylene-based, polystyrene-based or polyamide-based, or It is formed from a resin material such as urethane. The diaphragm may be formed from various composite materials.

  The piezoelectric element can be composed of a piezoelectric ceramic 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 connecting member can be formed of various materials such as metal and resin. In the case of metal, a relatively light metal is preferable, and examples thereof include metal materials such as magnesium, aluminum, titanium, beryllium, and alloys thereof. The It is preferable to form from.

  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. 1A is a plan view of the piezoelectric electroacoustic transducer according to Embodiment 1, and FIG. 1B is a cross-sectional view thereof. Referring to FIGS. 1A and 1B, a piezoelectric electroacoustic transducer 1 includes a piezoelectric element 2, a frame 4 that supports or houses the piezoelectric element 2, a piezoelectric element 2 that is supported on the end face of the frame 4, and is piezoelectric. A vibration plate 3 that is directly or indirectly connected to the element 2 and vibrates with the electrostrictive action of the piezoelectric element 2 is provided.

  In particular, referring to FIG. 1 (A), the diaphragm 3 includes a metal high-rigidity portion 3a formed so as to cross the diaphragm 3, and a resin-made material formed between the high-rigidity portion 3a and the frame 4. Low-rigidity portion 3b. The high-rigidity portion 3a is formed on the diagonal line of the diaphragm 3 and has an X shape. The low rigidity portion 3 b is formed between the edge of the high rigidity portion 3 a and the inner edge of the frame 4. The high-rigidity portion 3a is formed so as to gradually widen from the center or center of the diaphragm 3 toward the end.

  The diaphragm 3 can be formed by laminating a rib-like high-rigidity portion 3a and a film-like low-rigidity portion 3b. Alternatively, resin may be filled between the outer edge of the high-rigidity portion 3a and the inner edge of the frame 4 to form the low-rigidity portion 3b in the same layer as the high-rigidity portion 3a. Preferably, the high rigidity part 3a is joined to the frame 4 via the low rigidity part 3b.

  The central portion of one main surface (one surface) of the piezoelectric element 2 is connected to the central portion of the vibration plate 3 or the high-rigidity portion 3 a via the connecting member 5. In the illustrated embodiment, in particular, the center of one main surface of the piezoelectric element is connected to the center of the diaphragm 3 or the high-rigidity portion 3a through a connecting member 5 having a circular cross section.

  The other main surface (other surface) of the piezoelectric element 2 is supported by the frame 4 via the metal plate 6 and the elastic member 7. The metal plate 6 constrains the other main surface (other surface) of the piezoelectric element 2. Specifically, both ends of the piezoelectric element 2 are supported on the inner wall of the frame 4 via a metal plate 6 and a plurality of elastic members 7 and 7.

  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.

  A characteristic function of the piezoelectric electroacoustic transducer 1 will be described. The high-rigidity portion 3a prevents the divided vibration of the diaphragm 3, and the high-rigidity portion 3a itself is also deformed by vibration, thereby assisting the entire diaphragm 3 to perform a large piston motion. Since the low rigidity portion 3b has a large internal loss, the vibration of the diaphragm 3 is attenuated, the mechanical quality factor Q is reduced, and the rigidity of the end portion where the stress of the diaphragm 3 is concentrated is reduced. Increase the range of motion.

  Further, by locally propagating the vibration of the piezoelectric element 2 to the diaphragm 3 through the connecting member 5, stress is concentrated at the center or center of the diaphragm 3, and the vibration displacement of the diaphragm 3 is enlarged. Can be made.

Embodiment 2

  FIG. 2 is an exploded 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.

  Referring to FIG. 2, the piezoelectric electroacoustic transducer 11 includes a flat plate-shaped connecting member 15 bonded to one electrode of the piezoelectric element 2 and a flat plate-shaped elastic member bonded to the other electrode of the piezoelectric element 2. 17. The connecting member 15 is entirely bonded to one main surface of the piezoelectric element 2 to restrain the piezoelectric element 2 with relatively high rigidity. The other main surface of the piezoelectric element 1 is entirely bonded to the elastic member 17, and the elastic member 17 elastically restrains the piezoelectric element 2.

  Further, the central portion of one main surface (one surface) of the piezoelectric element 2 is connected to the central portion of the vibration plate 3 or the high-rigidity portion 3 a via a connecting member 15.

  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. In addition, stainless steel is used for the high-rigidity part (metal part) 3a of the diaphragm 3, polyethylene is used for the low-rigidity part 3b, urethane rubber is used for the connecting member 5, and PZT (titanium lead zirconate) is used for the piezoelectric ceramic 2a. .

  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 31 to restrain it. Both ends of the piezoelectric element 32 are supported on the inner wall of the frame 34 via a metal diaphragm 33 and an elastic member 37, respectively.

  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 High rigidity part (metal part)
3b Low rigidity part (resin part, resin film)
4 Frame 5 Connecting member 6 Metal plate 7 Elastic member 11 Piezoelectric electroacoustic transducer 15 Connecting member 17 Elastic member

Claims (10)

A piezoelectric element;
A frame for supporting or housing the piezoelectric element;
A vibration plate supported by the frame and directly or indirectly connected to the piezoelectric element, the high rigidity portion formed to cross the vibration plate, and between the high rigidity portion and the frame A diaphragm having a formed low rigidity portion, and
A piezoelectric electroacoustic transducer characterized by comprising:   2. The piezoelectric electroacoustic transducer according to claim 1, wherein the high-rigidity part is formed on a diagonal line of the diaphragm and has an X shape.   3. The piezoelectric electroacoustic transducer according to claim 1, wherein the low-rigidity portion is formed between an edge of the high-rigidity portion and an inner edge of the frame.   4. The piezoelectric electric device according to claim 1, wherein a central portion of one surface of the piezoelectric element is coupled to a central portion of the diaphragm or the high-rigidity portion via a coupling member. Acoustic transducer.   5. The piezoelectric electroacoustic transducer according to claim 4, wherein a center of one surface of the piezoelectric element is connected to a center of the diaphragm or the high-rigidity portion via the connecting member.   6. The piezoelectric electroacoustic transducer according to claim 1, wherein the other surface of the piezoelectric element is supported by the frame via at least an elastic member.   3. The piezoelectric electroacoustic transducer according to claim 2, wherein the high-rigidity portion gradually becomes wider from the center to the end of the diaphragm.   The piezoelectric electroacoustic transducer according to claim 1, wherein the high-rigidity part is made of metal and the low-rigidity part is made of resin.   The piezoelectric electroacoustic transducer according to claim 1, wherein the piezoelectric electroacoustic transducer is used as a parametric speaker.   An electronic apparatus using the piezoelectric electroacoustic transducer according to claim 1.

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