JP2014233027A - Piezoelectric type electroacoustic transducer and electronic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric type electroacoustic transducer which contributes to the increase in sound pressure level.SOLUTION: The piezoelectric type electroacoustic transducer comprises: a first piezoelectric actuator; a second piezoelectric actuator; a support member; and a resonance part. The first and second piezoelectric actuators each include: a piezoelectric element which vibrates when an electric signal is applied thereto; and a plate-like member serving to constrain the piezoelectric element. The support member supports the two piezoelectric actuators so that their acoustic radiation planes are opposed to each other, and has a first sound hole along a direction in parallel with the acoustic radiation planes of the two piezoelectric actuators. The resonance part is provided between the acoustic radiation planes of the two piezoelectric actuators, and has second sound holes to which acoustic waves radiated by the piezoelectric actuators are input. In addition the piezoelectric element included in each of the two piezoelectric actuators is provided to be surrounded by the plate-like member of the piezoelectric actuator and the support member; acoustic waves are radiated from the first sound hole.

Description

  The present invention relates to a piezoelectric electroacoustic transducer and an electronic device.

  Mobile terminals such as mobile phones are required to have various acoustic functions such as music playback and hands-free. In addition, the pursuit of mobility is promoting the thinning and miniaturization of devices. Under these circumstances, electro-acoustic transducers mounted on portable terminals are highly demanded for being small and thin and having high sound quality, and development of thin electro-acoustic transducers capable of reproducing high sound quality is required. Usually, in a portable terminal, an electroacoustic transducer that generates a sound wave by vibrating a vibrating membrane fixed to a voice coil by the action of a magnetic circuit of a stator using a magnet is used. .

  However, since the sound pressure level of the electrodynamic electroacoustic transducer depends on the volume exclusion amount, there is a limit in reducing the thickness and increasing the sound pressure level in principle. Large volume playback requires an increase in vibration amplitude, but considering the driving force of the magnetic circuit, a certain amount of magnet volume is required to secure the magnetic flux. There is a trade-off for

  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.

  Here, in Patent Documents 1 and 2, two actuators that generate acoustic radiation when input signals are respectively applied thereto, and a support body that supports these two actuators so that their acoustic radiation surfaces are opposed to each other with a predetermined gap therebetween. , An electroacoustic transducer is disclosed.

JP 2011-228966 A International Publication No. 2009/063905

  Each disclosure of the above prior art document is incorporated herein by reference. The following analysis was made by the present inventors.

  Usually, piezoelectric ceramics are used for the piezoelectric element, but since the mechanical quality factor Q is high, a large sound pressure level is obtained near the resonance frequency, but the sound pressure level is attenuated in other bands. That is, a valley occurs in the sound pressure frequency characteristic, and the flat sound pressure frequency characteristic, which is an indispensable design factor for improving the sound quality, deteriorates.

  Also, since piezoelectric ceramics have high rigidity, reproduction at a low sound pressure level is disadvantageous. Therefore, in order to reproduce the low-frequency sound pressure, it is necessary to reduce the fundamental resonance frequency of the vibrator itself, and when using a ceramic material with high rigidity, it is necessary to take measures such as expanding the shape of the piezoelectric ceramic.

  In view of the above situation, an object of the present invention is to provide a piezoelectric electroacoustic transducer and an electronic device that contribute to increasing the sound pressure level.

  According to a first aspect of the present invention, first and second piezoelectric actuators including a piezoelectric element that vibrates when an electric signal is applied thereto, a plate-like member that restrains the piezoelectric element, and the first and second The first and second piezoelectric actuators support the first and second piezoelectric actuators so that acoustic emission surfaces of the piezoelectric actuators face each other, and the first and second piezoelectric actuators are parallel to the acoustic emission surfaces. A second sound that is disposed between the support having the sound holes and the acoustic radiation surfaces of the first and second piezoelectric actuators and that inputs sound waves emitted by the first and second piezoelectric actuators. A piezoelectric element included in the first and second piezoelectric actuators, a plate-like member included in the first and second piezoelectric actuators, and the support. Is arranged to be surrounded in the body, to radiate sound waves from the first sound hole, a piezoelectric electro-acoustic transducer is provided.

  According to the 2nd viewpoint of this invention, an electronic device provided with the said piezoelectric electroacoustic transducer is provided.

  According to each aspect of the present invention, a piezoelectric electroacoustic transducer and an electronic device that contribute to increasing the sound pressure level are provided.

It is a figure for demonstrating the outline | summary of one Embodiment. 1 is a perspective view illustrating an example of an entire piezoelectric electroacoustic transducer 10 according to a first embodiment. It is a figure which shows an example of sectional drawing of the AA direction of FIG. It is a figure which shows an example of the cross section of the perpendicular direction of the resonator which consists of partition plates 19a and 19b. It is a graph which shows the frequency characteristic of the sound pressure level of the piezoelectric electroacoustic transducer 10 which concerns on 1st Embodiment, and the piezoelectric electroacoustic transducer which concerns on a comparative example, respectively. It is a figure which shows an example of the internal structure of the piezoelectric electroacoustic transducer which concerns on a comparative example.

  First, an outline of an embodiment will be described with reference to FIG. Note that the reference numerals of the drawings attached to the outline are attached to the respective elements for convenience as an example for facilitating understanding, and the description of the outline is not intended to be any limitation.

  As described above, a piezoelectric electroacoustic transducer that contributes to increasing the sound pressure level is desired.

  Therefore, as an example, a piezoelectric electroacoustic transducer 100 having a cross section shown in FIG. 1 is provided. The piezoelectric electroacoustic transducer 100 includes a first piezoelectric actuator 101, a second piezoelectric actuator 102, a support body 103, and a resonance unit 104. The first piezoelectric actuator 101 includes a piezoelectric element 105a that vibrates when an electric signal is applied thereto, and a plate-like member 106a that restrains the piezoelectric element 105a. The second piezoelectric actuator 102 includes a piezoelectric element 105b that vibrates when an electric signal is applied thereto, and a plate-like member 106b that restrains the piezoelectric element 105b. The support 103 supports the acoustic radiation surfaces of the two piezoelectric actuators 101 and 102 so that they face each other, and the first sound hole parallel to the acoustic radiation surfaces of the two piezoelectric actuators 101 and 102. Is provided. The resonance unit 104 is disposed between the acoustic radiation surfaces of the two piezoelectric actuators 101 and 102 and includes a plurality of second sound holes for inputting sound waves radiated from the respective piezoelectric actuators. The piezoelectric elements 105a and 105b included in the two piezoelectric actuators 101 and 102 are disposed so as to be surrounded by the plate members 106a and 106b of the piezoelectric actuator and the support 103, and the sound wave is the first sound. Radiated from the hole.

  The piezoelectric electroacoustic transducer 100 is disposed so that the two piezoelectric actuators 101 and 102 face each other. Further, the inside of the piezoelectric electroacoustic transducer 100 is sealed by the support 103 and the plate-like members 106a and 106b, and the piezoelectric elements 105a and 105b exist in the sealed space. Further, a resonance unit 104 is disposed in front of the two piezoelectric actuators 101 and 102, and sound waves radiated from the respective piezoelectric actuators are input from the second sound holes provided in the resonance unit 104. As a result, the sound pressure level of the input sound wave is amplified by the resonance generated in the resonance unit 104.

  Hereinafter, specific embodiments will be described in more detail with reference to the drawings.

[First Embodiment]
The first embodiment will be described in more detail with reference to the drawings.

  FIG. 2 is a perspective view illustrating an example of the entire piezoelectric electroacoustic transducer 10 according to the first embodiment. Referring to FIG. 2, the piezoelectric electroacoustic transducer 10 includes a cylindrical frame 11. A sound hole 12 is provided in the frame 11. Both end portions of the frame 11 are cut out, and a plate-like member described later is disposed on the bottom surface of the cut-out portion. The piezoelectric electroacoustic transducer 10 receives electrical signals from the terminals 14a and 14b through the lead wire 13a. Similarly, electrical signals related to audio reproduction are received from the terminals 14c and 14d via the lead wire 13b.

  FIG. 3 is a diagram illustrating an example of a cross-sectional view in the AA direction of FIG. 2. Referring to FIG. 3, the interior of the piezoelectric electroacoustic transducer 10 is substantially sealed by frames 11a to 11c, plate-like members 15a and 15b, and elastic members 16a and 16b. More specifically, the plate-like member 15a is attached to the frames 11a and 11b by being joined (adhering or the like) to the elastic member 16a. Similarly, the plate-like member 15b is attached to the frames 11a and 11c via the elastic member 16b. The elastic members 16a and 16b have a circular shape with a hollowed center portion, and for example, a resin material such as polyethylene terephthalate (PET) can be used. Note that each of reference numerals 11a to 11c shown in FIG. 3 is a part of the frame 11, but different reference numerals are given for convenience of explanation.

  The piezoelectric elements 17a and 17b are elements that generate vibration amplitude using the electrostrictive effect of piezoelectricity. The piezoelectric element 17a is joined (adhered or the like) to the plate-like member 15a on the main surface on the electrode 202a side. The piezoelectric element 17a has a structure in which a piezoelectric ceramic 201a is sandwiched between an electrode 202a and an electrode 202b. The electrodes 202a and 202b are conductive members joined to both sides of the main surface of the piezoelectric ceramic 201a. The electrodes 202a and 202b are electrically connected to a lead wire 13a (not shown in FIG. 3), and have a role of applying an electric signal from the lead wire 13a to the piezoelectric ceramic 201a. When a voltage is applied between the electrodes 202a and 202b of the piezoelectric element 17a, the piezoelectric ceramic 201a vibrates, and the plate-like member 15a joined to the piezoelectric element 17a vibrates to generate acoustic radiation. Thus, the piezoelectric actuator 18a is comprised by the piezoelectric element 17a and the plate-shaped member 15a. The electrode 202a can be omitted if the plate member 15a is a metal plate, and the piezoelectric ceramic 201a and the plate member 15a may be directly joined.

  For example, PZT (lead zirconate titanate) can be used as the piezoelectric ceramic 201a. Of course, various piezoelectric elements such as various piezoelectric ceramics can be selected and used as necessary. In addition, since the piezoelectric actuator 18b has the same configuration and function as the piezoelectric actuator 18a, further description is omitted. In the present embodiment, the piezoelectric actuators 18a and 18b are described as having the same shape and configuration, but they do not necessarily have the same shape.

  The plate-like members 15a and 15b are plate-like members and restrain the piezoelectric elements 17a and 17b of the piezoelectric actuators 18a and 18b. For the plate-like members 15a and 15b, for example, metal plates can be used. Examples of the metal material include phosphor bronze, stainless steel, magnesium, aluminum, titanium, beryllium, and alloys thereof. A piezoelectric element 17a is joined to the plate-like member 15a, and a piezoelectric element 17b is joined to the plate-like member 15b (adhesion or the like is also possible).

  Here, the piezoelectric actuator 18 a and the piezoelectric actuator 18 b are disposed so as to face each other, and are supported by the frame 11. More specifically, the piezoelectric actuators 18a and 18b are supported by the frames 11a to 11c via the elastic members 16a and 16b. For the frame 11, for example, a resin material, brass, stainless steel, or the like can be used.

  In addition, the piezoelectric electroacoustic transducer 10 forms a space sealed by the plate-like members 15 a and 15 b and the frame 11 inside. In other words, the piezoelectric electroacoustic transducer 10 constitutes the frame 11, the plate-like members 15a and 15b, the elastic members 16a and 16b, and the like so as to surround the piezoelectric elements 17a and 17b.

  As described above, the sound holes 12 are provided in the frame 11. The sound hole 12 is provided so as to penetrate the sealed space inside the piezoelectric electroacoustic transducer 10 and the atmosphere. The sound hole 12 is formed in a direction parallel to the acoustic radiation surfaces 301a and 301b of the two piezoelectric actuators 18a and 18b. The piezoelectric electroacoustic transducer 10 radiates sound waves to the atmosphere using sound holes 12. In FIG. 2, the circular sound hole 12 is illustrated, but this is not intended to limit the shape of the sound hole 12. The shape of the sound hole 12 may be any shape such as a rectangular shape or a star shape.

  Furthermore, the inside of the piezoelectric electroacoustic transducer 10 is partitioned by two partition plates 19a and 19b. The partition plates 19a and 19b have a mountain-valley shape in the parallel direction of the acoustic radiation surfaces 301a and 301b, respectively, and are arranged on the front surfaces of the piezoelectric elements 17a and 17b. That is, the two partition plates 19a and 19b are disposed between the two piezoelectric elements 17a and 17b and partition the space where the two acoustic radiation surfaces 301a and 301b face each other. Various materials can be used for the partition plates 19a and 19b. For example, a metal material such as aluminum or a resin material such as urethane can be used for the partition plates 19a and 19b.

  A sound hole 20 is provided in each of the mountain portions in the mountain valley shape of the partition plates 19a and 19b. Sound waves generated by the piezoelectric actuators 18a and 18b are radiated to the spaces formed inside the partition plates 19a and 19b through the sound holes 20. That is, the sound holes 20 of the partition plates 19a and 19b input sound waves radiated from the acoustic radiation surface 301a from the sound holes 20 arranged on the piezoelectric element 17a side, and the sound waves radiated from the acoustic radiation surface 301b. It inputs from the sound hole 20 arrange | positioned at the piezoelectric element 17b side. On the other hand, sound waves from the acoustic radiation surfaces 302a and 302b opposite to the acoustic radiation surfaces 301a and 301b are not input to the sealed space where the piezoelectric elements 17a and 17b exist.

  The piezoelectric actuators 18a and 18b generate sound waves that are in phase with each other. Then, the sound wave radiated into the space formed in the partition plates 19a and 19b resonates in the space, and the sound pressure level increases. As described above, the partition plates 19a and 19b function as a resonator (resonance unit) that resonates the sound waves emitted from the piezoelectric actuators 18a and 18b.

  As described above, the piezoelectric electroacoustic transducer 10 includes a resonator including the partition plates 19a and 19 therein. In other words, the inside of the partition plates 19a and 19b functions as an interference space in which sound waves generated by the piezoelectric actuators 18a and 18b interfere with each other. Alternatively, the sound waves that are in phase with each other generated by the piezoelectric actuators 18a and 18b resonate inside the partition plates 19a and 19b and then radiate to the atmosphere from the sound hole 12, so that the partition plates 19a and 19b are sound tubes. It also has the function as

  In addition, the shape of the partition plates 19a and 19b is not limited to a mountain-valley shape. For example, a corrugated shape or an uneven shape may be used. That is, if the shape of the partition plates 19a and 19b is a straight line, it is unsuitable because the resonance effect is attenuated in a high frequency band where the straightness is strong. Any shape can be used as long as resonance of sound waves can be expected. Further, the vertical shape of the resonator composed of the partition plates 19a and 19b may be a polygonal shape as shown in FIG. 4 (a), or a rectangular shape as shown in FIG. 4 (b). It may be. Alternatively, the resonator may have a cylindrical shape (circular or elliptical).

  The shape of the sound hole 20 can be a circular shape or a rectangular shape. Furthermore, the number of sound holes 20 provided in the partition plates 19a and 19b can be arbitrarily set. Furthermore, it is desirable that the opening area of each sound hole 20 on the side facing the piezoelectric elements 17a and 17b is a ratio of 10% to 30% of the radiation area of the piezoelectric elements 17a and 17b. We know by examination.

FIG. 5 is a graph showing frequency characteristics of sound pressure levels of the piezoelectric electroacoustic transducer 10 according to the first embodiment and the piezoelectric electroacoustic transducer according to the comparative example. In addition, the graph shown in FIG. 5 is an experimental result under the following conditions.
The piezoelectric ceramics 201a and 201b are mainly made of lead zirconate titanate (PZT) and have a diameter of 10 mm and a thickness of 0.1 mm.
The plate-like members 15a and 15b are mainly made of phosphor bronze and have a diameter of 12 mm and a thickness of 0.03 mm.
The elastic members 16a and 16b are made of polyethylene terephthalate (PET) as a main material and have a diameter of 17 mm and a cut-out diameter of 11 mm.
The frame 11 is mainly made of stainless steel and has a diameter of 17 mm and a cutout diameter of 15 mm.
The distance between the piezoelectric elements 17a and 17b is 1.5 mm.
The sound hole 20 has a rectangular shape of 3 × 8 mm.

  Here, the piezoelectric electroacoustic transducer 10 according to the first embodiment and the piezoelectric electroacoustic transducer according to the comparative example are different in that they do not include the partition plates 19a and 19b (see FIG. 6). In FIG. 6, the same components as those in FIG. 3 are denoted by the same reference numerals, and the description thereof is omitted.

  Referring to FIG. 5, it can be confirmed that the sound pressure level is generally higher in the first embodiment. In the piezoelectric electroacoustic transducer 10 according to the first embodiment, the back surfaces of the piezoelectric elements 17a and 17b and the interference space formed by the partition plates 19a and 19b are shielded, so that the piezoelectric actuators 18a and 18b Canceling between generated sound waves can be avoided. That is, since the sound wave having the opposite phase to the sound wave radiated to the sealed space does not enter the interference space, the radiation efficiency of the sound wave radiated from the sound hole 12 is increased.

  Moreover, the frequency which a sound wave resonates can be easily controlled by selecting suitably the specification and installation form of the partition plates 19a and 19b according to a use. For example, the frequency at which the sound wave resonates can be controlled by changing the internal volume of the interference space and the distance between the partition plates 19a and 19b. Alternatively, the resonance frequency of the piezoelectric actuators 18a and 18b can be set to be different from each other to control the frequency to resonate in the interference space. As a result, sound pressure in a low frequency band that is difficult to reproduce with one piezoelectric actuator can be complemented, and good sound quality can be obtained.

  The piezoelectric electroacoustic transducer 10 according to the present embodiment is suitably applied to devices such as mobile terminals. For example, mobile phones, smartphones, game machines, tablet PCs (Personal Computers), notebook PCs, PDAs (Personal Data). Assistants (portable information terminals), digital cameras, and the like. When the piezoelectric electroacoustic transducer 10 is mounted on an electronic device, the frame 11 may be attached to the frame of the electronic device, or the frame 11 of the piezoelectric electroacoustic transducer 10 and the frame of the electronic device may be integrated. Good.

  As described above, in the piezoelectric electroacoustic transducer 10 according to the present embodiment, high efficiency of the speaker can be realized by amplification of the sound pressure level by the resonance structure provided inside. Furthermore, by controlling the shape of the resonator composed of the partition plates 19a and 19b, the sound pressure level at a specific frequency can be complemented, and a flat sound pressure frequency characteristic can be realized.

  A part or all of the above embodiments can be described as in the following supplementary notes, but is not limited thereto.

[Appendix 1]
This is the same as the piezoelectric electroacoustic transducer according to the first aspect described above.
[Appendix 2]
The resonating unit includes a trough shape in a direction parallel to the acoustic radiation surface of each of the first and second piezoelectric actuators, and the second sound hole is formed in a crest portion of the trough shape. Piezoelectric electroacoustic transducer.
[Appendix 3]
The resonance part is disposed so as to partition a space formed by the acoustic radiation surfaces of the first and second piezoelectric actuators, and emits a first sound wave radiated from the acoustic radiation surface of the first piezoelectric actuator. A second sound wave input from the second sound hole disposed on the first piezoelectric actuator side and radiated from an acoustic radiation surface of the second piezoelectric actuator is converted into the second piezoelectric actuator. The piezoelectric electroacoustic transducer according to appendix 1 or 2, wherein the piezoelectric electroacoustic transducer is input from the second sound hole disposed on the side of the first electrode and resonates the first and second sound waves.
[Appendix 4]
The piezoelectric electroacoustic transducer according to any one of appendices 1 to 3, wherein the first and second piezoelectric actuators have different resonance frequencies.
[Appendix 5]
This is the same as the electronic apparatus according to the second aspect described above.

  Each disclosure of the cited patent documents and the like cited above 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. 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, Selection 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. In particular, with respect to the numerical ranges described in this document, any numerical value or small range included in the range should be construed as being specifically described even if there is no specific description.

10, 100 Piezoelectric electroacoustic transducer 11, 11a-11c Frame 12, 20 Sound holes 13a, 13b Lead wires 14a-14d Terminals 15a, 15b, 106a, 106b Plate members 16a, 16b Elastic members 17a, 17b, 105a, 105b Piezoelectric elements 18a, 18b, 101, 102 Piezoelectric actuators 19a, 19b Partition plate 103 Support body 104 Resonance parts 201a, 201b Piezoelectric ceramics 202a-202d Electrodes 301a, 301b, 302a, 302b Acoustic radiation surface (vibrator main surface)

Claims (5)

First and second piezoelectric actuators including a piezoelectric element that vibrates when an electrical signal is applied thereto, and a plate-like member that restrains the piezoelectric element;
The acoustic radiation surfaces of the first and second piezoelectric actuators support the first and second piezoelectric actuators so as to face each other, and the acoustic radiation surfaces of the first and second piezoelectric actuators are opposed to each other. A support having a first sound hole in a parallel direction;
A resonance unit including a plurality of second sound holes that are disposed between the acoustic emission surfaces of the first and second piezoelectric actuators and that input sound waves emitted by the first and second piezoelectric actuators;
With
The piezoelectric elements included in the first and second piezoelectric actuators are disposed so as to be surrounded by the plate-like members included in the first and second piezoelectric actuators and the support, and Piezoelectric electroacoustic transducer that emits sound waves from sound holes.   2. The resonance portion has a mountain-valley shape in a direction parallel to an acoustic radiation surface of each of the first and second piezoelectric actuators, and the second sound hole is formed in a mountain portion of the mountain-valley shape. Piezoelectric electroacoustic transducer.   The resonance part is disposed so as to partition a space formed by the acoustic radiation surfaces of the first and second piezoelectric actuators, and emits a first sound wave radiated from the acoustic radiation surface of the first piezoelectric actuator. A second sound wave input from the second sound hole disposed on the first piezoelectric actuator side and radiated from an acoustic radiation surface of the second piezoelectric actuator is converted into the second piezoelectric actuator. 3. The piezoelectric electroacoustic transducer according to claim 1, wherein the piezoelectric electroacoustic transducer is input from the second sound hole disposed on the side of the first electrode and resonates the first and second sound waves.   The piezoelectric electroacoustic transducer according to any one of claims 1 to 3, wherein resonance frequencies of the first and second piezoelectric actuators are different from each other.   An electronic device comprising the piezoelectric electroacoustic transducer according to any one of claims 1 to 4.

Images