JP2000134697A - Piezoelectric type electroacoustic transducer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a piezoelectric type electroacoustic transducer in which low frequency and wide band are attained with excellent acoustic efficiency. SOLUTION: Plural rectangular piezoelectric ceramic boards with different sizes, where driving electrodes 3a and 4a are formed on front surfaces, are joined with a rectangular metallic board 2 by facing. The metallic board 2 is housed in a case 10 and the part 2a of the metallic board 2 corresponding to the interstice part of the piezoelectric ceramic boards is restricted and supported by the support part 11 of the case 10. The peripheral edge part of the metallic board 2 is sealed by a sealing agent 15 so as to be displaced as against the case 10. A common frequency signal is inputted between the driving electrodes 3a and 4a and the metallic board 2. Then the metallic board 2 is bent and vibrated with the support part 11 as a fulcrum, a sound pressure peak is obtained at plural resonance frequencies and wide band is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a piezoelectric electro-acoustic transducer such as a piezoelectric buzzer, a speaker and a piezoelectric receiver.

[0002]

2. Description of the Related Art Conventionally, a piezoelectric electroacoustic transducer has been widely used as a piezoelectric receiver in a portable telephone or the like. This type of piezoelectric electroacoustic transducer is disclosed in, for example,
As described in JP-A-107593 and JP-A-7-203590, a unimorph diaphragm is formed by attaching a circular metal plate to a single-sided electrode of a circular piezoelectric ceramic plate, and forming a peripheral portion of the diaphragm. Support in a circular case,
In general, the case has a structure in which the opening of the case is closed with a cover.

[0003]

However, in the case of the conventional piezoelectric electro-acoustic transducer, a pair of drive electrodes on the front and back are interposed between the piezoelectric ceramic plates so that one diaphragm has one resonance frequency. It has a formed structure. When such a diaphragm is incorporated in a case, one sound pressure peak is obtained at the resonance frequency, but the sound pressure sharply drops before and after that frequency, so that a narrow band is obtained at a predetermined sound pressure level.

In recent years, a piezoelectric electroacoustic transducer capable of obtaining a predetermined sound pressure level in a wide band has been demanded.
In order to satisfy such demands, there has been proposed a piezoelectric electro-acoustic transducer in which a case constituting a resonance chamber is formed by a conductive thin plate, and a piezoelectric ceramic plate is bonded to two opposing surfaces of the case (Japanese Utility Model). No. 6-29300). In this case, two disc-shaped piezoelectric ceramic plates are used, a lead wire is commonly connected to the drive electrodes, and the other lead wire is connected to the case, and a frequency signal is applied between these lead wires. The application causes the respective piezoelectric ceramic plates to expand and contract in the opposite direction, and the expansion and contraction causes the entire case to bend and vibrate to generate sound.

[0005] In the case of this piezoelectric electroacoustic transducer, the whole inside of the case is a resonance chamber, so that there is an advantage that a broader band to a lower frequency side can be achieved. However, since the two piezoelectric ceramic plates resonate at the same frequency, a high sound pressure peak can be obtained at the resonance point, but a high sound pressure level cannot be obtained over a wide band. In addition, since the entire periphery of the case, which is a diaphragm, is constrained, the vibration frequency increases, and there is a limit to widening the band to the lower frequency side. further,
Since the disk-shaped piezoelectric ceramic plate is used, the maximum displacement point is only the center point, and the displacement volume is small. Since this displacement volume becomes energy for moving air, it has been difficult to increase the sound conversion efficiency.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a piezoelectric electro-acoustic transducer which achieves a lower frequency and a wider band and which has excellent acoustic conversion efficiency.

[0007]

In order to achieve the above-mentioned object, the invention according to claim 1 includes one rectangular metal plate,
A plurality of rectangular piezoelectric ceramic plates of different dimensions, each of which is joined to the metal plate face-to-face and has a drive electrode formed on the surface thereof, and a portion of the metal plate that accommodates the metal plate and corresponds to a valley portion of the piezoelectric ceramic plate. A case having a support portion for restraining and supporting, and a sealant for sealing the peripheral portion of the metal plate so as to be displaceable with respect to the case, wherein a common frequency signal is provided between each drive electrode and the metal plate. According to the present invention, there is provided a piezoelectric electro-acoustic transducer characterized in that the metal plate is caused to flexurally vibrate around the support portion as a fulcrum to obtain sound pressure peaks at a plurality of resonance frequencies.

When a plurality of piezoelectric ceramic plates are joined to a common metal plate and a common frequency signal is input between each drive electrode and the metal plate, the piezoelectric ceramic plate expands and contracts in the length direction.
In response to this, the metal plate generates bending vibration and emits sound. At this time, the portion of the metal plate corresponding to the valley portion of the piezoelectric ceramic plate is restrained by the supporting portion of the case, and the peripheral portion of the metal plate is freely supported by the sealant. The vibration frequency can be reduced as compared with the case where both ends are supported and the periphery is fixed.
Part of metal plate (vibration part) where each piezoelectric ceramic plate is joined
Vibrate at the same time, but since the valley between each vibrating part is restrained by the support part, each vibrating part is separated and the vibration of one vibrating part propagates to the other vibrating part via the metal plate. Can be prevented. Since each vibrating section is constituted by drive electrodes having different dimensions, the resonance frequency of each vibrating section is different. By making these resonance frequencies close to each other, a piezoelectric electroacoustic transducer having a high sound pressure level in a wide band can be obtained.

The resonance frequency of each vibrating part depends on the shape of the piezoelectric ceramic plate. Since the piezoelectric ceramic plate has a rectangular shape, an arbitrary resonance frequency can be easily obtained by changing the length or width. Also, in a conventional disk-shaped diaphragm, the maximum displacement point is only the center point, so the displacement volume is small, but in the case of a rectangular diaphragm, the maximum displacement point is in the length direction or width direction. , The displacement volume is large. Since this displacement volume becomes energy for moving air, a rectangular piezoelectric ceramic plate can increase the sound conversion efficiency as compared with a circular piezoelectric ceramic plate.

When the periphery of the metal plate is sealed to the case, a front air chamber and a rear air chamber, which are acoustic spaces, are formed on both sides of the metal plate. In particular, if the front air chamber having the sound emission hole is a common room, the volume of the front air chamber can be increased, and the resonance frequency can be reduced. For this reason, in addition to the sound pressure peak due to the resonance frequency of each vibrating part, a sound pressure peak due to the resonance frequency appears on the lower frequency side, and a wider band can be achieved.

In order to further increase the bandwidth, it is desirable to join three or more piezoelectric ceramic plates to the metal plate. In this case, a plurality of rectangular piezoelectric ceramic plates having different dimensions are joined to at least one side of the metal plate with the support portion interposed between the support portions, and the support portions correspond to the valley portions of these piezoelectric ceramic plates. It is desirable to form a slit in a direction orthogonal to the support portion at a portion of the metal plate to be formed, and bury a sealant made of a rubber elastic material in the slit.

In this case, by providing a slit in the metal plate, the propagation of vibration between adjacent vibrating parts can be prevented. When the slit is left open, the front air chamber and the rear air chamber formed on both sides of the metal plate communicate with each other and can not produce sound, so the slit is sealed with a sealant such as a rubber elastic material that does not hinder vibration. By doing so, the front air chamber and the rear air chamber are shielded while preventing vibration propagation.

According to a third aspect of the present invention, there is provided a rectangular piezoelectric ceramic plate having one rectangular metal plate and two rectangular drive electrodes having different dimensions formed on the surface and joined to the metal plate. And a case that accommodates the metal plate and has a support portion that restrains and supports a portion of the metal plate corresponding to the gap between the drive electrodes, and a seal that displaceably seals a peripheral edge of the metal plate with respect to the case. By providing a common frequency signal between each of the drive electrodes and the metal plate, the metal plate is bent and vibrated with the support portion as a fulcrum, and sound pressure peaks are obtained at a plurality of resonance frequencies. A piezoelectric electro-acoustic transducer characterized by the above is provided.

According to the present invention, a piezoelectric ceramic plate having a plurality of drive electrodes formed thereon is joined to one metal plate. The back side electrode of the piezoelectric ceramic plate may be one common electrode. Also in this case, similarly to the first aspect of the invention, the metal plate corresponding to the valleys of the plurality of drive electrodes is restrained and supported by the support of the case, so that the metal plate is cantilevered by the support. Thus, the vibration frequency can be reduced. Since each vibrating section is constituted by drive electrodes having different dimensions, the resonance frequency of each vibrating section is different. By bringing these resonance frequencies closer to each other, a piezoelectric electroacoustic transducer having a high sound pressure level over a wide band can be obtained.

[0015]

1 to 6 show a piezoelectric receiver according to a first embodiment of the piezoelectric electro-acoustic transducer according to the present invention. This piezoelectric receiver is generally a unimorph diaphragm 1
And a case 10 and a cover 20. The case 10 and the cover 20 constitute the case of the present invention.

The diaphragm 1 includes a rectangular metal plate 2 and a metal plate 2.
It is composed of two rectangular piezoelectric ceramic plates 3 and 4 electrically and mechanically joined face to face. Metal plate 2
For example, a material having both good conductivity and spring elasticity, such as phosphor bronze or 42Ni, is used. Metal plate 2 is 42Ni
In the case of (1), since the thermal expansion coefficient is close to that of ceramic (PZT or the like), a more reliable one can be obtained. The piezoelectric ceramic plates 3 and 4 are made of a piezoelectric ceramic such as PZT,
Electrodes 3a, 3b and electrodes 4a, 4b are formed on the front and back surfaces (see FIG. 4), and the back electrodes 3b, 4b are bonded to the surface of the metal plate 2 with a conductive adhesive (not shown). And are electrically conductive. The back electrodes 3b, 4b may be omitted by directly bonding the back surfaces of the piezoelectric ceramic plates 3, 4 to the metal plate 2 with a conductive adhesive.

The lengths x ₁ and x of the piezoelectric ceramic plates 3 and 4
₂ , at least one of the widths y ₁ and y ₂ and the thicknesses t ₁ and t ₂ is set to be different. for that reason,
The resonance frequencies of the two piezoelectric ceramic plates 3 and 4 are different from each other. In this embodiment, the following settings are made. x ₁ > x ₂ y ₁ = y ₂ t ₁ = t ₂ By appropriately selecting the above dimensions, for example, the vibrating part composed of one piezoelectric ceramic plate 3 and the metal plate 2 has a resonance frequency of 2.880 kHz. And the vibrating portion composed of the other piezoelectric ceramic plate 4 and the metal plate 2 has 3.97.
It can be set to have a resonance frequency of 3 kHz.

The case 10 is integrally formed of resin, and has two recesses 12 and 13 separated by a support wall (support portion) 11 therein. Positioning protrusions 1 extending to the upper surface of case 10 are provided at both ends of support wall 11.
4 have a function of guiding both side edges of the diaphragm 1 with the inner surfaces of the projections 14. The diaphragm 1 is housed in the case 10 with a predetermined gap, and the gap between the peripheral edge of the diaphragm 1 and the inner surface of the case 10 is sealed by a rubber elastic sealing agent 15 such as silicone rubber. As a result, two rear air chambers 16,
17 (see FIG. 3) are formed. Since the sealant 15 has rubber elasticity, the sealant 15 does not restrict the peripheral edge of the diaphragm 1.
Free displacement is allowed. On the top surface of the support wall 11, an intermediate portion 2a of the metal plate 2 corresponding to the gap between the piezoelectric ceramic plates 3 and 4 is fixed by an adhesive 18. The adhesive 18 becomes a hard member after curing like an epoxy adhesive, and restrains and supports the intermediate portion 2 a of the metal plate 2. By constraining and supporting the intermediate portion 2a of the metal plate 2 as described above, the metal plate 2 has a cantilevered support structure having the intermediate portion 2a as a fixed point, and the metal plate 2 can greatly bend and vibrate. Further, since the central portion 2a is restrained, the two vibrating portions are separated from each other, which has an effect of preventing the vibration generated in one vibrating portion from spreading to the other vibrating portion. In addition, braking holes 19 are formed on both sides of the bottom of the case 10, and the rear air chambers 16, 17 are formed.
Is open to the open air.

The cover 20 is also made of the same resin material as the case 10, and has one sound emission hole 21 formed in the center of the ceiling. The peripheral portion of the cover 20 is fixed to the upper edge of the opening of the case 10 by a method such as adhesion or ultrasonic welding. Therefore, one front air chamber 22 (see FIG. 3) is formed between the cover 20 and the diaphragm 1.

A common lead wire 23 is connected to the surface electrodes (drive electrodes) 3a, 4a of the piezoelectric ceramic plates 3, 4, and a lead wire 24 is connected to the metal plate 2, and these lead wires 23, 24 It is led out of the case 10. By applying a rectangular wave signal or a sine wave signal between the lead wires 23 and 24, the two vibrating sections can be driven simultaneously. Note that lead terminals may be used instead of the leads 23 and 24 to connect the surface electrodes 3a and 4a of the piezoelectric ceramic plates 3 and 4 and the metal plate 2 to the outside.

The operation of the above-structured piezoelectric receiver will be described below. When, for example, a rectangular wave signal is applied between the lead wires 23 and 24 and its frequency is changed, the impedance changes as shown in FIG. 5 and the vibration constituted by one of the piezoelectric ceramic plates 3 at a predetermined frequency. The part resonates, and the vibrating part composed of the other piezoelectric ceramic plate 4 resonates at another frequency. At this time, the intermediate portion 2a of the metal plate 2 is fixed by the support wall 11, and the peripheral portion is supported so as to be displaceable.
In a so-called cantilever support state, the metal plate 2 vibrates in a mode indicated by a broken line in FIG. Therefore, the vibration frequency of each vibrating part can be reduced as compared with the case where both ends are supported and the surroundings are fixed.

FIG. 6 shows a change in sound pressure with a change in frequency. As shown in FIG. 6, two sound pressure peaks appear, one sound pressure peak P ₁ is a resonance point of the vibrating portion constituted by the piezoelectric ceramic plate 3, and the other sound pressure peak P ₂ is a piezoelectric ceramic plate 4. This is the resonance point of the vibrating section composed of Since the sound pressure level between the _two sound pressure peaks P ₁ and P ₂ is close to the two resonance frequencies, the sound can be sounded in a wide band without a sharp drop. In FIG. 6, a broken line indicates a sound pressure peak due to resonance of the front air chamber 22. The sound pressure peak P3 by the resonance for generating from the sound pressure peak P _1, P ₂ in the low frequency range, it is possible to further broaden as a whole.

FIG. 7 shows a sound pressure characteristic A of a piezoelectric receiver using a diaphragm to which a single rectangular piezoelectric ceramic plate is bonded, and FIG.
This is a comparison between the sound pressure characteristics B of a piezoelectric receiver using a diaphragm to which two rectangular piezoelectric ceramic plates are bonded. Note that a rectangular wave having a peak-to-peak voltage of 3 V was used as the driving voltage. The size of the piezoelectric ceramic plate of the characteristic A is 14 mm × 8.5 mm × 50 μm, and the size of the piezoelectric ceramic plate of the characteristic B is 7.5 mm × 8.5 mm × 70.
μm, and 5.5 mm × 8.5 mm × 70 μm. Both metal plates used were 14 mm × 8.5 mm × 50 μm square plates.

As is apparent from FIG. 7, the frequency band at a sound pressure 6 dB smaller than the sound pressure peak value is 0.959 kHz when one piezoelectric ceramic plate is used, whereas the frequency band at FIG. As described above, when two piezoelectric ceramic plates (resonance frequencies of 2.880 kHz and 3.973 kHz, respectively) are used, the frequency is 2.010 kHz, and the band can be broadened approximately twice. The sound pressure levels A and B are different because the measurement points are different and the thickness of the piezoelectric ceramic plate is different.

FIGS. 8 to 10 show a second embodiment of the present invention. In the vibration plate 30 of this embodiment, one rectangular piezoelectric ceramic plate 32 is face-to-face bonded to the upper surface of a rectangular metal plate 31, and two rectangular shapes having different dimensions are formed on the surface of the piezoelectric ceramic plate 32. Surface electrodes (drive electrodes) 33, 3
4 is formed. The piezoelectric ceramic plate 32
Is formed on almost the entire surface.

The intermediate portion 31 a of the metal plate 31 corresponding to the gap between the surface electrodes 33 and 34 is provided on the support wall 1 of the case 10.
1 is bonded and supported by a hard adhesive 18. The peripheral portion of the metal plate 31 is sealed on the inner surface of the case 10 with an elastic sealant 15.

In this embodiment, similarly to the first embodiment, a common lead wire 23 is connected to the surface electrodes 33 and 34, and a lead wire 24 is also connected to the metal plate 31. Is applied with a square wave signal or a sine wave signal. At this time, since the length dimensions x ₁ and x _{2 of} the surface electrodes 33 and 34 are different, they have two different resonance frequencies,
Broadband sound pressure levels can be obtained.

FIG. 11 shows a sound pressure characteristic A of a piezoelectric receiver using a vibration plate to which a single piezoelectric ceramic plate having one drive electrode is bonded, and FIG. This is a comparison between the sound pressure characteristics C of a piezoelectric receiver using a diaphragm to which two rectangular piezoelectric ceramic plates are bonded.
In addition, as the driving voltage, the voltage from peak to peak is 3
A rectangular wave of V was used. The size of the piezoelectric ceramic plate (electrode) of the characteristic A is 14 mm × 8.5 mm × 50 μm, and the size of the piezoelectric ceramic plate of the characteristic C is 14 mm × 8.
5mm × 70μm, electrode dimensions 7.5mm × 8.5mm
And 5.5 mm × 8.5 mm. Both metal plates are 1
A square plate of 4 mm × 8.5 mm × 50 μm was used.

As apparent from FIG. 11, the frequency band at the sound pressure 6 dB smaller than the sound pressure peak value is 0.959 kHz when one drive electrode is formed, whereas the frequency band at the sound pressure is 0.959 kHz when one drive electrode is formed. Electrode (resonance frequency is 3.72k each)
Hz and 5.23 kHz), 2.475 kHz
z, and the band could be expanded about 2.5 times. The sound pressure levels A and C are different because the measurement points are different and the thickness of the piezoelectric ceramic plate is different.

FIGS. 12 to 14 show a third embodiment of the present invention. The diaphragm 40 of this embodiment has three rectangular piezoelectric ceramic plates 42, 4 having different dimensions on the upper surface of a single metal plate 41.
3, 44 are joined face-to-face. The vibrating plate 40 is accommodated in the case 10, and the piezoelectric ceramic plates 42 and 4
Intermediate portion 41 of metal plate 41 corresponding to the gorge between 3 and 44
a is supported by the support wall 11 of the case 10 and the hard adhesive 1
8 for fixing. The gap between the peripheral edge of the metal plate 41 and the inner surface of the case 10 is filled with an elastic sealant 15 and sealed. A slit 41 b is formed in a portion of the metal plate 41 corresponding to the gap between the piezoelectric ceramic plates 43 and 44 in a direction orthogonal to the support wall 11. The elastic sealant 15 is also filled in the slit 41b,
The communication between the front air chamber 22 and the rear air chambers 16 and 17 is prevented through the opening.

Also in the case of this embodiment, by applying a common signal (square wave signal or sine wave signal) between the surface electrodes of the piezoelectric ceramic plates 42, 43, and 44 and the metal plate 41, each vibration The parts can be vibrated simultaneously. At this time, an intermediate portion 41a of the metal plate 41 corresponding to the gap between the piezoelectric ceramic plates 42, 43, and 44 is fixed to the support wall 11, and a portion between the piezoelectric ceramic plates 43 and 44 is blocked by the slit 41b. Therefore, each vibrating part can vibrate independently. The vibration mode is the same as that indicated by the broken line in FIG. Since a sound pressure peak is generated at the resonance point of each vibrating part, a high sound pressure level can be obtained in a wide band by making each resonance point close. In particular, since the metal plate 41 has the intermediate portion 41a fixed and the periphery thereof can be freely displaced, the metal plate 41 has a so-called cantilever support structure, and the vibration frequency can be reduced. As a result, lower frequency and wider band can be realized.

FIGS. 15 to 17 show a fourth embodiment of the present invention. The diaphragm 50 of this embodiment has four rectangular piezoelectric ceramic plates 52, 5 having different dimensions on the upper surface of a single metal plate 51.
3, 54 and 55 are joined face to face. An intermediate portion 51 a of the metal plate 51 corresponding to the gap between the piezoelectric ceramic plates 52, 53 and 54, 55 is supported by the support wall 11 of the case 10 and bonded and fixed by the hard adhesive 18. The gap between the peripheral portion of the metal plate 51 and the inner surface of the case 10 is filled with the elastic sealant 15 and sealed. Slits 51 b and 51 c are formed in the metal plate 51 at positions corresponding to the valleys between the piezoelectric ceramic plates 52 and 53 and between the valleys between 54 and 55 in a direction orthogonal to the support wall 11. The elastic sealant 15 is also filled in the slits 51b and 51c, and the front air chamber 22 and the rear air chamber 16,
17 are prevented from communicating with each other.

Also in this embodiment, by applying a common signal (rectangular wave signal or sine wave signal) between the surface electrodes of the piezoelectric ceramic plates 52 to 55 and the metal plate 51, each vibrating part is formed. Can be vibrated at the same time. An intermediate portion 51a of the metal plate 51 located in the gap between the piezoelectric ceramic plates 52, 53 and 54, 55 is fixed to the support wall 11,
Since the portions between the piezoelectric ceramic plates 52 and 53 and between the portions 54 and 55 are isolated by the slits 51b and 51c, each vibrating portion can vibrate independently. for that reason,
By generating a sound pressure peak at the resonance point of each vibrating part and bringing each resonance point close to each other, a high sound pressure level can be obtained in a wide band. In particular, since the intermediate portion 51a of the metal plate 51 is fixed and the peripheral portion can freely vibrate, a lower frequency can be realized.

The present invention is not limited to the above embodiment, and various changes can be made without departing from the spirit of the present invention. For example, in the embodiments of FIGS. 15 to 17, individual piezoelectric ceramic plates are bonded on both sides of the middle of the metal plate as a boundary, but as in the embodiments of FIGS. One piezoelectric ceramic plate may be bonded over the straddle. In the above embodiment, the piezoelectric ceramic plate is attached to the surface of the metal plate, but the piezoelectric ceramic plate may be attached to the back surface of the metal plate. That is, a metal plate may be disposed on the front air chamber side having the sound emission holes, and a piezoelectric ceramic plate may be disposed on the rear air chamber side. In the above embodiment, a unimorph type vibration plate in which a piezoelectric ceramic plate is attached to one surface of a metal plate has been described. However, a bimorph type vibration plate in which a piezoelectric ceramic plate is attached to both surfaces of a metal plate may be used. The piezoelectric electro-acoustic transducer of the present invention is applicable not only to a piezoelectric receiver but also to a piezoelectric buzzer and a piezoelectric speaker.

[0035]

As is apparent from the above description, claim 1
According to the invention described in (1), a plurality of piezoelectric ceramic plates are joined to a common metal plate, an intermediate portion of the metal plate is restrained and supported by a supporting portion of the case, and both ends of the metal plate are displaceable by a sealant. Since the metal plate is sealed, the metal plate has a cantilever support structure with the middle part as a fulcrum, and can realize a lower vibration frequency compared to the both-end support and peripheral fixed system, and the metal plate can greatly bend and vibrate, and acoustic conversion Efficiency can be increased.

Also, since the dimensions of the rectangular piezoelectric ceramic plates joined to both sides of the metal plate are changed, the resonance frequency of each diaphragm can be changed. Therefore, a plurality of sound pressure peaks can be easily obtained, and a broadband piezoelectric electroacoustic transducer can be obtained. Furthermore, since only one metal plate is stored in the case, the number of parts can be reduced, the cost can be reduced, and the case can be downsized, as compared with a case where a plurality of metal plates are stored.

According to the third aspect of the present invention, similarly to the first aspect of the invention, by providing a plurality of drive electrodes on the piezoelectric ceramic plate, each part can be vibrated individually, and a piezoelectric element having a low frequency and a wide band is provided. Type electroacoustic transducer can be obtained.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of a first embodiment of a piezoelectric electro-acoustic transducer according to the present invention.

FIG. 2 is a plan view of the piezoelectric electroacoustic transducer shown in FIG. 1 with a cover removed.

FIG. 3 is a cross-sectional view of the piezoelectric electro-acoustic transducer shown in FIG.

FIG. 4 is a plan view and a front view of a diaphragm used in the piezoelectric electroacoustic transducer shown in FIG.

FIG. 5 is an impedance characteristic of the piezoelectric electroacoustic transducer shown in FIG.

FIG. 6 shows sound pressure characteristics of the piezoelectric electroacoustic transducer shown in FIG.

7 is a comparison diagram of sound pressure characteristics between the piezoelectric electroacoustic transducer shown in FIG. 1 and a piezoelectric electroacoustic transducer using a single piezoelectric body.

FIG. 8 is a plan view of the piezoelectric electroacoustic transducer according to a second embodiment with a cover removed.

9 is a cross-sectional view of the piezoelectric electroacoustic transducer shown in FIG.

10A and 10B are a plan view and a front view of a diaphragm used in the piezoelectric electro-acoustic transducer shown in FIG.

11 is a comparison diagram of sound pressure characteristics between the piezoelectric electro-acoustic transducer shown in FIG. 8 and a piezoelectric electro-acoustic transducer using a piezoelectric body having a single electrode.

FIG. 12 is a plan view of a piezoelectric electro-acoustic transducer according to a third embodiment with a cover removed.

13 is a sectional view of the piezoelectric electroacoustic transducer shown in FIG.

14 is a plan view of a diaphragm used in the piezoelectric electroacoustic transducer shown in FIG.

FIG. 15 is a plan view of a piezoelectric electroacoustic transducer according to a fourth embodiment with a cover removed.

16 is a cross-sectional view of the piezoelectric electro-acoustic transducer shown in FIG.

17 is a plan view of a diaphragm used in the piezoelectric electroacoustic transducer shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vibration plate 2 Metal plate 3, 4 Piezoelectric ceramic plate 3a, 4a Surface electrode (drive electrode) 10 Case 11 Support wall (support part) 15 Sealant 16, 17 Rear air chamber 18 Adhesive 20 Cover 22 Front air chamber

Claims (3)

[Claims] 1. A rectangular metal plate, a plurality of rectangular piezoelectric ceramic plates, which are face-to-face bonded to the metal plate and have drive electrodes formed on their surfaces, and have different dimensions, and the metal plate are housed therein.
A case having a supporting portion for restraining and supporting a portion of the metal plate corresponding to the valley portion of the piezoelectric ceramic plate, and a sealant for displaceably sealing a peripheral portion of the metal plate with respect to the case; By inputting a common frequency signal between each drive electrode and the metal plate, the metal plate is bent and vibrated with the supporting portion as a fulcrum, and a sound pressure peak is obtained at a plurality of resonance frequencies. Piezoelectric electroacoustic transducer. 2. A plurality of rectangular piezoelectric ceramic plates having different dimensions are joined to at least one side of the metal plate with the supporting portion interposed therebetween, and a metal plate corresponding to a gap between the piezoelectric ceramic plates is provided. 2. A slit formed in a portion in a direction orthogonal to the support portion, and a sealant made of a rubber elastic material is embedded in the slit.
4. The piezoelectric electro-acoustic transducer according to 1. 3. A single rectangular metal plate, a rectangular piezoelectric ceramic plate having two rectangular drive electrodes of different dimensions formed on the surface and joined to the metal plate facing each other, and the metal plate accommodated therein. A case having a support portion for restraining and supporting a portion of the metal plate corresponding to the gap between the drive electrodes, and a sealant for displaceably sealing a peripheral portion of the metal plate with respect to the case,
By inputting a common frequency signal between each of the drive electrodes and the metal plate, the metal plate is caused to flexurally vibrate around the support portion to obtain sound pressure peaks at a plurality of resonance frequencies. And a piezoelectric electroacoustic transducer.