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DESCRIPTION JPH099393

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DESCRIPTION JPH099393
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
piezoelectric acoustic device which uses a piezoelectric element and is used as an acoustic device
such as a receiver of a telephone or other communication device.
[0002]
2. Description of the Related Art A conventional piezoelectric acoustic device accommodates a
piezoelectric element in a tray-like case having a step-like piezoelectric element support at an
intermediate portion on the inner peripheral side, and supports the piezoelectric element at the
periphery of the diaphragm. It is placed on the part and fixed with an adhesive. In the
piezoelectric element, a piezoelectric film having an electrode on the surface is formed on the
surface of the diaphragm, and lead wires are respectively connected to the electrode on the
piezoelectric film and the diaphragm, and the lead wire is drawn out from the case to the outside.
It is done.
[0003]
Nowadays, miniaturization of home telephones called mobile phones and so-called cordless
phones is in progress, and along with this, there is an increasing demand for miniaturization of
the above-mentioned piezoelectric acoustic devices used as a receiver. In the conventional
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piezoelectric acoustic device as described above, the diameter of the diaphragm is at least 27φ,
specifically about 32φ, but nowadays, the diameter of the diaphragm is at most 20φ.
[0004]
However, when the thickness of the diaphragm is kept as it is and the diameter thereof is
reduced, the frequency characteristic is shifted to the high frequency side and the sound
pressure on the low frequency side is lowered. Therefore, high sound pressure can not be
obtained in the frequency band of 0.5 kHz or less in the conventional piezoelectric acoustic
device having the above-described structure, in which the diameter of the diaphragm is 20φ or
less. A receiver using a piezoelectric acoustic device having such frequency-sound pressure
characteristics has the disadvantage that only high noises and kinks are emphasized, resulting in
unnatural and difficult to hear reproduced sound.
[0005]
On the other hand, in order to improve such acoustic characteristics and obtain acoustic
characteristics equivalent to those of a piezoelectric acoustic device using a small diameter
piezoelectric element and a diaphragm having a relatively large diameter, the reduction of the
diameter of the piezoelectric element is necessary. It is necessary to reduce the overall thickness.
However, in order to reduce the thickness of the piezoelectric element as a whole, it is necessary
to reduce the thickness of both the piezoelectric ceramic and the diaphragm, which results in a
decrease in the strength of the piezoelectric element. That is, since a problem such as breakage is
likely to occur due to the reduction in strength, the yield is naturally reduced, and the thinning is
naturally limited. In view of the above-described conventional problems, the present invention
provides a resonance frequency equivalent to that using a piezoelectric element having a
relatively large diameter even with a small-sized piezoelectric acoustic device using a
piezoelectric element having a small diameter. It is an object of the present invention to provide a
piezoelectric acoustic device that emits various reproduced sounds.
[0006]
According to the present invention, in order to achieve the above object, the entire peripheral
portion of the diaphragm 21 of the piezoelectric element 2 is not directly supported by the inner
peripheral surface of the case 1, A structure was employed in which the peripheral portion of the
diaphragm 21 was supported at several places on the inner peripheral surface, and the gap
between the peripheral portion of the diaphragm 21 and the inner peripheral surface of the case
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1 was closed with an elastic adhesive 14.
[0007]
That is, the piezoelectric acoustic device according to the present invention comprises a case 1
and a piezoelectric element 2 housed in the case 1 and having a peripheral portion supported at
the middle portion of the inner peripheral surface thereof, and the circumferential direction of
the case 1 Support the periphery of the piezoelectric element 2 by a plurality of support
protrusions 15, 15 ... provided on the inner periphery thereof at an interval, and the space
between the periphery of the piezoelectric element 2 and the inner periphery of the case 1 is
elastic. It is characterized in that it is closed by an adhesive 14.
Furthermore, the tips of the plurality of projections 13, 13 ... provided on the inner
circumferential surface of the case 1 at intervals in the circumferential direction are
circumscribed around the piezoelectric element 2, whereby the case of the piezoelectric element
2 is Regulate radial movement with respect to 1.
[0008]
On the other hand, instead of providing the projections 13, 13 ... on the inner peripheral surface
side of the case 1, a plurality of projections 17, 17 ... are provided on the periphery of the
piezoelectric element 2 at intervals in the circumferential direction. It can be set as the structure
which supports the peripheral part of the piezoelectric element 2 by 17 .... In this case, the tips of
the plurality of projections 17 provided at the periphery of the piezoelectric element 2 at
intervals in the circumferential direction are inscribed in the inner peripheral surface of the case
1, and the projections 17 are piezoelectric. The radial movement of the element 2 with respect to
the case 1 is restricted. Further, a step 12 for holding the elastic adhesive 14 is provided on the
inner peripheral surface of the case 1, and the elastic adhesive 14 is fixed at a predetermined
position on the inner peripheral surface of the case 1.
[0009]
[Functions] As a structure for incorporating the piezoelectric element 2 into the case 1, there is a
so-called peripheral fixing method in which the peripheral part of the piezoelectric element is
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completely fixed, and a so-called supporting method without fixing the peripheral part of the
piezoelectric element There is a peripheral support system. The former fixes the peripheral
portion of the diaphragm 21 of the piezoelectric element 2 to completely suppress the vibration,
and means that the peripheral portion of the fixed diaphragm 21 is not inclined. The latter only
suppresses the free movement only in the thickness direction and the planar direction of the
peripheral portion of the diaphragm 21 of the piezoelectric element, and does not suppress the
vibration of the peripheral portion, and means that the inclination thereof is permitted.
[0010]
Here, the resonance frequency when the piezoelectric element 2 is incorporated in the case 1
with the peripheral portion of the diaphragm 21 fixed or supported is generally calculated by the
following equation. where ω 1 is the primary resonance frequency, α 1 is the reference constant
of the primary resonance, h is the thickness of the diaphragm, Y is the elastic coefficient of the
diaphragm, a Is the radius of the diaphragm, ρ is the density of the diaphragm, and σ is the
Poisson's ratio. In this resonance frequency equation, the reference constant α1 of the primary
resonance is about twice that in the case of the peripheral support as in the case of the
peripheral fixing. That is, when the diaphragm 21 of the piezoelectric element 2 is peripherally
supported, the same resonance frequency can be obtained with the diameter of the diaphragm
21 of approximately 70% in the case of peripheral fixing.
[0011]
As described above, in the present invention, without directly supporting the entire peripheral
portion of the diaphragm 21 of the piezoelectric element 2 by the inner peripheral surface of the
case 1, the peripheral portion of the diaphragm 21 at several places on the inner peripheral
surface of the case 1 The peripheral portion of the diaphragm 21 of the piezoelectric element 2
is ideal because it adopts a structure in which the elastic adhesive 14 closes the gap between the
peripheral portion of the diaphragm 21 and the inner peripheral surface of the case 1. Close to
supporting the That is, since the vibration of the peripheral part of the diaphragm 21 is not
suppressed but its inclination is allowed, the state is almost the same as the peripheral support.
As a result, even if the small piezoelectric element 2 having the diaphragm 21 with a small
diameter is used, a resonance frequency equivalent to the conventional one can be obtained.
[0012]
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings,
the embodiments of the present invention will be described in detail and specifically. 1 to 4 show
an embodiment in which the present invention is applied to a piezoelectric sounder. Here, the
case 1 is formed of a resin or the like in a tray shape having an open upper surface side, and a
sound release hole 11 consisting of a plurality of small holes is opened at the center of the
bottom surface. A lead wire lead-out groove 4 is provided in a part of the peripheral wall 5 of the
case 1.
[0013]
At the middle portion in the height direction of the inner surface of the peripheral wall 5 of the
case 1, the stepped portion 12 is formed along the entire circumference except the portion of the
lead wire lead-out groove 4. Support protrusions 15, 15... Are protruded in the central direction
of the case 1. Furthermore, a plurality of projections 13, 13... For centering of the piezoelectric
element project from the inner surface of the peripheral wall 5 on the step 12. In the illustrated
embodiment, the projections 13, 13... And the support projections 15, 15... Are provided on the
inner surface of the peripheral wall 5 of the case 1 at intervals of 90.degree.
[0014]
As shown in FIG. 1, the piezoelectric element 2 has a piezoelectric film 22 having electrode layers
on both main surfaces of a piezoelectric ceramic, fixed on a metal diaphragm 21, and is formed
on the diaphragm 21 and the piezoelectric film 22. The lead wires 3 are soldered to the
electrodes of FIG. Here, the diameter of the vibration plate 21 of the piezoelectric element 2 is
substantially the same as the inner diameter of the step 12, and is slightly smaller than the tip
interval of the opposing projections 13, 13. Ideally, it should be slightly larger than the tip
interval of ....
[0015]
As shown in FIG. 3 and FIG. 4, an elastic adhesive 14 such as a silicone adhesive is uniformly
applied in advance along the step 12 on the inner peripheral side of the peripheral wall 5 of the
case 1. The elastic adhesive 14 is held by the shoulder 12 and does not drop off. Next, the
piezoelectric element 2 is housed inside the case 1, and the peripheral portion of the diaphragm
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21 of the piezoelectric element 2 is embedded in the elastic adhesive 14. At this time, as shown
in FIG. 3, the piezoelectric elements 2 are centered on the center of the case 1 by the tips of the
projections 13, 13... And the radial movement of the diaphragm 21 is restricted. As a result, the
piezoelectric elements 2 are accommodated in the case 1 so that their centers coincide with each
other. Further, as shown in FIG. 4, the peripheral portion of the diaphragm 21 is placed on the
support protrusions 15, 15... With the elastic adhesive 14 interposed. The lead wire 3 is led out
of the lead wire drawing groove 4 of the case 1 to the outside of the case 1. 3 shows the cross
section of the portion A in FIG. 2 of the case 1, and FIG. 4 shows the cross section of the portion
B in FIG.
[0016]
In such a supporting structure of the piezoelectric element 2, the peripheral portion of the
diaphragm 21 is not fixed to the peripheral wall 5 of the case 1, and the projections 13, 13 ... and
the supporting projections 15, 15 ... via the elastic adhesive 14. The support structure is
supported by several points. For this reason, the vibration of the peripheral part of the
diaphragm 21 is not suppressed, and a state close to a so-called ideal peripheral support system
is obtained. As a result, the desired resonance frequency can be obtained even with the
diaphragm 21 having a small diameter.
[0017]
FIG. 5 shows acoustic characteristics of a piezoelectric acoustic device according to an
embodiment of the present invention and a comparative example thereof. The solid line uses a
piezoelectric element 2 in which a piezoelectric film 22 made of PZT piezoelectric ceramic with a
diameter of 12 mm and a thickness of 0.05 mm having electrodes on both sides is attached to a
diaphragm 21 of 15 mm in diameter. The frequency-sound pressure level of the piezoelectric
receiver attached to case 1 as shown is shown. The frequency-sound pressure level was
measured using an IEC-318 coupler, with the piezo receiver attached to an acoustically optimized
earpiece. Further, as a comparative example, a piezoelectric element 2 in which a piezoelectric
film made of PZT piezoelectric ceramic with a diameter of 15 mm and a thickness of 0.05 mm
having electrodes on both sides is attached to a diaphragm of 20 mm in diameter as a
comparative example The frequency-sound pressure level of the piezoelectric receiver attached
to the case by a fixed method is shown. As is clear from this result, although there is a difference
in sound pressure level between the piezoelectric receiver according to the embodiment of the
present invention and the piezoelectric receiver according to the comparative example, the
frequency bands at which high sound pressure levels can be obtained are almost the same. I
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understand that there is.
[0018]
FIG. 7 shows a case 1 of a piezoelectric acoustic device according to another embodiment of the
present invention. In the embodiment described above, the projections 13, 13 ... and the support
projections 15, 15 ... are shifted by 45 °, but in this embodiment, the projections 13, 13 ... and
the support projections 15, 15 ... All are provided at the same position at the same interval of 90
° inside the peripheral wall 5. Furthermore, in the case 1 of the piezoelectric acoustic device
according to this embodiment, two mounting brackets 16 are formed radially from the lower
outer peripheral portion of the peripheral wall 5. The piezoelectric acoustic device completed
with the piezoelectric element (not shown in FIG. 7) mounted in the case 1 is attached to the
device by the screw holes provided in the mounting brackets 16, 16. To use. Since the
projections 13, 13 ... and the support projections 15, 15 ... are provided at the same position,
there is an advantage that the application work of the elastic adhesive 14 to the step 12 can be
continuously performed by a dispenser or the like.
[0019]
FIG. 8 shows an example of another shape of the step 12 of the case 1 of the piezoelectric
acoustic device. In the embodiment described above, the stepped portion 12 is composed of a
wall surface rising from the bottom surface on the inner surface of the peripheral wall 5 of the
case 1 and a circumferential surface orthogonal to the wall surface. As already mentioned, this
step 12 is for holding the elastic adhesive 14 in a predetermined position, and in the case 1
shown in this FIG. The portion 12 is formed. Such a step 12 is effective to increase the surface
area of the inner surface of the peripheral wall 5 of the case 1 and to hold and fix the elastic
adhesive 14 having a certain degree of viscosity in that portion.
[0020]
FIG. 9 shows an example of the shape of the projections 13 of the case 1 of the piezoelectric
acoustic device. (A) shows an example in which rectangular projections 13 are provided, (b)
shows an example in which triangular projections 13 are provided, and (c) shows a trapezoidal
shape. An example in which the chevrons 13, 13... Of chevrons are provided, and an example in
which the semicircular chevrons 13, 13. The protrusions 13, 13... Preferably have a tip shape
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such that the contact area is as small as possible even if the tips contact the periphery of the
diaphragm 21. As shown in FIG. Therefore, among the parts shown in FIGS. 9 (a) to 9 (d), when
the projections 13, 13.. Therefore, the contact area is small and can be said to be the most
preferable. Such projections are provided at three or more places at equal intervals as possible
along the peripheral wall of the case 1, but if the number is large, the force for restraining the
peripheral part of the diaphragm 21 becomes strong, so six places are provided. The following is
good.
[0021]
10 to 12 show a piezoelectric acoustic device according to another embodiment of the present
invention. In the embodiment described above, the plurality of projections 13, 13 ... for
supporting the piezoelectric element centering and the support projections 15/15 ... are
projected from the inner surface of the peripheral wall 5 of the case 1 as shown in Figs. In the
embodiment, only the step portion 12 is provided on the inner surface of the peripheral wall 5 of
the case 1, and the projections 13, 13 ... and the support projections 15, 15 ... are not provided
there. Instead, protrusions 17, 17... Are provided radially from the periphery of the diaphragm
21 of the piezoelectric element 2. In the illustrated embodiment, four projections 17, 17... Are
projected from the periphery of the diaphragm 21 at intervals of 90 °.
[0022]
Here, the diameter of the peripheral portion of the diaphragm 21 of the piezoelectric element 2,
that is, the diameter of the portion excluding the projections 17, 17... Is substantially equal to or
slightly smaller than the inner diameter of the step 12. Moreover, the distance between the tips
of the opposing projections 17 is slightly smaller than the inner diameter of the peripheral wall 5
of the case 1 and slightly larger than the inner diameter of the step 12. Therefore, as shown in
FIG. 11 and FIG. 12, when the piezoelectric element 2 is housed inside the case 1 and the
projections 17, 17... Are mounted on the step 12, the portions of the projections 17, 17. Are
supported from below by the step 12, and the piezoelectric elements 2 are centered on the
center of the case 1 by their projections 17, 17... And their radial movement is restricted. Also in
this embodiment, the elastic adhesive 14 is uniformly applied in advance to the step 12 of the
case 1, and the projections 17, 17... It is similar to the previous embodiment.
[0023]
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In the supporting structure of such a piezoelectric element 2, the peripheral portion of the
diaphragm 21 is not fixed to the peripheral wall 5 of the case 1, and the projections 17, 17... Are
supported by the step 12 via the elastic adhesive 14. Support structure. For this reason, the
vibration of the peripheral part of the diaphragm 21 is not suppressed, and a state close to a socalled ideal peripheral support system is obtained. As a result, the desired resonance frequency
can be obtained even with the diaphragm 21 having a small diameter.
[0024]
The present invention is not limited to the embodiments described above. For example, the sound
output holes 11 have a large number of small holes, but have no sound output holes, or have one
relatively large sound output hole, or have a mesh attached to the sound output holes. Etc. can be
illustrated. Furthermore, in place of the lead wire drawing groove 4, a hole for lead wire drawing
may be provided, or one in which the lead wire 3 is drawn from the opening of the case 1
without providing such a groove or hole may be exemplified. .
[0025]
As described above, according to the present invention, even if a piezoelectric element having a
small diameter is used, a resonance frequency equivalent to that of a piezoelectric acoustic device
using a piezoelectric element having a relatively large diameter can be obtained. The effect is that
a good voice can be obtained. As a result, it is possible to obtain an effect that a piezoelectric
acoustic device having small but excellent acoustic characteristics can be manufactured with high
yield.
[0026]
Brief description of the drawings
[0027]
1 is a perspective view of the case where the case and the piezoelectric element of the
piezoelectric acoustic device according to the embodiment of the present invention are
separated.
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[0028]
2 is a plan view showing the case of the piezoelectric acoustic device according to the same
embodiment.
[0029]
3 is a longitudinal sectional side view of an essential part of a portion A in FIG. 2 in a state where
the periphery of the diaphragm is supported by an elastic adhesive in the piezoelectric acoustic
device according to the same embodiment.
[0030]
4 is a longitudinal sectional side view of an essential part of a portion B in FIG. 2 in a state in
which the periphery of the diaphragm is supported by an elastic adhesive in the piezoelectric
acoustic device according to the same embodiment.
[0031]
5 is a graph showing the frequency-sound pressure characteristics of the piezoelectric acoustic
device according to the embodiment of the present invention and the comparative example.
[0032]
6 is a perspective view of the case where the case and the piezoelectric element of the
piezoelectric acoustic device according to another embodiment of the present invention are
separated.
[0033]
7 is a plan view showing the case of the piezoelectric acoustic device according to the same
embodiment.
[0034]
8 is a longitudinal sectional view of an essential part of the case with an elastic adhesive applied,
showing an example of another shape of the step of the peripheral wall of the case in the
piezoelectric acoustic device according to the embodiment of the present invention.
[0035]
9 is a plan view of an essential part of the case showing an example of another shape of the
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protrusion of the peripheral wall of the case in the piezoelectric acoustic device according to the
embodiment of the present invention.
[0036]
10 is a perspective view of the case where the case and the piezoelectric element of the
piezoelectric acoustic device according to another embodiment of the present invention are
separated.
[0037]
11 is a plan view showing a case of the piezoelectric acoustic device according to the same
embodiment.
[0038]
12 is a vertical cross-sectional side view of the main portion C-C line in FIG. 11 in a state where
the periphery of the diaphragm is supported by an elastic adhesive in the piezoelectric acoustic
device according to the same embodiment.
[0039]
Explanation of sign
[0040]
1 case 2 piezoelectric element 12 step 13 case projection 15 case support projection 14 elastic
adhesive 17 projection of piezoelectric element
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