JPH114497

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DESCRIPTION JPH114497
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
piezoelectric receiver used as a handset of a voice communication terminal such as a portable
telephone.
[0002]
2. Description of the Related Art Piezoelectric receivers are extremely simple and robust in
structure, can be manufactured inexpensively, and their drive circuits are also simple in
structure, as compared with an electrodynamic receiver which in principle requires a coil and a
magnet. Therefore, it is widely used as a handset for voice communication terminals such as
mobile phones.
[0003]
FIG. 3 shows a typical structural example of a conventional piezoelectric receiver.
In FIG. 3, reference numeral 11 denotes a piezoelectric diaphragm in which a piezoelectric
element 11a having electrodes formed on both sides of the piezoelectric ceramic is adhered to a
metal plate 11b having a larger diameter than this; 12 has a predetermined volume; A circular
case made of resin held inside, a metal terminal 13 connected to the piezoelectric element 11a of
the piezoelectric diaphragm 11 and the metal plate 11b, and a back plate 14 made of resin to
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cover the case 12, the case 12 Together with the housing of the piezoelectric receiver. Reference
numeral 15 denotes a small hole for resonance damping provided in the back plate 14. A cloth is
attached to the small holes 15 as an acoustic resistance material. In some cases, a plurality of
thin tubes may be used instead of such forced braking small holes.
[0004]
The outer peripheral edge of the piezoelectric diaphragm 11 is fixed to the case 12 using an
adhesive such as silicon, and the metal terminal 13 for applying an AC voltage to the
piezoelectric element 11 a of the piezoelectric diaphragm 11 and the metal plate 11 b from the
outside. Are soldered, and then the metal terminal 13 is adhered to a predetermined portion of
the case 12. Then, the back plate 14 is pressed into the case 12 and fixed. Although not shown, a
sound emission hole is provided on the bottom of the case 12 for emitting a sound wave
generated by the vibration of the piezoelectric diaphragm 11 to the outside of the housing.
[0005]
As shown in FIGS. 4 and 5, the piezoelectric diaphragm 11 is bonded onto the shelf-shaped
piezoelectric diaphragm holding portion 12a provided on the inner side surface of the case 12
with the entire outer periphery of the metal plate 11b. It is fixed. FIG. 6 shows a vibration mode
when an AC voltage is applied to the piezoelectric vibration plate 11 to vibrate. The piezoelectric
diaphragm 11 vibrates as shown by a curve B by the expansion and contraction movement of the
piezoelectric ceramic by applying an alternating voltage to the piezoelectric ceramic 11a and the
metal plate 11b. The vibration of the piezoelectric diaphragm 11 is transmitted to the air to
generate a sound pressure. The magnitude of the output sound pressure of such a piezoelectric
receiver is proportional to the amount of air (volume exclusion amount) excluded by the
vibration of the piezoelectric diaphragm 11.
[0006]
However, in the above-described conventional piezoelectric receiver, since the entire periphery of
the outer peripheral edge of the metal plate 11b of the piezoelectric diaphragm 11 is bonded and
fixed to the piezoelectric diaphragm holding portion 12a of the case 12, As shown in FIG. 6, the
diameter of the effective portion of the piezoelectric diaphragm that actually vibrates becomes
smaller than the diameter of the piezoelectric diaphragm, and the portion close to the
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piezoelectric diaphragm holding portion 12a does not contribute to the generation of sound
pressure. There is a problem that the conversion efficiency to sound pressure is low. The present
invention solves such conventional problems, and an object of the present invention is to provide
a piezoelectric receiver having high conversion efficiency from an electrical signal to sound
pressure.
[0007]
In order to achieve the above object, in the piezoelectric receiver of the present invention, a
plurality of projections are provided on the outer peripheral edge of the piezoelectric diaphragm,
and only the projections are used as a piezoelectric diaphragm holder of the case. It is intended
to be held by As a result, the portion that does not contribute to the output sound pressure is
only the protrusion, and the conversion efficiency from electrical signals to sound pressure can
be increased with a limited area of the diaphragm without increasing the size of the piezoelectric
diaphragm .
[0008]
According to a first aspect of the present invention, there is provided a circular piezoelectric
diaphragm in which a piezoelectric element having electrodes formed on both sides of a
piezoelectric ceramic is bonded to a metal plate having a larger diameter than that, And a resin
housing for holding the outer peripheral edge of the piezoelectric diaphragm, wherein a plurality
of projections are provided on the outer peripheral edge of the piezoelectric diaphragm, and only
the projections are used as a housing. The piezoelectric receiver is characterized in that it is held
by a holding portion formed in the form of a shelf on the inner surface of the piezoelectric
diaphragm, and the area of the portion of the outer peripheral portion of the piezoelectric
diaphragm that does not contribute to sound pressure generation can be reduced. The
conversion efficiency from the electrical signal to the sound pressure can be enhanced without
increasing the size.
[0009]
The invention according to claim 2 of the present invention is characterized in that the gap
between the portion without projections of the outer peripheral edge of the piezoelectric
diaphragm and the holding portion of the housing is filled with a low-rigidity adhesive. The
piezoelectric receiver according to item 1, wherein the sound pressure output characteristic can
be stabilized.
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Hereinafter, embodiments of the present invention will be described using the drawings.
[0010]
(Embodiment) FIG. 1 is a partial plan view of a piezoelectric diaphragm and a case of a
piezoelectric receiver according to an embodiment of the present invention, and the overall
configuration of the piezoelectric receiver is the same as FIG. In FIG. 1, reference numeral 1
denotes a piezoelectric diaphragm in which a piezoelectric element 1a having electrodes formed
on both sides of a piezoelectric ceramic is bonded to a metal plate 1b having a larger diameter
than this, and plural protrusions 1c are formed on the outer peripheral edge of the metal plate
1b. Is formed. Reference numeral 2 is a circular case made of resin which has a predetermined
volume and holds the piezoelectric diaphragm 1 inside, a shelf-shaped piezoelectric diaphragm
holding portion 2a is formed on the inner side surface, and piezoelectric vibration is formed
thereon The protrusions 1c of the plate 1 are adhesively fixed. An adhesive material such as
silicon having a small rigidity is filled in the gap between the concave portion between the
adjacent projections 1 c of the piezoelectric diaphragm 1 and the piezoelectric diaphragm
holding portion 2 a.
[0011]
The piezoelectric receiver configured as described above holds only the protrusion 1c on the
outer peripheral edge of the piezoelectric diaphragm 1 in the piezoelectric diaphragm holding
portion 2a of the case 2 when an AC voltage is applied to the metal terminal to vibrate it.
Therefore, the invalid portion of the outer peripheral edge of the piezoelectric diaphragm 1 can
be reduced, and as shown by the curve A in the vibration mode of FIG. Can vibrate up to. Further,
as shown by the frequency characteristics of the output sound pressure in FIG. 2, characteristic A
of the piezoelectric receiver in the present embodiment has less ineffective portions on the outer
peripheral edge of the piezoelectric diaphragm than characteristic B in the conventional example.
Thus, it can be seen that the volume displacement of air by the diaphragm is increased and the
output sound pressure is high.
[0012]
As described above, according to the present invention, a plurality of projections are provided on
the outer peripheral edge of the piezoelectric diaphragm, and only the projections are held by the
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piezoelectric diaphragm holding portion of the case. The ineffective portion of the outer
peripheral edge of the piezoelectric diaphragm can be reduced, and the conversion efficiency
from electrical signals to sound pressure can be enhanced with a limited area of the diaphragm
without increasing the size of the piezoelectric diaphragm .
[0013]
Brief description of the drawings
[0014]
1 is a partial plan view of a piezoelectric diaphragm and a case of a piezoelectric receiver
according to an embodiment of the present invention.
[0015]
Fig. 2 Frequency characteristic diagram of output sound pressure showing characteristic A in the
embodiment of the present invention and characteristic B in the conventional example
[0016]
Fig. 3 An exploded perspective view of the piezoelectric receiver in the conventional example
[0017]
Fig. 4 Partial cross-sectional view of the piezoelectric diaphragm and the case of the piezoelectric
receiver in the conventional example
[0018]
Fig. 5 Partial plan view of the piezoelectric diaphragm and case of the piezoelectric receiver in
the conventional example
[0019]
Fig. 6 A vibration mode diagram showing characteristic A in the embodiment of the present
invention and characteristic B in the conventional example.
[0020]
Explanation of sign
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[0021]
Reference Signs List 1 piezoelectric diaphragm 1a piezoelectric element 1b metal plate 1c
protrusion 2 case 2a piezoelectric diaphragm holding portion
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