Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-08-01
2002-10-29
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S348000
Reexamination Certificate
active
06472797
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention The present invention relates to a piezoelectric electro-acoustic transducer such as a piezoelectric sounder, a piezoelectric speaker, a piezoelectric buzzer, and a piezoelectric receiver.
2. Description of the Related Art
Conventional piezoelectric electro-acoustic transducers have been widely used for piezoelectric buzzers and piezoelectric speakers. Typically, such a piezoelectric electro-acoustic transducer has a structure in which a unimorph diaphragm is constructed by adhering a circular metallic plate onto one surface of a circular piezoelectric ceramic plate, the peripheral portion of the unimorph diaphragm is supported in a circular case, and the opening of the case is closed by a cover. The unimorph diaphragm exhibits bending oscillations by adhering a ceramic plate having an outside diameter that expands and contracts by applying a voltage, to a metallic plate that does not change in size.
Conventional piezoelectric electro-acoustic transducers described above typically use three kinds of supporting structures for supporting the diaphragm in the case. These three kinds of support structures are illustrated in
FIGS. 1
to
3
.
FIG. 1
shows a supporting structure arranged such that a back-surface node portion of a diaphragm
1
is fixed by a silicon adhesive
3
to a supporting portion
2
a
which projects from a case
2
. A cover
4
is provided for closing the opening of the case
2
.
FIG. 2
shows a supporting structure arranged such that the peripheral portion of the diaphragm
1
is fixed to a supporting portion
2
b
of the case
2
by the silicon adhesive
3
.
FIG. 3
shows a supporting structure wherein tapered groove portions
2
c
and
4
a
are located where the case
2
and the cover
4
meet, and the peripheral portion of the diaphragm
1
is inserted into the groove portions
2
c
and
4
a
and is fixed by the adhesive
3
.
With the supporting structure using the node portion as shown in
FIG. 1
, since it is necessary to fix the back surface of the diaphragm
1
to the supporting portion
2
a
by the adhesive
3
, there are drawbacks in that the adhering process is difficult and a large quantity of the adhesive
3
cannot be supplied between the supporting portion
2
a
and the diaphragm
1
. Thus, the supporting strength of the diaphragm
1
is not sufficient.
With the supporting structure using the peripheral portion as shown in
FIG. 2
, the adhering process is easy but the supporting portion
2
b
of the case
2
has a flat surface and, therefore, the back surface of the diaphragm
1
is closely adhered to the surface of the supporting portion
2
b
, thereby restricting an angular change of the diaphragm
1
. Accordingly, there is a drawback in that an effective diameter d
1
of the diaphragm
1
is much smaller than the actual diameter d
0
of the diaphragm
1
and actuation of the diaphragm at low frequencies is difficult.
With the supporting structure using the tapered groove as shown in
FIG. 3
, the diaphragm
1
is obliquely arranged. If the diaphragm
1
deviates from the center of the case
2
when assembling the diaphragm
1
into the case
2
, the diaphragm
1
might be damaged if the cover
4
is forcibly fitted. The liquid adhesive
3
must be injected in the tapered groove portions
2
c
and
4
a
by utilizing a dispenser after assembling the case
2
and the cover
4
and, then, there is a drawback that the method of applying the adhesive
3
is difficult, thus increasing costs.
SUMMARY OF THE INVENTION
To overcome the problems described above, preferred embodiments of the present invention provide a piezoelectric electro-acoustic transducer in which adherence of a piezoelectric diaphragm to a casing is simply performed, a sufficient supporting strength is achieved, and the piezoelectric diaphragm is supported while minimizing hindrance of vibration of the piezoelectric diaphragm.
According to one preferred embodiment of the present invention, a piezoelectric electro-acoustic transducer includes a piezoelectric diaphragm having a piezoelectric ceramic plate, and a metallic plate onto which the piezoelectric ceramic plate is adhered, and a casing containing the piezoelectric diaphragm, the casing including a supporting portion arranged to support a peripheral portion of the piezoelectric diaphragm by fixing the peripheral portion thereof with an elastic adhesive, and a supporting surface provided on the supporting portion, the supporting surface having an substantially arcuate cross-section and a center of curvature of the supporting surface being positioned near a lower surface of the peripheral portion of the piezoelectric diaphragm.
When an alternating voltage is applied between electrodes of the piezoelectric diaphragm, the piezoelectric diaphragm is bent and vibrated as the piezoelectric ceramic plate expands/contracts. Although the peripheral portion of the piezoelectric diaphragm is fixed to the supporting portion of the casing by the elastic adhesive, the supporting surface (curved surface) with the substantially arcuate cross-section is provided on the supporting portion of the casing so that the center of curvature is positioned near the lower surface of the periphery of the piezoelectric diaphragm and, therefore, the piezoelectric diaphragm is supported in a substantially tangential direction of the curved surface. As the supporting surface approaches the approximate center portion of the piezoelectric diaphragm from the peripheral portion thereof, an opposing distance between the curved surface as the supporting surface and the piezoelectric diaphragm becomes larger. Therefore, an angular change is not limited when the piezoelectric diaphragm oscillates. Thus, the effective diameter of the piezoelectric diaphragm is increased and a low-frequency is achieved. When setting the piezoelectric diaphragm to the supporting portion of the casing, if the setting portion is slightly deviated in the lateral direction, the oblique disposition of the piezoelectric diaphragm is easily controlled by placing the peripheral portion of the piezoelectric diaphragm on the curved surface. Further, when fixing the piezoelectric diaphragm to the supporting portion of the casing, the peripheral portion of the piezoelectric diaphragm may be set to the supporting portion and the surface thereof may be coated with an adhesive, thus greatly simplifying the adhering process.
Preferably, the radius of curvature of the substantially arcuate supporting surface is smaller than a long surface or diameter of the piezoelectric diaphragm, because, if the radius of curvature is larger than the long surface or diameter of the piezoelectric diaphragm, vibration is easily obstructed at the peripheral portion of the piezoelectric diaphragm but also at an inner portion of the peripheral portion, which decreases the vibration area of the piezoelectric diaphragm.
By making the radius of curvature of the supporting surface smaller than a long surface or a diameter of the piezoelectric diaphragm, the vibration area of the piezoelectric diaphragm is greatly increased.
According to another preferred embodiment of the present invention, electrodes are disposed on front and back surfaces of the piezoelectric ceramic plate and a metallic plate is attached to the electrode of one surface of the piezoelectric ceramic plate to define a piezoelectric diaphragm having a unimorph configuration. As a result of this construction, the piezoelectric diaphragm is oscillated in a bending mode by applying an alternating signal between the electrode on the other surface of the piezoelectric ceramic diaphragm and the metallic plate.
The piezoelectric diaphragm may be constructed by adhering a substantially rectangular piezoelectric ceramic plate to a substantially rectangular metallic plate. In this case, two short surfaces of the metallic plate are attached to the supporting portion of the casing by an elastic adhesive and a space between two long surfaces of the metallic plate and the casing is sealed by an elastic sealing materia
Keating & Bennett LLP
Medley Peter
Murata Manufacturing Co. Ltd.
Ramirez Nestor
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