Piezoelectric acoustic component

Details Piezoelectric acoustic component Piezoelectric acoustic component

1999-05-13

2001-10-23

Budd, Mark O. (Department: 2834)

Electrical generator or motor structure

Non-dynamoelectric

Piezoelectric elements and devices

C310S324000, C310S348000, C310S345000

Reexamination Certificate

active

06307300

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric acoustic component, such as a piezoelectric buzzer or a piezoelectric receiver.
2. Description of the Related Art
Piezoelectric acoustic components, such as piezoelectric buzzers for producing an alarm or operation beep, or piezoelectric receivers, are widely used in, for example, electronic apparatuses, household electrical appliances, and cellular phones.
As described in Japanese Patent Application Laid-Open (kokai) Nos. 7-107593 and 7-203590, such a piezoelectric acoustic component typically has a structure in which a circular metallic plate is bonded to an electrode provided on one major surface of a piezoelectric plate to thereby constitute a unimorph-type vibration body. In such a structure, the vibration body is disposed within a circular housing such that the circumferential edge portion of the metallic plate is supported by the housing and the opening portion of the housing is covered by a cover.
However, use of such a circular vibration body results in poor production efficiency, low acoustic conversion efficiency, and difficulty in implementing a surface-mounting structure. These problems will be described in detail below.
First, production efficiency and acoustic conversion efficiency will be discussed. A process of manufacturing such a piezoelectric acoustic component includes the steps of: forming a circular piezoelectric plate
42
from a green sheet
40
by use of a blanking punch
41
as shown in
FIG. 1A
; electrically and mechanically bonding a circular metallic plate
43
to an electrode disposed on one major surface of the piezoelectric plate
42
as shown in
FIG. 1B
; applying a high-voltage direct-current electric field between electrodes located on the opposite main surfaces of the piezoelectric plate
42
for effecting polarization to thereby obtain a vibration body
44
; disposing the vibration body
44
within a housing
45
; and extending out to the exterior of the housing
45
lead wires
46
and
47
connected respectively to the electrode located on the other major surface of the piezoelectric plate
42
and the metallic plate
43
, as shown in FIG.
1
C.
However, forming the disc-like piezoelectric plates
42
from the green sheet
40
using a punch as shown in
FIG. 1A
results in a large portion of the green sheet
40
being unused, resulting in poor material utilization. Since formation of the electrodes and polarization are performed on an individual basis after blanking, processing efficiency is poor. Further, since the blanking punch
41
must be manufactured according to the size of the piezoelectric plate
42
, the overall production efficiency is even worse.
As shown in
FIG. 2A
, since the disc-like vibration body
44
is fixed at a circumferential portion by the housing
45
, a maximum displacement point P appears only at the center thereof, so that the volume of displacement is small and the acoustic conversion efficiency is low. As a result, the sound pressure is very low in relation to input energy. Further, since the vibration body
44
is circumferentially restricted, a high frequency is generated. In order to obtain a piezoelectric vibration body of a low frequency, the radius of the vibration body must be increased.
Next, implementation of a surface-mounting structure will be discussed. A piezoelectric acoustic component of a surface-mounting structure is disclosed in, for example, Japanese Utility Model Application Laid-Open (kokai) No. 3-125396. However, this structure has many drawbacks. More specifically, since lead terminals must be integrally formed on the metallic plate, the shape of the metallic plate becomes complicated. Also, the shape of the housing becomes complicated because of the need to extend the lead terminals out from the housing. Further, since the lead terminals are brought into contact with or are fixedly attached to the piezoelectric plate, a load is apt to be exerted on the piezoelectric plate. Therefore, implementation of such a piezoelectric acoustic component of a surface-mounting structure is inferior because of the poor reliability and the high cost of manufacture.
SUMMARY OF THE INVENTION
To overcome the above described problems, preferred embodiments of the present invention provide a piezoelectric acoustic component including a vibration body having a substantially rectangular piezoelectric plate with a first major surface and a second major surface, a first vibration body electrode provided on the first major surface of the piezoelectric plate and a substantially rectangular metallic plate provided on the second major surface of the piezoelectric plate, a mounting substrate including a first circuit electrode and a second circuit electrode disposed thereon, the first circuit electrode being connected to the metallic plate, the second circuit electrode being connected to the first vibration body electrode, support members being arranged such that the vibration body is mounted on the mounting substrate at longitudinal opposite end portions thereof via the support members such that a gap is defined between the mounting substrate and the longitudinal opposite end portions of the vibration body, an elastic sealing material sealing the gap between the mounting substrate and each of lateral opposite end portions of the vibration body to thereby define an acoustic space between the vibration body and the mounting substrate, and a cover having a sound release hole provided therein and which is bonded onto the mounting substrate so as to cover the vibration body without the cover contacting the vibration body.
Since the piezoelectric plate has a substantially rectangular shape, even if piezoelectric plates are blanked from a green sheet, the portion of the green sheet that remains unused is greatly reduced as compared to the prior art, so that the material utilization rate is greatly improved and very high in preferred embodiments of the present invention. Further, since formation of electrodes and polarization can be performed on a parent substrate, from which a plurality of piezoelectric plates are cut, production efficiency is greatly improved. In addition, since various kinds of piezoelectric plates having different design dimensions can be obtained by changing the cutting dimensions or positions of the parent substrate, it is unnecessary to make a blanking punch of a different size for each kind of piezoelectric plates, in contrast to the case of the conventional piezoelectric acoustic component. More specifically, the number of kinds of, for example, dies, jigs, and piezoelectric bodies used in production steps ranging from blanking of the green sheet to cutting of the parent substrate is greatly reduced, thereby significantly reducing the cost of production and improving production efficiency.
In the piezoelectric acoustic component according to preferred embodiments of the present invention, the longitudinal opposite end portions of the substantially rectangular vibration body are fixed onto the mounting substrate via the respective support members. Therefore, when a signal of a predetermined frequency is input between the metallic plate and the electrode provided on the other major surface of the piezoelectric plate, the piezoelectric plate expands and contracts, and thus, the substantially rectangular vibration body bends accordingly. At this time, the vibration body vibrates in a direction that is substantially perpendicular to a major surface thereof with the longitudinal opposite end portions functioning as nodes of vibration, and maximum-displacement points P are produced along the center line in the longitudinal direction. That is, displacement volume greatly increases. Since the displacement volume is in direct proportion to the amount of energy for moving the air, acoustic conversion efficiency is thereby greatly increased.
Although the gap between the mounting substrate and each of lateral opposite end portions of the vibration body is sealed by the sealing material, the sealing mater

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