Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-02-09
2002-09-03
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06445108
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to piezoelectric acoustic components, such as a piezoelectric buzzer and a piezoelectric earphone.
2. Description of Related Art
Generally, in electronic devices, household-electric-appliances products, portable telephones, or a piezoelectric earphone and other such products, a piezoelectric acoustic component has been widely used as a piezoelectric buzzer or a piezoelectric earphone which generates a warning sound and a sound of operation.
This kind of piezoelectric acoustic component is disclosed in Japanese unexamined patent publication No. 7-107593 and Japanese unexamined patent publication No. 7-203590, for example. The piezoelectric acoustic component has a unimorph type diaphragm including a circular piezoelectric plate and a circular metal plate disposed on an electrode of the circular piezoelectric plate. The circular metal plate of the diaphragm is supported in a circular case at the circumference portion of the circular metal plate, and the opening of the circular case is sealed by a cover.
However, when such diaphragm having such a circular shape is used, problems such as a very low production efficiency and low acoustic conversion efficiency occur. Further, it is difficult to reduce the size of the piezoelectric acoustic component.
The problem of the very low production efficiency will be explained hereinafter.
In a manufacturing process of a piezoelectric acoustic component including the diaphragm having a circular shape, a green sheet
40
is punched by a punching die
41
to produce circular piezoelectric plates
42
as shown in FIG.
1
. Next, a circular metal plate
43
is disposed at a electrode on one side of each of the circular piezoelectric plates
42
. Then, a diaphragm
44
is obtained by applying a high voltage DC electric field between the electrodes on both sides of the circular piezoelectric plate
42
and polarizing the circular piezoelectric plates
42
. The diaphragm
44
is stored in a case
45
, and lead wires
46
and
47
respectively connected to the other surface electrode and the metal plate
43
of the piezoelectric board
42
are arranged to extend out of the case
45
.
However, when the circular piezoelectric plate
42
is punched from a green sheet
40
, as mentioned above, punching sediment increases and the yield of material is very low. Moreover, the process efficiency is very low because the individual processes of electrode formation, polarization, and other steps must be done after the punching process. Furthermore, in order to determine the required size for the design of each element, the punching die
41
of a green sheet must be produced according to the element size. Therefore, the production efficiency is very low and the cost of manufacturing is very high.
The problem with the low acoustic conversion efficiency will be explained hereinafter.
As shown in
FIG. 2A
, since the diaphragm
44
is supported by a case
45
at the circumference portion thereof, the maximum displacing point P is only at the center portion of the diaphragm
44
. Therefore, the displacement volume is small and the acoustic conversion efficiency is low. That is, there is a disadvantage that sound pressure per input energy is comparatively low.
Furthermore, the frequency is high because the circumference portion of the diaphragm is constrained. When producing the piezoelectric diaphragm having a low frequency, there is a disadvantage that the radius size is increased and becomes very large.
SUMMARY OF THE INVENTION
To overcome the above described problems, preferred embodiments of the present invention provide a piezoelectric acoustic component which achieves a high production efficiency, excellent acoustic conversion efficiency and a very small size.
A preferred embodiment of the present invention provides a piezoelectric acoustic component which includes a diaphragm having a substantially rectangular piezoelectric plate including front and back surfaces, an electrode disposed on the front surface of the piezoelectric plate, a substantially rectangular metal plate bonded to the back surface of the rectangular piezoelectric plate directly or via an electrode disposed on the back surface of the rectangular piezoelectric plate, an insulating cap including an upper wall, four side walls extending from the upper wall, a pair of support members arranged to support the diaphragm at the inside of the side walls, a plate shaped substrate having a first electrode section and a second electrode section, the diaphragm being disposed in the insulating cap, two of four side edges of the diaphragm disposed opposite to each other being fixed to the pair of support members, a gap between the other two of the four side edges of the diaphragm and the cap being sealed by elastic sealing material, an acoustic space being provided between the diaphragm and the upper wall of the insulating cap, an opening edge of the four side walls of the insulating cap being bonded to the substrate, the metal plate being electrically connected to the first electrode section, and the electrode disposed on the front surface of the substantially rectangular piezoelectric plate being electrically connected to the second electrode section.
Since the piezoelectric plate has a substantially rectangular shape, even if the piezoelectric plate is produced by punching a green sheet, the generation of punching residue of the green sheet is minimized, and thereby the material efficiency is much improved.
Further, since the process of electrode formation, polarization, and other steps are performed on the parent substrate rather than individual components, production efficiency is very good.
Furthermore, since the required size of the piezoelectric plate is achieved by cutting the parent substrate, it is not necessary to prepare a punching die for punching individual green sheets as is required in the prior art.
In other words, compared with the prior art, the number of steps for punching a green sheet and cutting a parent substrate is greatly reduced and the number of dies, jigs, and types of piezoelectric bodies are reduced, thereby increasing production efficiency and reducing the cost of production.
In preferred embodiments of the present invention, two of four side edges of the diaphragm which are opposite to each other are fixed to the pair of support members, and the gap between the other two of the four side edges of the diaphragm and the cap are sealed by elastic sealing material. When a predetermined frequency signal is input between the metal plate and the electrode disposed on the front surface of the piezoelectric plate, the piezoelectric plate expands, and the diaphragm is deformed in a longitudinal bending mode. In this case, the diaphragm is vibrated so as to generate two nodes at both ends thereof which are fixed to the cap via the support members. As shown in
FIG. 2B
, a maximum displacement point P exists along the centerline in the longitudinal direction of the diaphragm.
That is, the displacement volume is very large compared with a conventional disc-shaped diaphragm. Since this displacement volume is the energy for moving air, the acoustic conversion efficiency is greatly increased.
According to the above described piezoelectric acoustic component, the gap between the other two of the four side edges of the diaphragm and the cap is preferably sealed by elastic sealing material. Since the elastic sealing material has elasticity, the vibration of the diaphragm is not interfered with, and the sound pressure is not decreased.
Furthermore, since the diaphragm is fixed at the two side edges thereof and the portion between the two side edges is arranged to be displaced freely, the component achieves a lower frequency compared with a conventional disc-shaped diaphragm. Alternatively, the size of the component is reduced when the same frequency is required.
In preferred embodiments of the present invention, the adhesive agent is Preferably one which has a high Young's modulus in the hardened conditi
Daidai Muneyuki
Fujino Masayuki
Kishimoto Takeshi
Nomura Akihiro
Takeshima Tetsuo
Addison Karen B
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
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