Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-11-01
2004-06-08
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S327000
Reexamination Certificate
active
06747395
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric loudspeaker having flat reproduced sound volume characteristics in a wide range of frequencies.
2. Description of the Related Art
Conventional piezoelectric loudspeaker structures are disclosed in, for example, Japanese Laid-Open Utility Model Publication No. 63-81595 and Japanese Laid-Open Patent Publication No. 1-135299.
FIG. 38
illustrates the structure of a conventional piezoelectric loudspeaker disclosed in Japanese Laid-Open Utility Model Publication No. 63-81595. This conventional piezoelectric loudspeaker includes a piezoelectric diaphragm, which is composed of two thin piezoelectric members
31
A and
31
B electrodes
32
A,
32
B,
32
C attached together, and a kneaded mixture
33
of metal powder and adhesive. Reference numerals
34
A and
34
B denote electrical input lines. The mixture
33
is adhered to the central portion of the piezoelectric diaphragm so as to damp the resonance peak Q at the resonance points of the piezoelectric loudspeaker, thereby improving the vibration mode characteristics. This technique of attaching visco-elastic member, i.e., the kneaded mixture
33
in a smaller diameter of the central portion of the diaphragm results in a somewhat reduced resonance peak. However, the amount of resonance attenuation obtained is well below a sufficient level. As a result, this conventional piezoelectric loudspeaker cannot attain sufficiently flat reproduced sound volume-frequency characteristics.
FIG. 39
illustrates the structure of a conventional piezoelectric loudspeaker disclosed in Japanese Laid-Open Patent Publication No. 1-135299. This conventional piezoelectric loudspeaker includes: a metal diaphragm
35
; a piezoelectric vibrator composed of a thin piezoelectric member
36
attached to one side of the diaphragm
35
; a soft damper plate
39
made of foam resin, rubber, or the like with the same outer diameter as that of the metal diaphragm
35
overlaid on the opposite side of the metal diaphragm
35
: and a frame
37
for sandwiching the metal diaphragm
35
and the damper plate
39
at their outer peripheries around their entire circumferences for providing stable support for the metal diaphragm
35
and the damper plate
39
. Reference numerals
38
A and
38
B denote electrical input lines. It is possible to impart this piezoelectric loudspeaker with various frequency characteristics by selecting the sandwiching pressure in accordance with the materials composing the metal diaphragm
35
and the damper plate
39
. However, in accordance with the above conventional structure, the soft damper plate
39
and the metal diaphragm
35
are sandwiched by the frame
37
at their outer peripheries. Such a soft damper plate
39
, extending all the way to the frame
37
, may allow the vibratory force induced by the vibrator
36
to be transmitted into the frame
37
. As a result, this conventional piezoelectric loudspeaker will not attain large vibration amplitude and hence it will not reproduce sounds at high sound volume.
Moreover, as the input voltage to the aforementioned conventional piezoelectric loudspeakers is increased, an excessive amplitude may occur, especially within the vicinity of the central portion of the piezoelectric vibrator. This may result in the ‘peeling’ of the piezoelectric member from the metal diaphragm, and even the destruction of the piezoelectrio vibrator.
It is known that the lowest reproducible frequency in the reproduced sound volume characteristics can be lowered as the diameter of the metal diaphragm is increased. However, this also creates a corresponding decrease in the highest reproducible frequency. Thus, it is difficult to attain a wide reproduction band width with the conventional piezoelectric loudspeakers of the type discussed above.
In a further case where a piezoelectric member is affixed on each side of the metal diaphragm, it is necessary to affix lead wires to both piezoelectric loudspeakers, and the lead wires must lead out from above and below the frame. This is aesthetically and electrically unpreferable, and may create problems such as peeling, entanglement, or even severance of the lead wires, resulting in a malfunction.
SUMMARY OF THE INVENTION
A piezoelectric loudspeaker according to the present invention includes: a piezoelectric vibrator including a diaphragm and a piezoelectric member provided on at least one face of the diaphragm, the diaphragm being vibrated by the piezoelectric member: a frame for supporting the piezoelectric vibrator: and a visco-elastic member provided on at least one face of the piezoelectric vibrator, wherein the visco-elastic member is disposed in a substantial center of the piezoelectric vibrator, and wherein the visco-elastic member has a bottom face area which accounts for about 11% to about 80% of a bottom face area of the diaphragm.
In one embodiment of the invention, the visco-elastic member includes two or more visco-elastic members stacked on top of each other, and the two or more types of visco-elastic members at least have different materials or different shapes.
In another embodiment of the invention, the visco-elastic member includes first and second visco-elastic members which are provided on opposite sides of the piezoelectric vibrator.
In still another embodiment of the invention, the first and second, visco-elastic members at least have different materials or different shapes.
In still another embodiment of the invention, the visco-elastic member includes two or more visco-elastic members having mutually different values in at least one of specific gravity, Young's modulus, and internal loss, and the two or more types of visco-elastic members are disposed in a concentric manner.
In still another embodiment of the invention, a rigid member is provided on the visco-elastic member, the rigid member having a specific gravity which is larger than a specific gravity of the visco-elastic member.
In still another embodiment of the invention, the piezoelectric vibrator has at least one aperture, the at least one aperture being at least partially filled by the visco-elastic member.
In still another embodiment of the invention, the frame has a horn-like configuration having an opening, the opening having a gradually increasing cross-sectional area away from the piezoelectric vibrator and toward a final opening at which soundwaves are emitted, and the visco-elastic member has a conical configuration having a gradually decreasing cross-sectional area away from the piezoelectric vibrator and toward the final opening.
In still another embodiment of the invention, the piezoelectric loudspeaker further includes an element provided in a central portion of the visco-elastic member, at least one of specific gravity and elastic modulus of the element being larger than specific gravity and/or elastic modulus of the visco-elastic member.
In still another embodiment of the invention, the visco-elastic member includes notches at least in one portion thereof.
Alternatively, the piezoelectric loudspeaker plurality of includes: a piezoelectric vibrator including a diaphragm and a piezoelectric member provided on at least one face of the diaphragm, the diaphragm being vibrated by the piezoelectric member; a frame for supporting the piezoelectric vibrator; and a support element for supporting the piezoelectric vibrator at a substantial center of the piezoelectric vibrator.
In one embodiment of the invention, the support element includes a conductive portion which is in electrical contact with the piezoelectric vibrator, and an electrical input is applied to the conductive portion.
In another embodiment of the invention, the loudspeaker further includes a visco-elastic member provided on at least one face of the piezoelectric vibrator.
Alternatively, the piezoelectric loudspeaker according to the present invention includes: a piezoelectric vibrator including a diaphragm and a plurality of piezoelectric members provided on at least one face of the diaphragm, the diaphragm being vi
Iwasa Mikio
Kuze Mitsukazu
Satoh Kazue
Takewa Hiroyuki
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