Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-11-03
2001-03-06
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S359000, C310S366000, C310S368000
Reexamination Certificate
active
06198200
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric resonator and a piezoelectric resonance apparatus for use in resonators, oscillators, or other electronic devices, and more particularly, to a thickness extensional vibration piezoelectric resonator and a piezoelectric resonance apparatus each operative to utilize higher harmonics in a thickness extensional vibration mode.
2. Description of the Related Art
Piezoelectric resonators are used in a variety of piezoelectric resonance apparatuses such as piezoelectric oscillators, piezoelectric filters, and so forth. Conventional piezoelectric resonators of this type are operative to utilize different piezoelectric vibration modes depending on the frequencies used.
Japanese Unexamined Patent Publication No. 1-117409 discloses an energy-trapping piezoelectric resonator operative to utilize the second harmonic in a thickness extensional vibration mode. This piezoelectric resonator will be described with reference to
FIGS. 19 and 20
.
The above-mentioned piezoelectric resonator is formed by laminating ceramic green sheets
61
and
62
made of a piezoelectric material, and firing the green sheets
61
,
62
integrally, as shown in the exploded perspective view of
FIG. 19. A
circular excitation electrode
63
is located on the ceramic green sheet
61
at the center thereof. The excitation electrode
63
extends to one of the side edges of the ceramic green sheet
61
through an outgoing electrode
64
. Further, a circular excitation electrode
65
is provided at the center of the upper side of the ceramic green sheet
62
. The excitation electrode
65
extends to one of the side edges of the ceramic green sheet
62
through an outgoing electrode
66
. Moreover, on the underside of the ceramic green sheet
62
, an excitation electrode
67
is provided and extends to one of the side edges of the ceramic green sheet
62
through an outgoing electrode
68
, as shown in the downward projection.
The above-mentioned ceramic green sheets
61
and
62
are laminated, pressed in the thickness direction, and then fired. The obtained sintered material is polarized so that a piezoelectric resonator
70
as shown in
FIG. 20
is produced.
In the piezoelectric resonator
70
, piezoelectric layers
71
and
72
defined by the sintered materials, are polarized evenly in the thickness direction indicated by the arrows in FIG.
23
.
In operation, the piezoelectric resonator
70
is resonated by connecting in common the excitation electrodes
63
and
67
to apply an AC voltage between the excitation electrodes
63
and
67
and the excitation electrode
65
. In this case, the vibration energy is trapped in the area where the excitation electrodes
63
,
65
, and
67
are overlapped, that is, a resonance portion A.
The conventional piezoelectric resonator
70
is operative to utilize higher harmonics in a thickness extensional vibration mode and is constructed to define an energy-trapping piezoelectric resonator, as described above. Accordingly, it is necessary to provide a vibration-attenuating portion on the periphery of the resonance portion A for attenuation of the vibration. That is, it is required to provide the vibration attenuating portion of which the area is larger than that of the resonance portion A. Therefore, it has been difficult to miniaturize the piezoelectric resonator
70
.
On the other hand, Japanese Unexamined Patent Publication No. 2-235422 discloses an energy-trapping piezoelectric resonator containing a strip-type piezoelectric ceramic, in which it is not necessary to provide an piezoelectric substrate portion with a large area on the periphery of its resonance portion.
In the energy-trapping type piezoelectric resonator, an excitation electrode
82
a
is provided on the upper side of an elongated piezoelectric substrate
81
, and an excitation electrode
82
b
is provided on the underside thereof, as shown in FIG.
21
. Each of the excitation electrodes
82
a
and
82
b
is extended to a pair of the longer sides of the piezoelectric substrate
81
and extends over an entire width thereof. Further, the back side of the excitation electrode
82
a
and the front side of the excitation electrode
82
b
are opposed to each other in the center in the longitudinal direction of the piezoelectric substrate
81
so as to define a resonance portion. Further, the excitation electrodes
82
a
and
82
b
are extended to the ends
81
a
and
81
b
in the longitudinal direction of the piezoelectric substrate
81
.
In the piezoelectric resonator
80
, when the thickness extensional vibration mode is excited, unnecessary vibrations are generated, based on the dimensional relationship between the width W and the thickness T of the piezoelectric substrate
81
. In Japanese Unexamined Patent Publication No. 2-235422, it is described that when the fundamental wave is utilized, the ratio of W/T of about 5.33 at a resonance frequency of 16 MHz is suitable, and when the third harmonic is utilized, unnecessary spurious components between the resonance frequency and the anti-resonance frequency can be reduced by setting the ratio of W/T at about 2.87 when the resonance frequency is about 16 MHz.
As described above, in the case of the energy-trapping piezoelectric resonator operative to utilize the second harmonic in a thickness extensional vibration mode, disclosed in Japanese Unexamined Patent Publication No. 1-117409, it is necessary to provide a large vibration attenuating portion on the periphery of its resonance portion. Accordingly, miniaturization of the energy-trapping type piezoelectric resonator is difficult.
Moreover, referring to the energy-trapping type piezoelectric resonator disclosed in Japanese Unexamined Patent Publication No. 2-235422, it is unnecessary to provide a vibration-attenuating portion on the side of the resonance portion, and therefore, miniaturization can be achieved. However, when higher harmonics in a thickness extensional vibration mode are practically utilized, spurious components appear between the resonance and anti-resonance frequencies. Accordingly, in some cases, effective resonance characteristics can not be obtained.
Referring to the piezoelectric resonator disclosed in Japanese Unexamined Patent Publication No. 2-235422, the electric capacity is relatively small so that the piezoelectric resonator is easily affected by a floating capacity generated from the circuit board or other components.
SUMMARY OF THE INVENTION
To overcome the problems described above, preferred embodiments of the present invention provide a thickness extensional vibration piezoelectric resonator and a piezoelectric resonance apparatus, each of which is operative to utilize higher harmonics in a thickness extensional vibration mode, has a greatly reduced size, has a large electric capacity, is not affected by a floating capacity generated by the circuit board or other components, effectively minimizes the generation of undesired unnecessary spurious components, and has excellent resonance characteristics.
Further, preferred embodiments of the present invention provide a thickness extensional vibration piezoelectric resonator and a piezoelectric resonance apparatus, each of which is operative to utilize the third harmonic in a thickness extensional vibration mode, has a greatly reduced size, has a large electric capacity, is not affected by a floating capacity generated by the circuit board or other components, effectively minimizes the generation of undesired unnecessary spurious components, and has excellent resonance characteristics.
One preferred embodiment of the present invention provides a thickness extensional vibration piezoelectric resonator having vibration-attenuating portions on both sides of a resonance portion and being arranged to be vibrated in N-order higher harmonics in a thickness extensional vibration mode. The thickness extensional vibration piezoelectric resonator includes a piezoelectric body, first and second excitation electrodes disposed on a pair of major surface
Kaida Hiroaki
Nagae Toru
Budd Mark O.
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
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