Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-12-01
2001-03-13
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S366000
Reexamination Certificate
active
06201337
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric resonator and a piezoelectric resonance device for use as different kinds of resonators, oscillators, or similar apparatuses, and more particularly, to a thickness extensional piezoelectric resonator and a piezoelectric resonance device each operative to use higher harmonics of a thickness extensional vibration mode.
2. Description of the Related Art
Piezoelectric resonators are used in a variety of piezoelectric resonation devices such as piezoelectric oscillators, piezoelectric filters, and so forth.
Japanese Unexamined Patent Publication No. 1-117409 discloses an energy-trap type piezoelectric resonator operative to utilize the second harmonic in a thickness extensional vibration mode. This piezoelectric resonator will be described with reference to
FIGS. 22 and 23
.
The above-mentioned piezoelectric resonator is formed by laminating ceramic green sheets
61
and
62
made of a piezoelectric material, and firing them integrally, as shown in the exploded perspective view of
FIG. 22. A
circular excitation electrode
63
is provided on the ceramic green sheet
61
in the center thereof. The excitation electrode
63
is led out to one of the side edges of the ceramic green sheet
61
through a lead electrode
64
. Further, a circular excitation electrode
65
is provided in the center of the upper side of the ceramic green sheet
62
. The excitation electrode
65
is led out to one of the side edges of the ceramic green sheet
62
through a lead electrode
66
. An excitation electrode
67
is provided on the underside of the ceramic green sheet
62
, and is lead out to the side edge of the ceramic green sheet
62
through an lead 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 baked. The obtained sintered material is polarized whereby a piezoelectric resonator
70
as shown in
FIG. 23
is produced.
In the piezoelectric resonator
70
, piezoelectric layers
71
and
72
are uniformly polarized in the thickness direction, namely, in the direction indicated by the arrows in FIG.
23
.
The piezoelectric resonator
70
can be resonated by connecting in common the excitation electrodes
63
and
67
, and applying an AC voltage between the excitation electrodes
63
,
67
, and
65
. In this case, the vibration energy is trapped in the area where the excitation electrodes
63
,
65
, and
67
overlap, which defines a resonance portion A.
The prior art piezoelectric resonator
70
which is operative to use higher harmonics in a thickness extensional vibration mode is provided as an energy-trapping piezoelectric resonator, as described above. Accordingly, it is necessary to provide a vibration-attenuating portion at the periphery of the resonance portion A for attenuation of the vibration. That is, it is necessary to provide the vibration attenuating portion having an area which is larger than that of the resonance portion A. Therefore, it becomes difficult to miniaturize the piezoelectric resonator
70
.
Japanese Unexamined Patent Publication No. 2-235422 discloses an energy-trap type piezoelectric resonator containing a strip-type piezoelectric ceramic, which does not require a piezoelectric substrate portion having a large area located at the periphery of its resonance portion.
In the energy-trap type piezoelectric resonator
80
, an excitation electrode
82
a
is provided on the upper side of an elongated piezoelectric substrate
81
, and an excitation electrode
82
b
on the underside thereof. Each of the excitation electrodes
82
a
and
82
b
is arranged to extend to a pair of the long sides of the piezoelectric substrate
81
, that is, to extend over the entire width. 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
whereby the resonance portion is defined by the overlapped portions. Further, these 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
, unnecessary vibrations are generated during the excitation of the thickness extensional vibration mode. Japanese Unexamined Patent Publication No. 2-235422 describes that when a fundamental wave is utilized, the ratio of WIT (width/thickness) equal to about 5.33 at a resonance frequency of 16 MHz is preferred, 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. In other words, when higher harmonics in a thickness extensional vibration mode are practically utilized, various unnecessary spurious vibrations appear in addition to the spurious components between the resonance and anti-resonance frequencies. Accordingly, a problem occurs that effective resonance characteristics can not be obtained.
Also 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 susceptible to a floating capacity generated from the circuit board other components.
SUMMARY OF THE INVENTION
To overcome the above described problems, preferred embodiments of the present invention provide a thickness extensional vibration piezoelectric resonator and a piezoelectric resonance device, each of which is operative to utilize higher harmonics in a thickness extensional vibration mode, is constructed to be miniaturized, has a large electric capacity, is not vulnerable to floating capacity generated from a circuit board, effectively suppresses the generation of undesired unnecessary spurious vibrations, and has excellent resonance characteristics.
One preferred embodiment of the present invention preferably provides a thickness extensional vibration piezoelectric resonator, including a resonance portion, a vibration-attenuating portion disposed at both sides of the resonance portion and adapted to be vibrated in an N-order higher harmonic in a thickness extensional vibration mode. The piezoelectric resonator further includes a piezoelectric body, a first excitation electrode and a second excitation electrode respectively disposed on both sides of the piezoelectric body and opposed to each other with the piezoelectric body disposed therebetween, at least one layer of an internal electrode arranged inside of the piezoelectric body and at least partially opposed to the first and second excitation electrodes through the piezoelectric layers, first and second terminal electrodes disposed on the ends in a first direction of the of the piezoelectric body and electrically connected to the first and second excitation electrodes, respectively. The first direction being a direction passing through the vibration-attenuating portions located on both sides of the resonance portion, respectively. The first and second terminal electrodes being defined by the portion of the first and second excitation electrodes and the internal electrode overlapped in the thickness direction with the piezoelectric body disposed therebetween. A ratio Go/D being substantially equal to or higher than about 2.0, in which Go is each of the distances extending in the first direction between the first and second excitation electrodes and the terminal electrodes, and D is substantially equal to T/N, wherein T is the thickness of the piezoelectric body and N is the order of harmonics of thickness extensional vibration.
According to the above described arrangement, the thickness extensional vibration piezoelectric resonator preferably includes a substantially rectangular plate-shaped piezoelectric body, first and second excitation electrodes disposed on both sides of the piezoelectric
Kaida Hiroaki
Nagae Toru
Dougherty Thomas M.
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
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