Note: Descriptions are shown in the official language in which they were submitted.
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01 -- 1 --
02 _C GROUND OF THE INVENTION
03 The present invention generally relates
04 to a piezoelectric resonator and more particularly,
05 to an improved strip type or rectangular type
06 piezoelectric resona-tor for use, for example, in
07 oscillators, electr:ical Eilters and -the like.
08 Wi.th -the recent progre~s in the Eield of
09 in-tegrated circuits, inexpens:ive ceramic resonators
have been widely utilized for the actual
11 applications, and normally, disc type or rectangular
12 plate type piezoelectric reso:nators are generally
13 employed ~or the purpose in a rang~ of resonance
14 frequencies Erom 100 KHZ up to 1 MHZ so as to
utilize the expansion mode of vibration thereof.
16 _RIEF_DESCRIPTION OF THE DRAWINGS
17 Objects and features of the present
18 invention will become apparent from the following
19 description taken in conjunction with the preferred
embodiment thereof with reference to the
21 accompanying drawings, in which:
22 Figure 1 is a perspective view showing a
23 construction of a conventional rectangular plate
24 type piezoelectric resonator (already referred to),
Figure 2 is a perspective view showing a
26 construction of a conventional strip type
27 piezoelectric resonator (already referred to),
28 Figure 3 is a perspective view showing a
29 strip type piezoelectric resonator according to one
preferred embodiment of the present invention,
31 Figure 4 is a graph showing a state of
32 resonance in the strip type piezoelectric resonator
33 according to the present invention, and
34 Figure 5 is a graph showing variations
in the characteristics of the strip type
36 piezo~lectric resonator according to the present
37 invent.ion when position of the groove is altered.
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01 ~ 2 -
02 As shown in Figure L, the known
03 rec-tangular plate type piezoelec-tric resonator
04 reerred to above includes, for example, a
05 piezoelectric ceramic substrate 1, main electrode
06 faces 2 and 3 Eormed on -the opposite surEaces of
07 sald p:iezoelectric ceramic substra-te 1, and lead
08 wires 4 respectively connected to said main
09 electrode faces 2 and 3. However, in the
rectangular plate type piezoelectric resonator as
11 described above or di5c type piezoelectric resona-tor
12 conventionally employed, there have been such
13 disadvan-tages that they are generally large in s:ize,
14 and moreover, tend to produce spurious waves due to
thickness mode vibrakion based on -the fundamental
16 wave.
17 Meanwhile, as shown in Figure 2, there
18 has also been conventionally available a strip type
19 piezoelectric resonator utili~ing length mode
vibration based on the fundamental wave, and having
21 a construction generally similar to that of the
22 rectangular plate type piezoelectric resonator in
23 Figure 1 as represented by like re~erence
24 numerals. Although advan~ageous in that the
dimensions are reduced as compared with the
26 rectangular plate type or disc type piezoelec~ric
27 resonator, the conventional strip type pieæoelectric
28 resona~or as described above still has disadvantages
29 in that undesirable spurious responses due to wid-th
mode vibration and thickness mode vibration tend to
31 be produced.
32 SUMMARY OF THE I~VENTIO
33 Accordingly, an essential object of the
34 present invention is to provide an improved strip
type piezoelectric resonator in which undesirable
36 spurious responses due to width mode vibration and
37 thickn~ss mode vibration are suppressed by forming a
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3~
01 ~ 3 ~
02 groove on one of oppos.ite main elec-trode faces of
03 the resonator, in a direc-t:ion parallel to the
04 longi-tudinal direction thereof and at a posi-tion
05 deviated from a center in a widthwise direction oE a
06 piezoelectric ceramic substrate, wi-th substantial
07 elimination of disadvantages inherent in the
08 conventional piezoelectric resonators of this kind.
09 Another important object of the pre~ent
invention is to provide a strip type piezoelec-tric
11 resonator of -~he above described type, which is
12 simple in construction and stable in functioniny a~
13 high reliability, and can be readily manufactured on
14 a large scale at low cost.
In accomplishing these and other
16 objects, according to one preferred embodiment of
17 the present invention, there is provided a strip
18 type piezoelectric resonator utilizing length mode
19 vibra~ion, which includes a piezoelectric ceramic
substrate, and first and second main electrode faces
21 formed on opposite surEaces of ~he piezoelectric
22 ceramic substrate, and is characterized in that
23 there is further provided a groove which i5 formed
24 in one of the first and second main electrode faces
so as to extend over an entire length of the
26 piezoelectric ceramic substrate in a direction
27 parallel to the longitudinal direction thereof, and
28 at a position deviated from a center in a widthwise
29 direction of the piezoelectric ceramic substrate by
more than 2~ of the width of said piezoelectric
31 ceramic substrate.
32 By arrangement according to the present
33 invention as described above, an improved strip type
34 piezoelectric resonator with suppressed spurious
responses has been advantageously presented through
36 simple constructionO
37 DETAILED DESCRIPTION OF THE INVENTION
01 - ~ -
02 BeEore the description of the pre~en-t
03 invention proceeds, it is to be noted tha-t like
04 parts are designated by like reference numeral~
05 throughout the accompanying drawings.
06 ReEerring now to ~he drawings, -there is
07 shown in Figure 3 a str.ip type piezoelectric
0~ resonator according to one preferred embodiment of
09 the present invention, w~ich generally includes a
piezoelectric ceramic substrate 10, and
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upper and lower main electrode faces lOA and los formed on
opposite surface& of the substrate 10. In one surface of
the piezoelectric ceramic substrate 10 at the side of the
upper main electrode face lOA, there is formed a groove 11
which extends ovex an entire lenyth of the substrate 10 in a
direction parallal to the longitudinal direction of said
substrate 10 and is located at a position deviated, at its
center line in a widthwise direction thereof, from a center
line in the widthwise direction of the upper main electrode
face lOA or the substrate 10 as illustrated. By the above
groove 11, the upper main electrode face lOA of the
substrate 10 is divided into a large region ]2 and a small
region 13, while the lower main electrode face lOB is formed
on the other entire surface of the substr~te 10 in the
similar manner as in the conventional arrangement of Figs. 1
or 2.
More specifically, by way of example, the
piezoelectric ceramic substrate 10 is set in dimensions to
be 4.65 mm in length, 0.8 mm in width W, and 0.3 rnm in
thickness, and the groove 11 has a width of 0.15 mm and a
depth of 0.15 mm, while a distance through which the groove
11 i5 deviated from the center in the widthwise direction of
the pie~oelectric cerarnic substrate 10, i.e. a distance S
from the center of the substrate 10 in its widthwise
direction to the center of said groove 11 in the widtilwise
direction thereof is set to be 0.1 mm, and the oscillation
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frequency of -the strip type piezoelectric resonator of Fig.
3 is 'tO0 ~ when used as an oscillator.
For the actual use of the piezoelectric resonator
of Fig. 3 as deseribed so far, the respective reglons 12 and
13 on the upper main electrode face lOA divided by the
groove 11 are short-circuited to each other so as to be
connected to a lead wire 14 for the upper side, while a lead
wire 4 is connected to the lower main electrode face 10~ in
the similar manner as in the conventional arrangement of
Fig. 1 or 2, and thus, a two terminal type resonator is
constituted.
Subsequently, in the piezoelectric resonator
having the construction as shown in Fig. 3, on the
assumption that the distance through which the groove 11 is
deviated from the center in the widthwise direction of the
piezoelectric ceramic substrate 10 is represented by S, and
the width of the piezoelectric ceramic substrate ln is
~denoted by W as referred to earlier, measurements were taken
on the characteristics thereof, with the value of S/W
employed as a parameter. As shown in Fig. 4, response level
was represented as a level difference between resonant point
and anti-resonant point.
~ s a result of the above measurements, it has been
found as shown in Fig. 5 that, as the value S/W increases,
2~ the main respcnse decreases only slightly, whereas the
spurious responses due to width mode vibration by third
harmonics (first excited overtone of width mode), ancl
thickness mode vibration and width mod~ vibration based on
the fundarnental wave are reduced to a large e:Yten-t.
Normally, for the spurious oscillation to be
suppressed, it is necessary that the spurious responses are
reduced to less than half of the main response, and in order
to satisfy the above requirement in -the result oE
measurement in Fig. 5, S/l~ must be laryer than 2%. On the
other hand, as the position of the groove 11 is gradually
spaced or deviated from the center of the piezoelectric
ceramic substrate 10, the arrangement for supporting the
piezoelectric ceramic substrate 10 may undesirably be
complicated, while the strength of the substrate 10 at the
region 13 which is narrow in width tends to be reduced, and
therefore, the upper limit o~ S/W should preferably be 30~.
Accordingly, as is seen from the above
description, the range for the positional deviation of the
groove 11 to be provided in the present inventic)n~ from the
center in the widthwise direction of the piezoelectric
ceramic substrate 10 should be more than 2~ of the wiclth of
the ceramic substrate 10.
In the arrangement of Fig. 3, although the groove
11 is provided in the upper main electrode face 10A, lt is
needless to say that such groove 11 may be so modified as to
be provided in the lower main electrode face 10~ to obtain
the same effect.
Moreover, in the foregoing embodiment, even when
the dimensions (width and depth) of the groovc 11 are
altered, results of measurements generally in th~ similar
trelld as in those of Fig. 5 have been obtained.
I-t should be noted here that, although the
arrangemen-t of the present invention i~5 prepared as a
resonator, it is best suited to applications to an
oscillator.
For manufacturing the strip type piezoelectric
resonator according to the present inverltion in an efficient
manner, processings may be effected by such steps as forming
electrode layers over the entire opposite surfaces, i.e.
uE)per and lower surfaces of a large piezoelectric ceramic
plate having a predetermined thickness, subsequently forming
grooves each having the predetermined wid-th and depth in one
of the electrode formed surfaces at equal intervals, and
inally cutting off the large piezoelectric cer~mic plate
thus processed into dimensions of individual piezoelectric
resonators as shown in Fig. 3.
As is clear from the foregoing descriptic~n,
according to the present invention, since the piezoelectric
resonator is constituted by forming the groove in one of the
main electrode faces of the strip type piezoelectric ceramic
substrate in a direction parallel to the longitudinal
direction thereof, and at a position deviated by more than
2~ of the width of said substrate rom the center in the
widthwise direction of said piezoelectric ceramic substrate,
spurious responses due to width mode vibration and thickness
rnode vibration may be suppressed to less than 35 dB with
_ 9 _
respect to the main response of 70 dB, and thus, the
piezoelectric resonator free from genera-tion of spurious
response has been advant~geously presented,
Although the present invention has been fu].].y
described bv way of example with reference to the
accompanyi.ng drawi.ngs, it is to be noted here that various
changes and modifications will be apparent to those skilled
in the art~ Therefore, unless otherwise such changes and
modifications depart from the scope o:E the present
invention, they should be construed as included therein.
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