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JP2001162228

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DESCRIPTION JP2001162228
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic transducer used in an ultrasonic detection device or the like, and more particularly to
an ultrasonic transducer whose band is broadened by optimizing the shape with respect to
thickness. .
[0002]
2. Description of the Related Art Heretofore, as an ultrasonic transducer, one obtained by
processing a piezoelectric substance into a disk shape having a uniform thickness or a
rectangular shape has been used. In this type of ultrasonic transducer, in order to realize highly
efficient electrical / acoustic conversion characteristics, the radiation surface of ultrasonic
vibration is oscillated back and forth (in the thickness direction) to make the density nearly
parallel to the radiation surface. It is configured to generate a wave.
[0003]
In the ultrasonic transducer, in addition to the desired vibration mode that generates
compression waves approximately parallel to the radiation plane, vibration of various different
modes is excited as an unnecessary component. Among such unnecessary components, one
whose vibration frequency is close to the vibration frequency of the desired component
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interferes with various measurement operations performed by the desired vibration component
and causes an error. Therefore, as shown in the plan view (A) of FIG. 2, in order to prevent the
vibration frequency of the unnecessary component from approaching the vibration frequency of
the desired component, the transducers t1, t2, t3. An arrangement is disclosed in another patent
application of the applicant of the present invention in which unnecessary components are
pushed up to high frequencies by creating a large-diameter transducer T by combining.
[0004]
In addition, when the frequency bandwidth of the electrical / acoustic conversion characteristic
of the ultrasonic transducer is narrow, the waveform of the pulse-like tone burst signal
transmitted and received becomes dull, and it becomes impossible to detect the time of reception
with high accuracy. . Therefore, in order to expand the frequency bandwidth, the thickness of the
large diameter vibrator T formed by combining small diameter vibrators is changed in the central
direction as shown in the front view (B) of FIG. The configuration is disclosed in the abovementioned other patent application of the applicant.
[0005]
As the resonance frequency changes due to such a thickness, the center frequency in the gainfrequency characteristic of transmission and reception of the ultrasonic transducer depends on
the thickness of each transducer as exemplified in the characteristic diagram of FIG. f 2, f 3... As a
result, the gain-frequency characteristics of a large ultrasonic transducer T in which small
ultrasonic transducers t1, t2, t3,... Of various thicknesses are gathered can be illustrated by a
dotted curve in FIG. This is enlarged compared to the case of being composed of a set of
transducers of the same thickness. With such expansion of the frequency band, the blunting of
the tone burst signal to be transmitted and received is avoided, a sharp waveform signal is
obtained, and the measurement accuracy is improved.
[0006]
According to the other patent application, as shown in FIG. 4, the diameter of the ultrasonic
transducers t1, t2, t3... Is 5 mm, the diameter D of the large diameter ultrasonic transducer T is
60 mm, and the outermost periphery thereof When the thickness T of the portion was 15 mm,
the optimum value R of the radius of curvature of the curved portion for broadening obtained by
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the experiment was 150 mm. In this example, the depression t in the central portion is 3 mm,
and the minimum thickness in the central portion is 80% of the maximum thickness T of the
outermost portion, or 20% of the thickness variation.
[0007]
In the vibrator of the above-described optimized shape, the center frequency of vibration was
103.5 kHz, and the bandwidth of 3 dB reduction of the transmission / reception sensitivity was
26.25 kHz. For comparison, a transducer of uniform thickness without forming a curved portion
was created and the characteristics were measured. In this oscillator, the center frequency of
vibration is 93.9 kHz, and the bandwidth of 3 dB reduction of transmission and reception
sensitivity is 5.8 kHz. By varying the thickness, the bandwidth is expanded about four times.
[0008]
As illustrated in FIG. 2, when the concave spherical surface is formed on the surface of the large
ultrasonic transducer T in order to make the thickness of the small diameter transducer different,
the directivity becomes sharp. Side effects occur. Sharpening this directivity may be
advantageous, but it may not be. When sharpening of the directivity is inconvenient, if the shape
of the curved surface is made convex upward to avoid this, conversely, the directivity may be too
blunt to be disadvantageous.
[0009]
Therefore, in order to change the thickness of the small diameter vibrator, as shown in the front
view of FIG. 6, it is also conceivable to monotonously increase and decrease the thickness from
one peripheral portion to the other peripheral portion. However, in such a configuration, the
surface to be the radiation surface of the ultrasonic wave is inclined, and the radiation direction
of the sound wave is disadvantageously deviated from the front.
[0010]
Therefore, one object of the present invention is to provide an ultrasonic transducer having wideband frequency characteristics by changing the thickness of a small diameter transducer without
affecting directivity or radiation direction.
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[0011]
SUMMARY OF THE INVENTION The ultrasonic transducer according to the present invention for
solving the problems of the prior art is a large-sized ultrasonic transducer having a large-area
radiation surface, in which a plurality of small transducers having a small-area radiation surface
are arranged. The thickness of each small transducer is randomly changed in the arrangement
direction in at least a central portion of the large transducer.
[0012]
According to a preferred embodiment of the present invention, the thickness of each small
transducer is separated into a plurality of groups.
[0013]
According to another preferred embodiment of the present invention, the variation range of the
thickness of each small transducer is set to approximately 20%.
[0014]
According to still another preferred embodiment of the present invention, each of the small and
large vibrators has a disk shape.
[0015]
DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a view showing the structure of an
ultrasonic transducer according to an embodiment of the present invention, wherein (A) is a plan
view and (B) is a cross-sectional view.
The ultrasonic transducer T of this embodiment is formed by closely combining a plurality of
small diameter transducers t1, t2, t3, ... each having a disk-shaped radiation surface and adhering
and fixing them to each other It is done.
The small diameter transducers t1, t2, t3... Are made of conventional piezoelectric ceramics
produced by conventional processing such as molding using a press or firing.
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[0016]
The small-diameter ultrasonic transducers t1, t2, t3... Are rigidly connected to each other by
interposing a layer of an appropriate adhesive such as a conventional epoxy resin or urethane
resin, respectively, and being firmly coupled to each other. A large disk-shaped ultrasonic
transducer T is formed.
The small diameter transducers constituting the large diameter ultrasonic transducer T are, as
shown in the sectional view (B) of FIG. 1, any of four groups having four different thicknesses T1,
T2, T3, T4. Belongs to one.
The four types of thickness differ by δ in the manner of T1-T2 = T2-T3 = T3-T4 = δ.
[0017]
For example, in the case where small diameter vibrators having a diameter of 5 mm are gathered
to form a large diameter vibrator having a diameter of 60 mm, the ratio of the area of the gap
formed between the three adjacent small diameter vibrators is If it is estimated to be about 5% of
the total area of these three transducers, approximately 136 small diameter transducers are
required.
The approximately 136 transducers are divided into four equal groups, each of which is divided
into approximately 34 groups of four. Assuming that the maximum thickness T1 is 15 mm and
the minimum thickness is 12 mm, which is 20% less than the maximum thickness, the
intermediate thicknesses T2 and T3 are 14 mm and 13 mm, respectively. A large diameter
transducer T is produced by collecting four groups of transducers having different thicknesses by
1 mm in random order and adhering and fixing them to each other.
[0018]
An irregular surface having no regularity is formed on the surface of the large diameter
ultrasonic transducer T thus formed. For this reason, a smooth concave surface as illustrated in
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FIG. 2B, a smooth convex surface as illustrated in FIG. 5, or a regular aspect or plane such as an
inclined surface as illustrated in FIG. 6 is formed. I will not. As a result, it is possible to effectively
avoid a situation in which the directivity of transmission and reception is sharpened or dulled, or
the direction of the radiation of the ultrasonic wave is inclined.
[0019]
Heretofore, the configuration has been exemplified in which the thickness is randomly changed
over the entire region in the central direction. However, in consideration of the convenience of
holding the peripheral portion, etc., the outermost peripheral portion may be configured to set a
uniform thickness over an appropriate width.
[0020]
As described above in detail, in the ultrasonic transducer according to the present invention, the
large-sized transducer having a large-area radiation surface in which a plurality of small-sized
transducers having a small-area radiation surface are arranged. As it is configured so that the
thickness of each small transducer is randomly changed in the arrangement direction at least at
the central portion of this large transducer, directivity and radiation direction are not affected.
The thickness of the small diameter transducer can be changed, and an effect that an ultrasonic
transducer having wide-band frequency characteristics can be realized is exhibited.
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