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DESCRIPTION JPH07154898

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DESCRIPTION JPH07154898
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic transducer having a function of emitting ultrasonic waves into the air and receiving
ultrasonic waves emitted into the air.
[0002]
BACKGROUND OF THE INVENTION Ultrasonic transducers with conventional acoustic matching
layers have prioritized sensitivity. Recently, however, there has been an increasing demand for
short distance type ultrasonic transducers that are applied to the detection of an object to be
detected in proximity to the transmission / reception surface of the ultrasonic transducer. And, in
such applications, what matters most as a measurement error at the time of distance
measurement is the interference between the reverberation wave of the transmission signal and
the reception signal. Therefore, in the close range, the reverberation characteristic determines its
reliability. Usually, in such applications, the ratio of the received signal to the reverberation
voltage is 1/10 to 1/100 (20 dB to 40 dB). Things are required.
[0003]
By the way, if this reverberation characteristic is further improved, for ultrasonic proximity
switches, object detection from nearer becomes possible, and several centimeters away, which is
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the weak point of conventional electrostatic and electromagnetic proximity switches. Object
detection is also possible. In addition, with sensors that measure the speed of sound and
temperature using the propagation time of ultrasonic waves, it was difficult to miniaturize due to
the problem of reverberation, but improvement of the reverberation characteristics can also
improve this problem. It will be.
[0004]
Then, correspondingly, as shown in FIG. 7, a piezoelectric element plate c having an electrode
layer formed on the front and back surfaces is joined to the bottom of the acoustic matching
layer consisting of a bottomed cylindrical case b, An ultrasonic transducer a having a
configuration in which a damping layer d is embedded in the case b has been proposed.
[0005]
By the way, in the above-mentioned configuration, when the characteristics thereof were tested,
it was found that the improvement of the reverberation characteristics was not always sufficient.
[0006]
An object of the present invention is to provide an ultrasonic transducer having a configuration
that can further improve the reverberation characteristics.
[0007]
SUMMARY OF THE INVENTION According to the present invention, a piezoelectric element plate
having electrode layers formed on the front and back surfaces is bonded to the upper surface of
an acoustic matching plate, and a damping molded layer is supported by the bonded body to
obtain the piezoelectric element. A plate is embedded in the damping molded layer, and the lower
surface of the acoustic matching plate is exposed to form an ultrasonic wave transmitting and
receiving wave surface.
[0008]
In addition, in the above-described basic configuration, a piezoelectric element plate having the
same planar shape as that of the acoustic matching plate is joined in a uniform manner on the
upper surface of the acoustic matching plate, and a damping molded layer is supported by the
joined body. Ru.
[0009]
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In comparison with the configuration of FIG. 6, the present invention corresponds to the
configuration without the peripheral wall of the acoustic matching layer.
And since this peripheral wall did not exist, the improvement of the reverberation characteristic
was confirmed.
Furthermore, in a configuration in which a piezoelectric element plate having the same planar
shape as the acoustic matching plate is joined in a uniform shape on the upper surface of the
acoustic matching plate, the acoustic matching layer is disposed only on the lower surface of the
piezoelectric element plate Furthermore, the reverberation characteristics improved.
[0010]
The invention will be described with reference to the accompanying drawings.
[0011]
FIG. 1 shows a first embodiment of the present invention.
[0012]
In the ultrasonic transducer 1a having this configuration, the disk-shaped piezoelectric element
plate 3 having the electrode layers 4a and 4b formed on the front and back surfaces is bonded to
the upper surface of the disk-shaped acoustic matching plate 2a.
The electrode layer 4a located on the side of the acoustic matching plate 2a extends its electric
lead-out end to the surface side, and connects the lead wires 6a and 6b of the lead wire 5 to the
electrode layers 4a and 4b on the surface side of the piezoelectric element plate 3 While
applying a voltage to the electrode layers 4a and 4b of the piezoelectric element plate 3, the
signal voltage generated between the electrode layers 4a and 4b is taken out.
In this configuration, the outer diameter of the piezoelectric element plate 3 is smaller than the
outer diameter of the acoustic matching plate 2a.
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[0013]
Furthermore, a damping molded layer 7 is supported on a bonded body composed of the acoustic
matching plate 2 a and the piezoelectric element plate 3 to cover the piezoelectric element plate
3 and lead wires 5 are drawn out.
Then, the lower surface of the acoustic matching plate 2 is exposed to form an ultrasonic wave
transmission / reception f.
[0014]
In the above-mentioned configuration, as the acoustic matching plate 2a, a foamable plastic
material, a material obtained by mixing a myriad of glass balloons with plastic, or the like is used.
The damping molding layer 7 is formed by molding on a joined body, and lead titanate and lead
zirconate titanate are used as materials having large internal friction such as silicone rubber and
urethane resin. And other ceramic powder, metal powder and the like, which is formed of a
material obtained by mixing powders having a high specific gravity.
[0015]
The effect of the damping formed layer 7 is that the reverberation time becomes shorter as the
acoustic impedance is larger (as the acoustic impedance of lead zirconate titanate is closer to
about [email protected]).
[0016]
Here, FIG. 4 shows the relationship between the acoustic impedance and the reverberation time
and the reception sensitivity.
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The reverberation time indicates the time from the rise of transmission to the periphery as
shown in FIG. 5, and the reception sensitivity indicates the maximum amplitude of the reception.
[0017]
FIG. 2 shows a second embodiment.
[0018]
In the ultrasonic transducer 1b having this configuration, the disk-like acoustic matching plate
2b has the same planar shape (outer diameter) as the piezoelectric element plate 3 bonded to the
upper surface thereof.
Then, the damping molded layer 7 supported on the bonded body covers the piezoelectric
element plate 3 including the peripheral surface thereof as an outer diameter surrounding the
periphery of the bonded body.
[0019]
FIG. 3 compares the sensitivity characteristics of the current product according to FIG. 7 with
that of the configuration according to FIG. 1 (Example 1) and the configuration according to FIG.
2 (Example 2), receiving sensitivity and reverberation time .
[0020]
Here, as the case b shown in FIG. 7, one formed into a thickness H2 by a composite material
(acoustic impedance [email protected] Ns / m @ 3) prepared by mixing 25 parts by weight of a
glass balloon having a diameter of 50 microns with 75 parts by weight of epoxy resin. The same
composite material as the acoustic matching plate 2b of FIG. 2 is used as the acoustic matching
plate 2a of FIG. 1, which is formed into a disk shape of an outer diameter D3 10 mm and a
thickness H4 of 2.2 mm using the same composite material. Thus, a disk-shaped product having
an outer diameter D5 8 mm and a thickness H6 2.2 mm was used.
[0021]
A composite material in which 75 parts by weight of lead titanate powder having a diameter of
10 microns is mixed with 25 parts by weight of urethane resin as the damping formed layer d of
FIG. 7 and the damping formed layer 7 of FIGS. In the case of FIG. 7, the case is filled with Ns / m
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3), in the case of FIG. 1 it is 10 mm the same size as the outer diameter D 3 of the aligning plate
and the height H 35.8 mm. It molded so that it might become diameter D4 10 mm and height H5
7 mm.
[0022]
Furthermore, in FIG. 7, FIG. 1, and FIG. 2, the piezoelectric elements c and 3 were formed into a
disc shape having a diameter of 8 mm and a thickness of 1 mm from lead zirconate titanate.
[0023]
In addition, the measurement of the transmission / reception sensitivity characteristic was
performed using the circuit apparatus shown in FIG.
[0024]
As understood from this figure, each of the above-described configurations is improved in both
the receiving sensitivity and the reverberation time as compared with the conventional
configuration (receiving sensitivity 2.1 Vpp, reverberation time 0.25 ms) shown in FIG. I
understand.
Further, it was found that the configuration of FIG. 2 (reception sensitivity 4.1 Vpp, reverberation
time 0.20 ms) is further improved than the configuration of FIG. 1 (reception sensitivity 4.1 Vpp,
reverberation time 0.10 ms).
[0025]
In the configurations shown in FIGS. 1 and 2 above, when used in a corrosive gas atmosphere, a
film excellent in weather resistance such as polyimide is adhered or coated on the gas contact
surface (film thickness 100 μm). It becomes possible to cope.
[0026]
According to the present invention, the piezoelectric element plate 3 is bonded to the upper
surfaces of the acoustic matching plates 2a and 2b, and the damping molded layer 7 is supported
by the joined body, and the piezoelectric element plate 3 is used as the damping molded layer 7.
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By embedding, the receiving sensitivity is improved and the reverberation time is shortened.
For this reason, even when used for short distance measurement, the transmission signal and the
reception signal do not interfere with each other, which is optimal for an ultrasonic proximity
switch.
In addition, by applying to a sensor that measures the speed of sound and temperature using the
propagation time of ultrasonic waves, there is an excellent effect such that the miniaturization
can be achieved.
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