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JPH04128498

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
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DESCRIPTION JPH04128498
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic transducer used in water for use in fish finders and the like.
[0002]
2. Description of the Related Art Heretofore, ultrasonic transducers have been used in
apparatuses for detecting fish and the like. A fish finder is an apparatus that transmits ultrasonic
waves in water and receives ultrasonic waves reflected from a reflector such as a fish school to
acquire information related to the fish school and the like. That is, it is an apparatus for obtaining
information such as the distance and size of a school of fish from a reflected wave.
[0003]
Therefore, in such a device such as a fish finder, an ultrasonic transducer is an essential
component. The ultrasonic transducer is a device that transmits ultrasonic waves into water in
response to the application of a voltage, and conversely receives reflected waves supplied from
the water and converts them into electrical signals. An ultrasonic transducer is usually
configured with an ultrasonic transducer formed of a piezoelectric material such as PZT.
04-05-2019
1
[0004]
FIG. 2 shows the structure of an ultrasonic transducer according to one prior art example. In the
ultrasonic transducer shown in this figure, an electrode 10 of silver or the like is attached to the
surface of an ultrasonic transducer 10 formed of PZT, and signal cables 14 and 16 are bonded to
the electrode 12 by soldering or the like. Configuration. The vibrator 10 is covered by the sound
insulator 18 except in the radiation direction. The sound insulator 18 has a function of
enhancing the radiation efficiency when transmitting the ultrasonic wave generated by the
vibrator 10 into water.
[0005]
In this conventional example, the transducer 10 is excited by applying a predetermined
transmission voltage from the transmitter between the signal cables 14 and 16, and as a result,
ultrasonic waves in the direction of the arrow in the figure are transmitted into the water. Be
waved. In the water, for example, in the case of a fish finder, a reflector such as a fish school is
present, and when a reflected wave from the reflector is received again by the vibrator 10, a
reception voltage is received between the signal cables 14 and 16 Will occur. This received
voltage is supplied to the receiver and used for calculation of the size of the fish school, distance,
and the like.
[0006]
However, in the case of adopting such a configuration, it is necessary to provide a matching layer
between the vibrator and water. Since the vibrator is usually made of PZT, it has an acoustic
impedance of 35 × 10 6 kg / m 2 s. On the other hand, water has an acoustic impedance of 1.5
× 10 6 kg / m 2 s. As such, since the acoustic impedances of the two have significantly different
values, a matching layer is generally used to ensure acoustic matching and reduce reflection. As
the matching layer, a urethane resin or the like having an acoustic impedance in between is used.
[0007]
On the other hand, a piezoelectric material such as PZT used as a vibrator is usually a non-
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perforated material. That is, Pb (Zr, Ti) O3 which has been densely fired so as not to have pores,
such as lead zirconate titanate (PZT), PbTiO3, barium titanate, PbTiO3, lead titanate and the like.
When such a material is used, the mechanical strength is high and destruction is less likely to
occur even when mechanical distortion occurs, so that large power (transmission power) can be
used for transmission. However, the reception sensitivity is low because the g constant
representing the generated charge amount per 1 N of applied force is small.
[0008]
Among these problems, the problem of the reception sensitivity can be solved by using a porous
piezoelectric material having a larger g constant. As such a piezoelectric material, there is the one
described in JP-A-1-172281 proposed by the applicant of the present invention. This material is
excellent in receiving sensitivity and low in acoustic impedance as 4 to 20 × 10 6 kg / m 2 s, so
it has good acoustic consistency with water. However, since there are holes, the mechanical
strength is weak, and there is a problem that transmission power can not be increased. The
present invention has been made to solve such problems, and can increase transmission power,
has high reception sensitivity, and is acoustically compatible with an ultrasonic wave propagation
medium such as water. It aims at obtaining a good ultrasonic transducer.
[0009]
SUMMARY OF THE INVENTION In order to achieve the above object, the present invention has
an acoustic impedance Z1 and has a thickness of λ / 4 (λ: wavelength) for converting an
ultrasonic wave into an electric signal. Z 1 = (Z 0 · Z 2) 1/2 (Z 0: super), which comprises: an
ultrasonic transducer for receiving wave; and an ultrasonic transducer for transmitting wave
which has an acoustic impedance Z 2 and generates an ultrasonic wave by application of a
voltage. Acoustic impedance of the sound wave propagation medium), at the time of
transmission, ultrasonic waves are transmitted by the ultrasonic transducer for transmission
using the ultrasonic transducer for reception as a matching layer, and at the time of reception,
ultrasonic waves are received by the ultrasonic transducer for reception It is characterized in that
ultrasonic waves are received.
[0010]
The second aspect of the present invention is characterized in that the receiving ultrasonic
transducer is formed of a porous piezoelectric material having a porosity of 5 to 90% and a pore
diameter of 1 to 100 μm.
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[0011]
A third aspect of the present invention is characterized in that the receiving ultrasonic transducer
is formed of a material containing Pb (Zr, Ti) O3, BaTiO3 or PbTiO3.
[0012]
A fourth aspect of the present invention is characterized in that the receiving ultrasonic
transducer is formed of an organic piezoelectric material.
[0013]
The organic piezoelectric material forming the ultrasonic transducer may be made of PVDF:
polyvinylidene fluoride, PVDF copolymer, P (VDF / TrFE): vinylidene fluoride and ethylene
trifluoride. Copolymer or P (VDCN / VAc): characterized by being formed from a copolymer of
vinylidene cyanide and vinyl acetate.
[0014]
In the present invention, at the time of transmission, the ultrasonic transducer for reception
functions as a so-called λ / 4 matching layer.
That is, while the acoustic impedance matching is secured by the ultrasonic transducer for wave
reception, the transmission by the ultrasonic transducer for wave transmission which can obtain
large mechanical power and large transmission power is performed.
At the time of wave reception, ultrasonic waves are directly received by the ultrasonic transducer
for wave reception that functions as a matching layer at the time of wave transmission.
[0015]
In the second aspect, a porous piezoelectric material is employed as the ultrasonic transducer
material for receiving wave.
In the third aspect, a material such as PZT is set as the base material of the porous piezoelectric
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material.
Similarly, in claim 4, an organic piezoelectric material is adopted as a material for forming the
ultrasonic transducer for receiving wave, and in claim 5, PVDF or the like is set.
These materials are materials that can realize the function according to claim 1, and the
reception sensitivity is secured because the g constant is large.
[0016]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the
present invention will be described below with reference to the drawings. The same reference
numerals as in the conventional example shown in FIG. 2 denote the same parts, and a
description thereof will be omitted.
[0017]
FIG. 1 shows the structure of an ultrasonic transducer according to an embodiment of the
present invention. The ultrasonic transducer shown in this figure includes an ultrasonic
transducer 10 formed by densely firing a piezoelectric material such as PZT as a base material.
Electrodes 12 made of silver or the like are formed on upper and lower surfaces of the ultrasonic
transducer 10, and signal cables 14 and 16 are soldered to the electrodes 12, respectively.
[0018]
In addition to the above-described transducer 10, another ultrasonic transducer 20 is used in this
embodiment. The ultrasonic transducer 20 is formed of a piezoelectric material such as PZT
similarly to the ultrasonic transducer 10, but is not compact but is a porous transducer. That is, it
is formed by mixing minute spheres formed of methacrylic resin into PZT at a predetermined
rate, pressing and sintering. By burning off the methacrylic resin in the process of firing, for
example, pores of about 100 μm are formed inside. An electrode 22 of silver or the like is
deposited on the surface of the ultrasonic transducer 20, and the lower electrode 22 of the
electrodes 22 is deposited with the electrode 12 of the transducer 10 by an epoxy resin 24. The
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epoxy resin 24 used in this embodiment has conductivity, and as a result, the electrodes 12 and
22 bonded by the epoxy resin 24 function as a common electrode for the signal cable 14.
Although not shown in the present embodiment for soldering the signal cable 14, the electrodes
12 and 22 are end-face printed on the corresponding portions, but may be a foil sand. Further,
the signal cable 24 is soldered to the upper electrode 22, and the vibrator 10 and 20 form an
integral vibrator structure 26. The structure of the vibrator 26 is covered with a sound insulator
18 as in the prior art.
[0019]
In this embodiment, when ultrasonic waves are to be transmitted into water, a predetermined
transmission voltage is applied between the signal cables 14 and 16 from the transmitter. Then,
the vibrator 10 is excited, and an ultrasonic wave generated by the excitation is transmitted into
water through the vibrator 20. The vibrator 20 has a thickness of λ / 4 (λ: wavelength) in this
embodiment, and further has a value of acoustic impedance Z1 (= Z0 · Z2) 1/2. Here, Z0 is the
acoustic impedance of water and has a value of 1.5 × 10 6 kg / m 2 s, and Z 2 is the acoustic
impedance of the ultrasonic transducer 10 and has a value of 35 × 10 6 kg / m 2 s ing.
Therefore, the transducer 20 functions as a matching layer at the time of transmission. That is,
even without providing a matching layer such as urethane resin, reflection generated at the
interface is reduced, and more efficient wave transmission can be realized. In addition, since the
vibrator 10, which is a vibrator related to transmission, is formed of dense PZT, a relatively large
transmission current can be injected.
[0020]
Conversely, when receiving a reflected wave from a reflector present in water, the ultrasonic
transducer 20 receives this wave and supplies it from the signal cables 14 and 24 to the receiver.
Since the ultrasonic transducer 20 is formed of PZT having holes, the g constant is large, and
hence the reception sensitivity is good. The porous material has relatively weak mechanical
strength, but transmission is performed by the vibrator 10, so destruction of the vibrator 20 due
to a large amount of transmission power is prevented.
[0021]
In this embodiment, in order to realize the relationship between the acoustic impedances Z1 and
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Z2 described above, the porosity of the material forming the vibrator 20 may be, for example,
30%. With this setting, the acoustic impedance Z1 of the vibrator 20 is 7 kg / m 2 s, so the value
approaches 5 × 10 6 kg / m 2 s satisfying the above equation, and matching with water is
secured. . Further, in this case, the g constant is 2.2 times that of the finely fired PZT, and good
reception sensitivity is secured. However, the porosity and the hole diameter can be arbitrarily
set from the range of 4 to 90% and 1 to 100 μm, respectively. In the above description, it is
assumed that the vibrator 20 is formed of PZT having pores, but as a material for forming the
vibrator 20, an organic piezoelectric material such as PVDF may be used. When using PVDF, its
acoustic impedance Z 1 is 4 × 10 6 kg / m 2 s, which is lower than close PZT and closer to
water, so that the compatibility with water is also ensured. Also, the g constant is 16 × 10 −2
mV / N, which is sufficiently large for PVDF, as compared with 2.5 × 10 −2 mV / N for fine
PZT. Therefore, the reception sensitivity is also ensured.
[0022]
When a piezoelectric ceramic material is used as a material for forming the vibrator 10 or as a
base of the vibrator 20, a material other than PZT may be used. For example, materials such as
barium titanate and lead titanate can also be used. Furthermore, although PZT and PVDF are
shown as materials for forming the vibrator 20, materials other than this may be used. For
example, a porous piezoelectric material based on barium titanate or lead titanate may be used,
and a PVDF copolymer, a copolymer of vinylidene fluoride and ethylene trifluoride, a copolymer
of vinylidene cyanide and vinyl acetate may be used. It may be an organic piezoelectric material
such as a polymer. Even with these materials, similar effects can be obtained.
[0023]
As described above, according to the present invention, the ultrasonic transducer for receiving
wave is used as a matching layer during transmission, and the ultrasonic transducer for receiving
wave during reception. Thus, the acoustic matching with the ultrasonic wave propagation
medium such as water can be secured. Furthermore, a transducer formed of a dense material
such as PZT can be used as a transmission ultrasonic transducer, and transmission power can be
increased. By using a transducer formed of a porous piezoelectric material or an organic
piezoelectric material having high reception sensitivity as the ultrasonic transducer for reception,
it is possible to enhance the reception sensitivity.
[0024]
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According to the second aspect of the invention, since the ultrasonic transducer for wave
reception is formed of the porous piezoelectric material, the effect of improving the reception
sensitivity can be obtained by increasing the g constant.
[0025]
According to the third aspect, such an effect can be easily realized while using a base material
such as PZT.
[0026]
According to the fourth aspect of the present invention, since the ultrasonic transducer for wave
reception is formed from the organic piezoelectric material, it is possible to realize the ultrasonic
transducer for wave reception having the above-described effect from a material which is easy to
process it can.
[0027]
Furthermore, according to claim 5, the effect can be easily realized by PVDF or the like which is
relatively widely known as such a material.
[0028]
Brief description of the drawings
[0029]
1 is a cross-sectional view showing the structure of an ultrasonic transducer according to an
embodiment of the present invention.
[0030]
2 is a cross-sectional view showing a configuration of an ultrasonic transducer according to a
conventional example.
[0031]
Explanation of sign
[0032]
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10, 20 ultrasonic transducer 12, 22 electrode 14, 16, 24 electrode 18 sound insulator 26
transducer structure
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