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JPH0690498

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DESCRIPTION JPH0690498
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic transducer in which a vibrator, a matching layer and a backing layer are disposed in a
case, and one end of a cable is connected to the vibrator.
[0002]
2. Description of the Related Art Ultrasonic transducers are used as probes for medical diagnostic
devices and metal flaw detection devices for nondestructive testing. The ultrasonic transducer
may be called an ultrasonic probe, an ultrasonic probe head, an ultrasonic probe or the like.
[0003]
Ultrasonic transducers can be divided into single probes and array probes according to their
forms. The array probe can be further subdivided into a linear array, an anchor array, and a twodimensional array. Also, as a special type mainly used in the medical field, a probe for a catheter
that can be inserted into a body cavity by incorporating it into a mechanical probe (usually called
a mechanical probe) that mechanically scans a single probe or an endoscope. However, these are
currently in the process of being commercialized.
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[0004]
The ultrasonic transducer is configured to convert an electric pulse sent from the apparatus main
body into an ultrasonic pulse and emit it toward the subject, and detect and convert the
ultrasonic pulse reflected from the subject into an electric signal. It has become.
[0005]
The basic configuration of the ultrasonic transducer will be briefly described.
The ultrasonic transducer has a case, and the case is provided with a transducer, a backing
material, a matching layer, and the like. The vibrator is an element that converts an electrical
signal into an ultrasonic wave or an ultrasonic wave into an electric signal, and is usually used for
both transmission and reception. Electrodes are formed on both sides of the vibrator, and the
electrodes are connected to the apparatus main body via lead wires and cables. A backing
material (back damping material) is bonded to the back of the transducer, and an acoustic
matching layer (matching layer) is disposed on the opposite radiation surface. An acoustic lens
may be attached to the acoustic matching layer to focus the ultrasonic waves. Generally, a
ceramic piezoelectric material (piezoelectric material) is used as a vibrator material, but a
polymeric piezoelectric material (piezoelectric material) such as PVDF or a composite
piezoelectric material (piezoelectric material) in which both are combined is also used.
[0006]
In recent years, cases where ultrasonic transducers are used in vivo or in water are increasing.
However, conventional ultrasonic transducers have not been designed with particular emphasis
on waterproofness. However, there was a case where a waterproof coating was formed on the
surface of the acoustic matching layer for routine waterproofing, and then the coating was
processed to a thickness of 4 wavelength.
[0007]
However, when a conventional ultrasonic transducer which is not waterproofed is used for a long
time in water or in vivo, water gradually becomes internal from the boundary surface of each
member and the surface of the acoustic matching layer. Intrusive, there were various problems.
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In other words, the acoustic matching layer is peeled off, the properties are deteriorated due to
swelling, and an electrical leak occurs between the electrodes.
[0008]
On the other hand, in the case of the conventional ultrasonic transducer in which the waterproof
coating material is formed on the surface of the acoustic matching layer as described above, the
thickness of the coating layer is adjusted to the thickness of wavelength / 4 after forming the
coating layer. It has to be done, and it takes time and effort, and it is expensive. In addition, water
may infiltrate from the boundary between the acoustic matching layer and other members, and
the waterproof effect is not sufficient.
[0009]
These problems become serious as the ultrasonic transducer is miniaturized and the frequency is
increased and the frequency of use in water or in vivo is increased, and it has been strongly
desired to provide an ultrasonic transducer which emphasizes waterproofness.
[0010]
An object of the present invention is to solve the problems of the prior art and to provide a
highly reliable and high performance ultrasonic transducer which has a long life even when used
in water.
[0011]
SUMMARY OF THE INVENTION According to the present invention, in an ultrasonic transducer
having a structure in which a vibrator, a matching layer and a backing layer are disposed in a
case and one end of a cable is connected to the vibrator, the acoustic impedance is 1.3- An
ultrasonic transducer is characterized in that the entire surface of the ultrasonic transducer is
coated with a waterproof coating material of 1.7 × 10 6 kg / m 2 · sec.
[0012]
Since the entire surface of the ultrasonic transducer is coated with the waterproof coating, water
does not directly enter the surface of the acoustic matching layer and the interface between the
acoustic matching layer and the case.
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Therefore, the life and reliability of the ultrasonic transducer are greatly improved.
[0013]
In addition, the acoustic impedance of the coating material is 1.3 to 1.7 × 10 6 kg / m 2 · sec,
which is close to 1.5 × 10 6 kg / m 2 · sec of the acoustic impedance of water. The interface
between the coating layer and the water can be neglected, and there is no need to adjust its
thickness after forming the coating layer.
[0014]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiments of the
present invention will be described below with reference to the drawings.
FIG. 1 is a cross sectional view conceptually showing an ultrasonic transducer 10 according to
the present invention.
[0015]
The ultrasonic transducer 10 includes a case 11, a vibrator 12, a matching layer 15, a backing
layer 16, and a cable 17.
The case 11 has a cylindrical shape as a whole, but can also be formed in a polygonal column
shape.
A convex portion 11 a for holding the vibrator is provided on the top of the case 11, and the
vibrator 12 is fixed thereto. The dimensions of the case 11 can be set to, for example, an outer
diameter 12 mm, an inner diameter 9 mm, and a length 10 mm, and the convex portion 11 a can
be formed to a diameter 10 mm and a depth 0.2 mm.
[0016]
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The vibrator 12 is formed of a piezoelectric material, for example, a PZT-based piezoelectric
material having a relative permittivity of ε / ε 0 = 2000 and a coupling coefficient Kt of 50%.
Further, this vibrator 12 is for 5 MHz, and the dimension and shape are 10 mm in outer diameter
and 0.4 mm in thickness.
[0017]
Electrodes 13 and 14 are formed on the sound wave emitting surface side and the back surface
side of the vibrator 12, respectively, and a winding electrode 13a is formed from the radiation
surface side to the back surface side. The electrodes 13, 14, 13a are formed by applying silver
paste to the vibrator 2 and baking it, and its thickness is set to, for example, 10 μm. The outside
diameter of the radiation side electrode is set to 10 mm, and the outside diameter of the back
side electrode is set to 8 mm. However, a part of the back side electrode is cut out and the lead-in
electrode 13a is formed there. The transducer 12 is polarized so that the ultrasonic radiation side
is the ground side.
[0018]
An acoustic matching layer 15 is disposed on the radiation surface side of the vibrator 12. The
acoustic matching layer 15 is made of, for example, an epoxy resin containing a filler material,
and the outer diameter is set to 12 mm, and the thickness is set to 0.2 mm. On the back side of
the vibrator 12, a backing layer 16 made of a filler-containing soft epoxy resin is formed. Further,
lead wires 18 and 19 from the cable 17 are connected to the electrode 14 and the winding
electrode 13a.
[0019]
The outer surface of the ultrasonic transducer 10 is coated with a fluorine-based moisture-proof
coating material 20. The acoustic impedance of the coating material 20 is 1.5.times.10@6
kg/m@2.sec and the breakdown voltage is 100 KV / mm. The thickness of the coating material
20 is set to about 0.1 mm in consideration of the electrical safety of the ultrasonic transducer.
The thickness of the coating material 20 is not particularly limited in terms of acoustic
characteristics. Therefore, the coating process of the coating material 20 is very simple. That is,
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after the ultrasonic probe is dipped in the solution of the coating material and taken out, it is only
necessary to naturally dry and cure it.
[0020]
Environmental performance tests were conducted using the ultrasonic transducer shown in FIG.
1 and a conventional ultrasonic transducer. In the test, the ultrasonic transducer was left in warm
water for a long time to investigate the occurrence of deterioration in sensitivity and occurrence
of failure.
[0021]
The state of sensitivity deterioration is shown in FIG. As apparent from FIG. 2, in the conventional
example, the sensitivity significantly decreased when 100 hours passed, whereas in the example,
the deterioration of the sensitivity was small even after 10,000 hours.
[0022]
Moreover, regarding the failure, the number of failure occurrences due to peeling of the
electrode lead or the matching layer after 10000 hours was examined. As a result, although
failure occurred in four out of ten samples in the conventional product, no failure was observed
in the ten samples in the embodiment of the present invention.
[0023]
Next, the relationship between the acoustic impedance of the coating layer and the characteristic
deterioration was investigated. That is, the acoustic impedance of the coating layer formed on the
surface of the acoustic matching layer was changed, and the rate of change in sensitivity of the
ultrasonic transducer was measured. The thickness of the coating layer was not adjusted. The
results are shown in FIG. The rate of change of sensitivity is based on the sensitivity when the
coating layer is not provided, and the rate of change is based on 0 on the vertical axis. It can be
seen from FIG. 3 that when the acoustic impedance of the coating material is in the range of 1.3
to 1.7.times.10@6 kg/m@2.sec, the same sensitivity characteristics as in the case where the
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coating layer is not provided can be obtained. Therefore, there is no need to adjust the thickness
of the coating layer. On the other hand, since the sensitivity characteristics fall outside this range,
the thickness of the coating layer needs to be adjusted, which takes time and costs.
[0024]
Thus, it has been found that the ultrasonic transducer of the present invention is excellent in
sealability, has a long life even in warm water, and does not need to adjust the thickness of the
coating layer.
[0025]
According to the ultrasonic transducer of the present invention, the entire surface of the
ultrasonic transducer is coated with the waterproof coating material, so that water directly
penetrates from the acoustic matching layer surface and the interface between the acoustic
matching layer and the case. There is nothing to do.
Also, even if water intrudes from the vicinity of the cable outlet, there is a considerable distance
to the acoustic matching layer and the transducer periphery, which are the most important
members for transmission and reception of ultrasonic waves, so water up to the periphery of
these members There is little risk of Therefore, the life and reliability of the ultrasonic transducer
are greatly improved.
[0026]
In addition, the acoustic impedance of the coating material is 1.3 to 1.7 × 10 6 kg / m 2 · sec,
which is close to 1.5 × 10 6 kg / m 2 · sec of the acoustic impedance of water. The interface
between the coating layer and the water can be neglected, and there is no need to adjust its
thickness after forming the coating layer. Therefore, the ultrasonic transducer can be
manufactured at low cost.
[0027]
The present invention is not limited to the embodiments described above. For example, the
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acoustic impedance of the coating material can be set to a range other than 1.3 to 1.7 × 10 6 kg
/ m 2 · sec in accordance with the acoustic impedance of the liquid so that it can be used in a
liquid other than water. . Also, a coating layer may be formed on the surface of the cable.
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