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JPS61278298

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DESCRIPTION JPS61278298
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic probe which is used in a medical diagnostic apparatus etc. and controls transmission
and reception of ultrasonic waves, and in particular, a portion having a central frequency in a
high frequency band of 10 MHz or more and a shallow portion from the surface. The present
invention relates to an ultrasonic probe that can be clearly drawn and a method of
manufacturing the same. (Conventional technology) Medical ultrasound probe is widely used for
non-invasive diagnosis where dynamic tissue observation is performed using soft tissue as an
image, which is applied to the skin surface and the abdomen and the chest, but in order to obtain
accurate diagnostic information recently There is an increasing demand for swallowing an
ultrasound probe with a high central frequency (usually 7.5 MHz or more) from the mouth and
clearly depicting the state of the mucous membrane of the stomach wall as an image. Similar to
electromagnetic waves, ultrasonic waves have a property that the wavelength becomes shorter as
the frequency becomes higher, and the propagation attenuation also increases accordingly.
Therefore, a high frequency ultrasound probe is unsuitable for the diagnosis of the deep part of
the human body. However, for the purpose of capturing a shallow part as a clear image like
inspection of the stomach wall, the high frequency probe has an advantage that the wavelength
of the ultrasonic wave becomes shorter and the resolution is improved by only the part. Is getting
rid of. An example of the structure of an ultrasonic probe conventionally used for a medical
ultrasonic diagnostic apparatus is shown in FIG. In FIG. 2, it is a 10 ti longitudinal wave
piezoelectric ceramic transducer, which is polarized in the thickness direction and is responsible
for generation and detection of ultrasonic waves by electromechanical energy conversion. 1.4
and 15 indicate electrodes, and arrows indicate polarization directions. Reference numerals
7'h11 and 12 denote acoustic matching layers that determine the acoustic impedance matching
between the object and the transducer 10, and contribute to the broadening and loss reduction of
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the probe. A backing 13 has a function of supporting the piezoelectric transducer and absorbing
an ultrasonic wave propagating to the rear of the transducer 10. In the probe shown in FIG. 2
having a double acoustic matching layer, the acoustic impedance density (density of the acoustic
matching layer 11 can be obtained to obtain good ultrasonic pulse transmission characteristics
with wide band low loss and low ripple characteristics. Is defined as the product of and the speed
of sound is 8. OX10’∼10. Ox10’KP/rn’@Sec。 The acoustic impedance
density of the acoustic matching layer 12 is P / + n ′ ′ sec to 2.0 × 10 ′ to 3.0 × 10 ′, and
the thickness of the Benin acoustic matching layer 11.12 is 1⁄4 of the resonant frequency of the
piezoelectric transducer The wavelength is required. In order to satisfy such acoustic impedance
density, conventionally, a composite material in which glass powder is mixed with borate glass,
chalcogen glass or epoxy resin as matching layer 11, epoxy resin, acrylic resin or the like is used
as matching layer 12. ing.
When the matching layer 9 is attached to the converter 10, if it is a glass plate, parallel plane
polishing is performed with high accuracy to process it into a thin plate, and the thin plate is
bonded to the converter 10. Further, in the case of a composite material in which a glass powder
is blended with a resin or resin in an appropriate amount, a sheet having a desired thickness is
bonded in advance with an adhesive or the converter 10 or 9 is on the matching layer 11.
Methods such as direct casting to are used. However, in order to realize the ultrasonic probe of
high frequency band by such a conventional method, it is not essential to make the matching
layer thin in inverse proportion to the frequency, but it is necessary to convert the transducer
and The existence of the matching layer and the adhesive layer between the matching layers is a
problem, and the interposition of the adhesive layer significantly impairs the performance of the
probe. In the case where the matching layer is formed by the composite material in which the
glass powder is mixed with the organic resin or the organic resin itself, it is difficult to realize the
matching layer having a uniform thickness as the matching layer becomes thinner. There is a
disadvantage that the performance of the probe is impaired. Furthermore, when the glass powder
is mixed with the organic resin and the organic resin and the matching layer is formed of the t
composite material, the thinner the matching layer is, the more easily the pinholes are opened
and the manufacturing yield of the probe decreases. Therefore, it has been extremely difficult to
stably obtain a probe having a matching layer with a thickness of 100 μm or less by
conventional manufacturing techniques. (Structure of the Invention) According to the present
invention, as a first invention, a piezoelectric transducer provided with electrodes on the front
and back surfaces, and an electrical target formed on the object side of the piezoelectric
transducer on the object side An ultrasonic probe comprising a single acoustic matching layer
having a thickness corresponding to one-half wavelength, wherein one conductive layer is
formed inside the acoustic matching layer, In the invention, an electrode is provided on the front
and back surfaces, and a piezoelectric transducer and an electrode on the subject side of the
piezoelectric transducer are laminated and formed, which corresponds to a quarter wavelength
of the resonance frequency of the piezoelectric transducer. An ultrasonic probe comprising: a
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plurality of acoustic matching layers having a thickness; a conductive film being formed at the
boundary of each acoustic matching layer; and a conductive layer being formed inside each of
the acoustic matching layers. As a third invention, the thickness corresponding to a quarter
wavelength of the resonance frequency of the piezoelectric transducer Forming an acoustic
matching layer by an electrodeposition coating method, forming a conductive layer on the
acoustic matching layer, forming an acoustic matching layer on the conductive layer by an
electrodeposition coating method, and finally And a step of forming an acoustic matching layer
having a thickness corresponding to the above-mentioned quarter wavelength, which is a
manufacturing method of an ultrasonic probe.
SUMMARY OF THE INVENTION The object of the present invention is to eliminate the abovementioned drawbacks of the conventional ultrasonic probe and the method of manufacturing the
same, and to stably obtain a high-performance ultrasonic probe applicable to a high frequency
region. It is a thing. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The method
of manufacturing an ultrasonic probe according to the present invention is based on
electrodeposition technology and precisely controlled by including the adjustment of the layer
thickness of the acoustic matching layer. By forming the matching layer, the problems of the
conventional ultrasonic probe and its manufacturing technology are solved. FIG. 1 is a
perspective view showing an example of a probe ultrasound probe according to the present
invention, and the structure and manufacturing method will be described in detail according to
the drawings. In FIG. 1, a piezoelectric ceramic transducer 20 is polarized in the direction of the
arrow in the figure. An electrode 24.25 is an electrode formed by baking, sputtering, vapor
deposition, plating or the like on the front and back surfaces of the piezoelectric ceramic.
Reference numeral 21a denotes an acoustic matching layer formed on the piezoelectric ceramic
plate by applying an electric potential to the memory electrode 25 and forming the electrode by
the electrodeposition coating method. As shown in FIG. 1, in the case of a probe having two
acoustic matching layers, this electrodeposition coating method uses an organic resin such as
tunol resin or epoxy resin as a matrix as a material of the acoustic matching layer 21a. A
compound in which inorganic fine particles are uniformly dispersed in an organic resin can be
used. In addition, as inorganic particles, graphite, Tie,, BN, Al! N 2, Al, O, etc. can be used. After
the matching layer 21 is electrodeposited a little bit more than the time required to obtain the
desired thickness, the matching layer 21 which is a viscous fluid is completely solidified. In
addition, vapor deposition, sputtering or plating on the surface of the matching layer 21a! J) A
conductive film 27a of A /, Nt, Ag, Au or the like is formed sufficiently thinner than the matching
layer 21a, and the film thickness of the matching layer 21a is measured. That is, it takes
considerable skill to realize the optimum thickness of the matching layer in one electrodeposition
coating method, and the present invention adjusts the thickness of the matching layer so that the
optimum thickness can be realized even by ordinary workers. It has a function. Next, a potential
is applied to the conductive film 27a so as to obtain an optimum thickness, and a matching layer
21b having the same acoustic impedance as the matching layer 21a is formed in exactly the
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same manner. Only then can the thickness of the matching layers 21a and 21b be made to match
the design values with high precision. Next, the conductive film 26 is formed sufficiently thinner
than the matching layer 21b by the same method on the surface of the matching layer 21b, and
the matching layer 22a1 conductive film 27b and the matching layer 22b are sequentially
formed by the completely same method.
As a material of the matching layers 22a and 22b, a composite material in which a small amount
of inorganic fine particles is dispersed in an epoxy resin or epoxy resin is convenient. In the case
where the conductive films 27a and 26.27b are used as electrodes for shields, external noise e
(which can be interrupted from the living body (subject) side and entering the transducer 20 can
be cut off, which is 8 / N ratio Contribute to improvement. The conductive films 27a, 26 and 27b
are the matching layers 21a. It should be formed sufficiently thinner than the matching layers
21a, 21b, 22a, 22b to prevent the movement of the members 21b, 22a, 22b. In the above
description, it goes without saying that the manufacturing method of the present invention can
be applied even if the piezoelectric transducer is a piezoelectric ceramic and t is a mere 5 force
organic piezoelectric material of PVF 2 as a piezoelectric transducer. Yes. Here, the
electrodeposition technique will be briefly described. The electrodeposition coating method is a
method in which a substrate to be coated and a counter electrode are immersed in a water-based
paint and electrically coated by passing a direct current between the two electrodes. Here, a
cationic electrodeposition paint will be described as an example. In the water-based paint, a resin
to be a water-soluble matrix is dissolved, and further, inorganic fine particles to be a filler in the
coating film are dispersed. (Of course, electrodeposition coating is possible without inorganic
particles. In this way, if the substrate to be coated and the counter electrode are immersed, and if
the substrate is negative and the counter electrode is positive if a cationic electrodeposition paint
is applied, a chemical reaction occurs on the surface of the substrate to cause a coating film. A
well-formed resin and filler precipitate out. The amount of resin and filler to be deposited can be
controlled by applied voltage, current, time, paint film thickness can be arbitrarily controlled, and
moreover it is possible to form pinholes uniformly on the surface of the object to be coated. . In a
conventional electrodeposition paint, it can be washed with water after electrodeposition and
heated to cure the resin to form a uniform copper coating. On the other hand, there are anionic
electrodeposition paints as well as cationic electrodeposition paints as an electrodeposition paint,
in which case a uniform coating film can be similarly formed by connecting the object to be
coated positive and the counter electrode negative. it can. That is, according to the production
method of the present invention, first, inorganic fine particles can be uniformly dispersed in the
first K organic resin, and furthermore, the blending degree of the inorganic fine particles can be
adjusted in a considerably wide range. Since the acoustic impedance naturally changes as the
blending degree of the inorganic fine particles changes, it is possible to easily realize a matching
layer having an ideal acoustic impedance as designed. Second, the thickness of the acoustic
matching layer can be easily controlled by adjusting at least one of the electrodeposition time,
the voltage and the current factor at the time of electrodeposition.
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In particular, the probe according to the present invention has an advantage that the thickness of
the acoustic matching layer can be finely adjusted in structure, and the thickness of the acoustic
matching layer can be optimally realized with high precision. Third, the matching layer formed
by the electrodeposition coating method is gradually formed thicker as snow is deposited as in
the case of vapor deposition and sputtering, so that the matching layer can be formed as thin as
possible, and particularly the high frequency band It can be said that it is a very effective method
for realizing an ultrasound probe of Fourth, no pinholes occur in the matching layer as a
characteristic of electrodeposition. (If pinholes occur during electrodeposition, the organic resin
and the filler are deposited so as to completely block the pinholes. 5.) There is an advantage that
the matching layer can be formed without interposing the adhesive layer. Therefore, according to
the present invention, a high performance ultrasonic probe can be obtained not only in an
ordinary ultrasonic probe having a center frequency in the 2 MHz to 7.5 MHz band but also in a
high frequency band of 10 MHz or more. EXAMPLE 1 As an example of an ultrasonic probe
according to the present invention, an ultrasonic probe for an I7 near array having a center
frequency of 15 MHz and having two layers of acoustic matching layers as shown in FIG. 1 will
be described. In the present embodiment, the piezoelectric transducer 20 made of PbTiO3 based
piezoelectric ceramic was used, and the electrodes 24.25 used Au / Cr vapor deposited
electrodes each having a thickness of 3000 ×. The matching layer 21a is made of a composite
material in which an epoxy resin is used as a matrix and the particle size O15 μm Altos Kl ′ ′
uniform amount is dispersed uniformly, and the acoustic impedance density 8.3 × 10 ′ ′ IF7
rr? ・ We realized see. Hardening matching layer 21a, hole diameter, person lf of zoooi
thickness: Vapor deposited to make conductive film 27m, and composite material identical to
matching layer 21a? The matching layer 21b was completely formed by using. The thickness of
the matching layer 21a is 92 quarters of the quarter wavelength for the resonance frequency of
15 MHz of the measurement result converter, so that the remaining eight inches of the matching
layer 21b is formed. Next, the AI of 2000 ^ thickness on the surface of the matching layer 21b!
Conductive film 26f: formed by vapor deposition, acoustic impedance density 2.4 × 10 'KP / rr?
Matching layers 22a and 22b made of epoxy resin having -5 ea f and a conductive film 26b made
of AJ were formed. Similarly, the thickness of the matching layer 22a + 22b was adjusted to be a
quarter wavelength with respect to the resonant frequency of the converter. The thickness of the
matching layer 21a + 21b is 51 μm, and the thickness of the matching layer 22a + 22b is 45
μm.
Next, using a gel-like sample having the same acoustic impedance density and ultrasonic
attenuation coefficient as the living body, the probe based on the present invention is evaluated
and as a result, a distance resolution of 0.5 or less is easily obtained. Also, the S / N ratio is good.
(Embodiment 2) As another embodiment based on the present invention, the acoustic matching
layer is a single-layer near-array ultrasonic probe with a center frequency of 15 MHz. In this
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embodiment, since the acoustic matching layer is a single layer, the structure shown in FIG. 1 has
a structure in which the matching layers 22a and 22b and the conductive film 26 are just
removed. As the piezoelectric transducer 20, PbTi0. The electrode 24.25 uses a Cr / Au vapor
deposition electrode of the same <3000 × thickness using a piezoelectric ceramic. The matching
layers 21a, 21bFi epoxy resin is mixed with an appropriate amount of AIN f having a particle
diameter of 0.5 μm and t is used, and the acoustic impedance is 4.5 × 10 'Kp / +? We have
realized see. The conductive film 273 is an AI vapor deposition film having a size of 2000, and
the method of forming the matching layers 21a and 21b is the same as that of the first
embodiment. The thickness of the matching layers 21a + 21, b is just a quarter wavelength, ie 55
μm, for the resonant frequency 15 MFlz of the transducer 20. In this probe, a relative bandwidth
of about 50 is obtained, and the probe is evaluated in the same manner as in Example 1 and as a
result, distance resolution of O37 μm or less is realized despite the fact that the acoustic
matching layer is one. , High 8 / N ratio could be maintained. (Effects of the Invention) As
described above, according to the present invention, a highly accurate acoustic matching layer
can be realized without interposing an adhesive layer, so a high performance ultrasonic probe
applicable to a high frequency region. You can get
[0002]
Brief description of the drawings
[0003]
FIG. 1 shows an example of an ultrasonic probe according to the present invention, and FIG. 2
shows an example of a conventional ultrasonic probe.
In the figure, 1 'C110 and 20 are piezoelectric ceramic transducers, 11.12. jl, a, 21b, 22a, 22b
are acoustic matching layers, 13.23 is a backing, 14, 15.24.25 are electrodes, 26, 27a, 27b are
conductive films. Penetration 1 Figure 20; Piezoelectricity X 21 a, 211), zza, nb: Acoustic
combination 123; Batkinwa "Z !!, Z5; Electric talent 2A; Zla, 27b: 4 t film Fig.
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