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JPS61278299

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DESCRIPTION JPS61278299
[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 probes are widely used
for non-invasive diagnosis, where dynamic observation is performed using soft tissues such as
the abdomen and chest as images by applying to the skin surface, 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 the property that as the frequency increases, the
wavelength decreases and the propagation attenuation also increases. 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 resolution is improved by the
shortening of the wavelength of the ultrasonic wave, and the high frequency of the probe
gradually Is being developed. An example of the structure of an ultrasound probe conventionally
used in a medical ultrasound diagnostic apparatus is shown in FIG. In FIG. 3, reference numeral
10 denotes a longitudinal wave piezoelectric ceramic transducer, which is polarized in the
thickness direction and is responsible for generation and detection of ultrasonic waves such as
electromechanical energy conversion. The values of 1.4 and 15 contribute to the broadening and
loss reduction of 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
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probe shown in FIG. 2 having a double acoustic matching layer, in order to obtain good
ultrasonic pulse transmission characteristics with wide band low loss and low ripple
characteristics, the acoustic impedance density (density of the acoustic matching layer 11
(density And a velocity of sound) are aOX10'-10. OX 10 'kg // crown, acoustic impedance density
of the acoustic matching layer 12 is 2.0 × 10 ′ to 3.0 × 10′J4 / Me, and the thickness of the
acoustic matching layer 11.12 with respect to the resonant frequency of the piezoelectric
transducer A quarter wavelength is required. In order to satisfy such an acoustic impedance
density, a conventional matching layer is used as a matching material such as borate glass,
chalcogen glass, a composite material in which glass powder is mixed with epoxy resin, and
epoxy resin, acrylic resin etc. as matching layer 12. ing. In the case of attaching the matching
layer to the transducer 10, a method is used in which, 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
transducer 10.
In the case of a composite material in which a resin or resin is blended with an appropriate
amount of glass fine powder, it is previously formed into a sheet having a desired thickness and
bonded with an adhesive, or on the converter 10 or matching layer 1). Methods such as direct
casting are used. However, although there is no high frequency in such a conventional method,
the presence of the adhesive layer between the transducer and the matching layer is a problem,
and the interposition of the adhesive layer significantly increases the performance of the probe.
There was a drawback of being lost. In addition, in the case of forming a matching layer with a
composite material in which a glass powder is mixed with an organic resin or the organic resin
itself, it is difficult to realize a matching layer having a uniform thickness as the matching layer
becomes thinner. There is a drawback that the performance of the probe is impaired.
Furthermore, when the matching layer is formed of the organic resin and the composite material
in which the glass powder is mixed with the organic resin, the thinner the matching layer is, the
more easily the bonhole opens and the manufacturing yield of the probe decreases. Therefore, in
the conventional manufacturing technology, it is extremely difficult to stably obtain a probe
having a matching layer having a thickness of 1100 p or less. Therefore, in a probe which is
practically used in a high frequency band, one matching layer is used. The main ones are those
having at most two acoustic matching layers. An ultrasonic probe having a triple matching layer
which can be broadened more than the double matching layer is not feasible. SUMMARY OF THE
INVENTION The object of the present invention is to eliminate the above-mentioned drawbacks
of the conventional ultrasonic probe and the method of manufacturing the same and to stably
obtain a high-performance broadband ultrasonic probe applicable to high frequency regions. It is
(Structure of the Invention) The present invention is formed by laminating a piezoelectric
transducer having electrodes on the front and back surfaces and an electrode on the subject side
of the piezoelectric transducer, and forming a quarter wavelength of the resonant frequency of
the piezoelectric transducer And a plurality of acoustic matching layers having a thickness
corresponding to the thickness of the conductive matching layer, a conductive film is formed at
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the boundary of each acoustic matching layer, and the other acoustic matching layers are formed
directly on the electrodes of the piezoelectric transducer An acoustic matching layer is formed by
electrophoresis on an electrode on the subject side of an ultrasonic probe characterized in that a
conductive layer is formed inside the matching layer, and a piezoelectric transducer having
electrodes on the front and back surfaces. Forming a conductive film on the acoustic matching
layer, and electrodepositing on the conductive film an acoustic matching layer thinner than a
thickness corresponding to a quarter wavelength of the resonance frequency of the piezoelectric
transducer Forming a conductive layer on the acoustic matching layer, and forming sound on the
conductive layer Forming a matching layer by an electrodeposition coating method and finally
forming an acoustic matching layer having a thickness corresponding to the quarter wavelength,
which is a method for manufacturing an ultrasonic probe .
(Detailed Description of Configuration) The ultrasonic probe according to the present invention is
based on electrodeposition technology to form a precisely controlled uniform matching layer by
including the adjustment step of the acoustic matching layer. Solves the problems of the
conventional ultrasonic probe and its manufacturing technology. FIG. 1 is a perspective view
showing an example of an ultrasonic probe according to the present invention. The structure and
the manufacturing method will be described in detail with reference to the drawings. In FIG. 1,
20 is a piezoelectric ceramic transducer, 24 is a backing, and 25 and 26 are electrodes formed
on the front and back surfaces of the piezoelectric ceramic plate by a method such as baking,
sputtering, vapor deposition or plating. An acoustic matching layer 21 is formed by applying a
potential to the electrode 25 and performing electrophoresis. An apparatus for forming an
acoustic matching layer is shown in FIG. The method of forming the low acoustic matching layer
21 (in this case, borosilicate glass) will be described with reference to FIG. In order to carry out
the electrophoresis method, the piezoelectric transducer 20 is placed in a tank 35 containing
slurry 34, and a DC voltage is applied to the electrode 25 by a DC power source 36 to apply glass
particles. The slurry 4 for electrophoresis may be, for example, a mixture liquid of ethyl alcohol,
polyvinyl butyral and water, in which a borosilicate glass fine powder is sufficiently uniformly
dispersed by a homogenizer. The tank 35 containing the slurry 4 is stirred using a stirrer 37 so
that the slurry 4 becomes uniform, and a DC voltage is applied between the electrode 25 and the
counter electrode 32. As a result, a uniform glass fine powder layer is formed on the surface of
the electrode 25. After that, an acoustic matching layer of glass can be formed by heat-treating
an object comprising a piezoelectric ceramic transducer and a glass fine powder layer at a high
temperature of 500 ° C to 900 ° C. Glass, in particular, borate glass is about twice as fast as an
organic resin in sound velocity, and it is easy to realize an optimum matching layer thickness by
controlling the time or voltage in the electrophoresis method. In addition, since the thickness of
glass can be controlled by polishing, it is also possible to realize an optimum thickness by planeparallel polishing. In the case of an ultrasonic probe having three acoustic matching layers as
shown in FIG. 1, the specific acoustic impedance (the product of density and sound velocity) is 10
× IO '˜15 × 10 @ kg as the material of the acoustic matching layer. Preferred materials are
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borate, borate glass, borate glass and the like. After the acoustic matching layer 21 is formed by
the electrophoresis method and the subsequent heat treatment as described above, a high DC
voltage is applied to the electrodes 25.26 to impart piezoelectricity to the piezoelectric ceramic
plate 20. A conductive layer 27m is provided on the surface by a method such as plating,
evaporation or sputtering, and the acoustic matching layers 22a, 22b, 23a, 23b are sequentially
formed by an electrodeposition coating method.
That is, reference numeral 22 & is an acoustic matching layer formed by applying a potential to
the conductive layer 27 m by electrodeposition coating. As shown in FIG. 1, in the case of an
ultrasonic probe having three acoustic matching layers, the material of the matching layer 22a
has an intrinsic acoustic impedance value of 3.0 × 10 ′ to 4.5 × 10′kq / co. The material of
the east is preferable, and in this electrodeposition coating method, an inorganic resin can be
uniformly dispersed in an organic resin, using an organic resin such as a phenol resin or an
epoxy resin as a matrix. In addition, as an inorganic fine particle, graf eye), TtO, and BN. AIN, Al,
O, etc. can be used. After electrodeposition of the matching layer 22b for a little less than the
time required to obtain the desired thickness, the matching layer 21 which is a viscous fluid is
completely solidified by heat treatment. Furthermore, conductive @ 28 & made of AJ, Ni, Ag, Au,
etc. is formed sufficiently thin on the surface of the solidified matching layer 22 & by
evaporation, sputtering or plating, and the film thickness of the matching layer 22 a is measured.
. Then, a potential is applied to the conductive film 28a based on the measured value so as to
obtain an optimum thickness, and the matching layer 22b having the same acoustic impedance
as the matching layer 21a is formed in the same manner. Only then can the thickness of the
acoustic matching layer consisting of 22 & and 22b be made to match the design value with high
precision. That is, in order to achieve the optimum thickness of the matching layer in one
electrodeposition coating method, the speed of sound of the organic resin as the matrix is
extremely slow compared to inorganic substances such as glass and porcelain, so it is necessary
to As the thickness becomes thinner, it requires much skill and considerable skill, and in the
present invention, the function of adjusting the thickness of the matching layer is provided so
that an ordinary worker can realize the optimum thickness. Next, the conductive film 27b is
formed thinner than the matching layer 22b sufficiently by sputtering, evaporation or plating on
the surface of the solidified acoustic matching layer 22b, and the matching layer 23a, the
conductive film 28a and the matching layer 23b are sequentially formed in the same manner. Do.
As a material of the matching layers 23m and 23b, the intrinsic acoustic impedance is 1.degree.
A urethane resin of 1 × 10 'kg / ld · 鴬, an epoxy resin, and the like are preferable. When the
conductive films 27m, 27b, 28m and 28b are used as electrodes for shielding, they can block
external noise coming into the converter 20 from the living body (subject) side, which has an S /
N ratio Contribute to improvement. The conductive films 27a, 27b, 28a and 28b are matching
layers 21 and 22a.
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It should be formed sufficiently thinner than the matching layers 21, 22m, 22b, 23a, 23b so as
not to impede the operation of 22b, 23a, 23b. Here, the electrodeposition technique will be
briefly described. The coating method 5 is a method in which a substrate to be coated and a
counter electrode are dipped in a water-based paint, and a DC current is passed between the two
electrodes to coat the substrate in a pneumatic manner. 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. ) When the substrate
and the counter electrode are immersed in such a paint, and a cationic electrodeposition paint is
applied with a direct current voltage with the substrate being negative and the counter electrode
being positive, a chemical reaction occurs on the surface of the substrate, and the coating film
Resin and filler for formation are deposited. The amount of resin and filler to be deposited can be
controlled by the applied voltage and current for 1 hour, the paint film thickness can be
arbitrarily controlled, and it is possible to uniformly attach on the surface of the object without
pinholes. In a conventional electrodeposition paint, it can be washed with water after
electrodeposition and heated to cure the resin to form a uniform coating film. 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 manufacturing method of the present invention, firstly, in the electrodeposition
coating method, inorganic fine particles can be uniformly dispersed in the organic resin, and
furthermore, the blending degree of the inorganic fine particles can be controlled over a
considerably wide range. it can. 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 factors of electrodeposition time,
voltage and current at the time of electrodeposition. In particular, the probe according to the
present invention has an advantage that the thickness of the acoustic matching layer can be
finely adjusted due to its structure, and an optimum thickness of the acoustic matching layer can
be realized with high accuracy. Third, since the matching layer formed by the electrophoresis
method and the electrodeposition coating method is gradually thickened so as to deposit snow as
in deposition and sputtering, the matching layer should be formed as thin as possible. In
particular, it can be said that the method is extremely effective for realizing an ultrasonic probe
in a high frequency band.
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.) The fifth advantage is that the matching layer can be formed
without interposing an 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
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center frequency in the 2 MHz to 7.5 MHz band but also in a high frequency band of 10 MHz or
more. EXAMPLE An ultrasonic probe for an IJ near array having a center frequency of 15 MHz
and having two acoustic matching layers shown in FIG. 1 will be described as an example of an
ultrasonic probe according to the present invention. In this embodiment, the piezoelectric
transducer 20 made of pbTiOm-based piezoelectric ceramic was used, and an Au / Cu vapor
deposition electrode having a thickness of 3000 × was used for each of the electrodes 25 and
26U. The matching layer 21 is formed in a large number by depositing fine borate glass powder
uniformly on the surface of the electrode 25 by electrophoresis, and then performing heat
treatment at 800 ° C. for 10 minutes. The measured value of the specific acoustic impedance
(defined by the product of density and sound velocity) of the matching layer 21 was 13.8 × 10
′ kg / n / set. After polarization treatment of the transducer 20, a conductive film 27 瓢 of 2000
A thick is formed on the surface of the matching layer 21 by evaporation, and the specific
acoustic impedance 4. An acoustic matching layer 22 'having I X 10' k4 / nl- '& was formed.
After the matching layer 22a was cured by heat treatment at 150 ° C. for 2 hours, 2000 Å thick
AJ was deposited to form the conductive film 28m, and the matching layer 22b was formed using
the same material as the matching layer 22a. Since the thickness of the matching layer 22a was
96g6 of a quarter wavelength for the resonance frequency of 15 MHz of the measurement result
converter, the remaining 4% of the matching layer 22b was formed. Both of the matching layers
22m and 22b were made of a composite material in which an appropriate amount of 0.5 μm
particle size A and O 8 were uniformly dispersed with an epoxy resin as a matrix. Next, an Aj
conductive film 27b having a thickness of 200 OA is vapor-deposited on the surface of the
matching layer 22b, and it is made of an acoustic matching layer 23m, 23b and AI having 9 / nlplexus at an acoustic impedance density 195X 10 @ by the electrodeposition coating method. A
conductive film 28b was formed. Similarly, the thickness of the matching layer 23m + 23b was
adjusted to be a quarter wavelength with respect to the resonant frequency of 15 MHz of the
converter. The thickness of the matching layer 22m + 22b was 4 bpm, and the thickness of the
matching layer 23m + 23b was 33 μm.
It has an extremely wide band characteristic of 90 g6 at the time of water load in the relative
bandwidth of the prototyped ultrasonic probe, and the ripple in the pass band is also less than i, s
dB. Furthermore, as a result of evaluating this probe using a gel-like sample having the same
acoustic impedance density and ultrasonic attenuation coefficient as a living body, a distance
resolution of 0.51 ff or less is easily obtained, and an S / 'N ratio Was also good. (Effects of the
Invention) According to the present invention as described above, a highly accurate acoustic
matching layer can be realized without interposing an adhesive layer, thereby obtaining a high
performance ultrasonic probe which can be used in a high frequency region. Can.
[0002]
Brief description of the drawings
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[0003]
1 shows an example of an ultrasonic probe according to the present invention, FIG. 2 shows an
example of an apparatus for electrodeposition coating, and FIG. 3 shows an example of a
conventional ultrasonic probe. Figure.
In the figure, 10.20 is a piezoelectric ceramic transducer, 11 ° 12.21.22 m, 22 b, 23 m, 23 b is
an acoustic matching layer, 13.24 is backing, 14.1 5.25, 26 is an electrode, 27 a = 27. b * 28 m28 b: conductive film, 32: counter electrode, 34: slurry, 35: bath, 36: DC power supply, 37: star 2
°
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