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DESCRIPTION JP2003309898

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DESCRIPTION JP2003309898
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic transducer mainly used in an ultrasonic endoscope which uses an ultrasonic wave to
image morphological tissue information in a living body as a tomogram.
[0002]
2. Description of the Related Art In recent years, an ultrasonic tomogram is obtained by
irradiating an ultrasonic wave to a living body, receiving the ultrasonic wave reflected by the
change part of the acoustic impedance in the living body, converting it into an electric signal, and
imaging it. Ultrasonic diagnostic apparatuses are widely used.
[0003]
For example, an ultrasonic endoscope is provided with an ultrasonic transducer at the tip of an
endoscope insertion portion which can be inserted into a body cavity such as a digestive tract,
and an ultrasonic tomographic image can be obtained by this ultrasonic transducer. It has been
put to practical use.
[0004]
The piezoelectric body of the ultrasonic transducer used in the ultrasonic endoscope is formed of,
for example, a piezoelectric material such as lead zirconate titanate (PZT) or lead titanate
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(PbTiO3).
The acoustic impedance of this piezoelectric body is about 20 to 30 MRayl, which is larger than
the acoustic impedance of living tissue about 1.5 MRayl, so it is not efficient in transmitting and
receiving ultrasonic waves, and matching of the acoustic impedance between the two is not
efficient. In order to achieve the above, it is necessary to mount a member as an acoustic
matching layer whose material properties are optimized.
In addition, it is desirable to arrange an acoustic lens to improve the resolution in a desired area
in the living body. As a specific method thereof, a concave-type acoustic lens having a function as
the acoustic matching layer has been conventionally configured. In such a configuration, the
relative band of the transmission and reception signals of ultrasonic waves in the vicinity of the
focus point of the acoustic lens is about 40%.
[0005]
In general, when the value of the relative band is small, the so-called depth of image penetration
and resolution of the ultrasonic tomogram is unique, and the selectivity of the clinical application
range at the time of image diagnosis is narrow. For this reason, in the examination of the
ultrasonic endoscope which mounted the transducer of about 40% of the conventional relative
band, the ultrasonic endoscope which mounted the several vibrator with the frequency and the
aperture according to the clinical purpose to apply As a result, the shape of the endoscope
insertion tip becomes large, and when inserting the endoscope into a patient, it often causes pain
to the patient who impairs the swallowing property. Alternatively, in the case of the conventional
transducer having a relative bandwidth of about 40%, it is necessary to prepare a plurality of
different types of ultrasonic endoscopes according to the clinical purpose, and in terms of
hospital management and management, efficiency is not always required. It was not target. For
this reason, there has been a demand for an ultrasonic transducer which has a wide band.
[0006]
In order to improve the specific band, a first matching layer and a second matching layer set to a
predetermined acoustic impedance for the piezoelectric body formed of PZT, PbTiO 3 or the like,
and the acoustic lens are separately provided. There is also an ultrasonic transducer. In the
ultrasonic transducer of this configuration, the ratio band of the ultrasonic transmission /
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reception signal in the vicinity of the acoustic lens focus point is improved to about 60 to 70
percent. And although it is known that a specific zone will be about 90 percent by making a
matching layer into a three-layer structure, it is difficult to form a matching layer, and many
manufacturing defects resulting therefrom It will occur.
[0007]
In order to provide the ultrasonic transducer with the above-mentioned wide band, for example,
in Japanese Patent Application Laid-Open No. 2001-178719, it is possible to reduce the diameter
of the insertion portion of the ultrasonic endoscope, and without broadening the sensitivity. An
ultrasound transducer with a fractional bandwidth of more than 100% with various image depths
is shown. Thus, for example, when the upper digestive tract is observed with the abovementioned ultrasonic endoscope, the gallbladder, the pancreas, the bile duct, and the luminal
structure of the pancreatic duct are extraordinarily single transducers from the epithelial tissue
of the digestive tract such as the stomach and esophagus. It became observable.
[0008]
In this ultrasonic transducer, as shown in the perspective view and the cross-sectional view for
explaining the composite piezoelectric body of FIGS. 6A and 6B, the piezoelectric body is formed
of, for example, a plurality of columnar piezoelectric members formed of PZT. A composite
comprising a body 21 and a resin member 22 such as an epoxy resin filled in a gap between the
columnar piezoelectric members 21 and setting the volume filling ratio of the columnar
piezoelectric members 21 so that the acoustic impedance falls within a predetermined range. The
piezoelectric body 20 is used. An acoustic matching layer having an acoustic impedance set in a
predetermined range and serving as an acoustic lens whose thickness continuously changes from
the central portion (not shown) toward the peripheral direction on the ultrasonic radiation
surface side of the composite piezoelectric body 20. To provide an ultrasonic transducer.
[0009]
However, in the ultrasonic transducer according to the above-mentioned JP-A-2001-178719, the
ultrasonic transducer shown in FIG. 7 is used in the case where the drive frequency of the
ultrasonic transducer exceeds 15 MHz. As shown in the conceptual view of the ultrasonic wave
transmission and reception characteristics in the vicinity of the acoustic lens focus, it is difficult
to secure the performance in the high frequency band, and the manufacturing yield is not
necessarily high.
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[0010]
When the manufacturing process and each part were reviewed in order to eliminate this
manufacturing yield problem, the surface condition of the ultrasonic radiation surface side 23a of
the composite piezoelectric body 20 and the backing material adhesion surface side 23b which is
the opposite side, in particular It was found by the observation of the electron microscope that
there was a difference in the surface roughness.
[0011]
The difference in the surface roughness occurs in the process of manufacturing the composite
piezoelectric material.
[0012]
Although the composite piezoelectric body 20 is manufactured through several steps when the
detailed description is added in this regard, the thickness dimension of the piezoelectric body is
set to the above-mentioned FIG. In order to set a predetermined value as shown in the above, it is
necessary to grind or polish both surfaces 23a, 23b of the piezoelectric body.
Although it is this predetermined thickness dimension t, it is a half of the sound wave wavelength
λo (= Vo / Fo) in the piezoelectric member calculated from the frequency Fo of the objective
transducer and the ultrasonic wave propagation velocity Vo in the piezoelectric member That is,
it is equivalent to λo / 2.
Grinding or polishing is carefully performed aiming at the predetermined thickness t = λo / 2,
but in the columnar piezoelectric body 21 and the resin member 22 constituting the composite
piezoelectric body, material characteristics, in particular, elastic modulus (= hardness) thermal
expansion coefficient When the grinding or polishing process is carried out, a process sag occurs
between the two, and appears as a thickness difference between the columnar piezoelectric
member 21 and the resin member 22 as shown in FIG.
It is impossible in terms of the characteristics of the material to process this level difference to be
zero and it is impossible, and that variations in the thickness level difference between the front
and back surfaces of the composite piezoelectric material may cause more unevenness. It is an
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unavoidable place in consideration of the characteristics. Then, when the relationship between
the thickness difference of the composite piezoelectric body and the characteristics of the
ultrasonic transducer was investigated, it was found that when the size of the thickness
difference is larger than 4% of the wavelength λo of the ultrasonic wave, desired wide band
characteristics Could not be manufactured.
[0013]
That is, in the conventional manufacturing process, when processing the composite piezoelectric
body to a predetermined thickness, only the accuracy of the thickness dimension is defined, and
the surface treatment state of the radiation surface and the backing material adhesion surface on
the opposite side, in other words, the surface There was no provision for roughness.
[0014]
In addition, there is only a definition of approximate dimensions for the film thickness of gold or
the like formed by means of sputtering or the like as an electrode responsible for signal
transmission on the radiation surface side and the backing material adhesion surface side of the
composite piezoelectric body. When the film thickness was too thick, the characteristics could
not be secured in the high frequency band as described above.
[0015]
The present invention has been made in view of the above circumstances, and it is an object of
the present invention to provide a composite piezoelectric ultrasonic transducer with a relative
bandwidth exceeding 100% with high yield in order to achieve a wide diagnostic area and high
spatial resolution. ing.
[0016]
SUMMARY OF THE INVENTION An ultrasonic transducer according to the present invention
comprises a plurality of columnar piezoelectric members and a composite piezoelectric member
formed of an organic substance filled in a gap between the columnar piezoelectric members and
having an acoustic impedance set in a predetermined range. And an acoustic lens provided on an
acoustic matching layer in which an acoustic impedance is set in a predetermined range, the
acoustic transducer being disposed on the ultrasonic radiation side of the composite piezoelectric
body. The thickness difference between the organic substance and the columnar piezoelectric
material on the radiation surface surface to which the sound wave is radiated is set smaller than
the thickness difference between the organic substance and the columnar piezoelectric material
on the backing material adhesion surface surface on the opposite side.
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[0017]
The thickness difference between the organic substance on the radiation surface of the
composite piezoelectric body and the columnar piezoelectric body is set to 4% or less of the
wavelength λo of the ultrasonic wave in the piezoelectric body.
[0018]
By defining these surface roughness, a composite piezoelectric material is provided which
satisfies the performance required as an ultrasonic transducer.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be
described below with reference to the drawings.
[0020]
1 to 5 relate to an embodiment of the present invention, and FIG. 1 is a perspective view showing
a schematic configuration of an ultrasonic transducer, FIG. 2 is a cross-sectional view taken along
line AA of FIG. FIG. 4 is a cross-sectional view for explaining the configuration, FIG. 4 is a view for
explaining the thickness step and the electrode, and FIG. 5 is a conceptual view of the ultrasonic
wave transmission / reception characteristics near the acoustic lens focus of the ultrasonic
transducer.
4 (a) is a view for explaining the thickness difference between the columnar piezoelectric body of
the composite piezoelectric body and the resin member, and FIG. 4 (b) is a front electrode and a
rear electrode formed on the front and back surfaces of the composite piezoelectric body. It is a
figure explaining.
[0021]
As shown in FIG. 1, FIG. 2 and FIG. 3, the ultrasonic transducer 1 of this embodiment is
composed of, for example, a plurality of columnar piezoelectric bodies formed of PZT and an
epoxy resin etc. filled in the gaps between these columnar piezoelectric bodies. The volume filling
factor of the columnar piezoelectric body is set so that the acoustic impedance formed by the
resin member falls within a predetermined range, and the composite piezoelectric body 2 having
a substantially circular shape in a flat plate emits ultrasonic waves or ultrasonic waves. Opposite
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to the ultrasonic wave emitting surface of the front electrode 3a, which is a gold electrode
provided with gold or the like by vapor deposition means such as sputtering on the ultrasonic
wave emitting surface or ultrasonic transmitting / receiving surface (also referred to simply as
the front surface) A back electrode 3b which is a gold electrode provided with gold or the like by
vapor deposition means such as sputtering on the side surface (referred to as the back surface
with respect to the front surface), and a composite piezoelectric laminated on the front electrode
3a of the composite piezoelectric body 2 by adhesion. Acoustic impedance of body 2 The
thickness dimension is also described as the wavelength (λ by epoxy resin that improves the
matching between the body and the acoustic impedance of the living body, more specifically, the
resin layer and the resin layer containing alumina powder, which are made of polyimide resin or
Urtem resin. Acoustic matching layer 4 formed to a predetermined ratio with respect to 1) and
resin acoustics as focusing means for focusing the ultrasonic wave emitted from the composite
piezoelectric body 2 at a desired position and emitting an ultrasonic beam A lens 4a, a backing
material 5 laminated with an adhesive on the back surface electrode 3b of the composite
piezoelectric body 2 and made of, for example, a rubber compounded with ferrite powder or
other additives for attenuating ultrasonic waves to the rear side; Water resistance and chemical
resistance covering the surfaces of the piezoelectric body 2, front electrode 3a, back electrode
3b, acoustic matching layer 4, acoustic lens 4a and part of the backing material 5 And the
protective film 6 formed by coating the excellent polyparaxylylene resin.
[0022]
A ground wire 7 is electrically connected to the front electrode 3a, and a signal wire 8 is
electrically connected to the back electrode 3b.
And these electric wires 7 and 8 are put together as the lead wire 9, extended, and are
respectively connected to the signal terminal and the earth terminal of the ultrasonic observation
apparatus which are not shown in figure.
[0023]
Further, the acoustic lens 4a provided in the acoustic matching layer 4 is formed and disposed
with respect to the acoustic matching layer 4 formed in a predetermined thickness dimension,
and is substantially equivalent to the acoustic matching layer 4 in acoustic terms. An epoxy resin
is laminated on the ultrasonic radiation surface of the acoustic matching layer 4 and formed into
a concave curved surface shape which changes so that the thickness dimension continuously
increases as it goes from the center to the circumferential direction, for example.
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[0024]
As shown in FIG. 3, the plurality of columnar piezoelectric bodies 2a constituting the composite
piezoelectric body 2 are arranged at a predetermined pitch (indicated by p in the figure) smaller
than the wavelength, for example, and a resin is interposed between the columnar piezoelectric
bodies 2a. The member 2b is filled.
Further, the thickness dimension to of the composite piezoelectric body 2 is processed to a
predetermined dimension λo / 2 as described above by grinding or polishing.
[0025]
When processing the thickness dimension of the composite piezoelectric body 2 to λo / 2, first,
one surface side 2c of the composite piezoelectric body 2 is ground or polished, and then the
other surface side 2d is ground or polished to obtain a thickness dimension To λo / 2.
In this case, when the other surface 2d is ground or polished, the one surface 2c already
processed is placed on the mounting table of the processing machine and clamped using a gellike temporary fixing material for grinding or polishing. enter.
In the present processing, on the one surface 2c clamped by the mounting table, a mechanical /
thermal processing load is generated on the columnar piezoelectric body portion 21 and the
resin portion 22 during grinding or polishing.
The columnar piezoelectric body portion 21 is made of so-called ceramic, so it is a material that
is very hard in terms of material mechanics and is a material that has little thermal expansion.
On the other hand, since the resin portion 22 is made of an epoxy resin, it is elastic and acts in a
direction extending to these loads.
Therefore, sagging occurs on the ridge line of the other surface 2c by the grinding or polishing
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process, and the thickness difference as described above may occur.
[0026]
Therefore, in the present embodiment, when the ultrasonic transducer 1 is configured, for
example, the other surface 2d which is the surface to be processed last, is set to the front surface.
Then, when processing the other surface 2d to be the front surface, that is, the final grinding or
polishing surface, as shown in FIG. 4A, the step (h) between the columnar piezoelectric body 2a
and the resin member 2b has a wavelength The measurement is performed so as to be 4% or less
(h <0.04 × λo). As a result, the thickness dimension is finished to a predetermined dimension,
and the composite piezoelectric body 2 in which the processing state of the front surface is
defined to the predetermined state is formed.
[0027]
Next, in order to input and output electric signals from the outside to the composite piezoelectric
element 2 processed as described above, a manufacturing process for forming an electrode is
necessary. Generally, the piezoelectric element 21 and the epoxy resin 22 are used. In the case of
forming an electrode on a composite piezoelectric body configured, it is often formed of a thin
film of gold or chromium by vapor deposition means such as sputtering. The thickness of the
electrode thin film of gold or the like, but taking into account the strength and acoustic
characteristics of the electrode, the wavelength λe (==) of the electrode material calculated from
the ultrasonic wave propagation velocity Ve of the material to be the electrode and the oscillator
frequency Fo Ve / Fo: Generally, it is set to one tenth or less of a value different from the abovementioned λo). However, when the thickness of the gold electrode thin film is about one tenth of
the thickness as described above, many transducers that can not maintain the characteristics in
the high frequency band as shown in FIG. 8 appear. Although this technical mechanism is
unclear, there is a tendency for the electromechanical coupling coefficient of the oscillator to
deteriorate as the electrode thickness increases, and as a result of various studies, the electrode
thickness dimension te is an excess of the electrode material. In the case where the wavelength
λe calculated from the sound wave propagation speed is set to be about 1⁄4 to 1/200, it is
possible to achieve a vibrator that satisfies the desired high frequency characteristics.
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[0028]
In summary, the thickness dimension to of the transducer is specified by λo / 2, and the
thickness difference between the columnar piezoelectric member 2a and the resin member 2b is
processed so as to be 4% or less of the ultrasonic wavelength of the piezoelectric member. As
shown in FIG. 4 (b), the thickness dimension (te) of the front surface of the composite
piezoelectric body 2 having the front surface and the back surface where the surface state is
somewhat roughened from this front surface is the ultrasonic wavelength of the electrode
material The front electrode 3a and the rear electrode 3b which fall within the range of te = λe /
400 to λe / 200 as λe are deposited. In the ultrasonic transducer having the composite
piezoelectric body formed in this manner, as shown in FIG. 5, the ultrasonic wave transmission /
reception characteristics in the vicinity of the acoustic lens focus have high band frequency
characteristics. The film formation of the front electrode 3a and the rear electrode 3b is
performed, for example, under the conditions of the sputtering film forming apparatus.
[0029]
Thus, when processing the thickness dimension of the composite piezoelectric body into a
predetermined dimension, the final machined surface side is set to the front side which is an
ultrasonic wave emitting surface, and the thickness difference between the columnar
piezoelectric body on the front surface and the resin member In order to form an ultrasonic
transducer having high-band frequency characteristics by processing so as to be 4% or less of the
wavelength and forming a gold electrode of a predetermined thickness dimension on the front
and back surfaces of this composite piezoelectric body The necessary composite piezoelectric
material can be stably supplied.
[0030]
As a result, when manufacturing an ultrasonic transducer having high band frequency
characteristics, it is possible to improve the yield caused by the failure of the composite
piezoelectric material.
[0031]
The present invention is not limited to the embodiment described above, and various
modifications can be made without departing from the scope of the invention.
[0032]
[Appendix] According to the above-described embodiment of the present invention as described
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above, the following configuration can be obtained.
[0033]
(1) A composite piezoelectric body in which a plurality of columnar piezoelectric bodies and an
acoustic impedance formed of an organic substance filled in a gap between the columnar
piezoelectric bodies are set in a predetermined range, and arranged on the radiation surface side
of the composite piezoelectric body In an ultrasonic transducer including an acoustic lens
provided in an acoustic matching layer in which an acoustic impedance is set in a predetermined
range, a thickness difference between an organic substance and a columnar piezoelectric
material on a radiation surface surface to which the ultrasonic wave of the composite
piezoelectric material is radiated. The ultrasonic transducer set smaller than the thickness
difference between the organic substance and the columnar piezoelectric material on the surface
on the opposite side.
[0034]
(2) The ultrasonic transducer according to appendix 1, wherein the thickness difference between
the organic substance on the emission surface of the composite piezoelectric body and the
columnar piezoelectric body is set to 4% or less of the wavelength of the ultrasonic wave
propagating through the piezoelectric body.
[0035]
(3) The ultrasonic transducer according to appendix 2, wherein a processing surface to be
processed last is a radiation surface when processing the thickness dimension of the composite
piezoelectric body into a predetermined dimension.
[0036]
(4) The thickness of an electrode such as gold provided on the surface of the radiation surface
processed to make the difference between the columnar piezoelectric body of the composite
piezoelectric body and the resin member equal to 4% or less of the wavelength The ultrasound
transducer according to appendix 1, defined in the range of 1/400 to 1/200 of the propagating
ultrasound wavelength.
[0037]
As described above, according to the present invention, it is possible to provide an ultrasonic
transducer having a wide band characteristic exceeding 100% of a relative band capable of
observing a wide range and achieving high spatial resolution with good yield. .
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[0038]
Brief description of the drawings
[0039]
Fig. 1 Fig. 1 is a perspective view showing a schematic configuration of an ultrasonic transducer.
[0040]
2 A-A cross-sectional view of FIG. 1
[0041]
Fig. 3 A cross-sectional view for explaining the structure of the composite piezoelectric body
[0042]
Fig. 4 illustrates the steps and electrodes
[0043]
Fig. 5 Conceptual diagram of ultrasonic transmission and reception characteristics near the
acoustic lens focus of the ultrasonic transducer
[0044]
6 to 8 relate to a conventional example, and FIG. 6 is a diagram for explaining a conventional
composite piezoelectric body.
[0045]
Fig. 7 Conceptual diagram of ultrasonic transmission and reception characteristics near the
acoustic lens focus of the ultrasonic transducer
[0046]
Fig. 8 A diagram for explaining the step between the columnar piezoelectric body of the
composite piezoelectric body and the resin member
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[0047]
Explanation of sign
[0048]
Reference Signs List 1 ultrasonic transducer 2 composite piezoelectric body 2 a columnar
piezoelectric body 2 b resin member h step
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