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JPS63314460

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DESCRIPTION JPS63314460
[0001]
FIELD OF THE INVENTION The present invention relates to an ultrasonic transducer used in an
ultrasonic imaging apparatus such as a nondestructive inspection apparatus, an ultrasonic
medical diagnostic apparatus, and an ultrasonic microscope using ultrasonic waves. 2.
Description of the Related Art In recent years, imaging devices using ultrasound have become
actively used in the fields of nondestructive inspection, medical diagnosis, ultrasound
microscopy, etc. In these devices, transmission and reception of ultrasound are performed.
Ultrasonic transducers are often used for waves. As such an ultrasonic transducer, for example,
the configuration described in the following paper is known. A conventional transformer will be
described below with reference to FIG. As shown in FIG. 5, the ultrasonic transducer 101
comprises an oscillator 102 for generating an ultrasonic wave, an acoustic lens 104 provided on
the vibration surface 103 on the front side of the oscillator 102, and focusing the ultrasonic
wave. There is. The vibrator 102 is provided with electrodes 106 ° 107 on both sides of the
piezoelectric element 105. Each electrode 106. Terminals 107 and 107 for inputting and
outputting electrical signals. 109 are connected. The front surface of the acoustic lens 104 is
divided into four by the curved surface 110. 111 is a sample, 112 is a liquid such as water as a
medium for propagating ultrasonic waves interposed between the acoustic lens 104 and the
sample 111. Next, the operation of the above conventional example will be described. First,
terminals 108. An ultrasonic pulse wave is generated from the vibrator 102 by the high
frequency pulse electric signal applied to 109, and dotted arrow S, S2. It propagates through the
acoustic lens 104 as shown by S, and is focused by the curved surface 110 of the acoustic lens
104 through the liquid 112 such as water to a point F in the sample 111. The reflected
ultrasound from the region of the focused ultrasound near point F of the sample 111 is indicated
by the dotted arrow 81. 82. 81 is converted to an electrical signal by the vibrator 102
through a path reverse to that of the terminal 81. It is output from 109. This electrical signal is
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generally amplified by the ultrasound image display device, and a signal corresponding to the
ultrasound reflectivity near the focusing point F of the sample 111 is displayed. In many cases,
the ultrasonic transducer 101 is moved relative to the sample 111 to display an ultrasonic image
of a large number of places. Problems to be solved by the invention However, in the
configuration of the conventional example as described above, as shown by dotted arrows R1, R2
and Ri in FIG. Part of the light beam 83 is reflected by the curved surface 110 which is the end of
the acoustic lens 104 to become a reflected ultrasonic wave.
In addition, the attenuation of the ultrasonic wave passing through the acoustic lens 104 is
increased and the sensitivity of the apparatus is lowered, and a part of the reflected ultrasonic
wave R1 is directly returned to the vibrator 102 and converted into an electric signal, which is an
unnecessary signal. (Spurious signal) significantly lowers S / N. In order to solve these problems,
it is desirable to provide an acoustic matching layer between the acoustic lens 104 and the water
112 as an ultrasonic wave propagation medium to prevent reflection due to acoustic impedance
matching. As a material of the acoustic lens 104, usually, quartz glass with low acoustic loss, soot
7 ayer, glass (BK 7 or the like) is used. The acoustic impedance (sound velocity x specific gravity)
of these materials is 13.4 to 44. The acoustic impedance of water 112, which is an ultrasonic
wave propagation medium, is very small at 1.48 (x 10 'g / cni-). As the acoustic matching layer,
usually, a material having an acoustic impedance of the square root of the product of the acoustic
impedances of both materials to be matched is used with a thickness of 1/4 wavelength. For
example, in the above case, it is desirable to use a material having an acoustic impedance of 4.4
to 8.1 (X 10 'g / cd 呵 or less. In the following description, the value of the acoustic impedance is
(X 10' g / Cr? The unit is r see). ). However, there are very few materials which have these
acoustic impedances and can be processed into a film of appropriate thickness. Metal materials
are easy to process into films, but stable metals have an acoustic impedance of 17.3 (At) or more,
and conversely, organic materials easy to process into films are polyethylene (1, 75), polystyrene
( 2, 48) nylon 66 (2, 86) epoxy (2, 9), polycarbonate (27), etc. conversely, the acoustic impedance
is 3 or less and there are very few practical materials. For this reason, conventionally, materials
in which acoustic impedance is increased to about 4 to 8 with a mixed material in which tungsten
powder having high acoustic impedance is mixed with epoxy resin are used. However, when
using tungsten powder in this way, it is difficult to mix uniformly, and when the frequency used
is as high as 20 MHz or more, the 1⁄4 wavelength becomes as short as 35 μm, and the particle
size of the powder becomes acoustic. It can not be ignored, and it is the practical limit. When the
vibrator 102 is directly brought into contact with water without using the acoustic lens 104, the
piezoelectric vibrator usually used is made of lead zirconate, LiNbOx, etc., which have an acoustic
impedance of 30 to 40. There is a similar problem.
There is also a method of directly attaching an ultrasonic transducer to a living body without
using water 112 as an ultrasonic wave propagation medium, but the acoustic impedance of the
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living body is almost the same as water, and the problem is not changed. The present invention
solves the problems of the prior art as described above, and provides an ultrasonic transducer
capable of easily producing an acoustic matching layer capable of performing good acoustic
impedance matching. The purpose is to Means for Solving the Problems In order to achieve the
above object, the present invention comprises at least a transducer for generating an ultrasonic
wave and an acoustic matching layer, the acoustic matching layer having a center frequency and
a wavelength of the ultrasonic wave. On the other hand, at least one metal layer of 1 / · 1
wavelength or less and at least one organic layer are laminated, and the whole thickness is
configured to be 1⁄2 wavelength or less. Operation According to the present invention, with the
above configuration, the acoustic impedance of the acoustic matching layer can be effectively set
to be intermediate between the metal layer and the organic layer, whereby the acoustic matching
can be performed well. EXAMPLES Examples of the present invention will be described below
with reference to the drawings. First, a first embodiment of the present invention will be
described. Fig. 1 GA), (B) shows an ultrasonic transducer in the first embodiment of the present
invention, Fig. 1 (A) is a longitudinal sectional view, Fig. 1 (Bl is an IB of Fig. 1 cAl) It is an
enlarged view of the arrow part. As shown in FIGS. 1 (A) and 1 (B), the ultrasonic transducer 1 is
provided on a vibrator 2 for generating an ultrasonic wave and on a vibration surface 3 on the
front side of the vibrator 2 and an acoustic wave for focusing the ultrasonic wave. A lens 4 and
an acoustic matching layer 6 provided on a curved surface 5 concaved spherically in front of the
acoustic lens 4 are provided. The vibrator 2 is provided with electrodes 8 and 9 on both side
surfaces of the piezoelectric element 7. Terminals 10.11 for inputting and outputting electric
signals are connected to the electrodes 8 and 9, respectively. The acoustic lens 4 is formed of
quartz, and the acoustic matching layer 6 is laminated on two layers of an organic layer (epoxy
resin layer) 12 and a metal layer (Au layer) 13 from the side of the acoustic lens 4. 14 is a
sample, and 15 is water which is an ultrasonic wave propagation medium interposed between the
acoustic matching layer 6 and the sample 14. Next, the operation of the above embodiment will
be described. First, an ultrasonic pulse wave is generated from the vibrator 2 by the high
frequency pulse electric signal applied to the terminal 10.11. The light propagates in the acoustic
lens 4 as indicated by S 3, and is focused by the curved surface 5 of the acoustic lens 4 through
the acoustic matching layer 6 and the water 15 to the point F of the sample 14.
At this time, the acoustic matching layer 6 provided on the curved surface 5 of the acoustic lens
4 prevents the loss due to the reflection of the ultrasonic wave and the generation of the
unnecessary spurious signal due to the reflected wave. And the reflected ultrasound from the
area ¦ region of the focused ultrasound in the vicinity of F point of the sample 15 is said dottedline arrow 81. 82. The signal is converted into an electric signal by the vibrator 2 through a
path reverse to that of the signal S3 and is output from the terminal 10.11. This electrical signal
is amplified and displayed on the ultrasound image display device. As described above, the
acoustic matching layer 6 is formed of the epoxy resin layer which is the organic substance layer
12 and the Au layer which is the metal layer 13. The acoustic lens 4 is formed of fused quartz,
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and water 15 is used as an ultrasonic wave propagation medium. FIG. 2 shows the calculation
results of the transmittance T with respect to the normalized frequency F of the acoustic
matching layer 6. The calculation was carried out by modeling the propagation of the sound
wave into the distributed constant transmission line of the electric circuit, etc. to make a circuit,
and the calculation program was performed by the computer. Table 1 below shows the
calculation conditions. The following blank table 1 epoxy resin used ME 106 (manufactured by
Japan Vernox Co., Ltd.). The horizontal axis of FIG. 2 is the normalized frequency F obtained by
dividing the frequency f by the center frequency f0, and the vertical axis is the energy
transmittance T. At the center frequency f, (F = 1), the transmittance T reaches 100, and perfect
matching is performed. At this time, the sum of the thickness of the epoxy resin layer 12 and the
thickness of the Au layer 13 is 0.12 as a value normalized by dividing by the ultrasonic
wavelength for the center frequency in each material (see Table 1). . The above calculation did
not show a specific frequency because it was standardized, but assuming that the center
frequency f0 is 40 MHz, for example, the thickness dl of the epoxy resin layer 12 and the
thickness d2 of the Au layer 13 are It becomes 7.98 micrometers and 031 micrometers,
respectively. The epoxy resin layer 12 of such a thickness is made of silicon rubber etc. in a
convex mold that conforms to the shape of the curved surface 5 of the acoustic lens 4 and epoxy
resin is poured between these to solidify or spin code method It can be easily formed by applying
and solidifying it. The Au layer 13 can be easily formed by a vacuum evaporation method, an
electric plating method, or the like. As described above, according to the present embodiment,
acoustic matching can be practically performed using a resin of an organic substance which can
easily form a film or a stable, corrosion-resistant metal or the like. That is, it is effective to set an
arbitrary acoustic impedance from the acoustic impedance 3.14 of the epoxy resin layer 12 to
the acoustic impedance 625 of the Au layer 13 by changing the thickness ratio of the epoxy resin
layer 12 and the Au layer 13 It is possible, and thus, possible to match the impedance of any
practical ultrasonic transducer material, such as with water 15 or the like.
Also, at this time, the thickness of the acoustic matching layer 6 is not determined to be constant
at 1⁄4 wavelength at the single layer matching layer, but there is a thickness that the entire
thickness always matches at 1⁄2 wavelength or less It is not a limitation. That is, in a specific
case, the thickness or the like may be determined numerically by a computer. In addition, it is the
same that any acoustic impedance between the two organic materials and other metal materials
can be similarly obtained with the same restriction, a material which can be practically easily
processed can be freely selected, and the effect is In addition, other effects such as weather
resistance, in particular deterioration of the resin in water, can be prevented by the metal layer
13 are also considered. In addition, when adhesion of the epoxy resin layer 12 and the Au layer
13 is poor, it can be improved by using several hundreds of A0 of Cr or the like as a base of Au,
and even if such a thin layer is inserted, There is no significant change in the acoustical
properties. The same is true between the acoustic lens 4 and the epoxy resin layer 12. In
addition, even if the thickness of the metal layer 13 is thin, the acoustic impedance is large (62.5
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for Au), so that sufficient acoustic matching can be obtained at 1⁄4 wavelength or less. In this
embodiment, although the case where the ultrasonic transducer 1 has the acoustic lens 4 has
been described, the acoustic wave can be detected on the vibrator 2 also when the vibrator 2 is
in direct contact with the water 15 which is an ultrasonic wave propagation medium. It is
essentially the same only by providing the matching layer 6, and it is the same even if the living
body as the sample 14 directly contacts the water 15 as the ultrasonic wave propagation
medium. The acoustic impedance between the organic layer 12 and the metal layer 13 can easily
be achieved even if they are both tens of layers thin, and can be multi-layered alternately, but it is
particularly effective even with two layers as described above. It is important that the acoustic
impedance be matched and matched. In addition, for example, a polyamide resin can also be used
as the organic material layer 12. When this polyamide resin is liquid and spin-coated to form a
film and is thermally cured, it has good weatherability, heat resistance, adhesion to metal, etc.,
and good practical properties. Next, a second embodiment of the present invention will be
described. 3 (A) and 3 (B) show an ultrasonic transducer in the second embodiment of the
present invention, FIG. 3 (A) is a longitudinal sectional view, and FIG. 3 (B) is FIG. 3 (A). [B is an
enlarged view of the arrow portion]. In the present embodiment, the same members as those in
the first embodiment are given the same reference numerals, and different configurations are
mainly described. In particular, as clearly shown in FIG. 3 (B), the acoustic matching layer 6
includes a polyethylene layer which is the organic layer 12a, an Aj layer which is the metal layer
13a, and a polyethylene layer which is the organic layer 12b and an Au layer which is the metal
layer 13b. Are alternately stacked in four layers from the acoustic lens 4 side.
In the present embodiment, the number of layers is increased in the four-layer structure as
compared with the two-layer structure in the first embodiment, but this enables the band
expansion of the ultrasonic wave transmission rate. FIG. 4 shows the calculation results of the
transmittance T with respect to the normalized frequency F according to this embodiment as a
solid line, and as a comparative example, a material having a square root of the product of
acoustic impedance of acoustic lens and water as conventionally known. (Acoustic impedance
4.4, but the lack of such materials was explained in the previous issue. Transmissivity T is shown
by a dotted line in the case where acoustic matching is performed by virtually attaching 1) so as
to become 1⁄4 wavelength. As apparent from this, according to the present embodiment, the
bandwidth is greatly improved. For example, the 70% bandwidth is extended 1,28 times, and the
90% bandwidth is expanded 31 times. Thus, the organic substance layer 12a as in this
embodiment. When the number of layers 12b and the metal layers 13a and 13b is increased,
wider band matching can be performed in a wider band than conventional quarter wavelength
single layer matching, and the practical effect is large. The calculation conditions are shown in
Table 2 above. The following can be formed into a film by the CVD method of forming a
polyethylene film by discharging in ethylene gas, and the At layer 13a1Au layer 13b can be
formed into a film by a vapor deposition method or the like. . The thickness in the conditions of
Table 2 is a value divided by the normalized wavelength, for example, the center frequency f.
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Assuming that 40 MHz, the specific thickness dl of the polyethylene layer 12a, the thickness d2
of the At layer 13a, the thickness d3 of the polyethylene layer 12b, and the thickness d4 of the
Au layer 13b are 1.22 μm and 12 respectively according to the following equation (2). .0 μm,
5.12 μm, 0.4461 zm. Thus, even the entire four layers have a thickness of only 0.21 wavelength,
and in general, it is possible to make matching at 1⁄2 wavelength or less even if multi-layered as
described above. Although not shown as an example, in addition to polyethylene as the organic
substance layers 12a and 12b, for example, an epoxy resin or the like can be multilayered to
achieve a wide band. That is, a wide band can be realized by forming a multilayer by the
combination of the organic material and the metal material other than polyethylene, kt, and Au
shown in this embodiment. Effect of the Invention As described above, according to the present
invention, at least one metal layer of 1/4 wavelength or less with respect to the wavelength of
the ultrasonic wave as the center frequency and at least one organic layer are laminated. The
acoustic matching layer is configured such that the total thickness is 1⁄2 wavelength or less.
As described above, since the acoustic matching layer is formed using an organic substance that
easily forms a film or a stable metal material, it is possible to perform good acoustic impedance
matching and easily manufacture it. Furthermore, since the thickness of the entire layer is set to
1/2 wavelength or less, it is possible to prevent the acoustic loss in the acoustic matching layer
even with a material having a somewhat large acoustic attenuation.
[0002]
Brief description of the drawings
[0003]
Fig. 1 CAB, (Bl shows the ultrasonic transducer in the first embodiment of the present invention,
Fig. 1 (A) is a longitudinal sectional view, Fig. 1 (B) is IB in Fig. 1 (A) FIG. 2 is an enlarged view of
the arrow portion, FIG. 2 is a graph showing the calculation results of transmittance in the first
embodiment, FIG. 3 k), FIG. 3 (B) is an ultrasonic transducer in the second embodiment of the
present invention. 3 (A) is a longitudinal sectional view, FIG. 3 (B) is an enlarged view of a portion
B in FIG. 3 (A), and FIG. 4 is a calculation result of transmittance in the second embodiment. FIG.
5 is a longitudinal sectional view of a conventional ultrasonic transducer.
DESCRIPTION OF SYMBOLS 1 ... Ultrasonic transducer, 2 ... Vibrator, 4 ... Acoustic lens, 5 ...
Curved surface, 6 ... Acoustic matching layer, 12 ... Organic substance layer (epoxy resin layer),
13: Metal layer (A-), 12a: organic layer (polyethylene layer), 13a: metal layer (At layer), 12b:
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organic layer (polyethylene layer), 13b: metal layer Au layer). Name of Agent Attorney Nakao
Toshio One other person 1 Fig. 2 Fig. 1 Fig. 1 Fig. 1 Fig. 4 Fig. 4 Fig. 4 Fig. 4 To the stomach
Succeeded to the stomach F Fig. 5
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