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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the
configuration of a probe of an apparatus for measuring the internal structure and physical
properties of an object using ultrasonic waves. [Background of the invention] Ultrasonic waves of
several MHz to several hundred MHz are transmitted to an object to be measured, such as a
medical ultrasonic diagnostic apparatus or an ultrasonic microscope, and a reflected wave or a
transmitted wave is received to examine the inside in detail. Devices are making significant
progress recently. Since the electro-acoustic transducer, that is, the probe used in these devices
has hitherto been a method using thickness expansion and contraction vibration of the
piezoelectric body, restrictions based on the manufacturing method of the piezoelectric body are
imposed on the operating frequency. It was being done. That is, assuming that the velocity of
sound in the thickness direction is v (m / s) and the thickness of the piezoelectric body is 1 (m),
the basic frequency f (Hz) is expressed by the following equation. In an O-v / (2t) medical
diagnostic apparatus, a ceramic is usually used, and it is difficult to reduce its thickness to about
200 μm or less, so f is 10 MHz in height. ただし、V=4000m/sとしている。 However,
there is a strong demand for further high-frequency and high-resolution diagnosis for
endoscopes or ophthalmology, and their improvement has been desired. On the other hand, in an
ultrasonic microscope, contrary to the former, since a piezoelectric semiconductor such as ZnO is
grown on a lens base made of sapphire by sputtering, only a very thin one can be made, and the
resonance frequency is also about 100 MHz. It was only used in high areas. However, if
ultrasonic waves of about 10 MHz to 200 MHz are used, attenuation in the inside of the sample
can be reduced, including attenuation in the ultrasonic wave propagation medium, so resolution
of biological samples and the like is not necessary. A wide range of applications in the field can
be expected. SUMMARY OF THE INVENTION The present invention has been made in view of
these points, and an object thereof is a high-performance probe which can be used in an
ultrasonic band of about 10 MHz to several 1100 MHz and which uses ceramics itself as an
unnecessary ultrasonic absorber. It is to provide a child. べろ。 FIG. 1 shows a cross section of a
ceramic and, by way of example, an interdigital electrode formed thereon. The lead wires 1 and 2
are alternately connected to the electrodes 4 on the ceramic 3. Unlike ordinary surface acoustic
wave devices, this ceramic is polarized by applying a voltage between the lead wires 1 and 2.
Therefore, the degree of polarization is the strongest under the electrode and gradually weakens
as it separates from the electrode It has become. The direction is the direction indicated by the
arrow. When a voltage for ultrasonic excitation is applied between the lead wires 1 and 2 this
time to the ceramic once polarized in this way, the direction of the polarization and the direction
of the applied voltage match for the region under the electrode. Because of this, they all expand
and contract in the same phase, and vertical motion occurs in the thickness direction.
However, with respect to the area between the electrodes, since the polarization directions are
alternately reversed, the lateral vibrations cancel each other and become extremely small. From
the above reasons, it can be seen that the thickness longitudinal vibration is mainly generated. In
this case, the polarized region exhibits non-resonance characteristics because it does not have a
clear boundary. Therefore, since the resonance frequency f (Hz) of such a probe depends on the
change in electrical impedance accompanying the lateral movement, the period of the electrode
is J (m), and the speed of sound in the lateral direction v (m / s) ) Is given by the following
equation. In the case of f = v / l ceramics, it is about V-4000 m / s, and since the period of the
electrode can be miniaturized to about 1 μm by using photolithography and X-ray
phosphorography, f = I GHz. In fact, since the particle size of the ceramic is about 0.5 μm, J = 5
μm is considered to be the limit at present, and at this time, f = 400 MHz. It goes without saying
that this value naturally increases as the particle size decreases. Now, when the frequency rises
in this way, if ultrasonic waves are emitted from the back of the electrode, the internal loss of the
ceramic itself causes the ultrasonic waves generated under the electrode to be attenuated while
propagating through the ceramic, leading to significant sensitivity deterioration. At low
frequencies, on the other hand, there is a drawback that an unwanted signal is generated by
internal multiple reflection. Then, the above-mentioned fault was solved and a high-performance
probe was achieved by the construction method using the electrode surface as an ultrasonic
radiation surface and using the ceramic under the electrode as a backing material, and therefore,
it will be described with reference to the following examples. . DESCRIPTION OF THE PREFERRED
EMBODIMENT FIG. 2 shows an embodiment of the present invention and shows the structure of
a probe for an ultrasonic microscope. An electrode 6 is formed on the ceramic 5 and subjected to
the same polarization processing as in FIG. The electrodes 6 are immersed in the ultrasonic wave
propagation medium 7 and exposed to water vapor in the air, so they are formed by vapor
deposition or sputtering of a corrosion resistant metal such as Au or Nl. However, when
spattering glass etc. on the electrode surface and covering with a protective film, metals such as
AJ may be used. Now, when a voltage is applied to the electrode 6, the generated ultrasonic
waves propagate 5 and 7. The ultrasonic wave propagating through 7 reaches the object to be
measured 8 and obtains information of 8 and reflects or transmits. Although n is a useful
ultrasonic component, the ultrasonic wave propagating through 5 is not preferable because it is
reflected by the end face 9 and reaches 6 again to generate an unwanted signal. However, if the
length L (m) of the ceramic 5 is attenuated during the propagation of the ultrasonic waves so that
it can be sufficiently ignored, an unnecessary signal will not be generated.
Fig. 3 shows the relationship between the propagation loss and the frequency of lead titanate
with a particle size of 1 μm, but an attenuation of 0.1 d B / crIL is obtained at 10 MHz, and the
amount of attenuation is about the frequency It can be seen that it increases in proportion to the
square. Moreover, since the attenuation is known to be proportional to the cube of the particle
diameter, for example, when a ceramic with a particle diameter of 5 μm and a thickness of about
2 is used, it is possible to achieve an attenuation of 5 QdB in both directions The unnecessary
reflected wave from the end face can be almost ignored. The thickness and type of ceramics may
be selected according to the amount of attenuation required. The dotted line in FIG. 2 indicates
the ultrasonic wave propagation area. As the electrode shape, in addition to the ones shown in
FIGS. 4 (a), (b) and (C), shapes combining these may be considered. In FIG. 4, 10.11 represents an
electrode and 12 represents a ceramic. FIG. 5 shows another embodiment of the present
invention and shows a probe of a structure for focusing an ultrasonic wave because the electrode
surface has a curvature. The lens 14 is formed on the ceramic 13 and the electrode 15 is formed
thereon. The generated ultrasonic waves are focused as shown by dotted lines in the figure and
reach the object 16 to be measured. The formation of the electrode can be performed as follows.
A metal thin film is formed on the entire concave surface of the ceramic by vapor deposition or
sputtering, and then a resist is applied, and then an electrode of an arbitrary shape is baked by
the optical system shown in FIG. That is, the light from the light source 17 passes through the
mask 19 by the lens 18 and passes through the mask 19 and is then narrowed by the focusing
lens 20 to form an image on the ceramic surface 21. The shape of the electrode is determined by
the mask 19. Here, since the ceramic surface has a curvature, it is necessary to give the same
curve to the mask. After baking the electrodes in this manner, etching is performed to focus
ultrasonic waves using a Fresnel zone plate as an electrode of the configuration example shown
as unnecessary. FIG. 7 (b) shows an ideal intensity distribution of polarization, but in practice it
may be binarized and polarized as shown in FIG. 7 (C). The polarization intensity distribution To
(x) in FIG. 7 (b) is expressed by To (x) = O + Ac0 ′ ′ ′ (kx2 / Zo). Here, 0 is a direct current
component, k is the wave number, and ZO is the distance to the focal point. Therefore, the width
Δ of the n-th term shown in FIG. 7 (a) may be selected as in the following equation. In addition,
since an electrode space | interval becomes narrow as an electrode shown here becomes an edge
part, it is necessary to polarize every adjacent ring.
FIG. 8 shows another embodiment of the present invention, in which a plurality of electrodes 23
are juxtaposed on a ceramic 22. As the shape of the electrode, those shown in FIG. 2, FIG. 5 and
FIG. 7 can be used. By using a probe in which a plurality of electrodes are formed as described
above, it is possible to obtain information from many areas in a short time, so it is possible to
increase the measurement speed. [Effects of the Invention] As described above, according to the
present invention, ultrasonic waves in a band (for example, 10 MHz to 200 MHz) which is
difficult to obtain with a probe having a conventional configuration can be obtained with high
Brief description of the drawings
FIG. 1 is a diagram for explaining the operation of the ceramic used in the present invention, FIG.
2 is a diagram showing an embodiment of the present invention, FIG. 3 is a diagram showing the
relationship between attenuation and frequency, FIG. FIG. 5 shows the shape of an electrode, FIG.
5 shows another embodiment of the present invention, FIG. 6 shows an optical system for
printing an electrode, and FIG. 7 (a) shows another embodiment of the present invention FIG. 7
(b) and FIG. 7 (C) are diagrams showing each n-polarization strength, and FIG. 8 is a diagram
showing another embodiment of the present invention.
Attorney Attorney Attorneys Ogawa Katsuo l So: + 2 Figure 圃 tM / 4z); J-4 '@ 2 (6) ya 5 Figure! 6
Figure + 7 Figure 10 B Continuation of the first page of the first page @ inventor Katakura
Kageyoshi Kunisuke "Inside the Kashiwa Kubo Research Institute"
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