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JPS5822978

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DESCRIPTION JPS5822978
[0001]
The present invention relates to an ultrasonic apparatus for observing the surface or the inside of
an object by ultrasonic waves. Ultrasound imaging has recently received great attention in the
fields of medical diagnostics, nondestructive testing, ultrasound imaging gIf #, and the like. As
means for generating and receiving ultrasonic waves used in such a device, there have
conventionally been various means such as one using an acoustic phase plate, one using an
annular array, one using an acoustic lens, and the like. A so-called interdigital transducer has
excellent characteristics for the emission and reception of ultrasonic waves in the inside. An
interdigital transducer is constructed by providing an electrode in which a pair of comb-like
electrodes are interdigitally combined on the surface of a piezoelectric body, and while the
electrode surface is in contact with a liquid, an alternating current signal is applied to the
electrode. The ultrasonic wave is emitted into the liquid, or the propagation sound wave in the
liquid is received and converted into an electric signal. The radiation and reception direction ?
of the ultrasonic beam into the liquid of such a transducer (where ? is the angle formed by the
normal to the surface of the piezoelectric material) has two directions, and the relationship of the
following equation is satisfied Do. ?1 = Sin?1vw / vR (1) ?2 = 5in? ? v ? 4ct (2) where vw is
the longitudinal wave velocity in the liquid, vR is the surface wave velocity on the piezoelectric
body, and f is the interdigital on the piezoelectric body The carrier frequency d of the AC signal
applied to the electrode is the electrode period of the interdigital electrode. As is clear from the
equations (1) and (2), ? 1 is constant regardless of the frequency, and ? 2 changes with the
frequency. And V, ? at fd! = ? 2, but otherwise there are two directions of radiation of the
ultrasound beam. The present invention is effective in observing the state of an object by utilizing
such a two-direction emitted ultrasonic beam! ! r To provide roots. A feature of the present
invention for achieving all the objects is to place a plate-like piezoelectric material having an
interplanar electrode on the-surface in contact with a liquid, and to set the frequency fNv / d
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(where v is the speed of sound on the piezoelectric material) , D is an alternating current signal of
the interdigital electrode to generate ultrasonic beams in two directions in the liquid by applying
an alternating current signal, each ultrasonic beam is focused on the plane of the object to be
observed, and each reflected wave is The ultrasonic wave * @ yi sister is used to obtain an
acoustic image of the object to be observed by receiving and electrically converting it with the
interapnotal electrode. FIG. 2 shows a specific example of the electrode structure. The reference
numeral 1 in the figure is a plate-like piezoelectric body, and the thickness thereof is a thickness
at which the surface wave is excited, specifically several times, preferably five times or more the
wavelength of the surface wave.
On one surface of the piezoelectric body 1, interdigital electrodes (2, 3) as shown in FIG. 2 are
provided. Each electrode is formed by combining an arc-shaped pair of comb tooth electrodes (2a
and 2b, 3m and 3b) in an interdigital manner, and -10,000 electrodes 2 are input 1 and the other
electrode 3 is output. Function as As the electrode configuration is arc-shaped, it is clear that the
focus of the ultrasound beam is on a vertical line passing through the center of the arc. The
transducer of the above configuration is placed in contact with electrodes (2, 3) @liquid 4. If an
alternating current signal of frequency f2 other than the center frequency f1 (at the center
frequency vR = fd is satisfied and the radiation direction of the ultrasonic beam is single) is
applied to the sword electrode 2 in this state, as shown in FIG. Thus, ultrasonic beams are
emitted in the 01 and 02 directions. The broken line in the figure indicates the equation (1), and
the solid line indicates the equation (2). Therefore, it is obvious that if the carrier frequency of
the alternating current signal is 11, a single directional beam according to the broken line is
emitted. The ultrasonic beam in each direction (?1.?,) is focused at point P1 and point P,
respectively. If the observation object 5 is arranged as shown in FIG. 1 while focusing the
ultrasonic beam on points P1 and P, the ultrasonic beam in the radiation direction ? is on the
surface of the object 50 (point P). Produces a reflected wave. On the other hand, the beam in the
radiation direction ? is refracted and focused at the entry point P inside the object to generate a
reflected wave. These reflected waves are received by the output electrode 3 and taken out as an
electric signal. At this time, a reflected wave received by the output electrode 3 has a phase
difference due to the presence of a path difference from the deviation in two directions of ? and
?, and this causes interference. Therefore, it is possible to extract the state inside the object 5 as
a change in elastic property using the phase difference between the reflected waves of the beams
in two directions. That is, since the propagation sound wave has the velocity specific to the liquid
and the velocity specific to the solid, the propagation velocity of the ultrasonic wave inside the
solid changes in the presence of a crack inside the solid, and hence the reflections in the ? and
02 directions. A corresponding change occurs in the phase difference between the waves.
Therefore, it is possible to obtain an acoustic image of the object 5 by the output signal of the
electrode 3. For example, if the output signal is configured to be displayed on a CRT, the inside of
the object can be observed with the naked eye. In the present embodiment, as is apparent from
FIG. 1, since the ultrasonic beam from the transducer is obliquely incident on the observation
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object, the percentage of the sound wave that can be transmitted into the object is much larger
than that in the normal incidence. Therefore, it is convenient only for the surface of the
observation object (it is also convenient to know the internal situation.
In addition, since the input and output are performed by separate electrodes, no directional
coupler is required to separate the input and output signals, and since the transducer has a
planar structure, the degree of freedom in electrode design is also large. In the present
embodiment, the case where the ultrasonic beam in the ? direction is focused on the object
surface has been described as an example, but even in the case of focusing on the inside of the
object, interference from the sister phase difference can be used as described above. Further,
although a transducer for surface wave excitation is used in the present embodiment, it is
possible to use Lamb wave as well. In the case of the Lamb wave, the thickness of the
piezoelectric body should be made approximately ? or less (? is the wavelength of the sound
wave on the piezoelectric body) (If the aforementioned surface wave velocity VR is replaced with
Lamb wave velocity, (2) The same holds true for ?. Although this configuration has the
advantage that it can be used without contacting the interdigital electrodes, it has problems with
high frequency and is therefore suitable for nondestructive inspection in a relatively low
frequency range. In the configuration of the present embodiment, since the interdigital electrode
vibrates by direct liquid immersion in the liquid, its mechanical and chemical protection is
necessary, for example, by forming a protective film on the electrode surface with a photoresist
film or the like. It can be done easily. In addition, when using a combination of a piezoelectric
thin film such as ZnO and a non-piezoelectric substrate instead of using a single piezoelectric
material, it is possible to place an interdigital electrode between the thin film and the substrate,
thus separately protecting There is an advantage that there is no need to configure means. In
order to confirm the effectiveness of the present invention described above, circular arc-shaped
interdigital electrodes are formed on a surface perpendicular to the thickness of a TDK
piezoelectric ceramic 91A material (length 20 mrx, width 20 ?, thickness 5 dragon) I have
already configured a transformer. Here, the polarization axis is in the direction parallel to the
thickness, the electrode period is 210 ?m, the distance between the circular arc interdigital
electrodes of 5.2 pairs of circular electrodes is 10 long, and the aperture length is 70 '. In this
case, ? is 45 ░, and the surface wave velocity VR is 2146 m / sec, which corresponds to the
value obtained by substituting the speed of sound 1497 m / sec in water at a temperature of 25
░ C. into equation (1). As an observation object, an acrylic plate having a hole near the surface
was used. Under the above specifications, a transducer and an acrylic plate were placed in water
as shown in FIG. 1, and the carrier frequency was changed. As a result, it was possible to observe
changes in the output signal corresponding to the presence of holes inside the acrylic plate. As
described above, according to the present invention, it is possible to observe the internal state of
an optically opaque object by utilizing an ultrasonic beam emitted in two directions, and it is
possible to use an ultra An acoustic wave device can be provided.
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[0002]
Brief description of the drawings
[0003]
FIG. 1 is an embodiment of an ultrasonic apparatus according to the present invention, and FIG. 2
is a specific example of an interdigital electrode.
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и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и liquid 5 и и и и и и и и и и и и
observation object Izumi Shimori Toyoei Patent application attorney Patent attorney Atsushi
Yamamoto-# / country / L2 concave
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