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JPS63313878

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DESCRIPTION JPS63313878
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic probe used in an ultrasonic diagnostic apparatus and the like, and more particularly to
an electroacoustic transducing material for an electronic scanning probe and an ultrasonic probe.
[Prior Art] In a conventional electronic scanning probe, a large number of strip vibrating
elements are one-dimensionally arrayed, and an ultrasonic beam pattern viewed from the array
direction (long axis direction) has the number of driving elements (thus, It can be controlled by
changing the aperture) and the phase of the electrical signal applied to each drive element.
However, since the aperture and the focal point are fixed in the direction perpendicular to the
arrangement direction (short axis direction), there is a problem that the resolution in the short
axis direction is insufficient depending on the depth. Therefore, in order to solve this problem,
the electrodes on the upper and lower surfaces of the piezoelectric vibrator are divided along the
major axis direction and the minor axis direction, respectively, and the aperture is changed in the
minor axis direction as well as the major axis direction. An ultrasound probe is known (JP-A-45621057). However, in this ultrasonic probe, even if the drive electric field is selectively applied
between the divided electrodes on the upper and lower surfaces of the piezoelectric vibrator, the
surrounding area is also excited by the leak electric field and mechanical coupling, and a
sufficient effect is obtained. May not be obtained. [Problems to be Solved by the Invention] One
object of the present invention is a composite which is a novel material which can be an
electroacoustic transducer whose piezoelectricity can be externally controlled and whose
mechanical coupling in the lateral direction is small. To provide an electrostrictive material.
Another object of the present invention is to make effective use of the properties of the
composite voltage material and drive peripheral elements by a leakage electric field or
mechanical coupling generated when a drive electric field is selectively applied between divided
electrodes on the upper and lower surfaces. It is an object of the present invention to provide a
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variable diameter ultrasonic probe which is not [Means for Solving the Problems] The feature of
the present invention is that the composite electrostrictive structure in which a large number of
columnar electrostrictive materials whose piezoelectricity is induced by the bias electric field in
the sheet-like organic material is vertically embedded in the sheet surface. It is in strained
material. Another feature of the present invention is an ultrasonic probe using the abovementioned composite electrostrictive material in an electric-ultrawave conversion unit.
[Operation] The electrostrictive material described in the present invention is a material which
exhibits piezoelectricity only when a bias electric field is applied, and as shown in the
characteristic example in FIG. 2, the electromechanical coupling coefficient is very high when the
bias electric field is small. There is also a material in which the electromechanical coupling
coefficient rapidly increases from the electric field strength E0 which is small. The composite
electrostrictive material (FIG. 1) in which such an electrostrictive material and a soft organic
material are compounded first has a weak mechanical bond in the lateral direction, so it is
effective only by patterning the array electrodes. In addition, it is possible to configure an array
vibrator in which each vibration element operates independently.
Furthermore, since only the portion under the electrode to which the bias electric field is applied
is piezoelectric active, if the bias electric field is selectively applied only to the portion to which
the drive pulse electric field is applied, the leakage of the drive electric field is These peripheral
elements are not driven even if they are applied to the [Example] As an electrostrictive material, a
so-called PLZT ceramic in which lead zirconate titanate Pb (Zr (14, Ti (1, 35) 03) is doped with L
'a was used. Although the bias electric field dependency of the piezoelectric characteristics differs
depending on the doping amount of La, PLZT ceramics in which 10 mol% is added to La1i-Pb are
used here. In this case, E in FIG. The value of was 2.5 KV / cm. An 80 mm square, 0.4 mm thick
flat plate of PLZT ceramic of the above composition was adhered onto a ferrite substrate with
electron wax. The ceramic plate was cut into a mesh with a 30 μm thick diamond blade. The
groove formed by cutting was filled with polyurethane resin and solidified, and the sheet-like
composite electrostrictive material having a thickness of 0 and 4111 m was dissolved in the
electron wax and separated from the ferrite substrate. On one surface of a rectangular plate 31
cut out from such a composite electrostrictive material, as shown in FIG. 3, ground electrodes 32,
33.degree. 34 divided into three along the long axis direction are formed, and the other is The
hot electrode array 35 was formed on the surface. The rectangular plate was bonded to the
backing material with the hot electrode side down, and an acoustic matching layer was provided
on the earth electrode to assemble an electronic scanning linear probe. In such an ultrasonic
probe, only when a direct current bias electric field is applied between the hot electrode and the
earth electrode, the portions where the respective electrodes face each other become
piezoelectrically active. Therefore, the aperture in the short axis direction can be effectively
changed by applying a bias electric field only between the hot electrode and the earth electrode
to be used. As a result of experiments of ultrasonic beam formation in practice, when a bias
electric field is applied and used only between the hot electrode and the central earth electrode, a
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bias electric field is applied between the hot electrode and all the earth electrodes. It was found
that the width of the ultrasonic beam viewed in the minor axis direction is narrower at a short
distance as compared with the case of using it. This is considered to be because the aperture in
the minor axis direction is effectively reduced. That is, it has been confirmed that the ultrasonic
beam pattern viewed from the minor axis direction can be controlled by changing the
distribution of the bias electric field.
In the above embodiments, the number of divisions of the ground electrode is set to three, but it
is obvious that the number of divisions may be any number without being limited thereto.
[Effects of the Invention] As described above, an electronic scanning linear probe in which the
aperture in the short axis direction is variable by using a composite electrostrictive material of an
electrostrictive material and an organic matter whose piezoelectricity is induced by a bias electric
field. However, according to the present invention, not only such an ultrasound probe but
generally any bias field distribution is provided. It is obvious that it is possible to realize a probe
capable of controlling an ultrasonic beam by giving an arbitrary weight distribution to the
electroacoustic conversion efficiency. For example, by providing a two-dimensional bias electric
field distribution, a two-dimensional array ultrasonic probe capable of selectively transmitting
and receiving an ultrasonic beam can also be realized.
[0002]
Brief description of the drawings
[0003]
FIG. 1 shows the concept of the composite electrostrictive material of the present invention, FIG.
2 shows an example of the characteristics of the electrostrictive material, and FIG. 3 shows an
example of the ultrasonic probe of the present invention It is a figure which shows.
11 · · · organic matter, 12 · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·
· · · · · · · · · · · · · · · · · · · · · · · · · · · · composite electric strain Materials, 32 to 34: Earth electrodes,
3.5: Hot electrode array.
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