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JPS5657391

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DESCRIPTION JPS5657391
Description 1, title of the invention
Ultrasonic transducer
The present invention relates to the shape of a vibrator that oscillates ultrasonic waves, and more
particularly to an ultrasonic vibrator in which the vibrator is curved to eliminate intensity
unevenness in a near-field. In recent years, techniques for diagnosing internal tissue of a living
body using ultrasonic waves and testing metal products and the like are becoming widespread,
and such ultrasonic diagnosis and testing are generally performed in the near field. There is a
problem that a high quality image can not be obtained because the waveform of the ultrasonic
wave is complicated. FIG. 1 is a view for explaining how an ultrasonic wave waveform changes as
it propagates. When an ultrasonic wave with a wavelength of ? is transmitted from the diskshaped transducer 1 whose production is r, the near-field is defined as a sound field between the
distance of the transducer and the eyebrow. Usually, in the near field, as shown in FIG. 1, the
sound field distributions A + to A5 of the ultrasonic wave have a complicated shape having a
plurality of peaks. Even in a far sound field having a distance of r7? or more, peaks (side ropes)
are present outside the main peak (main rope) of the central axis and also at places away from
the central axis. This side rope is also responsible for the degradation of the ultrasound image as
well as the waveform complexity in the near field. The object of the present invention is to
eliminate the above-mentioned problems, and in a disk-like vibrator for oscillating ultrasonic
waves by using a piezoelectric plate, the disk-like thickness of the central portion is thin and
circumferential. The part is achieved by means of an ultrasonic transducer which is curved in
order to be thick. Hereinafter, the present invention will be described in detail with reference to
the attached drawings. FIG. 2 FIG. 7 is an explanatory view of an embodiment according to the
present invention. The cross-sectional view (a) and the outline view (b) of the vibrator 2 are
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shown in FIG. 2, but when the thickness S of the vibrator is J / 2, EndPage: 1 is the maximum
amplitude and the thickness is As the efficiency gets worse as it gets thicker or thinner, it
becomes weak amplitude. Therefore, the thickness of the vibrator is set to 2/2 at the central part
and thicker and curved toward the peripheral part. Electrodes 2a on both sides of the vibrator as
shown in FIG. 3 (a). Even when the drive voltage E is constant and applied to the same 2b (as
shown by blK, the tone distribution has a strong central portion and a weak peripheral portion
has a Gaussian curve B distribution. FIG. 4 shows a Gaussian distribution curve B when the
distance r is taken on the horizontal axis and the sound pressure P (r) is taken on the vertical
axis. The relationship P of such Gaussian distribution curve B (rl is the relationship of the
following equation with respect to the distance r from the center (и r =-). Pfr1 = A6-r2 (1) where
man and ? are coefficients and ? has a relationship of ?> 0 It is a thing.
On the other hand, it is known that the thickness of the planar vibrator is assumed to be & of the
wavelength ?0 with respect to the resonant frequency fo, assuming that the resonant frequency
fo. Further, when a burst signal or a continuous signal of frequency f1 is applied to the vibrator
having the thickness of ?0 / 2, the curve of the frequency sound pressure characteristic
becomes a Gaussian distribution, which is given by the following equation. However, A / and ?
'are coefficients and satisfy a')-. Moreover, fO is a resonant frequency. This curve is shown as the
curve HCt of the 51st fungus. The equation (2) is converted into a variable relating to the
thickness i) and the following equation. Therefore, according to the equation, when a plurality of
transducers having different thicknesses are arranged and activated by signals of the same
frequency, it is possible to form an arbitrary sound pressure distribution. That is, for example, in
the equation (3), in order to make the sound pressure distribution of the predetermined sound
field plane be a Gaussian distribution, the thickness t is set to be a curve of the following
equation. -1-= r
иииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииии
иииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииии By introducing the same equation into the third equation, It
becomes equivalent to the Gaussian distribution curve shown by said 1st Formula. When the
fourth equation is a function of the thickness t and the radius r, the following equation is
obtained, and a cross-sectional view thereof is shown in FIG. t = 2 (r + 1)... (5) Therefore, when
the vibrator having the cross-sectional shape shown in FIG. As shown in the figure, the sound
pressure distribution of each sound field oscillated by one vibrator 2 is a Gaussian distribution in
any sound field, and can be formed in a simple shape in a near sound field. In the above
description, the sound pressure distribution is described to be Gaussian distribution. However, if
the thickness of the edge portion of the vibrator is made thicker than that of the center portion,
the sound pressure is near the center. It is needless to say that the distribution can be
concentrated, and in particular, oscillation can be performed from the back side of tc (, 'the back
side only by oscillating from the recess side of the oscillator. As described above, the use of the
ultrasonic transducer according to the present invention makes it possible to obtain 5-waveform
of simple Gaussian distribution in the near-field, and also significantly reduce the side rope in the
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far-field. Since the waveform which has been obtained can be obtained, if it is used in an
ultrasonic image forming apparatus, it is possible to obtain a better quality push pin.
4. Brief Description of the Drawings FIG. 1 is an explanatory view of the prior art, and FIGS. 2 to
7 are explanatory views according to the present invention. In the figure, 1, 2. Bs-5 ииииииииии
Indicates the sound pressure distribution. Attorney Attorney Hiroshi Matsuoka Part 6 1 EndPage:
2 27 27 3rd Section, dffi 11.5 Figure 6/2 ? 7 EndPage: ?
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