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DESCRIPTION JPS6193951

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DESCRIPTION JPS6193951
[0001]
The present invention relates to an ultrasonic probe used as an ultrasonic wave transmission /
reception source of an ultrasonic diagnostic apparatus and a flaw detection apparatus by an
electronic scanning method. Nowadays, while the ultrasonic scanner of the electronic scanning
system receives high evaluation as a leading-edge technology of the medical equipment and its
demand also increases, following this, the ultrasonic probe which is an ultrasonic wave
transmission source of the ultrasonic diagnostic device The feeler is also subject to technological
improvements. An ultrasonic diagnostic method by electronic scanning using this ultrasonic
probe is as already known, but is as follows. That is, an electric signal pulse is sequentially
applied to the piezoelectric vibrating reed of the ultrasonic probe provided with the rectangular
piezoelectric vibrating reed vibrating in the thickness direction arranged in plural in the width
direction, and the ultrasonic signal generated by this is generated For example, it is sent to a
subject such as a human body, and an ultrasonic signal by reflection from the subject is
sequentially converted into an electrical signal pulse by the piezoelectric vibrating reed and
displayed on a cathode ray tube etc. Delay time or waveform of this electrical signal pulse Is a
method for appropriately diagnosing an abnormal part of a subject or its m-piece in an instant.
Therefore, as the electric signal pulse containing more frequency components applied to the
piezoelectric vibrating reed which generates the ultrasonic signal becomes sharper, the
frequency characteristic of the ultrasonic probe responding to the electric 13 month pulse is
wider It is necessary to have flat characteristics across the. FIG. 1 is a view showing a so-called
array-type ultrasound probe used in this type of ultrasound diagnostic apparatus, and FIG. 1 (al
represents a piezoelectric imaging member that constitutes this ultrasound probe FIG. 1 (b), (c)
are a plan view and a cross-sectional view of this arrayed probe, respectively. Reference numeral
1 denotes a piezoelectric imaging piece made of, for example, a piezoelectric material of Namari
zirconate titanate (hereinafter referred to as "PZT") having electrodes 2 applied on both sides
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thereof. 3 is a damper for arranging a plurality of piezoelectric oscillation pieces 1 at
predetermined intervals. It is. By the way, when transmitting an ultrasound signal from the
arrayed probe to the subject, the acoustic impedances of the piezoelectric vibrating reed 1 and
the subject are different. In order to reduce the matching loss of the ultrasound signal due to the
difference, As shown in FIG. 2, an acoustic matching P4 is provided on the ultrasonic signal
transmission side of the arrayed probe. The thickness t of the acoustic matching layer 4 and the
acoustic impedance z1 are naturally determined when the oscillation frequency of the
piezoelectric vibrating reed 1 and the acoustic impedances of the piezoelectric vibrating reed 1
and the subject 5 are determined. For example, in the case where the subject 5 is a human body,
the oscillation frequency of the piezoelectric 'moving image pickup piece 1 is usually 3 MH2 to 5
HH2, and the thickness t of the acoustic matching layer 4 is one thousand to 0.51. When the
piezoelectric vibrating piece 1 is PZT and the object 5 is a human body, the impedance Z1 of the
matching FJ 4 is about 42 × 10 6 Kg / 1 TLs because each acoustic impedance ZO 1 zm is Zo-34
× 10 6 Kr / yds Become.
The relative bandwidth in the frequency characteristics of the ultrasonic probe having the
acoustic matching layer 4 selected in this manner, that is, the ratio of the 6 dB bandwidth of the
ultrasonic probe to the center frequency is usually 40%. Therefore, if it is desired to transmit an
ultrasonic signal in response to the sharp electric pulse signal as described above from this
ultrasonic probe, it is necessary to further increase this relative bandwidth. Therefore, as a
solution to this problem, there has also been proposed an ultrasonic probe in which the
frequency output characteristic is improved by, for example, forming the acoustic matching layer
4 in a multilayer structure of two layers and three layers. However, this multi-layered ultrasonic
probe actually has 9 difficulties in manufacture. By the way, in order to generate a good
ultrasonic signal from the ultrasonic probe shown in FIG. 1, the piezoelectric vibrating reed 1
mechanically vibrated in response to the electric signal pulse is as pure as possible in the
thickness direction, for example, longitudinal vibration. Alternatively, it is necessary to vibrate in
the height vibration mode and to avoid vibration in the width and length directions as much as
possible. For this reason, in order to excite the vibration only in the thickness direction mode, the
relationship between the thickness t and the width W at least W / l, the length 1 and the
thickness t, the width W is set to W / l ≦ 0. .6, and W 1 1 1. Therefore, for example, when it is
attempted to manufacture an ultrasonic probe in which the oscillation frequency is 38 H 2 and
the pressure N vibration piece whose sound N width is 1.5 is arranged when the object is a
human body, Since the thickness t of the vibrating reed is about 0.5 # l, / l is 3 or more, and the
condition of W / ≦ 0.6 is not satisfied. Therefore, in this case, instead of the 1.5 m wide
piezoelectric vibrating reed, 5 pieces of piezoelectric vibrating reeds of 0, 3 tm wide satisfying
the above condition / 1 ≦ 0.6 are used as one element. By arranging in parallel and
simultaneously exciting, it becomes a sound source body equivalent to a piezoelectric vibrating
reed of 1.5 m width, and thereby vibrates in a pure longitudinal vibration mode even at a
frequency of 3 MHz and a sound source width of 1.5 m. It is manufactured in. FIG. 3 shows an
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electric circuit and the like in the case where a plurality of piezoelectric vibrators having a block
width BW and a width of five elements arranged in parallel are arranged and driven. The present
invention is made by the above, and it aims at providing an ultrasonic probe which can respond
to a sharp electric signal pulse, and it is characterized by the point that the frequency constant of
pressure N material changes with the external shape Focusing on this point, the block width of
the piezoelectric vibrator is constant, and the element bandwidth of each element constituting
the piezoelectric vibrator is changed to widen the frequency bandwidth of the ultrasonic probe.
The present invention will be described below with reference to the drawings. FIG. 4 is a diagram
showing the relationship between the ratio / l of the width W and thickness t of the piezoelectric
vibrating reed 1, for example PZT, shown in FIG. 1 (a), and the frequency constant Ft of the
longitudinal vibration mode, the horizontal axis Is a ratio of width W to thickness t, and the
vertical axis is a frequency constant. As apparent from this figure, the frequency constant in the
longitudinal vibration mode of PZT is a frequency when the ratio / l between the width W of the
PZT and the thickness t becomes larger than 0.6! The number constant Ft decreases. That is, this
means that the thickness W of the PZT is made constant while the width W is broadened (if the
resonance frequency of the longitudinal oscillation f711 needs of the PZT is lowered. Therefore,
if this is applied to a piezoelectric vibrator comprising a plurality of elements described above, it
is possible to change the respective resonance frequencies of the elements without changing the
block width 3w of the piezoelectric vibrator. As a result, the pressure N moving body, which
electrically drives a plurality of elements having different resonance frequencies in parallel, can
transmit the condensed wave signal over a wide frequency range in response to the sharp
electric signal pulse. . FIG. 5 is a schematic diagram showing the ultrasonic probe of the present
invention for explaining this, and is a view in the case where a plurality of piezoelectric vibrators
consisting of three elements are arranged in parallel, for example. 5 (a) is a plan view, and FIG. 5
(bl is a cross-sectional view). Reference numerals 6a, 6b and 6c denote first block elements
having widths W1 and W2W3 (where yyl> w-2> w3) constituting a first piezoelectric moving
body and having a thickness t, and 7a, 7b and 7c. Is a second block element which constitutes
the first piezoelectric oscillator in the same manner as described above, 8 is a sound-matching
layer and 9 is a damper. Therefore, since the resonant frequencies of the block elements 6a, 6b
and 6C of the first piezoelectric vibrator of the ultrasonic probe are different in width, they have
resonant frequencies of fr1 and fr2fr3, respectively. FIG. 6 is a graph showing the frequency and
admittance of the block elements 6a 16b and 6c. Therefore, as expected from this characteristic
diagram, the admittance characteristics of the first piezoelectric vibrator in which three elements
6a, 6b and 6C having different resonance frequencies are electrically connected in parallel
according to the ratio of thickness t and width WIW2W3. Is added, so that it is considerably
flattened over a wide frequency range. For this reason, as described above, the ultrasonic probe
composed of the piezoelectric vibrator having a small change in admittance over a wide
frequency range can easily respond to sharp electrical signal pulses.
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Incidentally, when the inventor measured the frequency characteristics of an ultrasonic probe
consisting of a piezoelectric vibrator in which five elements having different widths were
electrically driven in parallel, the relative bandwidth was about 60 with only one matching layer.
Reached%. Since this is a value when the sound matching layer is a single layer, there is no
difficulty in manufacturing the manufacturing cost of the ultrasonic probe and the manufacturing
cost can be reduced, which is extremely effective economically. Next, a method of manufacturing
the ultrasonic probe according to the present invention will be described with reference to FIG.
First, the piezoelectric diaphragm 10 long in a predetermined thickness and width direction is
attached to the damper (not shown) shown in FIG. 1 and the like by an adhesive or the like. Next,
as shown in FIG. 7A, the right end of the piezoelectric vibrator plate 10 is cut to a predetermined
block width BW from the left end of the piezoelectric vibration plate 10. For example, in an
ultrasonic probe composed of 64 blocks, cutting is performed 64 times with the cutting width or
cutting pitch as BW. Next, as shown in FIG. 7 [b), in order to cut the first element 11a1.11a2 of
each block, the width of the first element 11a1.11a2.1lan from the left end of the piezoelectric
imaging plate 7 The cutting is performed again 64 times with the cutting width BW shifted by
W1. As shown in FIG. 7 (C) (d) (e) below, the second, third, fourth and fifth to (n + 7) elements llb,
11c, 11d and 11e-11n of the respective blocks are the same as the first two. The predetermined
width W2. W3. The cutting is performed 64 times with the cutting width BW by sequentially
shifting the widths so as to be W4 and W5. This FIG. 7 is a diagram for producing an array type
ultrasonic probe in which a plurality of piezoelectric vibrators composed of 1 block and 5
elements are arranged. In this case, the above-mentioned cutting operation is performed five
times. There is. In this FIG. 7, the gap G of the element opening caused by the cutting shown in
FIG. 5 is omitted. Therefore, after such cutting and processing, as in the usual manufacturing
method of arrayed probes, lead wire processing and attachment of the matching layer have a
plurality of elements having different widths and different resonance frequencies if processing is
performed. Piezoelectric AJ body? ! It is very easy to manufacture two or more ultrasonic probes
arranged in parallel. Although the ultrasonic probe of the present invention is described only in
the case of the one-dimensional arrangement direction in which the piezoelectric vibrating reeds
are arranged in the width direction, the present invention is not limited to this. For example,
taking advantage of the fact that the piezoelectric constant changes with the length of the
piezoelectric vibrating reed, two-dimensional arrangement when arranged in the length direction,
or arranged in both the width direction and the length direction It goes without saying that the
present invention is also applied to arrayed ultrasound probes.
As described above, according to the present invention, since the block width of the piezoelectric
vibrator is constant and the element width of each element constituting the piezoelectric vibrator
is changed, the frequency bandwidth of the piezoelectric vibrator is broadened. Can provide an
ultrasonic probe capable of responding to various electrical signal pulses.
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[0002]
Brief description of the drawings
[0003]
1 (a) is a perspective view of a piezoelectric vibrating reed that constitutes an ultrasonic probe,
FIGS. 1 (b) and 1 (c) are a plan view, a cross-sectional view, and FIG. Fig. 3 is an illustration of an
ultrasonic probe in which five elements are arranged in parallel, and a plurality of piezoelectric
vibrators having a block width of 8 W arranged and driven. FIG. 4 is a diagram showing the
relationship between the ratio / l of the width W to the thickness t of the PZT and the frequency
constant Ft of the longitudinal vibration 1h mode.
5 (a) (bl is a view for explaining the ultrasonic probe of the present invention, FIG. 5 (a) is a
sectional view, FIG. 5 (11) is a plan view, and FIG. It is an admittance characteristic and a figure
of the ultrasonic probe of this invention. FIG. 7 is a view showing a method of manufacturing an
ultrasonic probe according to the present invention. 1-piezoelectric vibrating reed, 2-electrode, 3
訃 -damper L9--IN matching layer, 5-analyte, 6a, 6b, 6C, 7a, 7b, 7 cm-block element, 1 o-voltage
imaging plate, 11a, 11 bilc, Nd, 1 le-block elements. Mlし]。 ) (C,) 菫 4m 1 '芋 60 O-OJ] 0
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