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JPS60113597

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DESCRIPTION JPS60113597
[0001]
The present invention relates to an ultrasonic probe using an organic piezoelectric material, and
it is an object of the present invention to achieve high resolution and wide band range of the
probe. As an ultrasonic probe used in an ultrasonic diagnostic apparatus, an ultrasonic probe
having a wide band and excellent pulse response is desired so that diagnosis can be made from
the deep part to the shallow part of the human body. In an ultrasonic probe using piezoelectric
ceramics as a conventional piezoelectric material, the electromechanical coupling coefficient of
the piezoelectric ceramics is very large, but the conversion efficiency is large, but the acoustic
impedance matching with the human body, water, etc. is poor. There is a drawback that the width
is narrow. FIG. 1 shows a configuration example of an ultrasonic probe using a conventional
piezoelectric ceramic. Or PbTi0a-based piezoelectric ceramic, 11 is a first matching layer, 9 / S-1
glass with acoustic impedance density of 10 × 106 to 13 × 106, or fused silica, 12 is an epoxy
resin, acrylic resin, etc. in a second matching layer And the acoustic impedance density is about
2.3 × 106 to 2.5 × 106, 16 is a sound pressure load such as human body water, and the
acoustic impedance density is about 1.5 × 106 Kr / S−1. . Reference numeral 13 denotes a
backing layer, which is obtained by blending an appropriate amount of tungsten powder into an
epoxy resin. In addition, 14.15 is an electrode for transmission and reception. As apparent from
FIG. 1, the piezoelectric ceramic 10 has a value of 20 times or more of the acoustic impedance
density of the human body as a subject, water, etc., and thus in the direction from the
piezoelectric ceramic to the subject to obtain impedance matching. The matching layer is
disposed so that the acoustic impedance density gradually decreases. However, even with an
ultrasonic probe having such a matching layer, the frequency ratio bandwidth is at most 80%,
and with the image processing technology of the ultrasonic diagnostic apparatus and software
improvement, the broadband of 1 probe is even wider Is required. In recent years, an ultrasonic
probe using a polymeric piezoelectric film such as polyvinylidene fluoride has emerged as an
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improvement to these drawbacks. Since this polymeric piezoelectric film has an acoustic
impedance density significantly lower than that of piezoelectric ceramics, it is inherently
excellent in acoustic impedance matching with the human body as compared with a probe using
a piezoelectric ceramic material. It is considered to be advantageous for the realization of a broad
probe. However, polyvinylidene fluoride (hereinafter referred to as PVDF). ) Has an acoustic
impedance density of 4, OX 106 Kp / S-one electro-mechanical coupling coefficient o, 22, and
copolymers of vinylidene fluoride with vinyl fluoride, ethylene trifluoride, ethylene tetrafluoride,
etc. (PVDF colymer) It has an acoustic impedance of 4.4 × 106, an electromechanical coupling
coefficient of 0.30, and it is about 2.6 to 2.8 times the acoustic impedance density of the subject
even though it has good acoustic consistency with the human body and water. is there.
Recently, a polymer piezoelectric film having almost the same acoustic impedance density as the
human body of water 9 has been studied, but its electroacoustic exchange efficiency is smaller
than that of PVDF 'or PVDF' copolymer. A typical configuration of a conventional PVDF-based
ultrasonic probe is shown in FIG. In FIG. 2, 20 is an organic piezoelectric material made of PVDF-,
21 is a backing material which is prepared by mixing tungsten powder with Ou, Fe or epoxy, and
22.23 is a transmitting / receiving electrode. Since this probe uses a material having a
characteristic acoustic impedance matching sufficiently larger than PVDP for the backing
material 21, it performs a quarter wavelength operation with almost a fixed end at the boundary
with the backing material 21. The ultrasonic waves are incident on the light source 22 and
partially reflected and returned from the electrodes 22 and 23 as electric signals. However, as
described above, PVDF has an acoustic impedance significantly smaller than that of piezoelectric
ceramics, but its impedance is 2.6 to 2.8 times larger than that of water, and impedance
matching is performed on an object such as human body 2 water. However, there is a
disadvantage that the frequency ratio bandwidth does not increase so much and sufficient
sensitivity as a probe can not be obtained. In order to eliminate such a defect, it is conceivable to
further provide a quarter wavelength matching) @ on the subject side of PVDF, and it is expected
that the sensitivity will be increased by the improvement of the acoustic impedance matching. It
has been difficult to significantly broaden the frequency bandwidth as compared to the
illustrated probe. The present invention has been made to solve the above-mentioned
disadvantages of the conventional probe. The present invention uses a PVDF or PVDF 'copolymer
as a piezoelectric material and is a probe having dual impedance matching J @ each having an
appropriate acoustic impedance, and is a probe with high sensitivity and wide band and excellent
pulse response. It is an attempt to realize a feeler. This will be described in detail according to the
drawings. FIG. 3 shows the structure of the ultrasonic probe of the present invention. In the
figure, 20 is an organic piezoelectric material made of PVDF or a PVDF copolymer, 21 is a
backing material, and 24.25 is the first. The second matching layer 16 is an object such as a
water 9 human body, and 22.23 is a transmitting / receiving electrode. The 24.25 first and
second matching layers are required to have an appropriate impedance density for broadband
acoustic impedance matching with the subject 16 and have a quarter wavelength with respect to
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the resonance frequency of PVDF or PVDF copolymer itself. The length of the degree is set.
As the backing material 21, in order to prevent the ultrasonic wave from escaping from the
organic piezoelectric material 20 through the backing material 21, it is preferable that the
acoustic impedance density is sufficiently lower or sufficiently higher than that of the organic
piezoelectric material 20. Of great importance for the ultrasound probe according to the
invention shown in FIG. 3 is the acoustic impedance density of the first and second matching
layers 24.25, the acoustic impedance density of the first matching layer being 5 × 106 to 3.6 ×
106 KL1 / S−n? The acoustic impedance density of the second matching layer is 9 / S-one at 1.6
× 10 6 to 22 × 10 6. At this time, broadband impedance matching is only possible for the first
time, and it is possible to significantly broaden the frequency bandwidth as compared with the
conventional ultrasonic probe, and PVDFf shown in FIG. 2! : It is much more sensitive than the
used ultrasonic probe. On the other hand, when a matching layer out of the range of the acoustic
impedance density is used, large ripples occur in the pass band, the pulse response deteriorates,
and the practical value is lost. The material for realizing the acoustic impedance density of the
first matching layer according to the present invention is epoxy resin, nylon resin and the like,
and the material satisfying the second matching layer is polyethylene, polyurethane, silicon resin,
polyimide resin and the like. An embodiment of the present invention having the configuration
shown in FIG. 3 will be described in detail below. In FIG. 3, for the backing material 20, a
composite material in which a considerable amount of tungsten powder is mixed with an epoxy
resin to realize an acoustic impedance density of 30 X 106 Ks + / S-i is used. As (23), an acoustic
impedance density is relatively small At of 16.9 Kq / S-. At this time, since the acoustic
impedance density of the backing material is considerably larger than P v D F, pvmp 20 omits the
operation close to the quarter wavelength resonance. Furthermore, an epoxy resin with an
acoustic impedance density of 2.72 x 106 Ky / S- is used for the second matching layer, and an
acoustic impedance density of 1.82 X 106 is used for the second matching layer. There is. Here,
the thicknesses of the first matching layer and the second matching layer are respectively set to
about a quarter wavelength with respect to the quarter wavelength resonant frequency of the
PVDF piezoelectric film. The center frequency of this probe is 4. S Ml + z K is designed. Next, a
probe according to the present invention shown in FIG. 1 is a conventional probe using a
piezoelectric ceramic and a backing material shown in FIG. 2 is a probe according to the present
embodiment using PVDF. The frequency characteristics are shown in FIG.
The frequency characteristics shown in FIG. 4 transmit ultrasonic waves from the probe into
water and reflect them back from an aluminum reflector provided at a depth of 5 crn in water
(the ultrasonic waves are transmitted by the same probe. It shows the round trip insertion loss
characteristics when receiving a wave. In FIG. 4, O dB shows the minimum insertion loss point of
the probe using the conventional piezoelectric ceramic shown in FIG. In the figure, the solid line
is the probe according to the present invention, the dotted line is the conventional probe using a
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piezoelectric ceramic, and the alternate long and short dashed line is the frequency flaw of the
conventional PVDF probe. It is clear from this graph that the probe of the present invention is
broadened. Furthermore, we evaluated pulse response characteristics, which are indicators of the
resolution of these three types of ultrasound probes. When the impulse is input to the probe and
the tailing time at this time (z30 dB is represented by time, the conventional probe shown in FIG.
2 is compared with the conventional transducer shown in FIG. 1). In the case of the stylus, it was
1.4.9 ° / 2.3 in the transformer user according to the present invention. On the other hand,
when a material having a characteristic impedance density in the range 1 of the present
invention is used for the matching layer, thick ripples fall within the pass band, and the tailing of
the impulse response also uses the conventional piezoelectric ceramic probe. There was not
much improvement compared to the child. As described above, the probe according to the
present invention has an optimum two positive matching layers, so that the acoustic impedance
matching with the human body is good over a wide band, facilitating high sensitivity, wide band
and high resolution characteristics. Can be realized. In the example, the case was described
where the parakink material had an acoustic impedance density considerably larger than that of
the PVDF but using a Hiko material, but the backing rattan is comparable to PVDF such as cork
onion skin pHer, tunite, silicone rubber, etc. It goes without saying that when a material having a
small acoustic impedance is used, PvDF only performs half-wave resonance and does not affect
the optimum value of the impedance of the other acoustic matching layers.
[0002]
Brief description of the drawings
[0003]
Fig. 1 is a block diagram of a conventional ultrasonic probe using a piezoelectric ceramic, and
Fig. 2 is a block diagram of an ultrasonic probe using an organic piezoelectric material such as a
conventional PVDF, Fig. 1 The figure is a block diagram of the ultrasonic probe of the present
invention, and FIG. 4 is a frequency characteristic diagram of the ultrasonic probe.
In the figure, 0 is a piezoelectric ceramic, 11.12 is a matching layer, 13 is a backing, 14.15 is an
electrode, 16 is an acoustic load, 20 is an organic piezoelectric material such as PVDF, 21 is a
backing, 22.23 is an electrode, 24 .25 is the matching layer. 1 1 1 2 Figure
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