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JPS57141199

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DESCRIPTION JPS57141199
Specification 1, Title of the Invention Ultrasonic Probe
2, the scope of claims
3. Detailed Description of the Invention The present invention relates to an ultrasonic probe, and
more particularly to the arrangement of a piezoelectric vibrator for transmitting and receiving an
ultrasonic beam, which emits an ultrasonic beam in a predetermined direction in a pulse shape.
An ultrasonic probe that receives a reflection echo from an object is used for various
measurements, and is suitable for flaw detection, sounding, ranging, etc., and in recent years, this
ultrasonic beam has been used in a subject It is used for an ultrasonic diagnostic apparatus that
non-invasively displays an image of the internal organs, organs and the like in the living body by
emitting radiation. Although the conventional ultrasonic probe uses a ceramic piezoelectric
material such as PZT as a vibrator, this conventional probe has a problem that a satisfactory
ultrasonic beam transmitting / receiving action can not be obtained 0 A conventional ultrasonic
probe is schematically shown in FIG. 1, and excitation electrodes 12 and 14 are attached or fixed
to both sides of the ceramic piezoelectric body 10. In the conventional probe of this type, since
the acoustic impedance of the ceramic piezoelectric body 10 is a large value, impedance
mismatch occurs with an object having a small acoustic impedance such as an object in
ultrasonic diagnosis. When transmitting and receiving an ultrasonic beam, as shown in FIG. 1, in
the conventional apparatus, a matching layer 16 made of epoxy or other polymer material is
provided on the ultrasonic beam emitting surface side of the ceramic piezoelectric body 10.
Impedance matching with the sample is shown. Furthermore, in an ultrasonic diagnostic
apparatus that displays EndPage: 1 image using reflected echoes of ultrasonic pulse beams, in
order to increase the resolution in the distance direction, it is usually better for the vibration time
of ultrasonic pulses to be shorter. As the vibration time increases, the resolution decreases and it
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becomes difficult to obtain a clear image. For this purpose, an excitation signal with a short pulse
width is applied to the piezoelectric 4 body 10 through the excitation electrode 12.14, but as is
well known, the actual vibration waveform is given by mechanical free vibration of the
piezoelectric body 10, As shown in FIG. 2, it is known that the pulse width T becomes longer as 1.
In the conventional device, in order to damp the mechanical free vibration, as shown in FIG. 1, a
sound absorbing wedge 18 is attached to the back surface sit of the ceramic piezoelectric body
10. By means of the sound absorbing material 18, the mechanical free vibration of the
piezoelectric body 10 is damped to some extent, and as shown in FIG. 3, it is possible to reduce
its pulse width T compared to FIG. However, even in the probe having the sound absorption
material 18, the acoustic impedance of the ceramic piezoelectric body 10 is as large as 5 to 10
times that of the sound absorption material 18, so that a large reflection occurs at the interface
between the two. The vibration waveform in FIG. 3 still has a long pulse width, and there is a
disadvantage that the resolution can not be sufficiently improved.
The present invention has been made in view of the above-described conventional problems, and
an object thereof is to provide a probe in which the characteristics of an ultrasonic probe using a
piezoelectric vibrator are significantly improved. In order to achieve the above object, the present
invention mounts a polymer piezoelectric film on the radiation surface side of a ceramic
piezoelectric body that emits an ultrasonic beam by applying an excitation signal. The preferred
embodiment of the present invention will be described below based on the drawings. explain. The
schematic configuration of the ultrasonic probe according to the present invention is shown in
FIG. 4, and the same members as those of the conventional apparatus of FIG. The characteristic
feature of the present invention is that the polymeric piezoelectric film 20 is mounted on the
ultrasonic beam shielding surface side of the ceramic piezoelectric body 10, and in the
embodiment, one of the piezoelectric films 20 is used as the electrode 12. The end face is stuck.
Preferred examples of the polymeric piezoelectric film 20 in the examples are polyvinylidene
fluoride, polyvinyl fluoride and the like, copolymers containing these as a main component, and a
piezoelectric material obtained by mixing inorganic powder such as ceramic, etc. The film 20 has
an acoustic impedance smaller than that of the ceramic piezoelectric body 10, the value of which
is approximately similar to that of the object, and according to the present invention, this
polymer piezoelectric fino 120 is substituted for the conventional matching layer 16 It becomes
possible to use. And, this polymeric piezoelectric film is different from the conventional
polymeric matching layer 16 and has good flexibility, and, for example, when the ultrasonic
probe is in close contact with the surface of the object directly, By exposing the polymer
piezoelectric film 20 shown in FIG. 4 and bringing it into close contact with the object, it is
possible to improve the compatibility between the two and reduce the attenuation of the
ultrasonic beam. In the embodiment of FIG. 4, the polymer piezoelectric film is used. Further, in
the embodiment, the acoustic lens 24 is disposed on the radiation surface side of the polymer
piezoelectric film 20, and it becomes possible to perform the protection of the probe and the
collection / flux of the beam and the like. In the embodiment, the acoustic impedance of each of
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the ceramic piezoelectric body 10, the polymeric piezoelectric film 20 and the acoustic lens 24 is
(G) Xlo 'kg / m2s, 4X10! It is set to kg 7 m 2 s and 4 to 1.5 × 10 6 kg / m 2 S. The embodiment
of the present invention has the above-described configuration, and as described above, the
polymer piezoelectric film 20 provided on the radiation surface side of the ceramic piezoelectric
member 10 comprises the ceramic piezoelectric member 10 and the object (acoustic impedance
1.5 × 10 6 kg / m 2 s Since it has an acoustic impedance value in the middle of the above, it acts
as a good impedance matching layer for the ceramic piezoelectric body 10, and the transmission
and reception efficiency of the ultrasonic beam can be remarkably improved.
Also in the present invention, the transmission of the ultrasonic beam is performed by the
transmitting circuit and the ceramic piezoelectric element 10 having a good matching, and the
oscillating action of the waveform shown in FIG. 5A similar to FIG. The waveform in the figure
has its pulse width T reduced by the sound absorbing material 18. Then, in the present invention,
the cancellation signal of the waveform shown in FIG. The function of shortening the vibration
pulse width of the ceramic piezoelectric body 10 is performed. That is, the cancellation signal of
FIG. 5B has a slight delay 1. than the excitation 1d of FIG. 5A. The combined ultrasonic beam
signal of both signals is significantly reduced in its pulse width T, as shown in FIG. It is
understood that it becomes a waveform. That is, the signal waveform of the rear end which is a
mechanical free vibration part of the normal excitation signal is canceled by the polymer
piezoelectric film 20, and as a result, it is possible to obtain an excitation signal having a short
pulse width. FIG. 6 shows a preferred embodiment circuit for supplying the excitation signal and
the cancellation signal to the ceramic piezoelectric body 10 and the polymeric piezoelectric film
20 respectively, and the main transmission circuit according to the trigger signal of the trigger
generator 26. The ceramic piezoelectric body 10 can be excited and driven by operating the side
and supplying the excitation signal of the main transmitter circuit to the electrode 1.1. On the
other hand, the trigger signal of the trigger generator 26 is supplied to the auxiliary transmission
circuit 32 through the delay line 3o and excites the polymer piezoelectric film 20 by supplying
the delayed cancellation signal of the auxiliary transmission circuit 32 to the electrode 22. It can
be driven. As described above, according to the present invention, it is possible to perform high
resolution image display by an ultrasonic beam with a short pulse width using a polymeric
piezoelectric film mounted on a ceramic piezoelectric material. Furthermore, in the present
invention, by using the polymeric piezoelectric film 2o, unlike the prior art, when receiving the
reflection echo of the probe, extremely good reception characteristics can be obtained. That is, at
the time of reception of the reflection echo, the polymer piezoelectric film 2o acts as a vibrator
for reception, and an electric signal corresponding to the reflection echo can be extracted from
between both the electrodes and 12.22. That is, since the acoustic impedance of the polymeric
piezoelectric film 2o according to the present invention is close to that of the object, its Q value
can be about 1 or less, and it has extremely wide frequency characteristics and the free vibration
decreases rapidly. As a result, an ultrasonic reflection echo can be faithfully converted to electric
diffusivity.
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That is, the polymer piezoelectric film 20 has extremely superior fidelity than the conventional
ceramic piezoelectric body 10 when receiving the reflection echo. FIG. 7 shows the reception
waveform of the reflection echo; 7, in FIG. 7A, the case where the conventional ceramic
piezoelectric material 10 is used, and FIG. 7B, the case where the polymeric piezoelectric film 20
according to the present invention is used. Show. As is apparent from FIG. 7, when the
conventional ceramic piezoelectric material O is used for reception, the reception pulse width
increases more than necessary, and the resolution at reception / reception significantly
decreases. However, if the polymeric piezoelectric film 10 according to the present invention is
used, it is possible to easily improve this reception characteristic. Further, the polymeric
piezoelectric film 20 has an advantage that it has an acoustic impedance close to that of the
object, unlike the ceramic piezoelectric body 10, it does not require any impedance matching
layer at the time of reception. As described above, according to the present invention, it is
possible to use a polymeric piezoelectric film provided on the conventional ceramic piezoelectric
body radiation surface side for various purposes, and a compact and low-cost ultrasonic probe
Can exhibit superior characteristics.
4. Brief description of the drawings FIG. 1 is a schematic explanatory view showing a
conventional ultrasonic probe, FIG. 2 and FIG. 3 are excitation signal waveforms of the probe of
FIG. 1, and FIG. FIG. 5 is a schematic explanatory view showing a preferred embodiment of the
ultrasonic probe according to the invention, FIG. 5 is an excitation waveform diagram in the
embodiment of FIG. 4, FIG. 6 is an excitation circuit diagram at the time of transmission in FIG. 7
is a waveform diagram showing the operation of the present invention, 10: ceramic piezoelectric
body 20: polymeric piezoelectric film. Applicant Aroka Co., Ltd. EndPage: 3
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