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DESCRIPTION JPH03110998

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DESCRIPTION JPH03110998
[0001]
The present invention relates to an ultrasonic probe for transmitting and receiving ultrasonic
waves used in an ultrasonic diagnostic apparatus and an ultrasonic flaw detector. (Prior Art)
Apparatuses for imaging the internal structure of an object by ultrasonic waves include
ultrasonic diagnostic apparatuses and ultrasonic flaw detection apparatuses. In these devices,
ultrasonic probes that transmit and receive ultrasonic waves are required to have higher
sensitivity. A piezoelectric material such as a piezoelectric ceramic is used as a transducer
between ultrasonic waves and electricity in the ultrasonic probe. The piezoelectric material is
generally in the form of a plate or a strip having electrodes on both sides. The sensitivity of such
an ultrasound probe is determined by its transmission capability and reception sensitivity, but
methods such as increasing the drive voltage and improving the piezoelectric material
(increasing the coupling coefficient) can be used to increase transmission capability. There is also
a method such as improvement of the piezoelectric material to increase the reception sensitivity.
Furthermore, as a method of reducing the electrical impedance of the piezoelectric body in order
to efficiently transmit the received signal to the receiving circuit system, a piezoelectric material
having a large dielectric constant is used, a piezoelectric body is laminated, or an impedance
converter is used. There is a method such as adding. Among them, the method of increasing the
coupling coefficient of the piezoelectric material is the most ideal, but the largest value of the
coupling coefficient in the existing piezoelectric ceramic material is about 0.7, which is an
improvement in recent years. I did not. Further, the method of reducing the electrical impedance
of the piezoelectric body is to reduce the electrical loss of the received signal by the cable or the
like, and basically does not increase the receiving sensitivity of the probe. In the method of
laminating the piezoelectric body, the wave receiving sensitivity of the probe itself is small, and
in an ultrasonic diagnostic apparatus or ultrasonic flaw detector, a high sensitivity ultrasonic
probe is required for high image quality by improving S / N. It is done. For that purpose, it is
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necessary to improve the transmission capability and the reception sensitivity. As a method of
improving sensitivity, a method of laminating piezoelectric materials using a piezoelectric
material having a large dielectric constant, as well as an increase in driving voltage and an
increase in coupling coefficient of the piezoelectric material, is considered. However, there is a
limit to the method by increasing the driving voltage, the coupling coefficient of the piezoelectric
material, and the dielectric constant, etc., and significant improvement in sensitivity can not be
expected. Further, in the method of laminating the piezoelectric body, there is a problem that the
receiving sensitivity itself of the probe is lowered even if the transmitting capability and the
electrical loss of the receiving signal are improved. An object of the present invention is to solve
such a problem and to provide a high sensitivity ultrasonic probe in which the receiving
sensitivity is improved without reducing the transmission capability. The present invention
divides a common plate-like or strip-like piezoelectric material or electrode thereof used for an
ultrasonic probe into a plurality of parts in a direction perpendicular to the thickness direction,
and physically divides the divided piezoelectric materials in parallel. , And electrically connected
in series.
A changeover switch is provided to switch the electrical connection between the plurality of
divided piezoelectric materials described above in parallel or in series, and when transmitting an
ultrasonic wave, the electrical connections of the piezoelectric materials are made parallel and a
normal plate or strip piezoelectric material is used. If it is in the same state as the body, and
when electrical reception between the piezoelectrics is connected in series, K and more are
configured. When the impedance of the piezoelectric body connected in series at the time of
wave reception is larger than the parallel composite impedance of the impedance due to the
capacitance of the cable connecting the piezoelectric body and the receiving portion and the
input impedance of the receiving portion, An impedance converter is added between the
piezoelectric body and a cable for transmitting the signal detected by the piezoelectric body to
the receiver. (Operation) According to the present invention, the plate-like or strip-like
piezoelectric material or its electrode is divided into a plurality of pieces, and each of the divided
piezoelectric materials is electrically connected in series while remaining physically parallel.
Therefore, the reception sensitivity can be improved by the number of times of the number of
piezoelectric bodies connected without changing the resonance frequency of the piezoelectric
body. When the applied voltage is equalized to the undivided piezoelectric material, the
transmission capability is reduced, but the overall sensitivity can be improved by increasing the
applied voltage so that the transmission capability becomes equal. Even when the increase in
applied voltage can not be achieved, by providing a changeover switch for switching the
electrical connection between the plurality of divided piezoelectric bodies in parallel or in series,
the electrical connection between the plurality of piezoelectric bodies can be carried out during
transmission. In parallel, the transmission capability can be maintained in the same manner as a
normal piezoelectric body, and when receiving waves, the number of piezoelectric bodies
connected in the above case is doubled by making the electrical connection between the
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piezoelectric bodies in series. Wave sensitivity can be improved. When the impedance of the
piezoelectric body connected in series at the time of wave reception is larger than the parallel
composite impedance of the impedance due to the capacity of the cable connecting the
piezoelectric body and the receiving portion and the input impedance of the receiving portion,
the piezoelectric body and the cable By adding an impedance converter between them, it is
possible to make an impedance converter, to efficiently transmit received signals to the receiving
circuit system, and to obtain an ultrasonic probe as a whole having high sensitivity. it can.
(Embodiment) FIG. 1 shows an embodiment of the present invention. What is shown in FIG. 3 is a
conventional ultrasonic probe, but it will be described below while comparing FIG. 1 and FIG. In
FIG. 1, the electrodes 12.degree. 13 on both surfaces of the piezoelectric body 8 in FIG. 3 are
divided into two at the center. Further, the electrode 3 on the acoustic matching layer 2 side is
connected to the electrode 6 on the backing 7 side, and a drive pulse is applied between the
electrode 4 on the backing 7 side and the electrode 5 on the acoustic matching layer 2 side.
The polarization directions (arrows) of the two divided piezoelectric members in FIG. 1 are the
same. When the same pulse is applied between the electrode 4 and the electrode 5 and between
the electrode 12 and the electrode 13 of FIG. 3 by a pulse driver having sufficient driving ability,
the applied piezoelectric material is applied to each divided piezoelectric body of FIG. The sound
pressure of the ultrasonic wave generated by the piezoelectric body of FIG. 1 is an ultrasonic
wave generated by the piezoelectric body of FIG. The sound pressure of the ultrasonic wave
generated by increasing the voltage of the pulse applied between the electrodes 4 and 5 can be
made equal to that of FIG. . When the same ultrasonic wave is received using the ultrasonic probe
shown in FIGS. 1 and 3, distortions generated in the piezoelectric body in FIGS. 1 and 3 are equal,
and thus the electrode 4 and the electrode The voltage generated between 50 is twice the voltage
generated between the electrodes 12 and 13. From the above, when the ultrasonic probes shown
in FIG. 1 and FIG. 3 are compared under the constant transmission sound pressure, the voltage
sensitivity of the structure of FIG. 1 is the same as that of the prior art shown in FIG. It is doubled
compared to the ultrasonic probe of FIG. 2 shows another second embodiment of the present
invention. The ultrasonic probe shown in FIG. 2 is obtained by dividing only one of the electrodes
of the piezoelectric body in FIG. 3, and the polarization direction is reversed at the divided
portions. The voltage is applied and taken out by the electrodes 9 and 10, but electrically the
same as the first embodiment and the effect thereof is equivalent. With such a structure, there is
no need to connect the electrodes 3 and 6 in the first embodiment, and the lead can be taken out
from the same surface, which simplifies the structure. FIG. 4 shows another embodiment of the
present invention. The piezoelectric body is divided similarly to that of FIG. The electrode 17 is
connected to the signal side of the cable and the electrode 14 is connected to the ground side.
Electrode 15 is connected via switch 19 to either electrode 16 or to ground. The electrode 16 is
connected via switch 18 to either the electrode 15 or the signal side of the cable. At the time of
transmission, the switch 19 is connected to the ground side, and the switch 18 is connected to
the signal side of the cable so as to be electrically in parallel, thereby being equivalent to the
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piezoelectric body of FIG. At the time of wave reception, the switch 19 is connected to the
electrode 16 side, and the switch 18 is connected to the electrode 15 side, so that the wave
reception sensitivity is doubled as in the embodiment shown in FIG. A sensitivity twice as high as
that of the conventional probe shown in FIG. 3 can be obtained as a whole. FIG. 5 shows another
embodiment of the present invention.
In FIG. 5, an impedance converter 20 is added to FIG. 1, and the impedance converter may be of
any type such as a coil, a transformer, or an FET. As described in the preceding paragraph, when
the piezoelectric elements divided in time of receiving are connected in series, the electrical
capacity decreases. For example, in the case of dividing into two as shown in FIG. 1 and FIG. 2,
the electric capacity is one fourth. The decrease of the electrical capacity directly leads to the
increase of the impedance. If the impedance of the piezoelectric body connected in series is
larger than the parallel composite impedance of the impedance due to the capacity of the cable
connecting the piezoelectric body and the receiver and the input impedance of the receiver, the
loss due to the cable is large and the received signal is It is not possible to achieve efficient
transmission to the receiving circuit system. Therefore, even if the wave receiving sensitivity of
the probe increases, the sensitivity as a system decreases. Therefore, in the present invention, an
impedance converter is added to the receiving system to efficiently transmit the received signal
to the receiving circuit system. In FIG. 5, although what added the impedance converter was
shown in FIG. 1, the same thing can be said also in cases like FIG. 2 and FIG. In the above
embodiment, only the case of two divisions has been described, but the effect can be easily
inferred even in the case of three divisions or four divisions. FIG. 6 shows an example of the
structure in the case where the number of divisions of the embodiment shown in FIG. 2 is
increased. [Effects of the Invention] As described above, according to the present invention, the
piezoelectric body of the ultrasonic probe is divided into a plurality of portions, and the even
number times of the piezoelectric bodies connected to the receiving sensitivity without changing
the resonant frequency of the piezoelectric body It can be improved.
[0002]
Brief description of the drawings
[0003]
1, 2 and 4 to 6 show the construction of an embodiment of the present invention, and FIG. 3
shows the construction of a conventional ultrasonic probe.
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1 иии Transmission / reception device, 2 и и и Acoustic matching layer, 3-6 и и и и и и и и и и и и и и и и и и и и и и и
и и и и и и и и и и и и и и и и и и и и и piezoelectric body, 9 to 1 pole, 18 и и и switch Switch, 2 dB impedance
converter, 21 to 24 electrodes, transmitter, 26: receiver, 27: electrodes. 7 и и и 0 и и и 25
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