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DESCRIPTION JP2012088113

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DESCRIPTION JP2012088113
PROBLEM TO BE SOLVED: To provide an ultrasonic wave transmitter-receiver which has a probe
in which piezoelectric elements are stacked, can obtain a large displacement without lowering the
impedance, and can transmit a high frequency, and an ultrasonic measurement apparatus
provided with the same. I will provide a. SOLUTION: An ultrasonic wave generator / receiver
comprises a probe 1 and a phased array pulser 2, and the probe 1 is a laminate of a plurality of
piezoelectric elements 11a and 11b, and the phased array The pulsar 2 includes pulsars of a
plurality of channels, and the piezoelectric elements 11a and 11b are connected to the pulsars of
the respective channels of the phased array pulsar 2. Further, the piezoelectric elements 11a and
11b are formed by joining two piezoelectric bodies 12 so that their polarization directions are
opposite to each other. The ultrasonic measurement device includes this ultrasonic wave
generator / receiver. [Selected figure] Figure 1
Ultrasonic generator and ultrasonic measurement apparatus
[0001]
BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an
ultrasonic generator including a probe in which piezoelectric elements are stacked and a phased
array pulser, and an ultrasonic measurement apparatus including the same.
[0002]
Conventionally, an ultrasonic measurement device has been used to investigate a flaw or a cavity
inside an object, but to improve the measurement accuracy, it is an issue to improve the SN ratio.
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For example, the invention of Patent Document 1 improves the SN ratio by providing a sound
absorbing material on the probe to attenuate an unintended signal so as not to be detected, that
is, reducing the noise level. On the other hand, it is conceivable to raise the signal level to
improve the S / N ratio, but in order to do so, it is necessary to displace the piezoelectric element
generating the ultrasonic wave more largely and to increase the amplitude.
[0003]
As a method of obtaining a large displacement for the piezoelectric element, there is an example
in which the elements are stacked in the case where the piezoelectric element is used as an
actuator. However, the actuator is statically displaced, and the response and followability are not
considered, and it is difficult to apply this technique as it is to the generation of ultrasonic waves
that are dynamic displacements. In addition, as in the invention of Patent Document 2, there is
also an ultrasonic probe in which piezoelectric elements are stacked, but it is possible that the
impedance is increased due to the miniaturization of the element and the impedance does not
match the impedance of the pulser. In order to prevent this, the impedance is lowered by
lamination, and it is not the purpose to obtain a large displacement. Here, experimental results on
what kind of displacement can be obtained when the piezoelectric elements are actually stacked
will be shown. In this experiment, a PZT element of 5 MHz resonance is used, and as shown in
FIG. 3, an element 111 and a single layer element (FIG. 3 (a)), an element in which five elements
111 are simply stacked (FIG. 3 (b)) And are respectively connected to the pulser 102 and excited.
FIG. 4 shows the spectrum of the output displacement, the effective element applied voltage, and
the impedance, respectively. As shown in the upper diagram of FIG. 4, the resonance frequency is
reduced to about 1⁄5 by stacking five sheets, and the amplitude slightly increases with the
decrease in frequency, but the expected five-fold increase in amplitude is obtained. I can not. This
is because, as can be seen from the middle and bottom diagrams, the impedance is lowered by
the lamination and the applied voltage of each element is lowered.
[0004]
JP, 2010-145357, A JP, 1-139041, A
[0005]
As described above, even if the piezoelectric elements are simply stacked, the impedance is
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lowered, and even if the same voltage is applied, the voltage applied to each element is
decreased, so that an increase in amplitude corresponding to the number of stacked layers can
not be obtained.
Also, for ultrasonic measurement of a wide range of objects, high frequency of MHz order is
essential to secure spatial resolution, but simply laminating the piezoelectric elements will lower
the resonance frequency by that amount, so kHz Another problem is that the order is at the limit.
[0006]
The present invention has been made in view of the above circumstances, and has a probe in
which piezoelectric elements are stacked, which can obtain a large displacement without
lowering the impedance and can emit a high frequency wave. An object of the present invention
is to provide a receiver and an ultrasonic measurement apparatus including the same.
[0007]
Among the present inventions, the invention according to claim 1 comprises a probe and a
phased array pulser, wherein the probe is a stack of a plurality of piezoelectric elements, and the
phased array pulser has a plurality of channels. A pulsar is provided, and each of the
piezoelectric elements is connected to a pulsar of each channel of the phased array pulsar.
[0008]
Among the present inventions, the invention according to claim 2 is characterized in that the
piezoelectric element is formed by joining two piezoelectric members so that their polarization
directions are opposite to each other.
[0009]
Among the present inventions, the invention of claim 3 is characterized by comprising the
ultrasonic generator / receiver according to claim 1 or 2.
[0010]
According to the invention of claim 1 of the present invention, since the piezoelectric elements to
which the respective pulsars are connected are individually applied, it is possible to avoid a drop
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in impedance due to the lamination.
Therefore, the applied voltage is increased, and a large displacement can be obtained.
In addition, the resonance frequency is also equivalent to that of the single layer, and it is
possible to generate a high frequency of MHz order.
[0011]
Also, if the polarization directions of the stacked piezoelectric elements are all the same, the
polarities of the contact surfaces in adjacent piezoelectric elements do not match, so an insulator
must be sandwiched between them, and this insulator serves to transmit vibration. According to
the invention of claim 2 of the present invention, the piezoelectric element is formed by joining
two piezoelectric members whose polarization directions are opposite to each other. No
insulation is required and vibration is transmitted more efficiently.
When the probe is configured in this way, if the number of channels of the phased array pulser is
N, N sheets of piezoelectric elements (2N sheets of piezoelectric material) can be stacked to
increase the amplitude by N times. .
[0012]
According to the invention of claim 3 of the present invention, since an ultrasonic wave with a
large amplitude can be generated, the noise becomes relatively small, and the SN ratio is greatly
improved.
Therefore, it becomes possible to measure a material with large attenuation and a material with
thick plate thickness, which was difficult in the conventional ultrasonic measurement device, and
air ultrasonic measurement and non-linear ultrasonic wave which have been performed only in a
limited manner. The range of practical use is greatly expanded also about measurement etc.
[0013]
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FIG. 1 is a schematic view showing the configuration of an ultrasonic wave generator / receiver
according to the present invention. The graph which shows the basic characteristic of 1 sheet of
piezoelectric elements (piezoelectric body double layer) and 2 sheets of piezoelectric elements
(piezoelectric body 4 layers). The schematic diagram which shows the state which connected
each of the piezoelectric element of single layer and the piezoelectric element which laminated
five sheets to the pulsar. 6 is a graph showing the basic characteristics of a single-layer
piezoelectric element and a five-layered piezoelectric element.
[0014]
The specific configuration of the ultrasonic wave generator / receiver of the present invention
will be described based on the drawings. As shown in FIG. 1, this ultrasonic wave generator /
receiver comprises a probe 1 and a phased array pulser 2. The probe 1 is a stack of two
piezoelectric elements 11a and 11b, and in each of the piezoelectric elements 11a and 11b, the
polarization directions (represented by arrows in the figure) of the two piezoelectric bodies 12
are opposed to each other. It is joined as follows. An electrode 13 is bonded to the upper and
lower surfaces of each piezoelectric body 12, and one of the piezoelectric elements 11a and 11b
is stacked in the order of the electrode 13, the piezoelectric body 12, the electrode 13, the
piezoelectric body 12, and the electrode 13 from the upper side. It has become. The electrodes
13 on the upper and lower surfaces of the piezoelectric elements 11a and 11b are negative
electrodes, and the electrode 13 sandwiched between the two piezoelectric members 12 is a
positive electrode, and the positive electrodes are pulsers for each channel (ch1 and ch2) of the
phased array pulser 2. It is connected, and the negative electrode is connected to ground (GND).
[0015]
In this ultrasonic wave generator / receiver, when a voltage is applied from each channel of the
phased array pulser 2, the piezoelectric elements 11a and 11b vibrate to transmit ultrasonic
waves. At this time, it is necessary to control the pulser of each channel so that the waveform of
the ultrasonic wave transmitted from each element is synchronized. That is, for example, when
transmitting an ultrasonic wave upward in FIG. 1, a voltage is first applied from ch2 to vibrate
the lower piezoelectric element 11b. Since this vibration is transmitted to the upper piezoelectric
element 11a, a voltage is applied from ch1 in synchronization with the transmitted vibration to
vibrate the upper piezoelectric element 11a, whereby the upper and lower piezoelectric elements
are generated. The waveforms of the ultrasonic waves transmitted from 11a and 11b are
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synchronized. Such control is possible by the standard function of a general phased array pulser.
[0016]
The ultrasonic generator thus configured individually applies the piezoelectric elements to which
the pulsers of each channel of the phased array pulser are respectively connected, so that a drop
in impedance due to lamination can be avoided, and the applied voltage becomes large. Large
displacement can be obtained. Further, the resonance frequency is also equal to that of one
piezoelectric element, and it is possible to generate a high frequency of MHz order. Furthermore,
by connecting two piezoelectric members so that their polarization directions are opposite to
constitute one piezoelectric element, it is not necessary to sandwich an insulator at the time of
stacking, so that vibration is transmitted more efficiently. Be done.
[0017]
Also, this ultrasonic wave generator / receiver can receive ultrasonic waves with the same
configuration. Also in reception, as in transmission, the pulser of each channel must be controlled
so that the waveform of the ultrasonic wave received by each element is synchronized. That is,
for example, when receiving an ultrasonic wave from the upper side in FIG. 1, first, the upper
piezoelectric element 11a vibrates by the ultrasonic wave and transmits a signal to ch1 and then
the lower piezoelectric element 11b vibrates to a signal in ch2 Send The thus phase-shifted
signals are synchronized in the phased array pulser 2 and detected as one signal. Such control is
possible by the standard function of a general phased array pulser.
[0018]
Next, experimental results for confirming the effect of the ultrasonic wave generator of the
present invention will be shown. In this experiment, a PZT element of 6 MHz resonance is used,
and one piezoelectric element (piezoelectric dual layer) is connected to a pulser of one channel
and excited, and two piezoelectric elements as shown in FIG. The four-layer body was connected
to a two-channel pulsar to compare excitation. Each displacement waveform and displacement
spectrum are shown in FIG. As shown in the upper diagram, compared to the case of one
piezoelectric element (piezoelectric two layers), the amplitude is approximately twice that of two
piezoelectric elements (four piezoelectric layers), and It was confirmed that a proportional
amplitude was obtained. In addition, as shown in the lower diagram, in the case of one
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piezoelectric element in which two layers of piezoelectric material are laminated, the center
frequency is 3 MHz, which is lower than half of the resonance frequency of the PZT element. In
the case of two piezoelectric elements in which four layers of the body are stacked, the center
frequency is also about 3 MHz. Therefore, it was confirmed that by applying each piezoelectric
element individually, even if a plurality of piezoelectric elements are stacked, a resonance
frequency equivalent to that of one sheet can be obtained, and high frequency can be emitted.
[0019]
Ultrasonic measurement can be performed by transmitting an ultrasonic wave toward an object
by such an ultrasonic wave generator and receiving the reflected wave. The ultrasonic
measurement apparatus of the present invention includes a display unit for displaying the
measurement result in addition to the ultrasonic wave generator / receiver, and further includes
a computer for analyzing the measurement result, a scanning mechanism for moving the probe,
and the like. You may have. According to the ultrasonic measurement apparatus of the present
invention, since the ultrasonic wave generator can generate ultrasonic waves with large
amplitude as described above, the noise is relatively reduced, and the SN ratio is greatly
improved. Therefore, the practical range is greatly expanded compared with the conventional
apparatus, and specifically, the following examples may be mentioned.
[0020]
First, the ultrasonic measurement device of the present invention can be used for the TOFD
method. The TOFD method is a method in which longitudinal ultrasonic waves are widely
incident on an object like a radar, and defect sizing is performed with high accuracy from the
reception time difference of diffracted waves when there is a defect. It is known that
measurement is quick and defect depth measurement accuracy is high, and the application is
progressing especially for thermal power generation equipment and various plant members. The
biggest problem is that the ultrasonic waves are widely incident, so the defect echo is weak and
the SN ratio is worse compared to the conventional end echo method. For this reason, it could not
be applied to a material such as stainless steel, which is used for nuclear power generation
equipment, etc., having a large attenuation, or a welding material having a large thickness.
However, according to the ultrasonic measurement device of the present invention, since the SN
ratio is greatly improved, defect sizing with high accuracy is possible even for members that can
not be applied conventionally.
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[0021]
Moreover, the ultrasonic measurement device of the present invention can be used for airborne
ultrasonic measurement. Airborne ultrasonic measurement is a measurement method that does
not use a coupler (a liquid sandwiched between a probe and an object), which is indispensable for
ordinary ultrasonic measurement, and is particularly in high demand for composite materials and
ceramics that do not like to be wet, It is put to practical use in production inspection of rocket
casings. However, this is a technology that propagates an ultrasonic wave at the kHz level in the
air where the ultrasonic wave hardly propagates, and the greatest problem is that the sensitivity
is extremely lowered to about 100 dB as compared with the contact type measurement.
Therefore, by using the ultrasonic measurement device of the present invention capable of
generating ultrasonic waves with large amplitude, an airborne ultrasonic measurement system
exceeding the conventional limit can be realized.
[0022]
Furthermore, the ultrasonic measurement device of the present invention can also be used for
non-linear ultrasonic measurement. If deterioration of members is progressing in electric power
equipment and plants etc. but cracks in the members are closed due to residual stress etc., even
with ultrasonic method which is the core of flaw detection method, cracks may be missed or
underestimated . Recently, it has been known that when a large amplitude ultrasonic wave about
10 times larger than usual is input to a crack, non-linear ultrasonic waves of frequencies (2 f, f /
2) other than the input frequency f are generated from the crack. . However, the cracks in
practical structural members have a large opening, and the cracks that cause non-linear
phenomena are limited. Therefore, if the ultrasonic measurement device of the present invention
is used, large amplitude ultrasonic waves of 10 times or more that of the present system can be
easily obtained, so the practical range is greatly expanded.
[0023]
The present invention is not limited to the above embodiments. For example, the number of
laminated piezoelectric elements can be appropriately increased according to the required
amplitude of ultrasonic waves. Of course, in that case, the number of channels of the phased
array pulser also has to be increased. Also, in the ultrasonic measurement apparatus, the
ultrasonic generator / receiver is used both for transmitting and receiving ultrasonic waves, but
may be used only for transmitting ultrasonic waves for ultrasonic processing etc. It may be used
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only for the purpose of receiving external ultrasonic waves without transmitting.
[0024]
1 probe 2 phased array pulser 11a, 11b piezoelectric element 12 piezoelectric body
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