JP5957758B2 - Ultrasonic transmitter / receiver and ultrasonic measuring device - Google Patents

Description

  The present invention relates to an ultrasonic transmitter / receiver including a probe in which piezoelectric elements are stacked and a phased array pulser, and an ultrasonic measuring apparatus including the ultrasonic transmitter / receiver.

  Conventionally, an ultrasonic measurement apparatus has been used for examining scratches and cavities inside an object. However, in order to increase the measurement accuracy, it is a problem to improve the SN ratio. For example, the invention of Patent Document 1 improves the S / N ratio by providing a sound-absorbing material on the probe to attenuate unintended signals so that they are not detected, that is, by reducing the noise level. On the other hand, it is conceivable to increase the signal level in order to improve the S / N ratio. To this end, however, the piezoelectric element that generates ultrasonic waves must be displaced more greatly to increase the amplitude.

  As a method of obtaining a large displacement for a piezoelectric element, there is an example in which elements are stacked when the piezoelectric element is used as an actuator. However, the actuator is statically displaced, and responsiveness / followability is not taken into consideration, and it is difficult to apply this technique as it is to ultrasonic generation that is dynamic displacement. In addition, as in the invention of Patent Document 2, there is an ultrasonic probe in which piezoelectric elements are stacked. However, this is because the impedance increases due to the miniaturization of the element and does not match the impedance of the pulser. In order to prevent this, the impedance is lowered by stacking, and the purpose is not to obtain a large displacement. Here, the experimental result about what kind of displacement is obtained when a piezoelectric element is actually laminated is shown. In this experiment, a PZT element having a resonance of 5 MHz was used. As shown in FIG. 3, a single-layer element 111 (FIG. 3A) and an element obtained by simply stacking five elements 111 (FIG. 3B) Were connected to the pulsar 102 and excited. FIG. 4 shows respective output displacements, effective element applied voltages, and impedance spectra. As shown in the upper diagram of FIG. 4, by stacking five sheets, the resonance frequency decreases to about 1/5, and the amplitude increases slightly as the frequency decreases, but the expected increase in amplitude by five times is obtained. I can't. This is because, as can be seen from the middle and lower stage diagrams, the impedance decreases due to the lamination, and the applied voltage of each element decreases.

JP 2010-145357 A Japanese Patent Laid-Open No. 1-139041

  Thus, even if the piezoelectric elements are simply laminated, the impedance is lowered, and even if the same voltage is applied, the applied voltage of each element is lowered. Therefore, an increase in amplitude corresponding to the number of laminated layers cannot be obtained. In addition, for ultrasonic measurement of a wide range of objects, high frequency in the order of MHz is indispensable to ensure spatial resolution. However, simply laminating piezoelectric elements lowers the resonance frequency accordingly, so kHz Another problem is that the order is limited.

  The present invention has been made in view of the above circumstances, and has a probe in which piezoelectric elements are laminated, and is capable of obtaining a large displacement without lowering impedance and transmitting ultrasonic waves. It is an object of the present invention to provide a receiver and an ultrasonic measurement apparatus including the receiver.

  An ultrasonic transmitter / receiver according to the present invention includes a probe and a phased array pulser, wherein the probe is formed by stacking a plurality of piezoelectric elements, and the phased array pulser includes a plurality of channels. Each piezoelectric element includes a pulsar, and is formed by bonding two piezoelectric bodies so that their polarization directions face each other, and electrodes are bonded to the upper and lower surfaces of each piezoelectric body. The electrodes on the upper and lower surfaces of each piezoelectric element are connected to the ground as a negative electrode, and the electrode sandwiched between the two piezoelectric bodies of each piezoelectric element is connected to the pulsar of each channel of the phased array pulser as the positive electrode It is characterized by being.

  Since the ultrasonic transmitter / receiver according to the present invention individually applies the piezoelectric element to which each pulsar is connected, it is possible to avoid a decrease in impedance due to lamination. Therefore, the applied voltage increases and a large displacement can be obtained. Further, the resonance frequency is equivalent to that in the case of a single layer, and it is possible to generate a high frequency on the order of MHz.

  In addition, if the polarization directions of the stacked piezoelectric elements are all the same, the polarities of the contact surfaces do not match in adjacent piezoelectric elements, so an insulator must be sandwiched between them, and this insulator can transmit vibration. According to the ultrasonic transmitter / receiver according to the present invention, since the piezoelectric element is formed by joining two piezoelectric bodies having opposite polarization directions, the polarity of the contact surface in the adjacent piezoelectric element is Therefore, an insulator is unnecessary and vibration is transmitted more efficiently. When the probe is configured in this manner, assuming that the number of channels of the phased array pulser is N, N piezoelectric elements (2N piezoelectric elements) can be stacked to increase the amplitude N times. .

  The ultrasonic measurement apparatus according to the present invention includes the ultrasonic transmitter / receiver according to the present invention.

  Since the ultrasonic measurement apparatus according to the present invention can generate ultrasonic waves with a large amplitude, the noise is relatively reduced, so that the SN ratio is greatly improved. Therefore, it is possible to measure materials with large attenuation and thick materials, which was difficult with conventional ultrasonic measurement devices, and it was also possible to perform aerial ultrasonic measurements and nonlinear ultrasonic waves that were performed only on a limited basis. In terms of measurement, the practical range is greatly expanded.

  According to the present invention, an ultrasonic transmitter / receiver having a probe in which piezoelectric elements are stacked, capable of obtaining a large displacement without reducing impedance, and capable of transmitting a high frequency, and a super A sound wave measuring apparatus can be provided.

The schematic diagram which shows the structure of the ultrasonic transmitter / receiver of this invention. The graph which shows the basic characteristic of one piezoelectric element (piezoelectric two layers) and two piezoelectric elements (piezoelectric four layers). The schematic diagram which shows the state which connected each of the single layer piezoelectric element and the piezoelectric element which laminated | stacked five sheets to the pulsar. The graph which shows the basic characteristic of the piezoelectric element which laminated | stacked the single-layer piezoelectric element and five sheets.

  A specific configuration of the ultrasonic transmitter / receiver of the present invention will be described with reference to the drawings. As shown in FIG. 1, the ultrasonic transmitter / receiver includes a probe 1 and a phased array pulser 2. The probe 1 is a laminate of two piezoelectric elements 11a and 11b, and each piezoelectric element 11a and 11b has two piezoelectric elements 12 facing each other in the polarization direction (indicated by arrows in the figure). Are joined together. An electrode 13 is bonded to the upper surface and the lower surface of each piezoelectric body 12, and one piezoelectric element 11a, 11b has a structure in which the electrode 13, the piezoelectric body 12, the electrode 13, the piezoelectric body 12, and the electrode 13 are laminated in this order from the upper side. It has become. The upper and lower electrodes 13 of the piezoelectric elements 11a and 11b are the negative electrode, the electrode 13 sandwiched between the two piezoelectric bodies 12 is the positive electrode, and the positive electrode is the pulsar of each channel (ch1, ch2) of the phased array pulser 2. The negative electrode is connected to the ground (GND).

  In this ultrasonic transmitter / receiver, when a voltage is applied from each channel of the phased array pulser 2, the piezoelectric elements 11a and 11b can vibrate to transmit ultrasonic waves. At this time, it is necessary to control the pulsar 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 so as to synchronize with the transmitted vibration, and the upper piezoelectric element 11a is vibrated, thereby causing the upper and lower piezoelectric elements to vibrate. Waveforms of ultrasonic waves transmitted from 11a and 11b are synchronized. Such control is possible by a standard function of a general phased array pulser.

  The ultrasonic transmitter / receiver configured in this way individually applies the piezoelectric elements to which the pulsars of each channel of the phased array pulsar are connected, so that it is possible to avoid a decrease in impedance due to lamination, and the applied voltage increases. Large displacement can be obtained. Further, the resonance frequency is equivalent to that of a single piezoelectric element, and it is possible to generate a high frequency on the order of MHz. In addition, by joining two piezoelectric elements so that their polarization directions oppose each other, a single piezoelectric element is constructed, so there is no need to sandwich an insulator when stacking, so vibration can be transmitted more efficiently. Is done.

  In addition, this ultrasonic transmitter / receiver can receive ultrasonic waves with the same configuration. At the time of reception, similarly to the case of transmission, the pulsar of each channel must be controlled so that the ultrasonic waveform received by each element is synchronized. That is, for example, when receiving ultrasonic waves from above in FIG. 1, the upper piezoelectric element 11a first vibrates with ultrasonic waves and transmits a signal to ch1, and then the lower piezoelectric element 11b vibrates and signals to ch2. Send. The phase-shifted signals are synchronized in the phased array pulser 2 and detected as one signal. Such control is possible by a standard function of a general phased array pulser.

  Next, experimental results for confirming the effect of the ultrasonic transmitter / receiver of the present invention will be shown. In this experiment, a 6 MHz resonant PZT element was used, and when one piezoelectric element (piezoelectric double layer) was connected to a one-channel pulsar and excited, and two piezoelectric elements (piezoelectric) as shown in FIG. Comparison was made with the case where the four-layer body was connected to a two-channel pulsar and excited. FIG. 2 shows each displacement waveform and displacement spectrum. As shown in the upper diagram, the amplitude of the two piezoelectric elements (piezoelectric four layers) is approximately twice that of the single piezoelectric element (piezoelectric two layers). It was confirmed that a proportional amplitude was obtained. Moreover, as shown in the lower diagram, in the case of a single piezoelectric element in which two piezoelectric layers are laminated, the center frequency is 3 MHz, which is reduced to half of the resonance frequency of the PZT element. In the case of two piezoelectric elements in which the body is laminated in four layers, the center frequency is also about 3 MHz. Therefore, by applying each piezoelectric element individually, it was confirmed that even when a plurality of piezoelectric elements were stacked, the resonance frequency was equivalent to that of a single sheet, and a high frequency could be transmitted.

  Ultrasonic measurement can be performed by transmitting an ultrasonic wave toward an object using such an ultrasonic transmitter / receiver and receiving the reflected wave. The ultrasonic measurement apparatus of the present invention includes a display unit for displaying measurement results in addition to the ultrasonic transmitter / receiver, and further includes a computer for analyzing the measurement results, 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 transmitter / receiver can generate a large amplitude ultrasonic wave as described above, the noise is relatively reduced, so that the SN ratio is greatly improved. Therefore, the range of practical use is broader than that of conventional devices, and specific examples include the following.

  First, the ultrasonic measurement apparatus of the present invention can be used for the TOFD method. The TOFD method is a method of sizing a defect with high accuracy from a difference in reception time of a diffracted wave when a longitudinal wave ultrasonic wave is widely incident on an object like a radar and there is a defect. It is known that the measurement is quick and the defect depth measurement accuracy is high, and the application is particularly advanced in thermal power generation equipment and various plant members. The biggest problem is that the defect echo is weak and the S / N ratio is poor as compared with the conventional end echo method because of the wide incidence of ultrasonic waves. For this reason, it could not be applied to a material such as stainless steel, which is used for nuclear power generation equipment, etc., which has a large attenuation, or a welding material having a large plate thickness. However, according to the ultrasonic measurement apparatus of the present invention, since the SN ratio is greatly improved, highly accurate defect sizing is possible even for members that could not be applied conventionally.

  Moreover, the ultrasonic measurement apparatus of the present invention can also be used for aerial ultrasonic measurement. In-air ultrasonic measurement is a measurement method that does not use the coupling agent (liquid sandwiched between the probe and the object) that is indispensable for normal ultrasonic measurement, and there is particularly high demand for composite materials and ceramics that do not want to be wet. It is used in production inspection of rocket housings. However, it is a technique for propagating ultrasonic waves at the kHz level through the air in which ultrasonic waves hardly propagate, and the biggest problem is that sensitivity is extremely reduced to about 100 dB compared with contact-type measurement. Therefore, by using the ultrasonic measurement apparatus of the present invention capable of generating a large amplitude ultrasonic wave, an aerial ultrasonic measurement system exceeding the conventional limit can be realized.

  Furthermore, the ultrasonic measurement apparatus of the present invention can also be used for nonlinear ultrasonic measurement. In power equipment and plants, when the deterioration of a member is progressing, but the crack in the member is closed due to residual stress, etc., the ultrasonic method, which is the core of the flaw detection method, overlooks and underestimates the crack. . Recently, it has been known that when a large-amplitude ultrasonic wave about 10 times larger than usual is input to a crack, nonlinear ultrasonic waves of frequencies (2f, f / 2) other than the input frequency f are generated from the crack. . However, a crack in a practical structural member is limited to a crack having a large opening and causing a nonlinear phenomenon. Therefore, if the ultrasonic measuring apparatus of the present invention is used, a large-amplitude ultrasonic wave 10 times or more than that of the current system can be easily obtained, and the practical range is greatly expanded.

  The present invention is not limited to the above embodiment. For example, the number of stacked piezoelectric elements can be appropriately increased according to the required amplitude of the ultrasonic wave. Of course, the number of Phased Array Pulser channels must be increased. Moreover, in the ultrasonic measurement device, the ultrasonic transmitter / receiver is used for both transmission and reception of ultrasonic waves, but it may be used only for the purpose of transmitting ultrasonic waves for ultrasonic processing, You may use only for the use which does not transmit but receives the ultrasonic wave from the outside.

DESCRIPTION OF SYMBOLS 1 Probe 2 Phased array pulser 11a, 11b Piezoelectric element 12 Piezoelectric body

Claims (2)

It has a probe and a phased array pulsar,
The probe is a laminate of a plurality of piezoelectric elements,
The phased array pulser comprises a multi-channel pulser,
Each of the piezoelectric elements is obtained by bonding two piezoelectric bodies so that their polarization directions face each other, and electrodes are bonded to the upper and lower surfaces of each piezoelectric body,
The electrodes on the upper and lower surfaces of each piezoelectric element are connected to the ground as a negative electrode, and the electrode sandwiched between the two piezoelectric bodies of each piezoelectric element is connected to the pulsar of each channel of the phased array pulser as the positive electrode. An ultrasonic transmitter / receiver characterized by the above. An ultrasonic measurement apparatus comprising the ultrasonic transmitter / receiver according to claim 1.

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