KR100941684B1 - Ultrasonic Transducer for Non-destructive Evaluation of Highly Attenuative Material using PMN-PT single crystal - Google Patents

Abstract

The present invention relates to an ultrasonic probe for non-destructive inspection of high attenuation material using PMN-PT piezoelectric single crystal, and more particularly, to non-destruction of high attenuation material for power generation equipment using PMN-PT piezoelectric single crystal material having superior piezoelectric properties than conventional PZT. It relates to the development of an ultrasonic probe suitable for evaluation.

To this end, the present invention is a piezoelectric element for transmitting and receiving ultrasonic waves; A front matching layer positioned at the front of the piezoelectric element to increase acoustic wave transmittance between the piezoelectric element and a load (a measurement object); A rear member positioned at a rear portion of the piezoelectric element to limit vibration of the piezoelectric element; And an electrical matching circuit that cancels the influence of the piezoelectric element due to the capacitance. The piezoelectric element is a PMN-PT piezoelectric single crystal. Provides ultrasonic transducer for

Ultrasonic, transducer, PZT, PMN-PT, capacitance, piezoelectric element, front matching layer, back material, electrical matching circuit, high attenuation

Description

Ultrasonic Transducer for Non-destructive Evaluation of Highly Attenuative Material using PMN-PT single crystal

The present invention relates to an ultrasonic probe for non-destructive inspection of high attenuation material using PMN-PT piezoelectric single crystal, and more particularly, to non-destruction of high attenuation material for power generation equipment using PMN-PT piezoelectric single crystal material having superior piezoelectric properties than conventional PZT. It relates to the development of an ultrasonic probe suitable for evaluation.

The safety issues of the facility are highlighted due to the deterioration of various members due to the severe use environment and the aging of large facilities such as nuclear power plant, thermal power plant, petroleum plant, etc. have.

Among these members, stainless steel (SUS) is mainly used as a material for high-temperature tubes, pipes, and various devices of power generation facilities because of excellent high temperature strength, heat resistance, and mechanical properties.

These members are embrittled due to thermal stress, thermal fatigue due to long-term use in a high temperature environment, and thus have a great effect on safety as well as functional deterioration of the structure.

Therefore, it is very important to quantitatively evaluate the safety and the remaining life of such equipment, and many of the non-destructive evaluation techniques using ultrasonic are applied to various non-destructive evaluation techniques.

  Conventional non-destructive inspection ultrasonic probes have been developed based on materials or materials that are not attenuated by elastic waves, and have mainly used piezoelectric ceramic elements such as PZT.

However, the application of the existing ultrasonic probe to the high attenuation material, especially among the power generation equipment composed of many different materials, has many limitations.

In other words, in order to detect defects in the material with high attenuation, high-power ultrasonic waves should be used, and for this purpose, it is desirable that the ultrasonic frequency be as low as possible.

However, since the sensitivity of the sensor is lowered when the ultrasonic frequency is low, efficient defect identification becomes difficult. For this reason, much effort has been made in developing foreign countries to develop nondestructive ultrasonic probes for materials with high attenuation.

Overseas, Panametrics, Ultran, Germany's KrautKramer, and Toray, Japan, are actively working to develop ultrasonic transducers for high damping materials.

Ultrasonic transducers currently being used are piezoelectric elements, most of which use PZT, and the main components include piezoelectric elements, backing materials, front matching layers (front matching layers), and electrical impedance matching circuits.

Recently, the lead magnesium niobate titanate (PMN-PT) single crystal has attracted attention as a new piezoelectric material. The PMN-PT single crystal is a ferroelectric single crystal. It is a material having ferroelectricity in which spontaneous polarization is not erased.

Since PMN-PT has excellent piezoelectric characteristics, it is excellent in application as an ultrasonic wave generating element.

  Therefore, it is necessary to develop an ultrasonic probe suitable for non-destructive testing of high damping material of power generation equipment using the PMN-PT piezoelectric element.

The present invention has been made in view of the above, by using the KLM model to simulate the characteristics of the ultrasonic transducer, and based on the ultrasonic transducer for the center frequency 1 and 2.25 MHz PMN-PT longitudinal wave to produce a commercial ultrasonic probe and By comparing the performance, the object is to provide an ultrasonic probe suitable for non-destructive testing of high attenuation material of power plant.

In the present invention for achieving the above object, in the non-destructive inspection ultrasonic probe of a high attenuation material,

Piezoelectric elements for transmitting and receiving ultrasonic waves; A front matching layer positioned at the front of the piezoelectric element to increase acoustic wave transmittance between the piezoelectric element and a load (a measurement object); A rear member positioned at a rear portion of the piezoelectric element to limit vibration of the piezoelectric element; And an electric matching circuit that cancels the influence of the piezoelectric element due to the capacitance. The piezoelectric element is a PMN-PT piezoelectric single crystal.

In a preferred embodiment, the acoustic impedance of the front matching layer is obtained as a geometric mean of the acoustic impedance of the piezoelectric element and the acoustic impedance of the load, and the thickness of the front matching layer is 1/4 wavelength thick.

In a more preferred embodiment, the material of the front matching layer is alumina.

In addition, the backing material is characterized in that the epoxy and tungsten powder is blended in a constant ratio.

In addition, the electric matching circuit is characterized in that the series tuning circuit using the inductance at the center frequency to cancel the effect of the capacitance in the desired frequency band.

의 관계를 이용하여 필요한 인덕턴스(L₀)를 결정하고, 임피던스 분석기로 중심주파수에 대한 인덕턴스를 측정하면서 고주파용 훼라이트 코어에 상기 식을 만족하도록 감겨진 코일을 포함하는 것을 특징으로 한다.In addition, the electrical matching circuit measures the capacitance (C ₀ ) of the piezoelectric element using an impedance analyzer, and then

The required inductance (L ₀ ) is determined using the relationship of, and the coil wound around the high frequency ferrite core to satisfy the above equation while measuring the inductance with respect to the center frequency with an impedance analyzer.

In addition, the backing material is mixed with an epoxy and a curing agent at a constant ratio, and then mixed while increasing the proportion of tungsten powder, and then a vacuum chamber is used to remove bubbles in the mixture of epoxy and tungsten powder, and finally, the mixture is cured. It is characterized by being completed.

In addition, a cylindrical case having both ends opened, a protective cap attached to the rear end of the case, and a connector mounted on the rear side of the case to transmit ultrasonic waves to the piezoelectric element, the inner direction from the front end of the case The front matching layer, the piezoelectric element and the back surface is characterized in that the installation.

In addition, the manufacturing conditions of the backing material is characterized in that it is analyzed through the ultrasonic transducer simulation program based on the KLM model.

As seen above, according to the ultrasonic transducer for high-damping material non-destructive inspection using PMN-PT piezoelectric single crystal according to the present invention, after producing the ultrasonic transducer simulation program based on the KLM model, by analyzing the conditions of the back material manufacturing, Ultrasonic fabrication conditions can be found, and by using a PMN-PT piezoelectric element to develop an ultrasonic probe suitable for non-destructive testing of high attenuation material, it is possible to improve the ultrasonic response characteristics and the performance of the transducer.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1, 2 and 5 are diagrams for explaining the ultrasonic transducer for high-damping material non-destructive inspection using PMN-PT piezoelectric single crystal according to an embodiment of the present invention, Figure 3 is an ultrasonic transducer based on the KLM model 4 is a circuit diagram for explaining the configuration of the simulation program, FIG. 4 is an image showing the ultrasonic measuring apparatus used in the present invention, and FIG. 6 is an image showing the ultrasonic measuring specimen used in the present invention.

Ultrasonic transducer 10 according to an embodiment of the present invention is a piezoelectric element 11 that is responsible for the transmission and reception of ultrasonic waves, and the front matching layer 12 to increase the transmission of sound waves between the piezoelectric element 11 and the load. And a backing material 13 for limiting vibration at the rear of the piezoelectric element 11 and an electric matching circuit for canceling the influence of the capacitance of the piezoelectric element 11.

In addition, the ultrasonic transducer 10 has a transducer case forming an outer shape is composed of an outer case 14, an inner case 15 and a protective cap 16. The outer case 14 is provided with a mounting hole for mounting the connector 17, the mounting jaw is formed in the lower inner case 15 so that the lower portion of the outer case 14 is coupled to the outer side of the lower inner case 15 It is.

The piezoelectric element 11 is an active element capable of transmitting and receiving ultrasonic waves and is the most important element in an ultrasonic transducer. PZT, which is a ceramic piezoelectric element, has been used as a piezoelectric element, but interest in piezoelectric single crystals having improved piezoelectric characteristics is increasing.

Of these piezoelectric single-crystal is a typical material for the PMN-PT, but the disadvantage that the manufacturing cost expensive than PZT ceramics, electricity than conventional PZT ceramics - about 20% electromechanical coupling coefficient (k _t) representing the sound conversion efficiency, transmission performance The piezoelectric coefficient which determines the performance is about 1.5 times or more.

The main characteristics of the PMN-PT applied in the present invention are shown in Table 1, and are compared with the data of PZT-5A and PZT-5H which are commonly used.

In this case, a signal line of the connector 17 is attached to the rear surface of the piezoelectric element 11 to transmit and receive electrical signals.

The front matching layer 12 is positioned between the piezoelectric element 10 and the load, thereby improving the acoustic impedance difference between the piezoelectric element 11 and the load and increasing the permeability of sound waves. The optimum acoustic impedance of the front matching layer 12 is obtained by the geometric average of the acoustic impedance of the piezoelectric element 11 and the acoustic impedance of the load, wherein the thickness of the front matching layer is calculated as 1/4 wavelength thickness.

At this time, the alumina is selected as the front matching layer 12 material in consideration of the acoustic impedance 45 ~ 50 MRayL of stainless steel, which is used as a load, that is, a high damping material, which is an ultrasonic measurement object. The sound velocity, density and acoustic impedance of the selected alumina are 3950 m / s, 11,000 kg / ㎥, 43 MRayL, and the thickness is 1.0 mm for the 1 MHz transducer and 0.45 mm for the 2.25 MHz transducer.

The backing material 13 acts as a damper to limit the vibration of the piezoelectric element 11 at the rear portion of the piezoelectric element 11, thereby increasing the resolution and widening the frequency bandwidth. In addition, the backing material 13 should be able to scatter or absorb the ultrasonic waves transmitted to the backing material to avoid unnecessary signal interference.

The backing material 13 according to an embodiment of the present invention is manufactured by mixing tungsten powder having an epoxy and an average particle size of 25 μm. Epoxy is Araldite GY 509 (USA), mixed with a curing agent in a ratio of 1: 4, mixed with increasing the proportion of tungsten powder, and then removed from the air bubbles using a vacuum chamber.

Finally, after curing for 24 hours at room temperature to complete the backing material 13, the acoustic impedance is calculated by measuring the density and ultrasonic transmission speed of the material of the backing material 13 produced according to the mixing ratio of epoxy and tungsten powder.

In order to measure the ultrasonic speed, the thickness of the backing material 13 was constantly made at 5 mm and measured using a through transmission method using two ultrasonic probes having a center frequency of 2.25 MHz.

Table 2 shows the density, the ultrasonic velocity, and the acoustic impedance, respectively, according to the mixing ratio of the epoxy and tungsten powder produced in this study.

 The piezoelectric element of the ultrasonic probe has a capacitance as a dielectric, and this capacitance increases the rise time of the ultrasonic signal when the piezoelectric element is used as the ultrasonic transmitter and at the same time shunts a signal source (signal source). shunt) increases the amount of current required.

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On the other hand, since the capacitance acts as a load of the ultrasonic transducer when the piezoelectric element is used as the ultrasonic receiver, it serves to reduce the reception sensitivity, so it is desirable to cancel the influence of the capacitance as much as possible.

The electric matching circuit can compensate for the influence of capacitance in a desired frequency band by configuring a series tuning circuit using inductance at the center frequency f ₀ .

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In order to manufacture an electric matching circuit according to an embodiment of the present invention, first, the capacitance C ₀ of the piezoelectric element 11 is measured using an impedance analyzer (HP 4194A, Hewlett Packard, USA), and then Equation (1) Determine the required inductance (L ₀ ) using the relationship of.

While measuring the inductance with respect to the center frequency with an impedance analyzer, the coil is wound around the ferrite core for high frequency to produce a coil satisfying Equation (1). Table 3 shows the capacitance measured at each center frequency and the inductance of the fabricated coil.

Experimental Example

In order to find the optimal design values of the ultrasonic transducer 10, the response signals of the ultrasonic transducer 10 were analyzed by changing the conditions of the front matching layer 12 and the backing material 13 using the KLM model and transmission line theory.

The KLM model, developed to analyze the electro-mechanical coupling effect of thin piezoelectric elements, is an equivalent circuit proposed by Krimholz, Leedom and Mattaei in 1970. In the KLM model, the acoustic part of the piezoelectric element 11 is assumed to be a transmission line, so that the physical analysis is easy even when the piezoelectric element 11 and the front matching layer 12 are connected in series.

In the ultrasonic transducer simulation program based on the KLM model, the ultrasonic transducer 10 is configured in a network form as shown in FIG. 3 and then expressed as a reciprocating transfer function to obtain an impulse response of the ultrasonic transducer.

Through this simulation process, it is possible to predict the optimum design variables and response signals required for manufacturing the ultrasonic transducer 10. The program for simulation was written in MATLAB software.

The load condition in the simulation was austenitic SUS316, and the variables required for the simulation were used in the data in Table 1. In this simulation, since the thickness of the epoxy for bonding between the piezoelectric element 11 and the front matching layer 12 and the thickness of the coupler for matching the acoustic impedance may greatly affect the characteristics of the ultrasonic probe, the thickness of each of the ultrasonic transducers may be reduced. It was simulated by fixing to 1μm.

In addition, since the electrode thickness of the piezoelectric element 11 was about several hundred micrometers as Au, the influence of the electrode thickness was ignored. Therefore, the piezoelectric element 11, the front matching layer 12, and the properties of the epoxy for bonding is fixed, so that the response characteristics of the ultrasonic probe 10 while simulating the acoustic impedance of the back material 13 was simulated.

The pulse-echo method was used to measure the characteristics of the developed ultrasonic transducer 10 for the high attenuation material, and the experimental apparatus constituted the ultrasonic measuring apparatus as shown in FIG. 4.

The Pulsar / Receiver used a 5601A / T from Panametrics (USA) and a LeCroy (USA) oscilloscope to store and analyze the received ultrasound signal.

The center frequencies of the high-damping ultrasonic transducer 10 are 1 MHz and 2.25 MHz transducers (FIG. 5), and a commercial transducer having a piezoelectric element of the same diameter was used for performance comparison. Commercially available transducers were Panametric (USA) 1 MHz ultrasonic transducer (A 103R) and Savelery (USA) 2.25 MHz (CMC-0204). The high attenuation material used in the ultrasonic test was used austenitic SUS316 specimen 18 provided by Doosan Heavy Industries, Ltd., as shown in FIG.

Assessment and analysis

As shown in Table 2, the acoustic impedance of the backing material was measured and prepared in advance by varying the mixing ratio of epoxy and tungsten particles. The response signal of the ultrasonic probe was analyzed by applying the mixing ratio of Table 2.

7 and 8 illustrate an ultrasonic probe 10 including a PMN-PT piezoelectric element 11, a backing material 13, a front matching layer 12, and an epoxy bonding layer having a center frequency of 1 MHz and 2.25 MHz, and SUS316. Test results of the experimental example constituted by the test piece 18, the ultrasonic probe 10, and the coupler layer, which is a contact medium between the test piece 18, are shown.

FIG. 7A shows a case where the compounding ratio of epoxy and tungsten particles is 1: 4, and the measured acoustic impedance at this time is 6.1 MRayL. FIG. 7B shows a case where the compounding ratio of epoxy and tungsten particles is 1: 6, and the acoustic impedance is 8.5 MRayL. Respectively.

When the acoustic impedance is increased from 6.1 MRayL to 8.5 MRayL, it can be seen that the magnitude of the ultrasonic response signal decreases by about 3 dB. In FIG. 7A, the peak frequency and the center frequency are about 1.2 MHz, and the bandwidth is about 33.3%. It was analyzed to show the characteristics of the probe.

8A shows the results when the mixing ratio of epoxy and tungsten particles is 1: 4, and FIG. 8B shows the results when 1: 6. Similar to the results of FIG. 7, it can be seen that when the acoustic impedance increases, the magnitude of the ultrasonic response signal decreases by about 3.5 dB. In FIG. 8A, the peak frequency is 2.15 MHz, the center frequency is 1.95 MHz, and the bandwidth is about 46.2%.

Based on the above simulation results, the PMN-PT ultrasonic probe was produced with the mixing ratio of epoxy and tungsten particles as 1: 4. 9 and 10 show the first reflection signal obtained by applying the pulse-echo method to the high-damping specimens of the manufactured 1 MHz and 2.25 MHz ultrasonic transducers, and the results of frequency analysis of the signals, respectively.

Figure 9a shows the magnitude of the reflected signal for the PMN-PT ultrasonic transducer 10 having a center frequency of 1 MHz according to an embodiment of the present invention, Figure 9b is a reflection of a commercial ultrasonic transducer having a center frequency of 1 MHz Indicates the magnitude of the signal.

Figure 10a shows the magnitude of the reflected signal for the PMN-PT ultrasonic transducer 10 having a center frequency of 2.25 MHz according to an embodiment of the present invention, Figure 10b is a reflection of a commercial ultrasonic transducer having a center frequency of 2.25 MHz Indicates the magnitude of the signal.

It can be seen that the reflected signal of the present invention is about 9.54 dB larger than that of a commercially available ultrasonic probe, and the center frequency is 1.4 MHz and the bandwidth is about 39%.

In addition, in the case of the 2.25 MHz transducer in FIG. 10, the probe according to the embodiment of the present invention showed a reflected signal about 11.13 dB greater than that of a commercial ultrasonic probe. At this time, the center frequency is 2.5 MHz, the bandwidth was about 40%.

The transducer manufacturing conditions according to an embodiment of the present invention can be applied to frequencies of 5 MHz and higher in the future.

While the invention has been shown and described with respect to certain preferred embodiments thereof, the invention is not limited to these embodiments, and has been claimed by those of ordinary skill in the art to which the invention pertains. It includes all the various forms of embodiments that can be carried out without departing from the spirit.

1 is a cross-sectional view showing an ultrasonic transducer for high-damping material non-destructive inspection using a PMN-PT piezoelectric single crystal according to an embodiment of the present invention,

Figure 2 is an exploded perspective view of Figure 1,

3 is a circuit diagram for explaining the configuration of the ultrasonic transducer simulation program based on the KLM model,

4 is an image showing an ultrasonic measuring apparatus used in the present invention,

5 is a perspective view of the combination of FIG.

6 is an image showing the ultrasonic measurement specimen used in the present invention,

7A to 8B are graphs showing acoustic impedances according to the combination of the backing material of the ultrasonic probe using PMN-PT piezoelectric elements having a center frequency of 1 MHz and 2.25 MHz, respectively.

9A to 10B are graphs comparing the magnitudes of reflected signals for a PMN-PT ultrasonic probe and a commercially available ultrasonic probe according to an embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

10: ultrasonic transducer 11: piezoelectric element

12: front matching layer 13: back material

14: outer case 15: inner case

16: protective cap 17: connector

18: Psalms

Claims (9)

delete In the ultrasonic probe for non-destructive inspection of high damping material, Piezoelectric elements for transmitting and receiving ultrasonic waves; A front matching layer positioned at the front of the piezoelectric element to increase acoustic wave transmittance between the piezoelectric element and a load (a measurement object); A rear member positioned at a rear portion of the piezoelectric element to limit vibration of the piezoelectric element; And An electric matching circuit canceling the influence of the capacitance of the piezoelectric element; It is configured to include, the piezoelectric element is a PMN-PT piezoelectric single crystal, The acoustic impedance of the front matching layer is obtained by the geometric mean of the acoustic impedance of the piezoelectric element and the acoustic impedance of the load, and the thickness of the front matching layer is 1/4 wavelength thick. Ultrasonic transducer for nondestructive testing of materials. delete In the ultrasonic probe for non-destructive inspection of high damping material, Piezoelectric elements for transmitting and receiving ultrasonic waves; A front matching layer positioned at the front of the piezoelectric element to increase acoustic wave transmittance between the piezoelectric element and a load (a measurement object); A rear member positioned at a rear portion of the piezoelectric element to limit vibration of the piezoelectric element; And An electric matching circuit canceling the influence of the capacitance of the piezoelectric element; It is configured to include, the piezoelectric element is a PMN-PT piezoelectric single crystal, The backing material is an ultrasonic probe for high-damping material non-destructive inspection using PMN-PT piezoelectric single crystal, characterized in that the epoxy and tungsten powder is blended in a constant ratio. In the ultrasonic probe for non-destructive inspection of high damping material, Piezoelectric elements for transmitting and receiving ultrasonic waves; A front matching layer positioned at the front of the piezoelectric element to increase acoustic wave transmittance between the piezoelectric element and a load (a measurement object); A rear member positioned at a rear portion of the piezoelectric element to limit vibration of the piezoelectric element; And An electric matching circuit canceling the influence of the capacitance of the piezoelectric element; It is configured to include, the piezoelectric element is a PMN-PT piezoelectric single crystal, The electrical matching circuit comprises a series tuning circuit using an inductance at a center frequency to offset the influence of capacitance in a desired frequency band by using a PMN-PT piezoelectric single crystal high-damping material ultrasonic inspection probe. The method according to claim 5, The electric matching circuit measures the capacitance (C ₀ ) of the piezoelectric element by using an impedance analyzer, and then

Determining the required inductance (L ₀ ) using the relationship of, and measuring the inductance with respect to the center frequency (f ₀ ) with an impedance analyzer, characterized in that it comprises a coil wound to satisfy the above equation in the ferrite core for high frequency Ultrasonic transducer for high-damping material nondestructive testing using PMN-PT piezoelectric single crystal. In the ultrasonic probe for non-destructive inspection of high damping material, Piezoelectric elements for transmitting and receiving ultrasonic waves; A front matching layer positioned at the front of the piezoelectric element to increase acoustic wave transmittance between the piezoelectric element and a load (a measurement object); A rear member positioned at a rear portion of the piezoelectric element to limit vibration of the piezoelectric element; And An electric matching circuit canceling the influence of the capacitance of the piezoelectric element; It is configured to include, the piezoelectric element is a PMN-PT piezoelectric single crystal, The backing material is mixed with an epoxy and a curing agent at a constant ratio, and then mixed while increasing the proportion of tungsten powder, and then a bubble is removed from the mixture of the epoxy and tungsten powder using a vacuum chamber, and finally, the mixture is cured. Ultrasonic transducer for high-damping material non-destructive inspection using PMN-PT piezoelectric single crystal. In the ultrasonic probe for non-destructive inspection of high damping material, Piezoelectric elements for transmitting and receiving ultrasonic waves; A front matching layer positioned at the front of the piezoelectric element to increase acoustic wave transmittance between the piezoelectric element and a load (a measurement object); A rear member positioned at a rear portion of the piezoelectric element to limit vibration of the piezoelectric element; And An electric matching circuit canceling the influence of the capacitance of the piezoelectric element; It is configured to include, the piezoelectric element is a PMN-PT piezoelectric single crystal, A cylindrical case having both ends opened, a protective cap attached to the rear end of the case, and a connector mounted on the rear side of the case to transmit ultrasonic waves to the piezoelectric element, and the front face inward from the front end of the case. Ultrasonic transducer for high-damping material non-destructive inspection using PMN-PT piezoelectric single crystal characterized in that the matching layer, the piezoelectric element and the backing material is installed. delete

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