• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.11a
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• pp.233-239
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• 1999

The feasibility of an ultrasonic technique using a pulse-echo method of normal-incident compressional waves was evaluated for its sensitivity to the worn surface and near surface damage due to wear. Worn surfaces were generated at various oscillation frequency under a given load and amplitude and these surface were in situ monitored using a ultrasonic wave detection system. Analysis of the ultrasonic waves received from the worn surface revealed a close relationship between the surface and near-surface damage and the maximum echo-amplitude of the compressional waves. The ultrasonic technique was successful in assessing the level of severity of the worn surface in real time during the wear process. It is also shown that the wear depth can be easily measured by the calculation of change of the specimen thickness based on the wave speed measured for the specimen medium.

• Tribology and Lubricants
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• v.16 no.5
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• pp.351-356
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• 2000

The feasibility of an ultrasonic technique using a pulse-echo method of normal-incident compressional waves was evaluated for its sensitivity to the worn surface and near surface damage due to wear. Worn surfaces were generated at various oscillation frequency under a given load and amplitude and these surface were in situ monitored using a ultrasonic wave detection system. Analysis of the ultrasonic waves received from the worn surface revealed a close relationship between the surface and near-surface damage and the maximum echo-amplitude of the compressional waves. The ultrasonic technique was successful in assessing the level of severity of the worn surface in real time during the wear process. It is also shown that the wear depth can be easily measured by the calculation of change of the specimen thickness based on the wave speed measured for the specimen medium.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1995.11a
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• pp.205-208
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• 1995

PZT powders were prepared by the molten salt synthesis method. The porous PZT specimens were prepared from a mixture of PZT and Polyvinylalcohol(PVA) powders by BURPS(Burnout Plastic Sphere) technique. The pulse-echo response of PZT-polymer 3-3 type composite transducer with various PVA wt.% were studied, The fall time of pulse-echo response of PZT-polymer 3-3 type composite transducer was shorten to that of solid PZT-maded transducer. Therefore, a good transmitting and receiving properties could be obtained. The distance between transducer and reflector was in good agreement both solid PZT and PZT-polymer 3-3 type composite fabricated transducer.

• Proceedings of the KIEE Conference
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• 1995.11a
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• pp.358-360
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• 1995

PZT powders were prepared by the molten salt synthesis method. The porous PZT specimens were prepared from a mixture of PZT and polyvinylalcohol(PVA) powders by BURPS(Burnout Plastic Sphere) technique. The pulse-echo response of porous PZT transducer with various PVA wt.% were studied. The fall time of pulse-echo response of porous PZT transducer was shorten to that of solid PZT-maded transducer. Therefore, a good transmitting and receiving properties could be obtained. The distance between transducer and reflector was in good agreement both solid PZT and porous PZT fabricated transducer.

• Electrical & Electronic Materials
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• v.8 no.2
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• pp.211-216
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• 1995

In this study, the piezoelectric ceramics/polymer composite transducers with 1-3 connectivity have been studied. A piezoelectric ceramics PZT prepared by Wet-Dry Combination method was used as a filler in polymer matrix Eccogel. We've got the pulse-echo response for 1-3 type piezc-electric composite transducers in water. It was shown that the transmitting and receiving sensitivity of 1-3 type piezoelectric composite transducers could be improved in comparison with that- of solid PZT transducers. The reason is for that 1-3 type Piezoelectric composites have low dielectric constant and density. There was in a good agreement between the resonant frequencies calculated from one period and observed results on the Ultrasonic Transducer Analyzer. According to these results we could be figured out the distance in water by virture of the pulse-echo response.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.2
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• pp.135-139
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• 1985

A J$_{IC}$ test procedure by ultrasonic method performed to observe the crack opening behavior of fatigue precrack and detect the initiation of crack propagation of compact tension specimen in this paper. Pulse-echo method with 5 MHz transducer was used on the Cr-Mo steel quenched and tempered at 593.deg. C. We obtained the following results in the elastic-plastic fracture toughness test by ultrasonic method. Echo height is a little increased linearly and rapidly at the early stage of loading . Then it is decreased considerably, finally at the unstable crack growth stage, it is rapidly increased at an unpredictable rae. The initiation of crack propagation is supposed to be at the stage deviated from linearly decreased region and then blunted. J$_{IC}$ value(10.15-12.15 Kgf/mm) by ultrasonic method is lower than that(12.2 Kgf/mm) by R-curve method. But, it is required that the research for the more exact evaluation about correlation between echo height and the crack opening behavior of precrack tip will be continued. continued.ued.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.6
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• pp.501-510
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• 2000

Recently, advanced signal analysis which is called "time-frequency analysis" has been used widely in nondestructive evaluation applications. Wavelet transform(WT) and Wigner Distribution are the most advanced techniques for processing signals with time-varying spectra. Wavelet analysis method is an attractive technique for evaluation of material characterization nondestructively. Wavelet transform is applied to the time-frequency analysis of ultrasonic echo waveform obtained by an ultrasonic pulse-echo technique. In this study, the feasibility of noise suppression of ultrasonic flaw signal and frequency-dependent ultrasonic group velocity and attenuation coefficient using wavelet analysis of ultrasonic echo waveform have been verified experimentally. The Gabor function is adopted the analyzing wavelet. The wavelet analysis shows that the variations of ultrasonic group velocity and attenuation coefficient due to the change of material characterization can be evaluated at each frequency. Furthermore, to assure the enhancement of detectability and naw sizing performance, both computer simulated results and experimental measurements using wavelet signal processing are used to demonstrate the effectiveness of the noise suppression of ultrasonic flaw signal obtained from austenitic stainless steel weld including EDM notch.

• Geophysics and Geophysical Exploration
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• v.16 no.3
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• pp.171-179
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• 2013

An automated ultrasonic velocity measurement system adopting pulse-echo-overlap (PEO) method has been constructed, which is known to be a precise and versatile method. It has been applied to velocity measurements for 5 kinds of engineering plastic cores and compared to first arrival picking (FAP) method. Because it needs multiple reflected waves and waves travel at least 4 times longer than FAP, PEO has basic restriction on sample length measurable. Velocities measured by PEO showed slightly lower than that by FAP, which comes from damping and diffusive characteristics of the samples as the wave travels longer distance in PEO. PEO, however, can measure velocities automatically by cross-correlating the first echo to the second or third echo, so that it can exclude the operator-oriented errors. Once measurable, PEO shows essentially higher repeatability and reproducibility than FAP. PEO system can diminish random noises by stacking multiple measurements. If it changes the experimental conditions such as temperature, saturation and so forth, the automated PEO system in this study can be applied to monitoring the velocity changes with respect to the parameter changes.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.6
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• pp.511-520
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• 2000

Ultrasonic pulse echo method comes to be difficult to apply to the multi-layered structure with very thin layer, because the echoes from the top and the bottom of the layer are superimposed. We can easily meet this problem when the silicon chip layer in the semiconductor is inspected by a SAM equipment using fairly low frequency lower than 20MHz by which severe attenuation in the epoxy mold compound of packaging material can be overcome. Conventionally, deconvolution technique has been used for the decomposition of superimposed UT signals, however it has disabilities when the waveform of the transmitted signal is distorted according to the propagation. In this paper, the wavelet transform based deconvolution(WTBD) technique is proposed as a new signal processing method that can decompose the superimposed echo signals with superior performances compared to the conventional deconvolution technique. WTBD method uses the wavelet transform in the pre-stage of deconvolution to extract out the common waveform from the transmitted and received signal with distortion. Performances of the proposed method we shown by through computer simulations using model signal with noise and we demonstrated by through experiments for the fabricated semiconductor sample with partial delamination at the top of silicon chip layer.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.84-89
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• 2001

Ultrasonic pulse echo method comes to be difficult to apply to the multi-layered structure with very thin layer, because the echoes from the top and the bottom of the layer are overlapped. Conventionally method, deconvolution technique has been used for the decomposition of overlapped UT signals, however it has disabilities when the waveform of the transmitted signal is distorted according to the propagation. In this paper, the wavelet transform based deconvolution (WTBD) technique is proposed as a new signal processing method that can decompose the overlapped echo signals in A-Scan signal with superior performances compared to the conventional deconvolution technique. Performances of the proposed method are shown by through computer simulations using model signal with noise and are demonstrated by through experiments for the fabricated acryl rod with a thin steel plate bonded to it.