• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.303-306
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• 1999

In this study, the piezoelectric ceramics PZT powder was synthesized by Wet-Dry combination method. The flexible 1-3-0 type composites were fabricated with piezoceramic PZT and Eccogel polymer matrix embedded 3rd phase. This paper represents the acoustic properties with various 3rd phase wt.%. The acoustic impedance of 1-3-0 type composites was lower than that of single phase PZT ceramics. The pulse-echo response of transducer fabricated with 1-3-0 type composites was better than solid PZT transducer.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.1
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• pp.27-32
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• 2000

In this paper, ultrasonic wave in the thermoelastic regime was generated in a steel disk by illuminating a pulse laser (Q-switched Nd:YAG) on the surface of the sample and was detected on the other side by Michelson interferometer which was stabilized by feed back control. The experimentally detected displacement waveform of the ultrasonic wave showed good agreement with the theoretically expected one. Also it was shown that sound speeds of longitudinal and shear wave were similar to ones measured by pulse-echo method using a contact transducer. As an application of the noncontact ultrasonic measurement by using laser based ultrasonics, the sound speed in the sample was monitored while the sample was heated in a furnace, and the result showed that it decreased according to the increase of sample temperature.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.5
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• pp.475-479
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• 2003

Traditional ultrasonic evaluation to detect micro/small surface cracks is the pulse-echo technique using the normal immersion transducer with high frequency, or the angle beam transducer with surface wave. It is difficult to make the automatic ultrasonic system that is to detect micro and small surface crack and position on the large structure like steel and ceramic rolls, because of the huge data of inspection and the ambiguous position data of transducer. The aim of this study using the high precision scanning acoustic microscope with 10MHz large aperture transducer was to display the real time A, B, C-scan for the automatic ultrasonic system in order to detect the existence and position of surface crack. The ultrasonic method with large aperture transducer was improved the scanning time and speed over 10times faster than traditional methods.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.8 no.1
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• pp.135-141
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• 1999

Recently, advance signal analysis which is called "Time-Frequency Analysis" has been developed. Wavelet and Wigner Distribution are used to the method. Wavelet transform(WT) is applied to time-frequency analysis of waveforms obtained by an ultrasonic pulse-echo technique. The Gabor function is adopted as the analyzing wavelet. Wavelet analysis method is an attractive technique for evolution of material characterization evoluation. In this paper, the feasibility of suppression of ultrasonic background noise signal using WT has been presented. These results suggest that ultrasonic background noise ginal can be suppressed and enhanced even for SNR of 20.8 dB. This property of the WT is extremely useful for the detecting flaw echos embedded in background noise.und noise.

• The Journal of the Acoustical Society of Korea
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• v.17 no.8
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• pp.58-63
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• 1998

저주파 영역의 음파의 투과속도 측정에 기존의 펄스에코방법이나 투과법 (transmission method)가 이용되는 경우, 탐촉자 및 시편의 크기, 시편과 탐촉자 사이의 거 리가 사용하는 음파의 주파수가 작아질수록 대형화되어 측정에 어려움을 나타내게 된다. 따 라서 본 연구에서는 고분자 재료의 음향특성을 평가할 수 있는 간단한 방법으로써 고분자 재료의 주파수에 따른 동적 탄성률(dynamic modulus)을 시간-온도 중첩의 원리를 이용하여 측정하고, 고분자 내에서 저주파 영역의 음파의 전달 속도와 주파수에 따른 탄성율(elastic modulus), 전단 탄성률(shear modulus) 그리고 밀도의 관계식으로부터 음속을 측정하였다. 실험결과 주파수가 증가함에 따라 고분자 재료의 동적 탄성률이 증가하였으며, 음속도 주파 수에 따라 증가하였다. 본 연구에서 사용한 폴리우레탄 재료의 음속은 100Hz∼10kHz영역에 서 약1500m/sec에서 3000m/sec를 나타내었다.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.36 no.3
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• pp.186-194
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• 2000

bottom as a reference basis, some theoretical elements which form bottom echoes during acoustic survey of demersal fish were considered. A stable bottom detection method based on maximum voltage difference, which was not influenced by variable levels and waveform transformation. The method has been shown to be effective using in-situ bottom echo waveforms and computer simulation data. A comparison between near-bottom SV profiles acquired in Funka Bay, Hokkaido, of Japan, the East China Sea and the Yellow Sea, of Korea, with the threshold method and maximum differential voltage method, shows that the SV obtained with the maximum differential voltage method is 4-6 dB higher than those with threshold method within 2m from the bottom.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.230-237
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• 2012

The ultrasonic resonance method was applied to detect the disbond interface and empty layer between steel and FRP of the exit cone. The ultrasonic resonance method can easily detect the disbond interface and empty layer by amplifying the ultrasonic signal, but pulse echo method is difficult to distinguish adhesive interface from disbond interface or empty layer. The resonance frequency was predicted using the pressure reflection coefficient of 3-layered medium, and measured from ultrasonic signal of the test block using Fast Fourier Transform. The ultrasonic resonance proved that the predicted resonance frequency was in good agreement with the measured resonance frequency.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.5
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• pp.363-368
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• 1999

Ultrasonic pulse-echo methods measuring the transit time through specimens have been widely used in determination of ultrasonic velocity and thickness of specimens. Usually, to determine the velocity of the ultrasonic. the transit time of the ultrasonic pulse through specimen is measured by using the ultrasonic measuring equipment such as the oscilloscope including ultrasonic pulser/receiver and the thickness of the specimen is measured by using the length measuring instrument such as micrometer or vernier calipers etc., i. e. each parameter is measured by using each measuring method. In the case of the measuring the thickness of a specimen by using the ultrasonics. the ultrasonic equipments, which measure the thickness, such as the ultrasonic thickness gauge must be calibrated by using the reference block of which the ultrasonic velocity is known beforehand. In the present work, we proposed a new method for simultaneous measurement of ultrasonic velocity and thickness without reference blocks. Experimental results for several specimens show that proposed method have good agreements with those by traditional ultrasonic method.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.5
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• pp.89-96
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• 2012

The rubber side could be contaminated using the existing pulse echo method because the ultrasonic wave was incident on the rubber side from the interior of the steel motor case, which could lead to the critical disbond defect. To develop the test method which can be replaced the existing method, the ultrasonic wave was incident on steel face of the steel/rubber adhesive test block. Rubber resonance frequencies measured from the steel/rubber adhesive test block were in good agreement with theoretically predicted rubber resonance frequencies. This paper was described about the ultrasonic resonance method to convert the rubber resonance frequency into the rubber thickness.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.11-16
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• 2006

The object of this study is to develop new examination techniques for detecting the debonds in adhesive interface of different kinds of the material. Ultrasonic signal was modeled by theoretically analyzing ultrasonic propagation phenomenon of the adhesive interface and debonding interface. The test method using the phase reversal of the debonding interface applied to the FRP/Rubber test block. Aluminum/Rubber test block with the flat bottom hole was manufactured to quantitatively evaluate the minimum detection ability of the defects. The pulse echo reflection method and the phase reversal method were mutually compared and it was estimated that the phase reversal method could detect the debonds on the basis of the theoretically predicted ultrasonic signal and ultrasonic test data.