• Structural Engineering and Mechanics
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• 제76권5호
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• pp.591-598
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• 2020

Ultrasonic waves provide a non-destructive and sensitive way to monitor the concrete hydration. However, limited works are reported to monitor the evolution of the mechanical parameter at early ages. In this study, modified piezoelectric aggregates are embedded inside a concrete beam to excite and receive primary waves. A hydration index, namely, the variation of ultrasonic waveform (VUW) is developed to characterize the variation of the transmitted waves during the hydration process. The recorded hydration indices are compared with the compressive strength measured by destructive test at different ages. The results show that the VUW is closer to the compressive strength than the other two traditional hydration indices, ultrasonic velocity and wave packet energy. The proposed VUW provides a simple and accurate way to monitor the concrete hydration at early ages.

• 비파괴검사학회지
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• 제12권1호
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• pp.9-15
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• 1992

Ultrasonic spectroscopy is likely to become a very powerful NDE method for detection of microfects and thickness measurement of thin film below the limit of ultrasonic distance resolution in the opaque materials, provides a useful information that cannot be obtained by a conventional ultrasonic measuring system. In this paper, we considered a thin film below the limit of ultrasonic distance resolution sandwitched between two substances as acoustical analysis model, demonstrated the usefulness of ultrasonic spectroscopic analysis technique using information of ultrasonic frequency for measurements of thin film thickness, regardless of interference phenomenon and phase reversion of ultrasonic waveform. By using frequency intervals(${\triangle}f$) of periodic minima from the ratio of reference power spectrum of reflective waveform obtained a sample to power spectrum of multiple reflective waves obtained interference phenomenon caused by ultrasonic waves reflected at the upper and lower surfaces of a thin layer, can measured even dimensions of interest are smaller than the ultrasonic wave length with simplicity and accuracy.

• Journal of Biosystems Engineering
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• 제23권6호
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• pp.615-620
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• 1998

The nondestructive internal quality evaluation of agricultural products has been strongly required from the needs for individual inspection. In recent, ultrasonic wave has been considered as a solution for this problem. It transmit well through most materials and can handle safely and easily. However, specially in a watermelon, it is known that general frequency band (higher than 20kHz) ultrasonic waves do not transmitted well due to severe attenuation. The objectives of this study were to find out the proper waveform and frequency of the ultrasonic waves that transmit well inside the watermelon, and to analyze the transmitted waveform in order to make clear the structure of wave propagation in watermelon. The result of several experiments showed that 2kHz shear wave was the most suitable for the detection of internal cavity in the watermelon. Also, it was found that the surface wave did not influence the directly transmitted bulk wave. These results could be a basis of application of ultrasonic wave on the evaluation of internal quality of the watermelon.

• 비파괴검사학회지
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• 제20권6호
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• pp.501-510
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• 2000

초음파 에코파형의 시간-주파수해석법으로 Wigner 분포와 웨이브렛 변환 등과 같은 새로운 신호처리 기법이 비파괴평가 분야에 널리 응용되고 있다. 본 연구에서는 웨이브렛 변환(wavelet transform)에 의한 음속과 감쇠계수의 주파수의존성과 초음파 결함신호의 잡음제거의 유용성 유무를 실험적으로 검증하였다. Gabor 함수를 웨이브렛의 기본함수로 사용하였다. 초음파의 에코파형에 포함된 각 주파수성분의 속도와 감쇠계수의 주파수의존성을 추정할 수 있었으며, 초음파탐상에서 결함의 검출능 향상과 결함크기 산정의 정량화에 접근하기 위해 웨이브렛 변환에 의한 S/N비 신호처리 시뮬레이션 결과를 오스테나이트강 스테인레스 용접부에 가공한 EDM 노치의 초음파 결함신호에 적용한 결과 임상에코를 저감하고 S/N비를 개선하는 것이 가능하였다.

• 한국멀티미디어학회논문지
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• 제20권10호
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• pp.1662-1670
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• 2017

A-Scan NDT equipment is widely used in the industrial field because it is inexpensive and easy to carry but it is necessary to have a skilled inspection specialist who is trained to analyze the waveform of ultrasonic signal. Since the welding quality is judged subjectively by the specialist, there is a problem in the reliability of the quality. In the C-Scan NDT which overcomes the shortcomings of the A-Scan, welding part can be represented in the form of two dimensional image by combining one dimensional ultrasonic waveform so that the quality of welding can be grasped without the help of specialist. In order to develop C-Scan NDT, it is necessary to develop an array type two dimensional transducer and an algorithm to composing image by combining ultrasonic signals generated from a two dimensional transducer. In addition, the noise component must be minimized in the ultrasonic signal in order to display the quality of welding in the form of images. Therefore we propose a method to remove noise component from the ultrasonic wave and construct a two dimensional ultrasonic image.

• 한국정밀공학회지
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• 제15권6호
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• pp.167-174
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• 1998

The ultrasonic test is recognized for its significance as a non-destructive testing method to detect volume defects such as porosity and incomplete penetration which reduce strength in the weld zone. This paper illustrates the defect detection in the weld zone of ferritic carbon steel using ultrasonic wave and the evaluation of pattern recognition by chaotic feature extraction using time series signal of detected defects as data. Shown in the time series data were that the time delay was 4 and the embedding dimension was 6 which indicate the geometric dimension of the subject system and the extent of information correlation. Based on fractal dimension and lyapunov exponent in quantitative chaotic feature extraction, feature value of 2.15, 0.47 is presented for porosity and 2.24, 0.51 for incomplete penetration The precision rate of the pattern recognition is enhanced with these values on the total waveform of defect signal in the weld zone. Therefore, we think that the ultrasonic pattern recognition method of weld zone defects of ferritic carbon steel by ultrasonic-chaotic feature extraction proposed in this paper can boost precision rate further than the existing method applying only partial waveform.

• 한국항해학회지
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• 제19권4호
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• pp.1-8
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• 1995

Although ship's draught information onboard is substantial for both the safety of navigation and the estimation of loaded cargoes, its accuracy depends, in conventional surveying method, on the skillfulness of observers and the condition of the sea surface round the vessel. To obtain more accurate information accessibly, measuring instruments with sophisticated sensors such as mechanical, electronic and ultrasonic transducers have been developed. However, they have still limitation in accuracy and in making up a system due to the complexity of processing signal. In this paper, we propose a new technique for analyzing ultrasonic pulse signal, in order to improve the measurement accuracy and simplify a remote sensing system of draught by ultrasonic waves. In this technique, pulse signal is translated into phase curve which is composed of the phase value defined in time domain. Then, the time interval between two signals different in waveform, is waveform, is analytically determined by calculating average time difference on phase curves. Also, analytical procedure can be carried out in real time with the successive five data sampled at T/4, for high speed digital processing with computer and A/D converter. This technique is useful for measuring draught under the influence of sea condition and for interfacing its data briefly to the integrated bridge system.

• 동력기계공학회지
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• 제10권2호
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• pp.89-92
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• 2006

In this study, the pressure vessel piping with corrosion used during long term were investigated from the time-frequency analysis method. The damage of piping could be evaluated the attenuation factor by ultrasonic parameters such as center frequency and echo waveform. Based on NDE analysis by time-frequency analysis method, it should also be possible to evaluate from various damages and defects in piping members.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.290-295
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• 2004

In this study, the pressure vessel piping with corrosion used during long term were investigated from the time-frequency analysis method. The damage of piping could be evaluated the attenuation factor by ultrasonic parameters such as center frequency and echo waveform. Based on NDE analysis by time-frequency analysis method, it should also be possible to evaluate from various damages and defects in piping members.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2014년도 추계학술대회
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• pp.965-966
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• 2014

초음파를 이용한 거리 및 속도측정에서는 PRF(Pulse Repitition Frequency) 선정에 따른 거리 및 속도 모호성 문제가 큰 장애 요인 중의 하나이다. 따라서 이러한 장애 극복을 위한 신호파형 발생시 PRF 선정 방법과 측정 결과에 미치는 영향을 분석하였다.