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3 August 2001 Design and modeling of signals by using wavelets for the pulse-echo NDT approaches
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In the pulse-echo NDT approaches, which use ultrasonic or electromagnetic pulse to detect damages in structures, a common task is to locate the echo pulses and to analyze characteristics of them. This paper discusses a physical wavelet method for pulse-echo NDT approaches. The physical wavelet is used to stimulate the test object. The time and frequency localization feature makes this kind of signal suitable for detection and localization of damages. Because the input to the structure is a wavelet, the measured signal can be seen as a combination of wavelets with different delay, scales and weights. It is proposed to model the measured signal by several wavelet atoms and to use parameters of the model as features of the signal. Algorithms for the proposed method are developed. Features of the measured waveform are estimated first by iterative matching and then by gradient search for optimizing. Numerical verification of above method was carried out. The simulated structure is a concrete beam to be inspected by electric time-domain reflectrometry method. By using a transmission line model, damages of different sizes, locations and types are simulated. It is shown that the simulated damages can be well described by this wavelet stimulating and modeling method.
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Lihua Shi, Bin Chen, Cheng Gao, and Bihua Zhou "Design and modeling of signals by using wavelets for the pulse-echo NDT approaches", Proc. SPIE 4336, Nondestructive Evaluation of Materials and Composites V, (3 August 2001);

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