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Imaging Enhancement for Deep Concrete Blocks by Wave-packet Decomposition and Amplitude Compensation

Nondestructive testing plays an important role in the detection of discontinuities and degradation in concrete structures. The synthesized aperture focusing technique (SAFT) improves imaging quality by superimposing the received signals from adjacent transducers. However, in testing of deep concrete blocks, the reflected ultrasonic signals from targets usually combine with scattering, and the amplitude of the useful signal decreases rapidly with its propagation distance. It is hard for traditional SAFT to give a clear display of the target near the bottom. This paper proposes an amplitude compensation technique to enhance the reflected signals from deep targets, and a wavepacket decomposition approach is used to identify these reflections. The relative attenuation coefficient of ultrasonic waves propagating in concrete is obtained by measuring the decay in amplitude of the first and second peaks of the processed envelope signal. Experimental results in an artificial concrete specimen (70 cm length × 60 cm width × 60 cm height) show that the proposed technique has higher imaging resolution than SAFT and the traditional wave-packet decomposition technique.

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