A New ultrasonic signal processing scheme for detecting echoes of different spectral characteristics in concrete using empirical mode decomposition

In this work, a new signal processing scheme is proposed to improve ultrasonic echoes detection in concrete, a construction material and inhomogeneous propagation medium, in which the backscattering and the grain noise mask the useful signals. Firstly, the time-domain ultrasonic signal is measured. Then the original signal is separated into Intrinsic Mode Functions (IMF) using Empirical Mode Decomposition. Secondly, the Fourier analysis is performed on each IMF. Examining the behaviors of the IMFs in the time and frequency domain, one can judge which IMF represents noise, echoes wave. Then we use nonlinear processing techniques to recombine the selected IMFs. Experimental results are presented and analyzed on a trapezoidal concrete/mortar/cement-paste prism specimen, showing that the proposed technique has an excellent performance. The improvement in defect detection was experimentally verified too on a prism based specimen of mortar with artificial defect.