Improving Impact-Echo Method by Wavelet Transform for Infrastructure Inspection

Abstract

Impact-echo, either in time domain or frequency domain, is one of the methods commonly used to measure thickness or strength of concrete structures. However, due to the anisotropic characteristics of concrete, the back-wall echoes are often very difficult to identify from received noisy time domain signals, and it is also frequently difficult to selecta dominant frequency peak on an impact-echo spectrum for thickness calculation. wavelet transform was explored to solve this problem. With assistance of this tool, received noisy time domain impact-echo signals can be transformed directly. Periodic patterns corresponding to the back-wall echoes of measured structure will emerge from a two dimensional scalogram which is the result obtained from a continuous wavelet transform(CWT). Consequently, thickness measurements for concrete structures become more confident and reliable. The effectiveness of wavelet transform for concrete structure measurements of some research nuclear reactors is discussed in this paper.