IMPROVING SIGNAL PROCESSING OF THE IMPACT-ECHO METHOD USING CONTINUOUS WAVELET TRANSFORM

摘要

Signal processing techniques can improve the feature identification of impact-echo signals obtained from buried objects in concrete. Steel reinforcement, steel tubes, and PVC tubes embedded in concrete slabs are tested. The received signals, both experimental and simulated, are analyzed using both fast Fourier transform (fft) and continuous wavelet transform. The amplitude spectra, based on fft, can only provide global information and lose - important local effects of frequency components. This is resolved by preserving the transient effects in the frequency domain using continuous wavelet transform. Features related to embedded steel bar and PVC and steel tubes can thus be recognized according to the difference in scales and lasting periods in the magnitude plot of wavelet coefficients. Furthermore, the same peak frequency found in the amplitude spectrum is now distinguishable between PVC and steel tubes at a resolution of 0.2 kHz or better. Such findings provide a more effective way to pick up true rebar signals using the impact-echo method.