Analysis of the acoustic signals backscattered by a tube using the time-frequency representations

Abstract

The normal excitation of a tube immersed in water by the acoustic plane wave permits the generation of circumferential waves inside the shell and around the shell-water interface. These circumferential waves form standing waves on the circumference of the tube for some frequencies. Moreover, the studies carried out on the diffusion of a plane acoustic wave by target were based primarily on the use of the monodimensional methods (Temporal domain and/or frequencial domain). To exceed the disadvantages of these methods, in this work, we used the time-frequency representations such as the Spectrogram (SP), the Wigner-Ville Distribution (WVD) and the Wavelet Transform (WT). These representations are applied to a theoretical signal backscattered by a tube. From the time-frequency images obtained we have visualized the circumferential waves dispersion (S0, A1, S1,...) and identified these different waves. This analysis allows comparing between these time-frequency representations. And also we have compared between the cut-off frequencies of circumferential waves obtained from these representations and those computed by the proper modes theory of the vibration.