Acoustic signals analysed by a parametric and non parametric time-frequency representations

In this article, the time-frequency representation, that takes into account both the time parameter and the frequency parameter of a signal, is used to analyse the acoustic signal backscattered by a thin elastic tube. The non parametric representation "Wigner-Ville distribution" and the parametric representation "modified version" are used in this study for their interesting properties. These representations are applied to the analysis of the dispersion of symmetric S0 and antisymmetric A1 circumferential waves propagating around a tube with a radii ratio equal to 0.95. The image obtained by Wigner-Ville distribution is compared with the modified Wigner-Ville image. From these time-frequency images, we have estimated the group velocity with a high precision. These velocities are compared with those computed by the proper mode theory given in the scientific literature. A good agreement is obtained.