Application of Spectral and Time-Frequency Analyses to Study an Acoustic Signal Backscattered from Composite Cylindrical Shell

In acoustic field, the non-destructive testing and characterization purposes are carried out from the analyzing of the acoustic scattering of a progressive plane wave from the target studied. The present paper studies the signal backscattered from the copper/polymer composite cylindrical shell submerged in a fluid medium using Fourier analysis and time-frequency method. The Fourier analysis is used to find the pulse response and the resonance frequencies of the composite cylindrical shell. From large ranges of time-frequency methods, the smoothed pseudo Wigner-Ville distribution (SPWV) is applied because of its most effective properties to study the surface waves generated by the acoustic scattering of a plane wave. The time-frequency image obtained by SPWV is used to estimate the cut-off dimensionless frequencies of the surface waves. In addition, the group delay property of the SPWV distribution is applied to study the dispersion phenomenon of the waves. At each frequency, the group delay may be estimated directly from the time-frequency plane of the wave investigated. The results achieved by time-frequency method show fair agreement with those achieved by the plane of modal identification.