Signal Processing Techniques of Circumferential Waves for Characterization of Bilaminated Cylindrical Shells

Acoustic scattering-based technique is one major approach for characterization purposes and non-destructive testing of structures. This paper investigates the acoustic scattering of a progressive plane wave from two-layered stainless steel/polymer cylindrical shell. The time–frequency techniques are used to study the acoustic scattering from the considered structure. The use of these techniques allows to extract the group velocity and cutoff frequency of circumferential waves. From a temporal signal it is difficult to identify the echoes of different circumferential waves due to the overlapping. To overcome this shortcoming, digital filtering is used to isolate the contribution of each circumferential wave to the total temporal acoustic signal. The time–frequency image of each wave is then constructed using Reassignment Smoothed Pseudo Wigner–Ville (RSPWV) and Reassignment Gabor Transform (RGT). The constructed image can be considered as an acoustic signature of the considered structure. The achieved results show that the time–frequency representation and plane of modal identification can be considered as an alternative of the proper modes theory which is practical in the case of homogeneous structures.