Evolution of the bistatic acoustic response obtained at oblique configuration from a bilaminated cylindrical shell

The analysis of the acoustic signal scattered at normal incidence by an elastic mono-layered cylindrical shell in a bistatic configuration (i.e., the transmitter and receiver are positioned at different locations), indicates the potential of this method to detect and locate defects in comparison with the monostatic method (i.e., the transmitter and receiver are positioned at the same locations). In addition, the bistatic method at normal and oblique incidence enables the identification of the mode of vibration n (n represents the required number of wavelengths around the circumference of the shell to excite a given resonant frequency) of the guided surface waves that propagate around and along the cylindrical shell. The primary objective of this study is to investigate the impact of receiver position (azimuthal angle θ) on acoustic scattering from an obliquely excited aluminium/stainless steel (Al/SST) bilaminated cylindrical shell immersed in water and filled with air. Frequency analysis of the signals collected at different positions of the receiver revealed that the frequency content of these signals is dependent on the θ angle. In addition, we investigate the evolution of these signals using other representations such as the temporal representation, modal identification plan, angular diagram, and azimuthal angle-frequency representation. Owing to the symmetry of the problem, most of the numerical results presented in this paper are primarily derived from half-turns (0° ≤ θ ≤ 180°) in increments of 1°. Furthermore, the findings obtained through the bistatic approach were compared with those derived from the special case of θ = 180°, where the angle of incidence was maintained at α = 12°.