Time-frequency analysis to a particular type of scattering problems involving metallic-polymer tubing structures

In this paper, recent studies of backscattered acoustic signals in thinner steel-polymer tubing structures have been presented. Reassigned smoothed pseudo Wigner-Ville (rspWV) analysis has been adopted in order to diminish the cross-term effect, and achieve high resolution spectral. Vibration modes, which are associated to the resonances of circumferential waves, have been determined by using the modal isolation plan representation. At normalized frequencies below 140, an appreciable influence from the polymer coating thickness on the A₀⁺ and S₀ modes has been noticed. Furthermore, the trajectory of the A₀^- wave has been modified in the normalized frequency band 40-42. Group velocity curves of the A₀^- wave have, then, been graphically illustrated. The findings have shown a particular curvature change at reduced frequency 41 in the case of an immersed two-layer tube in water. Studies of acoustic backscattering involving steel-polymer tubing structures have confirmed the significant coupling of A₀⁺ and S₀ waves. Besides, the disappearance of the A₀⁺ resonance trajectory has been observed; which is a very important phenomenon to understand.