“…7. Waveform of the reflected signal u i (t) from the ith interface is given by : u i ðtÞ ¼ IFTðK 0;k FTðu iÀ1 ðtÞÞe À2mx w;k a R;k ðf =f R;k Þ n k Àj4px w;k ðf =v p;k ðf ÞÞ Þ; (18) where FT and IFT denote the direct and inverse Fourier transform, respectively, K 0,k is the reflectivity coefficient, u iÀ1 (t) is the signal reflected from the front surface of the kth layer (interface iÀ1), and has been used as a reference, performing analysis of the back-surface reflection u i (t) from the kth layer (interface i), m is the conversion coefficient from dB to Np (m ¼ 0.115), a R,k is the attenuation coefficient at the reference frequency f R,k , n k is the power of the attenuation slope, x w,k is the wall thickness of the individual kth layer, v p,k (f) is the phase velocity dispersion. For the ith interface between adjacent layers, the reflectivity coefficient K 0,k is given by…”