Impedance and attenuation profile estimation of multilayered material from reflected ultrasound

Time-domain and spectral shift methods for determining the attenuation and impedance profiles of multilayered structures are presented. The time-domain technique utilizes two-sided interrogation to measure attenuation and acoustic impedance for individual layers separately under the assumption of a narrowband incident wave. This method is based solely on peak amplitude ratios of successive time-domain echo returns from both sides of the target. The spectral shift technique requires that the propagating pulse have a Gaussian-shaped spectrum, and the transfer function of each layer be characterized by either linear or quadratic frequency dependent attenuation. This method derives the attenuation coefficients and acoustic impedances for individual layers from the information of spectral shift and spectral amplitude peak ratios of the successive gated pulses from single sided interrogation. Experimental results are compared with published data to confirm the validity of these approaches