A direct determination of acoustical impedance of a thin layer on a thick elastic substrate by the ultrasound

A direct determination method of acoustical impedance of a linear-viscoelastic thin layer on a thick elastic substrate is proposed without the prior knowledge of other layer parameters. With the rectangular windows that start at the time zero and are rightward expanded, the successive windowing operations on the total ultrasonic reflected signals are performed. Using the transfer functions of the windowed signals and the analytical formula, the distribution characteristic of the calculated results of acoustical impedance with the different frequency intervals and the behavior of the corresponding estimated values are numerically investigated as the lengths of the sampling windows change. Acoustical impedance of the thin layer can be directly determined from the distribution characteristic of the calculated results and the behavior of the estimated values. The proposed direct determination method is independent of the parameters of the next substrates.