A calculation approach for acoustic impedance and time-of-flight of an embedded elastic thin layer by ultrasound

Abstract

A calculation approach for acoustic impedance and time-of-flight of an elastic thin layer embedded between a thin substrate and a substrate of infinite extent is described utilizing the reflection coefficients for the normally–incident ultrasonic reflected signals. As the difference of the phase-shift in the embedded layer at two neighbouring angular frequencies is not greater than π, analytical relational expressions for acoustic impedance and time-of-flight of the embedded layer with the measured data are derived, respectively. Utilizing two analytical relational expressions, acoustic impedance and time-of-flight can be calculated without considering acoustic impedance of the substrate of infinite extent. The influences of the changes in the parameters of the known layers and the experimental noises on calculating acoustic impedance and time-of-flight of the embedded layer are numerically investigated.