Anomalies in the ultrasound reflection from a solid-dissipative medium interface

The reflection of longitudinal acoustic waves from the interface between a solid and a strongly dissipative medium was theoretically studied. It is shown that the reflection coefficient and the reflected signal phase significantly depend on the coefficient of ultrasound absorption in the dissipative medium. An algorithm for restoring the time variation of the dissipative medium viscosity during solidification is proposed, which is based on the results of measurements of the amplitude reflection coefficient for a pulsed ultrasonic signal. The reflection and transmission coefficients are determined for the ultrasound wave amplitude, velocity, pressure, and intensity. An expression is derived for the acoustic energy absorbed upon reflection from a dissipative medium. A frequency dependence of the amplitude and generalized phase of the signals reflected from and transmitted through the interface are restored from the results of spectral calculations. The theoretical results are confirmed by experimental data on the reflection of acoustic pulses from an organic glass-epoxy compound resin interface measured during solidification of the latter medium. According to these data, the reflection coefficient and the reflected acoustic pulse duration decreased upon solidification of the epoxy compound.