The phase shift method for studying nonlinear acoustics in a soil

This paper describes a phase shift method for studying the non-linear acoustic behaviour of a soil. The method uses a phase-lock-in technique to measure the phase shift caused by increments in the amplitude of an acoustic excitation. The measured phase shift as a function of dynamic strain amplitude is used to curve fit the non-classic non-linear equation of state in order to extract the hysteretic non-linearity parameter. It is found that the non-linearity parameter obtained by this method is in good agreement with that obtained from the frequency shift method. This study also highlights several non-linear acoustic characteristics of the soil, including resonance frequency shift, high harmonic generation, energy transfer, and phase shift.