Low- and high-frequency nonlinear acoustic phenomena in a magnesite

The results of experimental and theoretical studies of nonlinear acoustic phenomena (amplitude-dependent losses, resonant frequency shifts, damping of weak ultrasonic pulses and their carrier frequency phase delay under action of a powerful low-frequency pumping wave as well as amplitude-phase self-action of the finite-amplitude ultrasonic pulses) in a magnesite rod are presented. Analytical description of the observed phenomena was carried out within the frameworks of the phenomenological state equations that contain low-frequency hysteretic nonlinearity and both high-frequency dissipative and elastic nonlinearity. From comparison of experimental and analytical amplitude-frequency dependences of nonlinear phenomena, the values of magnesite acoustic nonlinearity parameters were determined. The frequency dependences have been discovered for hysteretic (in a range 3.6-17.2 kHz) as well as dissipative and elastic nonlinearity (in a range 50-370 kHz).