Transversely Inhomogeneous Nonlinear Surface Ultrasonic Monopulses in Solid Film-Substrate System

Excitation of nonlinear acoustic monopulses, or baseband waves, is theoretically analyzed. The monopulses have a wide spectrum up till the gigahertz range ≤ 1 GHz. The propagation of waves is along the interface between a solid film and a solid substrate. A quadratic elastic nonlinearity in both contacting media of the system is taken into account. The nonlinear dynamics of waves depends essentially on the thickness of the film. The transverse inhomogeneity of the wave profile in the interface plane and the wave diffraction are taken into account, too. The baseband waves are not true solitons and manifest as single shock-like pulses in the case of an excitation from initial long rectangular pulses. The transverse inhomogeneity affects the dynamics of the shocks, and there is a possibility to focus the nonlinear monopulses.