Focusing of nonlinear surface ultrasonic monopulses in solid film-substrate system

Excitation of microwave, wide spectrum f ≤ 1 GHz, nonlinear solitary acoustic monopulses, propagating along the interface between a solid film and a solid substrate, is theoretically analyzed. A quadratic elastic nonlinearity in both contacting media of the system is taken into account in the case of baseband waves. The transverse inhomogeneity and diffraction in the interface plane are considered. The baseband waves are not true monopulse-like 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 monopulses.