Nonlinear surface acoustic waves in cubic crystals
R. E. Kumon (National Institute of Standards and Technology, Mail Stop 853, Boulder, CO 80305-3328).
Both the linear and nonlinear properties of surface acoustic waves (SAWs) in crystals are significantly different from those in isotropic media. Selected numerical results are presented for the propagation of initially monofrequency, finite-amplitude SAWs in a variety of surface cuts and directions in several nonpiezoelectric, cubic crystals. The underlying model equations possess a nonlinearity matrix that characterizes the interactions between harmonics of the SAW. When this matrix is real-valued, simulations show that the velocity waveforms can develop compression shocks in some propagation directions and rarefaction shocks in others. When this matrix is complex-valued, simulations indicate that velocity waveforms may exhibit asymmetric distortion as well as oscillations near peaks and shocks. Measurements of pulsed waveforms in the (001) and (111) surface cuts of crystalline silicon obtained by collaborators at the University of Heidelberg are shown to be quantitatively reproduced by the calculated results.