Effects of residual stress on linear and nonlinear surface
acoustic waves in thin film systems
R. E. Kumon (National Institute of Standards and Technology, Mail Stop 853, Boulder, CO 80305-3328).
Surface acoustic waves (SAWs), with most of their energy concentrated near the free surface of a material, are useful for probing the mechanical characteristics of thin film systems. One of the primary effects of a thin film on a SAW is to cause frequency dispersion, i.e., different frequency components to travel at different wave speeds. Furthermore, residual stresses cause changes in the effective density and elastic constants of the material and therefore also affect the wave speed. A theoretical model has been contructed to compute these changes on infinitesimal and finite-amplitude surface waves in systems with a single thin layer on a substrate. Numerical results are presented which show the dispersion curves of systems with films with zero and compressive stresses. In addition, the effects of stress on the waveform distortion of nonlinear SAWs are also computed.