Nonlinear surface acoustic waves and applications

Harvey, Alan Paul (1990) Nonlinear surface acoustic waves and applications. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

The recent interest in the nonlinear propagation of surface acoustic waves has been generated by developments in acoustic wave signal processing devices. This thesis extends the multiple scales analyses of Kalyanasundaram (Int. J. Engng. Sci. 19, p.279) and Lardner (Int. J. Engng. Sci. 21, p.1331) to consider the effects of anisotropy upon the propagation characteristics of surface acoustic waves. Evolution equations are derived for the harmonic amplitudes which are then solved for cubically anisotropic materials. The constitutive and field equations governing the deformation of a piezoelectric substrate are then derived and the analysis of anisotropic elasticity is extended to consider the propagation of surface waves on a general piezoelectric substrate. Harmonic growth and decay on the commonly used material substrate, lithium niobate, are presented and display transfer of energy between the fundamental frequency and the nonlinearly generated harmonic frequencies. The two cases of oppositely propagating and co-directional waves are considered in the particular configurations of acoustic devices. Numerical routines are used to calculate the efficiency of the degenerate acoustic convolver and harmonic generation assessed in such devices. The interaction of harmonic frequencies of co-directional waves, known as intermodulation distortion, is explored and evolution equations derived and solved for such frequencies.

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