Measurement of Surface Acoustic Wave Velocity Anisotropy with a Scanning Laser Acoustic Microscope

Abstract

The measurement of the velocity and power flow angle of surface acoustic waves (SAWS) using a scanning laser acoustic microscope is described. Data obtained from a single scan by the microscope and from a single direction of insonification is Fourier transformed from the spatial domain into the spatial frequency domain. The incident cw surface waves scatter from the s ides of the sample into all possible wavevectors. Thus, the Fourier transform in the spatial frequency domain is the inverse velocity or slowness curve for surface waves propagaging on the material. From this curve, the phase velocity, group velocity, and power flow angle versus propagation direction can be obtained. Experimental results for YZ lithium niobate, ST quartz, and (111) silicon are in good agreement w i t h the o ret i ca 1 c a1 cu 1 at i on s.