Measurement of longitudinal wave properties of low velocity materials using the acoustic microscope

In order to measure lateral wave properties for materials having low acoustic velocities, such as polymers, a ray analysis of the excitation, propagation, and subsequent detection of the longitudinal lateral waves was performed. Measurements of the output voltage V with defocus distance z were made using a 50-MHz microscope for several polymeric materials. Ordinary processing of V (z) was used to extract the longitudinal wave velocity for these materials. A least-squares fit of the theoretical to the measured V(z), over the range of validity of the lateral wave expression, was used to find the longitudinal wave attenuation constant