High-Precision Measurement of Surface Acoustic Wave Velocity by SAM.

Abstract

An attempt has been made to measure precisely the leaky surface wave velocity, VR, within a very localized region using a scanning acoustic microscope (SAM). To achieve the relative precision of VR, e.g., 10-4, required for acoustoelastic stress measurement, two major modification of the conventional SAM were made. The defocus distance was measured with a high-resolution displacement sensor. For each measurement, the distance as well as the output of V(z) were averaged many times. The very low as well as very high frequency components in V(z) curves were eliminated by the digital filtering technique, and temperature of water was controlled within 0.02 K. Thus the relative standard deviation of VR of less than 10-4 was achieved for fused silica.