Material Characterization by Line-Focus-Beam Acoustic Microscope

Abstmcf-A novel method of material characterization by means of the line-focus-beam acoustic microscope system with high measure-ment accuracy is described. The material characterization is carried out by measuring the propagation characteristics of leaky waves on the water-sample boundary; that is, the phase velocity and attenuation are determined through V ( z) curve measurements. A general measurement principle is developed to make experimental determination of the two acoustic quantities simultaneously from measured V ( z) curves. A spec-tral analysis method is introduced as a general means to analyze acous-tic properties from the V(z) curves. The system is constructed with spe-cial software for a signal-processing procedure developed on the basis of the measurement principle. Measurements using a variety of iso-tropic, as well as anisotropic materials where the velocities extend from 2000 to 11000 m/s, and some other typical samples of layered and mem-brane structures are reported. All the leaky wave modes, such as leaky surface acoustic wave (SAW), leaky pseudo-SAW, leaky surface-skim-ming compressional wave, leaky Lamb wave, and harmonic waves, which take part in the interference phenomena in V(z) curves, a r e investi-gated. The experimental results are in good agreement with the theo-retical results calculated by exact numerical analysis of propagation characteristics of relevant leaky waves. The measurement accuracy is estimated to be about k0.2 percent absolute in velocity measurements (less than 0.1 percent for relative measurements) and from a few per-cent to 20 percent in attenuation measurements. The material char-acterization method is applied to quantitative investigation of inhomo-geneity on wafers and structural analysis of polycrystalline materials. A I.