Evaluation of Scattering Loss in Polycrystalline Materials by Line-Focus-Beam Acoustic Microscope

Abstract

An application of the line-focus-beam acoustic microscope system is investigated to the structural and quantitative analysis of polycrystalline materials. This is made by measuring frequency dependence of propagation attenuation of leaky SAWs which are excited on the boundary between a coupling liquid of water and sample to be examined. A sample of Mn-Zn ferrite with average grain size of 8 um is employed for the investigation at a frequency range from 50 to 300 MHz. A measured propagation attenuation shows remarkable frequency dependence. The scattering loss for leaky SAWs is estimated from the measured propagation attenuation based on theoretical analysis of the propagation characteristics, taking the scattering effect at the grain boundary into consideration. Further, the relation of scattering loss between bulk wave and leaky SAW properties of materials is discussed by measurements of propagation attenuation of longitudinal waves for the same sample. By the experiments, the scattering loss for shear waves is measured to be about seven times as large as that of longitudinal waves. This result reveals that the scattering characteristics of leaky SAWs are dominated by the scattering loss of shear wave components.