Determination of ultrasonic attenuation in surface layer of materials by spectroscopy method with ultrasonic reflectivity measurement

It is well known that the attenuation of surface acoustic waves is a useful parameter to estimate the grain size, porosity and microstructure which are closely related to electrical and mechanical troperties of materials. In the present paper, a novel method for determination of ultrasonic attenuations in the surface layer of materials through an ultrasonic spectroscopic technique is proposed. The method is based on an absolute measurement of the reflection coefficient of the materials and its spectral behavior analysis. The attenuations are determined by detecting the frequency of least reflection and by estimating a locus of zero points of the reflection coefficients in the complex plane. An experiment with annealed carbon steel was demonstrated. The amplitude of the reflection coefficient calculated with the attenuations estimated by the present method indicated the frequency dependence similar to the experimental result. This reveals that the estimated attenuations are reasonable to evaluate the actual acoustic response of materials.