Scattering and velocity dispersion of ultrasonic waves in polycrystals of orthorhombic symmetry

Abstract

The scattering coefficients and the velocity of propagation of longitudinal and transverse ultrasonic waves in polycrystals of orthorhombic and higher symmetry are computed by the method of renormalization of the equations of motion. The formulas thus obtained are compared with the known asymptotic expressions for long and short waves. A numerical computation carried out for aluminum shows that for qa ∼ 1 (q is the wave number;a is the correlation scale) the power index determining the frequency dependence of the scattering coefficient decreases monotonically from 4 to 2 for the transverse waves, while for the longitudinal waves this dependence is nonmonotonic, i.e., the power index decreases from 4 to 1, after which it increases again to 2. In the Rayleigh region (q l a < 1.) the scattering coefficient of the longitudinal waves increases with a power index smaller than 4.