ASA 125th Meeting Ottawa 1993 May

2pPA9. Radiative transfer of ultrasound.

Joseph A. Turner

Richard L. Weaver

Dept. of Theor. and Appl. Mech., 104 S. Wright St., Univ. of Illinois, Urbana, IL 61801

Multiple scattering of ultrasound in an elastic medium containing discrete random scatterers is modeled using radiative transfer theory. The uncorrelated phases of the scattered field allow one to write an energy balance equation for the spatially incoherent intensity. This ultrasonic radiative transfer equation contains single-scattering and propagation parameters that are calculated using the elastic wave equation. Polarization effects are included through the introduction of an elastodynamic Stokes vector, which contains a longitudinal Stokes parameter and four shear Stokes parameters similar to the four Stokes parameters used in optical radiative transfer theory. The theory is applied to a statistically homogeneous, isotropic elastic half-space containing randomly distributed voids illuminated by a harmonic plane wave. Results on the angular dependence of backscattered intensity are presented. It is anticipated that this approach may be applicable to materials characterization through the study of the time, space, ultrasonic frequency, and angular dependence of multiply scattered ultrasound in elastic media with microstructure. [Work supported by NSF Grant No. MSS-91-14360.]