ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

4pPAb6. Concerning the extinction cross section of an arbitrary body in Stokesian fluid flow.

Scott A. Wymer

Dept. Eng. Sci. and Mech., Penn State Univ., 227 Hammond Bldg., University Park, PA 16802-1401

Akhlesh Lakhtakia

Renata S. Engel

Penn State Univ., University Park, PA 16802-1401

Time-dependent Stokesian fluid flow around an arbitrary body can be analyzed in terms of time-harmonic phasors. Analytical techniques commonly used for frequency-domain scattering can therefore be brought to use. The scattering response of a body is often quantitated by the extinction cross section. However, the wave number for Stokesian flows is necessarily complex, so the usual interpretation of the extinction cross section is untenable in the present instance. We show, however, that a detector-based interpretation of the extinction cross section is unambiguous and experimentally relevant. An almost exact formula is derived for the extinction coefficient for the far-field, forward scattering case. Computed values of extinction cross sections are presented for spheres and spheroids.