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