### 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
**

**
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*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
*

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*
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.