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

## 2aSA13. Enhanced backscatter in finite reverberant systems.

**Richard L. Weaver
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*Dept. of Theor. and Appl. Mech., Univ. of Illinois, 104 South Wright St.,
Urbana, IL 61801
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Enhanced backscatter, in which reverberant signal levels at the position
of a transient source are greater than mean reverberant signal levels
elsewhere, is studied analytically and numerically. Popular weak localization
arguments, in which descriptions of responses in terms of incoherent rays are
modified to include some effects of coherent interference, indicate that the
mean-square response at the source should be twice as large as it is at other
points. A modal analysis, however, shows that the actual ratio should be three.
A more detailed theory shows that the enhanced return factor is 2 at moderate
times, but 3 at late times comparable to the modal density. The theory
indicates that the factor of 2 is achieved only if the eigenfrequency
statistics have the spectral rigidity predicted by random matrix theory. Thus a
connection between spectral rigidity and weak localization is hinted at.
Numerical solutions in model undamped two-dimensional reverberation rooms are
found to agree with the theory. The effect of damping on these results is also
investigated.