J Acoust Soc Am. 2006 Jan;119(1):31-2. doi: 10.1121/1.2139071.
The Journal of the Acoustical Society of America
G A Kriegsmann
PMID: 16454259 DOI: 10.1121/1.2139071
The optical theorem is proven for impenetrable targets without using the method of stationary phase. The proof depends upon the divergence theorem, the Helmholtz representation of the scattered field, and the law of cosines.