IMA Journal of Applied Mathematics Advance Access originally published online on September 20, 2006
IMA Journal of Applied Mathematics 2006 71(6):898-923; doi:10.1093/imamat/hxl019
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Scattering by a perfect conductor in a waveguide: energy-preserving schemes for integral equations
1 Mathematical Sciences Department, Worcester Polytechnic Institute, 100 Institute Road, Worcester, MA 01609, USA, 2 Department of Mathematical Sciences, Center for Applied Mathematics and Statistics, New Jersey Institute of Technology, University Heights, Newark, NJ 07102, USA
** Email: darkovolkov{at}yahoo.ca, darko{at}wpi.edu
| Abstract |
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The scattering matrix for a perfectly conducting electrical cylinder (or a sound hard obstacle) in a waveguide is unitary. This is a well-known result which is a consequence of the conservation of power. When a numerical method is employed to approximate the reflection and transmission coefficients of the cylinder, an approximate scattering matrix can be constructed. An integral equation of the second kind for an unknown density can be solved, and the density can then be used for computing the entries of the approximate scattering matrix. We show that this approximate matrix is unitary for cylinders of symmetric cross-section, regardless of the order of the approximation. In the nonsymmetric case, the approximate scattering matrix still satisfies a conservation of energy condition, albeit in an unfamiliar form. As the order of the approximation is increased, conservation of energy is also satisfied in the more familiar form to machine accuracy.
Keywords: guided waves; scattering matrix; integral equations; continuous and discrete preservation of energy.
Received on 16 September 2005. accepted on 16 August 2006.