An analog/hybrid computer solution of electromagnetic scattering problems

• Main Author: Coffey, Edgar L.
• Other Authors: Electrical Engineering
• Format: Others
• Language: en
• Published: Virginia Tech 2014
• Subjects: LD5655.V856 1976.C635
• Online Access: http://hdl.handle.net/10919/40344; http://scholar.lib.vt.edu/theses/available/etd-11152013-040555/

A study of several techniques that may be used to solve exterior electromagnetic scattering problems was made. Analytical methods, moment methods, subsectional methods, probabilistic methods, integral equation methods, and analog/hybrid computer methods were considered in the study to determine the best method to use in a general approach to scattering problems. It was shown that while all these methods were able to solve certain classes of problems, no single technique qualified as a general solution method. A new scattering technique, the Unimoment — Monte Carlo method, was developed from the strengths and weaknesses of the more traditional methods. It is a probabilistic technique used to solve a deterministic problem. The original scattering problem is decoupled into a simple exterior problem and an interior problem by enclosing the scatterer with either a circle or a sphere. The resulting interior problem is then solved for several different boundary values using Monte Carlo techniques, and the linear combination of these solutions which gives the best continuity across the boundary is chosen as the solution to the scattering problem along this boundary. The electromagnetic fields at any other point may then be calculated from a series expansion. This new method was implemented on a hybrid computer to take advantage of the continuous, parallel nature of the analog portion of the computer when taking Monte Carlo random walks and when detecting boundaries that terminate these walks. A description of the Unimoment — Monte Carlo computer system along with various factors influencing performance of the method is included. Several scattering problems were solved using this method, and all results were within one percent of the exact solutions. This inaccuracy was found to be caused by the analog computer elements, not the method itself. The scatterers studied included circular cylinders, elliptical cylinders, and an annulus, and both perfect conductors and perfect dielectrics were considered. Also, scattering from an irregular object was studied to show the versatility of the method. === Ph. D.