Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636230
Title: Finite and infinite elements applied to normal and oblique scattering from 2-D inhomogeneous structures in the resonance region
Author: Charles, A.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 1998
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Abstract:
A problem inherent when using the finite element method to model an open bounded solution domain, such as required for electromagnetic scattering, is the termination of the finite element mesh. The terminating boundary must be constructed so that any scattered waves incident on it, are absorbed, thus eliminating any spurious reflections. A significant amount of work has been carried out in this field to ascertain the most efficient absorbing boundary condition; this work has been extended within this thesis to include the development of a new general order wave envelope infinite element. The implementation of these new general order infinite elements allowed the mesh boundary to be terminated closer to the scattering body, when compared with previously presented infinite elements, thus reducing the size of the solution domain. Results have been shown to compare these new general order infinite elements with the Bayliss Turkel ABC, they were however found to be, at best, comparable to this absorbing boundary condition. In addition to the problem of normally incident plane wave excitation, the problem of obliquely incidence excitation has been investigated. The new general order infinite elements have been formulated for this oblique incidence problem and they were again shown to give considerable improvement over previously presented infinite elements. The reduction of electromagnetic backscatter has important implications in the field of radar, to this end a number of radar absorbing materials have been developed. This text concentrates on the Jaumann absorber as a method of radar absorption. It is necessary to model these radar absorbers, either analytically or numerically, to this end a new edge element has been developed which allows the more efficient modelling of infinitely thin reactive sheets, to be used in the construction of a Jaumann absorber. Both the numerical and the analytical modelling of Jaumann absorbers were investigated and the analytical results were used in a formal sensitivity analysis. This analysis was carried out via the Taguchi method of parameter design, which constituted an investigation into the stability of both planar and cylindrical Jaumann absorbers. It was found that the absorbers were insensitive to changes in the spacer thickness' and sheet resistance and to their radius of curvature. In addition, the sheet resistances were found to be entirely independent of each other for the planar absorber and could therefore be individually optimised.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.636230  DOI: Not available
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