Electromagnetic scattering simulations using equivalent boundary condition models
Whites, Keith Wayne
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Permalink
https://hdl.handle.net/2142/19197
Description
Title
Electromagnetic scattering simulations using equivalent boundary condition models
Author(s)
Whites, Keith Wayne
Issue Date
1991
Doctoral Committee Chair(s)
Mittra, Raj
Department of Study
Electrical and Computer Engineering
Discipline
Electrical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Electronics and Electrical
Language
eng
Abstract
Equivalent boundary condition models are one approach to simplifying electromagnetic (EM) scattering problems while retaining a high degree of solution accuracy in the domain of interest. These models are successful when the dominant EM characteristics of the scattering body are captured within the model, and they are robust when the parameters in the model are capable of adjustment, in a systematic manner, to accurately simulate the scattering for physical variations in the target. Both of these properties are successfully integrated in this work to model two important classes of scatterers used in the modern low observable vehicle: dielectrically filled cavity-backed apertures and periodic structures at lower frequencies.
The reasons for using these simulation models fall into two general categories. The first is the large reduction in the computational expense as compared to more exact numerical approaches. The second is the potential for expanding the size of the target which can be analyzed beyond the capabilities of more exact solution methodologies.
For the first class of structure, filled cavity-backed apertures, the Impedance Boundary Condition (IBC) is used for high-contrast dielectrics in 2-D troughs and 3-D cavities embedded in an infinite impedance plane. In a thorough study, the solutions obtained using this simulation model are compared to more exact numerical approaches to precisely define when such a model is a valid approximation. In addition to the great computational savings, this model also lends insight into methods for significant reductions in the backscattering for plane wave illumination near grazing angles of incidence.
Models for the second class of structure, periodic geometries at lower frequencies (meaning only the lowest-ordered Floquet harmonic lies in the visible region), are divided into simulations for arrays of planar and nonplanar elements. For planar elemental arrays, a Tensor Resistive Boundary Condition (TRBC) simulation is developed for structures possessing at least a two-fold rotational symmetry in the plane of periodicity. Examples of this include strip gratings, and 2-D periodic arrays of patches, crosses and slots. The nonplanar elemental arrays (possessing the same rotational symmetry) are simulated using a Tensor Impedance Boundary Condition (TIBC) model and a Resistive/Modified Conductive (RMC) sheet approximation for thin periodic arrays. As with the cavity geometry, techniques are discussed for achieving meaningful reductions in the backscattering for finite periodic arrays of planar elements when illuminated by plane waves incident near grazing.
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