Date of Award

12-9-2009

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Department of Electrical and Computer Engineering

First Advisor

Peter J. Collins, PhD

Abstract

Transformation optics has shown the ability to cloak an object from incident electromagnetic radiation is possible. However, the material parameters are inhomogeneous, anisotropic, and, in some instances, singular at various locations. In order for a cloak to be practically realized, simplified parameter sets are required. However, the simplified parameters result in a degradation in the cloaking function. Constitutive parameters for simplified two-dimensional cylindrical cloaks have been developed with two material property constraints. It was initially believed satisfying these two constraints would result in the simplified cylindrical cloaks having the same wave equation as an ideal cloak. Because of this error, the simplified cloaks were not perfect. No analysis was done to determine all material parameter constraints to enable a perfect two-dimensional cylindrical cloak. This research developed a third constraint on the material parameters. It was shown as the material parameters better satisfy this new equation, a two-dimensional cylindrical cloak's hidden region is better shielded from incident radiation. Additionally, a novel way to derive simplified material parameters for two-dimensional cylindrical cloaks was developed. A Taylor series expansion dictated by the new constraint equation leads to simplified cloaks with significantly improved scattering width performances when compared to previous published results. During the course of this research, it was noted all cloak simulations are performed using finite element method (FEM) based numerical methods. A Green's function was used to accurately calculate scattering widths from a two-dimensional cylindrical cloak with a perfect electrically conducting inner shell. Significant time improvements were achieved using the Green's function compared to an FEM solution particularly as the computational domain size is increased. Finally, cloaks are physically realized using metamaterials. Design of metamaterials has typically been done empirically. Shifts in S-parameter measurements and the resulting extracted constitutive parameters are used to determine the impact to resonant regions due to various geometries. A new way to design and possibly optimize unit cell metamaterials was investigated using an eigendecomposition to identify the cell resonances. Different structures were shown to have different resonances, and control of the resonant locations can lead to optimum designs.

AFIT Designator

AFIT-DEE-ENG-09-13

DTIC Accession Number

ADA506707

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