Jason V. Paul

Date of Award

3-21-2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Department of Electrical and Computer Engineering

First Advisor

Peter J. Collins, PhD.

Abstract

Previously, Transformational Optics (TO) has been used as a foundation for designing cylindrical cloaks. The TO method uses a coordinate transform to dictate an anisotropic material parameter gradient in a cylinder coating that guides waves around the cylinder to reduce the Radar Cross Section (RCS). The problem is that the material parameters required for the TO cloak are not physically realizable and thus must be approximated. This problem is compounded by the fact that any approximation deviates from the ideal design and will allow fields to penetrate the cloak layer and interact with the object to be cloaked. Since the TO method does not account for this interaction, approximating the ideal TO parameters is doomed to suboptimal results. However, through the use of a Green's function, an optimized isotropic cloaked cylinder can be designed in which all of the physics are accounted for. If the contribution due to the scatterer is 0, then the observer, regardless of position, will only observe the contribution due to the source and thus the object is cloaked from observation. The contribution due to the scatterer is then used as a cost functional with an optimization algorithm to find the optimal parameters of an isotropic cloaked cylinder. Although the material parameters in this design method can be fulfilled by any material, metamaterials are used to study their viability and assumptions in this application. This process culminates in the design, fabrication and measurements of a cloaked cylinder made of metamaterials that operate outside of their resonant bands. We show bistatic RCS reduction for nearly every angle along with monostatic RCS reduction for nearly every frequency in the range of 5GHz-15GHz. Most importantly, the experimental results validate the use of a Green's function based design approach and the implementation of metamaterials for normally incident energy.

AFIT Designator

AFIT-ENG-DS-13-M-04

DTIC Accession Number

ADA579497

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