Identifying the Experimental and Theoretical Effective Characteristics of Nonaligned Anisotropic Metamaterials
AIR FORCE INSTITUTE OF TECHNOLOGY WRIGHT-PATTERSON AFB OH GRADUATE SCHOOL OF ENGINEERING AND MANAGEMENT
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Previous research into anisotropic materials has assumed certain properties in order to make the underlying mathematics tractable. One of the assumptions is the alignment of the optical axes with the laboratory frame of reference, such as split-ring resonators lying at on the material plane. This assumption does not hold true for many metamaterials, such as tilted nanorods. Techniques such as ellipsometry are needed to analyze the effective characteristics of these highly anisotropic structures. In this research, tilted nanorods are analyzed using generalized ellipsometry to extract the indices of the optical axes. The underlying physics of ellipsometry is then used to create a new effective characterization technique called Permittivity and Permeability Tensor Extraction PPTE, which makes fewer assumptions about the underlying structure of the material and allows for the analysis of a much larger class of structures. PPTE is used to find the effective characteristics of several structures, such as a structure with anisotropy-inducing inclusions and the tilted nanorods. Finally, PPTE is used to begin to examine some of the underlying presumptions about how metamaterials operate, demonstrating that some of the classically used models for calculating permittivity tensors are approximations. The utility of these models in determining the permittivity tensor is studied for several different materials with different properties.