Design improvements of negative refractive index metamaterial and characterization of refractive index discontinuity in effective parameters retrieval algorithm

Thesis (Ph.D.)--University of Washington, 2021For the past 20 years, metamaterials have been investigated as a promising tool for sub-wavelength image rendition and cloaking device. Sometimes termed ``double negative" materials, they possess the peculiar characteristic of displaying, over a certain range of frequencies, both negative permeability and negative permittivity, a characteristic which has been demonstrated to lead to a negative refractive index. Research on metamaterials faces many challenges, from constraints of negative refraction to impractical frequency spectra, to consistenly highly lossy designs. In this thesis, we present an overview of the history of the research on metamaterials, from its conceptual imagination by Veselago to a detailed analyzis of the currently most common designs. We discuss in details the Nicolson-Ross-Weir (NRW) algorithm and the Chien and Hsieh effective boundary retrieval algorithms, all of which are extensively used in the field of metamaterial research as a way to determine the effective parameters of metamaterials. In addition, we present a novel design and demonstrate its superior characteristics, for various ranges of frequencies and scales, compared to mainstream metamaterial: lower loss, lower negative refractive index and larger span of frequencies during which negative refraction occurs. Finally, we present an additional challenge observed in the literature: reports of discontinuity in the refractive index. We analyze those reports and offer explanations for this phenomenon, as well as a numerical method to overcome this challenge