Date of Award
Doctor of Philosophy (PhD)
Dentcho A. Genov
Metamaterials (MMs) are nanocomposite materials consisting of metal-dielectric resonators much smaller in size than the wavelength of the incident light. Common examples of metamaterials are based on split ring resonators (SRRs), parallel wires or strips and fishnet structures. These types of materials are designed and fabricated in order to provide unique optical responses to the incident electromagnetic radiation that are not available in naturally existing materials. The MMs can exhibit unusual properties such as strong magnetism at terahertz (THz) and optical frequencies. Additionally, negative index materials (NIMs) can provide negative index of refraction which can be used in many applications including invisibility cloaking devices and superlenses capable of overcoming the diffraction limit of light. Furthermore, NIMs manifest reversal of optical laws such as Snell’s law, the Doppler effect and Cerenkov radiation.
This dissertation demonstrates comprehensive analytical and theoretical studies of the magnetic and electric susceptibilities of prospective two dimensional MMs including metallic parallel strips and bowtie resonators. Accurate analytical theories are developed to describe the diamagnetic response of a pair of metallic nanostrips separated by a dielectric material using the transmission line theory, and of metallic bowtie MMs through a high frequency LZ circuit model. These theoretical models were compared to exact numerical simulations based on the finite difference frequency domain (FDFD) Comsol Multiphysics software. The magnetic response for both systems was extracted numerically iv by applying the polarization current approach and found to be in excellent agreement with the analytical theory. Our results show that strong optical magnetism can be realized by reducing the size of the resonators; however, the scaling breaks down at high frequencies where a clear saturation in the magnetic resonance frequency is manifested in both systems under investigation. Moreover, the proposed NIMs designs are shown to exhibit negative index of refraction in the case of metallic and semiconductor based strips resonators. A record high figure of merit (FOM) of -0.9 has been demonstrated for double negative index material (demonstrating simultaneously negative permittivity and permeability). The local electromagnetic response of the NIMs was extracted using two competing approaches, namely the field averaging and inverse methods. These methods have shown consistent results, specifically with respect to the predicted magnetic susceptibility, and thus have testified that the proposed magnetic resonance designs can lead to prospective high fidelity NIMs that should be implemented in practice.
As a separate effort related to this thesis, a ceramic material (i.e. yttria stabilized zirconia (YSZ)) was used to fabricate a NOx sensor. Since diesel engines emits more particulates and NOx exhaust gases compared to gasoline engine, a NOx sensor is required to monitor emission in diesels vehicle. The proposed NOx sensor consists of a porous electrolyte and dense electrode. The porosity of YSZ is studied with direct Archimedes measurements and through scanning electron microscopy (SEM) of the YSZ at different firing temperatures. The electrochemical performance of NOx sensor was finally examined and verified by using impedance spectroscopy (IS).
Alsaleh, Mona Hassan, "" (2018). Dissertation. 4.
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