Date of Award
2019
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Electrical and Computer Engineering
Committee Chair
Robert Lindquist
Committee Member
Junpeng Guo
Committee Member
Maria Pour
Committee Member
Abdalla Elsamadicy
Committee Member
Mark Tillman
Subject(s)
Metamaterials., Liquid crystals., Terahertz technology., Anisotropy.
Abstract
This dissertation reports on my research efforts towards optimizing tunable terahertz (THz) metamaterial (MM) performance using spatially varying liquid crystals (LC). First, gold wire grid polarizers and Y shape metamaterial designs with liquid crystal layer have intensely investigated and found important applications particularly in radar and microwave technologies to provide anechoic test chambers, or vehicle stealth. A change in the orientation of the LC molecules can change electromagnetic wave transmission in THz region. It has been shown that metamaterials including liquid crystals have great potential for tunable materials. However, tunable LC platforms requires transparent electrodes for some applications like displays. Fabrication methods of transparent electrodes for THz frequencies is shown in this dissertation. Second, this dissertation introduces a metamaterial absorber (MMA) with polyimide as spacer layer. Then, absorption performances of different designs of electric split ring resonator (eSRR) metamaterials are analyzed as well as their dependence on the unit cell size, eSRR length, capacitor gap, eSRR width, and substrate thickness of the metamaterial absorber obtained. It is concluded that the absorption peaks shift as the MMA parameters are increased or decreased, in excellent agreement with the previous studies. Third, THz MM absorbers have gained considerable interest and recent progress has let to tremendous results such as invisibility cloaking, THz detectors, switches and filters. Adding new features such as dynamic modulation and absorption frequency tunability are studied in this work by taking advantage of nematic liquid crystal properties whose orientation can be magnetically or electrically controlled. It is found that the structure employed in this work has tunability up to 100 GHz which can be accepted as noticeable improvement regarding previous works. Fourth, employing a liquid crystal material as a cavity medium in a Fabry-Perot etalon has many benefits such as low voltage, low insertion loss, and increasing the tunability. In this project, the focus will be on eSRR metamaterial absorbers as a potential device for controlling THz beams. These structures have the ability to control electric and magnetic responses, by matching the impedance of the MMs to that of free space. Adding modulation to MM absorbers will broaden their contribution especially in the THz region which is still growing as opposed to other frequency regions. With the recent developments in the THz technology, THz absorbers will be needed to realize THz detectors, imagers, and sensors. The techniques used in this work can be widely applied to guide the design and optimization of the metamaterial absorbers and sensors. The focus of this dissertation is incorporating conventional and novel methods to create some of the initial examples of optically controlled MM THz absorbers using microfabrication tools and COMSOL Multiphysics simulations.
Recommended Citation
Gulduren, Muhammed Emin, "Optically modulated terahertz metamaterials using liquid crystals" (2019). Dissertations. 182.
https://louis.uah.edu/uah-dissertations/182