Doctor of Philosophy, The Ohio State University, 2020, Physics

Light-matter interactions are key in providing fundamental information about materials. The terahertz (THz) frequency range is a critically important region of the electromagnetic spectrum where the electronic properties of many quantum materials have resonant responses. It has also long been difficult to access; a property which has been termed the THz gap. In recent decades though, new techniques and methods in THz spectroscopy have come a long way to filling in that gap with more efficient emitters and detectors. We describe here our contributions to the field of THz spectroscopy. We detail the development and construction of devices and development of techniques to explore new categories of materials and generally expand the capabilities of THz spectroscopy. We also demonstrate the efficacy of these techniques in novel and interesting material systems.

Committee: Rolando Valdés Aguilar (Advisor); Jay Gupta (Committee Member); Yuan-Ming Lu (Committee Member); Andrew Heckler (Committee Member) Subjects: Condensed Matter Physics; Optics; Physics

Doctor of Philosophy, The Ohio State University, 2017, Electrical and Computer Engineering

Electron-plasmonic devices are of strong interest for terahertz applications. In this work, we develop rigorous computational tools using finite difference time domain (FDTD) methods for accurate modeling of these devices. Existing full-wave-hydrodynamic models already combine Maxwell's and hydrodynamic electron-transport equation for multiphysical hybrid modeling. However, these multilevel methods are time-consuming as dense mesh is required for plasmonic modeling. Therefore, they are not suited for design and optimization. To address this issue, we propose new iterative ADI-FDTD-hydrodynamic hybrid coupled model. The new implementations provide time-efficient, yet accurate, modeling of these devices. It is demonstrated that for a typical simulation, up to 50% reduction in simulation-time is achieved with a nominal 3% error in calculations. Using the new tool-set, we investigate several devices that operate using the properties of 2D electron gas (2DEG). We provide one of the first multiphysical numerical analyses of these devices, giving accurate estimates of their terahertz performance. The developed tool allows simulation of arbitrary 2DEG based terahertz devices, providing useful and intuitive 2D field information. This has allowed understanding of the operation and radiation principles of these devices. Specifically, we examine the known plasma-wave instability in short-channel high electron mobility transistors (HEMTs) that leads to terahertz emissions at cryogenic temperatures. We also examine terahertz emitters that exploit resonant tunneling induced negative differential resistance (NDR) in HEMTs. Finally, using this tool we numerically demonstrate the existence of acoustic and optical-plasmonic modes within 2DEG bilayer systems in HEMTs. Methods for exciting and controlling these modes are also discussed enabling new physics among bilayer devices.

Committee: John Volakis (Advisor); Siddharth Rajan (Advisor); Kubilay Sertel (Committee Member); Teixeira Fernando (Committee Member); Niru Nahar (Committee Member); Karin Musier-Forsyth (Committee Member) Subjects: Electrical Engineering; Plasma Physics

Doctor of Philosophy, Miami University, 2012, Chemistry and Biochemistry

This dissertation contains six chapters demonstrating the use of Terahertz Time-Domain spectroscopy and imaging in a variety of applications, from the principle analysis of observed absorption features to the quantitation of threat agents. Chapter 1 focuses on the background of Terahertz, starting with its roots in Microwave and Infrared Spectroscopies and continuing on to modern time-domain techniques that dominate the field at present. Terahertz's interaction with different types of matter, various instrumentation setups, and several types of common time-domain measurements are also discussed. Chapter 2 discusses two separate studies attempting to further the understanding of collective mode absorption peaks observed in the THz spectral region. Absorption peaks found in the THz region of crystalline solids are typically described generically as collective modes or computationally analyzed with no supporting experimental data. These two studies demonstrate an experimental method that can be used concurrently with computational techniques to elucidate a more complete understanding of observed collective modes. Chapter 3 probes the feasibility of detecting a possible threat agent, dipicolinic acid, which is a major component in bacterial spores, such as Anthrax. It focuses on qualitative discovery and the ability to quantify its presence with Terahertz Spectroscopy and imaging. Chapter 4 presents a library of quality cryogenic and room temperature spectra for the 20 standard amino acids to be used as a reference for future research. In addition, trends observed by the groups of amino acids were assessed. Chapter 5 examines the spectral properties of a large biomolecule, heparin, in the terahertz spectral region. Several sample configurations are investigated, from heparin as-is to crystallized nitric acid digestion remnants. A novel trace metal analysis method of heparin utilizing Inductively Coupled Plasma Optical Emission Spectroscopy is also presented. Chapter 6 d (open full item for complete abstract)

Committee: Gilbert E. Pacey PhD (Advisor); Shouzhong Zou PhD (Committee Chair); Richard T. Taylor PhD (Advisor); C. Scott Hartley PhD (Committee Member); James R. Gord PhD (Committee Member) Subjects: Analytical Chemistry

Master of Science (MS), Wright State University, 2016, Physics

Terahertz radiation is invaluable for use in spectroscopy and imaging work due to its nondestructive nature. It has become a key focus for those wishing to develop sensors capable of detecting weapons and narcotics unobtrusively and at a distance as well as characterizing materials and identifying defects. An ultrafast pulsed (femtoseconds) laser incident on a superconducting ring has been predicted to cause the emission of terahertz (THz) radiation. It is theorized that the radiation is a result of the supercurrent being modulated by the breaking and recombining of Cooper pairs on the order of picoseconds, where the time scale determines the frequency of the emitted radiation. We propose to investigate the terahertz emission from Yttrium barium copper oxide (YBCO) superconducting ring arrays of various geometries. Specifically, we will investigate the dependence of the time dynamics of the terahertz radiation, the ultrafast femtosecond laser pump power dependence and time dynamics, the antenna geometry, and the efficiency of the system. The theoretical work completed thus far anticipates high power and bandwidth in the terahertz regime. Furthermore, a complete characterization of the emitted radiation will provide insight into the microscopic properties of the superconductor's supercarriers. To realize the experimental testing of the superconducting ring arrays, a time-domain terahertz emission spectroscopy system will be designed and tested with known terahertz source materials.

Committee: Jason Deibel Ph.D. (Advisor); Gregory Kozlowski Ph.D. (Committee Member); Jerry Clark Ph.D. (Committee Member) Subjects: Physics

Doctor of Philosophy (PhD), Wright State University, 2012, Engineering PhD

Terahertz radiation, a region in the electromagnetic spectrum which lies between the microwave and infrared, has gained considerable attention recently due to interesting properties exhibited by materials exposed to this radiation. Dielectric materials such as glass, paper, plastic, and ceramics that are usually opaque at optical frequencies are transparent to terahertz radiation. This led to interesting terahertz spectroscopy and imaging applications. Finite element method simulations of plain, tapered and periodically corrugated metal terahertz wire waveguides have been conducted at the end of the waveguides. This modeling was used to guide the choice of design parameters for the fabrication of waveguides with laser micromachining. The waveguides were characterized with a fiber-coupled terahertz time-domain spectroscopy and imaging system. The THz pulses emitted at the transmitter excite the surface plasmon polaritons in the metal waveguide and propagate as surface waves that are detected at the receiver. This work involved studying the propagation properties as well as the frequency dependent diffraction at the end of the wire waveguides. The temperature dependent propagation properties of the waveguides have also been studied. The THz waveguide properties propagating along the surface of the plain, corrugated and tapered wire waveguides have been successfully demonstrated using both simulations and experimental work.

Committee: Jason Deibel PhD (Advisor); Raghavan Srinivasan PhD (Committee Member); Sharmila Mukhopadhyay PhD (Committee Member); Douglas Petkie PhD (Committee Member); Peter Powers PhD (Committee Member) Subjects: Materials Science; Physics

Master of Science in Electrical Engineering (MSEE), Wright State University, 2024, Electrical Engineering

The uncertainty of the standard calibration procedure for radar cross-section (RCS) measurement is studied for different targets measured in the near-field from 550 to 700 GHz. Using common calibration spheres and squat cylinders mounted on a styrofoam pedestal at waterline (zero-degrees elevation), the calibration difference measure is determined for each target. Similarly, the difference metric is determined for square trihedral and tophat targets placed on a ground plane and measured at different elevation angles. The mean calibration measure is calculated using the dual calibration target method and repeated measurements in an anechoic chamber. The specific THz system is described and the results show how the near field scattering behaviors degrade the accuracy of the scattering measurement. Additional analysis shows the measurement uncertainty to be within a few decibels for frequencies within 580 to 650 GHz.

Committee: Michael A. Saville Ph.D., P.E. (Advisor); Josh Ash Ph.D. (Committee Member); Cheryl B. Schrader Ph.D. (Committee Member) Subjects: Electrical Engineering

Master of Science in Engineering, Youngstown State University, 2024, Department of Electrical and Computer Engineering

As part of this project, a complex terahertz (THz) antenna was fabricated using two-photon polymerization (2PP), a highly precise additive manufacturing method. The design and rigorous simulation testing were conducted using Ansys HFSS, with a focus on achieving minimal losses. Special emphasis was placed on impedance matching, confirmed by the S11 parameter showing minimal power reflection over a large part of the THz band. The antenna was fabricated using OrmoComp, a hybrid polymer. A significant portion of the thesis is dedicated to fine-tuning the intricate fabrication steps necessary for producing complex designs, demonstrating the capability to also fabricate simpler structures. The most significant outcomes of this work on the highly directional THz antenna are the optimized process parameters such as slicing direction, way of printing, power and speed settings of laser for 2PP and finally development time of post processing, which enabled the production of the complex structure. The fidelity of the final fabricated design was verified using electron and light microscopy.

Committee: Vamsi Borra PhD (Advisor); Frank X. Li PhD (Committee Member); Srikanth Itapu PhD (Committee Member); Pedro Cortes PhD (Committee Member) Subjects: Design; Electrical Engineering; Electromagnetics; Nanotechnology

Master of Science in Engineering, Youngstown State University, 2023, Department of Electrical and Computer Engineering

This thesis investigates a novel terahertz (THz) antenna for advanced THz communications and a performance analysis of a balun design fabricated using two additive manufacturing methods and a traditional method. It proposes a THz antenna with a peak gain of 0.38 dB at 0.125 THz, suitable for MIMO systems due to its multi-directional radiation and broad impedance bandwidth. The study also compares PCB with screen-printing and aerosol jet printing manufacturing techniques for balun production, highlighting the performance of the design when printed on flexible and rigid FR-4 substrates. Significant findings include the critical role of substrate material on the balun's RF performance, with different materials affecting bandwidth and efficiency. The research presented contributes to the THz field by offering insights into design and manufacturing impacts on high-frequency communication devices, supporting the development of more efficient THz communication technologies.

Committee: Vamsi Borra PhD (Advisor); Srikanth Itapu PhD (Committee Member); Frank Li PhD (Committee Member); Pedro Cortes PhD (Committee Member) Subjects: Electrical Engineering; Engineering; Materials Science; Nanotechnology

Master of Science in Electrical Engineering (MSEE), Wright State University, 2023, Electrical Engineering

Radar cross section (RCS) of electrically large targets can be challenging and expensive to measure. The use of scale models to predict the RCS of such large targets saves time and reduces facility requirements. This study investigates Ka-band (27 to 29 GHz) RCS prediction from scale model measurements at 500 to 750 GHz. Firstly, the coherent quasi-monostatic turntable RCS measurement system is demonstrated. Secondly, three aluminum 18:1 scale dihedrals with surface roughness up to 218 icroinches are measured to investigate how the roughness affects the Ka-band prediction. The measurements are compared to a parametric scattering model for the specular response, and indicate that the models' surface roughness have negligent effect on the RCS prediction.

Committee: Michael A. Saville Ph.D. (Advisor); Yan Zhuang Ph.D. (Committee Member); Elliott R. Brown Ph.D. (Committee Member) Subjects: Electrical Engineering; Electromagnetics; Engineering

Master of Science (MS), Wright State University, 2022, Physics

Terahertz (THz) frequency light has shown promise for a wide variety of applications due to its material characterization and imaging capabilities. Its nondestructive nature coupled with its submillimeter spatial resolution provides the most value for terahertz light as an imaging tool. The application of terahertz technology has been limited by a lack of novel and powerful sources. It has been shown that that Yttrium Barium Copper Oxide (YBCO), a type II superconductor, has certain properties that would allow YBCO to be an effective source for THz light. Recent microwave work has shown that when a persistent supercurrent is placed on a thin film YBCO ring and is discharged, the decelerating electrons could produce THZ electromagnetic radiation. An ultrafast femtosecond laser incident on such a YBCO ring would disrupt the superconducting mechanism of the material. A series of tests examining YBCO and its optoelectronic properties were conducted. These included ultrafast pump-probe measurements, inspection of the discharging and charging rates, and finally time-domain terahertz emission experiments. The pump-probe measurements revealed electron relaxation times in the picosecond range. While it was shown that the ultrafast laser was able to induce and discharge a super current in the thin film superconductor, it was dependent on laser fluence and had no detectable wavelength dependence. However, no THz radiation was detected with the time-domain measurement system.

Committee: Jason Deibel Ph.D. (Advisor); Brent Foy Ph.D. (Committee Member); Ivan Medvedev Ph.D. (Committee Member) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 2021, Physics

Time domain terahertz spectroscopy has allowed for a new way to analyze the properties of antiferromagnets. Since many materials have been explored using this technique, we took a different route for evaluating their properties. We evaluated how two different antiferromagnets (CaFe2O4 and TbMn2O5) interacted with metamaterials. CaFe2O4 was coupled to split ring resonators and TbMn2O5 was coupled to gammadion crosses. From the experiment performed on the CaFe2O4/split ring resonator sample, we did not find sufficient evidence indicating coupling between the sample and the metamaterial. For the TbMn2O5/gammadion sample, we observed an improvement in the efficiency of the electromagnon excitation compared to the bare sample. To understand why the expected anticrossing, an effect observed in coupled oscillator systems, was absent from either measurement, coupling effects between split ring resonators and a hypothetical antiferromagnet were analyzed more deeply utilizing numerical methods. From here we found that an anticrossing will occur when the spins in the crystal are parallel with the interface of the sample. This would allow for improved coupling between the magnetic moment of the split ring resonators and the antiferromagnet. From the data we were able to confirm the presence of an anticrossing. Following the metamaterial project, we began the development of an additional time domain terahertz technique, on chip terahertz, which allowed us to perform measurements on antiferromagnets that were not easily probed. This technique was applied to two different antiferromagnets, CaFe2O4 and MnPS3. For CaFe2O4, we observed a possible absorption in the spectrum that could be connected to on the magnon modes. For MnPS3, we detected three possible modes, one of which could be a low frequency magnon.

Committee: Rolando Valdes Aguilar (Advisor); Marc Bockrath (Committee Member); Ilya Gruzberg (Committee Member); Louis DiMauro (Committee Member) Subjects: Condensed Matter Physics; Physics

Master of Science (MS), Wright State University, 2020, Physics

A recently constructed novel analytical tabletop terahertz (THz) chemical sensor capable of detecting a wide range of gases with high sensitivity and specificity was characterized to assess its performance over a range of operational parameters. The sensor was designed with an objective of quantifying composition of exhaled human breath, where target concentrations span part per trillion (ppt) to part per billion (ppb) level of dilutions. The sensor utilizes terahertz rotational spectroscopy of sampled gases for quantification of dilutions. The sensor occupies a volume of ~ 2 ft3 and incorporates a coiled absorption cell, thermal desorption tubes, and all necessary electronic components necessary for autonomous operation. Coiled absorption cell minimizes the sensor footprint while maintaining a large path length for sensitive spectral measurements. Preconcentration aides the detection of compounds by removing the background gases which would negatively affect the absorption signal if present during spectral analysis. Spectral parameters of the sensor were studied to optimize its sensitivity. Efficiencies of preconcentration over a range of gas sampling parameters were determined by comparing concentrations measured by the sensor to concentrations of a reference gas mixture. The sensor was characterized in its ability to detect acetaldehyde, acetone, ethanol, isoprene, and methanol – all known breath analytes. These gases were chosen for their range of volatility and absorption strength. Minimum detectable sample concentrations are well suited for breath sampling making this sensor a valuable new tool for environmental sensing and biosensing.

Committee: Ivan Medvedev Ph.D. (Advisor); Brent Foy Ph.D. (Committee Member); Jason Deibel Ph.D. (Committee Member) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 2019, Electrical and Computer Engineering

Utility of wireless connectivity has been steadily increasing as broadband internet becomes widely available and having low-cost technology leads to more devices built with Wi-Fi capabilities and sensors. As the traditional radio-frequency (RF) bands (sub 3 GHz) become congested, the mmW band offering vast amount of spectrum, is poised to be the backbone of 5G wireless networks. Particularly, thanks to much smaller wavelengths, antenna-integrated transceivers are viable solutions for the future 5G wireless networks. However, key challenges still remain for on-chip implementation of efficient radiators at such high frequencies. Namely, poor antenna bandwidths, severely low radiation efficiencies, as well as laborious and expensive antenna-transceiver integration (wire bonds, flip-chip, ball grid arrays, etc.) limit the utility of truly-integrated on-chip antennas. To overcome these prevailing obstacles we present an ultra-wideband (UWB), low-profile, high efficiency, tightly-coupled array topology which is adopted from RF-frequency realizations and modified as a multilayered structure suitable for standard micro-fabrication process. Through this work, we show that on-chip radiation efficiency is well above 60% over the entire impedance bandwidth. The proposed array exhibits wideband performance, covering 35-75 GHz, achieving an unprecedented coverage that spans most of the bands allocated for mobile communications. Utilization of low-loss materials in such designs can address the substrate coupling issues and improve the radiation efficiency. Moreover, the structural support and packaging materials that exhibit low loss are indispensable for cost-effective realization of integrated high frequency systems. To effectively address these requirements, polymers are a natural, low-cost choice for structural support and packaging of microchips due to their favorable chemical, thermal, and mechanical properties. However, many polymers have not been studied for mmW and TH (open full item for complete abstract)

Committee: Kubilay Sertel (Advisor); Niru Nahar (Committee Member); Fernando Teixeira (Committee Member) Subjects: Electrical Engineering; Electromagnetics; Electromagnetism

Doctor of Philosophy, The Ohio State University, 2019, Physics

In crystalline materials, the symmetry of the crystal lattice imposes strict conditions on the observable properties of the material. These symmetry restricted conditions can be, in turn, probed by light via the electromagnetic interaction. Studying the electromagnetic excitations in solids can reveal many fundamental properties of these systems. A quick introduction and guide to symmetry in solids will be given, with an emphasis on how it can be used to interpret spectroscopic measurements. The measurement techniques used will also be described. Time domain Terahertz spectroscopy (TDTS) is the main technique used in this dissertation. Important experimental considerations pertaining to the construction of the THz spectrometer will be given. In the multiferroic Sr_2 FeSi_2O_7, we found multiple excitations in the few meV energy scale (THz), in the material's paramagnetic phase. Measurements with varying temperature and magnetic field revealed that these excitations are both electric and magnetic dipole active. By considering the ground state of the Fe 2+ magnetic ion in Sr 2 FeSi 2 O 7 , we concluded that our observation is coming from the spin-orbital coupled states of the ion. This realization demonstrated that spin-orbit coupling plays a crucial role in these exotic materials. Interestingly, these spin-orbital THz excitations persist into the magnetically ordered phase. The single-ion picture of the paramagnetic phase needs to be expanded theoretically to explain our observations. CaFe_2O_4 orders antiferromagnetically below ~ 200 K. Two co-existing magnetic structures (A and B phase) have been measured previously by neutron diffraction. The anti-phase boundaries between these two phases have been proposed to be the cause of the quantized magnetic excitations (magnons) measured by an inelastic neutron scattering study. We measured two antiferromagnetic resonances (magnons) with TDTS. Our observation can be explained by the orthorhombic crystal anisotropy of CaF (open full item for complete abstract)

Committee: Rolando Valdes Aguilar (Advisor); P. Chris Hammel (Committee Member); Nandini Trivedi (Committee Member); Douglass Schumacher (Committee Member) Subjects: Physics

Doctor of Philosophy (PhD), Wright State University, 2018, Interdisciplinary Applied Science and Mathematics PhD

The use of terahertz time-domain spectroscopy provides one of the most versatile and promising techniques for the robust determination of optical parameters, which is needed to enable identification of materials for quality control, materials science advancement, tamper prevention, drug enforcement, and hidden explosives detection. Previously, the state-of-the-art relied on legacy error measures for minimization of simulation error and the standard practice was to use a single unique measurement for each unknown material in a sample. Successful optical parameter extraction for uniformly varying optical property materials is correlated with low variation in extracted optical properties. This work advances the state-of-the-art in optimization-based physical parameter extraction using terahertz time-domain spectroscopy. This is achieved by standardizing the signal processing methodology, clearly defining the best optimization formulation to yield low simulation error and optical property variation, and leveraging multiple measurements to reduce the impact of system-dependent artifacts on extracted optical properties. A thorough analysis of alternative error measures across numerous objective function formulations demonstrates that a 28% reduction in the Fabry-Perot etalon effect in the optical property of materials is achievable, compared with legacy approaches. The research conclusively demonstrates that time-domain objective function formulations yields simulation error that is 83% less than frequency-domain objective function formulations. Furthermore, the research shows that multi-measurement optimizations reduce oscillations in optical properties caused by the Fabry-Perot etalon effect by as much as 92%, compared with single-measurement optimizations. The research validates the numerical solutions to less than 6% error compared with analytical solutions, for uniform and non-uniform optical property materials. Importantly, the research extends the state-of-the-art (open full item for complete abstract)

Committee: Jason Deibel Ph.D. (Advisor); Elliott Brown Ph.D. (Committee Member); Sara Pollock Ph.D. (Committee Member); Michael Saville Ph.D., P.E. (Committee Member) Subjects: Engineering; Mathematics; Physics

Master of Science in Electrical Engineering (MSEE), Wright State University, 2018, Electrical Engineering

A large area, square-gate Metal-Oxide/Insulator-Semiconductor (MOS or MIS) structured `Spatial Light Modulator' has been proposed for the Terahertz (THz) imaging at room temperature. This theoretical study has been done entirely by using the MATLAB platform. The 1D Poisson's equation has been solved iteratively by Euler's method with the exact Fermi-Dirac integral for n-doped Si-MOS and GaAs- MIS capacitors in deep accumulation mode. Free carrier density and the potential profile have been found for the degenerate case. The results have been compared with the analytical method, which is approximated by Boltzmann statistics, and clearly, show the difference between the degenerate case and non-degenerate Boltzmann approximation at higher bias. Then the sheet carrier density was calculated by performing the numerical integration over the depth of accumulation. The mobility was calculated for various scattering mechanisms at room temperature, and the total mobility was found by using Matthiessen's rule. The mobility and free carrier density were then used for calculating the bulk conductivity of the device. The sheet conductance and sheet resistance were found by the numerical integration of the bulk conductivity over the depth of accumulation. The sheet resistance is the DC resistance and was scaled to THz frequencies by using the Drude model. Then a lossless two-port transmission line model was adopted for studying the transmittances of the THz signal through the MOS or MIS devices for different bias and doping concentration and calculated the depth of modulation was calculated Vs frequency between 0.1 and 1 THz. In contrast to the GaAs-MIS device, it has been found that the depth of modulation of the Si-MOS device is much higher. The switching time has been calculated as the 10% to 90% charging time of the interface capacitor by solving the equivalent large-signal RC circuit. The GaAs-MIS displays lower switching time than Si-MOS because GaAs-MIS offers lower in (open full item for complete abstract)

Committee: Elliott R. Brown Ph.D. (Advisor); Michael A. Saville Ph.D., P.E. (Committee Member); Marian K. Kazimierczuk Ph.D. (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy, The Ohio State University, 2017, Physics

A time-domain terahertz spectrometer was built for the purposes of studying condensed matter systems.

Committee: Rolando Valdes Aguilar (Advisor); P. Chris Hammel (Committee Member); Christopher Hill (Committee Member); Mohit Randeria (Committee Member) Subjects: Physics

Master of Science (MS), Wright State University, 2017, Physics

Terahertz spectroscopy has found use as an analytical tool in determining chemical composition of exhaled human breath. This thesis demonstrates a novel application of this technology - analytical sensing of gaseous metabolic products of several types of human cell cultures. An innovative experimental system was developed for probing cellular metabolism using terahertz [THz] rotational spectroscopy. Gaseous emissions of cell cultures were analyzed and compared between several cell types. Cancerous and healthy lung cells as well as cancerous liver cells were studied. This technique carries a lot of promise as a noninvasive method of distinguishing between cell types and identifying cell pathologies. In this set of experiments, prominent variance in the rates of acetaldehyde metabolism was identified, which can potentially be used as a diagnostic method of cellular identification. Possible applications of this novel technique might extend to the medical field, where it will be used as a non-invasive detection and diagnostic tool.

Committee: Ivan Medvedev Ph.D. (Advisor); Jason Deibel Ph.D. (Committee Member); Jerry Clark Ph.D. (Committee Member) Subjects: Biology; Biomedical Engineering; Biomedical Research; Biophysics; Cellular Biology; Physics

Master of Science (M.S.), University of Dayton, 2017, Electro-Optics

Achieving high quality (Q)-factor resonant modes allows for drastic improvement of performance in many plasmonic structures. However, the excitation of high Q-factor resonances, especially multiple high q-factor resonances, has been a huge challenge in traditional metamaterials (MMs) due to ohmic and radiation losses. Here, we experimentally demonstrate simultaneous excitation of double Gaussian line shape resonances in a terahertz (THz) MM composed of an asymmetric 4-gap ring resonator. In a symmetric 4-gap ring resonator only the low Q-factor asymmetrically line shaped inductance-capacitive (LC) and dipole modes can be excited from an incident THz wave. By vertically displacing two adjacent arms a distance δ ≥ 40µm the fourfold symmetry of the planar MM breaks leading to two additional polarization dependent and frequency invariant higher Q-factor modes. The symmetry broken high Q-factor modes can be exploited for multi-band filters, slow light devices, and ultra-sensitive sensors. Therefore, we studied the performances of the symmetric and asymmetric MM devices as ultra-flexible biological sensors. An analyte of Bovine Serum Albumin (BSA) is applied to the surface of the MM causing each mode to uniquely red-shift linearly to the concentration of BSA. The results demonstrate the usefulness of a cost-effective THz planar MM-assisted biological sensor that could be used in food product quality, environmental monitoring, and global health care.

Committee: Jay Mathews (Advisor); Imad Agha (Committee Member); Andrew Sarangan (Committee Member); Thomas Searles (Committee Member) Subjects: Electrical Engineering; Optics; Physics

Master of Science (MS), Wright State University, 2017, Physics

In the phenomenon known as extraordinary optical transmission (EOT), a narrow band of selected frequencies are transmitted when incident on an array of subwavelength periodic apertures where the resonant frequency is determined by the geometry of the array of apertures and optical properties of the metal-dielectric interface. This takes place due to the excitation of surface plasmon polaritons (SPPs) at the metal and dielectric interface. Using the COMSOL Multiphysics software RF Module, a unit cell of a carbon nanotube (CNT) based EOT device is modeled in order to verify theoretical calculations of the resonant frequency using S-parameter calculations. The simulation of the interaction of the THz light with the CNT EOT device exhibits a resonant transmission at 235 GHz. Further, the transmission falls exponentially with increasing device thickness of the device, and the transmission peak reaches its maximum value at the skin depth. Although some of the transmission features, such as Wood's anomalies, are seen in the modeled device only, the other numerical results show good agreement with the experimental observations reported in literature. The fabricated single-walled carbon nanotube devices with 100 nm thickness do not indicate any resonances; however any such resonances might be weak due to the thin nature of the samples.

Committee: Jason Deibel Ph.D. (Committee Chair); Brent Foy Ph.D. (Committee Member); Jerry Clark Ph.D. (Committee Member) Subjects: Physics