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Articles 61 - 90 of 167
Full-Text Articles in Electromagnetics and Photonics
Development Of An Anatomically And Electrically Conductive Brain Phantom For Transcranial Magnetic Stimulation, Hamzah A. Magsood
Development Of An Anatomically And Electrically Conductive Brain Phantom For Transcranial Magnetic Stimulation, Hamzah A. Magsood
Theses and Dissertations
Transcranial Magnetic Stimulation (TMS) is a non-invasive technique for diagnostics, prognostic, and treatments of various neurological diseases. However, the lack of anatomically realistic brain phantoms has made the experimental verification of stimulation strength in the form of induced electric fields/voltages in the brain tissues an impediment to developing new TMS coils, stimulators, and treatment protocols. There are significant technological, safety, and ethical limitations to test the potential TMS treatment procedures or develop enhancements and refine them on humans or animals. This work aims to bridge the gap by introducing and developing an innovative manufacturing and fabrications process to produce a …
Optical Spectroscopy And Theoretical Modelling Of Carrier Dynamics In Group-Iv Alloy Quantum Dots, Rahnuma Rahman
Optical Spectroscopy And Theoretical Modelling Of Carrier Dynamics In Group-Iv Alloy Quantum Dots, Rahnuma Rahman
Theses and Dissertations
In recent years, Ge1−xSnx alloy quantum dots (QDs) have attracted significant interest due to their potential applications in photodetectors and light emitting devices in visible to mid IR spectral range and compatibility with silicon based platforms. While bulk Ge is an indirect bandgap semiconductor (0.66 eV), direct transitions can be made possible by incorporation of α-Sn at concentrations of ~10%, which however lowers the bandgap. Utilizing quantum confinement by reducing the size to below the Bohr radius also promotes direct transitions and more importantly increases the fundamental transition energies in GeSn alloy QDs, making them suitable for …
The Challenges Of Low-Energy Secondary Electron Emission Measurement, Matthew J. Vincie
The Challenges Of Low-Energy Secondary Electron Emission Measurement, Matthew J. Vincie
Theses and Dissertations
The phenomena known as secondary electron emission was discovered over a century ago. Yet it remains very difficult to model accurately due to the limited availability of reliable experimental data. With the growing use of computer simulations in hardware development, the need for accurate models has increased. This research focused on determining what factors may be causing measurement discrepancies and methods for increasing the accuracy of measurements. It was found that several assumptions are commonly invoked when these measurements are performed that may not always be consistent with reality. The violation of these assumptions leads to measurement bias that is …
Nondestructive Electromagnetic Characterization Of Perfect-Electric-Conductor-Backed Uniaxial Materials, Adam L. Brooks
Nondestructive Electromagnetic Characterization Of Perfect-Electric-Conductor-Backed Uniaxial Materials, Adam L. Brooks
Theses and Dissertations
As the use of anisotropic materials in electromagnetic applications continues to proliferate, it becomes increasingly important to develop non-destructive evaluation methods for those materials in their installed configuration. In many applications, these materials are permanently affixed onto conducting bodies to reduce unwanted reflections, making it impossible to collect S21 or S12 transmission measurements as used in many techniques based on the well-known Nicolson-Ross-Weir algorithm. It also makes it impractical to reorient the sample to collect orthogonal measurements aligned with the optical axes of the anisotropic material. The goal of this research is to develop a two-reflection coefficient measurement …
Targeted Germanium Ion Irradiation Of Aluminum Gallium Nitride/Gallium Nitride High Electron Mobility Transistors, Melanie E. Mace
Targeted Germanium Ion Irradiation Of Aluminum Gallium Nitride/Gallium Nitride High Electron Mobility Transistors, Melanie E. Mace
Theses and Dissertations
Microscale beams of germanium ions were used to target different locations of aluminum galliumnitride/gallium nitride (AlGaN/GaN) high electron mobility transistors (HEMTs) to determine location dependent radiation effects. 1.7 MeV Ge ions were targeted at the gap between the gate and the drain to observe displacement damage effects while 47 MeV Ge ions were targeted at the gate to observe ionization damage effects. Electrical data was taken pre, during, and post irradiation. To separate transient from permanent degradation, the devices were characterized after a room temperature anneal for at least 30 days. Optical images were also analyzed pre and post irradiation. …
Designing Liquid Crystal For Optoacoustic Detection, Michael T. Dela Cruz
Designing Liquid Crystal For Optoacoustic Detection, Michael T. Dela Cruz
Theses and Dissertations
This research impacts the development of a cost-saving, on-chip device that can replace a wide range of costly, bulky sensors for commercial and defense applications. In particular, the goals of this work were to design and test a sensor that uses the optical properties of liquid crystal (LC) to detect acoustic waves. This began with developing a method to fine-tune the optical features of the liquid crystal. Statistical analysis of select experimental variables, or factors, lead to ideal settings of those variables when creating the sensor. A two-factor and three-factor experiment were separately conducted and analyzed as a preliminary demonstration …
Electromagnetic Characterization Of Conductor-Backed Media Using Stepped Rectangular Waveguide, Avian Y. Hughes
Electromagnetic Characterization Of Conductor-Backed Media Using Stepped Rectangular Waveguide, Avian Y. Hughes
Theses and Dissertations
A new single stepped-iris waveguide technique is used to nondestructively determine the permittivity and permeability of conductor-backed media. This thesis will demonstrate a proof-of-concept that obtains two independent reflection measurements with a magnetic radar absorbing material (magRAM). Using a two measurement procedure, in which, the first measurement will apply a single rectangular waveguide to a known conductor-backed absorbing material under test (MUT) and the second measurement will insert a stepped-iris in between the single rectangular waveguide and MUT reducing the aperture to retrieve two independent electromagnetic properties (i.e. permittivity and permeability). The theoretical reflection coefficients are obtained using a rigorous …
Displacement Damage Effects In Gesn Light Emitting Diodes, Kevin K. Choe
Displacement Damage Effects In Gesn Light Emitting Diodes, Kevin K. Choe
Theses and Dissertations
Potential future use on Earth-orbiting satellites calls for investigation into the suitability of GeSn based photonic devices in high energy proton environments. The electroluminescence (EL) intensity of Ge1-xSnx (x = 0, 0.02, 0.069, and 0.094) light emitting diodes was measured before and after irradiation by 2 MeV protons at relatively high fluence levels. The results showed that GeSn devices with higher Sn content were up to 10 times more resistant against proton displacement damage than the pure Ge (x = 0) devices. As Sn concentration increased, the band gap decreased, and V-P hole trap energy level moved further from the …
Ballistic Evaluation Of Carbon Nanotube Sheet Material In Multifunctional Applications, Casey M. Keilbarth
Ballistic Evaluation Of Carbon Nanotube Sheet Material In Multifunctional Applications, Casey M. Keilbarth
Theses and Dissertations
Significant development of carbon nanotubes has occurred since they were first studied in the 1990's. Attempts to capture the phenomenal molecular properties in practical applications are gaining ground as new methods of producing CNTs have been developed. This thesis sought to determine if the addition of commercially produced CNT sheets to thin carbon fiber panels improved the ballistic properties of the panel. The difference between 0 and 4 CNT sheets was studied. The hypothesis was that inte- grating CNT sheets into the laminate would increase the projectile energy absorbed by the panel and reduce the damage to the panel incurred …
A Focal Plane Array And Electronics Model For Cmos And Ccd Sensors In The Afit Sensor And Scene Emulation Tool (Asset), Fernando D. Fernandez
A Focal Plane Array And Electronics Model For Cmos And Ccd Sensors In The Afit Sensor And Scene Emulation Tool (Asset), Fernando D. Fernandez
Theses and Dissertations
Electro-optical and infrared (EO/IR) sensor models are useful tools that can facilitate understanding a system's behavior without expensive and time-consuming testing of an actual system. EO/IR models are especially important to the military industry where truth data is required but is sometimes impractical to obtain through experimentation due to expense or difficulties in procuring hardware. This work describes implementation of a focal plane array (FPA) model of charge-coupled device (CCD) and complementary metal-oxide semiconductor (CMOS) photodetectors as a component in the Air Force Institute of Technology (AFIT) Sensor and Scene Emulation Tool (ASSET). The FPA model covers conversion of photo-generated …
Optical And Electron Paramagnetic Resonance Characterization Of Point Defects In Semiconductors, Elizabeth M. Scherrer
Optical And Electron Paramagnetic Resonance Characterization Of Point Defects In Semiconductors, Elizabeth M. Scherrer
Theses and Dissertations
Point defects in two semiconductor materials, both with promising optical properties, are investigated. The first material, CdSiP2, is a nonlinear optical material in which absorption bands due to point defects can hinder performance when used in frequency conversion applications in the infrared. The second material, Sn2P2S6, is a photorefractive material where point defects with specific properties are needed to optimize response in dynamic holography applications. Electron paramagnetic resonance (EPR) spectroscopy is used to identify the electronic structure of defects and their charge states. Correlations between EPR spectra and optical absorption allow assignments …
Optically Transparent Antennas And Filters For Smart City Communication, Ryan B. Green
Optically Transparent Antennas And Filters For Smart City Communication, Ryan B. Green
Theses and Dissertations
Incremental usage of mobile devices demand a new generation of wireless networks (5G) to provide faster data rates, more reliable coverage, monitor city infrastructure usage, and increase network capacity. The frequencies proposed for the upcoming 5G network would result in shorter broadcast distances and network dead zones, countered by incorporating transparent antennas into glass high rises. Transparent antennas possess, however a major challenge: low gain. This lower gain can be countered by means of employing antennas in an antenna array, boosting the gain and even giving the array the ability to beam form for the upcoming 5G network. The 5G …
Design Synthesis Of Flexible Antennas Using Artificial Neural Network, Ali Isam Hammoodi
Design Synthesis Of Flexible Antennas Using Artificial Neural Network, Ali Isam Hammoodi
Theses and Dissertations
Nowadays, flexible devices have witnessed a great deal of interest in both industrial and academia. Consistently, flexible electronic systems require the integration of a conformal and flexible antenna operating in specific frequency bands to provide wireless connectivity which is highly demanded in today’s information-oriented society. Designing of microstrip antenna has become the focus of modern technologies due to their light weight, ease of fabrication, and ability to integrate electronics devices. Simple structure such has square patch, circular patch, or rectangular patch are easy to maintain using empirical equations which based on some experimental results. However, more complicated structures are hard …
Dual Source Excitation Rectangular Waveguide Design And Evaluation For The Measurement Of Electromagnetic Material Properties, Daniel K. Koch
Dual Source Excitation Rectangular Waveguide Design And Evaluation For The Measurement Of Electromagnetic Material Properties, Daniel K. Koch
Theses and Dissertations
Broadband material parameter measurements are essential in understanding how materials interact with electromagnetic waves. Traditional rectangular waveguide material measurement systems are bandwidth limited. This results in multiple rectangular waveguides of different sizes used to conduct broadband material parameter extraction. Efforts to produce a broadband rectangular waveguide have focused on the inclusion of different guiding structures in the waveguide body. These designs have the drawback of requiring precise machining and time-consuming sample preparation. This research proposes a new broadband rectangular waveguide design which uses a dual source excitation design. This is enabled by the fact that rectangular waveguides are linear time …
Navigation Using Vector And Tensor Measurements Of The Earth's Magnetic Anomaly Field, Lauren A. Mount
Navigation Using Vector And Tensor Measurements Of The Earth's Magnetic Anomaly Field, Lauren A. Mount
Theses and Dissertations
This research explores the viability of using a navigation system that relies on measurements of the magnetic anomaly field as an alternative to GPS navigation. Previous research has been conducted on developing a navigation system using the intensity of the Earth's magnetic anomaly field as an alternative signal. This research focuses on using vector and tensor measurements, as opposed to scalar measurements of the anomaly field, as a means of obtaining accurate position and orientation solutions. This paper presents two navigation systems. The first uses an Extended Kalman Filter (EKF) with vector measurements of the magnetic anomaly field to aid …
Techniques For Low-Latency In Software-Defined Radio-Based Networks, Daniel D. Hart
Techniques For Low-Latency In Software-Defined Radio-Based Networks, Daniel D. Hart
Theses and Dissertations
Decreased budgets have pushed the United States Air Force towards using existing systems in new ways. The use of unmanned aerial vehicle swarms is one example of reuse of existing systems. One problem with the increased utilization of these swarms is the congestion of the electromagnetic spectrum. Software-defined or cognitive radios have been proposed as a basis for a potential robust communications solution. The present research aims to develop and test a genetic algorithm-based cognitive engine to begin looking at real-time engines that could be used in future swarms. Here, latency is the optimization objective of primary importance. In testing …
Novel Approaches For Mutual Coupling Reduction Among Vertical And Planar Monopole Elements, Ayman Abbosh Isaac
Novel Approaches For Mutual Coupling Reduction Among Vertical And Planar Monopole Elements, Ayman Abbosh Isaac
Theses and Dissertations
Modern wireless systems such as 4G LTE-A, RFID, Wi-Fi, WiMAX, and GPS utilize miniaturized antenna array elements to improve performance and reliability through diversity and increase throughput using spatial multiplexing schemes of MIMO systems. One original contribution in this thesis is to significantly reduce the complexity of traditional design approaches targeting mutual coupling reductions such as metamaterials, defected ground plane structures, soft electromagnetic surfaces using novel design alternatives. A decoupling network is proposed, which consists of a rectangular metallic ring along with two tuning strips printed on a dielectric substrate, surrounding a two-element monopole antenna array fed by a coplanar …
A Rectenna For 5g Energy Harvesting, Panagiotis Efthymakis
A Rectenna For 5g Energy Harvesting, Panagiotis Efthymakis
Theses and Dissertations
This thesis describes the design of a rectenna that is capable of operating in 5G. 5G’s availability will create the opportunity to harvest energy everywhere in the network’s coverage. This thesis investigates a Rectenna device with a new proposed topology in order to eliminate coupling between input and output lines and increase the rectification efficiency. Moreover, it is designed to charge a rechargeable battery of 3V, 1mA, with a 4.8mm diameter. The current design describes using one antenna for energy harvesting; this could be expanded to use an antenna array, which would increase the input power. This would lead to …
Optical Spectroscopy Of Wide Bandgap Semiconductor Heterostructures And Group-Iv Alloy Quantum Dots, Tanner A. Nakagawara
Optical Spectroscopy Of Wide Bandgap Semiconductor Heterostructures And Group-Iv Alloy Quantum Dots, Tanner A. Nakagawara
Theses and Dissertations
Efficient and robust blue InGaN multiple quantum well (MQW) light emitters have become ubiquitous; however, they still have unattained theoretical potential. It is widely accepted that “localization” of carriers due to indium fluctuations theoretically enhance their efficiency by moderating defect-associated nonradiative recombination. To help develop a complete understanding of localization effects on carrier dynamics, this thesis explores degree of localization in InGaN MQWs and its dependence on well thickness and number of wells, through temperature and power dependent photoluminescence measurements. Additionally, silicon-compatible, nontoxic, colloidally synthesizable 2-5 nm Ge1-xSnx alloy quantum-dots (QDs) are explored for potential visible to …
Absolute Positioning Using The Earth's Magnetic Anomaly Field, Aaron J. Canciani
Absolute Positioning Using The Earth's Magnetic Anomaly Field, Aaron J. Canciani
Theses and Dissertations
Achieving worldwide alternatives to GPS is a challenging engineering problem. Current GPS alternatives often suffer from limitations such as where and when the systems can operate. Navigation using the Earth's magnetic anomaly field, which is globally available at all times, shows promise to overcome many of these limitations. We present a navigation filter which uses the Earth's magnetic anomaly field as a navigation signal to aid an inertial navigation system (INS) in an aircraft. The filter utilizes highly-accurate optically pumped cesium (OPC) magnetometers to make scalar measurements of the Earth's magnetic field and compare them to a map using a …
Using Phase Screens To Synthesize Electromagnetic Gaussian-Schell Model Sources With Desired Amplitude, Coherence, And Polarization, Christopher K. Kokoczka
Using Phase Screens To Synthesize Electromagnetic Gaussian-Schell Model Sources With Desired Amplitude, Coherence, And Polarization, Christopher K. Kokoczka
Theses and Dissertations
An electromagnetic Gaussian-Schell model (EGSM) source is built with desired coherence, amplitude, and polarization using correlated phase screens based on re- search conducted in Refs. [2, 9]. A new method of amplitude control is presented and tested using spatial light modulators (SLM). A brief review of theory and concepts is discussed followed by methods of how to build an EGSM source, correlated phase screens, and control amplitude using SLM gratings. The experimental set-up is presented which builds EGSM sources that demonstrate desired amplitude, coherence, and polarization. Irradiance correlation, degree of polarization, and Stokes parameters S0 and S1 are …
Automated Sunspot Classification And Tracking Using Sdo/Hmi Imagery, Maclane A. Townsend
Automated Sunspot Classification And Tracking Using Sdo/Hmi Imagery, Maclane A. Townsend
Theses and Dissertations
Verification of an automated sunspot detection and classification algorithm is conducted utilizing two years of solar imagery from NASA's Solar Dynamics Observatory (SDO) satellite. Automated McIntosh classifications are compared against sunspot reports from the National Oceanic and Atmospheric Administration’s (NOAA) Space Weather Prediction Center (SWPC) using a three-tiered comparison metric. Statistical confidence is demonstrated for algorithm performance and consistency when compared against the SWPC data set, suggesting future applications of the algorithm will perform similarly. A sunspot tracking algorithm is added to the existing code and demonstrates reliable feature tracking for time periods out to four days between consecutive images. …
Utilization Of A Geodesic Sphere And Quadcopter As Two-Way Field Probe For Electro-Magnetic Field Measurements In An Indoor Radar Cross Section Range, Nathan Lett
Theses and Dissertations
Radar Cross Section (RCS) measurements rely heavily on multiple assumptions. Uncertainty in the final measurement is determined based on these assumptions. One source in particular is the non-homogeneous nature of the transmission path between radar test equipment and a target under test. The following research extends prior research. This thesis intends to provide a unique two-way field probe solution for measuring Electro-magnetic (EM) fluctuations in a test volume. In this thesis, the design, development, and demonstration of a geodesic sphere encased quadcopter two-way probe is explained. The Parrot® Bebop Drone quadcopter was used with a 2v frequency divided geodesic sphere …
Ultra–Low Power Straintronic Nanomagnetic Computing With Saw Waves: An Experimental Study Of Saw Induced Magnetization Switching And Properties Of Magnetic Nanostructures, Vimal G. Sampath
Theses and Dissertations
A recent International Technology Roadmap for Semiconductors (ITRS) report (2.0, 2015 edition) has shown that Moore’s law is unlikely to hold beyond 2028. There is a need for alternate devices to replace CMOS based devices, if further miniaturization and high energy efficiency is desired. The goal of this dissertation is to experimentally demonstrate the feasibility of nanomagnetic memory and logic devices that can be clocked with acoustic waves in an extremely energy efficient manner. While clocking nanomagnetic logic by stressing the magnetostrictive layer of a multiferroic logic element with with an electric field applied across the piezoelectric layer is known …
Beyond Conventional C-Plane Gan-Based Light Emitting Diodes: A Systematic Exploration Of Leds On Semi-Polar Orientations, Morteza Monavarian
Beyond Conventional C-Plane Gan-Based Light Emitting Diodes: A Systematic Exploration Of Leds On Semi-Polar Orientations, Morteza Monavarian
Theses and Dissertations
Despite enormous efforts and investments, the efficiency of InGaN-based green and yellow-green light emitters remains relatively low, and that limits progress in developing full color display, laser diodes, and bright light sources for general lighting. The low efficiency of light emitting devices in the green-to-yellow spectral range, also known as the “Green Gap”, is considered a global concern in the LED industry. The polar c-plane orientation of GaN, which is the mainstay in the LED industry, suffers from polarization-induced separation of electrons and hole wavefunctions (also known as the “quantum confined Stark effect”) and low indium incorporation efficiency that …
Optical Investigations Of Ingan Heterostructures And Gesn Nanocrystals For Photonic And Phononic Applications: Light Emitting Diodes And Phonon Cavities, Shopan D. Hafiz
Optical Investigations Of Ingan Heterostructures And Gesn Nanocrystals For Photonic And Phononic Applications: Light Emitting Diodes And Phonon Cavities, Shopan D. Hafiz
Theses and Dissertations
InGaN heterostructures are at the core of blue light emitting diodes (LEDs) which are the basic building blocks for energy efficient and environment friendly modern white light generating sources. Through quantum confinement and electronic band structure tuning on the opposite end of the spectrum, Ge1−xSnx alloys have recently attracted significant interest due to its potential role as a silicon compatible infra-red (IR) optical material for photodetectors and LEDs owing to transition to direct bandgap with increasing Sn. This thesis is dedicated to establishing an understanding of the optical processes and carrier dynamics in InGaN heterostructures for achieving …
Miniaturized Wideband Planar Soft Surfaces For Mutual Coupling Reduction Between Antenna Elements, Said A. Abushamleh
Miniaturized Wideband Planar Soft Surfaces For Mutual Coupling Reduction Between Antenna Elements, Said A. Abushamleh
Theses and Dissertations
Miniaturized electromagnetic soft surfaces have promising applications in contemporary wideband portable wireless devices including, Multiple Input Multiple Output (MIMO) systems, dual frequency applications, and mutual coupling reduction among antennas in user terminals utilizing MIMO schemes such as in 4th generation Long-Term Evolution (4G-LTE). The use of textured metallic surfaces over grounded dielectric slab with vias for the suppression of electromagnetic wave propagation for applications including, but not limited to, mutual coupling reduction among closely-spaced antenna elements in antenna arrays, bandwidth enhancement, and gain enhancement has been extensively researched during the past two decades. In this dissertation, novel one-dimensional (1-D) periodic …
Computational Electromagnetic Studies For Low-Frequency Compensation Of The Reflector Impulse-Radiating Antenna, Casey E. Fillmore
Computational Electromagnetic Studies For Low-Frequency Compensation Of The Reflector Impulse-Radiating Antenna, Casey E. Fillmore
Theses and Dissertations
The reflector impulse-radiating antenna (IRA) is considered to meet the requirement for a wideband, directional antenna with short temporal response and small electrical footprint. Standard reflector IRA designs are modeled and performance is simulated using full-wave computational electromagnetic (CEM) software. Characterization of the standard designs reveals the possible existence of wide, frequency-independent backlobes containing nearly 40% of the radiated power at high frequencies. These undesirable backlobes have never been hypothesized, predicted or measured, likely due in part to their alignment outside the primary measurement planes. At the lowest operating frequencies, the reflector IRA is unaffected by backlobes, but is characterized …
Hyperfine Interactions In The Electron Paramagnetic Resonance Spectra Of Point Defects In Wide-Band-Gap Semiconductors, Eric M. Golden
Hyperfine Interactions In The Electron Paramagnetic Resonance Spectra Of Point Defects In Wide-Band-Gap Semiconductors, Eric M. Golden
Theses and Dissertations
The focus of this research was to acquire definitive experimental data on predominant point defects in three important wide-band-gap semiconductors. Hyperfine interactions in electron paramagnetic resonance spectra were used to characterize the neutral nitrogen acceptor in zinc oxide, to identify a silicon interstitial impurity in titanium dioxide, and to determine the electronic structure of the singly ionized sulfur vacancy in stannous hexathiohypodiphosphate (SPS). Research on the basic properties of these technologically important materials plays a crucial role in the development of advanced optical and electronic systems. Zinc oxide is an electro-optic material with the potential to produce high performance electronics …
Photoacoustic Detection Of Terahertz Radiation For Chemical Sensing And Imaging Applications, Stjepan Blazevic
Photoacoustic Detection Of Terahertz Radiation For Chemical Sensing And Imaging Applications, Stjepan Blazevic
Theses and Dissertations
The main research objective is the development of photoacoustic sensor capable of detecting weak terahertz (THz) electromagnetic radiation. The feasibility of THz remote sensing is seen in the utilization of Microelectromechanical systems (MEMS) cantilever-based sensor. The overall sensing functionality of the detector in development is based on the photoacoustic spectroscopy and direct piezoelectric effect phenomena, as a result of which significant part of investigation has been conducted in the areas of terahertz electromagnetic radiation and its detection. The main focus of this research work was the detector analytical and Finite Element Method (FEM) simulation modeling, involving necessary material properties investigations …