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Articles 1 - 30 of 31
Full-Text Articles in Engineering
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 …
Adaptive-Hybrid Redundancy For Radiation Hardening, Nicolas S. Hamilton
Adaptive-Hybrid Redundancy For Radiation Hardening, Nicolas S. Hamilton
Theses and Dissertations
An Adaptive-Hybrid Redundancy (AHR) mitigation strategy is proposed to mitigate the effects of Single Event Upset (SEU) and Single Event Transient (SET) radiation effects. AHR is adaptive because it switches between Triple Modular Redundancy (TMR) and Temporal Software Redundancy (TSR). AHR is hybrid because it uses hardware and software redundancy. AHR is demonstrated to run faster than TSR and use less energy than TMR. Furthermore, AHR allows space vehicle designers, mission planners, and operators the flexibility to determine how much time is spent in TMR and TSR. TMR mode provides faster processing at the expense of greater energy usage. TSR …
Target Detection In Heterogeneous Clutter With Low Resolution Radar, Kyle G. Stankowski
Target Detection In Heterogeneous Clutter With Low Resolution Radar, Kyle G. Stankowski
Theses and Dissertations
This thesis develops a framework for SAR target detection and super-resolution in low-resolution environments. The primary focus in this research is the background clutter heterogeneity that often accompanies low range and cross-range resolutions. A corrective model which accounts for clutter replacement is developed to define the detection and false alarm rates of the detector more accurately than a traditional model in which the radar return from the target supplements the existing clutter. In a heterogeneous clutter cell, the clutter replacement model leverages the different scattering distributions among the individual clutter types to generate a probability distribution function for the areas …
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 …
Digital Holography Efficiency Experiments For Tactical Applications, Douglas E. Thornton
Digital Holography Efficiency Experiments For Tactical Applications, Douglas E. Thornton
Theses and Dissertations
Digital holography (DH) uses coherent detection and offers direct access to the complex-optical field to sense and correct image aberrations in low signal-to-noise environments, which is critical for tactical applications. The performance of DH is compared to a similar, well studied deep-turbulence wavefront sensor, the self-referencing interferometer (SRI), with known efficiency losses. Wave optics simulations with deep-turbulence conditions and noise were conducted and the results show that DH outperforms the SRI by 10's of dB due to DH's strong reference. Additionally, efficiency experiments were conducted to investigate DH system losses. The experimental results show that the mixing efficiency (37%) is …
Autonomous And Resilient Management Of All-Source Sensors For Navigation Assurance, Juan D. Jurado
Autonomous And Resilient Management Of All-Source Sensors For Navigation Assurance, Juan D. Jurado
Theses and Dissertations
All-source navigation has become increasingly relevant over the past decade with the development of viable alternative sensor technologies. However, as the number and type of sensors informing a system increases, so does the probability of corrupting the system with sensor modeling errors, signal interference, and undetected faults. Though the latter of these has been extensively researched, the majority of existing approaches have constrained faults to biases, and designed algorithms centered around the assumption of simultaneously redundant, synchronous sensors with valid measurement models, none of which are guaranteed for all-source systems. This research aims to provide all-source multi-sensor resiliency, assurance, and …
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. …
Active Control Of A Morphing Wing Aircraft And Failure Analysis For System Reliability, Madison J. Montgomery
Active Control Of A Morphing Wing Aircraft And Failure Analysis For System Reliability, Madison J. Montgomery
Theses and Dissertations
A morphing wing aircraft has the ability to increase the efficiency of an aircraft by better optimizing lift and drag characteristics during a flight. A morphing wing UAV was designed and constructed by AFRL/RQVS and required a means of control and method of characterizing the performance of the aircraft through flight testing. This research presents the design and construction of a control system capable of adjusting the morphing wing shape based on pilot commands and current flight status. The control system was tested and improved following a flight test crash utilizing failure mode analysis.
Plasma Treatment Method For Ohmic Contacts On Zinc Oxide Thin Film Transistors, Blaine Z. Underwood
Plasma Treatment Method For Ohmic Contacts On Zinc Oxide Thin Film Transistors, Blaine Z. Underwood
Theses and Dissertations
This research utilizes plasma treatments as a method to decrease the contact resistance on zinc oxide (ZnO) thin film transistors (TFT). In recent years, researchers have achieved gigahertz RF switch cutoff frequency with ZnO TFTs. To further increase the cutoff frequency, the total resistance of this device must be minimized. Modern ZnO TFTs are fabricated with submicron channel lengths, which contains minimal resistance due to the TFT channel, making contact resistance significant to the total resistance of the device. This research developed a method to integrate plasma treatments into the fabrication of ZnO TFT to decrease the contact resistance, thus …
Convolutional Neural Network Architecture Study For Aerial Visual Localization, Jedediah M. Berhold
Convolutional Neural Network Architecture Study For Aerial Visual Localization, Jedediah M. Berhold
Theses and Dissertations
In unmanned aerial navigation the ability to determine the aircraft's location is essential for safe flight. The Global Positioning System (GPS) is the default modern application used for geospatial location determination. GPS is extremely robust, very accurate, and has essentially solved aerial localization. Unfortunately, the signals from all Global Navigation Satellite Systems (GNSS) to include GPS can be jammed or spoofed. To this response it is essential to develop alternative systems that could be used to supplement navigation systems, in the event of a lost GNSS signal. Public and governmental satellites have provided large amounts of high-resolution satellite imagery. These …
Improved Fabrication For Micromirror Arrays, Enoc Flores
Improved Fabrication For Micromirror Arrays, Enoc Flores
Theses and Dissertations
Micromirror devices which consisted of one SU-8 2050 layer, two different exposures, and a series of metal depositions were constructed and evaluated. By varying the exposure, a micromirror structure was fabricated with different thicknesses, a ratio of 1.083 µm/(mJ/cm2) was found. The initial design consisted of four layers. The pillar was made of one SU-8 layer, and the top portion had three layers in the following order: gold, SU-8, and gold. This design could not be released and did not have characteristics of a flat and conformal reflective surface. Several variations of the initial design were explored and all of …
Machine Translation With Image Context From Mandarin Chinese To English, Brooke E. Johnson
Machine Translation With Image Context From Mandarin Chinese To English, Brooke E. Johnson
Theses and Dissertations
Despite ongoing improvements in machine translation, machine translators still lack the capability of incorporating context from which source text may have been derived. Machine translators use text from a source language to translate it into a target language without observing any visual context. This work aims to produce a neural machine translation model that is capable of accepting both text and image context as a multimodal translator from Mandarin Chinese to English. The model was trained on a small multimodal dataset of 700 images and sentences, and compared to a translator trained only on the text associated with those images. …
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 …
Serious Game Design Using Mda And Bloom’S Taxonomy, Senobio V. Chavez
Serious Game Design Using Mda And Bloom’S Taxonomy, Senobio V. Chavez
Theses and Dissertations
The field of Serious Games (SG) studies the use of games as a learning tool and it has been in existence for over forty years. During this period the primary focus of the field has been designing systems to evaluate the educational efficacy of existing games. This translates to a lack of systems designed to aid in the creation of serious games, but this does not have to remain an issue. The rise in popularity of games means that there is no shortage of ideas on how to methodically create them for commercial production which can just as easily be …
Direct Path Interference Suppression And Received Signal Processing For Ofdm Passive Radar, Aileen Nundu
Direct Path Interference Suppression And Received Signal Processing For Ofdm Passive Radar, Aileen Nundu
Theses and Dissertations
Passive bistatic radar (PBR) is a fairly active area of research due to the opportunities offered by the ability to use emitters of opportunity for target detection and tracking as well as Synthetic Aperture Radar (SAR) imaging. There is an increasing variety and availability of signals that can be exploited for passive radar and there is also the advantage of angular diversity offered by the bistatic geometry and the potential for stealth operations afforded a passive receiver. Notwithstanding its merits, PBR is complicated by the inevitable presence of Direct Path Interference (DPI) from the transmitter to the receiver, which can …
Two-On-One Pursuit With A Non-Zero Capture Radius, Patrick J. Wasz
Two-On-One Pursuit With A Non-Zero Capture Radius, Patrick J. Wasz
Theses and Dissertations
In this paper, we revisit the "Two Cutters and Fugitive Ship" differential game that was addressed by Isaacs, but move away from point capture. We consider a two-on-one pursuit-evasion differential game with simple motion and pursuers endowed with circular capture sets of radius l > 0. The regions in the state space where only one pursuer effects the capture and the region in the state space where both pursuers cooperatively and isochronously capture the evader are characterized, thus solving the Game of Kind. Concerning the Game of Degree, the algorithm for the synthesis of the optimal state feedback strategies of the …
High Fidelity Satellite Navigation Receiver Front-End For Advanced Signal Quality Monitoring And Authentication, Andrew D. Braun
High Fidelity Satellite Navigation Receiver Front-End For Advanced Signal Quality Monitoring And Authentication, Andrew D. Braun
Theses and Dissertations
Over the last several years, interest in utilizing foreign satellite timing and navigation (satnav) signals to augment GPS has grown. Doing so is not without risks; foreign satnav signals must be vetted and determined to be trustworthy before use in military applications. Advanced signal quality monitoring methods can help to ensure that only authentic and reliable satnav signals are utilized. To effectively monitor and authenticate signals, the front-end must impress as little distortions upon the received signal as possible. The purpose of this study is to design, fabricate, and test the performance of a high-fidelity satnav receiver front-end for advanced …
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 …
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 …
Side Channel Anomaly Detection In Industrial Control Systems Using Physical Characteristics Of End Devices, Ryan D. Harris
Side Channel Anomaly Detection In Industrial Control Systems Using Physical Characteristics Of End Devices, Ryan D. Harris
Theses and Dissertations
Industrial Control Systems (ICS) are described by the Department of Homeland Security as systems that are so \vital to the United States that their incapacity or destruction would have a debilitating impact on our physical or economic security." Attacks like Stuxnet show that these systems are vulnerable. The end goal for Stuxnet was to spin centrifuges at a frequency rate outside of normal operation and hide its activity from the ICS operator. This research aims to provide a proof of concept for an anomaly detection system that would be able to detect an attack like Stuxnet by measuring the physical …
Preserving Privacy In Automotive Tire Pressure Monitoring Systems, Kenneth L. Hacker
Preserving Privacy In Automotive Tire Pressure Monitoring Systems, Kenneth L. Hacker
Theses and Dissertations
The automotive industry is moving towards a more connected ecosystem, with connectivity achieved through multiple wireless systems. However, in the pursuit of these technological advances and to quickly satisfy requirements imposed on manufacturers, the security of these systems is often an afterthought. It has been shown that systems in a standard new automobile that one would not expect to be vulnerable can be exploited for a variety of harmful effects. This thesis considers a seemingly benign, but government mandated, safety feature of modern vehicles; the Tire Pressure Monitoring System (TPMS). Typical implementations have no security-oriented features, leaking data that can …
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 …
Autonomous Association Of Geo Rso Observations Using Deep Neural Networks, Ian W. Mcquaid
Autonomous Association Of Geo Rso Observations Using Deep Neural Networks, Ian W. Mcquaid
Theses and Dissertations
Ground-based non-resolved optical observations of resident space objects (RSOs) in geosynchronous orbit (GEO) represent the majority of the space surveillance network’s (SSN’s) deep-space tracking. Reliable and accurate tracking necessitates temporal separation of the observations. This requires that subsequent observations be associated with prior observations of a given RSO before they can be used to create or refine that RSO’s ephemeris. The use of astrometric data (e.g. topocentric angular position) alone for this association task is complicated by RSO maneuvers between observations, and by RSOs operating in close proximity. Accurately associating an observation with an RSO thus motivates the use of …
Uranium Dioxide Actinide Detection Device Support Design For Space Applications, Jennifer N. Ramos
Uranium Dioxide Actinide Detection Device Support Design For Space Applications, Jennifer N. Ramos
Theses and Dissertations
Attention concerning the proliferation of nuclear weapons and materials has generated many research initiatives to detect, identify, and locate radiation emitted by actinides. In support of this effort, the `Fission Induced Neutron Detection of Nuclear Materials' (FIND'NM) program was established to comprise a joint effort to explore this issue. The objective also co-extends the Air Force Research Laboratory uranium dioxide (UO2) detection sample growth, characterization, and electrical interface research. AFIT's study accomplishes the design and fabrication of a space-tolerant PCB to support a UO2-based neutron detector. Further design considerations are made with the expectation of the platform to be inside …
Orthogonal Frequency Division Multiplexed Waveform Effects On Passive Bistatic Radar, Forrest D. Taylor
Orthogonal Frequency Division Multiplexed Waveform Effects On Passive Bistatic Radar, Forrest D. Taylor
Theses and Dissertations
Communication waveforms act as signals of opportunity for passive radars. However, these signals of opportunity suffer from range-Doppler processing losses due to their high range sidelobes and pulse-diverse waveform aspects. Signals such as the long term evolution (LTE) encode information within the phase and amplitude of the waveform. This research explores aspects of the LTE, such as the encoding scheme and bandwidth modes on passive bistatic Doppler radar. Signal space-time adaptive processing (STAP) performance is evaluated and parameters are compared with the signal to interference-plus-noise ratio (SINR) metric.
Multi-Sensor Data Fusion Between Radio Tomographic Imaging And Noise Radar, Christopher Vergara
Multi-Sensor Data Fusion Between Radio Tomographic Imaging And Noise Radar, Christopher Vergara
Theses and Dissertations
The lack of situational awareness within an operational environment is a problem that carries high risk and expensive consequences. Radio Tomographic Imaging (RTI) and noise radar are two proven technologies capable of through-wall imaging and foliage penetration. The intent of this thesis is to provide a proof of concept for the fusion of data from RTI and noise radar. The output of this thesis will consist of a performance comparison between the two technologies followed by the derivation of a fusion technique to produce a single image. Proposals have been made for the integration of multiple-input multiple-output (MIMO) radar with …
Physical Layer Discrimination Of Electronic Control Units Using Wired Signal Distinct Native Attribute (Ws-Dnda), Rahn M. Lassiter
Physical Layer Discrimination Of Electronic Control Units Using Wired Signal Distinct Native Attribute (Ws-Dnda), Rahn M. Lassiter
Theses and Dissertations
The Controller Area Network (CAN) bus is a communication system used in automobiles to connect the electronic components required for critical vehicle operations. These components are called Electronic Control Units (ECU) and each one exercises one or more functions within the vehicle. ECUs can provide autonomous safety features and increased comfort to drivers but these advancements may come at the expense of vehicle security. Researchers have shown that the CAN bus can be hacked by compromising authorized ECUs or by physically connecting unauthorized devices to the bus. Physical layer (PHY) device fingerprinting has emerged as one of the accepted approaches …
Confirmation Bias Estimation From Electroencephalography With Machine Learning, Micah Villarreal
Confirmation Bias Estimation From Electroencephalography With Machine Learning, Micah Villarreal
Theses and Dissertations
Cognitive biases are known to plague human decision making and can have disastrous effects in the fast-paced environments of military operators. Traditionally, behavioral methods are employed to measure the level of bias in a decision. However, these measures can be hindered by a multitude of subjective factors and cannot be collected in real-time. This work investigates enhancing the current measures of estimating confirmation bias with additional behavior patterns and physiological variables to explore the viability of real-time bias detection. Confirmation bias in decisions is estimated by modeling the relationship between Electroencephalography (EEG) signals and behavioral data using machine learning methods.
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 …
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 …