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

Global Navigation Satellite System Reflectometry (GNSS-R) is a remote sensing technique that utilizes GNSS signals reflected off of the Earth's surface to make geophysical measurements. Potential applications include the measurement of ocean surface wind speed, soil moisture, sea ice extent, and more. Since the existing GNSS satellites serve as transmitters in this passive, bistatic radar system, the reflectometer instrument can be made less expensive, less complex, and smaller than a traditional monostatic radar. Using a GNSS-R receiver on a spaceborne platform offers the ability to perform remote sensing with potentially global coverage. To date, almost all spaceborne GNSS-R instruments have utilized LHCP receive antennas with peak gains of 14 dBi or less, which limits the capabilities of these systems. Recently, the radar instrument onboard NASA's Soil Moisture Active Passive (SMAP) satellite has been tuned to receive GPS frequencies, which provides a unique opportunity for advanced spaceborne GNSS-R research. Equipped with a dual-polarized antenna with a peak gain of 36 dBi, SMAP can observe phenomena not otherwise available to existing instruments. In this work, raw signals collected by the SMAP satellite are processed in order to experimentally evaluate GNSS-R polarimetry, carrier phase characteristics, and off-specular scattering. This provides insight into the feasibility and requirements for implementing these novel, advanced GNSS-R capabilities and may serve to influence the design and operational considerations for future spaceborne GNSS-R missions.

Committee: Joel Johnson PhD (Advisor); Andrew O'Brien PhD (Committee Member); Inder Gupta PhD (Committee Member); Robert Burkholder PhD (Committee Member); Graeme Smith PhD (Committee Member) Subjects: Electrical Engineering; Electromagnetics

Master of Science (MS), Ohio University, 2010, Civil Engineering (Engineering and Technology)

Electrical Time Domain Reflectometry (TDR) and Optical Time Domain Reflectometry (OTDR) were utilized to monitor a zone suspected to have a slope stability problem on SR 690, 7.8 miles east of the city of Athens, in southeast Ohio. Two pairs of cables – one coaxial (electrical TDR) and one fiber optic (OTDR) in each pair – were installed at the suspected location. The cables were installed in pairs to facilitate a comparison of the results from the two methods. The data from the coaxial cables were acquired using TDR100 unit, whereas a Yokogawa AQ7275 OTDR system was used to acquire that data from the fiber optic cables. After assessment of the electrical TDR and OTDR results and no evidence of movement of the slope at the suspected zone, the site was further investigated to determine the possible causes of the embankment failure. A comprehensive geostratigraphic profiling of the site was conducted using a cone penetration test (CPT). Weak layers of soils that are prone to consolidation, at depths of up to 6 ft, and layers of over-consolidated fine-grained soils, at depths of below 6 or 7 ft, were seen that potentially contributed to settlement of the road embankment and development of cracks in the pavement structure. A new method of cable installation using a heavy-duty CPT truck was developed and practiced successfully in this study. The coaxial and fiber optic cables were pushed along with the cone rods by the hydraulic system integrated with the CPT truck. A disposable tip--unable to carry tension along the axes of the rods--for the cone rods was designed and built to stay at the desired depth of installation holding the cables after the cone rods are pulled out.

Committee: Shad Sargand PhD (Advisor); Deborah McAvoy PhD (Committee Member); Munir Nazzal PhD (Committee Member); Gaurav Sinha PhD (Committee Member) Subjects: Civil Engineering

Doctor of Philosophy, The Ohio State University, 2023, Nuclear Engineering

Nuclear energy is a promising solution to growing global energy consumption. Challenges such as initial investment, siting constraints, and concerns over safety, waste, and proliferation persist. Advanced reactor designs offer solutions to many of these challenges. In Parallel, there is a growing demand for innovative sensors, especially optical fiber-based sensors, to support the developmental endeavors of nuclear technology. Optical fiber sensors, which are resistant to electromagnetic interference, have the capability to provide multi-parameter sensing and multiplexing, offer potential advantages in monitoring various operational parameters in extreme conditions. The focus of this work is on both silica and sapphire optical fibers, aimed to serve as distributed temperature sensors in high-temperature radiation environments. Silica optical fibers, which have found extensive use in telecommunications, have been researched for nuclear applications. However, their practical deployment as distributed sensors in fueled experiments has yet to be realized. Sapphire optical fibers are being developed for fabrication and sensing, including exposure to temperatures and conditions previously unexplored. This research delves into the intricacies of designing, calibrating, and deploying these fiber optic-based sensors in high-temperature and radiation environments. Silica fibers were exposed to various conditions, from transient irradiation to high fluence levels, to ascertain their efficiency and robustness. Sapphire fibers, on the other hand, were tested in temperature and irradiation experiments, revealing their potential for ultra-high temperature applications. This work sheds light on the potential of optical fiber-based sensors, especially in high temperature radiation environments. It offers a roadmap for their deployment, including design considerations, calibration methods, and practical applications. The findings suggest silica optical fibers' robustness under dive (open full item for complete abstract)

Committee: Thomas Blue (Advisor); Joshua Daw (Committee Member); Marcello Canova (Committee Member); Raymond Cao (Committee Member) Subjects: Engineering; Nuclear Engineering

Doctor of Philosophy, University of Akron, 2023, Polymer Science

Plasma polymerization is a facile method of depositing robust films on a wide variety of substrates. While the nanoscale structure of films plasma polymerized in vacuum has been studied some, little is known of the nanoscale structure of the films deposited in the more complex atmospheric plasma polymerized (APP) films. To explore how deposition conditions affect APP film structures, APP films were deposited using hexamethyldisiloxane (HMDSO) precursor at varying power and in varying levels of relative humidity (RH). X-ray and neutron reflectivity measurements reveal that these APP-HMDSO films have a three-layer structure. A transition region of low mass density and carbon content forms next to the substrate as the deposition starts and etching by the plasma initially dominates deposition; a center region which still experiences some etching displays a uniform scattering length density (SLD) with respect to depth; a surface layer next to the air of mass density less than or equal to that of the center region forms whose SLD depends on how “filled in” the layer was when plasma generation was halted. Mass density was found to be sensitive to high humidity, which reduces the flux of monomer fragments to the substrate and allows them to pack more densely. Complementary analysis of depth-resolved X-ray photoelectron spectroscopy and water contact angle measurements show that composition and hydrophilicity are power-dependent. Films deposited at lower power lose more of their carbon to etching, making their composition more silica-like and making them more hydrophilic. Films deposited at higher power retain more of the carbon from the HMDSO monomer thanks to higher deposition rates; a film layer is buried by additional layers before all the residual carbon can be etched away. Neutron reflectivity measurements of the same APP-HMDSO films while exposing them to deuterated solvent vapor showed that vapor easily penetrated them without causing their thickness to increase, (open full item for complete abstract)

Committee: Mark Foster (Advisor); Mesfin Tsige (Committee Chair); Toshikazu Miyoshi (Committee Member); Ali Dhinojwala (Committee Member); Bi-min Newby (Committee Member) Subjects: Chemistry; Materials Science; Physics; Plasma Physics

Doctor of Philosophy, The Ohio State University, 2023, Electrical and Computer Engineering

Observing dynamic changes in the Earth's surface water is crucial for understanding and modeling the global hydrological cycle. Rapid changes in surface water, such as flooding and wetland inundation, are some of the most important events, yet quantitative observations of these events are among the most challenging to acquire. Current satellite-based flood and wetland inundation products are largely based on optical remote sensing methods, which exhibit limited ability to detect surface water through rain, clouds, and vegetation. While current satellite microwave remote sensing using radar can overcome some of these limitations, these instruments are on single satellite platforms and may overpass regions on multi-week timescales, missing flash flooding and dynamic inundation events. Recently, a novel remote sensing technique known as Global Navigation Satellite System Reflectometry (GNSS-R) has shown great potential in the detection of terrestrial surface water beneath clouds and vegetation. NASA's Cyclone Global Navigation Satellite System (CYGNSS) mission is a small satellite constellation using GNSS-R instruments that receive reflections of L-band GPS signals known to penetrate rain, clouds, and vegetation, and has a regional sub-daily revisit rate. CYGNSS has recently shown the potential to resolve small-scale and dynamic hydrological features over land, such as rivers, lakes, wetlands, and urban flooding. CYGNSS is an eight-satellite constellation, resulting in sub-daily measurement frequencies that provide a unique opportunity to observe short timescale changes. However, CYGNSS measurements occur in sparse, quasi-random tracks since GPS reflections can occur anywhere in the field of view. This makes understanding the observability of dynamic events more difficult as compared to simpler imaging instruments. Changes in signal-to-noise ratio (SNR) that indicate a dynamic change in the scene are confounded by inherent variability due to other sources, incl (open full item for complete abstract)

Committee: Joel Johnson (Advisor); Lee Potter (Committee Member); Robert Burkholder (Committee Member); Andrew O'Brien (Committee Co-Chair) Subjects: Remote Sensing

Master of Science, The Ohio State University, 2021, Electrical and Computer Engineering

NASA's next generation bistatic radar receiver (NGRx) is currently under development as part of an instrument incubator program. The instrument receives GNSS signals reflected off of the Earth as part of a novel remote-sensing system to measure land and water surface properties in a variety of scientific applications. Although designed for spacecraft, it will be first deployed on a commercial passenger aircraft in New Zealand as part of a unique international collaboration. Not only will this provide a source for valuable science data products for New Zealand, but it will also facilitate calibration and validation for NASA CYGNSS Mission and the new instrument prior to future satellite deployment. This thesis describes a collection of work performed to support planning and deployment of the new instrument on a commercial aircraft. Simulations were performed to analyze instrument coverage over its first year of deployment by utilizing historical ADS-B flight data, measured and simulated antenna patterns, GNSS satellite orbits, and topographic models of New Zealand. Results from this analysis provide operational visualizations that facilitated engineering design decisions, selection of in-situ calibration sites, aircraft antenna installation location, data-volume estimation, and more. Software tools were developed which produce initial simulated data products to support operation-center development at the University of Auckland. The simulations indicate the aircraft deployment offers exciting opportunities for science and also helped to mitigate uncertainty associated with airborne GNSS-R deployment. Simulation code developed under this effort has been documented, containerized, and published to an internet repository.

Committee: Joel Johnson Prof. (Advisor); Andrew O'Brien Dr. (Committee Member); Nima Ghalichechian Dr. (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy, The Ohio State University, 2020, Electrical and Computer Engineering

Global Navigation Satellite System Reflectometry (GNSS-R) is a remote sensing technique that uses reflected GNSS signals to make measurements of geophysical properties of the Earth's surface. The significant roughness of typical ocean and land surfaces at L-band frequencies commonly result in diffusely scattered GNSS reflections. However, it has been observed that the surfaces of lakes, rivers, wetlands, and other inland water bodies are often sufficiently smooth to produce coherent reflections. Coherent reflections are of particular interest for remote sensing due to their high reflected power, fine spatial resolution, and phase information. Utilizing these reflections enables a unique capability to monitor the global surface water distribution underneath rain, clouds, and dense vegetation. To take full advantage of coherent reflections and best retrieve geophysical information, it is necessary to develop new scattering models, perform simulation studies, and understand how future GNSS-R receivers can be optimized to receive these types of signals. Until now, a comprehensive investigation of this type had not been undertaken. In this work, an electromagnetic scattering model is developed for coherent GNSS reflections over complex scenes with a number of varying surface parameters. The model is utilized to evaluate the accuracy of current water extent retrieval approaches and to propose a novel measurement of wind vector and wave heights from inland waters. Finally, two new algorithms are proposed to improve the science value of coherent GNSS reflections in future GNSS-R instruments.

Committee: Inder Gupta (Advisor); Andrew O'Brien (Committee Member); Johnson Joel (Committee Member); Burkholder Robert (Committee Member) Subjects: Computer Engineering; Electrical Engineering

Doctor of Philosophy, The Ohio State University, 2015, Physics

Double perovskites have proven to be highly interesting materials, particularly in the past two decades, with many materials in this family exhibiting strong correlations. These materials are some of many novel complex oxides with potential spintronics application. Sr2CrReO6, in particular, is a double perovskite with one of the highest Curie temperatures of its class (> 620 K in bulk and ∼510-600 K in thin films), as well as high spin polarization, ferrimagnetic behavior, and semiconducting properties. This dissertation covers recent work in exploring and tuning physical properties in epitaxial films of Sr2CrReO6. It starts by providing a background for the field of spintronics and double perovskites, bulk and thin film synthesis of Sr2CrReO6, and standard and specialized characterization techniques utilized in both university and national laboratories, and then provides reports of work on Sr2CrReO6 epitaxial films. Examples of exploration and engineering of properties of Sr2CrReO6 include: (1) tuning of electrical resistivity, such as at T = 7 K by a factor of 18,000%, via control of oxygen partial pressure during film growth; (2) enhancement of interfacial double perovskite ordering, demonstrated with high-angle annular dark-field scanning transmission electron microscopy, via the use of double perovskite buffer layer substrates; (3) measurement of magnetization suppression near film/substrate interfaces via polarized neutron reflectometry, which reveals a reduction of thickness (from 5.6 nm to 3.6 nm) of the magnetically suppressed interface region due to buffer layer enhancement; (4) strain tunability of atomic spin and orbital moments of Cr, Re, and O atoms probed with x-ray magnetic circular dichroism, which demonstrates ferrimagnetic behavior and reveals important magnetic contributions of the oxygen sites (∼0.02 µB/site); (5) strain tunability of large magnetocrystalline anisotropy via applied epitaxial strain, revealing anisotropy fields of up to 10s of te (open full item for complete abstract)

Committee: Fengyuan Yang (Advisor); P. Chris Hammel (Committee Member); Ciriyam Jayaprakash (Committee Member); Richard Hughes (Committee Member) Subjects: Condensed Matter Physics

Master of Science (MS), Ohio University, 1997, Civil Engineering (Engineering)

Performance of instrumented flexible pavement

Committee: Shad Sargand (Advisor) Subjects: Engineering, Civil

Master of Science (MS), Ohio University, 2004, Civil Engineering (Engineering)

A comparative study of inclinometers and time domain reflectometry for slope movement analysis

Committee: Shad Sargand (Advisor) Subjects: Engineering, Civil

Master of Science (MS), Ohio University, 1997, Civil Engineering (Engineering)

This research deals with the potential use(s) of Time Domain Reflectometry (TDR) to determine and monitor Non-Aqueous Phase Liquids (NAPLs) in soils. TDR is an established method to determine water content and electrical conductivity of soils. Other applications include solute transport and NAPLs migration in subsurface. A two phase experiment was implemented to study NAPLs in soils. In the first phase, three NAPLs (gasoline, diesel and tetrachloroethylene) and five soils (fine sand, coarse sand, and 10%, 30%, and 50% silty sand) were used. The NAPL was added to the soil which contained a specific water content, until it was saturated, and the dielectric constant was monitored after each addition. In the second phase, the NAPL's transport in the subsurface was monitored in a polyethylene cell. Two NAPLs (diesel and tetrachloroethylene) and two soils (fine and coarse sand) were used in this phase. Three TDR probes were inserted into the soil, spaced 12.7 cm apart. The NAPLs migration was monitored by the reduction of the dielectric constant determined by TDR. The volumetric fraction of water displaced by the NAPL was estimated. The results of phase I revealed that the NAPLs caused the dielectric constant to increase when the soil was not saturated and to decrease when it was at saturation. In phase II, the dielectric constant was reduced as a result of the transport of the NAPL in the soil and replacing the water. The dielectric constant, however, remained unchanged under the water table in the LNAPL experiments.

Committee: Gayle Mitchell (Advisor) Subjects: Engineering, Civil

Doctor of Philosophy, Case Western Reserve University, 2011, Civil Engineering

The dissertation describes the development and validation of a new instrument based on Time Domain Reflectometry (TDR) for measuring properties of fresh and early age concrete. It provides an alternative to traditional quality control methods that rely heavily on the slump value and compressive strength that do not always produce durable concrete. Work in the first stage focused on the design and development of a prototype sensor system for use on fresh and early age concrete. An experimental program systematically evaluated the sensor system's ability to measure the performance properties of concrete. The program tested several representative types of concrete specimens used in highway pavement, bridges, and industrial and residential structures. TDR signals were collected from concrete specimens subjected to different curing conditions, including early freezing, and the results were correlated with data obtained by standard test methods. The results indicated that the TDR sensor system can reliably measure or estimate concrete properties, such as free water content, density, air void content, initial and final setting times, and mechanical strength. The technology was found not only suitable to measure the physical and electrical properties of materials at common temperature but also works non-destructively under freezing-thawing cycles.

Committee: Xiong Yu (Committee Chair); Xiangwu Zeng (Committee Member); Adel Saada (Committee Member); Steve Hauck (Committee Member) Subjects: Civil Engineering

Doctor of Philosophy, Case Western Reserve University, 2009, Civil Engineering

Scour is a major threat to the safety of bridges. Instruments for the measurement and monitoring of bridge scour are necessary to study scour processes and to support bridge management. The lack of robust and economical scour monitoring devices prevents the implementation of a bridge scour monitoring program among bridge owners. This dissertation explores the design and analyses of scour sensors using principles of Time Domain Reflectometry (TDR). The performance of a scour probe was first tested in laboratory simulated scour experiments. Three different signal analyses methods were developed to obtain the scour depth from TDR signals. Besides scour depth, additional information related to scour assessment, i.e. sediment density and electrical conductivity of water, were also determined from TDR signals. The sensing principles and analysis algorithms were validated from simulated scour tests under various conditions which are expected to be encountered in the field. The field conditions considered included: variation of sediment types, water conductivity, turbidity, air entrapment, and water elevation. These further validated the robustness of the scour sensing principles. Upon validation, a field worthy sensor was designed. The sampling area and effective measured dielectric constant were determined using a finite element analysis method. Evaluation of the sensor indicated that it was able to successfully monitor the scour processes (scour and refill) in real-time with high accuracy.

Committee: Xiong Yu (Committee Chair); Xiangwu Zeng (Committee Member); Adel Saada (Committee Member); Chung-Chiun Liu (Committee Member) Subjects: Civil Engineering

Doctor of Philosophy, University of Akron, 2011, Polymer Science

The effects of a topology with no chain ends on interfacial segregation in binary polymer blends and the surface fluctuations of films of macrocycles were studied using well-defined macrocyclic polystyrenes (CPS) blended with analog, linear polystyrenes (LPS). A series of well-defined CPSs (Mn = 2,800; 8,600; 17,000; 38,000 g/mol) were synthesized using a combination of anionic polymerization and ring closure metathesis reactions. The macrocyclic polymers were uniquely characterized by Matrix Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS) using peaks that were characteristically 28 m/z units less than those of the corresponding precursor peaks, due to the loss of an ethylene unit. The preferential segregation of one component to the air/ polymer and polymer/ substrate interfaces of macrocyclic/ linear blend films of 2k or 37k chains was studied by Surface MALDI-TOF MS (SMALDI-TOF MS), Static TOF Secondary Ion Mass Spectrometry (STOF-SIMS), and Neutron Reflectometry (NR). Blends of bulk composition with 20 wt% of the hydrogenous species were studied. The isotopic effect is not significant for the 2k blends and the chain architecture plays an important role in determining the surface segregation. Measurements with three complementary techniques show the linear species to be enriched at the surface, counter to a self-consistent field theory that considers only the conformational entropic effect of eliminating chain ends. A iv Wall-PRISM theoretical treatment that accounts will for packing effects close to a wall, does, however, correctly predict the surface enrichment by linear chains for a blend of short linear and short cyclic chains. In the case of 37k macrocyclic/linear blends the macrocyclic polymer enriches both the surface and the substrate interfaces, and the surface excess is comparable with the prediction of a modified SCF theory. Surface flucturations of melt films of unentangled CPS with Mn = 2k, 7k, and 14k g/mol were (open full item for complete abstract)

Committee: Mark D. Foster Dr. (Advisor); Ali Dhinojwala Dr. (Committee Member); Roderic P. Quirk Dr. (Committee Member); Chrys Wesdemiotis Dr. (Committee Member); Alamgir Karim Dr. (Committee Member) Subjects: Polymers