Master of Science, The Ohio State University, 2014, Electrical and Computer Engineering

Radar images are created from measurements of the electromagnetic field scattered from an object or scene of interest. The scattered field defines the radar signature as a function of frequency and aspect angle. High resolution radar images and radar signatures are used for target recognition, tracking, and hardware-in-the-loop testing. High resolution radar images of electrically large targets may require a large amount of data to be measured, stored, and processed. A sparse representation of this data may allow the radar signature to be efficiently measured, stored, and rapidly reconstructed on demand. Compressed sensing is applied to obtain the sparse representation without measuring the full data set. “Compressed sensing” has different interpretations, but in this thesis it refers to using non-adaptive, random samples of the measured signal, with no a priori knowledge of the signal. According to compressed sensing theory, this is possible if the radar signature can be expressed in terms of a sparse basis. If a signal y can be approximated by K non-zero coefficients in the sparse basis (“K-sparse”), the coefficients may be obtained with random sampling of the signal at sub-Nyquist rates provided that K is much smaller than the total number of Nyquist samples. The random sampling is non-adaptive (i.e., future samples are independent of previous samples) and the number of samples required is primarily related to the sparseness of the signal, and not the bandwidth nor the size of the dictionary from which the basis functions are selected. The objective of this thesis is to investigate the effectiveness of physical basis functions, defined as point scatter functions with frequency-dependent amplitudes characteristic of physical scattering mechanisms, to provide an improved sparse basis in which to expand radar signatures. The goal is to represent a radar signature accurately with the fewest terms possible and with the fewest measurements. Use of physical basi (open full item for complete abstract)

Committee: Robert Burkholder (Advisor); Lee Potter (Committee Member) Subjects: Electrical Engineering; Electromagnetics

Doctor of Philosophy, The Ohio State University, 2012, Electrical and Computer Engineering

Range-resolved interferometric phase and Doppler spectra are two subjects of interest with regard to the retrieval of sea surface height profiles from coherent marine radar measurements. The studies of this dissertation attempt to improve understanding of the properties and associated measurement errors of these quantities through the use of numerically simulated low-grazing-angle backscatter data. In the first part of the dissertation, studies of the interferometric phase are described. Backscattered fields computed using the method of moments for one dimensional ocean-like surface profiles are used to examine statistical properties of the single-look interferometric phase estimator, in order to investigate the applicability of standard expectations for height retrieval accuracy in this problem. The results show that shadowing and multipath propagation effects cause errors in interferometric phase estimation beyond those caused by speckle effects alone. In addition, the decorrelation between the fields received at two antennas is found to be impacted by shadowing and multipath propagation effects, making standard models for this quantity less applicable as well. These results show that modeling the expected performance of interferometric sea surface height retrieval approaches at low grazing angles is difficult. The second part of the dissertation involves studies of the range-resolved Doppler spectra at low-grazing-angles. Backscattered fields are computed for a single realization of a one-dimensional ocean-like surface profile as the realization evolves in time. Transformation into the range-Doppler domain enables examination of properties of the resulting Doppler spectra (for both HH and VV polarizations) and their relationship to properties of the surface profile. In general, a strong correspondence between the long wave orbital velocity of the surface and the Doppler centroid frequency is observed for visible portions of the surface, as well as some evidence (open full item for complete abstract)

Committee: Joel Johnson (Advisor); Robert Burkholder (Committee Member); Fernando Teixeira (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy, The Ohio State University, 2007, Electrical Engineering

The Small Perturbation Method (SPM) is a low frequency approximation to the electromagnetic scattering from rough surfaces. The theory involves a small height expansion in conjunction with a perturbation series expansion of the unknown scattering coefficients. Recently, an arbitrary order, iterative solution procedure has been derived for SPM: kernels at any order are expressed as a summation over lower order kernels in an iterative fashion. Such a form is very useful, because it allows evaluation of the field statistical moments in a direct manner, when considering stochastic surfaces. In this dissertation, this procedure is extended to the two layer (two rough surfaces on top of each other) problem and the complete solution is given. Utilizing this formulation, the second and fourth order bi-static scattering coefficients for two rough surfaces characterized by two uncorrelated Gaussian Random Processes (GRP) are obtained. The effects of upper and lower roughnessesand the interaction effect in the total fourth order cross section can be identified in the theory. Studies on the ratio of the interaction effect to the total cross section are presented for example cases, investigating the relative importance of interactions among surfaces. Results show the interaction term contributes most to the cross-pol cross sections when surfaces are close to each other at near grazing incidence. In addition, the previously developed arbitrary order SPM solution for the single layer problem is utilized to derive the fourth order term in the small slope approximation (SSA) of thermal emission from the sea surface. It is shown that this term has the form of a four-fold integration over a product of two sea spectra for a Gaussian random process sea, thereby describing emission “interaction” effects among pairs of sea waves. Interaction effects between “long” and “short” waves are considered, both through numerical and approximate evaluations of the fourth order theory. The approxima (open full item for complete abstract)

Committee: Joel Johnson (Advisor) Subjects:

Doctor of Philosophy, Case Western Reserve University, 2017, Materials Science and Engineering

The construction of mesoscale assemblies using a bottom-up approach is an emerging research area in recent years, while understanding the interactions that control the organization of the constructing building blocks turns out to be a prerequisite for effective assembly design. The intrinsic electronic structures of materials determine their optical properties, which give rise to long-range interactions including electrostatic and van der Waals (vdW) components. And electrostatic along with vdW interactions, are the fundamental interactions that drive mesoscale assembly. In this research, the long range interactions of inorganic material and bio-molecules are investigated using both experiment and computation optical methods, and then a functional mesoscale assembly based on an inorganic substrate and biomolecular particles are built. In terms of the inorganic material, the full spectral optical properties and van der Waals-London interaction of bulk SiC crystal is investigated with a combination of vacuum ultraviolet spectroscopy and Liftshiz theory-based Hamaker coefficient calculation, and compared with OLCAO electronic structure calculations of the band structure and ab initio optical properties of SiC. Cylindrical biomolecules, DNA, is selected as a biomolecular example. The effect of nitrogen base polarizability on the optical properties and electronic structures of double-strand DNA are studied by optical characterization and ab initio density functional theory modeling; then G-quadruplex DNA consisting of human telomere sequence are characterized by spectroscopy, static light scattering and ab initio modeling, and compared with corresponding double-strand DNA, giving rise to the structural dependent electronic structures and pH dependent pair-wise interactions. Finally, the first semi-ordered, layered, mesoscale self-assembly capable of photon management comprised of plant viruses is created and characterized. Anti-reflection and photon-trapping properti (open full item for complete abstract)

Committee: Roger French Dr. (Advisor); Nicole Steinmetz Dr. (Committee Member); Alp Sehirlioglu Dr. (Committee Member); Rudolf Podgornik Dr. (Committee Member); Hongping Zhao Dr. (Committee Member) Subjects: Materials Science

Doctor of Philosophy, The Ohio State University, 1985, Graduate School

Committee: Not Provided (Other) Subjects: Engineering

Doctor of Philosophy, The Ohio State University, 1978, Graduate School

Committee: Not Provided (Other) Subjects: Engineering

Doctor of Philosophy, The Ohio State University, 1968, Graduate School

Committee: Not Provided (Other) Subjects: Engineering

Master of Science, The Ohio State University, 2011, Electrical and Computer Engineering

Nowadays, multi-scale or multi-physics modeling plays a very important role in many important problems. In the past few years, there have been increasingly growing research activities aiming at developing novel multi-scale computational methods. In this thesis, we will focus on one computational electromagnetics method (CEM) which is based on the homogenization theory and considers the microscopically heterogeneous system to be a macroscopically homogeneous system by averaging the local electromagnetic fields and current distributions. The averaging process adopted here is to replace the original inhomogeneous structure by a homogeneous material with effective anisotropic permittivity and permeability tensors.

Committee: Jin-Fa Lee (Advisor); Fernando L. Teixeira (Committee Member) Subjects: Electrical Engineering; Electromagnetics; Electromagnetism

Doctor of Philosophy, The Ohio State University, 2008, Electrical Engineering

The spatial/time spectrum of short sea waves and radar observed signals are locally modulated by the presence of longer waves or currents. There are two different modulations: tilt modulation and hydrodynamic modulation. Variations in the short sea waves spectrum are described by the "hydrodynamic modulation transfer function" (HMTF). The nonlinear interaction between short sea waves and longer waves makes such modulation. Variations of radar signals are described by the "radar modulation transfer function" (RMTF). In this study, new numerical methods based on numerical nonlinear hydrodynamics and computational electromagnetics are developed to examine modulation in sea surface scattering and to examine the accuracy of existing analytical models. Electromagnetic scattering from sea surface at low-grazing-angles (LGA) is studied by comparing analytical scattering models. The two-scale model (TSM) is found to yield the most reasonable performance among these models. Ocean surface profile retrieval based on the TSM is also shown to have an acceptable accuracy. Numerical methods are developed to calculate the HMTF, and RMTF by use of the fast nonlinear hydrodynamics, and by use of the fast computational electromagnetics techniques. These techniques allow us to study the scattering from a stochastic "Pierson-Moskowitz" like surface with Monte-Carlo simulation. HMTF values obtained from the simulations are compared to those from a first order wave action solution, and found to be in reasonable agreement, although differences on the order of 10% are observed. A numerical evaluation of long wave effects on the short wave dispersion relation is also provided. The numerical method provides a quantitative way to examine the "third- scale" effect in the two-scale model. The results demonstrate that the intermediate waves influence the RMTF and are modulated by longer waves. This effect explains the RHMTF polarization dependence. Numerical results of the (open full item for complete abstract)

Committee: Joel Johnson Ph.D (Advisor) Subjects: Electrical Engineering; Electromagnetism

Doctor of Philosophy, The Ohio State University, 2005, Electrical Engineering

It is well known that the scope and application of numerically-rigorous techniques for full-wave electromagnetic characterization is limited to problems of moderate electrical size and simplified complexity. These limitations stem from the vast computational resources required by numerical methods such as finite element method (FEM), boundary element method (BEM) or finite difference method (FDM). During the last decade a number of fast and memory efficient numerical algorithms such as Multigrid methods and the Fast Multipole Algorithm (FMA), have been proposed to further reduce storage and computational requirements of full-wave methods. In this dissertation an alternative proposition will be presented, that is a fast and efficient Domain Decomposition (DD) methodology, appropriately tailored for the solution of time-harmonic Maxwell's equations. The DD method proposed here is a non-conforming one, namely it allows for different mesh on either side of domain interface. This not only relaxes and speeds up automatic mesh generation algorithms, but at the same time opens the road of efficient and robust adaptive field computations. The DD technique is based on a divide-and-conquer philosophy. Instead of tackling a large and complex problem directly (as a whole), it divides the computational domain into smaller, possibly repetitive, and easier to solve partitions called domains. Such domains can be solved with a variety of numerical methods, e.g. finite elements, boundary elements, etc. The algorithm proceeds iteratively by appropriately communicating information across domains and ultimately reaching the solution for the original (whole) problem. A detailed presentation of the proposed DD method for electromagnetic problems will be given, along with a novel methodology called "cement" finite elements, for the coupling of domains with non-matching meshes. In addition, a variant of the Finite Element Tearing and Interconnecting (FETI) sub-structuring algorithm will be i (open full item for complete abstract)

Committee: Jin-Fa Lee (Advisor) Subjects:

Doctor of Philosophy (PhD), Ohio University, 1999, Electrical Engineering & Computer Science (Engineering and Technology)

This dissertation presents the methodologies used to develop and validate protective zoning requirements for Microwave Landing System (MLS) azimuth and elevation guidance signals. Typically, the aviation community refers to these protective zoning requirements as critical areas. The purpose of defining critical areas about the azimuth and elevation antennas is to protect the radiated guidance signals from multipath errors caused by electromagnetic scattering of these signals by transient vehicles and aircraft. A method for applying the Federal Aviation Administration MLS Mathematical Model to characterize the guidance signal errors caused by interfering aircraft located ahead of the azimuth or elevation antenna is presented. This method was used to generate error-contour plots characterizing the guidance signal errors caused along a standard precision approach profile as a function of interfering aircraft type, location, and orientation. Error budgets were developed, including allocations to the error permitted to be caused by interfering aircraft. Based on these allocations, error-contour plots were analyzed to determine the areas that bound all of the interfering aircraft locations that have the potential to cause guidance-signal error that exceed the allocations. Methods for adapting these criteria to protect non-standard, computed-centerline, and advanced approach procedures are presented. The dissertation provides azimuth and elevation critical-area criteria for basic, computed-centerline, and advanced MLS procedures. Also, it presents the status of critical-area criteria development for Precision Distance Measuring Equipment. The dissertation recommends that validation and refinement of the criteria be performed as indicated by operational experience.

Committee: Roger Radcliff (Advisor) Subjects: