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

This study examines the aging effects of GaN HEMTs, focusing on the CG2H40010 device under conditions that mimic the high-power, high-frequency environments of wireless communication systems. With the increasing adoption of GaN technology in RF applications, understanding its degradation mechanisms under CW stress and modulated signal characterization is essential for predicting device lifetime and ensuring performance standards for modern communication systems. RFALT was employed to stress the device using CW signals, while key performance metrics, such as gain compression, gate leakage, ACP, and EVM, were assessed using W-CDMA signals to replicate real-world dynamic stresses. The findings reveal that CW stress accelerates thermal and electrical degradation in GaN HEMTs, while W-CDMA characterization highlights the impact of complex modulation on linearity and spectral containment. Degradation mechanisms such as ohmic contact wear and dielectric failure significantly affect performance, especially under high peak-to-average ratio conditions. This research underscores the importance of combining CW-based RFALT with modulation-specific testing to evaluate device reliability comprehensively. By addressing thermal management, enhancing dielectric materials, and employing linearization techniques, these insights pave the way for optimizing GaN HEMTs to meet the stringent requirements of 5G and future wireless communication systems.

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

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

Doctor of Philosophy, University of Akron, 2024, Electrical Engineering

Researchers worldwide are fervently working on developing efficient, lightweight, and compact electric machines across various industries to meet the growing demands of today's world. To achieve these goals, a holistic system-level approach is necessary, moving beyond motor design alone. In the heating, ventilation, and air conditioning (HVAC) industry, where motor-driven compressors are extensively used, optimizing overall system efficiency is paramount. Recent advancements are focused on integrating the motor directly into the compressor housing, resulting in a more streamlined, cost-effective, and energy-efficient system. Radial-flux induction machines used in HVAC systems are less efficient than advanced permanent magnet (PM) machines. Axial-flux machines (AFMs) offer superior torque and power density but face adoption challenges due to cost and infrastructure. AFMs are well-suited for space-constrained applications like electric vehicles. Their planar design and adjustable airgaps provide advantages over radial-flux machines (RFMs). This dissertation proposes integrating the compressor impeller into the rotor of an electric motor for centrifugal motor-compressor systems in HVAC. The ideal motor for this integration is determined to be the axial-flux permanent magnet (AFPM) motor. While the Slotted version of this motor fits the design requirements, this study proposes the use of a Slotless structure due to its ease of manufacturability and smooth torque performance with a dual Slotless stator and single Coreless rotor (SL-AFPM) motor. Foremost, the research compares SL-AFPM with its counterpart, the Slotted axial-flux permanent magnet (S-AFPM) motor, focusing on two different slot/pole configurations. The study aims to explore the full potential of both designs while disregarding their application in integrated motor-compressor systems and associated limitations. The findings reveal that the SL-AFPM motor has smoother torque quality. Although the SL-AFPM (open full item for complete abstract)

Doctor of Philosophy, The Ohio State University, 2024, Electrical and Computer Engineering

We present an exposition on Koopman operator-based reduced-order modeling of high-dimensional electromagnetic (EM) systems exhibiting both linear and nonlinear dynamics. Since the emergence of the digital age, numerical methods have been pivotal in understanding physical phenomena through computer simulations. Computational electromagnetics (CEM) and computational plasma physics (CPP) are related yet distinct branches, each addressing complex linear and nonlinear electromagnetic phenomena. CEM primarily focuses on solving Maxwell's equations for intricate structures such as antennas, cavities, high-frequency circuits, waveguides, and scattering problems. In contrast, CPP aims to capturing the complex behavior of charged particles under electromagnetic fields. This work specifically focuses on the numerical simulation of electromagnetic cavities and particle-in-cell (PIC) kinetic plasma simulations. Studying electromagnetic field coupling inside metallic cavities is crucial for various applications, including electromagnetic interference (EMI), electromagnetic compatibility (EMC), shielded enclosures, cavity filters, and antennas. However, time-domain simulations can be computationally intensive and time-consuming, especially as the scale and complexity of the problem increase. Similarly, PIC simulations, which are extensively used for simulating kinetic plasmas in the design of high-power microwave devices, vacuum electronic devices, and in astrophysical studies, can be computationally demanding, especially when simulating thousands to millions of charged particles. Moreover, the nonlinear nature of the complex wave-particle interactions complicates the modeling task. Data-driven reduced-order models (ROMs), which have recently gained prominence due to advances in machine learning techniques and hardware capabilities, offer a practical approach for constructing "light" models from high-fidelity data. The Koopman operator-based data-driven ROM is a powerful met (open full item for complete abstract)

Doctor of Philosophy, The Ohio State University, 2024, Electrical and Computer Engineering

With rapidly increasing demands for high-speed and data-intensive wireless communications, mm-wave technology has become a promising way to provide unparalleled data rates, ultra-reliable low latency, and a massive increase in device connectivity. However, there are some fundamental challenges in the deployment of mm-wave networks. Considering the same communication distance, the mm-wave suffers from a higher free-space path loss due to its shortened wavelength. The path loss becomes an issue especially when the device is working in rural areas where a longer coverage distance is required. Also, a shorter wavelength can result in extra attenuation brought by random obstacles, for example, the raindrops whose diameter is comparable to the wavelength. For the mm-wave antenna systems with a fixed narrow beam, even light mechanical motions can cause misalignment between the transmitter and receiver leading to intermittent communication. To address these challenges, mm-wave antennas are designed to be highly directional, concentrating energy in narrow beams to combat the high path loss. Besides, beam-steerable antennas, which can dynamically adjust the radiation direction, have been developed to maintain reliable communication links. While the conventional phased array designs have a planar aperture with beam-forming capability, their usage in the mm-wave band is limited by its cost, potentially low efficiency, and high power consumption due to numerous active RF components. The reflector antennas, which have been widely adopted thanks to their decent gain level and high efficiency, face the challenges of a complex reflecting aperture and a large volume due to the separated feeding source. Similar limitations have been observed in other designs using metasurfaces or lenses as well. Therefore, there is an innovation gap for a simple low-cost, low-volume, high-efficiency, high gain, and beam-steerable antenna design for the next-generation mm-wave applications. A low-prof (open full item for complete abstract)

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

This research details the development of a cutting-edge Low Noise Amplifier (LNA) using advanced 28nm CMOS technology. The study focuses on achieving optimal performance in high-frequency wireless communication systems. The LNA design showcases a significant gain of 40.39 dB at 6.31 GHz and an impressive noise figure of 6.68 dB at 6.31 GHz. The total area of the chip is 0.576 mm2. The methodology includes utilizing a common-stage LNA configuration with inductive source degeneration and cascade structures to enhance gain and noise performance. Special emphasis is placed on impedance matching, with a meticulous design of input and output networks to minimize signal loss and noise addition. The paper also explores key aspects of LNA design, such as transistor sizing, stability, and linearity. Stability is rigorously analyzed using S-parameters, ensuring the LNA's resistance to self-oscillations. Linearity is addressed through measures like the Third-Order Intercept Point (IIP3), ensuring signal integrity in the presence of strong interfering signals.

Doctor of Philosophy (Ph.D.), University of Dayton, 2024, Electrical and Computer Engineering

The advent of 5G technology has catalyzed a spectrum expansion across various frequency bands, including a low band below 1 GHz, a midband spanning 1-7 GHz, and a high band above 24 GHz. Therefore, researchers and engineers are currently engaged in exploring reconfigurable and tunable devices capable of adapting multi-band front-end modules to accommodate this expanded spectrum range. In this work, there are three types of reconfigurable and tunable filters that have been investigated. Each of them has its unique features and advantages. The surface-mounted technology (SMT) 5th-order elliptic tunable filter is first investigated. It exhibits three consecutive tunable bands within and above the L-band frequency range, specifically at 2.0-2.5 GHz, 2.5-3.0 GHz, and 3.0-3.5 GHz. Utilizing PIN diodes and capacitor banks, tunability is achieved through the DC voltage-controlled capacitance of PIN diodes, with in-band insertion loss maintained below 3 dB. This work already met the design limitation of the pure SMT filter in spite of the limited quality factor of the inductor and capacitor components. This dissertation contributed to two other designs. One is the bulk acoustic wave (BAW) filter, using the piezo effect to realize a filter function with high out-of-band rejection. Another one is the microstrip-coplanar waveguide (MS-CPW) filter, utilizing the coupling effect to guarantee a wide bandwidth and low in-band loss. The BAW resonator and filter, integrating tunable dielectric material barium strontium titanate (BST), offer a solution for sub-10 GHz applications. The BST material grants the BAW device a switchable coupling coefficient (Kt2), resulting in a switchable passband. This dissertation delves into the physical behavior and electrical models of the BAW resonator. In this work, the surface-mounted structure is adopted, and a highly efficient Bragg reflector is designed and fabricated to achieve a better isolation for BAW resonator. Furthermore, the perfo (open full item for complete abstract)

Master of Science (M.S.), University of Dayton, 2024, Electro-Optics

Light Detection And Ranging (LiDAR) technology continues to gain significance across various industries, including autonomous vehicles, surveying, mapping, and defense. The demand for precise 3D spatial data necessitates active sensing methods. Flash imaging and scanning LiDAR are two ways of achieving direct-detection LiDAR. Flash imaging LiDAR captures the entire scene instantaneously by emitting a single pulse and measuring the return. Scanning LiDAR, on the other hand, operates by directing a focused laser pulse in a controlled pattern, typically through mechanically steered mirrors, and measures the reflected signals at each point. Due to the losses in the optical system and light propagation in the atmosphere, the received light is at a much lower intensity than the emitted. This calls for the demand of sensitive detectors that are able to convert the returned light into a measurable electrical signal. Traditionally, low-light sensing has been achieved using linear mode or Geiger mode avalanche photodiodes (APDs). While linear mode APDs offer amplification akin to low-noise amplifiers, their gain values are often limited, and higher gain variants like those in HgCdTe are costly. Geiger mode APDs, despite their increased sensitivity, operate as switches with a notable dead time. In contrast, the discrete amplification photon detector (DAPD) offers a promising alternative by aiming to achieve single-photon detection without the drawbacks associated with APDs. This study gives comparison between flash and scanning LiDAR systems then focuses on the performance of the DAPD, evaluating the viability of the DAPD for LiDAR applications. As detector technology advances, it not only enhances LiDAR system performance but also broadens its applicability across diverse domains. This research contributes to advancing LiDAR technology, unlocking its potential for even broader adoption and innovation.

Doctor of Philosophy, The Ohio State University, 2024, Electrical and Computer Engineering

The central theme of this dissertation is to explore material interaction with electromagnetic waves in millimeter-wave (mmWave) and terahertz (THz) frequency bands spanning the range from 30 GHz to 3 THz. The implications of these interactions in the context of on-vehicle integration of mmWave automotive radars is discussed. Furthermore, specific mechanisms are exploited for broadband material characterization, and biomedical imaging. First, this research outlines the traditional broadband methods to characterize the electromagnetic properties of isotropic non-magnetic dielectric materials. In mmWave and THz regime, this data is not readily available in many cases. Utilizing established free-space techniques such as terahertz time-domain spectroscopy (THz-TDS) and quasi-optical transmission measurements, this research extracts this data for a diverse range of materials. In particular, we discuss the challenges related to the reliability of the permittivity extraction process in situations where the measurement may not have a high SNR across the bandwidth of interest. We circumvent this problem by cross-validating the data across multiple modalities to ensure consistency. Additionally, for thin dielectric films for which conventional methods fail, this research proposes a novel permittivity extraction technique from calibrated two-port S-parameter measurements of a coplanar waveguide. Interaction of mmWave radar signal with the near zone radome and bumper layers can impair the radar performance through reduction of signal-to-noise ratio and distortion of the pattern. Therefore, towards the goal of a `transparent' radome, the dissertation proposes a novel textured radome design aimed at optimizing transmission efficiency for mmWave automotive radar. Through a strategic optimization based on first-principles, this design exhibits an enhanced signal transmission throughout the entire automotive radar band of 76 – 81 GHz. The optimized design demonstrates an avera (open full item for complete abstract)

Master of Science, The Ohio State University, 2024, Electrical and Computer Engineering

As manufacturing techniques such as topology optimization and additive manufacturing develop, components with increasing geometric complexity are becoming more common. Thus, it is necessary to develop automated non-destructive evaluation techniques that are adaptable to various surface geometries. This project seeks to leverage robotic simulation software to virtually plan and optimize eddy current inspections of various airplane components to detect flaws while eliminating false positives. The final deliverable will be a Robot Operating System (ROS) software package that generates an optimal tool path plan based on probe output for various scan resolutions.

Doctor of Philosophy, Case Western Reserve University, 2024, EECS - Electrical Engineering

5G promises higher speed for data communication when Internet-of-Things (IoT) makes enormous number of devices connected to each other. Preserving the security and trust in such systems are one of the critical. To create secure and trustworthy system while preserving the low power nature of such circuits, this work introduces a novel concept: embedded analog Physically Unclonable Functions (PUFs). Embedded analog PUFs provide enable lower power consumption than conventional hardware security methods because they are implemented in target circuits such as Voltage Controlled Oscillator (VCO) or Low Noise Amplifier (LNA). Also, the proposed approach allows for using performance parameters of the target circuits to develop required unique Challenge-Response Pair (CRP) mechanisms instead of bit streams of conventional PUF designs. In this work, power hungry parts of a radio frequency front-end (RF-FE), i.e. VCO and LNA, are targeted. Prototype low power 28 GHz trusted VCO and trusted LNA are developed in 65-nm standard CMOS and 22-nm FDSOI processes. Embedded analog PUF in VCO and LNA allows adjusting the DC (e.g. current consumption) and AC (e.g. frequency and noise figure (NF)) properties of the VCO and LNA to authenticate the designs while providing competitive performance with the VCO achieving figure of merit (FoM) of 195.2 dBc/Hz @1 MHz offset, and LNA showing NF ~ 3.7 dB @ 28 GHz.

Doctor of Philosophy (PhD), Ohio University, 2024, Electrical Engineering (Engineering and Technology)

This dissertation presents four design methodologies for circularly periodic multi-band and wideband High Impedance Surfaces (HISs). The resulting HIS designs are integrated with wideband spiral antennas to demonstrate unidirectional multi-band and/or wideband performance. For many applications (e.g., Global Navigation Satellite Systems (GNSS)), antennas having unidirectional radiation patterns are desirable to provide good signal reception and to minimize multi-path reflections. Spiral antennas, due to their wideband nature, can be used to cover a wide range of frequency bands using a single antenna element. However, in order to make their radiation characteristics unidirectional, a conductive and/or lossy ground plane is often used. Typically, such types of wideband spiral antennas use a metallic cavity filled with Radio Frequency (RF) absorber material or a lossy magnetic type back-plane. These antennas will typically have an increased height profile or sacrifice gain, and/or multipath mitigation performance. This dissertation is focused on using an HIS (also called metamaterial) as a perfect magnetic conductor (PMC) ground plane, as opposed to common perfect electric conductor (PEC) ground planes. HISs can be a good alternative because they can be placed relatively close to the antenna while still preserving the 0° reflection-phase characteristics at the surface of the HIS. Most HISs proposed in literature use rectangular and tend to have a relatively narrow bandwidth and are often referred to as Frequency Selective Surfaces (FSS). It has been previously shown that for curvilinear radiating elements like spiral or loop antennas, better performance is achieved by using circularly periodic HISs. Using a cylindrical wave and concentric circular waveguides to model circularly periodic HISs provides a better approximation of sources with curvilinear radiating elements. In addition, most HISs proposed so far tend to have relatively narrow band (open full item for complete abstract)

Master of Science, The Ohio State University, 2024, Electrical and Computer Engineering

Radiofrequency (RF) technology has found numerous medical applications due to its ability to generate heat and create electromagnetic fields. One of the most prominent RF applications in medical industry is detection or monitoring of development of tumor or other diseases in various parts of the human body. However, most of the developed applications are monolithic and not very flexible when it comes to using the same technology for different applications. This thesis presents the design of a scalable board which can be used in creating a modular system that can be used in different applications like detection of lymphedema, pulmonary edema and can also be used to monitor the cardiac muscle activity. We present the basic idea of the board followed by the reason for choosing each component in the board followed by the RF budget calculations and also calculation of several RF parameters like P1dB, IIP3, NF. At the end we present the schematic and layout of the board and also simulation results of the core mixer system at different frequencies.

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

A complete procedure of dealing with frequency-selective surfaces (FSS) in electromagnetic is addressed in this dissertation, including automatic design and fast numerical simulation. The design of the FSS contains the design of periodic structure and the arrangement of the periodic structure on an arbitrary platform. For the design of periodic structure, an adaptive artificial neural network (ANN) is presented herein to meet the desired frequency response automatically. Afterward, the designed periodic structure is arranged on an arbitrary platform by some seed points to approximate the locations, and the generation of seed points uses some electrons reaching an electrostatic distribution. For the fast numerical simulations of FSS, a generalized transition condition (GTC) is presented herein to reduce computation resources of both memory computation time due to the complex geometry. In this method, GTC serves as a field relationship to represent the electromagnetic interaction effect from the original FSS. The proposed GTC is inspired by the generalized sheet transition condition (GSTC) but gets rid of the zero-thickness assumption to build a relationship between the electric field and magnetic field on both sides of the FSS. The process of the proposed numerical simulation method of FSS includes three steps. The first is to obtain the reflection and transmission coefficients by the numerical simulation of FSS as an infinite periodic structure with periodic boundary conditions (PBC). Secondly, a self-consistent scheme is adopted to compute the coefficient in GTC with a required order. Finally, the constructed GTC can be used to replace the FSS in a real model. The collaboration of GTC with both surface integral equation (SIE) method and finite element method (FEM) are addressed in this dissertation. Especially for FEM, GTC is modified to bypass the edge effects and results in a conformal mesh on both sides of the transition condition. The accuracy of the pr (open full item for complete abstract)

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

Automotive radar systems are poised to become key enablers for improving the overall functionality and safety of commercial automobiles. In this proposal, three separate investigations into improving the electromagnetic modeling, design, and testing, of current automotive radar systems are presented. Due to their extremely low profile and ease of manufacturing, patch antenna arrays are the common choice of these radar systems. A particular problem with patch arrays is the inter-element coupling though substrate modes. In particular, such mutual coupling introduces radiation pattern ripple, or distortion, from observation angles between -30 and +30 degrees in the elevation plane. To mitigate mutual coupling, we propose a double-slot array with an integrated alumina lens to maintain low mutual coupling between radiating elements while simultaneously reducing radiation pattern ripple from 5dB in the microstrip patch array to 0.8dB in the double-slot array. In addition, an improvement of 4.5dB in maximum gain was achieved for the individual element patterns with the inclusion of the alumina lens. The proposed double-slot array is also presented with a “common-differential” mode functionality that can aid in beam scanning the intended area of the radar system with finer resolution than traditional constructive phase beam forming. As the demand for bandwidth across the electromagnetic (EM) spectrum continues to grow, the need for technology in vacant frequency bands of the spectrum also increases. Reconfigurable filters are one way to increase the efficacy of devices in all parts of the EM spectrum allowing applications to coexist in nearby frequency bands. Our vanadium dioxide (VO2) reconfigurable filters were designed on a thin, transparent, flexible, polyimide substrate intended to operate in the Far-IR. We present novel fabrication recipes for VO2 on a polyimide substrate, and verify that it exhibits a prodigious metal to insulator transition at 48⁰C that is (open full item for complete abstract)

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

Array signal processing algorithms for direction finding and adaptive beamforming require accurate in-situ calibration of the antenna array. Unfortunately, calibrating the array inside an anechoic chamber is often not possible because the array, or the platform it is mounted on, is too large. In addition, simulations of the array using Computational Electromagnetic (CEM) software can miss crucial information about the manufacturing defects present in the real system. The limitations of these methods has lead to the development of in-situ calibration techniques that can exploit the signals the array receives while deployed in its operational environment (i.e. Signals of Opportunity [SoOp]). In-situ calibration is advantageous because the incident signals include the effects of platform scattering and manufacturing defects without the need for an anechoic chamber. However, without any coordination between the array and the sources generating the SoOp, the transmitted signals are unknown to the array and multiple SoOp can be received simultaneously. Current methods capable of using SoOp for calibration rely on restrictive models for the array response, such as the Mutual Coupling Matrix, and are unable model the effects of platform scattering. In this dissertation, we present an in-situ calibration technique that incorporates a flexible model for the array response based on a Spherical Mode Expansion (SME). By expressing the far-field patterns of the antenna elements as a SME, we are able to model the response of an array placed in a complex scattering environment using a relatively compact representation. Because the spherical harmonics are only orthogonal over the full sphere, computing the expansion coefficients is difficult when the measurement region is limited, which is a common occurrence in in-situ calibration. We resolve this issue by employing a regularized least-squares solution and an efficient regularization parameter selection procedure. The propose (open full item for complete abstract)

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

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

Doctor of Philosophy, Case Western Reserve University, 2023, Physics

Much of the utility of liquid crystals comes from the tendency for their highly anisotropic molecules to align with surfaces, electric fields, and other liquid crystal molecules. In the commercial world, this alignment is sometimes undesirably interrupted by stable structures known as topological defects. However, defects are not always undesirable. For instance, liquid crystal defects are commonly used as a surrogate testbeds for systems which are too large or small to easily study directly. Discoveries relating to liquid crystal defects may find important analogies in such systems, and improvements in defect manipulation may open doors to new kinds of research. In this work, I explore a myriad of ways in which topological defects re- act to electric fields and electric field-originating phenomena. I begin with studies on the merging and splitting of low-strength defects under dielectric anisotropy-mediated forces. I then explain the discovery and eventual identification of electrohydrodynamic instability-mediated circular motion in defects (called co-revolution), providing the experimental evidence which led to that identification as well as the basic techniques first used to characterize this unexpected motion. Following this I present Professor Hillel Aharoni's simple phenomenological model of this circular motion, various experimental means in which this model has and has not yet been tested, where it has shown itself to be surprisingly accurate for such a simple model, and where limitations in the model have been found. I then branch out into a variety of subtopics in instability-mediated defect motion, including how changes in the defect's strength and chirality influence motion, each interesting in their own right. In this same chapter, I also use a modification to the shadowgraph technique to determine the relative alignments of defects and instability rolls. This information is brought together to create conclusions on what may be causing defects to mov (open full item for complete abstract)

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

Rough surface scattering is an essential aspect of modern remote sensing research, as virtually all real-world surfaces exhibit some degree of roughness whose effects cannot be adequately accounted for using simple planar surfaces. However, knowledge of what each rough surface model is capable of is critical, as choosing an appropriate model will aid in providing accurate results while minimizing the computational cost incurred. To explore these capabilities, four studies were conducted to assess how various rough surface scattering models fare in scenarios of current interest to the remote sensing community. The first two studies involve the Kirchhoff approximation (KA), with the first study assessing its applicability when the normalized coherent reflected field (which the KA is commonly used to model) is -20dB or lower, and the second study comparing it to a second-order correction term based on the second-order small slope approximation (SSA2) for ocean surface scattering. The first study shows that the KA continues to be applicable for such low amplitude cases, and the second study shows that the second-order correction shows no marked improvement over the base KA overall. The third study uses the SSA2 to validate retrieved zero-Doppler delay waveforms as part of a campaign to explore off-specular ocean scattering, and found the model waveforms to match the retrieved waveforms well in most cases considered. The fourth and final study uses simulated SAR imagery to determine under what conditions a monostatic radar system will observe the same surface scattering as a bistatic radar system, and revealed that cases with near-normal incidence angles and minor roughness yield the best agreement, with effects such as shadowing and multiple reflections accounting for most of the disagreements.

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

We present a discussion on the reduced-order modeling of electromagnetic simulation in general, and kinetic plasma simulations in particular, using the Proper Orthogonal Decomposition technique. Computational electromagnetics has been an important tool for physicists and engineers since the mid-1960s, when the increasing availability of modern high-speed computers started to allow the numerical solution of practical problems for which closed-form analytic solutions did not exist or were impractical to calculate. The study of kinetic plasmas is of great interest both for theoretical exploration and technological applications such as design of vacuum electronic devices, the study of the interaction of space-borne assets and cosmic radiation, fusion experiments, among others. Due to the theoretical complexity of these problems and the difficulty in performing physical experiments, simulations are instrumental for obtaining new insights or developing new device designs by resolving the field and plasma behaviors when changes are made. Several variants of simulations exist, but particle-in-cell algorithms for solving particle dynamics coupled with finite-differences or finite-elements field solvers are particularly successful. Despite their success, such algorithms are still constrained by computational cost such as processing time and memory/storage limitations. The Proper Orthogonal Decomposition is a technique that extracts the spatiotemporal behavior from a function of interest or a set of data points. This spatiotemporal behavior is characterized by a set of coupled spatial and temporal modes, which makes the Proper Orthogonal Decomposition especially suitable for analyses and applications in dynamic systems; it has been used for creation of reduced-order models in the past, especially in the fluid dynamics community where it originated from but also in many other areas. We have explored the application of the Proper Orthogonal Decomposition technique to co (open full item for complete abstract)