Doctor of Philosophy, The Ohio State University, 2025, Electrical and Computer Engineering

Electromagnetic (EM) waves propagating through the lower atmosphere are significantly influenced by the environmental factors. Variations in the index of refraction can lead to ducting events, altering the expected spherical spreading of transmitted waves and resulting in trapping of these waves. Developing methods to characterize, estimate, and predict these occurrences is crucial for understanding their impact and mitigating performance degradation in systems such as naval and land-over-sea based radar and communication systems. Traditionally, sensing atmospheric ducts involves sounding launches or applying Monin-Obukhov Similarity Theory (MOST) to meteorological sensor data (humidity/temperature/wind), often in costly and non-real-time processing scenarios. Given that ducting enhances clutter through signal trapping, this dissertation explores radar systems' sensitivity to range-dependent clutter and how radar power returns from sea and land clutter can be utilized to estimate oceanic ducts. Refractivity-From-Clutter (RFC) involves estimating the atmospheric index of refraction variation with altitude using radar clutter data. The inversion process in RFC utilizes a best-fit algorithm to align with a known refractivity profile. The Parabolic Wave Equation (PWE) model is widely used for simulating path loss in RFC scenarios. Accurate land and sea surface modeling for both forward and backward propagation is the propelling force that enables RFC to have an accurate real-time estimation of lower tropospheric refractivity profiles. Previous RFC work primarily used only sea clutter with a single launch angle. The motivation behind this research is to enhance the RFC method by exploring the advantages of multiple launch angles and by incorporating land clutter. This dissertation is structured in three main sections, each aimed at advancing the precision and applicability of the RFC technique. The first section extends prior work by incorporating the Multip (open full item for complete abstract)

Doctor of Philosophy, The Ohio State University, 2025, Electrical and Computer Engineering

The proliferation of counterfeit integrated circuits (ICs) poses a critical threat to the global electronics supply chain, with ramifications ranging from product failures to national security risks. This dissertation presents the design, implementation, and evaluation of a rapid, non-destructive counterfeit detection method leveraging a microwave resonant cavity, termed the Resonant Cavity (ResCav) System. The system captures electromagnetic (EM) signatures of ICs by measuring shifts in reflection coefficient values when components are placed inside a rectangular microwave cavity. These signatures are influenced by the IC's impedance, internal structure and material properties, enabling differentiation between authentic and counterfeit devices. The ResCav System was engineered through multiple design iterations. Coupled with a vector network analyzer (VNA), the cavity records EM data across a broad frequency band. These signatures are then analyzed using supervised, semi-supervised, and unsupervised machine learning techniques. Experimental evaluations demonstrate the system's ability to distinguish ICs from different manufacturers, families, and production lots, as well as to detect a range of counterfeit types, including recycled, remarked, tampered, and cloned devices. A specialized machine learning model employing a modified radial basis function kernel identified certain types of tampered ICs where modifications were made solely to the silicon die. Additionally, tests incorporating total ionizing dose (TID) exposure revealed the system's sensitivity to radiation-induced internal changes in some IC types, providing further validation of the method's robustness. The dissertation also addresses intra-system measurement variability, showing consistent results across multiple environmental and setup conditions. While certain limitations exist—such as the requirement to test chips outside of circuit boards and difficulty detecting counterfeits that are phy (open full item for complete abstract)

Doctor of Philosophy, The Ohio State University, 2025, Electrical and Computer Engineering

Remote sensing has revolutionized our ability to observe and understand Earth's surface processes, providing critical insights into environmental dynamics that are otherwise difficult to capture through ground-based methods alone. Remote sensing technologies enable large-scale and continuous observations of environmental conditions that are essential for natural resource management and hazard monitoring, including assessments of susceptibility and recovery efforts. Given the proliferation of Synthetic Aperture Radars and the upcoming NASA/ISRO Synthetic Aperture Radar (NISAR) mission, there is an unprecedented opportunity to improve our understanding of surface and ecological dynamics and to enhance the accuracy, reliability, and utility of satellite-derived products. To harness the potential of SAR applications and address the scientific objectives of the NISAR mission, this dissertation focuses on the development and assessment of a mission specified soil moisture retrieval algorithm as well as wildfire applications of remotely sensed products. An emphasis is placed on using SAR data when available and supplemented with other sensors when necessary to provide a comprehensive analysis of NISAR's potential. The first phase of research centers on the development of the time-series ratio (TSR) algorithm for soil moisture retrievals, selected for its simplicity and independence from complex scattering models and ancillary information. The algorithm is evaluated using field campaign data and in-situ sampling networks under NISAR-like conditions to establish baseline performance. Recognizing that retrievals are sensitive to environmental and observational uncertainties, the next phase of research quantifies the algorithm's error budget. This analysis identifies key factors—such as vegetation cover, surface roughness conditions, system noise, and other ecological variables—that influence retrieval accuracy, providing critical guidance for interpreting the NISAR soil (open full item for complete abstract)

Doctor of Philosophy, The Ohio State University, 2025, Electrical and Computer Engineering

The performance of a radio frequency Direction of Arrival (DOA) estimation system strongly depends on the antenna array and the estimation algorithm used in the system. In many applications, one is limited to fixed aperture (few antenna elements with interelement spacing on the order of half a wavelength) antenna arrays for DOA estimation. In general, antenna elements in these arrays are placed with uniform interelement spacing. We show that the uniform interelement spacings do not lead to the best DOA estimation. It is well known that the accuracy of the estimated DOA is related to the information content in the antenna array spatial covariance matrix. Our investigation found that non-uniform spacings in the antenna array can increase the information in the covariance matrix, without changing the size or shape of the array. This leads to superior DOA estimation performance. We also show that using dissimilar antenna elements in the antenna array, one can further increase the information in the covariance matrix. For arrays with fixed aperture, closely spaced antenna elements will exhibit strong mutual coupling. Although this is typically seen as a nuisance effect, mutual coupling makes the radiation patterns of even similar elements dissimilar. When included in DOA estimation, mutual coupling can improve the DOA estimation performance of an antenna array. In our work, we use a Cramer-Rao Bound (CRB) based metric to evaluate various arrays for DOA estimation and show that antenna arrays with mutual coupling included in DOA estimation leads to better DOA estimates. We also propose a design metric that can quickly evaluate an antenna array's usefulness for DOA estimation. This metric computes the number of independent entries in the array spatial covariance matrix obtained directly from the array response over the desired field of view, and thus, is independent of the signal scenario. The metric is computationally efficiently and is applicable to antenna arrays wit (open full item for complete abstract)

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.

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

In recent decades, many techniques have been developed to analysis resonant structures, and one of the most popular numerical methods in frequency-domain is the method of moments (MOM). However, to purchase the resonant reaction for the high-Q device is an ill-conditioned problem. Over-sampling in space and frequency domain. To avoid over-sampling the space and frequency domain, this dissertation provides some efficient numerical techniques. The first part, A new adaptive rational interpolation method is proposed to obtain the wideband frequency response of a resonant cavity simulated with the method of moments (MoM). This interpolation method uses both the Loewner matrix to construct a rational expression for the solution vector of the MoM's matrix system and an error estimator generated by the solution vectors and their derivatives. This error estimator is implemented in the adaptive procedure to gain a minimum set of frequencies and solution vectors required in the interpolation. The resulting set of frequencies and solution vectors is applied to interpolate other system variables, such as shielding effectiveness and input impedance. Numerical results of a slotted cylindrical cavity supporting high-quality factor resonances are presented, showing that the new rational interpolation method is accurate and efficient in interpolating the complicated resonant response of the solution vector functions. Secondly, an automatic mesh refinement process designed to produce accurate resonant reactions in high-quality factor devices using surface integral equations. To validate the method, a solution-based error estimator is introduced to evaluate solution quality and identify elements requiring local mesh refinement. The sensitivity of local error distribution to frequencies near numerical resonance is analyzed. To effectively capture the resonant behavior, an automatic h-refinement strategy, combined with frequency sweeping, is employed. Numerical (open full item for complete abstract)

Master of Science in Engineering, Youngstown State University, 2024, Rayen School of 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, Rayen School of 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)