Doctor of Philosophy, The Ohio State University, 2015, Electrical and Computer Engineering

For satellite communications, traditional phased array antennas could offer advantages over reflector antennas such as increased functionality, conformality, and no feed blockage. However, phased array systems are complex and expensive and, thus, not commonly used for satellites. Indeed, many applications (radar, electronic warfare, communications, etc.) would greatly benefit from less expensive phased array systems. Thus, much effort has been invested into addressing these challenges. This dissertation aims to greatly improve the feasibility of traditional phased arrays by eliminating the array backend (the main source of cost and complexity). Specifically, we introduce a traveling wave array (TWA) concept using a single feedline whose propagation constant can be controlled to enable scanning. This is done using a small mechanical movement (<100mil) to adjust the feedline propagation constant. In this manner, the phase delivered to each element can be altered, enabling scanning. Of importance, beam steering is achieved with only one feed and one small mechanical movement (for any size linear array) without using individual phase shifters. Four specific TWA implementations are presented: 1) parallel plate waveguide (PPW) array, 2) trapezoidal wedge coplanar stripline (TWCPS) array, 3) vertical PPW array, and 4) metal PPW array. Each of these three TWAs is comprised of a 20+ element linear array with stable realized gain and low side lobe level (SLL) across -25°≤θ≤25° scanning range. This dissertation describes the design procedure for each TWA, including element, feed, termination, and aperture excitation. Fabrication procedures and challenges are provided. Fabrication for these unique TWA geometries is found to be a key challenge for the concept. Prototype measurements are compared to simulations. The dissertation culminates in the metal PPW array which overcomes many of the challenges encountered by the previous designs. The array achieves st (open full item for complete abstract)

Committee: John Volakis (Advisor); Chi-Chih Chen (Advisor); Christopher Baker (Committee Member) Subjects: Electrical Engineering; Electromagnetics; Engineering

Master of Science, University of Akron, 2006, Physics

Dielectric materials have been widely used in electronic industry. Recently an oxide ceramic CaCu3Ti4O12 (denoted as CCTO) is reported to be very promising because it possesses a very high dielectric constant. However, further research on its dielectric properties indicates that this material has a high dielectric loss, which seriously blocks its practical application. In this work, pure CCTO ceramic, and two series of CCTO derivatives, i.e., “CCTO + CaTiO3” and “CCTO + MnO2” ceramics were prepared, and their phase assemblies, structure, dielectric properties, and conducting properties are studied. The relaxation mechanism was investigated for CCTO and its derivatives. It is for the first time revealed that the relaxation time follows the Vogel-Fulcher relation instead of the Arrhenius relation.

Committee: Ang Chen (Advisor) Subjects:

PHD, Kent State University, 2024, College of Arts and Sciences / Materials Science Graduate Program

The discovery of ferroelectric nematic liquid crystal (FNLC) was envisioned by Born already in 1916, but it was only 100 years later that Nishikawa et. al. and Chen et. al reported macroscopic polarization of 5-6 μC/cm^2 on newly synthesized highly polar (dipole moment of ~ 10 Debye) rod-shape molecules called DIO and RM734. Large number of researchers also reported very large ε~10^4 dielectric permittivity at 1 kHz. Our group began investigating FNLCs in 2020 on chiral RM734 and RT10011 synthesized by Prof Twieg in the Department of Chemistry and Biochemistry at KSU. Since then, supported by an NSF grant Twieg and his students synthesized over 100 FNLC materials that we have been characterizing by measuring their novel physical properties. My role in this group was to measure the ferroelectric polarization, dielectric permittivity , electro-optical properties and electric field-induced shift of phase transitions of newly synthesized FNLC materials. For this I have explored several ways to deduce the magnitude of the ferroelectric polarization using several geometries, learned dielectric spectroscopy, characterized the phase sequences of the materials using polarized optical microscopy (POM). After introduction and description of the experimental techniques I used, I will describe my experimental results in four chapters. Firstly, I will give a detailed analysis of about fifty FNLC materials that I have received to determine their phase sequences and the temperature dependencies of the ferroelectric polarization. I found that the measured polarization of materials with isotropic-nematic-ferroelectric nematic phase sequence has polarization that can be explained by their molecular dipoles, a large number of FNLC materials with direct isotropic-ferroelectric nematic transition, the measured polarization values are too high to explain based on the magnitude of their dipole moments. I will discuss possible reasons for these discrepancies. (open full item for complete abstract)

Committee: Antal Jákli (Advisor) Subjects: Materials Science

Master of Science in Electrical Engineering, University of Dayton, 2021, Electrical and Computer Engineering

Over the past decade, Additive Manufacturing (AM) has advanced as a novel manufacturing technique used to develop rapid prototypes for custom and complex geometries and multilayer devices in many different industries. Recent advances in emerging technologies such as dual-extrusion FDM 3D printing, along with newly introduced conductive polymer filament materials, have created the potential to use low-cost, readily available 3D printing methods to fabricate electronic devices on-the-fly in remote environments. This study explores the use of Protopasta conductive filament and various common thermoplastic filament materials (PLA, PP, PC) and an Ultimaker s5 Pro dual-extrusion FDM printer with high-resolution 0.25 mm diameter print nozzles to fabricate a fully-fused 50 mm x 50 mm plate capacitor. A maximum capacitance of 328 pF was measured with a 0.25 mm thick dielectric layer of extruded PLA. This demonstrates a 215% increase in capacitance when compared to measurements for a similar plate capacitor constructed with wrought sheet aluminum (104 pF) using the same dielectric material and thickness. An EVAL-AD5940 impedance analyzer was used to measure the capacitance with PLA, PP, and PC dielectric layers at 1 kHz, 5 kHz, 7.5 kHz, and 10 kHz. From these measurements, the dielectric constant of each material was calculated for a dielectric thickness of 1 mm, as follows: 1 kHz (PLA: 3.00, PP: 2.96, PC: 3.00); 5 kHz (PLA: 2.83, PP: 2.74, PC: 2.83); 7.5 kHz (PLA: 2.82, PP: 2.76, PC: 2.910; and 10 kHz (PLA: 2.39, PP: 2.63, PC: is 2.99).

Committee: Amy Neidhard-Doll Ph.D., P.E. (Committee Chair); Carrie Bartsch Ph.D. (Committee Member); Guru Subramanyam Ph.D. (Committee Member); Vamsy Chodavarapu Ph.D., P.E. (Committee Member) Subjects: Electrical Engineering; Engineering

Master of Science (M.S.), University of Dayton, 2020, Electro-Optics

As the range of applications for electro-optic materials continues to grow, so does the need to identify and characterize new materials with improved electro-optic responses. A promising electro-optic material which has yet to be widely utilized is Lead Magnesium Niobate-Lead Titanate (PMN-PT) ceramic. In an effort to better characterize and understand the material, this work employed FTIR spectroscopy to calculate the refractive index of PMN-PT over a wide range of optical frequencies. Through analysis of interference fringes, the dispersion curve is calculated between 10,500 cm-1 and 1200 cm-1 (approximately 955 nm and 8.3 μm) containing nearly two thousand data points with an assumed accuracy of three decimal places. Additionally, capacitance bridge analysis is used to characterize the effect of temperature on the dielectric constant of PMN-PT. Special attention is given to the relationship of refractive index and dielectric constant so that a temperature study of the dielectric constant can be used to infer additional physical characteristics of PMN-PT.

Committee: Paul McManamon Ph.D. (Advisor) Subjects: Electrical Engineering; Electromagnetics; Experiments; Materials Science; Optics; Physics

Doctor of Philosophy, Case Western Reserve University, 2021, Macromolecular Science and Engineering

This study focused on the investigation of electromechanical deformation and failure of monolithic and multilayered polymeric films when subjected to an instantaneous voltage using a needle-plane electrode setup. The first and the second chapters concentrated on the electromechanical deformation on monolithic films, including polycarbonate (PC), poly (vinylidene fluoride (PVDF), polystyrene (PS), polypropylene (PP) and high-density polyethylene (HDPE). The third chapter focused on the effect of layer thickness on the electromechanical deformation of PC/PVDF multilayered films. The strong effect of scaling, layer thickness, was elucidated on the complex damage mechanisms. In Chapter One, electrically induced mechanical stress was applied on monolithic PC films. Three different experimental methods were used to investigate the electrically induced mechanical deformation on the glassy PC film, namely, morphological observation, energy loss analysis, and dielectric hysteresis. The PC film exhibited reversible elastic behavior at electric field below 200 MV/m, showing no indentation on the film surface. When the field was above 200 MV/m, an irreversible spherical indentation was created at the needle tip. Subsequent thermal annealing of the deformed film revealed a recoverable “delayed elastic” and an irreversible “plastic” deformation. A three-stage mechanism was proposed based on these experimental results, which includes the correlation between the energy loss and the deformed volume. Chapter Two investigated the electromechanical deformation on other polymers and compared with PC. The additional amorphous materials, PS, and two semi-crystalline materials, HDPE and PP, having dielectric constants all around 2.5, exhibited a similar onset of observable deformation. However, PVDF, having a dielectric constant of 12.0, showed an onset at very low electric field. The depth and diameter of the deformation for all polymers increased with increasing electric field. Th (open full item for complete abstract)

Committee: Eric Baer (Committee Chair); Lei Zhu (Committee Member); Gary Wnek (Committee Member); Ya-Ting Liao (Committee Member) Subjects: Materials Science; Plastics; Polymers

Doctor of Philosophy, Case Western Reserve University, 2020, Chemistry

Organic semiconductors have great potential for enabling cost-effective and flexible electronic products, such as organic photovoltaics (OPVs). However, many issues related to the intrinsic properties of organic semiconductors limit their device performance and progress towards commercialization. Understanding of the relationship between the device performance and molecular structure is needed for the design of better organic semiconductors. This thesis mainly focus on the design, synthesis and device characterization of organic semiconducting materials for OPV application. p-Type semiconducting polymers with high dielectric constant and n-Type semiconducting polymers by using azadipyrromethane (ADP)-based zinc complexes as electron deficient units were synthesized and characterized. Functionalized ADP-based zinc complexes were synthesized and their n-Type properties were studied in electronic devices. High dielectric constant (ɛr) organic semiconductors have the potential to further enhance device performance by promoting exciton dissociation, reducing bimolecular charge carrier recombination and potentially enhancing charge carrier mobility via charge-screening. In this work, a new class of semiconducting polymers (P1-P3) with high εr, i.e., sulfinylated and sulfonylated poly(3-alkylthiophene)s (P3ATs), were synthesized. High εr values were achieved for P1-P3(sulfinylated, sulfonylated and ester-sulfonylated P3ATs, respectively). For example, the ɛr at 1 MHz and room temperature increased from 3.75 for the regioregular poly(3-hexylthiophene) (P3HT) to 7.4 for P1, 8.1 for P2 and 9.3 for P3. These values are amongst the highest εr reported for conjugated polymers to date. Though the polar groups interfered with the long-range π-π stacking in the crystalline structure, P1 maintained favorable polythiophene π-π stacking structure and is promising for device applications. Zinc chelated ADP derivatives have been tested as n-type materials with poly(3-hexylthiophe (open full item for complete abstract)

Committee: Emily Pentzer (Committee Chair); John Protasiewicz (Committee Member); Lei Zhu (Committee Member); Ina Martin (Committee Member); Geneviève Sauvé (Advisor) Subjects: Chemistry; Materials Science

PhD, University of Cincinnati, 2018, Engineering and Applied Science: Chemical Engineering

The understanding of dielectric constant and its temperature and compositional dependencies for dielectric liquids at microwave frequency is needed in many important technologies such as microwave heating, microwave chemical synthesis, electric insulation, and electric device cooling, microwave sensing, and design and synthesis of alternative dielectric fluids, etc. However, there are limited effective techniques for fast and accurate measurement of liquid dielectric constants in high frequency ranges. The technical issues of the current dielectric constant measurement technologies may include the requirement of repeated calibrations, complicated sample preparation, costly precision device fabrication, challenging control of operation conditions, and limited testing frequency ranges. From fluid thermodynamics standpoint, because the molecular interactions and interfacial phenomena in signal phase or multiphase mixtures can significantly influence the fluid permittivity under electromagnetic fields, the overall volumetric and weight fractions are inefficient for correlating the mixture dielectric properties. Therefore, the conventional mixing rules that are established based on the Clausius-Mossotti model are often ineffective in representing the compositional dependencies of dielectric constants for highly non-ideal liquid mixtures. This dissertation deals with (1) the establishment of a novel metal-ceramic coaxial cable Fabry-Perot interferometer (MCCC-FPI) sensor platform and the physical model of its sensing operation, (2) demonstration of the new MCCC-FPI sensor for measuring dielectric constants of liquid fluids in a wide frequency range of 1-6 GHz, (3) studies on dielectric constants of different types of liquid mixtures, and (4) establishment of a new mixing rule for improved correlation between dielectric constant and liquid composition. The dissertation work is also extended to measurement of dielectric constants of the nanoporous zeolite crystals under gas (open full item for complete abstract)

Committee: Junhang Dong Ph.D. (Committee Chair); Yoonjee Park Ph.D. (Committee Member); Vesselin Shanov Ph.D. (Committee Member); Hai Xiao Ph.D. (Committee Member) Subjects: Chemical Engineering

Doctor of Philosophy, Case Western Reserve University, 2018, Chemistry

Organic solar cells (OSCs) that use carbon-based organic semiconductors are attractive alternatives to inorganic solar cells due to their unique properties such as easy processing, flexibility, and scalability. However, OSCs have not attained power conversion efficiencies (PCEs) as high as silicon solar cells. A fundamental understanding of the relationship between an organic semiconductor's chemical structure and its solar cell properties is needed to design new small molecules and polymers, and to optimize processing conditions. In this dissertation, zinc(II) azadipyrromethene (Zn(ADP)2)-based complexes and functionalized poly(3-hexylthiophene) (P3HT) were investigated as potential organic semiconductors for organic electronics. The Sauve group demonstrated that the zinc(II) azadipyrromethene complex with phenylethynyl pyrrolic substituents (Zn(WS3)2) is a promising electron acceptor for OSCs. While this acceptor worked well with P3HT as the donor, it did not work well with other state-of-the-art electron donors. That is because most donors were optimized to phenyl-C61-butyric acid methyl ester's (PCBM) energy levels, which are lower than those of Zn(WS3)2. To deepen the energy levels of Zn(WS3)2, fluorine atoms were installed in different positions (Zn(L1-L4)2). In this dissertation, the organic photovoltaic (OPV) device performances of these fluorinated complexes were evaluated in blends with P3HT. PCEs for three out of the four complexes increased compared to Zn(WS3)2, and the highest PCE of 3.7% was obtained with fluorine in the pyrrolic position. Charge carrier mobilities showed all fluorinated acceptors (except for one) had higher mobilites and recombination studies revealed that fluorine suppressed bimolecular recombination. Interestingly, the electrochemical properties and resulting estimated energy levels of the fluorinated complexes were not as deepened as anticipated. Therefore, another popular electron withdrawing gro (open full item for complete abstract)

Committee: Genevieve Sauve Ph.D. (Advisor); Anna C. Samia Ph.D. (Committee Chair); Carlos E. Crespo-Hernandez Ph.D. (Committee Member); Emily B. Pentzer Ph.D. (Committee Member); Ina T. Martin Ph.D. (Committee Member) Subjects: Chemistry

Master of Science (MS), Wright State University, 2012, Physics

A new technique to obtain local dielectric constant of thin films was developed using atomic force microscopy system. This technique, in addition to other characterization methods such as AFM imaging and X-Ray diffraction, was used to study, as an example, dielectric constant of thin films of 0.3BiScO3 - 0.7BaTiO3. The thin films were fabricated by using pulsed laser deposition technique under following temperature of the substrate: 6500C, 7000C and 7500C. At each temperature, two different oxygen pressures were used in deposition chamber: 50 mTorr and 100 mTorr. Our goal was to find optimal growth conditions with the highest dielectric constant and compare it with their structural properties. In addition, our dielectric constant calculations were generalized to include a wider range of film thicknesses.

Committee: Gregory Kozlowski PhD (Advisor); Douglas Petkie PhD (Other); Gary Farlow PhD (Committee Member); Ivan Medvedev PhD (Committee Member); Gregory Kozlowski PhD (Committee Member) Subjects: Physics

PhD, University of Cincinnati, 2003, Engineering : Electrical Engineering

In this research, a unique fabrication technology to build high-aspect-ratio via interconnects in 3D MMIC multilayer integration was developed from a combination of microelectronic and traditional MEMS microfabrication technologies. Based on these techniques, a set of test structures have been successfully fabricated to facilitate the vertical interconnect characterization. Fully cured polyimide thin films possess favorable electric and mechanical properties for the 3D MMIC applications. Using quarter wavelength T-junction resonator structure, polyimide was characterized for its microwave properties. High-frequency characterization of polyimide thin films was obtained in a wide frequency range. Experimental results have shown the feasibility of this method. In order to correctly evaluate the conductor loss in thin planar transmission lines, a modified conductor loss model was derived from conventional Wheeler's incremental inductance rule to account for the field penetration as the physical strip thickness approaches the skin depth or even smaller. The closed-form formulas or simplified equations have been developed for microstrip and stripline with wide strip cases, and for general coplanar waveguide including SCPWG line. Meanwhile, experimental results verified the validity of the modified conductor loss model in evaluating the losses in thin transmission lines. It has been shown that as the conductor thickness becomes approximately greater than four times of the skin depth, both conventional Wheeler's rule and its modified model agree with each other very well on the conductor loss estimation. Experimental results have revealed that at RF frequency, e.g. X band (8-12 GHz), the vertical interconnection discontinuities may contribute significantly to the insertion loss and the phase change. With the advanced conductor loss models for evaluating the characteristics in the test structures, lumped-element equivalent circuit models can be derived from the via module me (open full item for complete abstract)

Committee: Dr. Altan Ferendeci (Advisor) Subjects:

Doctor of Philosophy, The Ohio State University, 2003, Physics

We discuss the effective macroscopic properties of inhomogeneous materials, such as composite or polycrystalline media, ferromagnetic domain structures and inhomogeneous superconductors. In particular, we use Bergman's spectral theory to analyze the effects of disorder on a periodic composite system such as a colloidal crystal; we further extend that spectral theory to describe polycrystalline media and use that extension to analyze the third-order nonlinear response of a polycrystalline material. For the problem of inhomogeneous materials in an external magnetic field, we demonstrate that in certain 3-constituent composites the Hall effect in the metallic component can lead to either saturating or non-saturating effective magnetoresistance, depending on the constituent volume fractions; we identify and study the percolation problem discriminating between those two cases. We also demonstrate that metallic ferromagnets can exhibit negative magnetoresistance originating from the changes in the magnetic domain structure; we suggest quantitative models describing this behavior for some domain structure geometries. For superconducting media, we demonstrate that inhomogeneities in the magnitude of the order parameter lead to an additional absorption at finite frequencies, and develop sum rules for this absorption for a number of possible models. We then discuss how the fast suppression of the superconductivity in Zn-doped YBa 2 Cu 3 O 7-δ can be described by a simple percolation model based on the local suppression of the order parameter in the regions surrounding Zn atoms. We also discuss how those various changes in the magnitude of the order parameter affect the nonlinear properties such as the intermodulation current. Finally, in the last chapter we consider a problem that is somewhat complimentary to the other problems discussed in this thesis, and analyze the origin of inhomogeneities in the Mg 1-x Al x B 2 at certain Al concentrations. We use the results of ab init (open full item for complete abstract)

Committee: David Stroud (Advisor) Subjects: Physics, Condensed Matter

PHD, Kent State University, 2009, College of Arts and Sciences / Chemical Physics

Mixtures are prepared from a thermotropic nematic liquid crystal, E7, surfactant and organic fluid for the purposes of creating a high dielectric constant, low loss material. The mixtures prepared have much better dielectric properties than the individual components. The surfactants studied included the traditional surfactant Didodecyldimethyl ammonium bromide DDAB and triblock polymers. The two organic fluids used are N-Methyl Formamide (NMF) and 1-Methyl 2 Pyrrolidione (NMP). The complex dielectric permittivities of these mixtures are studied at room temperature at frequencies between 0.01Hz and 1MHz. The mixtures and composites of these mixtures with polymers have low loss and high permittivity. The effect of conductor-dielectric interface, surfactant chain length, and surfactant mixing are also reported. Representative permittivies of 280 for mixtures containing low molecular weigh surfactants and 217 for mixtures containing high molecular weight surfactants.

Committee: Liang Chien PhD (Advisor); Michael Fisch PhD (Advisor); Antal Jakli PhD (Committee Member); Dengke Yang PhD (Committee Member); Mikhail Chebotar PhD (Committee Member) Subjects: Materials Science; Physics

PhD, University of Cincinnati, 2013, Engineering and Applied Science: Materials Science

Barium titanate is one of the most extensively studied dielectric and ferroelectric ceramic, continuing to be the material of choice for many applications. Its use as a dielectric for capacitors, thermisters, piezoelectric transducers and memory devices are well known. This research reveals that exceptionally high dielectric constants and other attributes desired for electronic and energy storage device applications are achievable by selected isovalent and aliovalent doping of barium titanate. Doping of barium titanate with Nd3+ and co-doping with Zr4+ is being studied to elucidate the complex interactions involved in the formation of grain boundary and surface barrier layers and other morphological characteristics. Observed dielectric relaxations of the system are related to charge compensation mechanisms and dielectric properties in terms of equivalent circuits, brick layer and Maxwell Wagner-Debye models. The perovskite structure of barium titanate admits either isovalent or aliovalent substitutions depending on dopant ionic radii. Isovalent substitutions generally modify the morphology of the ceramics and induce phase changes. Aliovalent substitutions, notably trivalent rare earth ions such as Nd, modulate electronic properties inducing semiconductivity at lower concentrations. At higher concentrations or under oxidizing conditions, ionic compensation retains insulation. The most remarkable feature observed in this study is the oxygen partial pressure driven solubility of Nd in barium titanate at intermediate dopant concentrations, generating surface barrier layer morphologies with gradient variations in Ti3+ from surface to the interior, exhibiting complex relaxation mechanisms. The study confirmed that macroscopic barrier layers over the sample surface and microscopic barrier layers in the grain boundaries profoundly influence dielectric properties, offering avenues for developing materials of high dielectric constant, low loss and good stability. Nd2O3 do (open full item for complete abstract)

Committee: Relva Buchanan Sc.D. (Committee Chair); Rodney Roseman Ph.D. (Committee Member); Jainagesh Sekhar Ph.D. (Committee Member); Vijay Vasudevan Ph.D. (Committee Member) Subjects: Materials Science