Doctor of Philosophy, Case Western Reserve University, 2005, Physics

Short pulse tunable sources in the mid-infrared optical region have been an indispensible tool of research for several years. Yet the complexity of these systems limits their usefulness in many applications. In this study, pulse compression in a synchronously pumped optical parametric oscillator (SPOPO) is investigated as an alternative to these systems. Although pulse compression has been known for several years, a full understanding of the process has not been developed. This has inhibited its full exploitation. In this work, a search of the input parameter space is conducted in order to illucidate the mechanisms involved in pulse compression. The experiments conducted correlated compression to the input energy, optical parametric oscillator (OPO) wavelengths, and OPO cavity length detuning. The 10 ps pump pulses from a pulsed Nd:YAG laser interact in the parametric oscillator to generate infrared output pulses as short as 400 fs—a 20 fold compression. Experiments indicate that the compression varies directly with the input energy and inversely with the signal-idler group velocity mismatch (GVM) across the 2.5 – 4.0μm spectral range. It is also found that the cavity detuning length affected the dynamics of the nonlinear interaction. To gain physical insight into the experimental findings, numerical modeling is employed. Using nominal values for the input parameters, it is found that the model predicts the compression within about 30% and accurately predicts the input energy and signal-idler GVM trends. This agreement is then the basis for employing the model to extract physical insight into the compression mechanism. The dependence of compression on the signal-idler GVM is found to be more than an order of magnitude stronger than the signal-pump GVM usually thought to be responsible for the pulse compression. The model further predicts that using a 1 ps pump source should yield pulses on the order of 50 fs and that strong pulse compression could also be observed i (open full item for complete abstract)

Committee: Kenneth Singer (Advisor) Subjects:

Doctor of Philosophy in Clinical-Bioanalytical Chemistry, Cleveland State University, 2018, College of Sciences and Health Professions

Hyperspectral imaging is a set of techniques that has contributed to the study of advanced materials, pharmaceuticals, semiconductors, ceramics, polymers, biological specimens, and geological samples. Its use for remote sensing has advanced our understanding of agriculture, forestry, the Earth, environmental science, and the universe. The development of ultra-compact handheld hyperspectral imagers has been impeded by the scarcity of small widefield tunable wavelength filters. The widefield modality is preferred for handheld imaging applications in which image registration can be performed to counter scene shift caused by irregular user motions that would thwart scanning approaches. In the work presented here an electronically tunable widefield wavelength filter has been developed for hyperspectral imaging applications in the visible and near-infrared region. Conventional electronically tunable widefield imaging filter technologies include liquid crystal-based filters, acousto-optic tunable filters, and electronically tuned etalons; each having its own set of advantages and disadvantages. The construction of tunable filters is often complex and requires elaborate optical assemblies and electronic control circuits. I introduce in the work presented here is a novel widefield tunable filter, the surface plasmon coupled tunable filter (SPCTF), for visible and near infrared imaging. The SPCTF is based on surface plasmon coupling and has simple optical design that can be miniaturized without sacrificing performance. The SPCTF provides diffraction limited spatial resolution with a moderately narrow nominal passband (<10 nm) and a large spurious free spectral range (450 nm-1000 nm). The SPCTF employs surface plasmon coupling of the ϖ-polarized component of incident light in metal films separated by a tunable dielectric layer. Acting on the ϖ-polarized component, the device is limited to transmitting 50 percent of unpolarized incident light. This is higher than the through (open full item for complete abstract)

Committee: John Turner II, PhD (Committee Chair); David Ball PhD (Committee Member); Mekki Bayachou PhD (Committee Member); Baochuan Guo PhD (Committee Member); Petru Fodor PhD (Committee Member) Subjects: Analytical Chemistry; Chemistry; Electromagnetism; Optics; Physics

Doctor of Philosophy (Ph.D.), University of Dayton, 2024, Electro-Optics

Tunable optical filters play a crucial role in various applications including telecommunications, spectroscopy, and sensing. Among different approaches for achieving tunability, phase change materials (PCMs) have garnered significant attention due to their reversible transition between amorphous and crystalline states in response to external stimuli such as temperature, electric field, or optical irradiation. The unique optical properties of PCMs, such as changes in refractive index, transmission, and absorption, during phase transition enable the creation of dynamically reconfigurable optical devices. By integrating PCMs into photonic structures such as Fabry-Perot cavities, photonic crystals, or metamaterials, researchers have demonstrated tunable filters with capabilities ranging from spectral filtering to wavelength-selective switching. In this work we have developed the fundamental principles underlying the operation of PCM-based thin film tunable optical filters, and highlight the key considerations in material selection, device design, and integration. Additionally, we systematically explore the incorporation of PCMs in optical thin film designs, and analyze the performance and conceptual gaps in conventional approaches. This dissertation addresses the design, fabrication, and testing of tunable filters for a few select applications to showcase their utility. It also addresses the initial implementation of electrical switching for multilayer thin-film stacks.

Committee: Andrew Sarangan (Advisor); Partha Banerjee (Committee Member); Arka Majumdar (Committee Member); Keigo Hirakawa (Committee Member); Imad Agha (Committee Member) Subjects: Engineering; Optics

Master of Science (M.S.), University of Dayton, 2024, Chemical Engineering

There is a continuous thrust for cleaner and more sustainable alternatives for energy conversion with the increasing global energy demand. Among them, photovoltaics, specifically thin film solar cells are highly promising and are one of the fastest growing clean energy technologies in the United States. This research presents the synthesis and characterization of a set of novel multinary copper chalcogenide semiconductor nanocrystals (NCs), CuZn2ASxSe4-x consisting primarily of earth-abundant elements for applications in photovoltaic devices. A modified hot-injection method was used to synthesize these semiconductor NCs containing both S and Se chalcogens. The novelty of the new semiconductor NCs lies in the incorporation of multiple cations as well as two different chalcogen anions within the crystal lattice, which is an achievement from the materials synthesis aspect. The composition-controlled optical and photoluminescence properties of the CuZn2ASxSe4-x NCs were investigated via multi-modal material characterization including x-ray diffraction (XRD), ultraviolet-visible (UV-vis) spectroscopy, and photoluminescence spectroscopy (PL). The crystal structure, as determined from the XRD primarily consisted of the metastable wurtzite (P63mc) phase. The NCs exhibited direct band gap in the visible range that could be tuned both by varying the group III cation within the composition as well as the ratio of S/Se, based on the Tauc plot obtained from the UV-vis characterization. This work lays the groundwork for future investigations into the practical applications of copper chalcogenide NCs in solar energy conversion.

Committee: Soubantika Palchoudhury (Committee Chair); Guru Subramanyam (Committee Member); Robert Wilkens (Committee Member); Robert Wilkens (Committee Member); Guru Subramanyam (Committee Member); Kevin Myers (Advisor); Soubantika Palchoudhury (Committee Chair) Subjects: Aerospace Materials; Alternative Energy; Analytical Chemistry; Biochemistry; Chemical Engineering; Chemistry; Energy; Engineering; Environmental Science; Industrial Engineering; Information Science; Inorganic Chemistry; Materials Science; Nanoscience; Nanotechnology; Nuclear Chemistry; Nuclear Engineering

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)

Committee: Guru Subramanyam (Committee Chair); Hailing Yue (Committee Member); Robert Penno (Committee Member); Monish Chatterjee (Committee Member) Subjects: Electrical Engineering; Electromagnetics; Engineering; Materials Science

Master of Science (M.S.), University of Dayton, 2024, Electrical Engineering

With the rapid development of 5G technology and the explosive growth of the mobile industry, existing technologies have become increasingly mature. As a result, researchers and manufacturers are gradually focusing on designing more compact and cost-effective devices. The use of tunable devices is one of the promising technologies to achieve a compact size with few extra costs. In this thesis, a novel Sprout-Shaped Defected Ground Structure(DGS) and its tunable modification with thin film vanadium dioxide(VO2) are proposed. It has the advantage of compact size, clear in-band performance, and frequency tunability. The proposed single-stage structure provides -13.5 dB rejection at 4.008 GHz and has no harmonic before 10 GHz. With two-stage cascading, the rejection can be enhanced to -50.12 dB. This study also represents the tunable potential of the proposed DGS structure after modification, which can be tuned from the center frequency of 4.056 GHz to 5.987 GHz.

Committee: Guru Subramanyam (Committee Chair); Monish Chatterjee (Committee Member); Alex Watson (Committee Member); Guru Subramanyam (Advisor) Subjects: Electrical Engineering

PHD, Kent State University, 2023, College of Arts and Sciences / Materials Science Graduate Program

In imaging system, de-focus and astigmatism are the most common optical aberrations, and finding non-mechanical approach of correcting these aberrations is of great interest. Although non-mechanical correction of de-focus has been widely studied, astigmatism correction remains relatively unexplored. Motivated by this gap, this Ph.D. thesis focuses on the development of a new type of gradient refractive index (GRIN) liquid crystal (LC) lenses capable of non-mechanical correction of both astigmatism and de-focus. The proposed device consists of a stack of three electrically tunable cylindrical lenses that implement a concentric stripe electrode and segmented phase profile design. This system offers several advantages, including a simple, low-cost structure, a large aperture size (50 mm), low voltage drive, and a compact design. Compared to conventional mechanical approaches, this non-mechanical solution has significant potential for various applications such as wavefront correction in large telescopes, microscopy, augmented reality/virtual reality, and prescription eyeglasses. In the second part of the thesis, challenges associated with concentric electrode-based large aperture (50 mm) LC lenses with segmented phase profile designs are investigated, including haze-related and diffraction-related issues. Effective solutions are provided to enhance the optical quality of these lenses (reduction of fringing field effect with an insulator layer and inclusion of black mask). By addressing these challenges, a 50 mm aperture size electrically focus tunable LC spherical lens with enhanced optical quality is developed. The proposed tunable lenses exhibit lightweight (<2 g), slim (<2 mm), and compact flat designs with fast switching speeds (<750 ms) and low driving voltages (<5 V), making them suitable for important near-to-eye applications such as accommodation-convergence mismatch correction in augmented reality (AR)/virtual reality (VR) head-mounted displays (HMDs) and pr (open full item for complete abstract)

Committee: Philip Bos (Committee Chair); Liang-Chy Chien (Committee Member); Syed Shihab (Committee Member); John Portman (Committee Member); Deng-Ke Yang (Committee Member) Subjects: Chemical Engineering; Materials Science; Optics

PHD, Kent State University, 2023, College of Arts and Sciences / Materials Science Graduate Program

Waveguide liquid crystal display (WLCD) is a newly developed transparent display technology. Since polarizers and color filters are not necessary for the WLCD, high transparency is easily reached. A light-emitting diode (LED) is installed on the edge of the display and the produced light is coupled into the display. When no voltage is applied, the liquid crystal is uniformly aligned and is transparent. The incident light propagates through the display in waveguide mode due to the total internal reflection at the interface between the substrate and air, and no light comes out of the viewing side of the display. The display appears transparent. When a voltage is applied, the liquid crystal is switched to a micrometer-sized polydomain state and becomes scattering. The incident light is scattered out of the waveguide mode and comes out of the viewing side of the display. We developed a few methods to improve the performance of the waveguide display. First, by using patterned photo-polymerization or patterned ITO electrode, the scattering efficiency of the liquid crystal in the voltage-on state is significantly enhanced. Second, the spatial uniformity of the light intensity of the display is significantly improved by the light waveguide plate. Third, we achieved 8 inch full color transparent light waveguide LCD prototype that utilizes field sequential color (FSC) scheme to display full color images. Fourth, we developed a light waveguide LCD based on the flexoelectric effect using dimer, which exhibits high contrast ratio. Lastly, based on the flexoelectric effect we developed a reconfigurable liquid crystal diffraction grating whose diffraction angle and efficiency can be controlled by the applied voltage. The light waveguide liquid crystal transparent display has the merits of high contrast ratio, suitable driving voltage, and a sub-milli second ultrafast response time. It does not use polarizers and color filter as in conventional LCDs. It also has an ultrahigh tra (open full item for complete abstract)

Committee: Dengke Yang (Advisor); Philip J. Bos (Committee Member); Songping Huang (Committee Member); Sam Sprunt (Committee Member); Hiroshi Yokoyama (Committee Member) Subjects: Materials Science; Optics; Physics

Doctor of Philosophy (Ph.D.), University of Dayton, 2021, Electrical Engineering

Tunable passive rf/microwave devices are the building blocks of reconfigurable electronics. Barium Strontium Titanate (BST) based tunable devices are being studied over for two decades now and this technology is very mature. Researchers have tried different material compositions, substrates, and deposition techniques to increase the tunability of the BST thin films. Researchers have also demonstrated reconfigurable devices at rf/microwave frequencies, however with only limited applications. In this work a novel technique of integrating high tunable dielectric materials such as BST, in combination with a germanium telluride (GeTe) phase change material (PCM) is demonstrated. Integrating phase change material thin films with BST thin films gives additional tuning. The idea of integrating PCM with BST initiates a new era of reconfigurable electronics. These new devices can be implemented with very less fabrication constraints. A low loss rf switch with 0.23 dB insertion loss and more than 19.75 dB isolation at 15 GHz is presented. v An MIM varactor with increased tunability of about 6.3:1 (57%) is achieved, compared to 4:1 tuning of conventional varactor by integration of BST and GeTe thin films. Analog phase shifters with 360° phase shift in the frequency range of 24 GHz to 50 GHz has been demonstrated with good figure of merit (FOM) of 46.64 degrees/dB at 50 GHz and 19.07 degrees/dB at 24 GHz using MIM varactors with BST and GeTe thin films and 319° phase shift at 24 GHz with FOM 12.8 degrees/dB and more than 360° phase shift at 50 GHz with FOM(2V-10V) >21.5 degrees/dB using MIM varactor with only BST thin films. A defected ground structure (DGS) band stop filter with enhanced band-rejection behavior with a notch depth of -39.64 dB @ 27.75 GHz by cascading two-unit cells using BST thin films is achieved. Tunable DGS band stop filters were demonstrated by integration of BST and GeTe with 2.25 GHz tunability from 30.75 GHz to 33 GHz (7.32%) using a single filter a (open full item for complete abstract)

Committee: Dr. Guru Subramanyam (Advisor) Subjects: Electrical Engineering

Master of Science (M.S.), University of Dayton, 2021, Electro-Optics

Material characteristics and crystallinity of germanium antimony telluride (GST) using various design methods for simulation and fabrication are presented. Experimental verification of designs in the mid-infrared are presented for GST-Ag structures and amorphous-crystalline GST structures. Baking an amorphous state GST sample at 200°C for 2 minutes will produce a crystalline state GST which causes the refractive index to increase significantly. Gradually increasing the temperature of an annealed phase change material, such as GST, controls the amount of crystallinity which allows the index of refraction to increase continuously over a significant range. Changing the amorphous state optically allows a lithography-free grating device. The use of GST in these metasurface structures uncovers unique properties that cover transmittance of devices, diffraction orders and tunable optical filters that are angular independent.

Committee: Imad Agha (Committee Chair); Joshua Hendrickson (Committee Member); Shiva Vangala (Committee Member); Swapnajit Chakravarty (Committee Member) Subjects: Design; Electromagnetics; Optics; Physics

Doctor of Philosophy (Ph.D.), University of Dayton, 2021, Electro-Optics

Mode-locked oscillators are the building blocks to generate ultrafast pulses which can then be used for many applications, including optical communication, metrology, spectroscopy, microscopy, material processing, as well as many applications in the healthcare industry. Mode-locked fiber oscillators are especially popular for their compactness, efficiency, and beam quality compared to their solid-state counterparts such as Ti: Sapphire lasers. Apart from their practicality, the mode-locked fiber lasers are an interesting object for studies, as they represent dynamically rich nonlinear systems. For ultrafast fiber oscillators at normal dispersion, a spectral filter is the utmost important optical component that determines the behavior of these systems in terms of the spectral bandwidth, pulse duration, central wavelength of the output spectra, multipulse dynamics, pulse structure as well as pulse velocity. Recently, there is a growing interest in fiber based spectral filters as they facilitate the construction of all-fiber laser cavities. This dissertation investigates the laser performance parameters by developing an all-fiber spectral filter and exploiting its characteristics. Especially, this dissertation reports the first experimental observation of dissipative solitons of the complex Swift Hohenberg equation. This is very important as it births multiple future projects related to implementing higher order spectral filtering in mode-locked fiber lasers. Although most of the ultrafast oscillators in this dissertation are built at 1 μm, ideas to build mode-locked lasers at visible wavelengths are also presented along with primary numerical simulation and experimental results. Finally, all the upcoming research directions are discussed in detail.

Committee: Andy Chong Ph.D. (Committee Chair); Andrew Sarangan Ph.D. (Committee Member); Todd Smith Ph.D. (Committee Member); Imad Agha Ph.D. (Committee Member) Subjects: Electrical Engineering; Engineering; Optics; Physics

Master of Science in Electrical Engineering, University of Dayton, 2020, Electrical Engineering

Radio Frequency/Microwave filter is a key component that defines the performance of the front-end portion of the modern wireless communication system. A well-designed Radio Frequency/Microwave filter is able to select and pass/reject the frequency of the signals to be transmitted/received or attenuated with minimum added loss and interference. With the rapid development of wireless communication technologies, the modern handset device needs to integrate multiple technologies, services, and applications (LTE, Wi-Fi, Bluetooth, GPS, GNSS) covering the frequency spectrum from a few hundred megahertz to 7GHz, posing extreme challenges to the spectrum filtering functions and size reduction. The filters in the modern RF frontend are realized with filter banks, which means that each filter is dedicated to a certain frequency range for a specific service. On the other hand, filters with reconfigurable characteristics can be a good candidate to replace the traditional filter banks due to their flexibility, smaller size, and lower cost. The challenge from the current literature is the limited tuning capability and added filter losses from the tuning circuit. In this thesis, a 3rd order Chebyshev planar comb-line band-pass filter is designed at a center frequency of 1.5GHz with 20% fractional bandwidth, and 0.01 Ripple factor on a Microstrip substrate. Tuning capability is achieved by replacing the resonator-loaded capacitors with varactors. The final measurements show a tuning range from 1.45GHz to 1.71GHz, an insertion loss of 3.6dB, a return loss better than 10dB, and an out-of-band rejection better than 35dB. The size of the standalone comb-line filter is 20.8mm by 24.6mm, and the varactor-tuned filter with the biasing circuit is 63.5mm by 43.7mm. In wireless communication, the wider bandwidth allows the higher speed of signal transmission. And for tunable components, it is important to keep their performance constant. Compared to previously published works, this desig (open full item for complete abstract)

Committee: Hailing Yue (Committee Chair); Guru Subramanyam (Committee Member); Robert Penno (Committee Member) Subjects: Electrical Engineering

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

A new design methodology providing optimal mixed-mode operation for dual-input class-F outphasing Chireix amplifiers is presented. The design starts with single-transistor class-F simulations at the intrinsic I-V reference planes to directly select the optimal peak and backoff resistive loads Rmin and Rmax and input RF gate drives yielding the best combination of efficiencies and output powers without needing to perform a load pull simulation or measurement. New analytic equations expressed only in terms of Rmin and Rmax are given for designing the Chireix combiner at the current source reference planes. Nonlinear embedding is then used to predict the incident power and multi-harmonic source and load impedances required at the package reference planes to physically implement the power amplifier (PA). An analytic formula solely expressed in terms of Rmin and Rmax is reported for the peak and backoff outphasing angles required at the PA input reference planes. A Chireix outphasing PA designed with two 15-W GaN HEMTs exhibits a peak efficiency of 72.58% with peak power of 43.97 dBm and a 8-dB backoff efficiency of 75.22% at 1.9 GHz. Measurements with 10-MHz LTE signals with 9.6-dB PAPR yield 59.4% average drain efficiency at 1.9 GHz while satisfying the 3GPP linearity requirements. A novel frequency-agile PA designed with a modified class-J theory enforcing constant maximum and minimum instantaneous drain voltages for all frequencies is presented. The resulting high efficiency class-J mode which requires a reconfigurable drain supply exhibits clockwise fundamental and second harmonic load impedance trajectories versus frequency facilitating the PA design. This clockwise-loaded class-J (CLCJ) mode enables frequency-agile capability with enhanced efficiency when the proper drain supply voltage co-designed with the clockwise fundamental and harmonic loads is applied. A broadband power amplifier designed with a clockwise-loaded class-J theory is selected for demo (open full item for complete abstract)

Committee: Patrick Roblin (Advisor); Ayman Fayed (Committee Member); Waleed Khalil (Committee Member) Subjects: Electrical Engineering

Master of Science in Electrical Engineering, University of Dayton, 2020, Electrical Engineering

In this study, a novel BST varactor design is presented that was originally designed as a way to optimize the Quality Factor, (Q), through an extensive analysis of the physical parameters of a varactor that would perform in the 2 to 20 GHz range. However, through simulations, it was seen to have higher Q past 25 GHz after resonance. The novel design is presented for high tunability and with potential to have high Q in the millimeter wave frequencies. The study goes further to optimize the device through designing variations at different capacitance values from 1 pF to 0.06 pF and varying different physical parameters and seeing their effects on its Q. This study goes through design structure calculations, developing electrical models for the varactor designs and some fabrication results on the wafer tunability.

Committee: Guru Subramanyam Ph.D. (Committee Chair); Robert Penno Ph.D. (Committee Member); Monish Chatterjee Ph.D. (Committee Member) Subjects: Electrical Engineering; Engineering; Materials Science

Master of Science in Electrical Engineering, University of Dayton, 2020, Electrical and Computer Engineering

Demands for self-sustainable energy sources are rising as we become more and more reliable on electronic devices in our daily lives. Scientists and engineers have been exploring various novel methods to harvest energy from existing resources in order to eliminate or reduce the usage of battery and/or conventional power equipment. Solar, water, tide, wind, and terrestrial heat are renewable and green resources that have been widely adopted and commercialized[1]. With the rapid development of technology, more resources can be used for providing energy and compressing the size of devices. For example, piezoelectricity, vibration, and electromagnetic energy can also be used in the large-scale area[2]. Electromagnetic energy, especially in WIFI frequencies, is recently gaining more and more interest because of the wide signal coverage on campus and residential areas. An unique advantage of harvesting electromagnetic energy is its little dependence from weather related factors, unlike solar, water, tide, wind and terrestrial heat[3]. Given the circumstances, the interest in this work is to design a novel rectenna device to harvest energy from WIFI frequencies and to provide a parametric study in efficiency improvement. Our comfort and fast life in modern society roots in massive volumes of data exchange through wireless transmission. In modern communication systems, different radio spectrum's only use is for single media to prevent interference between users and different devices. International telecommunication Union (ITU) established rules to allocate spectrums for various purposes; the chart [4] shows specific distributions for mobile, broadcast, satellite, and other devices. Since antenna is the only component worked as receiver and transmitter in a device, the main problem in communication systems are the versatility of antenna. So, antenna with reconfigurability is desired in today's multi-band multi-mode communication system front end. The key solution is to wide (open full item for complete abstract)

Committee: Hailing Yue (Advisor) Subjects: Electrical Engineering; Electromagnetism

Master of Sciences, Case Western Reserve University, 2020, EMC - Mechanical Engineering

TCERA (Tunable Compliance Energy Return Actuator) is a biologically inspired robotic actuator which captures the variable stiffness properties of the human leg. This actuator emulates a femur-tibia system and uses two co-contracting air muscles as springs to alter the torsional stiffness about its knee axis. In human legs this mechanism, as well as the ability to store and return energy in the muscle-tendon system, allows for exemplary long distance locomotion capabilities. A central mechanism was designed that allows for dual actuator input which independently controls the system stiffness and the femur-tibia joint angle. This research presents the design of such an actuator, as well as the development of an Artificial Neural Network that is able to accurately control an otherwise complex dynamic system. Loading tests confirmed the desired elastic parameters and energy return characteristics of the system were achieved, and the controller was able to successfully navigate the stiffness-angle space.

Committee: Roger Quinn PhD (Committee Chair); Richard Bachmann PhD (Committee Member); Kathryn Daltorio PhD (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy (PhD), Wright State University, 2019, Electrical Engineering

Recent advanced radio frequency (RF) microwave device demands for low power consumption, light weight, compact package, and high performance. To achieve the high performance, applying magnetic materials is becoming indispensable in many of those devices. Thus, the role of magnetism in those devices is important high-quality magnetic materials not only improves the performance of microwave devices but also opens opportunities in developing novel concepts of devices utilizing spin wave excitation, non-reciprocal wave propagation, and the electromagnetic coupling in multiferroic materials. Among all the others, manipulating magnetic properties in multiferroic material started a couple years ago. Multiferroic materials are a group of materials that exhibit both ferrimagnetic and ferroelectric properties. By controlling its magnetic property such as ferromagnetic resonance, the low loss and tunable RF/Microwave electronics can be generated. However, the multiferroics currently under investigation suffer severely from the weak magnetoelastic effect in part due to the poor crystallinity, and in part due to the inappropriate materials chosen. Thus, the fabrication of high-quality ferrite and discovery of the suitable ferrite are paramount to apply in multiferroic material. In this research, we report a high-quality Yttrium Iron Garnet thin film and an unique Aluminum alloyed Nickel Zink Ferrite thin film. The former exhibits an extremely low magnetic damping factor, and the later show a larger magnetostriction coefficient. The microstructures of these films were characterized using X-ray diffraction, Atomic force microscopy, and transmission electron microscope. and - the magnetic properties -were characterized by Ferromagnetic Resonance. Additionally, we have observed the inverse spin-hall effect between magnetic and metal layer and demonstrated non-reciprocal wave propagation in a 20nm thin YIG film.

Committee: Yan Zhuang Ph.D. (Advisor); Marian K. Kazimierczuk Ph.D. (Committee Member); LaVern A. Starman Ph.D. (Committee Member); Michael A. Saville Ph.D. (Committee Member); Henry Chen Ph.D. (Committee Member) Subjects: Electrical Engineering

Master of Science in Engineering, University of Akron, 2019, Electrical Engineering

The first objective of this thesis is to explore an accurate two-scale homogenization technique of periodic electromagnetic structures or metamaterials having any number of dimensions. The fine-scale fields are approximated with a suitable set of basis functions in a unit cell. The coarse-grained field amplitudes are calculated as the boundary averages of the fine-scale fields. The effective material tensor is obtained in the least-squares sense. The proposed method accurately predicts the scattering parameters of a periodic layered medium, and of a 3-D plasmonic medium with any reasonable size and composition of the unit cell. A novel Bloch wave extraction procedure has been implemented for the 3-D case. A trade-off between the accuracy and the range of applicability of the effective material tensor has been discussed. In addition, metamaterials with resonating elements have been applied to dynamic beam steering. The resonators act as micro- or nano-antennas fed by a tunable metamaterial guide or metasurface. The novelty lies in the absence of any individual tuning circuitry for each resonator. Rather, a global control is effected by tuning the permittivity of the host material, or alternatively, by a multiguides concept. Optimized radiation profiles, and beam-scanning controlled in a dynamic fashion have been demonstrated.

Committee: Igor Tsukerman (Advisor); Nathan Ida (Committee Member); Nghi Tran (Committee Member) Subjects: Electrical Engineering

Master of Science (M.S.), University of Dayton, 2019, Electrical Engineering

Electroporation is a process that uses high voltage pulsed electric field to permeate cell membrane for drug infusion or cell death. Changing the voltage level, pulse period, or pulse width modifies the effect of the treatment. The purpose of this paper is to present a new alternative to high power pulsed field electric generators that, for the first time, reduces the system to a single custom complementary metal-oxide semiconductor (CMOS) chip, as well as allows various customizations in terms of frequency or duty cycle. A 206 kHz, 500V square wave was obtained from our chip design. The chip schematic simulation showed a duty cycle variation from 12.5% to 34.9%.

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

Doctor of Philosophy, The Ohio State University, 2019, Biomedical Engineering

Natural plant surfaces, such as lotus leaves, rice leaves, and rose petals, possess unique wetting properties. Lotus leaves contain hierarchic micro/nano-topographies with a waxy coating and exhibit isotropic and ultralow flow resistance. A water droplet can roll off the surfaces that are tilted at a small angle regardless of the tilting direction. Rose petals also own hierarchic micro/nano-topographies, but with larger characteristic dimensions. The petal surfaces possess a high water flow resistance and can pin small water droplets on the surfaces even if the surfaces are positioned vertically or upside down. On the other hand, the petal surfaces are superhydrophobic so that the droplets can move without leaving any residue. A rice leaf has linearly arranged micro/nanopapillae, which lead to anisotropic flow resistance that can move water droplets preferably along the alignment. In this dissertation, bioinspired smart surfaces are investigated to mimic the distinct wetting properties on natural plant surfaces. In-plane mechanical stretching of the smart surfaces can dynamically and repeatedly modulate the characteristic dimensions of the micro-wrinkles, and in turn switch the surface wetting properties. With proper hydrophobic treatment, the wetting properties of the smart surfaces can be switched between lotus-like and rose-like; or lotus-like and rice-like. The surface wetting states can also be changed from Cassie Baxter state to Wenzel state by mechanical straining. In order to validate the efficacy of the smart surfaces in biomedical applications, droplet-based open channel microfluidics, and strain activated drug release are established respectively. In particular, lossless droplet transfer, droplet splitting, and modulation of droplet mobility are demonstrated on the lotus-rose switchable smart surfaces. Dynamic modulation of wetting anisotropy is exhibited on the lotus-rice switchable smart surfaces. Mechanical strain activated stepwise drug releas (open full item for complete abstract)

Committee: Yi Zhao (Advisor); Derek Hansford (Committee Member); Jun Liu (Committee Member); Kubilay Sertel (Other) Subjects: Biomedical Engineering