Philosophiae Doctor - PhD / This research study investigated the effectiveness of Peer Instruction (PI) in enhancing preservice teachers’ understanding of Electromagnetism I in a Nigerian college of education. PI as a research-based pedagogy was invented for the teaching of introductory science courses to large classes. Lectures in PI is made of short presentations on the main points, each followed by short conceptual questions known as ConcepTest, posed in a multiple-choice format, on the subject under discussion. Electromagnetism is a branch of Physics where students perform poorly at Colleges of Education in Nigeria. Electromagnetism I covers electrostatics, magnetostatics, current electricity, electrolysis, and capacitance. Each of these themes has different topics under it. Most students studying Electromagnetism I, cannot relate or connect what they learned in the classroom to real-world situations because they often learn by memorization (rote learning).

Reciprocity is a fundamental physical precept that governs wave propagation in a wide variety of physical domains. The various reciprocity theorems state that the response of a system remains unchanged if the excitation source and the measuring point are interchanged within a medium, and are closely related to the concept of time reversal symmetry in physics. Lorentz reciprocity is a fundamental characteristic of linear, time-invariant electronic and photonic structures with symmetric permittivity and permeability tensors. However, breaking reciprocity enables the realization of nonreciprocal components, such as isolators and circulators, which are critical to electronic, optical and acoustic systems, as well as new functionalities and devices based on novel wave propagation modes. Nonreciprocal components have traditionally relied on magnetic materials such as ferrites that lose reciprocity under the application of an external magnetic field through the Faraday Effect. The need for a magnetic bias limits the applicability of such approaches in small-form-factor Complementary Metal–Oxide–Semiconductor (CMOS)-compatible integrated devices. One of the main features of CMOS technology is the availability of high-speed transistor switches which can be turned ON and OFF, modulating the conductance of the medium. In this dissertation, a novel approach to break Lorentz reciprocity is presented based on staggered commutation in Linear Periodically-Time-Varying (LPTV) circuits. We have demonstrated the world’s first CMOS passive magnetic-free nonreciprocal circulator through spatio-temporal conductivity modulation. Since conductivity in semiconductors can be modulated over a wide range (CMOS transistor ON/OFF conductance ratio at Radio Frequency (RF)/millimeter-wave frequencies is as high as 103-105), commutated LPTV networks break reciprocity within a deeply sub-wavelength form-factor with low loss and high linearity. The resulting nonreciprocal components find application in antenna interfaces of wireless communication systems, connecting the Transmitter (TX) and the Receiver (RX) to a shared antenna. This is particularly important for full-duplex wireless, where the TX and the RX operate simultaneously at the same frequency band and need to be highly isolated in order to maintain receiver sensitivity. Multiple fully-integrated full-duplex receivers are demonstrated in this dissertation that best show the synergy between the physical concept and application-based implementations by using circuit techniques to benefit the system-level performance, such as TX-side linearity enhancement and co-design and co-optimization of the antenna interface and the RX and utilization of the multi-phase structure of our antenna interfaces for analog beamforming in multi-antenna systems. Finally, this dissertation discusses some of the fundamental limits of space-time modulated nonreciprocal structures, as well as new directions to build nonreciprocal components which can ideally be infinitesimal in size. A novel family of inductor-less nonreciprocal components including circulators and isolators have been demonstrated that achieve a wide tuning range in an infinitesimal form-factor. This family of devices combine reciprocal and nonreciprocal modes of operation, through the transfer properties of fundamental and harmonics of the system and enable a wide variety of functionalities.

Surpassing the fundamental limits that govern all electromagnetic structures, such as reciprocity and the delay-bandwidth-size limit, will have a transformative impact on all applications based on electromagnetic circuits and systems. For instance, violating principles of reciprocity enables non-reciprocal components such as isolators and circulators, which find application in full-duplex wireless radios, radar, biomedical imaging, and quantum computing systems. Overcoming the delay-bandwidth-size limit enables ultra-broadband yet extremely-compact devices whose size is not fundamentally related to the wavelength at the operating frequency. The focus of this dissertation is on using time-variance as a new toolbox to overcome these fundamental limits and re-imagine circuit and system design. Traditional non-reciprocal components are realized using ferrite materials that loose their reciprocity under the application of external magnetic bias. However, the sheer volume, cost and weight of these magnet based non-reciprocal components coupled with their inability to be fabricated in conventional semiconductor processes, have limited their application to bulky and large-scale systems. Other approaches such as active-biased and non-linearity based non-reciprocity are compatible with semiconductor processes, however, they suffer from other poor linearity and noise performance. In this dissertation, using passive transistor switch as the modulating element, we have proposed the concept of spatio-temporal conductivity modulation and have demonstrated a gamut of non-reciprocal devices ranging from gyrators to isolators and circulators. Through novel circuit topologies, for the first time, we have demonstrated on-chip circulators with multi-watt input power handling, operation at high millimeter-wave frequencies, and tailor made circulators for emerging technologies such as simultaneous-transmit-and-receive MRI and quantum computing. Delay-bandwidth-size trade-off is another fundamental electromagnetic limit, that constrains the delay imparted by a medium or a device within a fixed footprint to be inversely proportional to the signal bandwidth. It is this limit that governs the size of any microwave passive devices to be inversely proportional to its operating frequency. As a part of this dissertation, through intelligent clocking of switched capacitor networks we overcame the delay-bandwidth-size limit, thus resulting in infinitesimal, yet broadband microwave devices. Here we proposed a new paradigm in wave propagation where the properties such as the propagation delay and characteristic impedance does not depend on the constituent elements/materials of the medium, but rather heavily rely on the user-defined modulation scheme, thereby opening huge opportunities for realizing highly-reconfigurable passives. Leveraging these concepts, we demonstrated wide range of reciprocal an non-reciprocal devices including ultra-compact delay elements, highly-reconfigurable microwave passives, ultra-wideband circulators with infinitesimal form-factors and dispersion-free chip scale floquet topological insulators. Application of these devices have also been evaluated in real-world systems through our demonstrations of wideband, full-duplex receivers leveraging switched capacitors based true-time-delay interference cancelers and floquet topological insulator based antenna interfaces for full-duplex phased-arrays and ultra-wideband beamformers. Furthermore, to cater the growing RF and microwave needs of future, large-scale quantum computing systems, we demonstrated a low-cryogenic, wideband circulator based on time modulation of superconducting devices. This superconducting circulator is expected to operate alongside the superconducting qubits, inside a dilution refrigerator at 10mK-100mK, thus enabling a tightly integrated quantum system. We also presented the design and implementation of a cryogenic-CMOS clock driver chip that will generate the clocks required by the superconducting circulator. Finally, we also demonstrated the design and implementation of a low-noise, low power consumption, 6GHz - 8GHz cryogenic downconversion receiver at 4K for cryogenic qubit readout.

Variational principles in classical fluid mechanics and electromagnetism have sprinkled the literature since the eighteenth century. Even so, no adequate variational principle in the Eulerian description of matter was had until 1968 when an Eulerian variational principle was introduced which reproduces Euler's equation of fluid dynamics. Although it successfully produces the appropriate equation of motion for a perfect fluid, the variational principle requires imposition of a constraint which was not fully understood at the time the variational principle was introduced. That constraint is the Lin constraint. The Lin constraint has subsequently been utilized by a number of authors who have sought to develop Eulerian variational principles in both fluid mechanics and electromagnetics (or plasmadynamics). How-ever, few have sought to fully understand the constraint. This dissertation first reviews the work of earlier authors concerning the development of variational principles in both the Eulerian and Lagrangian nomenclatures. In the process, it is shown rigorously whether or not the Euler-Lagrange equations which result from the variational principles are equivalent to the generally accepted equations of motion. In particular, it is shown in the case of several Eulerian variational principles that imposition of the Lin constraint results in Euler-Lagrange equations which are equivalent to the generally accepted equations of motion. On the other hand, it is shown that neglect of the Lin constraint results in Euler-Lagrange equations restrictive of the generally accepted equations of motion. In an effort to improve the physical motivation behind introduction of the Lin constraint a new variational constraint is developed based on the concept of surface forces within a fluid. The new constraint has the advantage of producing Euler-Lagrange equations which are globally correct whereas the Lin constraint itself allows only local equivalence to the standard classical equations of fluid motion. Several additional items of interest regarding variational principles are presented. It is shown that a quantity often referred to as "the canonical momentum" of a charged fluid is not always a constant of the motion of the fluid. This corrects an error which has previously appeared in the literature. In addition, it is demonstrated that there does not exist an unconstrained Eulerian variational principle giving rise to the generally accepted equations of motion for both a perfect fluid and a cold, electromagnetic fluid.

Terahertz (THz) reflection and transmission spectroscopy is a promising new field with applications in imaging and illicit material detection. One particularly useful application is for the detection of improvised explosive devices (IEDs) which is a favorite weapon of global terrorists. Explosive materials have been shown to have a unique spectral signature in the THz band which can be used to identify the explosives. However, the initial measurements performed on the explosive samples do not account for the modulation of the spectral features by random scattering that will be prevalent with actual samples encountered in applications. The intent of this work is to characterize and quantify the effects of random scattering that may alter the spectral features. Specifically, the effect that a randomly rough surface and granular scattering has on the scattered THz wave (T-Rays) will be investigated and characterized using the Finite-Difference Time-Domain (FDTD) simulation method. The FDTD method is a natural choice for this work as it can handle complicated geometries (i.e., multiple scatterers, arbitrarily rough interfaces, etc.) arbitrary materials (i.e., dispersive media, etc.) and provides broadband frequency data with one simulation pass. First, the effect that the randomly rough surface of the sample explosive has on the extracted spectral signature will be studied using a Monte-Carlo analysis. Then the effect of the complex structure inside the explosive material (the granular scatterers) will be considered. Next, when the physics of the rough surface and granular scattering are understood, a robust method to extract the spectral signature from the reflected T-rays will be developed.

Vibration energy harvesting has been widely investigated by academia and industry in the past decade with focus on developing distributed power sources. One of the prime goals of energy harvesters is to provide power to wireless sensors allowing for the placement of these sensors in the remote and inaccessible areas where battery is not an option. Electromechanical modeling approaches have been developed for enhancing the mechanical to electrical conversion efficiencies utilizing electromagnetic, piezoelectric, and magnetostrictive mechanisms. Models based upon the constitutive equations for these three conversion mechanisms, supported by extensive experimental results available in literature, suggest that power requirement through energy harvesters can be met only when the total volume is in the range of 1-100 cm3. There exists a critical volume of 0.5 cm³ at which above which the electromagnetic mechanism exhibits higher power density as compared to the other mechanisms. Therefore, in this thesis electromagnetic energy conversion was adopted to develop high power energy harvesters. We also present a novel vibration energy harvesting method which rivals the power density and bandwidth of the traditional methods. The overarching theme throughout the design process was selecting the structure and fabrication methodology that facilitates the transition of the technology. The experimental models were characterized at accelerations and frequencies typically found in the environmental vibration sources. The thesis provides in-depth the design, modeling, and characterization of a vibration energy harvester which creates relative motion differently than the conventional harvesters. Conventional designs rely on amplifying the original source displacement operating at the resonance condition. In the harvester design proposed in this thesis, the relative motion is created by cancelling the vibration at one location and transferring the source vibration directly to another location by combining a vibration isolator with a vibration absorber. In this novel configuration, termed as Direct Vibration Harvester (DVH), the energy is harvested directly from the vibrating source mass rather than a vibrating seismic mass attached to the source increasing the harvesting bandwidth and power density. Four bar magnet and magnetic levitation architectures were modified and modeled to reach closer to the theoretical maximum power densities. Extensive FEM was utilized to understand the performance limitations of the existing structures and the results from this analysis paved the pathway towards the development of the DVH. �A comparative analysis of the performance of the DVH with the traditional harvesting methods in terms of normalized power output and bandwidth was conducted. Performance improvements of DVH required development of the high efficiency rotational generators as linear to rotational conversion occurs in the DVH. The optimized rotational generator was modeled and all the predicted performance metrics were validated through experiments. The generator was applied towards the fabrication of DVH and also in a micro windmill. The power density of the micro windmill was found to be better than all the other results reported in literature. Extensive fluid and structural modeling was conducted to tailor the performance of the micro windmill in the desired wind speed range. Combined, this thesis provides significant advancement on many fronts. It pushes the magnetic levitation and four-bar mechanism harvester systems to their theoretical limits. It demonstrates a novel direct vibration harvester that has the possibility of surpassing the power density and bandwidth of all the known vibration harvester with large magnitude of output power. It provides a design process for an efficient small scale electromagnetic generator that can form for the backbone of many rotational and linear harvesters. This generator was used to develop the world's highest power density micro windmill in the small wind speed range. / Ph. D.

Over the past decades, integrated photonics has revolutionized the way we generate and manipulate light, employing micro- and nanoscale structures to shrink full optical systems into chips smaller than a fingernail. By leveraging the infrastructure of semiconductor foundries and fabrication processes, the development and deployment of integrated photonic technologies has been greatly accelerated. The main focus has been in applications for infrared light, such as optical interconnects and communication. Nevertheless, photonic integrated circuits (PICs) have quickly found applications in many other fields, including sensing, ranging, imaging, quantum technologies, biomedicine, spectroscopy, microwave generation, astrophysics, and displays. However, many of these technologies require light at visible wavelengths, where PIC technology is still in its infancy. Visible-light photonics presents several additional and stricter challenges when compared the infrared portion of the spectrum. First, laser sources are not as developed or available. Second, the sensitivity of devices to fabrication variations and the coupling losses are intensified. Third, the range of transparent materials available for waveguiding is more limited, and their technology is not as mature. Lastly, techniques that work well in the infrared spectrum are not as effective in the visible range due to the remarkably different material properties in this spectral window.In this thesis, we explore integrated photonics in the visible spectrum and focus on solving two of its main challenges: the lack of high-performance laser sources, and the high losses of PICs. We develop a low loss, high-confinement silicon nitride (SiN) platform and use it to demonstrate high-performance visible-light lasers from near-ultraviolet (near-UV) to near-infrared (near-IR), to probe the limits of absorption and scattering across the visible spectrum, and to generate multi-octave frequency combs with simultaneous infrared and visible light of all colors of the rainbow. Since our SiN platform is compatible with current photonic foundries, our work lays the foundation for fully-integrated, dense and scalable visible-light PIC systems that combine high-performance lasers and ultra-low loss devices. We envision such chip-scale platform to not only transform existing technologies, but to also enable a whole new generation of applications that have so far been impossible, causing tremendous impact in science, medicine and industry.

No description available.

A numerical approach to including electromagnetism with general relativity is developed using GRAXI as a starting point. We develop a mathematical model describing electromagnetism coupled to a scalar field in an evolving axisymmetric spacetime. As there are numerous formulations of electromagnetism, we evalute different formulations in a limited flat space case. The full curved space system is then developed, using the flat case as a guide to implementing electromagnetism. This model is then implemented using GRAXI as a code base.

Mesoscale optical phenomena occur when light interacts with a number of different types of materials, such as biological and chemical systems and fabricated nanostructures. As a framework, mesoscale optics unifies the interpretations of the interaction of light with complex media when the outcome depends significantly upon the scale of the interaction. Most importantly, it guides the process of designing an optical sensing technique by focusing on the nature and amount of information that can be extracted from a measurement. Different aspects of mesoscale optics are addressed in this dissertation which led to the solution of a number of problems in complex media. Dynamical and structural information from complex fluids—such as colloidal suspensions and biological fluids—was obtained by controlling the size of the interaction volume with low coherence interferometry. With this information, material properties such as particle sizes, optical transport coefficients, and viscoelastic characteristics of polymer solutions and blood were determined in natural, realistic conditions that are inaccessible to conventional techniques. The same framework also enabled the development of new, scale-dependent models for several important physical and biological systems. These models were then used to explain the results of some unique measurements. For example, the transport of light in disordered photonic lattices was interpreted as a scale-dependent, diffusive process to explain the anomalous behavior of photon path length distributions through these complex structures. In addition, it was demonstrated how specialized optical measurements and models at the mesoscale enable solutions to fundamental problems in cell biology. Specifically, it was found for the first time that the nature of cell motility changes markedly with the curvature of the substrate that the cells iv move on. This particular work addresses increasingly important questions concerning the nature of cellular responses to external forces and the mechanical properties of their local environment. Besides sensing of properties and modeling behaviors of complex systems, mesoscale optics encompasses the control of material systems as a result of the light-matter interaction. Specific modifications to a material’s structure can occur due to not only an exchange of energy between radiation and a material, but also due to a transfer of momentum. Based on the mechanical action of multiply scattered light on colloidal particles, an optically-controlled active medium that did not require specially tailored particles was demonstrated for the first time. The coupling between the particles and the random electromagnetic field affords new possibilities for controlling mesoscale systems and observing nonequilibrium thermodynamic phenomena.