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This thesis investigates and determines the design considerations to be addressed when designing switched reluctance machines (SRMs) operating at high surface-speeds and high-loads. A new method is introduced to the traditional machine design procedure that captures all of the mechanical, thermal and electro-magnetic considerations for such electric machines. This method is applicable to any motor design; however, is most suitable for machines with rotors that sustain mechanical stresses near the rotor core material limits. The method begins by using common application specifications to identify the maximum diameter and length of a rotor through a series of structural analyses. Maximizing rotor diameter and axial length enables designers to evaluate a machine's theoretical mechanical and electro-magnetic performance limits. The design method is structured such that the designer must use theoretical limits as a constraint for assessing future design decisions which ultimately influence machine cost and performance. The proposed design method is applied to a case study example typical of a large electric vehicle traction machine, a 22,000rpm, 150 kW switched reluctance machine, while attempting to adhere with design practices commensurate with automotive mass manufacturing. To achieve this, a parallel connected 12/8 pole topology was finally developed. The thesis research suggest that a 440 MPa yield strength, 0.27mm thickness lamination with 30 turn stator coils is sufficient to meet the specification requirements within a prescribed power electronic converter voltage and current constraints, while satisfying material mechanical and thermal considerations. Detailed analysis of AC effects, performance characteristics, thermodynamics, noise and vibration is presented to simultaneously demonstrate and validate the proposed machine design and design method. / Thesis / Doctor of Philosophy (PhD)

Terahertz region in the electromagnetic spectrum is the region between Infrared and Microwave. As the Terahertz region has both wave and particle nature, it is difficult to make a room temperature, fast, and sensitive detector in this region. In this work, we fabricated a Palladium based IR detector and a CNT based THz bolometer. In Chapter 1, I give a brief introduction of the Terahertz region, the detectors already available in the market and different techniques I can use to test my detector. In Chapter 2, I explain about the Palladium IR bolometer, the fabrication technique I have used, and then we discuss the performance of the detector. In Chapter 3, I explained about the Roll to Roll based THz bolometer, its working and fabrication techniques, and at the end we discussed its performance.

A new technique is presented to study radio propagation and rough surface scattering problems based on a reformulation of the Magnetic Field Integration Equation (MFIE) called the Single-Scatter Subtraction (S^3) method. This technique amounts to a physical preconditioning by separating the single- and multiple-scatter currents and removing the single-scattering contribution from the integral term that is present in the MFIE. This requires the calculation of a new quantity that is the kernel of the MFIE integral call the kernel integral or Gbar. In this work, 1-dimensional deterministically rough surfaces are simulated by surfaces consisting of single and multiple cosines. In order to truncate the problem domain, a beam illumination is used as the source term and it is shown that this also causes the kernel integral to have a finite support. Using the Single Scatter Subtraction method on these surfaces, closed-form expressions are found for the kernel integral and thus the single-scatter current for a well defined region of validity of surface parameters which may then be efficiently radiated into the far field numerically. Both the closed-form expressions, and the computed radiated fields are studied for their physical significance. This provides a clear physical intuition for the technique as an augmentation to existing ones as a bent-plane approximation as shown analytically and also validated by numeric results. Further analysis resolves a controversy on the nature of Bragg scatter which is found to be a multiple-scatter phenomenon. Error terms present in the kernel integral also raise new questions on the effect of truncation for any MFIE-based solution. Additionally, a dramatic enhancement of backscatter predicted by this new approach versus the Kirchhoff method is observed as the angle of incidence increases due to the error terms. / Doctor of Philosophy / A new technique is presented to study the interaction of electromagnetic waves with rough surfaces. Building on the technique called the Magnetic Field Integral Equation (MFIE) which allows the solution for the electromagnetic fields scattered from the surface by considering only the induced electric and magnetic currents on the surface, the Single-Scatter Substraction (S 3 ) method separates the surface currents into those that interact with the surface only once or single-scatter, and those that interact multiple times called multiple-scatter. Since this is the introduction of this technique, only the former is investigated. In this study, a new quantity which is an integral of one of the components of the standard MFIE is studied and closed-form approximations are presented along with bounds of validity. This provides closed form solutions for the single-scattering currents, from which the radiated fields may be efficiently found numerically. Since they are closed form, the expressions provide insight into the nature of the physical scattering process. Numerical results of these expressions are compared to the standard approximate technique as well as the ”exact” solution found by numerically solving the MFIE. Compared to the standard approximate technique which approximates the surface by a tangent plane at each point on the surface, the single-scatter currents approximate the surface with a bent-plane at each point. This shifts the scattered fields from certain directions to others, and highlights where single- and multiple-scattering have an effect.

Yes / Potential demodulating ability in biological tissue exposed to Radio Frequency (RF) signals intrinsically requires an unsymmetrical diode-like nonlinear response in tissue samples. This may be investigated by observing possible generation of the second harmonic in a cavity resonator designed to have fundamental and second harmonic resonant frequencies with collocated antinodes. Such a response would be of interest as being a mechanism that could enable demodulation of information-carrying waveforms having modulating frequencies in ranges that could interfere with cellular processes. Previous work has developed an experimental system to test for such responses: the present work reports an electric circuit model devised to facilitate calibration of any putative nonlinear RF energy conversion occurring within a nonlinear test-piece inside the cavity. The method is validated computationally and experimentally using a well-characterised nonlinear device. The variations of the reflection coefficients of the fundamental and second harmonic responses of the cavity due to adding nonlinear and lossy material are also discussed. The proposed model demonstrates that the sensitivity of the measurement equipment plays a vital role in deciding the required input power to detect any second harmonic signal, which is expected to be very weak. The model developed here enables the establishment of a lookup table giving the level of the second harmonic signal in the detector as a function of the specific input power applied in a measurement. Experimental results are in good agreement with the simulated results. / Engineering and Physical Science Research Council through Grant EP/E022936A

<p dir="ltr">Quantum photonics is one of the leading platforms to realize quantum information technologies. Quantum emitters embedded in host materials which can readily form photonic circuitry elements have received significant research interest in recent years for on-chip quantum information processing applications. In this work, we report on the discovery of bright, stable, and linearly polarized quantum emitters in SiN films with room temperature single photon generation. We suggest that the emission originates from a specific defect center in SiN because of the narrow wavelength distribution of the observed luminescence peak.</p><p dir="ltr">We further probe these emitters’ fundamental photophysical properties through measurements of optical transition wavelengths, linewidths, and photon antibunching as a function of temperature. Important insight into the potential for lifetime-limited linewidths is provided through measurements of inhomogeneous and temperature-dependent broadening of the zero-phonon lines. At 4.2K, spectral diffusion was found to be the main broadening mechanism, while spectroscopy time series revealed zero-phonon lines with instrument-limited linewidths.</p><p dir="ltr">Along with the optical properties of the quantum emitters, we study their formation mechanisms by investigating the effects of sample composition and thermal annealing parameters. From these measurements, we gain critical insight into the fundamental nature of the quantum emitters in SiN, as well as the dependence of their photophysical properties on the changes in the host material. Additionally, we explore alternative SiN fabrication approaches and the optical properties of the SiN films developed with these techniques. We then investigate quantum emitter formation and hypothesize why the optical properties of the defects in each type of film differ.</p><p dir="ltr">Finally, we begin preliminary investigations into the possible existence of near-infrared (NIR) emitting defects in SiN, as well as single-photon electroluminescence from thin SiN-on-silica films embedded in p-n heterojunctions.</p><p dir="ltr">The single-photon emitters in SiN we have studied extensively in this work have the potential to enable scalable and low-loss integration of quantum light sources with a mature on-chip photonics platform.</p>

The widespread adoption of photovoltaic (PV) and electric vehicle (EV) technologies is crucial for mitigating greenhouse gas emissions. A Multi-Port Converter (MPC) connects multiple PV panels, improving efficiency and reducing costs. In EVs, MPCs extend battery lifespan by adding energy sources, enhancing system quality beyond reliance on Li-ion batteries. This dissertation proposes a Quad-input LLC topology for PV microinverters. It utilizes a single LLC resonant tank and two Y switches configurations. An MPPT control strategy based on Perturb and Observe (P&O) method ensures independent MPPT for each panel. The zero-voltage switching (ZVS) is achieved across all switches for wide input range and load variations. A 500W prototype validates the operation, achieving peak efficiency of 94.3% with individual MPP tracking. Also, a high gain DC-DC converter for hybrid inverter is proposed. The proposed converter can be used in the PV panel level for hybrid inverter where the low voltage of PV must be increased to DC-link voltage. The proposed converter uses two inductors connected either in series or parallel during discharge or charge mode. The designed hybrid system based on this high gain converter has three ports that can be connected to PV, battery, and grid/ac load. In addition, a bidirectional hybrid DC-DC converter (BHDC) is proposed for hybrid energy storage systems in electric vehicles. The converter can connect both batteries and supercapacitors to the DC-link. With a wide voltage-gain range, low voltage stress on power switches, and common ground between low and high voltage ports, the converter achieves zero-voltage switching (ZVS) via synchronous rectification, improving efficiency. A 300W prototype with a 94.8% maximum efficiency in step-up mode and 94.2% in step-down mode was built to validate the wide voltage gain range and voltage control scheme.

The rise of satellites in Low Earth Orbit (LEO) is causing more terrestrial electromagnetic interference in the important L- and X-band frequencies which are crucial for astronomical observations. This thesis introduces reflectarray design which can serve as a basis for an interference mitigation solution for radio telescopes. In the envisioned application, When the reflectarray is placed around the circumference of an existing radio telescope, it can drive a null into the radio telescopes radiation pattern sidelobe distribution. Since the reflectarray only occupies a small potion of the rim of the paraboloidal main reflector, its presence does not significantly effect the main lobe peak gain. Since Iridium and Starlink are the target mega-constellations, the reflectarray must be dual band. To cover the operational bandwidths of these constellations, the target bandwidth in the L-band (Iridium) is 0.7%, and that in the X-band (Starlink) is 17.1%. This makes the design of the reflectarray challenging as the frequencies are widely separated and the bandwidth in the X-band is wide The work of this thesis marks a first step in this effort. It includes a reflectarray design containing a multi-layer stack consisting of: (1) a grounded substrate, (2) an X-band slot loaded unit cell geometry, (3) a dielectric superstrate, and (4) an L-band layer containing crossed dipoles. The dual band reflectarray is dual linearly polarized to maintain symmetric response. The reflectarray is designed and simulated using full-wave solvers. The results show that the reflectarray designs are capable of pattern shaping at both bands and operate across the required bandwidths. This architecture could serve as a basis for future reflectarrays capable of nulling satellite interference from mega-constellations in observatory applications in the future. / Master of Science / The signal clarity issues stemming from the increasing number of satellites in Low Earth Orbit (LEO), particularly in the vital L- and X-band frequencies essential for global communications and radio astronomy, are the motivation of this thesis. The endeavor concentrates on designing a dual-band dual-polarized reflectarray antenna which may ultimately be used to help mitigate interference in these bands in radio telescopes. The work is focused on the frequency ranges utilized by the major satellite networks Iridium and Starlink, which operate within the L-band (1616-1626.5 MHz) and X-band (10.7-12.7 GHz). Recognizing the significance of these frequencies for global communication and also to radio astronomy, the reflectarray is designed to contribute to a an interference mitigation system which would ultimately allow for coexistence between radio telescopes and communications systems satellites. Targeting bandwidth achievements of 0.7% for the L-band and 17.1% for the X-band, the focus is on nulling interference arising across these frequency bands and thereby increasing the sensitivity of the radio telescope operating amongst these mega-constellations. The thesis documents a multilayered reflectarray antenna, containing a wide-band X-band layer of slot antennas on one layer and an L-band superstrate layer containing crossed dipoles at another, both of which utilize dual linear polarization for symmetric operation. The completed reflectarray can operate simultaneously in both bands. It has been shown in the two papers cited by {ellingson2021sidelobe,budhu2024design} that reflectarrays placed along the rim of radio telescopes main reflector can be used to drive nulls in the sidelobe envelope of its radiation pattern thereby nulling incoming interference. The antenna design of this thesis suggests a possible candidate for these interference mitigation systems where both bands are targeted.