<p> This thesis introduces several novel antenna systems with extended performance capabilities achieved by either enabling multiple operation bands or by widening the bandwidth. Proposed theoretical concepts are successfully tested through simulations and experiments with excellent agreement are demonstrated. The designs developed in this thesis research are low-profile or flush mountable, enabling simple platform integration.</p><p> In the HF/VHF bands, the development of a novel low-profile multiband antenna for vehicular applications is presented. Specifically, an inverted-F antenna is used as a driven element, to operate at the lowest frequency of 27 MHz, whereas two parasitic elements are built as inverted-L monopoles to enable resonances at 49 and 53 MHz. To eliminate the need for an external matching network, an offset feeding technique is used. When the antenna is mounted on a vehicle and bent to follow its profile, a very low-profile is achieved (lambda/44) while good impedance and far-field performance are maintained across all three bands. The developed antenna system is not only electrically smallest among others found in the literature, but it is easily modified for other band selections and tuning of each band can be readily achieved.</p><p> Vehicular antennas are often used for high power applications, which may cause exposure of nearby individuals to possibly dangerous electromagnetic fields. To assess this hazard, the RF exposure of a vehicle's crew is discussed and an original and fast modeling approach for prediction thereof is demonstrated. The modeling approach is based on eigenmode analysis for acquiring a range of frequencies where the shielding effectiveness of a vehicle cabin is expected to be lower than average. This approach is typically much faster and requires less computational resources as compared to classical full-wave analyses. This analysis also shows that the position of an antenna system is critical and must be considered when high-power RF emissions are planned.</p><p> Following the same trend of antenna system size reduction with extension of capabilities in a congested spectral environment, the millimeter wave spectrum is explored next. Specifically, antenna systems for wideband amplitude only (AO) direction finding (DF) are thoroughly considered. Theory and design considerations are developed to fill gaps in open literature. Typical sources of errors are theoretically analyzed, and a discussion on limitations and advantages of different AO DF architectures is given.</p><p> Practical millimeter wave realizations of AO DF antenna front-ends in the K/Ka/Q bands (18-45 GHz) are developed using two different architectures: a passive phased-array and a squinted antenna system. For the former, a tightly coupled two-element tapered slot antenna (TSA) array with a stacked arrangement is developed. A novel enclosure of the array inside an absorbing cavity is proposed and improved system performance with flush mounted configuration is demonstrated. The squinted antenna system avoids the use of a beamformer, therefore reducing insertion loss and amplitude/phase imbalances to reduce DF errors. For design robustness, the same TSA element used in the phased-array configuration is used. A novel tapered cavity is also developed to stabilize H-plane radiation patterns and suppress sidelobes. It is seen that the squinted antenna AO DF front-end has better performance than the phased-array antenna system at the expense of larger size.</p>

Efficient computation in deterministic and uncertain electromagnetic propagation environments, tackled by parabolic equation methods, is the subject of interest of this dissertation. Our work is comprised of two parts. In the first part we determine efficient absorbing boundary conditions for propagation over deterministic terrain and in the second part we study techniques for efficient quantification of random parameters/outputs in volume and surface based electromagnetic problems. Domain truncation by transparent boundary conditions for open problems where parabolic equation is utilized to govern wave propagation are in general computationally costly. For the deterministic problem, we utilize two approximations to a convolution-in-space type discrete boundary condition to reduce the cost, while maintaining accuracy in far range solutions. Perfectly matched layer adapted to the Crank-Nicolson finite difference scheme is also verified for a 2-D model problem, where implemented results and stability analyses for different approaches are compared. For the random problem, efficient moment calculation of electromagnetic propagation/scattering in various propagation environments is demonstrated, where the dimensionality of the random space varies from N = 2 to N = 100. Sparse grid collocation methods are used to obtain expected values and distributions, as a non-intrusive sampling method. Due to the low convergence rate in the sparse grid methods for moderate dimensionality and above, two different adaptive strategies are utilized in the sparse grid construction. These strategies are implemented in three different problems. Two problems are concerned with uncertainty in propagation domain intrinsic parameters, whereas the other problem has uncertainty in the boundary shape of the terrain, which is realized as the perfectly conducting (PEC) Earth surface.

This document address the feasibility of low-cost, dual-polarized, X-band phased array antennas for use in dense radar networks for weather surveillance. The “phase-tilt” architecture under investigation combines one-dimensional, electronic beam steering with mechanical actuation (tilting) to achieve a low-cost design capable of rapid, two-dimensional beam positioning without the use of a large scanning pedestal. This architecture is less complex and costly than a full, two-dimensional “phase-phase” array. In addition to meeting requirements for cost, it has the potential to meet requirements for off-axis polarization performance and other key requirements. A prototype antenna already has been designed, fabricated and tested. It defines a new state-of-the-art for remote sensing of weather using small radars. The prototype antenna also serves as a test bed and proof of concept for exploring a potential future network comprised of many antennas arranged in a dense network. This dissertation reviews the current state-of-the-art (in weather radars, dense radar networks, dual-polarized radars, and phased arrays); presents the design, implementation, testing, and validation experiments of the prototype array; and establishes performance requirements for this technology for deployment in future networks of small weather radars.

<p> The purpose of this study is to design, fabricate and test a CMOS compatible 3-axis Hall effect sensor capable of detecting the earth&rsquo;s magnetic field, with strength&rsquo;s of &sim;50 &mu;T. Preliminary testing of N-well Van Der Pauw structures using strong neodymium magnets showed proof of concept for hall voltage sensing, however, poor geometry of the structures led to a high offset voltage. A 1-axis Hall effect sensor was designed, fabricated and tested with a sensitivity of 1.12x10^-3 mV/Gauss using the RIT metal gate PMOS process. Poor geometry and insufficient design produced an offset voltage of 0.1238 volts in the 1-axis design; prevented sensing of the earth&rsquo;s magnetic field. The new design features improved geometry for sensing application, improved sensitivity and use the RIT sub-CMOS process. The completed 2-axis device showed an average sensitivity to large magnetic fields of 0.0258 &mu;V/Gauss at 10 mA supply current.</p>

The Finite Element Tearing and Interconnecting (FETI) and its variants are probably the most celebrated domain decomposition algorithms for partial differential equation (PDE) scientific computations. In electromagnetics, such methods have advanced research frontiers by enabling the full-wave analysis and design of finite phased array antennas, metamaterials, and other multiscale structures. Recently, closer scrutiny of these methods have revealed robustness and numerical scalability problems that prevent the most memory and time efficient variants of FETI from gaining widespread acceptance. This work introduces a new class of FETI methods and preconditioners that lead to exponential iterative convergence for a wide class of problems, are robust and numerically scalable. First, a two Lagrange multiplier (LM) variant of FETI with impedance transmission conditions, the FETI-2λ, is introduced to facilitate the symmetric treatment of non-conforming grids while avoiding matrix singularites that occur at the interior resonance frequencies of the domains. A thorough investigation on the approximability and stability of the Lagrange multiplier discrete space is carried over to identify the correct LM space basis. The resulting method, although accurate and flexible, exhibits unreliable iterative convergence. To accelerate the iterative convergence, the Locally Exact Algebraic Preconditioner (LEAP), which is responsible for improving the information transfer between neighboring domains is introduced. The LEAP was conceived by carefully studying the properties of the Dirichlet-to-Neumann (DtN) map that is involved in the sub-structuring process of FETI. LEAP proceeds in a hierarchical way and directly factorizes the signular and near-singular interactions of the DtN map that arise from domain-face, domain-edge and domain-vertex interactions. For problems with small number of domains LEAP results in scalable implementations with respect to the discretization. On problems with large domain numbers, the numerical scalability can only be obtained through ``global'' preconditioners that directly convey information to remotely separated domains at every DDM iteration. The proposed ``global" preconditiong stage is based on the new Multigrid FETI (MG-FETI) method. This method provides a coarse grid correction mechanism defined in the dual space. Macro-basis functions, that satisfy the curl- curl equation on each interface are constructed to reduce the size of the coarse problem, while maintaining a good approximation of the characteristic field modes. Numerical results showcase the performance of the proposed method on one-way, 2D and 3D decomposed problems, with structured and unstructured partitioning, conforming and non-conforming interface triangulations. Finally, challenging, real life computational examples showcase the true potential of the method.

<p> Mechanical gears can be as small as those in traditional mechanical watches or as large as those in mechanical marine turbines. They can be seen in almost all transportation tools, for example, bicycles, cars, trains and airplanes. Though they have been studied and refined for centuries, there are still some disadvantages. For instance, mechanical gears often create a large amount of noise and vibration. They require regular maintenance as the gears need to be lubricated. In addition, if a gear is overloaded it can catastrophically fail. </p><p> Unlike conventional mechanical gears, magnetic gears can create speed change without physical contact. The force between magnetic gears is not created by geared teeth but instead, it is created by the magnetic poles. There will be a small air gap between different rotors which means no lubricant or maintenance is required. When one rotor rotates, the other one will also rotate driven by magnetic forces. Since the permanent magnets are used, the forces will not recede or disappear as long as the magnets are not overheated. If overloaded, a magnetic gearbox will simply slip poles. Therefore, in many applications, magnetic gears can be more reliable, efficient and safer. </p><p> The goal of this research has been to investigate the torque capabilities of high gear ratio magnetic geared devices. The performance has been investigated based on the gear ratio and torque density. </p><p> A new type of flux focusing cycloidal magnetic gear (MG) was investigated that could operate at a gear ratio of -25:1. The flux focusing topology was used because it increased the air gap flux density and therefore enabled a higher torque density. Using 2-D finite element analysis (FEA), the volume torque density was calculated to be 291 Nm/L with an outer diameter of 0.228 m. A -20:1 prototype cycloidal magnetic gear was designed. It had a calculated volumetric torque density of 260 Nm/L. The cycloidal magnetic gear was mechanically difficult to construct and therefore only the inner rotor of the cycloidal magnetic gear was constructed. In addition, the eccentric air gap will cause bearing failure. </p><p> To achieve an even higher gear ratio, a nested multistage magnetic gear (MSMG) was designed with a 2-D FEA calculated torque density of 424 Nm/L. The desired gear ratio was 59:1 so that the performance could be compared with a Sumitomo mechanical gearbox which had the same gear ratio. In order to minimize the rotor torque ripple, the harmonic field interaction between the inner stage and the outer stage of the magnetic gear had to be mitigated. A unique flux concentration Halbach rotor structure was proposed. The rotor structure was shown to shield the outer rotor from the inner rotor harmonics. The nested multistage magnetic gear contains 4 rotors and complex mechanical structure. In order to provide sufficient mechanical support, the mechanical axial length had to be very large and this negated many of the benefits of using the nested coaxial rotor structure. </p><p> A two-stage series connected 59:1 gear ratio multistage magnetic gear was also designed for wind turbines. The 6.45:1 first stage magnetic gearbox had a diameter of 0.633 m and the 3-D FEA calculated peak torque and torque density were 4.79 kNm and 159 Nm/L. The measured torque and torque density were 4.25 kNm and 141 Nm/L. While the 9.14:1 second stage magnetic gearbox had a diameter of 0.507 m and the 3-D FEA calculated peak torque and torque density were 1.04 kNm and 136 Nm/L, respectively. The series connected multistage magnetic gear had the advantage of being more modular as different gear ratios can be obtained by changing the pole pair combinations for one of the series connected magnetic gears. </p><p> A two-stage series connected 59:1 gear ratio multistage magnetic gear was also designed for a hydropower application. Non-magnetic rods were used to reduce the losses and the mechanical deflection. The 2-D calculated torque density for the stage 1 magnetic gear was 371 Nm/L. And the 2-D calculated torque density was 344 Nm/L for the stage 2 magnetic gear. A stator was also designed that was inserted inside the stage 2 magnetic gear. In order to try to reduce the torque ripple, the stator had a fractional winding distribution with 1.25 slots/pole/phase. (Abstract shortened by ProQuest.) </p><p>