Notre thèse propose d'étudier la précision des calculs par la méthode des éléments finis (MEF) au moyen "d'indicateurs de qualité". Les indicateurs de qualité représentent des formules simples qui permettent d'évaluer la qualité des calculs par éléments finis. La qualité de l'analyse numérique est évaluée par rapport à la discrétisation. Le modèle mathématique est considéré correct et les erreurs résultant du choix des propriétés des matériaux ne sont pas pris en compte. Nous avons défini les formulations mathématiques de ces indicateurs de qualité, ainsi que leurs limites inférieures et supérieures. Grâce au choix de formulations simples, il est facile de les introduire dans un logiciel de calcul par éléments finis. Ils ont été implémentés dans le code de calcul CESAR-LCPC, module Mécanique en Comportement Non Linéaire. Afin de démontrer qu'ils ont été correctement définis et de tester leur fiabilité, ces indicateurs de qualité sont testés sur un certain nombre de problèmes simples en 2D et en 3D. Après avoir prouvé leur capacité à caractériser la qualité de la discrétisation des modèles d'éléments finis, nous les avons testés sur le cas d'une excavation de palplanches butonnées (site expérimental de Hochstetten, près de Karlsruhe). La précision des résultats en termes de propriétés mécaniques choisies pour le sol et les structures n'a pas été étudiée. Nous avons également démontré que les résultats sont indépendants des propriétés mécaniques choisies pour le sol ou la structure / The thesis proposes to study the accuracy of the finite element method (FEM) analyses by means of « quality indicators ». The quality indicators represent simple mathematical formulas that are designed to evaluate the reliability of the numerical analyses. The accuracy of the discretization modeling of these analyses is determined ; the mathematical model is considered correct and the errors resulting from the choice of the mechanical properties of the soil are not taken into account. We proposed the mathematical formulations of the quality indicators and also established their lower and upper bounds. Due to their simple mathematical formulation, the quality indicators are easily implemented in any finite element computer code. We have introduced them in the CESAR-LCPC finite element computer code, namely in the nonlinear mechanical execution module. The proposed quality indicators are used on a number of simple 2D and 3D problems elastic and elastoplastic problems in order to assess the jump in stress values in the nodes of the generated mesh. After testing the accuracy of the discretization modeling of these numerical analyses, we evaluated the discretization modeling quality of a braced sheetpile excavation (Hochstetten experimental site, near Karlsruhe). The accuracy of the results based on the mechanical properties of the soil and the structure has not been studied. Also, we proved that the quality indicator results are independent of the chosen mechanical properties for the soil or structure

A major limitation of acousto-optic (AO) leaky-mode modulator based holographic displays is their inability to present full-parallax. We propose that full-parallax capabilities can be bestowed on these displays by integrating an electro-optic (EO) phased array into the architecture. We validated this concept by rendering computational models and by fabricating and testing a basic two-axis AO/EO deflector prototype in lithium niobate. This was, to our knowledge, the first instantiation of an integrated, hybrid AO/EO deflector. The prototype had a 6° deflection range along the AO-axis, and a 3° deflection range along the EO-axis. A series of models provide us with a clear path forward for optimizing this deflector. They suggest that an AO/EO modulator with an EO deflection range of 24.5° and that requires less than 7.5 V can be fabricated within the limitations of standard photolithography.

Indiana University-Purdue University Indianapolis (IUPUI) / This thesis proposes a reconfigurable phased array of antennas for wireless power transfer. The array finds use in many applications, from drone destruction (for defense) to wireless charging of robots and mobile devices. It utilizes a novel feeding architecture to greatly reduce the number of high cost elements (such as amplifiers and phase shifters) as well as the quantity of unused resources in the system. Upon the instruction of the CPU, the array can separate into any number of subarrays, each of which transmits power to a single receiver, steering its beam as the receiver changes location. Currently dormant elements in the array can be used to provide position information about the receivers, either via Radar, or by listening for beacons pulses from the receiver. All of this is made possible, with only 4 amplifiers and 3 phase shifters, by the proposed 4-Bus Method. The source signal is divided into four buses, which are respectively phase shifted by 270 degrees, 180 degrees, 90 degrees, and 0 degrees (no shifter required) and then amplified. The CPU calculates, based on the number and positions of the receivers / targets, what the amplitude and phase excitation must be at each element. Any phase and amplitude which could be required can be achieved by simply adding together appropriate quantities of the correct two buses. In order to achieve this, the key piece is the variable power divider. These differ from Wilkinson dividers in that the dividing ratio can be changed via an applied DC voltage. Therefore, at each junction, by properly diverting the power levels on each phase bus to their proper location, complete delocalization of both amplifiers and phase shifters can be achieved. A method has also been developed which helps overcome the limitations of each variable power divider. That is, in certain instances, it may be desirable to pass all the power to a single output port or the other, which is not a possibility inherently possible with the device. With the use of a unique combination of RF switches, the nodes achieve much enhanced flexibility. Finally, an intensive study is carried out, in an attempt to yield greater understanding, as well as quick, useful approximations, of the behaviors of both rectangular and hexagonal arrays of various sizes and beam steering angles for wireless power.

This thesis presents the design, layout, and measurements of a bi-directional amplifier with variable vector (in-phase / quadrature) gain control that will be part of an electronically steered phased array system. The electronically steered phased array has many advantages over the conventional mechanically steered antennas including rapid scanning of the beam and adaptively creating nulls in desired locations. The 10-bit bi-directional Vector Variable Gain Amplifier (VVGA) is part of the transmit and receive module of each antenna element where transmit and receive functionality is determined through a simple switch. The VVGA performs amplification of the IF IQ pair by an adjustable complex coefficient. At receive, the VVGA functions as a Vector Variable Gain Current Amplifier (VVGCA) and at transmit, the VVGA functions as a Vector Variable Gain Transadmittance Amplifier (VVGTA). Design procedure, layout entry, schematic and parasitic extracted simulation results, and measurements are presented in this thesis.

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Radio frequency interference has become a large problem to radio astronomers. This thesis proposes the idea that radio frequency interference can be mitigated using a phased array feed in conjunction with a large reflector. A phased array feed would allow radio astronomers to observe fainter signals than is currently possible, while at the same time enabling rapid sky surveys. A phased array feed was designed and simulated, and sensitivity optimization was performed on the array feed. It was shown that higher sensitivity can be achieved using a 7-element phased array feed than with a conventional waveguide feed. Simulations were ran using RFI mitigation algorithms on the array to show that interference cancellation can, in principle, be performed using a phased array feed. In addition to these simulations, improvements were made to a previously designed RF receiver so that radio astronomy observations could be made and interference mitigation algorithms tested on a receiver platform.

The Brigham Young University (BYU) Radio Astronomy group, in collaboration with Cornell University, the University of Massachusetts, and the National Radio Astronomy Observatory (NRAO), have in recent years developed and deployed PAF systems that demonstrated the advantages of PAFs for astronomy. However, these systems lacked the necessary bandwidth and acquisition times to be scientifically viable. This thesis outlines the development of a 20-MHz bandwidth system that can acquire for much longer periods of time and across much larger bandwidths than previous BYU systems. A report of the deployment of this system on the 305-meter reflector at the Arecibo Observatory in Puerto Rico is also summarized.The Commonwealth Scientific and Industrial Research Organisation (CSIRO) is currently constructing a PAF-equipped synthesis imaging array named the Australian Square Kilometre Array Pathfinder (ASKAP) that offers great promise for widening FOVs and enhancing RFI mitigation techniques. Previous work in RFI mitigation has demonstrated effective cancellation for synthesis imaging arrays under the assumption that the processing bandwidth is narrowband and correlator dump times are short. However, these assumptions do not necessarily reflect real-world instrument limitations. This thesis explores simulated adaptive array cancellation algorithm effectiveness as applied on the ASKAP instrument given realistic bandwidths and correlator dump times. The results demonstrate that active RFI mitigation performed across long baselines is largely ineffectual.

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