Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The world's astronomy community is working together to build the largest and most sensitive radio telescope in the world namely: the SKA (Square Kilometre Array). It will consist of approximately three thousand dishes which will each require accurate positioning. The Square Kilometer Array has a testbed called the Phased Experimental Demonstrator (PED) in Observatory, Cape Town. A hexapod positioning mechanism is required to position a 3.7 m radio telescope which forms part of an array of seven radio telescopes. This thesis details the design process of the hexapod system. The design consists of the mechanical design of the joints and linear actuators, a kinematic and dynamic model, a controller and a user interface. In order to verify the design for the PED hexapod a scaled prototype was designed, built and tested. The hexapod's repeatability as well as ability to track a path was tested using an inclinometer. The tests confirmed the design feasibility of the PED hexapod and also highlight issues that require care when constructing the full scale hexapod, such as the amount of play in the platform joints. The designed full scale hexapod will have an error angle less than 0.13°, a payload capacity of 45 kg, withstand wind speeds of 110 km/h and cost R160 000. / AFRIKAANSE OPSOMMING: Die wêreld se sterrekundige gemeenskap is besig om saam te werk om die grootste en mees sensitiewe radioteleskoop in die wêreld te bou, naamlik: die SKA (Square Kilometre Array). Dit sal uit ongeveer drie duisend skottels bestaan wat elkeen akkurate posisionering benodig. Die SKA het 'n toetssentrum, genaamd die “Phased Experimental Demonstrator” in Observatory, Kaapstad. 'n Sespoot posisionering meganisme word benodig om die 3.7 m radioteleskoop te posisioneer, wat deel vorm van 'n stelsel van sewe radioteleskope. Hierdie tesis beskryf die proses om die sespoot stelsel te ontwerp. Die ontwerp bestaan uit die meganiese komponent van die koppelings en lineêre aktueerders, 'n kinematiese en dinamiese model, 'n beheerder, asook 'n gebruikersintervlak. 'n Geskaleerde prototipe is ontwerp, gebou en getoets om die ontwerp te verifieer. Die platform se herhaalbaarheid sowel as akkuraatheid om 'n pad te volg was getoets met 'n oriëntasie sensor. Die toetse het probleme uitgelig wat versigtig hanteer moet word gedurende die konstruksie van die volskaalse sespoot, veral die hoeveelheid speling in die koppelings. Die volskaalse sespoot ontwerp het 'n hoek fout van minder as 0.13°, 'n ladingsvermoë van 45 kg en kan 'n windspoed van 110 km/h weerstaan en kos R160 000.

Approved for public release, distribution is unlimited / A military deployment is visible and vulnerable. But, deployments are currently planned assuming they can be completed with surprise, or defended from any threat. JFAST, the current deployment planning and visualization tool of choice, uses heuristics of unknown reliability that yield deployment plans of unknown quality, and ignores vulnerability. We introduce LIFTER, an integer-linear program (ILP) that optimizes a time-phased force deployment (TPFDD) by day, by asset cycle, and by TPFDD line (individual shipment from an origin to a destination), and ATTACKER, also an ILP, representing a smart enemy's resource-limited interdictions to maximally disrupt LIFTER's subsequently re-optimized TPFDD plan. LIFTER activates transport assets from an allocation list, and yields a complete logistic plan that minimizes disruption represented by penalties for early, tardy, late, or dropped shipments, and for under-utilization of asset capacity. We use LIFTER to qualitatively assess JFAST heuristic plans. We also link both ILPs in a decomposition-based search for the best deployment plan around the worst-case interdiction, given that the actions of deployer and interdictor are transparent to both parties. We explain how JFAST could be embellished with its own version of ATTACKER. A key discovery here is a gauge of the value of intelligence, deception, and secrecy. / Lieutenant, United States Navy

Cette thèse s'intéresse à montrer l'intérêt aussi bien conceptuel qu'empirique de l'approche optionnelle de l'évaluation et du timing des projets de fusions-acquisitions. Pour ce faire, nous avons, tout d'abord, mobilisé une large littérature sur les fusions-acquisitions et les options réelles qui y sont liées. Constatant le manque de contributions empiriques au niveau de cette littérature, nous avons procédé à la réalisation de deux études empiriques. La première est une étude qualitative exploratoire réalisée auprès d'experts en fusions-acquisitions. Les résultats de cette étude nous ont permis d'étudier d'une manière approfondie les particularités de l'évaluation et du timing des fusions-acquisitions et de faire émerger de nouvelles catégories d'options réelles présentes dans les différentes phases du processus d'évaluation et dans les moments de choix de timing.Ces options ont été par la suite classées en options stratégiques de croissance et en option de flexibilité. Une fois les options identifiées, nous sommes passés à notre deuxième étude empirique qui est une étude de cas réel. Celle-ci vise, à partir d'un projet de fusion-acquisition réel, à expliciter les problématiques d'évaluation et de choix de timing lorsque l'acquéreur utilise les techniques traditionnelles d'évaluation telles que la Valeur Actuelle Nette. Les limites de ces méthodes nous amènent à proposer des solutions pour une meilleure approche de l'évaluation et du timing des fusions-acquisitions en contexte d'incertitude: la méthode par les options réelles. Pour ce faire, nous proposons d'évaluer l'opportunité d'acquisition et d'étudier le choix de timing opportun à sa conclusion à partir de la méthodologie de l'option simple. Trois méthodes d'évaluation sont alors adoptées: le modèle d'évaluation en temps continu (Black et Scholes), le modèle développé en temps discret ( arbres binomiaux) et la technique des simulations de Monte Carlo. La deuxième solution proposée est celle de l'approche de l'évaluation et du timing des fusions-acquisitions par la méthodologie de l'option composée multi-séquentielle. A ce titre, nous mobilisons le modèle binomial adapté par Mun (2010) et proposons une modélisation sur mesure sous Visual Basic des séquences d'options sur options liées au processus d'évaluation et au choix du timing / The aim of this thesis is to study the conceptual and the empirical role when valuation and timing of mergers and acquisitions are approached by real options theory. To reach this aim, we started by analyzing a huge litterature on real option approach of mergers and acquisitions. We noticed a big lack on empirical contributions of real options in the mergers and acquisitions field, specially in pre-closing phases, where the acquirer value his project and choose the optimal timing to conclude it. To more investigate on that, we led deux studies. The first one is an exploratory study, in which we interviewed professionals on mergers and acquisitions on partucularities of valuation and timing on mergers and acquisitions. Then we asked them to identify real options on valuation and timing. Identified options were divided on strategic growth options and flexibility options. After the identification, we led our second study which is a real case study of a merger and acquisition project. The aim of this study is to prove limits of traditionnal valuation methods like the Net Present Value. As solutions to these limits, we proposed to use the real option approach. First, we used the simple option methodology and then the multi-phased compound options methodology to ameliorate valuation results and the timing choice of concluding mergers and acquisitions

Much research regarding efficiency in manufacturing industry has historically been focused on the material activities of the shop floor. However, companies that merely focus on material activities when trying to improve lead times, risk losing potential for improvements within immaterial activities such as planning, engineering, design, and purchasing, which often constitute the most time consuming parts of the order fulfillment processes. Engineer to order (ETO) products are particularly time consuming regarding their immaterial activities, and the customer is waiting for the products from the very beginning of the order fulfillment process. Shortening the lead time to customer for ETO products is therefore important for customer satisfaction. The aim of this study is to adapt an existing lead time tree model currently focused on material activities to also include immaterial activities, enabling a full visualization of all activities contained in order fulfillment processes. The lead time tree model would thereby be able to use as a tool when working on shortening the lead time to customer. A further aim of the study is to investigate how the adapted lead time tree model can be used in further areas as well, in addition to visualizing immaterial activities. The adaption of the lead time tree model has been based on the original literary source of the lead time tree model. The original lead time tree model has been analyzed towards theoretical data from a literature study, and towards empirical data about immaterial activities in order fulfillment processes for ETO products, from the case company Kongsberg Maritime Sweden AB (previously Rolls-Royce AB). The result of this has been an adapted lead time tree model that can visualize immaterial activities. Several adaptions of the original lead time tree model have been made for it to be able to visualize immaterial activities, while still keeping the basics of the original model. The adapted lead time tree model comprises information that is normally kept separated and that is important when planning and improving a process. Additional information that is needed for each specific case can also easily be included in the lead time tree. The adapted lead time tree model has proven to have additional areas of use within project planning, improvement work regarding lead time reduction and root-cause analysis, and as a boundary object for communication between internal actors and between internal and external actors. The adapted lead time tree model is presumably able to map and visualize immaterial activities in other fields of business as well, other than manufacturing, as the nature of immaterial activities remains the same across business environments.

The delivery of tunable millimetre-wave components at 60GHz is of research and development interests with the advent of 5G era. Among applications such as high-data-rate wireless communications, high-precision automotive radars and hand-gesture sensing, variable phase shifters are vital components for antenna arrays to steer an electromagnetic beam without mechanical movement. However, present microwave technology has limited scope in meeting more and more stringent requirements in wavefront phase control and device performance for those cutting-edge applications in the millimetre-wavelength range. Although some existing microwave switchable techniques (such as RF MEMS and solid-state p-i-n diodes) can offer ultra-fast speed for phase modulation, their binary beam-steering nature is resolution-limited and thereby degrades the beam-scanning performance. In response to this, continuously-tunable phase shifting can be realised by using tunable dielectric materials such as ferroelectric BST and liquid crystals (LCs). BST thin films can offer relatively fast switching and modest tunability. However, the increased dielectric loss beyond 10GHz impedes their implementation for higher frequency applications. By comparison, liquid crystals (LCs) have drawn attention in recent years because of their continuous tunability as well as low losses especially at millimetre-wavebands. The principle of shifting the phase continuously is based on the shape anisotropy of LC molecules for variable polarizabilities and hence tunable dielectric constants, which allows wave speed to be controlled with ease by a low-frequency field of only up to 10V. However, LC-based tunable delay lines are not well established in the frequency regime of 60GHz-90GHz because of the limited status of LC microwave technology in which most of the LC based devices have been designed for below 40GHz. It is the aim of this PhD research to bridge the gap and address future societal needs based on our group's focus and experience in developing cutting-edge LC-based agile microwave components. In this work, a liquid crystal (LC) based 0-180˚continuously-variable phase shifter is developed with insertion loss less than -4.4dB and return loss below -15dB across a wide spectrum from 54GHz to 67GHz. The device is driven by a 0-10V AC bias and structured in a novel enclosed coplanar waveguide (ECPW) including an enclosed ground plate in the design, which significantly reduces the instability due to floating effects of the transmission line. This structure screens out interference and stray modes, allowing resonance-free quasi-TEM wave propagation up to 90GHz. The tunable ECPW is optimised by competing spatial volume distribution of the millimetre-wave signal occupying lossy tunable dielectrics versus low-loss but non-tunable dielectrics and minimising the total of dielectric volumetric loss and metal surface loss for a fixed phase-tuning range. A variety of influences affecting the actual device performance are studied, experimented and optimised. Fabricated prototypes exhibit wideband low-loss performance and 0-π continuous tuning with low power consumptions and high linearity compared with the state-of-the-arts. Potentially, the ECPW-fed phased antenna array will be incorporated with advanced beam-forming algorithms to develop compact beam-steering systems of improved performances and targeted for ultra-high-data-rate wireless communications, inter-satellite communications, current road safety improvement, futuristic autonomous driving, and other smart devices such as the hand-gesture recognition.

Le projet Iseult-Inumac mené au sein d’un consortium franco-allemand vise à développer les techniques associées à l’imagerie par résonance magnétique à ultra haut champ, notamment à travers la construction d’un imageur à 11,7 teslas. La résolution accrue du nouvel imageur devrait apporter une meilleure compréhension du système nerveux et de ses dysfonctionnements pour aboutir à un dépistage plus précoce des pathologies telles que la maladie d’Alzheimer, les accidents vasculaires cérébraux ou les tumeurs.La principale difficulté technique du projet, en dehors de la construction de l’aimant statique, réside dans la capacité d’émettre une onde électromagnétique d’amplitude uniforme dans tout le cerveau du patient : problème de l’inhomogénéité de B1 (ou radiofréquence). Une solution proposée consiste à utiliser une antenne réseau à transmission parallèle et des séquences d’excitation IRM spécifiques dites de compensation.Cette thèse se concentre sur la conception des antennes réseaux à transmission parallèle pour l’IRM à 7 et 11,7 T. Un prototype à 8 canaux indépendants utilisant une technologie innovante de résonateurs linéaires est présentée pour l’IRM 7 T. Il a été conçu par la simulation numérique. Un protocole de validation a été développé pour la caractérisation et l’analyse des performances des antennes réseaux. Le succès de cette validation a permis de développer par la simulation une nouvelle antenne à 12 canaux et une stratégie de pilotage innovante permettant de n’utiliser que 8 chaînes de pilotage au lieu de 12. Enfin, la même méthodologie a été appliquée pour concevoir et prédire les performances d’une antenne réseau à 11,7 T. / The Iseult-Inumac project led by a franco-german consortium aims at developing the ultra-high field MRI technologies, especially with the building of an 11.7 tesla scanner. The high resolution of this new scanner may improve the understanding of human nervous system and its dysfunctions in order to detect pathologies like the Alzheimer disease, strokes or tumors earlier.The biggest technical difficulty, besides the building of the static magnet itself, lies in the emission of a uniform electromagnetic wave in the entire brain of the patient. It is usually referred as to B1 (or RF) inhomogeneity issues. A solution consists in using a phased array RF coil and specific MRI sequences for shimming in a parallel transmit approach.This thesis deals with the study of parallel transmit phased arrays RF coils for 7 T and 11.7 T MRI. An eight independent channels prototype-coil that uses a new planar strip array technology is described for 7 T MRI. It was designed based on numerical simulation. A validation methodology has been developed for characterization and performance analysis of transmit phased arrays. After a successful validation of this first prototype, a more efficient 12-channel coil and a new driving strategy that only requires 8 driving channels instead of 12 were designed. Finally, the same methodology was applied to a phased array RF coil for 11.7 T MRI.

Modern radar technology relies heavily on digital signal processing. As radar technology pushes the boundaries of miniaturization, computational systems must be developed to support the processing demand. One particular application for small radar technology is in modern drone systems. Many drone applications are currently inhibited by safety concerns of autonomous vehicles navigating shared airspace. Research in radar based Detect and Avoid (DAA) attempts to address these concerns by using radar to detect nearby aircraft and choosing an alternative flight path. Implementation of radar on small Unmanned Air Vehicles (UAV), however, requires a lightweight and power efficient design. Likewise, the radar processing system must also be small and efficient.This thesis presents the design of the processing system for a small Frequency Modulated Continuous Wave (FMCW) phased array radar. The radar and processing is designed to be light-weight and low-power in order to fly onboard a UAV less than 25 kg in weight. The radar algorithms for this design include a parallelized Fast Fourier Transform (FFT), cross correlation, and beamforming. Target detection algorithms are also implemented. All of the computation is performed in real-time on a Xilinx Zynq 7010 System on Chip (SoC) processor utilizing both FPGA and CPU resources.The radar system (excluding antennas) has dimensions of 2.25 x 4 x 1.5 in3, weighs 120 g, and consumes 8 W of power of which the processing system occupies 2.6 W. The processing system performs over 652 million arithmetic operations per second and is capable of performing the full processing in real-time. The radar has also been tested in several scenarios both airborne on small UAVs as well as on the ground. Small UAVs have been detected to ranges of 350 m and larger aircraft up to 800 m. This thesis will describe the radar design architecture, the custom designed radar hardware, the FPGA based processing implementations, and conclude with an evaluation of the system's effectiveness and performance.

The Brigham Young University (BYU) Radio Astronomy Systems group, in collaboration with the National Radio Astronomy Observatory (NRAO), the Center for Astrophysics at West Virginia University (WVU), and the Green Bank Observatory (GBO) have developed, and commissioned, a broadband real-time digital back end processing system for a 38-element phased array feed (PAF) with 150 MHz of instantaneous bandwidth. This system is capable of producing coarse and fine channel correlations, and implements a real-time beamformer that forms 7 simultaneous dual-polarized beams. This thesis outlines the hardware and software development for the digital back end and presents on-telescope commissioning results. This system has been measured to provide an unprecedented low Tsys/η noise level of 28 K and can perform maps of galactic hydrogen observations in a fraction of the time of a conventional single horn feed. The National Radio Astronomy Observatory (NRAO) has recently announced the concept and development of the next generation Very Large Array (ngVLA), a large interferometric array consisting of 300 radio telescopes and longest baseline (distance between a pair of antennas) of 300 km. Large interferometric arrays have been shown to attenuate radio frequency interference (RFI) because it is decorrelated as it propagates across long baselines. This is not always sufficient, especially with dense core array geometries and with the ever-increasing amount of strong RFI sources. Conventional RFI projection-based mitigation techniques have performed poorly on large interferometers because of covariance matrix estimation error due to decorrelation when identifying interference subspace parameters. This thesis presents an algorithm that overcomes the challenge of decorrelation by applying subspace projection via subarray processing (SP-SAP). Each subarray is designed to have a set of elements with high mutual correlation in the interferer for better estimation of subspace parameters. In simulation, compared to the former approach of applying subspace projection on the full array, SP-SAP improves mitigation of the RFI on the order of 9 dB. A signal of interest is shown then to be observable through the RFI in a full synthetic image.

<p>This thesis considers integration of antennas and active electronics manufactured on the same substrate. The main topic is on-chip antennas for commercial silicon processes, but hybrid integration using printed circuit board technology is also addressed.</p><p>The possible use of micromachining techniques as a means of reducing substrate losses of antennas manufactured on low resistivity silicon wafers is investigated. Compact dipole, loop, and inverted-F antennas for the 20-40 GHz frequency range are designed, implemented, and characterized. The results show significantly improved antenna efficiency when micromachining is used as a post-processing step for on-chip antennas manufactured in silicon technology.</p><p>High resistivity wafers are used in a commercial silicon germanium technology to improve the efficiency of dipole antennas realized using the available circuit metal layers in the process. Monolithically integrated 24 GHz receivers with on-chip antennas are designed and evaluated with regard to antenna and system performance. No noticeable degradation of the receiver performance caused by cross talk between the antenna and the integrated circuit is observed.</p><p>For low frequency antenna arrays, such as base station antennas, hybrid integration of active devices within the antenna aperture is treated. A compact varactor based phase shifter for traveling wave antenna applications is proposed and evaluated. Electrically steerable traveling wave patch antenna arrays, with the phase shifters implemented in the same conductor layer as the radiating elements, are designed and manufactured in microstrip technology. It is experimentally verified that the radiation from the feed network and phase shifters in the proposed antenna configuration is small.</p>

This thesis considers integration of antennas and active electronics manufactured on the same substrate. The main topic is on-chip antennas for commercial silicon processes, but hybrid integration using printed circuit board technology is also addressed. The possible use of micromachining techniques as a means of reducing substrate losses of antennas manufactured on low resistivity silicon wafers is investigated. Compact dipole, loop, and inverted-F antennas for the 20-40 GHz frequency range are designed, implemented, and characterized. The results show significantly improved antenna efficiency when micromachining is used as a post-processing step for on-chip antennas manufactured in silicon technology. High resistivity wafers are used in a commercial silicon germanium technology to improve the efficiency of dipole antennas realized using the available circuit metal layers in the process. Monolithically integrated 24 GHz receivers with on-chip antennas are designed and evaluated with regard to antenna and system performance. No noticeable degradation of the receiver performance caused by cross talk between the antenna and the integrated circuit is observed. For low frequency antenna arrays, such as base station antennas, hybrid integration of active devices within the antenna aperture is treated. A compact varactor based phase shifter for traveling wave antenna applications is proposed and evaluated. Electrically steerable traveling wave patch antenna arrays, with the phase shifters implemented in the same conductor layer as the radiating elements, are designed and manufactured in microstrip technology. It is experimentally verified that the radiation from the feed network and phase shifters in the proposed antenna configuration is small.