Le milieu plasma correspond au 4ème état de la matière présentant une permittivité diélectrique complexe qui peut être exploitée pour les systèmes de communication. Sa permittivité négative a été étudiée dans de nombreux travaux de recherche démontrant que le plasma peut avoir des caractéristiques similaires à celles d'un métal en termes de conductivité électrique. En considérant une perméabilité positive, le plasma peut ainsi réagir de la même manière qu'un métal en présence d'une onde électromagnétique. Cette thèse a pour objectif de démontrer que le plasma est une alternative au métal pour la réalisation d'antennes reconfigurables. La première partie du travail concerne la caractérisation du milieu plasma en utilisant des sources plasma commerciales à savoir des lampes à Néon. Cette caractérisation est primordiale afin de pouvoir ensuite simuler ce type de source. La seconde partie des recherches a concerné la conception et la réalisation d'antennes plasma reconfigurables en rayonnement et ceci à la fréquence de 2.4 GHz. Le premier concept est un réflecteur circulaire et le second un réflecteur à angle droit tous les deux réalisés à partir de différentes lampes à Néon et illuminés par une antenne source monopole. Le réflecteur circulaire permet de dépointer le faisceau d'antennes sur 360° alors que le réflecteur à angle droit permet de reconfigurer le faisceau rayonnant et de passer d'un faisceau directif à deux faisceaux avec un creux dans l'axe. Ces dispositifs rayonnants innovants basés sur des lampes à Néon ont été validés expérimentalement et les résultats de mesure (S11 et rayonnement) sont en bonne adéquation avec les résultats de simulation. Ces deux types d'antennes réflecteurs possèdent également de bons résultats en termes de gain, ce qui valide l'utilisation et la caractérisation des lampes plasma de commerce utilisées. Dans la troisième partie du travail, ce même type de lampe à néon a été utilisé pour concevoir cette fois un élément rayonnant excité par couplage capacitif. La réalisation d'un prototype à permis de démontrer la faisabilité d'une telle source rayonnante. Enfin, la dernière partie des recherches concerne une étude de la Surface Equivalente Radar des antennes réflecteur conçues précédemment. L'étude a démontré que ces antennes réflecteurs plasma présentent des SER largement inférieures lorsqu'elles sont éteintes ainsi qu'à fréquence haute (8 GHz) comparativement à celles d'antennes métalliques équivalentes ce qui en fait des antennes furtives d'un point de vue radar. / Plasma is the 4th state of matter with complex permittivity that can be exploited to give advantages in communication system. Its negative permittivity has been studied in many research papers and it was proven to have similar characteristics as metal material in terms of electrical conductivity. While keeping permeability in the positive region, plasma will respond to electromagnetic waves in the similar manner as metal. Therefore, this thesis aimed to use plasma as an alternative to metal in the construction of reconfigurable antennas. The first part of this thesis is dedicated to characterize a plasma model based on the commercially available plasma source. Since there are many type of plasma source in terms of their electrical properties and physical shapes, it is important to characterize a particular plasma source so that it can be modeled in simulations to construct other types of plasma antennas. The second part presents the realization of plasma reflector antennas. Two types of plasma reflector antennas have been simulated, fabricated and measured at 2.4 GHz. The first one is are round reflector antenna (RRA) and the second one is corner reflector antenna (CRA). The performances of RRA have been validated and it was proven to provide beam shaping and beam scanning capability. The measured radiation patterns are in a good agreement with simulation ones. The capability of RRA is exceptional since it can steer its main beam from 0° up to 360°. Moreover, the scanning gain remains the same as the main beam is being moved from one direction to another. The CRA that has been introduced in this thesis is a novel design since it integrates two corner-reflector antennas on a single ground plane. The CRA offers three beam shapes which are electrically switchable from one shape to another. The CRA was simulated, fabricated and finally its performances were validated throughout a series of agile measurements. The measured reflected radiation patterns are in good agreements with the simulation ones. The measured gains of the RRA and CRA are 5 dB higher than the gain of classical monopole antenna with an identical size of finite ground plane. The fourth part deals with plasma as radio waves radiator. Two plasma antennas using commercially available U-shaped compact fluorescent lamp (CFL) have been fabricated and measured and it was proven that these antennas can be to radiate radio signal. The last part discusses about radar cross section performance of the plasma reflector antennas. The two plasma reflector antennas (RRA and CRA) were tested and measured for their RCS performance.

Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The triple layer pillbox antenna is an antenna topology well suited for use as a stackable "plank" element in radar applications. Its suitability arises from the folding which makes it compact, and from the layered nature which can be exploited for low cost manufacture. Existing designs of these "cheese" antennas, whether two or three layers, suff er from two drawbacks: a) The bend or fold between layers introduces undesirable reflections and b) Due to their parabolic sector geometry virtually no pattern control is available to the designer. This work addresses both of these shortcomings. A low reflection transition is realized by introducing simple compensating elements into the design which, with minimal manufacturing complexity, off er high performance over a broad frequency and incidence angle range. To cater for pattern control the concept of "dual shaped reflectors" is borrowed from the high performance dish antenna literature and implemented in the pillbox geometry. This shaping off ers limited but useful control of the aperture distribution and thus indirectly over the radiation pattern. To test these innovations three X-band antennas have been designed, built and measured. An initial unshaped geometry is used for the fi rst design to show the fold or bend performance. This antenna has a simulated and measured 2GHz usable bandwidth, with a reflection coeffi cient below -10dB and side-lobes below -27dB over a bandwidth in excess of 20%. Shaping is then added to show how either side-lobe levels can be lowered to below -32dB, or the gain enhanced by 2dB. The enhanced designs have been built and experimentally veri fied. / AFRIKAANSE OPSOMMING: Die drie-dubbel gevoude pildoos antenna is `n antenna topologie wat goed gepas is vir die gebruik as `n stapelbare "plank" element vir radar aanwending. Sy geskiktheid kom vanwee die vou van die struktuur wat dit meer kompak maak sowel as die konstruksie moontlik goedkoper maak. Huidige ontwerpe van die antenna strukture, hetsy twee of drie lae, ly aan twee tekortkominge: a) Die buiging of vou tussen die lae veroorsaak ongewensde weerkaatsings en b) Weens hul paraboliese meetkunde is feitlik geen beheer oor die stralings patroon beskikbaar nie. Hierdie werk spreek beide hierdie tekortkominge aan. `n Lae weerkaatsing by die oorgang is verkry deur eenvoudige kompenserende elemente by die ontwerp in te voeg wat, met minimale vervaardigings kompleksiteit, hoë werkverrigting lewer oor `n breë frekwensie en invals hoek spektrum. Om patroon beheer te voorsien is die konsep van "dubbele gevormende weerkaatsers" geleen vanaf die hoë verkverrigting skottel antenna literatuur en in die pildoos meetkunde ingestel. Hierdie vorming lewer beperkte dog nuttige beheer oor die openings verspreiding en dus indirek oor die stralings patroon. Om hierdie nuwighede te toets is drie X-band antennas ontwerp wat gebou en gemeet is. 'n Aanvanklike ongevormende meetkunde is gebruik vir die eerste ontwerp om die vou of buiging se werksverrigting te bewys. Hierdie antenna het `n gesimuleerde en gemete 2GHz bruikbare bandwydte met `n weerkaatsings kwosiënt onder -10dB en sylobbe van minder as -27dB oor `n bandwydte van meer as 20%. Vorming is dan bygevoeg om te bewys dat of verlaagde sylobbe van onder -32dB of verhoogde aanwins met 2dB verkrygbaar is. Die verbeterde ontwerpe is gebou en eksperimenteel bewys.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The o set Gregorian dual re ector antenna is eminently well suited to a radio telescope antenna application as it o ers a narrow beam width pattern (i.e high gain) and good e ciency. The focus of this work is on the analysis of characteristics of such a Gregorian antenna. The design of the class of re ector antennas is normally based on the use of ray-optics, with this simpli ed approach being able to predict antenna performance based on approximate formulas for example the beam width against aperture size. However for compound antennas such as the Gregorian re ector there are several interdependent parameters that can be varied and this reduces the applicability of the simple ray-optic approach. It was decided that, if a fast enough analysis of a con guration can be found, the technique of design through interactive analysis would be viable. To implement a fast analysis of the main beam performance of such a Gregorian antenna, a solution algorithm has been implemented using a plane wave spectrum approach combined with a custom aperture integration formulation. As this is able to predict the beam performance within about a second on a PC, it is suitable for iterative design. To implement the iterative design in a practical manner a user interface has been generated that allows the user to interactively modify the geometry, see the physical layout, and then nd the antenna pattern. A complete working system has been realised with results comparing well to a reference solution. The limitations of the technique, such as its inaccuracy in predicting the side lobe structure, are also discussed. / AFRIKAANSE OPSOMMING: Die afset Gregoriaanse dubbelweerkaatser antenna is uiters gepas vir radioteleskoop toepassings aangesien dit 'n nou bundelwydte (ho e aanwins) en 'n goeie benuttingsgraad bied. Die fokus van hierdie werk is op die analise van die eienskappe van so 'n Gregoriaanse antenna. Die ontwerp van die klas van weerkaatsantennas is normaalweg gebaseer op straal-optika, waar hierdie vereenvoudigde tegniek, deur benaderde formules, gebruik kan word om antennawerkverrigting af te skat soos bv. die bundelwydte teen stralingsvlakgrootte. Vir saamgestelde antennas soos die Gregoriaanse weerkaatser is daar egter verskeie onafhanklike parameters wat verstel kan word en die toepaslikheid van die eenvoudige straal-optiese benadering verminder. Dit was besluit dat, indien die analise van die kon gurasie vinnig genoeg uitgevoer kon word, die tegniek van ontwerp deur interaktiewe analise werkbaar kan wees. Om 'n vinnige analise van die hoofbundelwerkverrigting van so 'n Gregoriaanse antenna te bewerkstellig, is 'n oplossingsalgoritme gemplementeer wat gebruik maak van 'n platvlakgolfspektrum benadering in kombinasie met 'n doelgemaakte stralingsvlakintegrasieformulering. Aangesien hierdie strategie die hoofbundel binne ongeveer 'n sekonde op 'n persoonlike rekenaar kan voorspel, is dit gepas vir iteratiewe ontwerp. Om die iteratiewe ontwerp op 'n praktiese wyse te implementeer is 'n gebruikerskoppelvlak geskep wat die gebruiker toelaat om, op 'n interaktiewe wyse, die geometrie aan te pas, die siese uitleg te sien en dan die stralingspatroon te bereken. 'n Volledige werkende stelsel is gerealiseer met resultate wat goed ooreenstem met 'n verwysingsoplossing. Die tekortkominge van die tegniek, soos die onakkuraatheid in die voorspelling van die sylobstruktuur, word ook bespreek.

ITC/USA 2011 Conference Proceedings / The Forty-Seventh Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2011 / Bally's Las Vegas, Las Vegas, Nevada / A novel dual-band S and C band antenna for high-performance autotracking applications is described. The antenna provides simultaneous dual band coverage for targets with circular or linear polarization. A vertex mounted C-band multi-mode common aperture feed is added in a Cassegrain configuration augmenting the existing ViaSat patented [1-4] ESCAN® S-band prime focus feed. A dichroic subreflector is also added allowing simultaneous dual band operation for the prime focus and Cassegrain configurations with minimal interaction. Existing S-band antennas are easily upgraded for dual band capability with only the additions of the vertex mounted C-band feed and dichroic subreflector.

Selectively-transparent and conducting photonic crystals (STCPCs) made of alternating layers of sputtered indium-tin oxide (ITO) and spin-coated silica (SiO2) nanoparticle films have potential applications in micromorph solar cells and building integrated photovoltaics (BIPVs). In this work, theoretical calculations have been performed to show performance enhancement of the micromorph solar cell upon integration of the STCPC an intermediate reflector. Thin semi-transparent hydrogenated amorphous silicon (a-Si:H) solar cells with STCPC rear contacts are demonstrated in proof-of-concept devices. A 10% efficiency increase in a 135nm thick a-Si:H cell on an STCPC reflector with Bragg peak at 620nm was observed, while the transmitted solar irradiance and illuminance are determined to be 295W/m2 and 3480 lux, respectively. The STCPC with proper Bragg peak positioning can boost the a-Si:H cell performance while transmitting photons that can be used as heat and lighting sources in building integrated photovoltaic applications.

Thesis advisor: John E. Ebel / This research describes a method to carry out quantitative analyses of sub-seabed sediments using high-resolution chirp seismic profiles in order to estimate the properties of subsurface sediments. The method identifies significant sedimentary interfaces, extracts them from the seismic record, and measures the inelastic attenuation coefficients (k) of the sedimentary layers. The k values and their variations with increasing depth of sediments are indicative of the amount of compaction of the sediment. The k values are correlated with borehole lithology to provide a relationship between k measurements and local borehole lithology. Once determined for an area, the correlation can be applied to other seismic records from the area to analyze sedimentary properties even if no borehole lithology is locally available. / Thesis (MS) — Boston College, 2016. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

Le but de cette étude est de développer un modèle quantitatif pour l’interaction et la propagation des neutrons de faible énergie dans les milieux nanodispersés (en utilisant la nanopoudre de diamant comme exemple), qui prend en compte l’influence de la densité moyenne nanodispersée sur les processus de la propagation et la diffusion des neutrons à basse énergie, et les informations sur la structure d'une nanopoudre de diamant.L'urgence du problème à résoudre est due au manque d'informations sur la complétude des concepts des systèmes étudiés, sur les mécanismes d'interaction des neutrons de basse énergie avec les matériaux nanostructurés, sur les caractéristiques des propriétés de la structure des nanodispersés. médias, sur l'évolution des systèmes nanodispersés sous l'influence des rayonnements. Le développement du modèle quantitatif proposé est nécessaire pour l'évaluation qualitative et l'interprétation de diverses données expérimentales. L’élaboration d’un modèle quantitatif et de méthodes de calcul quantitatif de l’interaction et de la propagation des neutrons de faible énergie dans les milieux nanodispersés permettra d’interpréter des données expérimentales indépendantes dans le cadre de concepts unifiés et de réduire considérablement la quantité de paramètres empiriques. interprétation quantitative des résultats expérimentaux.L'auteur recommande d'utiliser le modèle quantitatif proposé et l'ensemble de programmes informatiques conçus pour les estimations qualitatives et quantitatives et l'interprétation de divers résultats expérimentaux, ainsi que pour des calculs quantitatifs préliminaires au stade de la planification de l'expérience.La thèse consiste en une introduction, quatre chapitres, une bibliographie et des conclusions.Le premier chapitre présente les résultats de la recherche sur le niveau de développement technique mondial actuel des nanotechnologies nucléaires. Il est à noter qu’à l’heure actuelle, les nanotechnologies nucléaires sont au stade de la recherche universitaire fondamentale et exploratoire, principalement axée sur l’extraction et l’accumulation de nouvelles connaissances.Le deuxième chapitre propose un modèle pour la propagation des neutrons à faible énergie dans un milieu nanodispersé. Une expression est obtenue pour l'équation de transfert de neutrons dans la forme de diffusion, c'est-à-dire l'équation de type Boltzmann. Les conditions aux limites sont analysées et établies pour l'équation du transfert de neutrons dans l'approximation de diffusion, en tenant compte des processus cohérents et incohérents d'interaction des neutrons avec le matériau. La méthode variationnelle permet une solution analytique de l'équation de transfert pour la fonction de distribution des neutrons dans l'approximation de la diffusion des neutrons aux petits angles par les nanoparticules dans la poudre. Les données expérimentales permettent de développer un modèle de nanopoudre de diamant à utiliser dans les calculs.Le troisième chapitre décrit la conception d'un algorithme de simulation numérique du transfert de neutrons dans une nanopoudre de diamant. Les calculs de modèle de la section efficace pour la diffusion élastique cohérente des neutrons par les nanoparticules sphériques sont effectués: 1) calculs quantiques précis par la méthode de la fonction de phase; 2) calculs dans l'approximation de Born. À titre de référence, nous décrivons brièvement des méthodes standard pour simuler des valeurs aléatoires d'angles de diffusion et des transformations de systèmes de coordonnées dans une méthode de Monte Carlo par ordinateur pour simuler la propagation des neutrons en nanopoudre.Le quatrième chapitre présente les résultats des calculs numériques effectués après le modèle quantitatif suggéré. Les résultats des calculs numériques sont analysés et comparés avec des données expérimentales. La comparaison montre un accord satisfaisant de calculs avec les données d'expériences indépendantes. / The aim of the present study is to develop a quantitative model for the interaction and propagation of low-energy neutrons in nanodispersed media (using the diamond nanopowder as an example), which takes into account the influence of the nanodispersed medium density on the processes of propagation and scattering of low-energy neutrons, and the information about the structure of a diamond nanopowder.The urgency of the problem being solved is due to the lack of information about the completeness of the concepts of the systems under study, about the mechanisms of interaction of low energy neutrons with nanostructured materials, about the features of the properties of the structure of nanodispersed media, about the evolution of nanodispersed systems under the influence of radiation. The development of the proposed quantitative model is necessary for qualitative evaluation and interpretation of various experimental data. The development of a quantitative model and methods for the quantitative calculation of the interaction and propagation of low-energy neutrons in nanodispersed media will allow to interpret independent experimental data within the frames of unified concepts, and will significantly reduce the amount of empirical parameters in the quantitative interpretation of experimental results.The author recommends using the proposed quantitative model and the designed set of computer programs for qualitative and quantitative estimates and interpretation of various experimental results, and for preliminary quantitative calculations at the stage of experiment planning.The thesis consists of an introduction, four chapters, a bibliography and conclusions.The first chapter presents the results of the research into the level of current global technical development of nuclear nanotechnologies. It is noted that at present, the nuclear nanotechnologies are at the stage of fundamental and exploratory academic research, predominantly focused on the extraction and accumulation of new knowledge.The second chapter suggests a model for the propagation of low-energy neutrons in a nanodispersed medium. An expression is obtained for the neutron transfer equation in the diffusion form, i.e. Boltzmann type equation. The boundary conditions are analyzed and established for the neutron transfer equation in the diffusion approximation, accounting for coherent and incoherent processes of neutron interaction with the material. The variational method enables an analytical solution of the transfer equation for the neutron distribution function in the approximation of small angle neutron scattering by nanoparticles in the powder. The experimental data allows to develop a model of diamond nanopowder, which is to be used in calculations.The third chapter describes the design of an algorithm for numerical simulation of neutron transfer in a diamond nanopowder. Model calculations of the cross section for elastic coherent scattering of neutrons by spherical nanoparticles are carried out: 1) precise quantum-mechanical calculations by the phase-function method; 2) calculations in the Born approximation. For reference, we briefly describe standard methods for simulating random values of scattering angles and transformations of coordinate systems in computer Monte Carlo method simulation of neutron propagation in nanopowder.The fourth chapter presents the results of numerical calculations carried out after the suggested quantitative model. The results of numerical calculations are analyzed and compared with experimental data. The comparison shows a satisfactory agreement of calculations with the data of independent experiments.

Thesis (Elec. E.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science; and, (B.S.)--Massachusetts Institute of Technology, Dept. of Mathematics, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING / Vita. / Includes bibliographical references. / by Carey Milford Rappaport. / B.S. / Elec.E.

abstract: Demand for green energy alternatives to provide stable and reliable energy solutions has increased over the years which has led to the rapid expansion of global markets in renewable energy sources such as solar photovoltaic (PV) technology. Newest amongst these technologies is the Bifacial PV modules, which harvests incident radiation from both sides of the module. The overall power generation can be significantly increased by using these bifacial modules. The purpose of this research is to investigate and maximize the effect of back reflectors, designed to increase the efficiency of the module by utilizing the intercell light passing through the module to increase the incident irradiance, on the energy output using different profiles placed at varied distances from the plane of the array (POA). The optimum reflector profile and displacement of the reflector from the module are determined experimentally. Theoretically, a 60-cell bifacial module can produce 26% additional energy in comparison to a 48-cell bifacial module due to the 12 excess cells found in the 60-cell module. It was determined that bifacial modules have the capacity to produce additional energy when optimized back reflectors are utilized. The inverted U reflector produced higher energy gain when placed at farther distances from the module, indicating direct dependent proportionality between the placement distance of the reflector from the module and the output energy gain. It performed the best out of all current construction geometries with reflective coatings, generating more than half of the additional energy produced by a densely-spaced 60-cell benchmark module compared to a sparsely-spaced 48-cell reference module.ii A gain of 11 and 14% was recorded on cloudy and sunny days respectively for the inverted U reflector. This implies a reduction in the additional cells of the 60-cell module by 50% can produce the same amount of energy of the 60-cell module by a 48-cell module with an inverted U reflector. The use of the back reflectors does not only affect the additional energy gain but structural and land costs. Row to row spacing for bifacial systems(arrays) is reduced nearly by half as the ground height clearance is largely minimized, thus almost 50% of height constraints for mounting bifacial modules, using back reflectors resulting in reduced structural costs for mounting of bifacial modules / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2019

Antennas play a crucial role in communication systems since they are the transmitting/receiving elements that transition information from guided transmission to open-space propagation. Antennas are used in many different applications such as aerospace communications, mobile phones, TVs and radios. Since the dimensions of antennas are usually physically proportional to the wavelength at their operating frequencies, it is important to develop large antennas and arrays that can be stowed compactly and easily deployed. Also, it is important to minimize the number of antennas on a platform by developing multifunctional antennas. The first aim of this research is to develop new deployable, collapsible, light-weight and robust reconfigurable antennas based on origami principles. All designs will be validated through simulations and measurements. Paper as well as other substrates, such as, Kapton and fabric, will be used to develop our origami antennas. The second aim of this research is to derive integrated analytical and simulation models for designing optimal origami antennas for various applications, such as, satellite or ground communications. This dissertation presents research on origami antennas for novel reconfigurable communication systems. New designs of reconfigurable monofilar, bifilar and quadrifilar antennas based on origami cylinders are developed and validated. Novel fabrication methods of origami antennas are presented with detailed geometrical analysis. Furthermore, multi-radii origami antennas are proposed, analyzed, fabricated and validated and they exhibit improved circular polarization performance and wide bandwidths. An actuation mechanism is designed for these antennas. For the first time, a low-cost and lightweight reconfigurable origami antenna with a reflector is developed here. In addition, an array is developed using this antenna as its element. Finally, a kresling conical spiral antenna and a spherical helical antenna are designed with mode reconfigurabilities.