This thesis project investigates, analyzes, designs, simulates, constructs and tests a dual-axis solar tracker system to track the sun and concentrates the heat of the sunlight, using a Fresnel lens, into a small area, which is above of an evaporator, to increase the temperature of the seawater to convert it into freshwater. The dual-axis solar tracker was designed with the main objectives that the structure was portable, dismountable, lightweight, low cost, corrosion resistant, wires inside pipes, accurate, small size, follow the sun automatically, off-grid (electrical), use green energy (solar powered), and has an empty area right below of the lens. First, a 500 mm diameter flat Fresnel lens was selected and simulated based on an algorithmic method achieved by a previous PhD student at UNT using MATLAB®, to give the optimization lens dimensions. The lens profile was drawn with AutoCAD®, then output profile lens was simulated in COMSOL Multiphysics®. The objective was to provide the high efficiency, optimum and high precision of the focal rays and heat to the receiver of the evaporator. A novel dual-axis solar tracker system was then designed that is portable, dismountable, lightweight and corrosion resistant. The solar tracker tracks the sun in two axis of rotation automatically during the day time, maximizing the angles of inclination on each axis. After testing computer simulations, the dual-axis solar tracker system was constructed and tested. Last, a detailed cost analysis was performed of the entire project. The outcome of this work can be applied for desalination seawater purposes or other any Fresnel lens application that require a focal high temperature directed by dual-axis solar tracker system.

Ce travail a pour objet de développer une nouvelle technologie de l’énergie solaire à concentration. Il porte sur la présentation du concept, la réalisation prototypique et l’étude optique et énergétique d’un nouveau concentrateur solaire QingSun™. Ce concentrateur a une forme de parallélépipède rectangulaire et comporte des lentilles de Fresnel linéaires, des parois tapissées de miroir et d’un récepteur solaire mobile entraîné par un système de suivi à l’intérieur du caisson de concentration. Un modèle optique et un modèle énergétique ont été élaborés et validés avec une série d’expériences. Ils ont permis d’étudier le fonctionnement et les performances énergétiques du concentrateur. Une étude de l’influence paramétrique de l’inclinaison et l’orientation a été effectuée et a montré que l’inclinaison a plus d’influence que l’orientation sur les performances. Enfin, les performances énergétiques optimales du concentrateur ont été estimées. / This work is for the purpose to develop a new solar concentrating technology. It covers the presentation of the concept, the prototype realization and the optical and energy study of a new solar concentrator QingSun™. This concentrator has a shape of rectangular parallelepiped and includes linear Fresnel lenses, mirror-lined walls and a mobile solar receptor controlled by a tracking system inside the casing. An optical model and an energy model were developed and validated with a series of experiments. The both models permitted us to examine the function and the energy performance of the concentrator. A parametric study of the influence of the tilt and the orientation was performed and showed that the tilt had more influence than the orientation. Finally, the optimal energy performance of this concentrator was estimated.

Baigiamajame magistro darbe suprojektuotos ir pagamintos dviejų rūšių šviesos koncentratorinės sistemos: jungtinė parabolinė ir sistema su Frenelio lęšiu. Atlikta saulės elementų efektyvumo analizė, išnagrinėtos šviesą koncentruojančių sistemų rūšys bei aptarti jų optiniai parametrai. Frenelio lęšis ir koncentratorinių sistemų laikančiosios konstrukcijos pagamintos vakuuminio formavimo būdu, ieškant pigesnės gamybos technologijos. Baigiamajame darbe atlikti optinio pralaidumo ir lūžio rodiklio, matomos šviesos bangų ilgių ruože, tyrimai bei saulės elementų, esančių šviesos koncentratorinėse sistemose,voltamperinių ir voltvatinių charakteristikų tyrimai. Iš tyrimų rezultatų nustatyti šviesos koncentravimo laipsniai. Darbe diskutuojama apie pigių optinių sistemų galimus pritaikymus ir jų tobulinimo būdus. Išnagrinėjus teorinę ir praktinę dalis, pateiktos išvados ir pasiūlymai. Darbą sudaro 8 dalys: įvadas, saulės elementų efektyvumo ribos, saulės šviesos koncentratoriai ir jų panaudojimas fotoelektrinėse sistemose, eksperimentinių tyrimų metodika, prototipų gamyba, eksperimentiniai tyrimai, išvados, literatūros sąrašas. Darbo apimtis – 82 p. teksto be priedų, 95 pav., 13 lent., 22 bibliografiniai šaltiniai. Atskirai pridedami darbo priedai. / Concentrated PV systems (compound parabolic and Fresnel CPV) have been designed and investigated. The efficiency of solar cells and the types of light concentrated systems have been analyzed and their optical parameters have been discussed. Fresnel lens and the CPV system holding structure have been fabricated by means of vacuum forming machine in this way making the technology of production less expensive. Optical transmittance and refractive index of Fresnel lens were measured in the range of visible light wavelengths. Current-voltage and voltage-power characteristics of solar cells built inside the CPV systems were investigated, based on results the degree of light concentration by Fresnel lens and compound parabolic CPV has been determined. Some discussions regarding possible applications of concentrated PV systems containing the Fresnel lens as well as possible ways of CPV design improvements are given in current work. After analysed theoretical and practical parts, conclusions and suggestions are proposed. Thesis structure: introduction, theoretical and experimental parts, results of experiments, conclusions and references. Thesis consist of: 82 p. text without appendixes, 95 pictures, 13 tables, 22 bibliographical entries. Appendixes included.

Les travaux présentés dans cette thèse sont une contribution à l’étude des systèmes d’imagerie active en bande millimétrique et plus spécifiquement sur les parties antennaires et le traitement de signal. Ces travaux ont été menés dans le cadre d’une collaboration entre Canon Research Center France et l’ETR. Une première étude a porté sur les antennes focalisantes et plus spécifiquement sur la lentille de Fresnel avec un procédé de fabrication de matériau à gradient d’indice qui a permis d’améliorer l’efficacité (59%) et la largeur bande de fréquence (75-110 GHz). Cette antenne a été utilisée sur un système rotatif pour imager une scène réelle extérieure. L’étude s’est ensuite focalisée sur la conception d’une configuration Multiple-Input Multiple-Output ou MIMO (entrées multiples, sorties multiples) grâce notamment à l’utilisation d’un dispositif compressif passif 4×1 permettant de réduire, par compression, le nombre de chaînes RF. Ces chaînes sont décompressées par post-traitement. Le dispositif, placé à l’émission, a été associé avec un scanner qui permet de synthétiser un réseau d’antennes à la réception. Cette configuration a permis de générer virtuellement un réseau de plus grande taille, permettant d’améliorer la résolution azimutale du système tout en limitant le nombre de chaînes RF. Cette configuration est utilisée pour imager une scène en chambre anéchoique afin de valider le concept. Pour améliorer encore plus la résolution du système avec un nombre limité de chaînes RF, l’étude d’algorithmes de haute-résolution, ou méthodes d’estimation spectrales, sont utilisés dans des configurations à large bande de fréquences pour imager des cibles en champs proche. L’association de la configuration MIMO, du dispositif compressif passif et des méthodes d’estimation spectrales permet d’améliorer la résolution du système tout en limitant le nombre de chaînes RF nécessaire. / The broad topic of the presented Ph.D. thesis consists in the contribution to the study of Radar imaging systems at millimeter-wave and more specifically to the antennas and signal processing. These works have been carried out during a partnership between Canon Research Center France and IETR. A first study on focusing antennas, particularly on Fresnel lens antennas, thanks to a technological process to manufacture inhomogeneous materials, has allowed to improve the efficiency and the frequency bandwidth. The antenna has been mounted on a rotary system to image a real outdoor scene. Then, the study has been focused on the realization of a Multiple-Input Multiple-Output (MIMO) configuration notably using a 4 × 1 passive compressive device allowing to reduce, by compression, the number of radiofrequency (RF) chains. The chains are decompressed by post-processing. The device, used at the transmitting part, is associated with a scanner that synthetizes a receiving array of antennas. This configuration allows to generate a large virtual array, to improve the azimutal resolution of the system while maintaining acceptable the number of RF chains. This configuration has been used to image a scene in an anechoid chamber to validate the concept. To further improve the spatial resolution of the system for a given number of RF chains, the study of high resolution algorithms, or spectral estimation methods, are used to image scenes in near field and wide-band configurations. The combination of MIMO configurations, the passive compressive device and the spectral estimation methods have allowed to drastically improve the spatial resolution of the radar imaging system while limiting the number of RF chains.

This work investigates the Fresnel-lens-based solar concentrator-receiver system in a multi-perspective manner to design, test and fabricate this concentrator with high-efficiency photon and heat outputs and a minimized effect of chromatic aberrations. First, a MATLAB®-incorporated algorithm optimizes both the flat-spot and the curved lens designs via a statistical ray-tracing methodology of the incident light, considering all of its incidence parameters. The target is to maximize the solar ray intensity on the receiver's aperture, and therefore, achieve the highest possible focal flux. The algorithm outputs prismatic and dimensional geometries of the Fresnel-lens concentrator, which are simulated by COMSOL® Multiphysics to validate the design. For the second part, a novel genetically-themed hierarchical algorithm (GTHA) has been investigated to design Fresnel-lens solar concentrators that match with the distinct energy input and spatial geometry of various thermal applications. Basic heat transfer analysis of each application decides its solar energy requirement. The GTHA incorporated in MATLAB® optimizes the concentrator characteristics to secure this energy demand, balancing a minimized geometry and a maximized efficiency. Two experimental applications were selected from literature to validate the optimization process, a solar welding system for H13 steel plates and a solar Stirling engine with an aluminum-cavity receiver attached to the heater section. In each case, a flat Fresnel-lens with a spot focus was algorithmically designed to supply the desired solar heat, and then a computer simulation of the optimized lens was conducted showing great comparability to the original experimental results. Thirdly, the prismatic geometry of the Fresnel lens was further optimized through a statistical approach that incorporates laws of light refraction and trigonometry. The proposed design produces high focal irradiance that is more suitable for thermal applications. The motivation was to enhance the tolerability of a flat Fresnel-lens concentrator to tracking errors, without the use of secondary optics or sophisticated, and normally costly, meticulous tracking equipment. A comparative simulation analysis was conducted for two case studies from literature, each with a different design method. Fresnel lenses optimized by this work enhanced the concentration acceptance product (CAP) significantly, compared to that in literature. Then, this work introduced an innovative code-based, detailed, and deterministic geometrical approach, which couples the optimization of the Fresnel lens primary optical element (POE) and the dome-shaped secondary optical element (SOE). The objective was to maximize the concentration acceptance product, while using the minimum SOE and receiver geometries at a given f-number and incidence angle (also referred to as the tracking error angle). The laws of polychromatic light refraction along with trigonometry and spherical geometry were utilized to optimize the POE grooves, SOE radius, receiver size, and SOE–receiver spacing. Two literature case studies were analyzed to verify this work's optimization, and the equivalent POEs designed by this work, with optimized SOEs, showed a significant enhancement in the CAP values compared to that of literature. Lastly, four methods for prototyping the Fresnel lens were discussed and experimentally tested; 3D printing, acrylic resin casting, direct CNC machining in acrylic and hot embossing. Once tested, the methods of CNC machining and hot embossing of acrylic proved to be the most promising in terms of cost, fabrication time, and concentration effectiveness. Future work will focus on enhancing the algorithmic design and improving the quality of lens fabrication.