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Tesi sul tema "Reflector"
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1
Mousari, Bafrooei Seyed Pedram. "Reflector feeds for large adaptive reflector antennas". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ57513.pdf.
Testo completo
2
Durnan, Gregory J. "Parasitic Feed Elements for Reflector Antennas". Thesis, Griffith University, 2005. http://hdl.handle.net/10072/368077.
Testo completoAbstract (sommario):
The use of parasitic wire dipoles are examined when placed in the proximity of a focused dipole feed in a parabolic reflector antenna. These parasitic elements are rotated around the feed dipole and a search is performed for the ideal positioning so as to yield maximum radiated power and main beam shift in order to develop a novel form of angle diversity. In addition a comparison is made between 2 element dipole feed structures and linearly and circularly polarised patch feed structures. In order to analytically model the structure, mutual coupling between feed elements is calculated taking into account a varying reflection coe±cient due to an impedance mismatch between the transmission line and driven element. An analytical treatment of the calculation of the radiated co-polar and cross-polar feed pattern is presented in addition to the projected field at the reflector surface. A comparison is made to the results presented by E.M.T Jones in the 1954 IRE Transactions of Antennas and Propagation paper entitled 'Paraboloid Reflector and Hyperboloid Lens Antennas'. A theoretical treatment of the reflected field and far field radiation pattern is then presented using the methods of Geometrical Optics, Physical Optics and Fourier analysis. The author derives analytical equations for multiple element incident feed fields and surface current equations for half wave feeds of arbitrary position and number. The fndings are confirmed using a comparison of three methods. These are; original code developed from analytical derivations, the NEC2 Method of Moments using a meshed reflector model and finally, by experimental methods. Analysis of a 30cm 0.4 F/D prime focus reflector at 3GHz using a 2 element feed yields up to 2dB gain over a single dipole feed when the element is displaced either laterally or at 60 or 120 degrees from the feed axis. The optimum offset from the driven element is in the 0.4 to 0.6¸ range. Maximum beam shift for this structure at the half power points is shown to be approximately 10 degrees. When designed as a low-cost system with undemanding polarisation requirements the structure presented provides an easily implemented or retrofitted alternative to multiple antenna diversity solutions.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Microelectronic Engineering
Full Text
3
Shen, Bing. "Multiple reflector scanning antennas". Diss., Virginia Tech, 1993. http://hdl.handle.net/10919/40108.
Testo completo
4
Wang, Yang. "Time-modulated reflector-arrays". Thesis, University of Sheffield, 2015. http://etheses.whiterose.ac.uk/8510/.
Testo completoAbstract (sommario):
This PhD thesis introduces the time-modulated reflector-arrays which are a hybrid of conventional time-modulated array (TMA) systems and reflectarrays. The TMRAs use a similar layout of reflectarray feed by a source. Compared to conventional phased arrays, reflectarrays and time-modulated arrays, a TMRA is potentially simpler to implement in hardware as it does not need a complicated feeding network or the use of the phase shifting units. Instead of phase shifting units, TMRAs use discrete time-switching to achieve beamforming functions. The concept and operating mechanism of the TMRA is explained using a simple model based on isotropic scatterers. A more sophisticated TMRA based on an 8 element array of PIN-diode controlled bow-tie dipole elements is designed and analysed using a full-wave commercial simulator. A hardware implementation of the bowtie dipole TMRA system, including control circuitry, is also described and measured data is presented. The simulated and measured results confirm that the time-modulated reflector array system performs the required function of harmonic beam steering. Moreover, TMRAs can provide functions such as sidelobe suppression and adaptive beamforming. The thesis also provide solutions to the challenges of TMRAs such as low system efficiency and phases variances caused by feeding paths. Overall TMRAs combine the benefits of conventional TMA systems and reflectarrays. They can provide similar functions of conventional TMAs, phased arrays and reflectarrays without the need of expensive phase shifters and lossy transmission lines. This makes TMRAs a very good candidates in applications over millimetre-wavelength frequency band.
5
Mas, Baixeras Albert. "Optimization of inverse reflector design". Doctoral thesis, Universitat de Girona, 2011. http://hdl.handle.net/10803/22705.
Testo completoAbstract (sommario):
Aquesta tesi presenta un nou mètode pel disseny invers de reflectors. Ens hem centrat en tres temes principals: l’ús de fonts de llum reals i complexes, la definició d’un algoritme ràpid pel càlcul de la il•luminació del reflector, i la definició d’un algoritme d’optimització per trobar més eficientment el reflector desitjat.
Les fonts de llum estan representades per models near-field, que es comprimeixen amb un error molt petit, fins i tot per fonts de llum amb milions de raigs i objectes a il•luminar molt propers. Llavors proposem un mètode ràpid per obtenir la distribució de la il•luminació d’un reflector i la seva comparació amb la il•luminació desitjada, i que treballa completament en la GPU. Finalment, proposem un nou mètode d’optimització global que permet trobar la solució en menys passos que molts altres mètodes d’optimització clàssics, i alhora evitant mínims locals.This thesis presents new methods for the inverse reflector design problem. We have focused on three main topics: the use of real and complex light sources, the definition of a fast lighting simulation algorithm to compute the reflector lighting, and the definition of an optimization algorithm to more efficiently find the desired reflector. The light sources are represented by near-field datasets, that are compressed with a low error, even with millions of rays and for very close objects. Then, we propose a fast method to obtain the outgoing light distribution of a reflector and the comparison with the desired one, working completely in the GPU. Finally, a new global optimization method is proposed to search the solution in less steps than most other classic optimization methods, also avoiding local minima.
6
Stewart, Scot Howard. "Multiple feed reflector antenna analysis". Thesis, Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/94472.
Testo completoAbstract (sommario):
A method of calculating the secondary pattern of a reflector illuminated by a feed array is developed. Geometrical optics is used to determine the incident field via a coordinate transformation approach. The incident field from each element is superimposed to form the total field used in finding the surface currents of the physical optics radiation integral. The technique allows each element to be arbitrarily excited, positioned and oriented. The element patterns may be different allowing mutual coupling to be included.M.S.
7
Fournier, Florian. "FREEFORM REFLECTOR DESIGN WITH EXTENDED SOURCES". Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3146.
Testo completoAbstract (sommario):
Reflector design stemmed from the need to shape the light emitted by candles or lamps. Over 2,000 years ago people realized that a mirror shaped as a parabola can concentrate light, and thus significantly boosts its intensity, to the point where objects can be set afire. Nowadays many applications require an accurate control of light, such as automotive headlights, streetlights, projection displays, and medical illuminators. In all cases light emitted from a light source can be shaped into a desired target distribution with a reflective surface. Design methods for systems with rotational and translational symmetry were devised in the 1930s. However, the freeform reflector shapes required to illuminate targets with no such symmetries proved to be much more challenging to design. Even when the source is assumed to be a point, the reflector shape is governed by a set of second-order partial non-linear differential equations that cannot be solved with standard numerical integration techniques. An iterative approach to solve the problem for a discrete target, known as the method of supporting ellipsoids, was recently proposed by Oliker. In this research we report several efficient implementations of the method of supporting ellipsoids, based on the point source approximation, and we propose new reflector design techniques that take into account the extent of the source. More specifically, this work has led to three major achievements. First, a thorough analysis of the method of supporting ellipsoids was performed that resulted in two alternative implementations of the algorithm, which enable a fast generation of freeform reflector shapes within the point source approximation. We tailored the algorithm in order to provide control over the parameters of interest to the designers, such as the reflector scale and geometry. Second, the shape generation algorithm was used to analyze how source flux can be mapped onto the target. We derived the condition under which a given source-target mapping can be achieved with a smooth continuous surface, referred as the integrability condition. We proposed a method to derive mappings that satisfy the integrability condition. We then use these mappings to quickly generate reflector shapes that create continuous target distributions as opposed to reflectors generated with the method of supporting ellipsoids that create discrete sets of points on the target. We also show how mappings that do not satisfy the integrability condition can be achieved by introducing step discontinuities in the reflector surface. Third, we investigated two methods to design reflectors with extended sources. The first method uses a compensation approach where the prescribed target distribution is adjusted iteratively. This method is effective for compact sources and systems with rotational or translational symmetry. The second method tiles the source images created by a reflector designed with the method of supporting ellipsoids and then blends the source images together using scattering in order to obtain a continuous target distribution. This latter method is effective for freeform reflectors and target distributions with no sharp variations. Finally, several case studies illustrate how these methods can be successfully applied to design reflectors for general illumination applications such as street lighting or luminaires. We show that the proposed design methods can ease the design of freeform reflectors and provide efficient, cost-effective solutions that avoid unnecessary energy consumption and light pollution.Ph.D.
Optics and Photonics
Optics and Photonics
Optics PhD
8
Parkinson, Joseph R. "The analysis of microwave reflector antennas". Thesis, University of Birmingham, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342108.
Testo completo
9
Sterr, U. "Radiation characteristics of corner reflector antennas". Thesis, Queen Mary, University of London, 1998. http://qmro.qmul.ac.uk/xmlui/handle/123456789/1686.
Testo completoAbstract (sommario):
This thesis presents a study of the radiation characteristics of corner reflector antennas. The influence of the design parameters on the radiation characteristics are assessed using an analytical method and the Finite Difference Time Domain (FDTD) method. The FDTD method for corner reflector antennas which are electrically small to medium sized antennas is developed in detail. The important subject of the Absorbing Boundary Conditions (ABCs) is studied including a study of Mur ABC and Perfectly Matched Layers. It is shown that both methods reduce the reflections from the boundaries sufficient so that the far-field radiation pattern can be computed accurately. An analytical solution to compute the far-field radiation pattern for infinite comer reflector antennas is derived and used to understand the radiation mechanisms. Based on those results, the FDTD method is used to conduct a parametric study on finite sized comer reflector antennas. Experimental antennas have been built and measured in order to verify the computational predictions. Very good agreement is reported The novel idea of a variable beam-width comer reflector antenna is developed and practical designs of such an antenna are presented. The principle is to design the comer reflector antenna such that the beam-width of the antenna can be precisely modified. Data on the gain and beam-width are presented. This has been done both by computational and by an experimental model. The influence on the performance of the comer reflector antenna when substituting the solid reflector plates by rods has been investigated. The computational predictions have been verified by measurements of an experimental antenna. Very good agreement has been achieved. III[ The possibility of modifying the shape of the comer reflector antenna is investigated. It is shown that a modified comer reflector antenna with less depth produces the same far-field pattern as a standard corner reflector antenna. It is also shown that the performance of small aperture size corner reflector antennas is superior to a cylindrical parabolic reflector antenna.
10
PEREIRA, LUIS CLAUDIO PALMA. "ASYMPTOTIC ANALYSIS OF SHAPED REFLECTOR ANTENNAS". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1988. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=8374@1.
Testo completoAbstract (sommario):
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOEste trabalho apresenta uma nova técnica para aproximação de uma superfície refletora definida numericamente, i.e., por pontos fornecidos pelo processo de síntese da antena. As limitações inerentes às técnicas usuais são aqui eliminadas pela utilização de Pseudo-Splines Quínticas que interpolam uma distribuição arbitrária de pontos por uma superfície suave, com derivadas primeiras e segundas contínuas, assegurando uma representação única para o domínio de interesse. O procedimento é, então, aplicado ao subrefletor modelado de uma antena Cassegrain, com subseqüente cálculo do campo eletromagnético espalhado, permitindo uma análise detalhada de sua aplicabilidade. Uma teoria assintótica uniforme de difração é, também, aqui desenvolvida de modo a acomodar o espalhamento de feixes Gaussianos, descritivos, em freqüências altas, do diagrama de irradiação de alimentadores comumente empregados em sistemas refletores, por superfícies condutoras, através do rastreamento do campo eletromagnético ao longo de raios no espaço complexo. A análise do problema canônico (difração por semi-plano) estabelece as particularidades do método e a comparação com a solução rigorosa existente comprova sua acurácia, permitindo a extensão a problemas tridimensionais vetorais. A teoria Complexa da Difração, assim formulada, é, então aplicada ao cálculo do campo espalhado por diferentes geometrias de antenas refletoras, ilustrando a versatilidade do método bem como suas limitações.
In order to evaluate the electromagnetic field scattered by shaped reflector antennas, one has to fit a surface to a set of points furnished by a synthesis technique. A new method, capable of interpolating arbitrarily located data points by a smooth surface is here presented. The interpolating function, called Quintic Pseudo-Spline, has continuous first and seconde order derivatives and yields a unique representation for the entire domain. The method is tested on the shaped subreflector of a Cassegrain antenna providing a thorough investigation of its applicability. Also, an uniform asymptotic theory of diffraction is derived in order to analyse the scattering of Gaussin beams, descriptive of the high-frequency radiation pattern of feed horns commonly employed in reflector systems, by conducting surfaces with edges. The constraints inherent to usual methods of analysis are hereby avoided by tracking these beam-type fields along straight rays in a complex coordinate space. Investigation of the canonical problem of scattering of a Gaussian beam by a conducting half-plane establishes the characteristics of the complex ray diffraction process. Comparison of the results thus obtained with the rigorous solution reveals the accuracy of the proposed theory and permits its extension to the three-dimensional vector problem. The resulting Complex Theory of Diffraction is then applied to the evaluation of the scattered field for several reflector antenna geometries, illustrating the versatility of the method as well as its limitation.
11
Tan, Lin Tze. "Thin-walled elastically foldable reflector structures". Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.619853.
Testo completo
12
Crabtree, Karlton. "Polarization Conversion Cube Corner Retro-Reflector". Diss., The University of Arizona, 2010. http://hdl.handle.net/10150/195564.
Testo completoAbstract (sommario):
This document presents the polarization conversion cube-corner retroreflector (PC-CCR). The PCCCR is a cube-corner retroreflector which transforms the electricfield as follows: the major axis is rotated by 90° and the handedness is reversed.Since the polarization properties of a CCR are dependent on the polarization properties of each surface, exploration of the space of Mueller matrices is organized by surface type. The Mueller matrix of CCR having each of several surface types is calculated, including the traditional hollow metal and solid glass CCR types. PCCCR only occur for non-isotropic surface types. Four particular surface polarization properties are found which produce PCCCR. Three examples of PCCCR are presented using sub-wavelength grating surfaces. Several other interesting CCR are presented, including a 45° polarization rotator.
13
ZANG, SANDRO ROGERIO. "SYNTHESIS AND RIGOROUS ANALYSIS OF OMNIDIRECTIONAL DUAL-REFLECTOR ANTENNAS: THE CASE OF THE MAIN REFLECTOR WITH CIRCULAR GENERATRIX". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2010. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=20767@1.
Testo completoAbstract (sommario):
PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Este trabalho aborda o projeto de antenas omnidirecionais de duplorefletores, onde o refletor principal é obtido a partir de uma geratriz circular. A antena é composta de refletores circularmente simétricos e concêntricos que são alimentados por uma corneta cônica coaxial excitada pelo modo TEM para a produção de polarização vertical. Para realizar este estudo são utilizadas técnicas de síntese e de análise eletromagnética rigorosa. A técnica de análise eletromagnética rigorosa é baseada na associação do Método de Casamento de Modos para representar os campos no interior do alimentador e do Método dos Momentos para solucionar as equações integrais para o campo elétrico e para o campo magnético e determinar a corrente elétrica induzidas sobre as paredes metálicas externas e a amplitude dos modos sobre a abertura da corneta. A técnica de síntese destas antenas é baseada na aplicação dos princípios da Ótica Geométrica para modelar o subrefletor que irá produzir uma distribuição de fase uniforme em uma abertura cônica colocada em frente ao refletor principal com geratriz circular. O estudo exploratório sobre o desempenho destas antenas é dividido em três partes. Na primeira, as soluções fornecidas pela síntese ótica e aproximações para os campos na abertura são utilizadas para identificar configurações de antenas compactas ou que maximizem o ganho ao longo do plano horizontal. Entretanto, pode-se obter uma melhor iluminação da área de cobertura através da inclinação do lobo principal (down tilt). Para reduzir o custo de fabricação de um conjunto de antenas que atendam diferentes áreas de cobertura, pode-se utilizar o mesmo refletor principal e modelar os subrefletores para deslocar a direção de máximo do diagrama. Assim, em uma segunda etapa do estudo paramétrico, são considerados alguns refletores principais, e, para cada um deles, é obtida uma família de subrefletores modelados para deslocar o máximo do diagrama no plano vertical. Esta estratégia se torna efetiva na medida em que o custo de fabricação do subrefletor é menor do que o do refletor principal. Na terceira parte, utilizando o método híbrido composto pelo Método do Casamento de Modos e pelo Método dos Momentos, é feito o modelamento da corneta coaxial TEM com o objetivo de reduzir sua perda de retorno e estender sua banda de operação. Por fim, ainda utilizando este método híbrido, é feita uma análise rigorosa das antenas duplo-refletoras propostas neste trabalho, procurando otimizar o desempenho destas antenas em termos do diagrama de radiação e da perda de retorno.
This work presents a design study of omnidirectional dual-reflector antennas, where the main reflector is obtained from a circular generatrix. The antenna is composed of two concentric circularly symmetric reflectors and it is fed by a coaxial conical horn excited by TEM mode to produce vertical polarization. To obtain the subreflector surface, the study employs a GO synthesis technique to shape the subreflector in order to produce a uniform phase distribution in a conical aperture placed in front of the main reflector. To validate the results, it is employed a rigorous electromagnetic analysis technique based on the association of Mode Matching Technique to represent the fields inside the horn and Method of Moments to solve the integral equations of electric and magnetic fields. The solution of Method of Moments yields the induced electric current on the outer surface of the horn and the amplitude of the modes on the aperture of the horn. The exploratory study is divided in three parts. First, by using the GO approximations for the aperture fields, the geometry parameters are explored to identify compact antenna configurations that maximize the gain along the horizontal plane. However, a more uniform coverage of the ground can be obtained by tilting the main lobe. Thus, in a second step of the parametric study, it is considered a family of designs with the same main reflector and a set of subreflectors that are designed for different tilt angle of main lobe. This strategy is effective to reduce the manufacturing costs of a family of antennas designed to provide different coverage. Third, by using the hybrid method, the TEM coaxial horn is shaped to reduce the return loss and extend its operating band, and, finally, the overall antennas performance is optimized by controlling radiation pattern and return loss.
14
Armas, Nelson A. "Low sidelobe reflector antenna design for communications". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1993. http://handle.dtic.mil/100.2/ADA276079.
Testo completo
15
Graham, R. K. "Numerical synthesis of dual-reflector antenna systems". Thesis, University of Southampton, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.373929.
Testo completo
16
Rosenbusch, Peter. "Atom optics with an adaptable magnetic reflector". Thesis, University of Sussex, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341516.
Testo completo
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You, Zhong. "Deployable structures for masts and reflector antennas". Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240014.
Testo completo
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MOREIRA, FERNANDO JOSE DA SILVA. "FEED ARRAY REFLECTOR ANTENNAS FOR SHAPED BEAMS". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1992. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=8839@1.
Testo completoAbstract (sommario):
Este estudo tem como tema a análise dos campos radiados
por um conjunto de alimentadores para a iluminação de um
sistema único refletor embarcado em satélite, utilizando
para a produção de diagramas modelados. É usada uma
técnica para o tratamento do acoplamento mútuo entre os
campos de aberturas retangulares num plano condutor
elétrico infinito, de forma que os alimentadores aqui
tratados serão guias retangulares abertos e cornetas
piramidais. Uma formulação assintótica inédita foi
desenvolvida para o aclopamento entre duas aberturas
afastadas entre si. Como aplicação foram realizadas
diversas sínteses para a iluminação do território
brasileiro.This study aims the analysis of the radiated fields of na array feeding a single reflector system for satellite applications, used to produce shaped beams. It is used a technique for the treatment of the mutual coupling effects between rectangular apertures in an infinite electric conductor plane, so the feeds used are open-ended rectangular waveguides and pyramidal horns. It is also presented a new asymptotic approach for the mutual coupling between far-distanced apertures. In order to study the application of these formulations, some synthesis for the illumination of the Brazilian territory were made.
19
Im, Myung Jin. "Tolerance analysis of synthesized dual-reflector antennas". Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/12472.
Testo completo
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Cortes-Medellin, German, Stefan O'Dougherty, Christopher Walker, Paul F. Goldsmith, Chris Groppi, Steve Smith e Pietro Bernasconi. "Optical design for the large balloon reflector". SPIE-INT SOC OPTICAL ENGINEERING, 2016. http://hdl.handle.net/10150/622510.
Testo completoAbstract (sommario):
We present the details of the optical design, corrector system, mechanical layout, tolerances, pointing requirements, and overall performance of the sub-millimeter wavelength Large Balloon Reflector telescope (LBR).
21
Pokhrel, Shiva Prasad. "Design of a plasmonic Bragg reflector cavity". Thesis, University of Massachusetts Boston, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=1599250.
Testo completoAbstract (sommario):
A plasmon based Bragg reflector cavity is designed and studied. In order to design the plasmon based Bragg cavity, reflectivity with and without loss are calculated using the transfer matrix method. The simulated Bragg reflector showed better performance as the period increased and achieved 95.16% reflectivity with no loss and 94.94% reflectivity when the predominantly plasmon based losses are included in the 120 period calculation. Plasmon based cavities have been proposed for those instances where high field interactions are required to occur in the near surface region of a semiconductor such as when exciting surface depleted quantum dots for integrated quantum optics applications or when acting as a cavity for short period quantum cascade lasers. Quantum dots and integrated quantum cascade lasers have been proposed as a means to produce and manipulate single photons. The production and detection of single photons is considered the key enabling technology for the realization of a variety of diverse engineered quantum systems such as quantum communication, quantum metrology and quantum computation.
22
Vered, Nissan. "Method of moments analysis of displaced-axis dual reflector antennas". Thesis, Monterey, Calif. : Naval Postgraduate School, 1992. http://handle.dtic.mil/100.2/ADA247970.
Testo completo
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Pye, John Downing Mechanical & Manufacturing Engineering Faculty of Engineering UNSW. "System modelling of the compact linear Fresnel reflector". Publisher:University of New South Wales. Mechanical & Manufacturing Engineering, 2008. http://handle.unsw.edu.au/1959.4/41244.
Testo completoAbstract (sommario):
The Compact Linear Fresnel Reflector is a solar thermal energy system currently at prototype stage in Australia. The system uses parallel rows of mirrors lined up underneath a long, elevated thermal absorber. The mirrors move so as to focus solar radiation onto the absorber; the absorber contains a bank of high-pressure water pipes through which water is pumped and gradually boils. The process of ??direct steam generation?? in very long pipes, up to 300 m in a straight run, has not previously been performed at this scale; other systems use shorter pipe runs, or use other fluids such as non-boiling oil. This thesis addresses a broad range of design issues relating to the CLFR prototype and its components. Beam solar radiation at the prototype site is estimated from available data including satellite-derived and ground-based measurements. Existing correlations for the beam component of global radiation do not apply well to Australian conditions so a new correlation is proposed. Computational fluid dynamics simulations establish radiative heat-loss as the dominant mode for the thermal absorber. Results are gathered for a range of sizes and shapes, and heat-loss correlations are derived for use in subsequent simulation. Two-phase flow in the absorber direct-steam-generation process is examined, and a detailed model including, pipe-friction pressure drops, flow-boiling heat transfer and cavity heat loss is presented, with validation against the experimental results of other workers. A series of ??performance maps?? give the predicted outlet flow regime for varied inlet conditions, allowing selection of desired operating points. A full system model is given that integrates this absorber model with ancillary components including the pump and connecting pipework; the model is used to evaluate pumping requirements and to establish expected operating conditions. The inherent pressure instability arising from the two phase flow is examined and orifice plates are sizes to stabilise this effect. A dynamic model for the absorber pipe flow using fully implicit finite difference techniques and accurate IAPWS-IF97 steam properties gives the predicted behaviour during solar transients at both long and short time-scales.
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REGO, CASSIO G. "APPROXIMATION OF SHAPED REFLECTOR SURFACES BY PSEUDO-SPLINES". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1991. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=9254@1.
Testo completoAbstract (sommario):
Neste trabalho, a técnica de interpolação de superfícies
definidas numericamente por pseudo-splines é aplicada a
antenas refletoras offset e com alto grau de modelagem. É
feito um estudo comparativo com técnica de interpolação
alternativa levando-se em conta os diversos métodos de
análise de antenas refletoras.In this work, the pseudo-spline technique for numerically defined surfaces is applied to the approximation of single and dual-shaped offset reflector antennas. A comparative study with an usual alternative technique is undertaken, emphasizing the implications observed when different methods are employed for the evaluation of the antenna radiation field.
25
Lai, Cheuk-Yan. "Analysis and design of a deployable membrane reflector". Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621226.
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Alphonse, Stephanie. "Fast analysis of a compound large reflector antenna". Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/20196.
Testo completoAbstract (sommario):
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.
27
Bahadori, Keyvan. "Spaceborne reflector antennas for advanced remote sensing applications". Diss., Restricted to subscribing institutions, 2007. http://proquest.umi.com/pqdweb?did=1562125061&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
Testo completo
28
Luo, Hui. "Tapered cavity surface emitting distributed Bragg reflector lasers". Diss., The University of Arizona, 2000. http://hdl.handle.net/10150/284102.
Testo completoAbstract (sommario):
High power, diffraction-limited semiconductor lasers are required for a wide range of applications such as pumping for EDFAs, Raman amplifiers, and for free space optical communications. Unstable resonator has been identified as a very promising concept to develop these lasers. The objective of this research is to investigate and develop tapered cavity unstable resonator grating coupled surface emitting lasers (TCSELs). The laser consists of a ridge section, a tapered gain section and a DBR grating section. The ridge is used to ensure single lateral mode operation. The taper is used to achieve high power from a large aperture. The grating is used to provide feedback and surface outcoupling. This laser design has several key features including high output power, near diffraction-limited beam, low divergence angle, single longitudinal mode operation, and integration with dynamic functionality such as wavelength tuning and beam steering. In this dissertation the design, fabrication and characterization of TCSELs are discussed. The theory of TCSELs is presented. As a theoretical investigation, a comprehensive numerical modeling based on finite difference beam propagation method (FD-BPM) for semiconductor laser is developed. The model includes major parameters affecting device performance such as current spreading, carrier diffusion, nonlinear gain-carrier relation, gain saturation, carrier induced antiguiding and thermal lensing. The simulation results are presented and effects of design parameters on device performance are discussed. TCSELs with different device design and functionality are fabricated. The characterization results are discussed. High power operation is obtained under both pulsed and continuous wave (CW) operation. Collimated near diffraction-limited beam is demonstrated with moderate power. Single longitudinal mode operation with high side mode suppression ratio is observed. Wavelength tuning and beam steering is achieved using current injection to the suitable grating section through indium tin oxide (ITO). Several approaches for the improvement of the laser performance are discussed.
29
Cheng, Chin-Yuan. "Numerical electromagnetic modeling of a small aperture helical-fed reflector antenna". Ohio : Ohio University, 1998. http://www.ohiolink.edu/etd/view.cgi?ohiou1176838193.
Testo completo
30
Nilsson, Josefine. "Optical durability of reflector materials for solar energy applications". Thesis, Umeå universitet, Institutionen för fysik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-144908.
Testo completoAbstract (sommario):
In line with The Paris Agreement, the world is now changing towards more sustainable options for all sorts of energy development. The solar energy sector is growing rapidly as a result of this. One area that holds great potential in changing many of the worlds heating processes, is concentrating solar power (CSP). The basic principle of CSP is to reflect incoming sunlight and concen- trate it to heat a fluid. To do so, it is crucial to find a reflector material that shows both good optical performance initially as well as over time to produce heat in the most efficient way possible and compete with the fossil fueled options. In this investigation, four different, commercially available reflecting materi- als, for concentrating solar power, have been tested under accelerated aging conditions to simulate the wear of outside conditions for many years. Impacts from humidity, temperature fluctuations, UV radiation and acid rain have been included in the study. From the results, it will be argued that a silver based polymer film is the best option, out of the four tested, in terms of the combination of durability and high reflectance properties. However, conclusions about how to properly mea- sure the reflectance of a solar reflector is also presented and advices on how to get reliable results in a similar investigation in the future is presented.
31
CARVALHO, SERGIO ANTENOR DE. "OPTICAL SYNTHESIS OF DUAL REFLECTOR FEED BY DIELETRIC HORN". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1991. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=9249@1.
Testo completoAbstract (sommario):
A síntese de duplos refletores com um alimentador
dielétrico é estudada sob as considerações da ótica
geométrica. A análise ótica do problema leva a uma
equação
diferencial parcial não-linear de 2ª ordem do tipo Monge-
Ampére. Soluções particulares desta equação, as
geometrias
Cassegrain e Gregoriana off-set, são apresentadas e
estudadas. Estas são usadas como soluções iniciais no
processo iterativo de síntese.The synthesis of offset dual reflectors with dieletric feed is studied under the assumptions of geometrical optics. The optical analysis leads to a nonlinear second- order partial differential equation of the Monge-Ampére type. Particular solutions described by offset Cassegrain or Gregorian configurations are presented. These are used as initial solutions in the iterative process of synthesis.
32
Wing, Christopher (Christopher John). "Bragg reflector geometries for colorimetric orientation and deformation sensing". Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/104295.
Testo completoAbstract (sommario):
Thesis: Nav. E., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016.Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016.
Cataloged from PDF version of thesis.
Includes bibliographical references (page 49).
Propulsion systems of commercial and naval ships are typically large and expensive. They must be kept well-aligned and free of corrosion to efficiently and reliably transfer torque to a ship's propeller. Early identification of misalignment or surface corrosion is therefore crucial, making an easily deployable, reliable, lightweight system that visually indicates potential alignment and structural integrity issues desirable. This thesis demonstrates the design of a system for visual deformation and orientation indication based on naturally occurring micro-scale surface geometries that show a strong variation in their optical appearance as a function of illumination and observation directions. Specifically, the fabrication of a micro-structured surface covered with appropriately modified mimics of the spherical cavities on Papilio blumei butterfly wings is the first step in developing a low-cost, easy-to-install detection and indication system. For a specific illumination and observation geometry, the cavities' material and structural characteristics define the surface's reflection characteristics and the resulting visual signature for a far-field observer. Here we present an evolution and screening of the cavity design space, including cavity wall height and the combination of conformal and flat Bragg reflectors in order to identify suitable cavity designs. A MATLAB-based simulation environment was created to estimate the surfaces' intensity profile in monochromatic light and color chromaticity under any illumination source and incidence angle as a function of observation angle. The theoretical results are validated through characterization of a succession of physical prototypes a macro-scale cavity before and after addition of a planar Bragg reflector cover as well as a conformally-clad microcavity array. The resulting data provides a basis for identifying the most suitable cavity designs for determination of misalignments, bends, and localized surface pitting in marine propulsion system components. The future development of specific in situ prototypes for the demonstration of the described visual sensing paradigm is facilitated through the results reported in this thesis.
by Christopher Wing.
Nav. E.
S.M.
33
Harun, Mahmud. "Modification of Large Reflector Antennas for Low Frequency Operation". Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/29455.
Testo completoAbstract (sommario):
Modifications of large reflector antennas, such that their observing capabilities are enhanced in the range of about 10-500~MHz without affecting operation of the pre-existing higher-frequency systems, are addressed in this dissertation. The major contributions of this dissertation can be divided into two parts: 1) designing new low frequency feeds, and 2) developing new analysis methodologies which, as opposed to traditional techniques, are suitable for analyzing low frequency systems.
First, we consider the performance of existing schemes that provide low frequency capability. Then, a new class of dipole-based low frequency feeds - namely, the ``distributed feed array'' - is designed to cover the frequency range of interest without affecting operation at higher frequencies. As an example, distributed feed arrays are designed for the Expanded Very Large Array (EVLA) to cover the range of 50-250~MHz. A method of moments (MoM) model of an EVLA antenna is developed for this purpose. The new design shows performance comparable to the existing 4 m system on the EVLA in the range of 50-88~MHz, and introduces observing capabilities in the range of 110-250~MHz (currently not covered by the EVLA). Moreover, the blockage presented to the existing EVLA L-band system is reduced significantly when the existing 4 m system is replaced by the proposed system.
At low frequencies, external noise can be a significant or dominant contribution to the total noise of the system. This, combined with mutual coupling between the array elements of the distributed feed array, makes it difficult to predict the sensitivity of these systems. This dissertation describes a system model and procedure for estimating the system equivalent flux density (SEFD) - a useful and meaningful metric of the sensitivity of a radio telescope - that accounts for these issues.
We consider the efficiency of methods other than MoM - in particular, Physical Optics (PO), Uniform Geometrical Theory of Diffraction (UTD), and hybrid methods - for accelerated computation at low frequencies. A method for estimating the blockage presented by low frequency systems to the pre-existing higher-frequency systems is also described.Ph. D.
34
Lee, Teh-Hong. "A new approach for shaping of dual-reflector antennas /". The Ohio State University, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487327695623512.
Testo completo
35
LaPean, James William. "Beam scanning offset Casegrain reflector antennas by subreflector movement". Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-06302009-040304/.
Testo completo
36
Liu, Yu. "Plasmonic Bragg reflector and its application on optical switching". [Ames, Iowa : Iowa State University], 2009. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1468113.
Testo completo
37
Xu, Shenheng. "Optimization and compensation techniques for modern reflector antenna designs". Diss., Restricted to subscribing institutions, 2009. http://proquest.umi.com/pqdweb?did=1973590611&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
Testo completo
38
Wong, Yau. "Geometric analysis of reflector systems for solar cell modules". Thesis, The University of Sydney, 1988. https://hdl.handle.net/2123/26247.
Testo completoAbstract (sommario):
This thesis is a study of the design, analysis and experimentation, of developing a feasible solar cell collector module, which in turn, can improve the output performance of a solar cell.
The first Chapter is devoted to defining the background, structure and abilities of a solar cell, and to illustrating the long—term attraction to utilising solar energy. The extent of solar energy falling on earth in relation to its orientation with the earth is treated in Chapter two. Chapter three deals with various stages of module development and analysis; Chapter four illustrates the module experiment with simulated sunlight and confirms the result which was analysed previously. The remaining Chapter describes the cost-effectiveness of the module and the limitations, products, and achievements of the solar cell overseas and in this country.
39
Maysami, Mohammad, e Felix J. Herrmann. "Seismic reflector characterization by a multiscale detection-estimation method". European Association of Geoscientists & Engineers, 2007. http://hdl.handle.net/2429/553.
Testo completoAbstract (sommario):
Seismic transitions of the subsurface are typically considered as zero-order singularities
(step functions). According to this model, the conventional deconvolution problem aims
at recovering the seismic reflectivity as a sparse spike train. However, recent multiscale
analysis on sedimentary records revealed the existence of accumulations of varying order
singularities in the subsurface, which give rise to fractional-order discontinuities.
This observation not only calls for a richer class of seismic reflection waveforms, but it
also requires a different methodology to detect and characterize these reflection events.
For instance, the assumptions underlying conventional deconvolution no longer hold.
Because of the bandwidth limitation of seismic data, multiscale analysis methods based
on the decay rate of wavelet coefficients may yield ambiguous results. We avoid this
problem by formulating the estimation of the singularity orders by a parametric nonlinear
inversion method.
40
Sikström, Johannes. "Vibro-acoustic analysis of a satellite reflector antenna using FEM". Thesis, Umeå universitet, Institutionen för fysik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-39875.
Testo completoAbstract (sommario):
The acoustic environment generated during launch is the most demanding structural load case for large, lightweight satellite reflector antennas. The reflector is exposed to extremely high sound pressure levels originating from the structural excitation of the rocket engines and exterior air flow turbulence. This thesis aims to predict the structural responses in the reflector due to the acoustic pressure load with a model based on Finite Element Modelling (FEM). The FE-model is validated against a previously performed Boundary Element Method (BEM) analysis. An approach called Split Loading together with a combination of BEM and FEM will be utilized to handle the surrounding air mass and the applied sound pressures. The idea of Split Loading is to divide the structure into several patches and apply a unit pressure load to each patch separately. In the last step the unit pressure is scaled and correlated by a power spectral density calculated from the acoustic pressures. Split Loading will be implemented in software packages MSC.NASTRAN/PATRAN. The model developed in this thesis handles both the added mass of the surrounding air and the sound pressure applied to the reflector. The model can qualitatively well reproduce the results of the BEM-analysis and the test data. However, the model tends to overestimate responses at low frequencies and underestimate them at high frequencies. The end results is that the model becomes too conservative at low frequencies to be used without further development.
41
Duggan, Jason. "Adaptive beamforming with a focal-fed offset parabolic reflector antenna". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq20630.pdf.
Testo completo
42
Yun, Han. "Design and characterization of a dumbbell micro-ring resonator reflector". Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/44535.
Testo completoAbstract (sommario):
A dumbbell shape micro-ring resonator reflector fabricated using the silicon-on-insulator (SOI) technology for use as a reflective notch filter is presented. The development of this dumbbell micro-ring reflector is motivated by the increasing demand for highly confined resonant structures as integrated optical components in modern optical communication and sensor applications. In this thesis, we have analyzed and simulated the reflection properties of dumbbell micro-ring reflectors based on SOI strip waveguides. We have optimized our design based on the analytic modeling and simulation results and had our devices fabricated at a foundry. An automated optical probe station has been developed for characterizing the performance of the fabricated dumbbell micro-ring reflectors. Measurement results on the reflection spectrum showed an extinction ratio of 20 dB with a quality factor of ~11,000. Thermal tuning responses showed the potential for those resonators in sensor applications.
43
Lee, C. K. "Modelling and design of frequency selective surfaces for reflector antennas". Thesis, University of Kent, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376318.
Testo completo
44
COSTA, LUISENRIQUE PIERRE NUNES DA. "APPLICATION OF SUCCESS OF PROJECTION USE SYNTHESIS OF REFLECTOR ANTENNAS". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1994. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=8956@1.
Testo completoAbstract (sommario):
TELECOMUNICAÇÕES BRASILEIRAS S/AO modelamento de superfícies refletoras embarcadas em satélites tem se apresentado como uma alternativa eficiente à síntese de conjuntos de alimentadores. Existem várias técnicas disponíveis para a determinação do formato adequado para esta superfície, baseados em aproximações da ótica geométrica ou da ótica física. Neste trabalho, estudamos a aplicação da técnica das Projeções Sucessivas, um método interativo genérico, à síntese de superfície refletora e à síntese da distribuição de fase sobre a abertura. Este método é baseado nas aproximações da Ótica Física, o que garante uma boa precisão. Entre suas principais vantagens, estão a sua simplicidade e a sua eficiência computacional.
The shaping of reflector surfaces for satellites hás been considered na efficient alternative to the available for the determination of the optimum shape for this surface, base don Geometrical Optics or Physical Optics approximations. This work investigates the application of the Technique of Sucessive Projections, a generic interative method, to the synthesis of a single reflector antenna and to the phase distribution on the aperture. This method is based on Physical Optics Techniques, which guarantees a good precision. Among its main advantages are its simplicity and its computational.
45
Remaggi, Luca. "Acoustic reflector localisation for blind source separation and spatial audio". Thesis, University of Surrey, 2017. http://epubs.surrey.ac.uk/842217/.
Testo completoAbstract (sommario):
From a physical point of view, sound is classically defined by wave functions. Like every other physical model based on waves, during its propagation, it interacts with the obstacles it encounters. These interactions result in reflections of the main signal that can be defined as either being supportive or interfering. In the signal processing research field, it is, therefore, important to identify these reflections, in order to either exploit or avoid them, respectively. The main contribution of this thesis focuses on the acoustic reflector localisation. Four novel methods are proposed: a method localising the image source before finding the reflector position; two variants of this method, which utilise information from multiple loudspeakers; a method directly localising the reflector without any pre-processing. Finally, utilising both simulated and measured data, a comparative evaluation is conducted among different acoustic reflector localisation methods. The results show the last proposed method outperforming the state-of-the-art. The second contribution of this thesis is given by applying the acoustic reflector localisation solution into spatial audio, with the main objective of enabling the listeners with the sensation of being in the recorded environment. A novel way of encoding and decoding the room acoustic information is proposed, by parametrising sounds, and defining them as reverberant spatial audio objects (RSAOs). A set of subjective assessments are performed. The results prove both the high quality of the sound produced by the proposed parametrisation, and the reliability on manually modifying the acoustic of recorded environments. The third contribution is proposed in the field of speech source separation. A modified version of a state-of-the-art method is presented, where the direct sound and first reflection information is utilised to model binaural cues. Experiments were performed to separate speech sources in different environments. The results show the new method to outperform the state-of-the-art, where one interferer is present in the recordings. The simulation and experimental results presented in this thesis represent a significant addition to the literature and will influence the future choices of acoustic reflector localisation systems, 3D rendering, and source separation techniques. Future work may focus on the fusion of acoustic and visual cues to enhance the acoustic scene analysis.
46
Su, Nan-Ching, e 蘇楠清. "Fabricaton of the micro-reflector with total reflection". Thesis, 2004. http://ndltd.ncl.edu.tw/handle/45709350399815530252.
Testo completoAbstract (sommario):
碩士淡江大學
機械與機電工程學系碩士班
94
In this thesis, the Si mold containing inverted pyramid patterns with 54.74 degree between {111} planes and (100) plane was manufactured by photolithography process and Si (100) was prepared with KOH etching process for the anisotropic wet etching process. The polydimethylsiloxane was used to reprinted the structure of the si mold. Because polydimethylsiloxane was elongated easily, polydimethylsiloxane was forced to elongate single-axially to change the degree of the angle between {111} planes and (100) plane and the dimension of the structure. By using UV curing technology, the structure of the elongated PDMS would be reprinted. And then the electroforming technology was used to reprinted the UV curing agent with the structure of the inverted pyramid patterns for being the mold of polymer hot embossing. Finally, polymer was used for optical test and get diffraction pattern of the photo.
47
Mousari, Bafrooei Seyed Pedram. "Reflector feeds for large adaptive reflector antennas". 2000. http://hdl.handle.net/1993/1840.
Testo completoAbstract (sommario):
A novel Feed-Reflector system for large Cassegrain antennas for Radio Astronomy and Deep-Space Communication applications is investigated. This Feed-Reflector is used to illuminate a hyperboloid sub-reflector with 5-10 m diameter located 500 m above the ground. Because the sub-reflector is located in the near field of the Feed-Reflector antenna, a theory based on the near field focusing properties of paraboloid reflectors is established. The focusing at near distance is formed by moving the feed horn away from the focal point of the Feed-Reflector. In this theory the properties of axial defocused paraboloid reflectors at near distance are investigated in some detail. By using equivalence path law, sub-reflector shape is obtained. It is found that the hyperbola can approximate the sub-reflector well. A detailed ray tracing analysis is performed on the entire system which reveals that some part of the sub-reflector receive three rays per point from the feed. The performance of the system over the operating band (1-22 GHz) is also studied and shown that the lower frequency limit is dependent on sub-reflector and Feed-Reflector sizes. To obtain higher efficiencies, three sets of shaping techniques, based on the genetic algorithm and Jacobi Fourier surface expansion, are performed. An efficiency of 78.5% for a 5 m sub-reflector is obtained. In another method of analysis, the Feed-Reflector aperture field distribution is expanded into a set of Gaussian-Laguerre modes. These modes propagate from the Feed-Reflector aperture in a simple and well defined way. The Feed-Reflector near field radiation pattern is calculated at the sub-reflector location. The sub-reflector parameters in this system are found by maximizing the Large Adaptive Reflector (LAR) aperture efficiency which includes phase and taper efficiencies, and minimizing the LAR spillover loss. An exact equation for the offset LAR surface is obtained in this thesis. To scan the beam up to 60, which is one of the LAR requirements, the concept of the dual offset LAR with the Feed-Reflector is introduced. In this design the cross-polarization is eliminated by proper orientation of the sub-reflector. The parameters of the configuration are obtained by utilizing generalized Gauss-Laguerre beam modes and matrix representation of beam mode transformation factor. In this design the blockage effect due to the Feed-Reflector is totally removed.
48
Loewen, Nathan. "Conceptual design of reflector structure for the large adaptive reflector". Thesis, 2003. http://hdl.handle.net/2429/14484.
Testo completoAbstract (sommario):
The Large Adaptive Reflector (LAR) is a very large radio telescope proposed by the
Dominion Radio and Astrophysical Observatory in Penticton, B C . Two innovative
components make the L A R unique from traditional radio telescopes. Firstly, the focal
receiver is supported by an airborne helium balloon. The position of the focal receiver is
controlled by multiple tethers running to the ground. Secondly, the ground-based
reflector structure is "adaptive" in nature, which allows it to be configured in a
continuous range of parabolic shapes. The reflector structure is required to be 300m in
diameter, with a surface height range of 0 to 15 meters above a level reference plane.
The reflector surface must be accurate to within 9mm rms from the ideal paraboloid
shapes. The realistic design of the reflector structure with emphasis on fabrication and
economy is the focus of this paper.
The driving factor in the conceptual design is minimizing the cost per unit area while
meeting the surface accuracy requirements under a wide range of operating conditions.
Since an adaptive structure of this magnitude is unprecedented, solutions cannot be easily
derived from existing structures. Therefore, the methodology of converging towards a
design solution must involve creativity, as well as a systematic way of eliminating less
optimal solutions. The approach taken here first defines the load requirements, which are
mainly governed by environmental loads such as thermal, wind, and snow loads. Various
materials and general structural configurations are then compared for their suitability to
this application. Once a preliminary design is developed, an analysis is carried out that
gives quantitative results for structural performance. Methods of structural fabrication,
and dynamic motion of the structure are also considered.
49
Santos, Mafalda Ho de Almeida. "Inflatable Reflector Antenna". Master's thesis, 2021. https://hdl.handle.net/10216/135756.
Testo completoAbstract (sommario):
SARIA (Radar de Abertura Sintética usando uma Antena Insuflável) é uma experiência selecionada para voar num balão estratosférico, no âmbito do programa REXUS/BEXUS ciclo 13, e utilizará uma antena insuflável, operando a 5.8 GHz, para criar imagens de radar de abertura sintética (SAR). Vários problemas, como a seleção de material, impediram a SARIA de desenvolver uma antena insuflável operacional. O objetivo desta dissertação é projetar e implementar uma antena parabólica refletora insuflável, a 5.8 GHz, com um diâmetro de 1 m, bem como controlar a pressão da antena insuflável usando um sistema de inflação ativo.
Este trabalho usa métodos de elementos finitos (FEM) para auxiliar nas fases iniciais de desenvolvimento de uma antena insuflável. Para simular o formato da antena insuflável, com diversos valores de pressão diferencial, foi escolhido o software de análise de elementos finitos (FEA) Abaqus/FEA . Um script Matlab foi utilizado para determinar o padrão de radiação de uma antena insuflável. Como resultado, é possível estimar o intervalo de pressão diferencial ideal e caracterizar as propriedades radio-frequência (RF) de uma antena insuflável antes do seu fabrico. Usando estas ferramentas, propõe-se uma nova modificação de design para a antena insuflável da SARIA. Uma antena insuflável é fabricada manualmente usando Mylar® para a parte refletora e plástico transparente para a cobertura. A pressão desta antena é controlada por um sistema de inflação ativo, responsável por manter a pressão diferencial da antena insuflável dentro de um intervalo ótimo.
Foi obtida uma antena insuflável com ganho de 23.77 dBi a 5.8 GHz. A sua caracterização revelou uma perda de ganho de 5.6 dBi, em relação ao ganho simulado, devido a dificuldades de implementação, nomeadamente do processo de fabrico, que são explicadas na tese. Este trabalho contribui, assim, para o know-how de desenvolvimento de antenas insufláveis para aplicações de baixa pressão e em ambiente orbital.SARIA (Synthetic-Aperture Radar using an Inflatable Antenna) is an experiment selected to fly in a stratospheric balloon, in the scope of the REXUS/BEXUS programme cycle 13, and will use an inflatable antenna, operating at 5.8 GHz, to create Synthetic-Aperture Radar (SAR) images. Several problems, such as material selection, have prevented SARIA from developing an operational inflatable antenna. The objective of this dissertation is to design and implement an inflatable parabolic reflector antenna, at 5.8 GHz, with a diameter of 1m as well as to control the inflatable antenna pressure using an active inflation system. This work uses Finite Element Method (FEM) to assist on the initial developing phases of an inflatable antenna. To simulate the inflatable antenna shape, at several differential pressure values, the Finite Element Analysis (FEA) software Abaqus/FEA was chosen. A Matlab script was used to compute the radiation pattern of an inflatable antenna. As a result, it is possible to estimate the optimal differential pressure interval and characterize the Radio Frequency (RF) properties of an inflatable antenna prior to manufacturing. Using these tools, a new design modification for SARIA inflatable antenna is proposed. An inflatable antenna is manufactured by hand using Mylar® for the reflective part and transparent plastic for the canopy. The pressure of this antenna is controlled by an active inflation system which is responsible for keeping the inflatable antenna differential pressure inside an optimal interval. An inflatable antenna with a gain of 23.77 dBi at 5.8 GHz was obtained. Its characterization has revealed a gain loss of 5.6 dBi, in respect to the simulated gain, due to implementation difficulties, namely the manufacturing process, which are explained in the thesis. This work contributes to the expertise of developing inflatable antennas for low pressure applications and in orbital environment applications.
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Santos, Mafalda Ho de Almeida. "Inflatable Reflector Antenna". Dissertação, 2021. https://hdl.handle.net/10216/135756.
Testo completoAbstract (sommario):
SARIA (Radar de Abertura Sintética usando uma Antena Insuflável) é uma experiência selecionada para voar num balão estratosférico, no âmbito do programa REXUS/BEXUS ciclo 13, e utilizará uma antena insuflável, operando a 5.8 GHz, para criar imagens de radar de abertura sintética (SAR). Vários problemas, como a seleção de material, impediram a SARIA de desenvolver uma antena insuflável operacional. O objetivo desta dissertação é projetar e implementar uma antena parabólica refletora insuflável, a 5.8 GHz, com um diâmetro de 1 m, bem como controlar a pressão da antena insuflável usando um sistema de inflação ativo.
Este trabalho usa métodos de elementos finitos (FEM) para auxiliar nas fases iniciais de desenvolvimento de uma antena insuflável. Para simular o formato da antena insuflável, com diversos valores de pressão diferencial, foi escolhido o software de análise de elementos finitos (FEA) Abaqus/FEA . Um script Matlab foi utilizado para determinar o padrão de radiação de uma antena insuflável. Como resultado, é possível estimar o intervalo de pressão diferencial ideal e caracterizar as propriedades radio-frequência (RF) de uma antena insuflável antes do seu fabrico. Usando estas ferramentas, propõe-se uma nova modificação de design para a antena insuflável da SARIA. Uma antena insuflável é fabricada manualmente usando Mylar® para a parte refletora e plástico transparente para a cobertura. A pressão desta antena é controlada por um sistema de inflação ativo, responsável por manter a pressão diferencial da antena insuflável dentro de um intervalo ótimo.
Foi obtida uma antena insuflável com ganho de 23.77 dBi a 5.8 GHz. A sua caracterização revelou uma perda de ganho de 5.6 dBi, em relação ao ganho simulado, devido a dificuldades de implementação, nomeadamente do processo de fabrico, que são explicadas na tese. Este trabalho contribui, assim, para o know-how de desenvolvimento de antenas insufláveis para aplicações de baixa pressão e em ambiente orbital.SARIA (Synthetic-Aperture Radar using an Inflatable Antenna) is an experiment selected to fly in a stratospheric balloon, in the scope of the REXUS/BEXUS programme cycle 13, and will use an inflatable antenna, operating at 5.8 GHz, to create Synthetic-Aperture Radar (SAR) images. Several problems, such as material selection, have prevented SARIA from developing an operational inflatable antenna. The objective of this dissertation is to design and implement an inflatable parabolic reflector antenna, at 5.8 GHz, with a diameter of 1m as well as to control the inflatable antenna pressure using an active inflation system. This work uses Finite Element Method (FEM) to assist on the initial developing phases of an inflatable antenna. To simulate the inflatable antenna shape, at several differential pressure values, the Finite Element Analysis (FEA) software Abaqus/FEA was chosen. A Matlab script was used to compute the radiation pattern of an inflatable antenna. As a result, it is possible to estimate the optimal differential pressure interval and characterize the Radio Frequency (RF) properties of an inflatable antenna prior to manufacturing. Using these tools, a new design modification for SARIA inflatable antenna is proposed. An inflatable antenna is manufactured by hand using Mylar® for the reflective part and transparent plastic for the canopy. The pressure of this antenna is controlled by an active inflation system which is responsible for keeping the inflatable antenna differential pressure inside an optimal interval. An inflatable antenna with a gain of 23.77 dBi at 5.8 GHz was obtained. Its characterization has revealed a gain loss of 5.6 dBi, in respect to the simulated gain, due to implementation difficulties, namely the manufacturing process, which are explained in the thesis. This work contributes to the expertise of developing inflatable antennas for low pressure applications and in orbital environment applications.