[pt] Neste trabalho, o Método dos Momentos é aplicado na análise de antenas microfita excitadas por cabo coaxial, utilizando Funções de Green no modelamento dos campos no interior da camada de dielétrico, o que permite considerar as ondas de superfície excitadas no substrato. Para obter a impedância de entrada da antena microfita, foi implementado um algoritmo numérico para a solução do problema. Neste trabalho, atenção especial é dada à análise de singularidades e ao comportamento assintótico dos integrandos envolvidos na solução numérica do problema. A validação do algoritmo é feita através da comparação com resultados apresentados em referências. Os resultados fornecidos pelo Método dos Momentos são comparados com os obtidos na aplicação de outros métodos na solução do problema. Para esta comparação, são utilizados dois programas comerciais de simulação eletromagnética, o Ansoft HFSS e o CST. São feitas simulações com a variação dos parâmetros de entrada do problema, com o objetivo de assegurar a convergência dos resultados e permitir a comparação com os resultados obtidos pelo Método dos Momentos. São apresentadas diferenças entre os resultados obtidos pelos diversos métodos e analisadas as possíveis causas das discrepâncias. / [en] In the present work, the Method of Moments is applied to the analysis of probe fed antennas. The approach uses Green Functions to model the fields within the dielectric layer, which allows to take into account the surface waves excited in the substrate. A numerical algorithm was implemented in order to obtain the microstrip antenna input impedance. The latter is then verified through the comparison with results presented in references. Special attention is given to the analysis of singularities and to the asymptotic behavior of the integrands involved in the numerical solution. A comparison is drawn between the results obtained with the Method of Moments and those obtained with other methods by employing two electromagnetic simulation commercial softwares, Ansoft HFSS and CST. Simulations with different input parameters are performed in order to ensure convergence of the results and allow comparison with results obtained by the Method of Moments. The differences among the results obtained by the several methods addressed in the analysis are presented and the potential causes of them are analyzed.

Superimposition of contractional structures is widely observed in different scales in the world. Superimposed structures form due to different processes: change in strain accommodation from one type of structure to another during a single progressive shortening; successive coaxial shortening phases separated by an unconformity; superimposition of different non-coaxial shortening phases. Using results of a series of systematic analogue models and detailed field structural mapping, this thesis focuses on the geometry and kinematics of such superimposed structures that are formed by these three processes. During a single progressive folding, thrusts develop within a fold to accommodate stain variations in different regime of the fold. Limited displacement along these thrusts does not significantly modify the geometry of the fold. However, during multiple shortening phases (coaxial or non-coaxial), early formed structures are modified by the later phase ones. The later thrusts can cut and displace the pre-existing structures. The early folds are tightened or interfered by the later folding phase. Pre-existing thrusts may be reactivated either in dip direction and/or along strike during the later shortening. The pre-existing structures in turn influence development of the later structures, which results in change in structure spacing. An angular unconformity between two shortening phases clearly truncates the early phase structures and separates structures of different levels. Unlike in the post-erosional layers, in the layers below the unconformity, complicated superimposed structures are visible. This thesis shows that geometry and sequence of structures formed during one progressive shortening or multiple shortening phases strongly depend on the mode of the superimposition (coaxial, orthogonal or oblique) and the orientation of pre-existing structures.

[pt] Este trabalho examina, sob o enfoque de custos, de investimento e operação, dois sistemas de telecomunicações usualmente empregados no estabelecimento da ligação entre dois pontos: sistema de transmissão por cabo coaxial e sistema de transmissão em microondas em visibilidade. Cada sistema está dividido em suas partes componentes, cujos custos são levantados. Calculados estes em ambos os sistemas, define-se uma grandeza que os relaciona. Um sistema é apresentado a partir do número de canais e do comprimento do enlace, ficando perfeitamente caracterizado qual dos sistemas de transmissão é mais econômico, de acordo com o critério de decisão adotado. / [en] This work examines two telecomunications systems which are usually used in the establishment and operation - the transmission system by coaxial cable and the transmission system by microwaves line-of-sight. Both are divided in their campontent parts, which calculation in surveyd. After the surveying of costs of both system, one can define a relating magnitude. The moment a system is defined, considering the number of system is the most economic, according to the adopted criterion of decision.

Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Unmanned aerial vehicles with vertical take-off and landing capabilities have received extensive attention worldwide in the last decade. Their low detectability, high manoeuvrability in confined spaces, and their capability for out-of-sight operations make them practical solutions for an array of military and civilian missions. The main advantage of shrouded rotors in hover and low speed conditions is the decreased blade tip induced drag when the tip gap is small enough. A well-designed shroud augments the rotor thrust in hover and low axial flight conditions. It also provides noise reduction and safety. A contra-rotating rotor system eliminates the need for separate anti-torque devices, thus producing a smaller footprint and a more compact vehicle. In this study a more efficient coaxial rotor for the ducted coaxial rotor system as published by (Lee 2010) was developed. The first phase of the design process consisted of the selection and numerical analysis of the best suited parent airfoils for the rotors by using XFOIL and XFLR 5. The second phase dealt with the design of a counter-rotating rotor system for the existing cambered shroud as published by (Lee, 2010), using the DFDC-070ES2a two dimensional code, specifically written for ducted rotor optimization. The final phase of the study dealt with the Computational Fluid Dynamic (CFD) verification of the design in ANSYS-CFX 15.07. A comparison between the CFX predictions of the newly designed rotor system and the reference design indicates a 33% improvement in hover thrust at the design power input. / AFRIKAANSE OPSOMMING: Onbemande lugvaartuie met vertikale opstyg en landings vermoëns het uitgebreide aandag wêreldwyd in die laaste dekade geniet. Hul lae waarneembaarheid, hoë beweegbaarheid in beperkte ruimtes, en hul vermoë om buite-sig operasies uit te voer maak dat hulle praktiese oplossings vir 'n verskeidenheid van militêre en burgerlike missies is. Die grootste voordeel van gehulde rotors in hangvlug en lae spoed omstandighede is die afname in die lem punt sleepkrag wanneer die lem punt gaping klein genoeg is. 'n Goed ontwerpde omhulsel dra by tot die rotor stukrag in hangvlug en lae aksiale vlug omstandighede. Dit bied ook geraasreduksie en veiligheid. 'n Kontra-roterende rotorstelsel skakel die vereiste van afsonderlike anti-wringkrag toestelle uit, wat lei tot 'n kleiner voetspoor en 'n meer kompakte voertuig. In hierdie studie is 'n meer doeltreffende koaksiale rotor vir die gehulde koaksiale rotor stelsel soos gepubliseer deur (Lee 2010) ontwikkel. Die eerste fase van die ontwerp-proses het bestaan uit die seleksie en numeriese analise van die mees geskikte lemprofiele vir die rotors deur die gebruik van XFOIL en XFLR 5. Fase twee het die ontwerp van 'n teen-roterende rotor stelsel vir die bestaande omhulsel soos gebruik in (Lee, 2010) se publikasie behels. Die ontwerp is met behulp van DFDC-070ES2a, ‘n twee dimensionele kode wat spesifiek vir gehul-rotor optimering geskryf is, gedoen. Die verifikasie van die nuwe ontwerp is in die finale fase met behulp van die berekeings vloeidinamika sagteware, ANSYS-CFX 15.07 gedoen. ‘n Vergelyking tussen die CFX prestasie voorspelling vir die nuwe rotorstelsel en die gepubliseerde data van (Lee, 2010) toon ‘n 33% toename in hangvlug stukrag by die ontwerpsdrywing.

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

Field emission cathodes have proven themselves to be excellent candidates for some special medical X-ray applications. Spindt cathode and CNT (carbon nanotube) based field emission cathode have been widely studied for many years. Spindt cathode has the near perfect structure, but the material property limits its applications. On the other hand, low density vertically aligned CNT array has been proved the best candidate of field emission material. Several attempts have been made to combine the advantages of the Spindt cathode and CNT array, but some most important advantages of Spindt cathode have not been successfully utilized in CNT emitter design, for example: ballast resistor, self-aligned fabrication process, sub-micron scale gate electrode, and low control voltage. In this thesis, the design, fabrication and test of CNT based field emission cathode with a novel ballast resistor and coaxial cylinder shape gate electrode is reported. A connection pad has been reported for the first time. This structure makes the ballast resistor can be utilized in a CNT field emitter array. Therefore, the uniformity and stability of field emission current is improved significantly. In addition, the stabilized emission current heated up the sample to a high temperature and changes the emission from field emission to Schottky emission regime. This is the first report of the self-heating Schottky emission from a CNT emitter array. Coaxial cylinder shape gate electrode is another important improvement in the CNT emitter design. The gate electrode adopts the self-alignment property of the Spindt cathode, and adjusted to fit the structure and synthesis process of CNT array. This new design and fabrication process has all the advantages of both the Spindt cathode and CNT emitter. In addition to the field emission cathode design, a novel PMMA (poly methyl methacrylate) based FEM (field emission microscope) is designed to evaluate the emission uniformity and capture high resolution images of the distribution of field emitted electrons. Compare to the conventional phosphor screen based FEM, the PMMA based FEM has a much higher resolution and sensitivity. Images of this new FEM have a resolution of as high as 0.34 nm and clearly show the boundary of crystal facets.

The limit of current technology for mobile base station filters is the multimode filter, in which each cavity supports two (or possibly three) independent degenerate resonances. Shielded dielectric resonators with a rectangular cross-section are useful in this application. In the design of these filters, manufacturers are using software packages employing finite element or finite difference time domain techniques. However, for sufficient accuracy these procedures require large numbers of points or elements and can be very time consuming. Over the last decade research using the mode matching technique has been used to solve this kind of difficulty for various types of filter design and waveguide problems. In this thesis a mode matching method and computer program is developed to calculate the propagation coefficients and field patterns of the modes in a shielded rectangular dielectric rod waveguide. Propagating, complex, evanescent and backward wave modes are included and the work shows the presence of a dominant mode, and other fundamental modes, not previously identified. The effect of the shield proximity on the propagation characteristics and mode spectrum is investigated, together with the limitations on the accuracy of the mode matching method. In addition, the fields within the shielded rectangular dielectric rod waveguide, are used to calculate the attenuation coefficient of the dominant and fundamental modes. The influence on the attenuation coefficient of the proximity of the shield to the rod is also evaluated for these modes and limitations on accuracy are discussed. The calculated numerical results for the propagation and attenuation coefficient values are verified by measurement. The propagation coefficients results are typically within 2% of those measured. Verification of the attenuation coefficient results is achieved by comparing calculated and measured Q at the resonant frequencies of a number of shielded rectangular dielectric rod resonators. The difference between calculated and measured Q values is on average less than 4%. In the absence of a full solution of the shielded rectangular dielectric rod resonator, these results provide useful design information for this structure. In addition, the work reported in this thesis provides a basis for a full electromagnetic solution of this type of resonator. This would encompass the cubic dielectric resonator in a cubical cavity.

Thesis (M.S.)--Missouri University of Science and Technology, 2008. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed March 31, 2008) Includes bibliographical references (p. 48-49).

Thesis (Ph. D.)--State University of New York at Binghamton, Department of Chemistry, 2006. / Includes bibliographical references.

Thesis (MS)--Montana State University--Bozeman, 2009. / Typescript. Chairperson, Graduate Committee: Brock LaMeres. Includes bibliographical references (leaves 44-47).