Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: An investigation of the functional similarities and di erences between a combline lter and an evanescent-mode waveguide lter is presented. The design theory of the two types of lters is outlined. Two lters are designed to operate at a centre frequency of 2 GHz with a 5% bandwidth using similar waveguide dimensions, but using the two di erent design theories. The bandpass characteristics of the two lters are then compared over the primary passband and over a broad range of frequencies to observe the stopband characteristics. It is shown that a combline lter with a large groundplane spacing behaves like an evanescent-mode waveguide lter but a di erence in bandwidth exists between the two. Di erent aspects related to the manufacture of coaxial cavity lters are addressed with speci c emphasis on cost reduction. The considerations to be made when choosing the right materials, manufacturing techniques and surface nishes for microwave coaxial cavity lters so that good performance is obtained while reducing the overall costs associated with manufacturing are discussed. The concept of Design for Manufacture (DFM) is discussed. Three combline lters are designed for reduced manufacturing cost, applying di erent changes in the physical structure to suit the speci c manufacturing technique used. Two of these have the same design speci cations, operating at a centre frequency of 1.3 GHz with a 10% bandwidth but are designed for manufacture using two di erent manufacturing techniques: milling and wire-cutting EDM. The third lter is designed for manufacture using a combination of the milling and wirecutting processes to have a bandwidth of 1.8% with the primary passband centred at 2.125 GHz. Problems encountered in manufacturing are explained, one of which results in the use of waterjet cutting for the manufacture of lters initially supposed to be manufactured using wirecutting EDM. Measurement results for the manufactured lters show a good agreement between the bandwidths of the 3D electomagnetic simulation results. The obtained results also show the e ects of poor surface nishing and of deformations on the resonant frequency and the unloaded Q of the lters. / AFRIKAANSE OPSOMMING: 'n Studie van die funksionele ooreenkomste en verskille tussen kamlyn lters en gol eier-onder-afknip lters word aangebied. Die ontwerpstegnieke van beide tipes lters word aangebied. Twee lters word ontwerp met 'n senterfrekwensie van 2GHz en 'n bandwydte van 5%, met soortgelyke gol eierafmetings maar deur gebruik te maak van die verskillende ontwerpstegnieke. Die gedrag van die twee lters word vergelyk in die deurlaatband sowel as oor 'n wye stopband. Dit word getoon dat 'n kamlyn lter met 'n groot grondvlakspasi ering soos 'n gol eier-onder-afknip lter optree, met 'n verskil in bandwydte. Verskillende aspekte wat verband hou met die vervaardiging van koaksiale lters, met spesi eke klem op koste vermindering, word aangebied. Die oorwegings wat die keuses van materiaal, vervaardigingstegnieke en oppervlakte afwerking be nvloed word bespreek. Die konsep van Ontwerp vir Vervaardiging (DFM in Engels) word bespreek. Drie kamlyn lters word ontwerp vir verminderde vervaardigingskoste deur die siese sruktuur aan te pas by die spesi eke vervaardigingstegniek. Twee van die lters het dieselfde spesi kasie, naamlik 'n senterfrekwensie van 1.3GHz en 'n 10% bandwydte, maar word ontwerp vir twee verskillende vervaardigingsprosesse, naamlik frees en draadsny. 'n Derde lter word ontwerp vir 'n kombinasie van hierdie twee prosesse, en met 'n senterfrekwensie van 2.125GHz en 'n bandwydte van 1.8%. Probleme met die vervaardiging word bespreek, onder andere die verandering van draadsny na water-sny tegnieke. Gemete resultate toon goeie ooreenstemming met die teoretiese analise wat die bandwydtes betref, maar swak oppervlak afwerking het 'n verswakking van die onbelaste Q van die resoneerders tot gevolg.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: An investigation into the cause of undesired sidelobes in the 3D radiation pattern of slotted waveguide arrays is conducted. It is hypothesized that the cross-polarization of the antenna is at fault, along with the possibility that an error is made when designing a linear array. In investigating and finding a solution to the problem, the “Z-slot ” is introduced in conjunction with polarizer plates. The base components are used by a custom optimization algorithm to design reference and solution antennas. Results of the antennas are then compared to ascertain the cause and possible solutions for the unwanted sidelobes. The generic nature of the process may be used to characterize other arbitrary aperture configurations and to design larger antennas. / AFRIKAANSE OPSOMMING: ‘n Ondersoek om die oorsaak van ongewensde sylobbe in die 3D uitstraalpatroon van golfleier-antennas vas te stel. Die hipotese is dat die probleem ontstaan uit die kruis-polarisasie van die antenna, tesame met ‘n verkeerdelikke aanname dat die opstelling liniêr is. Die “Z-Gleuf” tesame met polariseringsplate word voorgestel as hulpmiddel om die moontlikke oorsake te ondersoek. ‘n Gespesialiseerde optime erings-algoritme benut hierdie basiskomponente om beide verwysings- en oplossing-antennas te ontwerp. Resultate van die ontwerpde antennas word dan vergelyk om die oorsaak van die ongewensde sylobbe te vas te stel. Die generiese aard van die proses kan toegepas word op enige gleuf-konfigurasie en om groter antennas mee te ontwerp.

No description available.

Acoustic emission (AE) is a natural phenomenon that occurs when a solid is subjected to stress. These emissions are produced by all materials during pre failure. In soil, AE results from the release of energy as particles undergo small strains. If these emissions can be detected, then it becomes possible to develop an early warning system to predict slope failure. International research has shown that AE can be used to detect ground deformations earlier than traditional techniques, and thus it has a role to play in reducing risk to humans, property and in mitigating such risks. This thesis researches the design of a system to quantify the AE and calculate the distance to the deformation zone, and hence information on the mechanism of movement. The quantification of AE is derived from measuring the AE event rate, the output of which takes the form of a displacement rate. This is accurate to an order of magnitude, in line with current standards for classifying slope movements The system also demonstrates great sensitivity to changes within the displacement rate by an order of magnitude, making the technique suitable to remediation monitoring. Knowledge of the position of the shear surface is critical to the planning of cost effective stabllisation measures. This thesis details the development of a single sensor source location technique used to obtain the depth of a developing or existing shear surface within a slope. The active waveguide is used to reduce attenuation by taking advantage of the relatively low attenuation of metals such as steel. A method of source location based on the analysis of Lamb wave mode arrival times at a smgle sensor is summansed. An automatic approach to source location is demonstrated to locate a regular AE source to within one metre. Overall consideration is also given to field trials and towards the production of monitoring protocols for data analysis, and the implementation of necessary emergency/remediation plans.

Harsh environment acoustic emission and ultrasonic wave sensing applications often benefit from placing the sensor in a remote and more benign physical location by using waveguides to transmit elastic waves between the structural location under test and the transducer. Waveguides are normally designed to have high fidelity over broad frequency ranges to minimize distortion - often difficult to achieve in practice. This thesis reports on an examination of using nonlinear ball chain waveguides for the transmission of acoustic emission and ultrasonic waves for the monitoring of thermal protection systems undergoing severe heat loading, leading to ablation and similar processes. Experiments test the nonlinear propagation of solitary, harmonic and mixed harmonic elastic waves through a copper tube filled with steel and elastomer balls and various other waveguides. Triangulation of pencil lead breaks occurs on a steel plate. Data are collected concerning the usage of linear waveguides and a water-cooled linear waveguide. Data are collected from a second water-cooled waveguide monitoring Atmospheric Reentry Materials in UVM's Inductively-Coupled Plasma Torch Facility. The motion of the particles in the dimer waveguides is linearly modeled with a three ball and spring chain model and the results are compared per particle. A theoretical nonlinear model is presented which is capable of exactly modeling the motion of the dimer chains. The shape of the waveform propagating through the dimer chain is modeled in a sonic vacuum. Mechanical pulses of varying time widths and amplitudes are launched into one end of the ball chain waveguide and observed at the other end in both time and frequency domains. Similarly, harmonic and mixed harmonic mechanical loads are applied to one end of the waveguide. Balls of different materials are analyzed and discriminated into categories. A copper tube packed with six steel particles, nine steel or marble particles and a longer copper tube packed with 17 steel particles are studied with a frequency sweep. The deformation experienced by a single steel particle in the dimer chain is approximated. Steel ball waveguides and steel rods are fitted with piezoelectric sensors to monitor the force at different points inside the waveguide during testing. The corresponding frequency responses, including intermodulation products, are compared based on amplitude and preloads. A nonlinear mechanical model describes the motion of the dimer chains in a vacuum. Based on the results of these studies it is anticipated that a nonlinear waveguide will be designed, built, and tested as a possible replacement for the high-fidelity waveguides presently being used in an Inductively Coupled Plasma Torch facility for high heat flux thermal protection system testing. The design is intended to accentuate acoustic emission signals of interest, while suppressing other forms of elastic wave noise.

High-order wavefront correction is not only beneficial for high-contrast imaging, but also spectroscopy. The size of a spectrograph can be decoupled from the size of the telescope aperture by moving to the diffraction limit which has strong implications for ELT based instrument design. Here we present the construction and characterization of an extremely efficient single-mode fiber feed behind an extreme adaptive optics system (SCExAO). We show that this feed can indeed be utilized to great success by photonic-based spectrographs. We present metrics to quantify the system performance and some preliminary spectra delivered by the compact spectrograph.

O presente trabalho tem como objetivo estudar a produção e caracterização de filmes finos do tipo GeO2-Bi2O3 (BGO) produzidos por sputtering-RF com e sem nanopartículas (NPs) semicondutoras, dopados e codopados com íons de Er3+ ou Er3+/Yb3+ para a produção de amplificadores ópticos. A produção de guias de onda do tipo pedestal baseados nos filmes BGO foi realizada a partir de litografia óptica seguida por processo de corrosão por plasma e deposição física a vapor. A incorporação dos íons de terras-raras (TRs) foi verificada a partir dos espectros de emissão. Análises de espectroscopia e microscopia foram indispensáveis para otimizar os parâmetros dos processos para a construção dos guias de onda. Foi observado aumento significativo da luminescência do Er3+ (região do visível e do infravermelho), em filmes finos codopados com Er3+/Yb3+ na presença de nanopartículas de Si. As perdas por propagação mínimas observadas foram de ~1,75 dB/cm para os guias pedestal em 1068 nm. Para os guias dopados com Er3+ foi observado aumento significativo do ganho na presença de NPs de silício (1,8 dB/cm). O ganho óptico nos guias de onda amplificadores codopados com Er3+/Yb3+ e dopados com Er3+ com e sem NPs de silício também foi medido. Ganho de ~8dB/cm em 1542 nm, sob excitação em 980 nm, foi observado para os guias pedestal codopados com Er3+/Yb3+ (Er = 4,64.1019 átomos/cm3, Yb = 3,60.1020 átomos/cm3) com largura de 80 µm; para os guias codopados com concentração superior de Er3+/Yb3+ (Er = 1,34.1021 átomos/cm3, Yb = 3,90.1021 átomos/cm3) e com NPs de Si, foi observado aumento do ganho óptico de 50% para guia com largura de 100 µm. Os resultados apresentados demonstram que guias de onda baseados em germanatos, com ou sem NPs semicondutoras, são promissores para aplicações em dispositivos fotônicos. / This work aims to study the production and characterization of GeO2-Bi2O3 (BGO) thin films produced by RF-sputtering with and without semiconductor nanoparticles (NPs),doped and codoped with Er3+ or Er3+/Yb3+ ions for the production of optical amplifiers. The pedestal type waveguide production based on BGO thin film was done trough optical lithography followed by reactive ion etching and physical vapor deposition processes. The incorporation of the rare-earth ions was verified from the emission spectra. Spectroscopy and microscopy analysis were indispensable to optimize the processes parameters for the waveguide fabrication. It was observed minimum propagation losses of ~1,75 dB/cm, at 1068 nm for the pedestal type waveguides. Optical gain was also measured in the Er3+/Yb3+ codoped waveguides with and without Si nanoparticles. Optical gain of 8 dB/cm, at 1542 nm, under 980nm pumping were obtained for 80 µm width Er3+/Yb3+ codoped waveguides (Er = 4,64.1019 atoms/cm3, Yb = 3,60.1020 atoms/cm3). For waveguides doped with higher concentration of Er3+/Yb3+ (Er = 1,34.1021 átomos/cm3, Yb = 3,90.1021 átomos/cm3) and containing silicon nanoparticles, it was observed 50% enhancement of the optical gain for 100 µm width waveguides. For the Er3+ doped waveguides, it was observed significant gain enhancement in the presence of silicon nanoparticles (1.8 dB/cm). The present results demonstrate that germanate waveguides, with or without semiconductor NPs are promising for applications in photonic devices.

<p>In this study, a novel and systematic methodology for the design and optimization of conductor-backed coplanar waveguide (CB-CPW) based low pass filter (LPF) is proposed. The width of the signal trace is continuously varied using a truncated Fourier series, and the adjacent gaps are designed in several types established on a specific optimization setup to obtain predefined electrical characteristics with maximum compactness taking into account physical constraints. Trust-region-reflective algorithm (TRRA), genetic algorithm (GA), and particle swarm optimization algorithm (PSO) are taken into account to minimize the developed bound-constrained non-linear objective function respectively.<br></p><p>All types are programmed and analytically verified in MATLAB. Solutions include design parameters such as the physical length and width of the structure, which will be drawn in AutoCAD later on. Also, the optimized layouts are exported to Ansys High Frequency Structure Simulation (HFSS) software for simulation and validation. Non-uniform CB-CPW LPFs are optimized and simulated over a frequency range of 0-6 GHz with a cutoff frequency of 2 GHz. Simulation results show a good agreement with the analytical ones.<br></p>

A method was developed to access the interior of light-guiding structures in order to exploit the enhanced sensing potential of the highly confined electromagnetic field distributions, located within the core of a waveguide. The work presented in this thesis explores therefore the possibilities of optical waveguide spectroscopy utilising transparent mesoporous thin-film waveguides deposited on top of athin gold layer. These multi-layer assemblies are employed in a prism-coupling attenuated total internal reflection (ATR) configuration. The angular read-out of the reflected light intensity allows label-free detection schemes with high sensitivity to changes of the dielectric environment in the case of the presence of analyte molecules within the probing region. This optical waveguide spectroscopy technique has been used to study the real-timediffusion of Ruthenium 535-bisTBA (N-719) dye into mesoporous nanocrystalline titaniumdioxide films. The porous films were prepared on top of gold substrates and prism coupling was used to create a guided wave in the nanocrystalline film. Dying was carried out by bring the film into contact with a 3 x 10-4 moldm-3 dye solution and using optical waveguide spectroscopy to monitor the change in both the refractive index and theextinction coefficient of the nanoporous layer as dye diffused into the porous network. Dyeuptake in a 1.27 μm film was slow with the refractive index of the film still increasing after 22 hours.

Optical switchers can fulfill the same functions as all-electrical switching systems and are expected to play a key role in the near future. In this thesis an analysis if an optical system that can potentially behave as an optical switcher is discussed. This configuration consists of three microring resonators which are coupled and tangential to one another in a topology that is similar to the Leibniz packing or Apollonian gasket. The ray-transfer matrix approach is used in order to represent the whole system by a single matrix. The structure receives an initial input signal and gives an output signal, which is changed by only a scalar factor. This description is equal to an eigenvalue problem, where the matrix of the system operates over an initial vector and results a product of a scalar (the eigenvalue) times the initial vector. Due to its unique geometry each ring is divided into two unequal segments. We introduce the loss coefficients to express the attenuation along those segments. The relation between the loss coefficients is being examined and the results are verified by simulations.