No description available.

M.Ing. (Electrical & Electronic Engineering) / Please refer to full text to view abstract

The classic problem of achieving high Q, band pass, inductorless filters has been traditionally attacked by applying active RC networks. This approach suffers from the faults of poor economy, lack of stability of performance with time and temperature, and high network performance sensitivity to component changes. The problem is reviewed from the aspect of applying techniques other than operational amplifier RC filters. The techniques presented are those of N-Path (switching) and Digital Filters. The underlying theory of both methods is explored and a design example for each of the techniques is presented. These designs are then compared on the basis of design complexity, parts cost (count) and ease of fabrication. On the basis of the comparison of designs, it is shown which technique is more economical for the problem under discussion.

Two aids for the design of switched-capacitor filters (SCFs) are examined: breadboard modelling and computer simulations. A breadbroad was constructed based upon the same passive prototype of a seventh-order integrated filter. The breadboard met the original design specifications better than the integrated filter because the schematic and parasitics of the integrated filter were unknown. Three computer programs, SPICE, DIANA, and TCAPS, are compared to determine their abilities and limitations in SCF design. SPICE is of limited value since it models switched capacitors as resistors. DIANA and TCAPS directly simulate the digital nature of switched capacitors, so they track in their predictions of 1) increased passband ripple, 2) increased cutoff frequency, 3) increased third notch frequency, 4) increased OBR. On the basis of this comparison, it is not possible to determine if DIANA or TCAPS is the better program. However, both DIANA and TCAPS simulate SCFs far more accurately than SPICE. / Master of Science

The excellent particulate removal efficiency of ceramic candle filters has prompted efforts to develop a more durable and economical alternative to existing ceramic candle filters. Porous ceramic candle filter elements were successfully fabricated from calcium aluminate cement, calcined fireclay aggregate, and organic pore formers using refractory concrete casting techniques. Methods used to characterize the porous ceramic filter elements included determination of pore size and distribution, permeability, resistance to alkali attack, and mechanical strength. Various pore formers and casting, curing, and sintering conditions were examined to produce highly permeable and structurally sound filter elements. The optimized fabrication procedure produced porous ceramic candle filter elements with pore diameters between 20.3 to 43.1 tlm, porosities of 38 to 60%, and pressure drops of 3 to 24 mbars at a face velocity of 100 mjh. These characteristics are comparable to existing ceramic filters which are noted for their > 99% collection efficiencies of submicrometer-sized particles, but short-term durability in advanced coal combustion clean-up systems. Test specimens of the alumino silicate refractory concrete proved more durable by showing no severe attack following exposures to alkali-containing atmospheres at 700-1000°C. The strength of the cast samples ranged from 200 to 1139 psi depending on the relative densities and pore formers. Porous fliter elements with different porous structures, permeabilities, and shapes can be easily produced with this technique. / Master of Science

Experiments were performed to determine a suitable binder material for silicon carbide-based ceramic filter. These experiments included exposure of 42% and 60% alumina, aluminosilicates to potassium and sodium containing environments for the purpose of determining the phases that would form and to determine concentration profiles. In addition, thermodynamic calculations were performed to predict the phases that would form when the alkali reacted with the aluminosilicate. The results of the thermodynamic calculations indicated that the alkali compounds will react at temperatures as low as 800°C. The exposure experiments verified this result. The phases that formed during the sodium vapor exposures and confirmed the thermodynamic calculations and were as follows: 1. sodium metasilicate and a solid solution of sodium aluminum silicates and carnegieite and for potassium vapor exposure. 2. potassium disilicate, kaliophilite-nepheline, potassium aluminate, and 5K₂O-5Al₂O₃-8SiO₂. Experiments also revealed that penetration depth by alkali compounds was restricted to a region near the surface of the material when the combination of temperature and sodium concentration alowed a melt to form. The results also indicated that the 42% alumina, aluminosilicate had superior resistance to alkali attack than the 60% alumina, aluminosilicate at temperatures below 1225°C. / Master of Science

"March, 2009". / Thesis (PhD)--Macquarie University, Faculty of Science, Dept. of Physics & Engineering, 2008. / Bibliography: p. 145-158. / Introduction -- Frequency selective surfaces -- Absorb/transmit frequency selective surface absorber -- Switchable frequency selective surface for wireless applications -- Energy-saving glass characterisation -- Frequency selective surface solution for energy-saving glass -- Conclusion. / This thesis presents three topics related to frequency selective surfaces (FSSs), namely bsorb/transmit FSSs, active FSSs and passive bandpass FSSs for energy-saving glass used in modern buildings. These three FSSs are unique in their design and functionalities. The absorb/transmit FSS is a novel dual-layer frequency selective surface for 5 GHz WLAN applications. This FSS can stop propagation of specific bands by absorbing as opposed to re ecting, while passing other useful signals. This is in contrast to the conventional Salisbury and Jaumann absorbers, which provide good absorption in the desired band while the out-of-band frequencies are attenuated. The second topic is a single-layer bandpass active FSS that can be switched between ON and OFF states to control the transmission in 2.45 GHz WLAN applications. Previously, researchers have focused on the bandstop and dual-layer versions of the active FSS. This is in contrast to the design presented in this thesis which is single-layer and provides extra advantage in a practical WLAN environment. Also the dc biasing techniques that were used for the active FSS design are easier to implement and provide good frequency stability for different angles of incidence and polarisations in both ON and OFF states. The last topic is on the use of a bandpass FSS in energy-saving glass panels used in building design. The manufacturers of these glass panels apply a very thin metal-oxide coating on one side of the glass panels to provide extra infrared (heat) attenuation. However, due to the presence of the coating, these energy-saving glass panels also attenuate communication signals such as GSM 900, GSM 1800/1900, UMTS and 3G mobile signals etc. This creates a major communication problem when buildings are constructed with windows of this glass. In this thesis, a solution to this problem is presented by designing and etching a cross-dipole bandpass FSS on the coated side of the glass to pass the useful signals while keeping infrared attenuation at an acceptable level. One of the advantages of this FSS design is that measured material values of the metal-oxide coating are used for simulations, which have not been done previously. / Mode of access: World Wide Web. / 166 p. ill. (some col.)

Nas últimas décadas, vários sistemas de comunicação baseados em sincronismo caótico têm sido propostos na literatura como alternativa a sistemas de espalhamento espectral que melhoram o nível de privacidade na transmissão da mensagem. No entanto, devido à falta de robustez do sincronismo caótico, um pequeno nível de ruído ou uma simples imperfeição no canal é suficiente para impedir a comunicação. Neste trabalho, equalizadores adaptativos são utilizados para permitir a comunicação em um sistema de comunicação baseado em caos quando a resposta em frequência do canal não é ideal. São propostos algoritmos de equalização baseados em versões modificadas do algoritmo normalized least-mean-squares para a versão de tempo discreto do sistema de comunicação baseado no modelo de sincronismo de Wu e Chua. Para esses algoritmos, é calculado o intervalo para a escolha do passo de adaptação para evitar a divergência. Como geradores de sinais caóticos (GSC), são utilizados os mapas de Hénon e de Ikeda e, para a codificação da mensagem, são consideradas duas funções, sendo uma baseada na multiplicação da mensagem por um dos estados do GSC e a outra baseada na soma da mensagem com um dos estados do GSC. Os resultados de simulação indicam que os algoritmos propostos são capazes de equalizar o canal de comunicação e permitir o sincronismo caótico em diferente cenários. / In the last decades, many communication systems applying synchronism of chaotic systems have been proposed as an alternative spread spectrum modulation that improves the level of privacy in data transmission. However, due to the lack of robustness of chaos synchronization, even a low level of noise or minor channel imperfections are enough to hinder communication. In this work, adaptive equalizers are used to enable chaotic synchronization when the communication channel is not ideal. Adaptive equalization algorithms are proposed based on a modified version of the normalized least-mean-squares algorithm, considering the discrete-time version of the communication system based on Wu and Chuas synchronization model. For these algorithms, the interval for the choice of the step-size is computed, in order to avoid divergence. The Hénon and the Ikeda maps are used as chaotic signal generators (CSG) and two functions are considered to encode the message, one based on the multiplication of the message by one of the states of the CSG and the other based on the addition of the message to one of the states of the CSG. Simulation results show that the proposed algorithms can successfully equalize the channel in different scenarios.

O objetivo da desconvolução autodidata de imagens é reconstruir a imagem original a partir de uma imagem degradada sem usar informação da imagem real ou da função de degradação. O processo de reconstrução é crítico em aplicações em que a imagem original ou suas características estatísticas não são conhecidas. Fazendo um mapeamento da imagem digital antes de sua transmissão, ela pode ser interpretada como um sinal de comunicação com modulação do tipo PAM (Pulse Amplitude Modulation). Utilizando essa interpretação, técnicas clássicas de equalização de canais de comunicação podem ser usadas para restauração de imagens. Além disso, é usual considerar os pixels de uma imagem como um sinal não-estacionário, o que justifica o uso de algoritmos adaptativos. Neste trabalho, técnicas adaptativas usadas em equalização de canais de comunicação são aplicadas para restauração de imagens. Inicialmente, é proposta uma nova técnica de varredura a fim de minimizar alterações bruscas no sinal de entrada do filtro adaptativo. Utilizando o algoritmo Least Mean Squares, obtém-se uma equivalência entre funções de degradação de imagens e canais de comunicação variantes no tempo. Isso possibilitou comparar algumas funções de degradação com relação à distorção causada em imagens. Em seguida, usando um rearranjo dos elementos da matriz de entrada em um vetor, o algoritmo multimódulo regional (RMMA - Region-based Multimodulus Algorithm) foi estendido para restauração de imagens. Esse algoritmo é então usado para adaptação dos coeficientes do equalizador linear transversal e também do equalizador de decisão realimentada. Cabe observar que o RMMA trata um sinal de módulo não-constante como se fosse de módulo constante, o que proporciona um desempenho melhor quando comparado ao algoritmo do módulo constante (CMA - Constant Modulus Algorithm) convencional, usado em equalização autodidata de canais de comunicação. Esse comportamento também foi observado na reconstrução de imagens, através das simulações apresentadas nesta dissertação. Este estudo abre novas perspectivas de extensão de técnicas usadas em equalização de canais de comunicação para restauração imagens. Uma delas é a possibilidade de restauração de imagens coloridas usando diversidade espacial. / The aim of blind image deconvolution is to reconstruct the original scene from a degraded observation without using information about the true image and the point spread function. The restoration process is critical in applications, where the true image or its statistical characteristics are unknown. Mapping the pixels of the original image before its transmission, the mapped image can be interpreted as a pulse amplitude modulation (PAM) signal, used in communications systems. With this interpretation, classic equalization techniques of communication channels can be used to image restoration. Furthermore, the pixels of a true image constitute a nonstationary signal, which justifies the use of adaptive filters. In this dissertation, adaptive techniques used for equalization of communication channels are applied to image restoration. Firstly, we propose a new update path through the blurred image that consists in a combination of horizontal and vertical alternate paths. This update path minimizes the problem of abrupt changes in the adaptation of the filter and provides better conditions to the image recovery. Using the least mean squares (LMS) algorithm, we obtain an equivalence between a point spread function and a time-variant communication channel. This equivalence was used to compare some point spread functions in relation to the distortion caused in images. Secondly, reshaping the input matrix into a column vector, we extend the regional-based multimodulus algorithm (RMMA) to blind image deconvolution. This algorithm is used to update the coefficients of the linear transversal equalizer and also of the decision feedback equalizer. RMMA treats nonconstant modulus signals as constant modulus ones, which provides a better performance when compared to the conventional constant modulus algorithm (CMA), used in blind equalization of communication channels. This behavior was also observed in image restoration, through the simulations presented in this dissertation. This study pushes back the frontiers of image processing, since different techniques used in equalization can be extended to image restoration. One of the new possibilities is the color image restoration using the spatial diversity.

by Lai Wai Kuen. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1993. / Includes bibliographical references (leaves [119-125]). / Abstract --- p.i / Acknowledgement --- p.ii / Table of Contents --- p.iii / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Background - The Need for Nonlinear Filtering --- p.1.1 / Chapter 1.2 --- Nonlinear Filtering --- p.1.2 / Chapter 1.3 --- Goal of the Work --- p.1.4 / Chapter 1.4 --- Organization of the Thesis --- p.1.5 / Chapter Chapter 2 --- An Overview of Robust Estimator Based Filters Morphological Filters / Chapter 2.1 --- Introduction --- p.2.1 / Chapter 2.2 --- Signal Representation by Sets --- p.2.2 / Chapter 2.3 --- Robust Estimator Based Filters --- p.2.4 / Chapter 2.3.1 --- Filters based on the L-estimators --- p.2.4 / Chapter 2.3.1.1 --- The Median Filter and its Derivations --- p.2.5 / Chapter 2.3.1.2 --- Rank Order Filters and Derivations --- p.2.9 / Chapter 2.3.2 --- Filters based on the M-estimators (M-Filters) --- p.2.11 / Chapter 2.3.3 --- Filter based on the R-estimators --- p.2.13 / Chapter 2.4 --- Filters based on Mathematical Morphology --- p.2.14 / Chapter 2.4.1 --- Basic Morphological Operators --- p.2.14 / Chapter 2.4.2 --- Morphological Filters --- p.2.18 / Chapter 2.5 --- Chapter Summary --- p.2.20 / Chapter Chapter 3 --- Multi-Structuring Element Erosion Filter / Chapter 3.1 --- Introduction --- p.3.1 / Chapter 3.2 --- Problem Formulation --- p.3.1 / Chapter 3.3 --- Description of Multi-Structuring Element Erosion Filter --- p.3.3 / Chapter 3.3.1 --- Definition of Structuring Element for Multi-Structuring Element Erosion Filter --- p.3.4 / Chapter 3.3.2 --- Binary multi-Structuring Element Erosion Filter --- p.3.9 / Chapter 3.3.3 --- Selective Threshold Decomposition --- p.3.10 / Chapter 3.3.4 --- Multilevel Multi-Structuring Element Erosion Filter --- p.3.15 / Chapter 3.3.5 --- A Combination of Multilevel Multi-Structuring Element Erosion Filter and its Dual --- p.3.21 / Chapter 3.4 --- Chapter Summary --- p.3.21 / Chapter Chapter 4 --- Properties of Multi-Structuring Element Erosion Filter / Chapter 4.1 --- Introduction --- p.4.1 / Chapter 4.2 --- Deterministic Properties --- p.4.2 / Chapter 4.2.1 --- Shape of Invariant Signal --- p.4.3 / Chapter 4.2.1.1 --- Binary Multi-Structuring Element Erosion Filter --- p.4.5 / Chapter 4.2.1.2 --- Multilevel Multi-Structuring Element Erosion Filter --- p.4.16 / Chapter 4.2.2 --- Rate of Convergence of Multi-Structuring Element Erosion Filter --- p.4.25 / Chapter 4.2.2.1 --- Convergent Rate of Binary Multi-Structuring Element Erosion Filter --- p.4.25 / Chapter 4.2.2.2 --- Convergent Rate of Multilevel Multi-Structuring Element Erosion Filter --- p.4.28 / Chapter 4.3 --- Statistical Properties --- p.4.30 / Chapter 4.3.1 --- Output Distribution of Multi-Structuring Element Erosion Filter --- p.4.30 / Chapter 4.3.1.1 --- One-Dimensional Statistical Analysis of Multilevel Multi-Structuring Element Erosion Filter --- p.4.31 / Chapter 4.3.1.2 --- Two-Dimensional Statistical Analysis of Multilevel Multi-Structuring Element Erosion Filter --- p.4.32 / Chapter 4.3.2 --- Discussions on Statistical Properties --- p.4.36 / Chapter 4.4 --- Chapter Summary --- p.4.40 / Chapter Chapter 5 --- Performance Evaluation / Chapter 5.1 --- Introduction --- p.5.1 / Chapter 5.2 --- Performance Criteria --- p.5.2 / Chapter 5.2.1 --- Noise Suppression --- p.5.5 / Chapter 5.2.2 --- Subjective Criterion --- p.5.16 / Chapter 5.2.3 --- Computational Requirement --- p.5.20 / Chapter 5.3 --- Chapter Summary --- p.5.23 / Chapter Chapter 6 --- Recapitulation and Suggestions for Further Work / Chapter 6.1 --- Recapitulation --- p.6.1 / Chapter 6.2 --- Suggestions for Further Work --- p.6.4 / Chapter 6.2.1 --- Probability Measure Function for the Two-Dimensional Filter --- p.6.4 / Chapter 6.2.2 --- Hardware Implementation --- p.6.5 / References / Appendices