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(1993)ThesisIn view of the specific advantages of using vacuum as device medium and field emission cathode as electron source, a renewed interest in vacuum microelectronics utilizing advanced IC technology is emerging. This thesis demonstrates an application of field emission emitters in two novel pressure sensors. One is based on a diode structure with one electrode fabricated on a pressure sensitive thin diaphragm. The other has two tip-to-tip cantilever beam emitters with a small gap between tips. Both cone-shape and wedge-shape emitters are studied. Some new results on the analysis of the two generic emitter array diodes regarding the geometric design parameters, which are essential to device design, are presented. Various wet and dry etching techniques of forming emitter arrays are compared. A combined wet/dry fabrication process is developed to achieve array uniformity and reproducibility. The characteristics of pressure sensor with ideal field emission array are simulated, methods to take into consideration the nonuniformity of array tips, an inevitable result from fabrication practice, is also discussed. A study of field emission from silicon-based emitter array is present and various factors to affect the stability of emission are investigated. The performance of two fabricated experimental pressure sensors are evaluated, one with cone-shape emitter array and the other with cantilever beam field emitters.
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(1992)ThesisThe work in this thesis consists of research into a study of design issues of packet voice protocols in an interconnected local area network environment. The key parameters of performance are defined. The relationship of, and the trade-off between the parameters is also discussed. The material covered in this thesis is mainly separated in two parts, as follows: In the first part, we examine the behaviour of the speech signal, with the aim to analyse the special characteristics of voice signal, useful in the integration of voice and data. The actual voice data samples generated by using embedded coding technique is collected and analysed, as a result of the investigation and analysis a computer model based on the “Time Series” and “Markov Chain” is developed. This model is useful in a sense that it simulates the two most important characteristics( intensity and frequency) of voice signals, statistically acceptable, to represent the real voice data without the need of a costly hardware to generate them. In addition, by analysing the talker activity model of speech, the cumulative probabilities of active talkers in “talkspurt” in an integrated services of voice and data is used as a measure to indicate the required bandwidth for current voice users. A statistical model is developed to represent this phenomena. The model is studied in some detail. Based on these studies a protocol is proposed to avoid the congestion in the interconnected environment of local area networks. In order to verify the validity of the model, a simple fair resource allocation is defined and an algorithm is used to exercise control at the gateway. Numerical and simulation results are compared to verify the effectiveness of the proposed scheme. In the second part, based on the requirements of the packetised voice communications as a real-time data, an experimental investigation is performed on a laboratory model of interconnected local area networks through a FDDI backbone. The throughput of the gateways as well as host-to-host are measured. In our experimental measurement the Internet(TCP/IP) protocol family as a present defacto standard is used. The aim of this investigation was to verify the throughput of the gateways and its quick response to congestion based on the proposed gateway protocol. As part of our investigation, in order to remove ambiguities and as a basis for the development and verification of the voice protocols using the TCP/IP services, NPN(Numerical Petri Net) a high level inhibitor net, are used to characterise the TCP/IP protocols, the computer model is developed and the possible causes of the “deadlocks” are identified.
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(1995)ThesisStand-alone power systems, also known as Remote Area Power Supply (RAPS) systems, are increasingly being used as an alternative to the extension of reticulated electricity supply in many areas of the world. State-of-the-art Hybrid RAPS systems consisting of one or more diesel/petrol engine generators, photovoltaic generation, battery storage and associated power conditioning equipment, are considered in this thesis. Typical applications of Hybrid RAPS systems include the supply of electricity to isolated communities or homesteads, and power for remote telecommunications sites. This thesis describes a new method for optimising the operation of Hybrid RAPS systems. Previous approaches to the RAPS operation optimisation problem are described. An existing mathematical optimisation method, based on linear programming and dynamic programming techniques, is selected and modified to allow incorporation of diesel generator on/off state and diesel generator start-up costs. The new optimisation method is applied to a Hybrid RAPS model for a deterministic future, and implemented on a computer. It is compared to a discrete dynamic programming method, previously representing the best approach to the RAPS operation optimisation problem, and shown to provide superior performance characteristics, in particular giving a faster solution time and higher solution accuracy. Example RAPS control actions produced by the new optimisation method are presented and discussed. The optimisation method is compared to a conventional RAPS control algorithm, implemented in a RAPS simulation program. The comparison has identified that the new method has a potential to reduce system operating costs. At present, the new method is most effectively used as a benchmark for other RAPS control algorithms. It could be extended to model the stochastic nature of future load demand and photovoltaic power, which would increase its practical value.
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