Thesis (MScEng (Electical and Electronic Engineering))--University of Stellenbosch, 2008. / A Cryogenic CMOS-based Control System for Testing Superconductor Electronics P.C. van Niekerk Department of Electrical and Electronic Engineering University of Stellenbosch Private Bag X1, 7602 Matieland, South Africa Thesis: M.Sc.Eng. (E&E) March 2008 A complete control system, with accompanying software, is designed to interface superconductive digital and sensory circuits for use in cryogenic vacuumed environments. It acts as an inter-mediator between superconductor electronics and room temperature electronics for research purposes. In order to facilitate low bit-error rate communications with superconductive electronics, the system is designed to have ultra low-noise current and voltage sources for transmitting data to superconductor electronics. Very high sensitivity voltage inputs are also implemented for data extraction from superconductor electronics. It implements both digital as well as analog design components, including ADC and DAC devices. The data is transmitted via a USB cable connection at 1Mbaud to a computer where the data is processed by specially designed software and graphically displayed for user interfaced research. Extensive research is done on the electronic components, such as CMOS devices, for functioning in an average temperature of 70 Kelvin inside cryogenic environments. This is done to reduce the thermal noise and heat transfer to superconductor electronics. An integrated temperature control system also ensures a stable environment for the electronics to operate at 70 K.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009. / In this thesis the mathematical modelling and simulation of an autonomous underwater vehicle is presented. A generic six degree of freedom model suitable for AUV control applications is presented. This model is then tailored to the AUV testbed developed by IMT. The model parameters are determined from vehicle geometry alone. In addition to this, a linear model is presented and analysed in order to determine the modes of motion for AUV. The development of a generic visualisation system suitable for underwater vehicle simulations is also presented. A generic MATLAB based AUV simulation system is developed, and used to supply the visualisation system with the necessary simulation data. Lastly, two example simulations are shown

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2005. / Orthogonal Frequency Division Multiplexing (ODFM) has gained considerable attention the past couple of years. In our modern world the need for faster data transmission is never-ending. OFDM modulation provides us with a way of more densely packing modulated carriers in the frequency domain than other existing Frequency Multiplexing schemes, thus achieving higher data rates through communications channels. Software Defined Radio (SDR) creates a very good entry point for designing any communications system. SDR is an architecture that aims to minimise hardware components in electronic communications circuits by doing all possible processing in the software domain. Such systems have many advantages over existing hardware implementations and can be executed on various platforms and embedded systems, given that the appropriate analogue front ends are attached to the system.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / This thesis relates to the development of an automated sorting cell as part of a flexible manufacturing line, with the use of object recognition. Algorithms for each of the individual subsections creating the cell, recognition, position calculation and robot integration were developed and tested. The Fourier descriptors object recognition technique is investigated and used. Invariance to scale, rotation or translation of the boundary of an object recognition. Stereoscopy with basic trigonometry is used to calculate the position of recognised objects, after which they are handled by a robot. Integration of the robot into the project environment is done with trigonometry as well as Euler angles. It is shown that a successful, automated sorting cell can be constructed with object recognition. The results show that reliable sorting can be done with available hardware and the algorithms development.

Thesis (MScEng (Electrical and Electronic Engineering))--Stellenbosch University, 2007. / The finite element method is a very efficient numerical tool to solve geometrically complex problems in electromagnetics. Traditionally the method is applied to bounded domain problems, but it can also be forged to solve unbounded domain problems using one of various mesh termination schemes. A scalar finite element solution to a typical unbounded two-dimensional problem is presented and the need for a proper mesh termination scheme is motivated. Different such schemes, specifically absorbing boundary conditions, the finite element boundary integral method and infinite elements, are formulated and implemented. These schemes are directly compared using different criteria, especially solution accuracy and computational efficiency. A vector finite element solution in three dimensions is also discussed and a new type of infinite element compatible with tetrahedral vector finite elements is presented. The performance of this infinite element is compared to that of a first order absorbing boundary condition.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / The topic of millimeter wave radar systems is introduced. These radars are used in a wide range of applications in both the aviation and automotive field due to the resolution advantages which MMW systems have above their counterparts. MMW components are studied and characterised to improve on an existing linearisation technique. Different possible linearisation techniques are discussed and compared to choose the best possible technique for this application. This technique was developed and implemented in the existing system.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009. / The PBMR has called for research into the possibility of distributed in-core temperature measurement. In this thesis, several methods for distributed temperature measurement in high-pressure, -radiation and -temperature environments have been investigated by means of a literature study. The literature study has revealed FBG temperature sensors as the most feasible solution to the temperature measurement challenge. Various parameters affecting the propagation of light in optical fibres and consequently the FBG reflection profile was researched. The differential equations describing FBG structures were solved and implemented in Matlab in order to simulate WDM of a distributed FBG sensing system. Distributed sensing with apodized FBGs written in sapphire optical fibre show the most promise of becoming a solution to the measurement challenge. However, practical testing of sapphire FBGs exposed to the environment in the PBMR core is required. With this long-term goal in mind, a general test platform for FBG temperature sensors was assembled. A heater controller was built for a specialized fibre heating element capable of controlling the temperature of a single FBG up to 1600 C. Temperature measurement using wavelength division multiplexing of apodized FBGs written in silica optical fibre were demonstrated in the test platform with great success. The measured results corresponded very well with the theory. Finally, the implementation of FBGs in the PBMR is discussed and recommendations are made for future work

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2007. / During an imaging pass of a remote sensing satellite, the satellite’s attitude has to be controlled so that the imager bore-sight sweeps out equal distances over time and so that images with a square aspect ratio are produced. The satellite attitude control system uses forward motion compensation (FMC) and time delay and integration (TDI) techniques to increase the quality of images. The motion of the scene relative to the satellite camera can be described by a two dimensional translation motion and a rotation about the camera bore-sight. This thesis describes an algorithm for measuring ground motion from viewfinder video data that can aid the satellite control system during imaging missions. The algorithm makes use of existing motion-from-video techniques – it operates in a hierarchical, feature-tracking framework. Features are identified on camera frames, and correspondences on consecutive frames are found by the Lucas and Kanade algorithm. A pyramidal image representation enables the estimation of large motions. The resultant sparse disparity map is used to estimate the three motion parameters, using a least squares fit to the projected motion equations. The algorithm was developed and implemented as part of the MSMI project. Results of tests carried out on simulated satellite viewfinder data (using the Matrix Sensor camera that was also developed for the MSMI project) confirms that the requirements are met.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / The successful operation of a pulsed monostatic borehole radar system requires that cur- rent on the antenna due to transmitter pulses subsides quickly. Deterioration of the radar antenna feed-point current settling times when deployed in water-¯lled boreholes showed that the radar system's performance is highly environmentally sensitive. Electromagnetic models are used to investigate this e®ect, since measuring the feed-point and radiative characteristics of an insulated antenna deployed in a borehole is practically impossible at present. A transmission line model for insulated antennas is utilized to model the borehole radar antenna in electrically dense media. Predicted input impedance values however do not correspond well to those from numerical ¯eld simulation software and the model is shown to be inadequate for modelling insulated antennas in environments of low conductivity. Radiated ¯eld results are however found to be accurate. A study of the feed-point and radiative characteristics of the borehole radar antenna in a range of di®erent borehole environment is performed using electromagnetic ¯eld simulation software. Results con¯rm that the borehole radar antenna has longer feed- point current settling times and degraded radiated pulse waveforms when deployed in water-¯lled boreholes. Simple lumped element networks with driving-port impedances approximately equal to antenna input impedances are synthesized from simulated input impedance results for a range of borehole environments. This allows diagnostics on the radar system to be performed in the laboratory, with the antenna load appearing as if the system were deployed in a borehole. The use of an antenna with distributed resistive and capacitive loading is proposed as a modi¯cation that would result in improved feed-point characteristics in water-¯lled boreholes. Results from simulations and experiments are presented that con¯rm that the new antenna design substantially reduces feed-point current settling times after the transmitter ¯res.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2005. / This thesis presents the design and implementation of a Neutral-Point-Clamped (NPC) shunt Active Filter (AF) for non-linear loads. A NPC shunt AF is an attractive solution for AFs at the medium volage level, because it eliminates the need for cosly injection transformers. The balance of the capacitors of the direct current (dc) bus of the NPC inverter needs to maintained for stable and satisfactory operation though. Modulation techniques and their associated balancing techniques of the NPC inverter are analysed and discussed in the shunt AF setup. Specifically, the effect of Power Factor (PF), harmonics and unbalance of non-linear loads are considered. The practical design and implementation of the NPC shunt AF is presented. Practical and simulation results are presented which validates the presented theory.