The detection of weak, ground-moving targets can be improved through effective utilization of additional target signal energy collected over an extended dwell time. The signal model used in conventional radar processing limits integration of signal energy over an extended dwell. Two solutions that consider the complexity of the extended-dwell signal model and effectively combine signal energy collected over a long dwell are presented. The first solution is a single-channel algorithm that provides an estimate of the optimal detector to maximize output signal-to-interference-plus-noise ratio for the extended dwell time signal. Rather than searching for the optimal detector in an intractably large filter bank that contains all combinations of phase components, the single-channel algorithm projects dictionary entries against the data to estimate the signal’s linear and nonlinear phase components sequentially with small, phase-specific dictionaries in a multistage process. When used as the detector, the signal model formed from the estimated phase components yields near optimal performance for a wide range of target parameters for dwell times up to four seconds. In comparison, conventional radar processing methods are limited to an integration time of approximately 100 milliseconds. The second solution is a multichannel, multistage algorithm based on element-space pre-Doppler space-time-adaptive processing with two modifications that make it suitable for detection of weak targets whose energy is collected over an extended dwell time. The multichannel solution detects targets with lower radial velocities at significantly lower signal-to-noise ratios (SNRs) than conventional radar processing methods. The decrease in required input SNR for the multichannel solution as compared to conventional methods nearly doubles the detection range for a typical target of interest. Future related research includes extension of these concepts to other radar applications and investigation of algorithm performance for the multiple-target scenario.

This thesis presents a design and implementation of a long-range communication subsystem for a UAV and a ground control station. The subsystem is a low-cost alternative employing a line of sight, local communication network for optimal communications between a low-altitude UAV and a portable ground control station. In this thesis, real world experiments are conducted to model the time-variant wireless channel between a low-altitude micro-UAV and a portable ground control station operating in an urban environment. The large-scale and small-scale fading coefficients are calculated and analyzed for this dynamic channel. The channel properties, along with the fading distribution parameters, are computed and analyzed for two most popular antenna configurations for UAV systems (Yagi to omnidirectional and omnidirectional to omnidirectional). For the Yagi-to-omnidirectional link, the effects of three major impacting factors i.e. propagation distance, antenna gains in specific spherical angles and polarization mismatch factor on the overall fading distribution is investigated. Through regression analysis, a multiple-regression model is derived that estimates the instantaneous fading parameter, given these channel conditions. For this model, a modified particle-swarm optimization algorithm is designed and implemented to estimate the underlying model coefficients, given the instantaneous fading information. The implementation of this algorithm, along with the regression model, demonstrates that a sufficient approximation of the fading parameter can be provided for any given wireless channel when the impacting factors and instantaneous fading information is available. / February 2016

The need of making arsenic contaminated ground water potable is urgent in parts of Burkina Faso. An implementation of a treatment design using Granular Ferric Hydroxide (GFH) is under development. Water from a tube-well in Lilgomdé, Yatenga province, Burkina Faso, has been treated with the adsorbent GFH through column experiments. The water had an arsenic concentration varying between 99 and 215 μg/L and an average pH of 7.9. The study has shown that arsenic, predominantly in the form of arsenate, can be adsorbed to the material in significant amounts despite a high natural pH and the presence of ions competing with arsenic for adsorption sites on the GFH. When run through the column, the pH of the effluent water drastically decreased in the beginning. However, the low pH was soon followed by a slower readjustment towards the pH of the influent water. The adsorption of phosphates and fluorides was also studied. Both competitors exist in higher molar quantities than arsenic in the ground water. Even though arsenic displays a higher affinity for the GFH, an average 44 % of total phosphate and 64 % of the fluoride were adsorbed, making them a factor affecting the results of the study. Hydrogen carbonate is also believed to affect the adsorption process but this could not be confirmed. The empty bed contact time (EBCT), describing the average time of contact between the adsorbent and the water, has shown to be of importance. Increasing the EBCT resulted in notably more arsenic being adsorbed per volume GFH. When increasing the contact time, the study showed that reducing the speed of the flow was more effective than increasing the volume of the adsorbent. The GFH was also found to have a self-regenerating ability to a certain extent. When interrupting the experiment and leaving the column material in the aqueous solution for several days, the arsenic adsorption capacity after the break was shown to be higher than just before it. A 13 % increased capacity was shown in one experiment. Conclusively, the results of this study suggest no hindrances towards developing larger scale columns and prototypes to be applied at tube-well pump stations. Further investigations on the treatment method with GFH, on arsenic contaminated water, are recommended.

Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 2003. / The imaging of platiniferous reefs in the Bushveld Igneous Complex (BIC) is of great economical and sociological importance. Borehole radar technology has been identified as a viable mapping tool to be used in day-to-day mining operations, but a critical assessment has to be made on the feasibility of this postulation. The system analysis made of the borehole radar deployed in the BIC is presented in this dissertation. The analysis is done using a specific example - the GeoMole borehole radar system. A novel procedure, based on the basic theory of electromagnetic radiation and propagation, is proposed by which the entire physical radar system can be characterized. The power transmitted by an unconventional borehole-deployed transmitter is estimated by a sequence of free space measurements, numerical simulations and theoretic derivations and approximations. Antenna transfer functions (magnitude and phase) are numerically simulated for a variety of deployment configurations. The total system transfer function of the receiver analogue and digital chain is determined. This enables the calculation of the radar's performance figures necessary to determine the applicability of the radar in a specific geological setting. A radar system is only complete when considered in its environment. The BIC is a stratified system of numerous rock layers. An in-depth study is done on the propagation of radiowaves in stratified lossy media. Only the case for non-magnetic media is discussed in this dissertation. The developed theory is used to predict the system response to a typical transmitted radar pulse in the UG1 - UG2 stratigraphy of the BIC, determine the maximum detection range of reef horizons and estimate the reflectivity of the reefs. Resolution is one of the key parameters that determine the performance and accuracy of imaging. An algorithm is proposed, developed and tested by which the resolution of the system is increased and overlapping echoes become resolvable. Even though some of the techniques are developed with a specific system in mind, the applicability of the concepts and algorithms is universal.

Large Eddy Simulation (LES) is carried out using the Rolls-Royce Hydra CFD code in order to investigate and give further insight into highly turbulent, unsteady flow structures for automotive applications. LES resolves time dependent eddies that are modelled in the steady-state by Reynolds-Averaged Navier-Stokes (RANS) turbulence models. A standard Smagorinsky subgrid scale model is used to model the energy transfer between large and subgrid scales. Since Hydra is an unstructured algorithm, a variety of unstructured hexahedral, tetrahedral and hybrid grids are used for the different cases investigated. Due to the computational requirements of LES, the cases in this study replicate and analyse generic flow problems through simplified geometry, rather than modelling accurate race car geometry which would lead to infeasible calculations. The first case investigates the flow around a diffuser-equipped bluff body at an experimental Reynolds number of 1.01 times 10 to the power 6 based on model height and inlet velocity. LES is carried out on unstructured hexahedral grids of 10 million and 20 million nodes, with the latter showing improved surface pressure when compared to the experiments. Comparisons of velocity and vorticity between the LES and experiments at the diffuser exit plane show a good level of agreement. Flow visualisation of the vortices in the diffuser region and behind the model from the mean and instantaneous flow attempts to explain the relation or otherwise between the two. The main weakness of the simulation was the late laminar to turbulent transition in the underbody region. The size of the domain and high experimental Reynolds number make this case very challenging. After the challenges faced by the diffuser-equipped bluff body, the underbody region is isolated so that increased grid refinement can be achieved in this region and the calculation is run at a Reynolds number of 220, 000, reducing the computational requirement from the previous case. A vortex generator mounted onto a flat underbody at an onset angle to the flow is modelled to generate vortices that extend along the length of the underbody and its interaction with the ground is analysed. Since the vortex generator resembles a slender wing with an incidence to the flow, a delta wing study is presented as a preliminary step since literature on automotive vortex generators in ground effect is scarce. Results from the delta wing study which is run at an experimental Reynolds number of 1.56 times 10 to the power 6 are in very good agreement with previous experiments and Detached Eddy Simulation (DES) studies, giving improved detail and understanding. Axial velocity and vorticity contours at several chordwise stations show that the leading edge vortices are predicted very well by a 20 million node tetrahedral grid. Sub-structures that originate from the leading edge of the wing and form around the core of the leading edge vortex are also captured. Large Eddy Simulation for the flow around an underbody vortex generator over a smooth ground and a rough ground is presented. A hexahedral grid of 40 million nodes is used for the smooth ground case, whilst a 48 million node hybrid grid was generated for the rough ground case so that the detailed geometry near the ground could be captured by tetrahedral cells. The geometry for the rough surface is modelled by scanning a tarmac surface to capture the cavities and protrusions in the ground. This is the first time that a rough surface representing a tarmac road has been computed in a CFD simulation, so that its effect on vortex decay can be studied. Flow visualisation of the instantaneous flow has shown strong interaction with the ground and the results from this study have given an initial understanding in this area.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2004. / The use of ground penetrating radar, and especially borehole radar in underground mines, is becoming increasingly attractive. This is due to the improvements in the user friendliness of this system. Borehole radar is able to sense accurately geological faults and structures hidden inside the rock body and this information is of value to geologists. In the quest to increase the accuracy of the radar, it was realized that the borehole trajectory and surrounding rock properties are needed. This thesis discusses a rock permittivity and loss sensor which is designed to be deployed in cylindrical hard rock boreholes with diameter of about 50 mm. The sensor consists of electrodes to produce capacitance that is dependant on the rock properties, and electronics to measure this dependency. The biggest problem foreseen is that the probe will not be in direct contact with the rock body. Cylindrical Electrodes were designed using numerical simulations and physical models. Sensitivity and noise attributes received attention. Electronic components were used to sense the small capacitance produced by the electrodes. The resulting signals are slow changing "DC• voltages from which an indication of the needed properties could be extracted. The system was integrated and tested in both laboratory and mine conditions. Test-result-b,ased improvements were introduced and led to satisfactory working of the probe. However, the deployment method will need attention before this probe can be used in field conditions.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2003. / Ground penetrating radar is currently proving itself as an invaluable tool for the prediction of geological structures in the mining environment. Borehole radar is a specific application of this technology, useful in the prediction of the course of rock layers between boreholes ahead of mining. Establishing borehole radar as an industrial tool requires a system that is more userfriendly and easier to deploy than the bi-static radar systems currently available. The development of a monostatic radar system is discussed. It is an ultra wide band, pulse radar system that operates at VHF (10-100 MHz). The system is required to detect reflections from objects 5 m away and further. This translates to a total electromagnetic propagation time of approximately 100 ns or more in the rock medium. The complete design process - from fundamental requirements, through a conceptual design, to a final electronic circuit - is discussed. The design is also built, measured in the laboratory and taken for initial field trails. The following aspects are considered: • Pulse generation by means of an original circuit based on power MOSFETs. • Routing of the transmitted- and received signal between transmitter, receiver and antenna. This is done using a novel, active quasi circulator topology. • Methods of increasing isolation (actively and passively) between transmitter and receiver. • Interfacing with a specific receiver, antenna and data acquisition system.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2001. / Over the last decade, as the mining industry of South Africa is moving to ever deeper mines, the borehole radar is becoming an increasingly important field of research. In December 2000, Burger completed his thesis on Electromagnetic Modelling of a Borehole Radar Environment with the FDTD Method. The goal of this thesis is to extend the research presented in Burger's thesis, considering how more advanced modelling techniques can be applied to the FDTD analysis of the borehole radar environment. Some of these techniques include implementation of dispersive and conductive material models, and developing Uniaxial Perfectly Matched Layer boundary conditions for matching these model. Simulations were run to measure the performance of these boundary condition for matching dispersive and conductive materials. The thesis also includes the implementation of a parallel version of the FDTD algorithm using the Message Passing Interface library. Finally several realistic borehole models where simulated to test the accuracy of the code and to show how the code can be used to model real world problems.

Thesis (MEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2002. / An efficient radiating strucllire was needed for borehole pulsed radar applications in the 10-100 MHz frequency band. Both resistively loaded and insulated wire antennas were investigated and an active antenna is proposed as a fmal solution. The study proceeded from the characterization of the origin of radiation on a conductive dipole wire antenna when excited with a transient. Different radiation mechanisms were identified when the antenna was excited with a current or voltage source. The wire antenna in insulated surroundings was modelled using transmission line theory to simulate the antenna in the borehole environment. The transmission line model proved to be useful for investigating conducting and resistively loaded antennas for the dimensions associated with borehole surveys. From the modelling results, it became apparent that the asymmetric resistively loaded antenna might provide the best practical solution. This antenna displays reasonably stable input impedance and low far-field variations for different theta angles across the desired frequency band. Different percentage Wu-King resistive profiles were studied to show that a 50% reduction in the normal Wu-King resistor values will add only a little ringing but have better amplitude response than the 100% Wu-King loading. The asymmetric resistively loaded antenna has better sensitivity to receiving transients when combined with a high impedance source load than when symmetrically loading the antenna. An active antenna incorporating the asymmetric resistively loaded antenna and a low noise current feedback front end amplifier was built and measured in an air environment. The results show that the active antenna has a flat transfer function and reacts as a wide band electric field probe with better resolution than in the conventional 50 Q loaded case

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2008. / Modern technology is reducing the cost of electronic devices. The speed of these devices and their reliability is improving. They can be used to implement low cost systems without compromising performance. The design of two linear FM-CW radars using direct digital synthesis (DDS) is discussed. The use of the DDS simplifies the generation of the linear frequency sweep that is required. The systems are analysed mathematically and by computer simulation, before being implemented in hardware. The first system is to be used to measure the position of pedestrians, at short range. The other system is to be used as a ground penetrating radar to measure the depth of objects located close to the surface. The design of a micro-strip patch array with a corporate feed network is also discussed. The antenna is constructed, measured and used in the pedestrian measurement system. Both systems are tested and used for initial radar measurements and the results obtained are presented.