published_or_final_version / abstract / Industrial and Manufacturing Systems Engineering / Master / Master of Philosophy

Localization and motion control (navigation) are two major tasks for a successful mobile robot navigation. The motion controller determines the appropriate action for the robot’s actuator based on its current state in an operating environment. A robot recognizes its environment through some sensors and executes physical actions through actuation mechanisms. However, sensory information is noisy and hence actions generated based on this information may be non-deterministic. Therefore, a mobile robot provides actions to its actuators with a certain degree of uncertainty. Moreover, when no prior knowledge of the environment is available, the problem becomes even more difficult, as the robot has to build a map of its surroundings as it moves to determine the position. Skilled navigation of a differential drive mobile robot (DDMR) requires solving these tasks in conjunction, since they are inter-dependent. Having resolved these tasks, mobile robots can be employed in many contexts in indoor and outdoor environments such as delivering payloads in a dynamic environment, building safety, security, building measurement, research, and driving on highways. This dissertation exploits the use of the emerging Radio Frequency IDentification (RFID) technology for the design and implementation of cost-effective and modular control techniques for navigating a mobile robot in an indoor environment. A successful realization of this process has been addressed with three separate navigation modules. The first module is devoted to the development of an indoor navigation system with a customized RFID reader. This navigation system is mainly pioneered by mounting a multiple antenna RFID reader on the robot and placing the RFID tags in three dimensional workspace, where the tags’ orthogonal position on the ground define the desired positions that the robot is supposed to reach. The robot generates control actions based on the information provided by the RFID reader for it to navigate those pre-defined points. On the contrary, the second and third navigation modules employ custom-made RFID tags (instead of the RFID reader) which are attached at different locations in the navigation environment (on the ceiling of an indoor office, or on posts, for instance). The robot’s controller generates appropriate control actions for it’s actuators based on the information provided by the RFID tags in order to reach target positions or to track pre-defined trajectory in the environment. All three navigation modules were shown to have the ability to guide a mobile robot in a highly reverberant environment with variant degrees of accuracy.

A wireless sensor network (WSN) consists of a large number of networked sensor nodes deployed to sense and report a particular phenomenon to a base station. Currently, most WSNs use radio frequency (RF) communications, and this accounts for a significant amount of energy expended. Free space optical (FSO) communications using modulating retroreflectors is potentially attractive for WSNs, due to the lower communications energy required. However, for FSO communications, line of sight (LOS) is required between the transmitter and the receiver. In this thesis, a hybrid Radio Frequency/Free Space Optical (RF/FSO) WSN is proposed. FSO links are used for communications, with RF links providing backup in the absence of LOS. This network has the potential to lower the overall energy consumption of a traditional RF-only WSN. Chapter 1 introduces the WSN and outlines the motivation for the RF/FSO WSN. Chapters 2 and 3 describe the RF and FSO link models used for the RF/FSO WSN. Chapter 4 describes how the WSN networks are configured. The energy model for the sensor node is discussed in Chapter 5. Chapter 6 discusses how network traffic and energy consumption are modelled. The results of the RF/FSO WSN simulations are presented in Chapter 7. Chapter 8 discusses the conclusions from the thesis and suggests areas for future work. Simulations show that for the wide range of scenarios considered, the RF/FSO WSN consumes less energy and has a lifetime at least twice as long as the RF-only WSN. For low and average optical blocking conditions, the RF/FSO WSN is also able to offer at least the same level of network coverage as the RF-only WSN.

It is desirable in many applications that a mobile robot is able to track and follow a person. There have been various efforts in literature to create person-tracking robots. However, current person-tracking robots are not capable of operating in unstructured environments. The problem of creating a person-tracking mobile robot has been studied by many researchers in literature. There are two main issues associated with this problem. The first issue is to equip a robot with proper sensory devices so that it is able to identify and locate the target person in a crowd in real time. Various approaches have been investigated, including vision, infrared sensors, ultrasonic sensors, and other approaches. The second issue is to control and navigate the robot so that it follows the target person within a certain distance. This seems to be simple, but in reality it is a fairly difficult task. For example, if the target person is in a busy corridor with many people standing and walking, the robot has to constantly avoid other people while following the target. There is still no reported evidence that a person-tracking robot has been implemented that is able to track a person in arbitrary environmental conditions. In this research, by using an innovative RF/ultrasonic sensor system, an intelligent person-tracking mobile robot is to be implemented that is able to follow the target person in unstructured, practical environments. The main focus of the thesis is development and implementation of control algorithms.

This thesis investigates the RF characteristics of Mica-Z wireless unattended sensor networks for military and commercial applications. Several experimental configurations were designed and experiments carried out to observe and analyze the behavior of the Mica-Z sensor network. The Mica-Z moteâ s propagation characteristics and network performance were measured under near free-space, indoor and outdoor environments to provide a comprehensive perspective of typical sensor network characteristics. Link-break and re-association distances with their corresponding RF power measurements were recorded to determine the Mica-Zâ s range characteristics under these different operating environments. Power loss exponents were also estimated to provide Mica-Z users a faster and more convenient way to estimate operating ranges in the different environments. A graphical numeric electromagnetic code (GNEC) simulation was also used to investigate some of the possible improvements that could be made to the existing Mica-Z antenna design to enhance the performance of the sensor network. This thesis substantiates the difficulties of operating such sensor networks in the most hostile environments. Although the measurements and analyses demonstrated that controlled deployment was possible to some extent, the effectiveness of deployment remains challenging especially for random ad-hoc deployment.

Master of Science / Food Science Institute / Karen A. Schmidt / Radio frequency dielectric heating (RFDH) can provide rapid and uniform heating throughout the products' mass, and can be used to bake, dry, and defrost foods. Studies have shown that when RFDH induced a 5-log reduction of Salmonella spp. in nonfat dry milk (NDM), whey protein nitrogen index (WPNI) decreased, suggesting that functional properties of the NDM might be impacted. This research was conducted to determine if RFDH affected the functional properties of NDM [high-heat (HH) and low-heat (LH)]. Nonfat dry milk were treated to 75, 80 and 85°C in the RFDH unit, then were held for 125, 63 and 43 min for LH-NDM or 115, 52 and 43 min for HH-NDM, and cooled to ~23 ± 1°C. Powders were evaluated for WPNI , nitrogen solubility index, and color. Maillard browning and functional properties of NDM samples were evaluated after NDM was rehydrated to 3.5% protein with deionized water, and adjusted to pH 7.00. Glucono-delta-lactone was added in rehydrated NDM (3.5% protein; natural pH) as an acidifying agent to form milk gels, and the physical properties of the gels were determined. Two replications were conducted and data were analyzed with two-way ANOVA (RFDH and NDM) and Tukey mean differentiations (p ≤ 0.05). Results showed that LH-NDM (collapsed for RFDH treatments) had 5.7% less viscosity, 20.9% less overrun, 27.4% less foam stability, as well as 15% less water holding capacity compared with HH-NDM (collapsed for RFDH treatments). This can be explained by the natural whey protein denaturation differences in the HH-NDM and LH-NDM. Viscosity and surface tension were impacted by the RFDH treatment. NDM (HH and LH) treated to 85°C had 10% greater viscosity than the control, and the NDM treated to 75°C had less surface tension compared with samples treated to 80°C, 85°C and the control. Overall, RFDH decreased WPNI in LH-NDM, but not HH-NDM. The SDS-PAGE gel images provided supportive evidence to the WPNI results. RFDH is a processing technology that could change a few functional properties of NDM in this study, which makes it a promising method that may be further exploited for various food applications, such as emulsifiers, foaming agents, etc. However, potential negative impacts, such as color change caused by Maillard reaction, loss of WPNI in LH-NDM, cannot be neglected.

Thesis (M.M. (ICT Policy and Regulation))--University of the Witwatersrand, Faculty of Commerce, Law and Management, Graduate School of Public and Development Management, 2013. / Radio frequency spectrum, a scarce national strategic asset, has not enjoyed the necessary attention and protection it deserves. Spectrum has been managed by the same approach over the last two decades and it is only recently that attention has been given to it due to the pressure of increased competition and technological advancements. The purpose of this study was to explore the policy and regulatory approaches to the management of radio frequency spectrum prevalent in South Africa today. Internationally there is a shift from the traditional command and control spectrum management approaches to more market-based mechanisms, such as auctions and spectrum trading. The South African approach has been marked by delays in the usage of spectrum as a result of the current institutional arrangements where there is an apparent overlap between the policy and regulatory function. The study concludes that the delays could be circumvented by separating the spectrum allocation and assignment into policy and regulatory functions respectively. Efficient spectrum management policy and regulation is important for the next stage of electronic communications revolution because of the advances in the technology such as broadband and agile radio.

Research report submitted to the School of Economic and Business Sciences, Faculty of Commerce, Law and Management, University of the Witwatersrand, 2013. / In recent years, Radio Frequency Identification (RFID) Technology has transformed from being unknown to mainstream applications that help facilitate the managing of manufactured goods and materials. Its information storage capacity as well as its ability to transfer information through contactless means without line-of-sight translates to significant advantages to deliver various benefits for retailers and their clients in the retail settings. However, up until now RFID technology has gained very little momentum and the status of adoption particularly of retail organisations in South Africa is unknown. To fill this research gap, an exploratory study that draws on the Technology-Organisation-Environment (TOE) framework was employed to provide a deeper understanding of South African retailers’ perceptions of RFID adoption. Five interviewees representing their respective organisations participated in the study. The findings suggested that the adoption level is very low and only one organisation from the sample used had done a pilot project. The results also indicated that cost, standardisation and government support influenced the adoption of the technology. Complexity and technology competence were not considered to have any influence in the adoption of the technology. Competitive pressure was not deemed influential if the technology was not embedded in the whole supply chain, a somewhat surprising result. There were no anticipated impacts on the employees if this technology was implemented. Methodological and practical implications are also discussed.

Radio frequency (RF) techniques have the potential to provide blood glucose readings through sensing the glucose dependent change in dielectric properties of the biological tissue. Such technique can enable much desired non-invasive and continuous monitoring of blood glucose level. In this work, we present realistic glucose dependence of dielectric properties as well as basic understanding of resonator behaviour while radiating towards the lossy biological tissue. To investigate the potential of RF techniques, two resonators, operating at microwave frequencies when placed radiating towards the biological tissue, are designed and fabricated. The spiral resonator is tested with liquid and semi-solid phantoms containing different amounts of sugar. An analytical formulation to retrieve the dielectric properties of the biological tissues is improved. In order to perform realistic tests, novel tissue mimicking materials for an extremely wide frequency range are proposed. Glucose dependance of the blood mimicking material dielectric properties are further investigated by adding realistic glucose amounts to the blood mimicking material and dielectric spectroscopy is performed. Next, a single pole Cole-Cole model is fitted to the median of the dielectric property measurements. In addition, a patch resonator is simulated with four-layered digital phantom and tested with the four-layered physical tissue mimicking phantom. Finally, a double parameter measurement platform is constructed by combining the patch resonator and a commercial force sensor to perform controlled experiments with humans. Also, the force dependant response of the patch resonator is quantified. Soda tests is performed on five subjects with the platform, all subjects were asked to apply the same level of force. Spiral resonator is also applied to examine the glucose changes of two human subjects during the soda test. The results suggests that, although the glucose-dependance of the dielectric properties is relatively small, the input impedance of a microwave resonator is still sensitive to such small alterations.

Magnetic Resonance Imaging (MRI) is a non-invasive procedure used in the medical community as a powerful way of creating images of the human anatomy. MRI is preferred over other examination techniques such as X-ray computed tomography (CT) because of its excellent soft tissue discrimination as well as the absence of ionizing radiation. Currently most clinical MRI systems use the single radio frequency coil imaging. However over past several years research has increasingly focused on the concept of using arrays of mutually decoupled surface coils. These surface coil arrays can simultaneously acquire multiple images, resulting in an increase in the field of view. This thesis pursues the design and construction of a high impedance preamplifier with the goal of investigating the decoupling of a surface coil array in a 4.7T magnetic resonance system.