Research Articles (Electrical and Electronic Engineering)

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The accuracy of electromagnetic equivalence theorem models of microstrip patch antennas
(Stellenbosch : Stellenbosch University, 1991) Theron, Isak Petrus; Cloete, J. H.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
ENGLISH ABSTRACT: In this report the application of an equivalence theorem model to a patch in a microstrip medium is considered. The problem originated with the application of the Leontovich boundary condition to an equivalent surface current in a moment method technique used by Mosig and Gardiol [1, 2] for the analysis of microstrip antennas and circuits. Their formulation consists of an equivalent electric source Js which satisfies a boundary condition Et = Zs Js. They thus apply a physical boundary condition to an equivalent source, completely ignoring the magnetic sources in the equivalent model. This approximation is analyzed to assess its accuracy. The Leontovich boundary condition is examined and it is found to be applicable to the physical or true current on a patch. The full equivalence model is then developed and compared to the Leontovich model to find the relationship between the true current flowing on the conductor and the equivalent current. It is found that, although the equivalent electric current is equal to the true current on each of the two sides of the patch, an equivalent magnetic current also exists. The contribution of this current to the total field is then examined for a patch on a single dielectric layer above a ground plane. This also gives an idea of what to expect in the case of a multi layered medium. To do the comparison the fields (also called Green's functions) radiated by an electric and a magnetic dipole on the surface of the dielectric are determined from the boundary conditions. This is done in the spectral domain and the spatial fields are then found by an inverse Fourier transform. The spectral functions are too complicated to have closed form solutions in the near field region and thus the integrals are solved numerically using the Hankel transform. The dipoles are scaled according to a relation between the electric and magnetic currents resulting from the application of the equivalence theorem. It is found that, for frequencies up to 30 GHz, the contribution of the magnetic current can be ignored over the whole region p ≠ 0 with an error of less than 0.5%. (This is for a pure copper patch on a substrate with Er = 2.5 and thickness of 0.04 λ.) At the point p = 0 the magnetic current causes a discontinuity in the electric field normal to the dipole axis and tangential to the surface of the dielectric. In the last chapter of this report a theory is developed assuming that the tangential electric fields on top of the patch are negligible in comparison to those on the bottom. The magnetic current then causes a jump in the field to comply with the condition of zero fields in the conductor. This is also the value of the tangential fields directly above the conductor. The boundary condition is then applied on the dielectric side of the patch while ignoring the magnetic sources completely. The value of the error in ignoring the magnetic sources is thus quantified enabling the accuracy of the approximations to be analyzed for any particular application.
Afrikaans and Dutch as closely-related languages : a comparison to West Germanic languages and Dutch dialects
(University of Stellenbosch, Department of General Linguistics, 2015) Heeringa, Wilbert; De Wet, Febe; Van Huyssteen, Gerhard B.
Following Den Besten’s (2009) desiderata for historical linguistics of Afrikaans, this article aims to contribute some modern evidence to the debate regarding the founding dialects of Afrikaans. From an applied perspective (i.e. human language technology), we aim to determine which West Germanic language(s) and/or dialect(s) would be best suited for the purposes of recycling speech resources for the benefit of developing speech technologies for Afrikaans. Being recognised as a West Germanic language, Afrikaans is first compared to Standard Dutch, Standard Frisian and Standard German. Pronunciation distances are measured by means of Levenshtein distances. Afrikaans is found to be closest to Standard Dutch. Secondly, Afrikaans is compared to 361 Dutch dialectal varieties in the Netherlands and North-Belgium, using material from the Reeks Nederlandse Dialectatlassen, a series of dialect atlases compiled by Blancquaert and Pée in the period 1925-1982 which cover the Dutch dialect area. Afrikaans is found to be closest to the South-Holland dialectal variety of Zoetermeer; this largely agrees with the findings of Kloeke (1950). No speech resources are available for Zoetermeer, but such resources are available for Standard Dutch. Although the dialect of Zoetermeer is significantly closer to Afrikaans than Standard Dutch is, Standard Dutch speech resources might be a good substitute.
Analysis of template-based detection algorithms for inshore Bryde’s whale short pulse calls
(Institute of Electrical and Electronics Engineers, 2020) Ogundile, Olayinka O.; Versfeld, Daniel J. J.
Marine mammals use sound for communication and echolocation within their ecosystems. The detection of these sounds is an important aspect of signal processing, such that we can estimate the spatial position and direction of arrival of these mammals, and have an understanding of their ecology. Passive acoustic monitoring (PAM) is widely used to understand marine mammal movement and vocal repertoire. In PAM, datasets are accumulated over days, months or years. Thus, it is impracticable to manually analyse the datasets because it is very large. This motivated the development of automated sound detection techniques for marine mammals, which most often varies depending on the vocal duration, frequency range and call type. In this paper, continuous recordings of Bryde’s whale ( Balaenoptera edeni edeni ) short pulse calls (< 3.1s long) were collected on a weekly basis from December 2018 to April 2019 on sighting of the individual in a single site in the endmost South-West of South Africa. The sound, previously not documented off South Africa, was observed on visual confirmation of the presence of inshore Brydes’s whale. In addition, the paper develops and analyses two automated template-based detection algorithms for this short pulse call, employing dynamic time warping (DTW) and linear predictive coding (LPC) techniques. These proposed template-based detectors are novel, as they have not being previously used in Bryde’s whale sound detection in the literature. When applied to the continuous recordings of the short pulse calls, the DTW-based and LPC-based detection algorithms obtained a sensitivity of 96.04% and 97.14% respectively for high signal-to-noise ratio (about 10dB above the ambient sound). Otherwise, for low SNR, the DTW-based and LPC-based detection algorithms obtained a sensitivity of 94.98% and 96.00% respectively. These detection algorithms exhibit low computational time complexity and can be modified to analyse the movement of obscure but vocal marine species instead of manual identification.
Analytical modeling of surface-mounted and consequent-pole linear vernier hybrid machines
(Institute of Electrical and Electronics Engineers, 2021) Botha, Christoff D.; Kamper, Maarten J.; Wang, Rong-Jie; Chama, Abdoulkadri
ENGLISH ABSTRACT: This paper presents an analytical method for modeling the no-load air gap ux density of a surface-mounted and a consequent-pole linear Vernier hybrid machine (LVHM). The approach is based on simple magneto-motive force (MMF) and permeance functions to account for the doubly-slotted air gap of the LVHM. These models are used to determine the ux linkage, induced electromotive force (EMF) and average thrust force of each machine. The accuracy of the two analytical models is validated by comparison with 2D nite element method (FEM) solutions. Based on the analytical models, it is found that the working harmonics of both surface-mounted and consequent-pole LVHMs are essentially the same. However, the magnitudes of these working harmonics in the consequent-pole LVHM are invariably greater than those of surface-mounted LVHM. Further, using the analytical model, the contribution to the thrust force of the machine by each individual working harmonic can be shown clearly, and is used to explain why the consequent-pole LVHM has improved performance despite using only 50% of the permanent magnet (PM) material compared to the surface-mounted LVHM.
Animal-borne behaviour classification for sheep (Dohne Merino) and rhinoceros (Ceratotherium simum and diceros bicornis)
(BioMed Central, 2017-11-21) Le Roux, Solomon Petrus; Marias, Jacques; Wolhuter, Riaan; Niesler, Thomas
Background: The ability to study animal behaviour is important in many fields of science, including biology, behavioural ecology and conservation. Behavioural information is usually obtained by attaching an electronic tag to the animal and later retrieving it to download the measured data. We present an animal-borne behaviour classification system, which captures and automatically classifies three-dimensional accelerometer data in real time. All computations occur on specially designed biotelemetry tags while attached to the animal. This allows the probable behaviour to be transmitted continuously, thereby providing an enhanced level of detail and immediacy. Results: The performance of the animal-borne automatic behaviour classification system is presented for sheep and rhinoceros. For sheep, a classification accuracy of 82.40% is achieved among five behavioural classes (standing, walking, grazing, running and lying down). For rhinoceros, an accuracy of 96.10% is achieved among three behavioural classes (standing, walking and lying down). The estimated behaviour was established approximately every 5.3 s for sheep and 6.5 s for rhinoceros. Conclusions: We demonstrate that accurate on-animal real-time behaviour classification is possible by successful design, implementation and deployed on sheep and rhinoceros. Since the bandwidth required to transmit the behaviour class is lower than that which would be required to transmit the accelerometer measurements themselves, this system is better suited to low-power and error-prone data communication channels that may be expected in the animals habitat.
Biosensors for the detection of Escherichia coli
(South African Water Research Commission, 2017-10) Maas, M. B.; Perold, W. J.; Dicks, L. M. T.
ENGLISH ABSTRACT: The supply of safe potable water, free from pathogens and chemicals, requires routine analyses and the application of several diagnostic techniques. Apart from being expensive, many of the detection methods require trained personnel and are often time-consuming. With drastic climate changes, severe droughts, increases in population and pollution of natural water systems, the need to develop ultrasensitive, low-cost and hand-held, point-of-use detection kits to monitor water quality is critical. Although Escherichia coli is still considered the best indicator of water quality, cell numbers may be below detection limits, or the cells may be non-culturable and thus only detected by DNA amplification. A number of different biosensors have been developed to detect viable, dead or non-culturable microbial cells and chemicals in water. This review discusses the differences in these biosensors and evaluates the application of microfluidics in the design of ultra-sensitive nano-biosensors.
Canary in the coliform mine : exploring the industrial application limits of a microbial respiration alarm system
(Public Library of Science, 2021-03-04) Stone, Wendy; Louw, Tobi M.; Booysen, Marthinus J.; Wolfaardt, Gideon M.; Zhang, Dawei
Fundamental ecological principles of ecosystem-level respiration are extensively applied in greenhouse gas and elemental cycle studies. A laboratory system termed CEMS (Carbon Dioxide Evolution Measurement System), developed to explore microbial biofilm growth and metabolic responses, was evaluated as an early-warning system for microbial disturbances in industrial settings: in (a) potable water system contamination, and (b) bioreactor inhibition. Respiration was detected as CO₂ production, rather than O₂ consumption, including aerobic and anaerobic metabolism. Design, thresholds, and benefits of the remote CO₂ monitoring technology were described. Headspace CO₂ correlated with contamination levels, as well as chemical (R² > 0.83–0.96) and microbiological water quality indicators (R² > 0.78–0.88). Detection thresholds were limiting factors in monitoring drinking water to national and inter- national standards (0 CFU/100 mL fecal coliforms) in both open- (>1500 CFU/mL) and closed-loop CO₂ measuring regimes (>100 CFU/100 mL). However, closed-loop detection thresholds allow for the detection of significant contamination events, and monitoring less stringent systems such as irrigation water (<100 CFU/mL). Whole-system respiration was effectively harnessed as an early-warning system in bioreactor performance monitoring. Models were used to deconvolute biological CO₂ fluctuations from chemical CO₂ dynamics, to optimize this real-time, sustainable, low-waste technology, facilitating timeous responses to biological disturbances in bioreactors.
Capacitive seat sensors for multiple occupancy detection using a low-cost setup
(IEEE -- Institute of Electrical and Electronics Engineers, 2013-02) Zeeman, Adriaan Siebrits; Booysen, Marthinus J.; Ruggeri, Giuseppe; Lagana, Bruno
The Minibus public transportation sector and road safety remains a significant challenge in Africa. We propose a low cost system to monitor the taxi industry and encourage safe driving. A low cost capacitive proximity sensor for seat occupancy detection based on the loading mode capacitive sensing technique is designed. The capacitive sensor uses a single electrode to detect an occupant. We use ZigBee modules for a dynamic wireless system integration where sensors can be added or removed without modifications. A mathematical model of the capacitive sensor is developed and we determine the capacitance on the sensor’s electrode. The occupied capacitance is double the unoccupied capacitance. Our results show that the proposed capacitive sensor can distinguish clearly between an unoccupied and occupied seat.
Classification learning of latent bruise damage to apples using shortwave infrared hyperspectral imaging
(MDPI, 2021-07-22) Nturambirwe, Jean Frederic Isingizwe; Perold, Willem Jacobus; Opara, Umezuruike Linus
Bruise damage is a very commonly occurring defect in apple fruit which facilitates disease occurrence and spread, leads to fruit deterioration and can greatly contribute to postharvest loss. The detection of bruises at their earliest stage of development can be advantageous for screening purposes. An experiment to induce soft bruises in Golden Delicious apples was conducted by applying impact energy at different levels, which allowed to investigate the detectability of bruises at their latent stage. The existence of bruises that were rather invisible to the naked eye and to a digital camera was proven by reconstruction of hyperspectral images of bruised apples, based on effective wavelengths and data dimensionality reduced hyperspectrograms. Machine learning classifiers, namely ensemble subspace discriminant (ESD), k-nearest neighbors (KNN), support vector machine (SVM) and linear discriminant analysis (LDA) were used to build models for detecting bruises at their latent stage, to study the influence of time after bruise occurrence on detection performance and to model quantitative aspects of bruises (severity), spanning from latent to visible bruises. Over all classifiers, detection models had a higher performance than quantitative ones. Given its highest speed in prediction and high classification performance, SVM was rated most recommendable for detection tasks. However, ESD models had the highest classification accuracy in quantitative (>85%) models and were found to be relatively better suited for such a multiple category classification problem than the rest.
Classified atmospheric states as operating scenarios in probabilistic power flow analysis for networks with high levels of wind power
(Elsevier, 2021) Dalton, Amaris; Bekker, Bernard; Koivisto, Matti Juhani
ENGLISH ABSTRACT: Large-scale atmospheric circulation patterns are the primary drivers of wind power variability on power networks at timescales of hours to days. This paper proposes a methodology that allows power system operators and planners working on networks with high levels of wind generation, to conduct probabilistic power flow (PPF) analyses by defining network ‘operating scenarios’ – i.e. the probability density functions of generators, and correlations between generators representative of a future system state – based on concurrent classified atmospheric states. The most significant contribution made by this paper is in illustrating how PPF operating scenarios derived from clustering historic generation data as a function of a set of classified atmospheric states reduces simulation uncertainty within a PPF analysis. It is anticipated that the proposed methodology may provide network planners with more appropriate operating scenarios for PPF analyses when compared to an unclustered base state, and may assist network operators in converting wind power point-forecasts into probabilistic forecasts whereby the spatial correlations between generators are incorporated. This methodology is illustrated through a case study considering 11 geographically disperse wind generators on the South African transmission network.
Clustering acoustic segments using multi- stage agglomerative hierarchical clustering
(Public Library of Science, 2015) Lerato, Lerato; Niesler, Thomas
Agglomerative hierarchical clustering becomes infeasible when applied to large datasets due to its O(N2) storage requirements. We present a multi-stage agglomerative hierarchical clustering (MAHC) approach aimed at large datasets of speech segments. The algorithm is based on an iterative divide-and-conquer strategy. The data is first split into independent subsets, each of which is clustered separately. Thus reduces the storage required for sequential implementations, and allows concurrent computation on parallel computing hardware. The resultant clusters are merged and subsequently re-divided into subsets, which are passed to the following iteration. We show that MAHC can match and even surpass the performance of the exact implementation when applied to datasets of speech segments.
Combining speed and acceleration to detect reckless driving in the informal public transport industry
(IEEE -- Institute of Electrical and Electronics Engineers, 2013-10) Zeeman, A. S.; Booysen, Marthinus J.
The informal transport industry in Sub-Saharan Africa is notoriously dangerous, leading to many fatalities annually. This paper presents an innovative way of monitoring driver behaviour, in real-time, by taking into account road design standards, vehicle dynamics, and passenger comfort. Two models are presented that each combines acceleration and speed data into an erratic driving detection algorithm. The first model is developed though the evaluation of empirical results taken from trips in a minibus taxi, and subjectively gauging recklessness from a passenger’s perspective. The second model presents a novel use of commonly used civil engineering principles, used in road design. Evaluation of the models, using actual minibus data, demonstrates that both successfully detect reckless driving, but the second model proves to be simpler and less processor intensive.
Compact conical line power combiner design using circuit models
(Institute of Electrical and Electronics Engineers, 2014) Beyers, Ryno D.; De Villiers, Dirk I. L.
ENGLISH ABSTRACT: A simple equivalent circuit model with empirical equations describing the peripheral feeding ports of conical line power combiners is presented. The model allows the entire structure to be designed using transverse electromagnetic circuit theory without the need for any full-wave simulations. A summary of the model extraction process is given and the accuracy of the proposed model is confirmed by favorable comparisons with full-wave simulations. The circuit based design method is used to design a compact conical line combiner showing measured performance similar to the current state of the art combiners in this technology, while being significantly smaller.
Compact high-power broadband absorptive filters using slotted waveguide harmonic pads
(The Institution of Engineering and Technology - IET, 2014-06) Stander, Tinus; Meyer, Petrie; Van der Walt, Pieter Willem; Electrical and Electronic Engineering
A compact high-power broadband absorptive filter is designed by cascading a slotted waveguide harmonic pad with a wide stop-band reflective filter. Absorption is achieved by coupling a surface current standing wave to absorptive external auxiliary waveguides through a cascade of transversal broad-wall slots in rectangular waveguide
A comparative evaluation of the impact of average speed enforcement (ASE) on passenger and minibus taxi vehicle drivers on the R61 in South Africa
(South African Institution of Civil Engineering, 2016) Akoku Ebot Eno Akpa, Nelson; Booysen, M. J.; Sinclair, M.
Average speed enforcement (ASE) is an emergent alternative to instantaneous speed limit enforcement to improve road safety, and is used to enforce an average speed limit over a road segment. This paper presents a study on the response of passenger vehicles and minibus taxis to ASE on the R61 in South Africa. A spatio-temporal quantitative study of speed compliance was conducted, where metrics such as speed variability, average speed and 85th percentile speed measured prior to, and during enforcement, were analysed for two prominent modes of transport - passenger vehicles and minibus taxis. These measurements were taken on the enforcement route and on control routes adjacent to and further away from the enforcement route. A qualitative study was also conducted to evaluate the relationship between speed compliance and driver understanding of the system. The impact of the system on crash risk and injury severity was also examined before and during enforcement. For passenger vehicles, results showed that the introduction of ASE was followed by a reduction in mean speed on the enforcement route and adjacent control route. For minibus taxis, it was found that ASE appears to have little influence on improving speed compliance, which is likely associated with a lack of driver understanding of how the system operates.
A computationally inexpensive energy model for horizontal electric water heaters with scheduling
(2016-03) Nel, P. J. C.; Booysen, M. J.; Van der Merwe, A. B.
ENGLISH ABSTRACT: Electric water heaters (EWHs) remain one of the main contributors to energy consumption in countries where they are used. EWH models serve as a step towards achieving optimised control, and can also be used to inform users of expected savings due to changes, if the model is energy-based. Various models have been proposed, but none of them include more than half of the six key features that the model presented in this paper supports: horizontal orientation; schedule control; low computational complexity; validation of the model; multinodal stratification; and multinodal standing losses. The presented model is validated against six datasets: four comprising 900 hours with multiple water usage events; and two with only standing losses. The results show that the model estimates energy consumption over ten days including usage with an error of less than 2% and 5% for schedule control and thermostat control respectively. The simulation model is simple enough to execute ten days of simulation in less than 100 milliseconds on a standard desktop machine, 150 times faster than a prominent model from literature, making it also suitable for large scale simulations or for use on mobile devices.
Constant radiation characteristics for log-periodic dipole array antennas
(Institute of Electrical and Electronics Engineers, 2014) Lehmensiek, Robert; De Villiers, Dirk I. L.
Given the correct terminal voltages on each element of a log-periodic dipole array constant radiation characteristics can be achieved for an omni-directional radiation pattern. In this communication it is shown that this can only be achieved through optimization, correcting a previously reported oversimplification which resulted in an analytical approach being tractable. This oversimplification assumed that vanishing terminal currents on a dipole’s terminal/feed element implies no radiation from that dipole. This is clearly non-physical because, zeroing the terminal current on a dipole’s feed element is the same as disconnecting its two arms, while having no radiation from that dipole implies that in effect both arms be entirely removed. We show that the effect of currents induced in the disconnected arms of a dipole cannot in general be ignored.
Cross-coupling inductance parameter estimation for more accurate performance evaluation of wound-field flux modulation machines
(MDPI, 2020-10-22) Mabhula, Mkhululi; Akuru, Udochukwu B.; Kamper, Maarten J.
ENGLISH ABSTRACT: In this paper, a proposed numerical frozen permeability modeling procedure is fully derived to accurately estimate the parameters of two variants of wound-field flux modulation machines (WF-FMMs) namely: wound-field flux switching machine (WF-FSM) and DC-excited vernier reluctance machine (DC-VRM). During the procedure, the contribution of saturation to the variation of the machine parameters is investigated. The parameter variation effects on the machine performance is also investigated. It is shown that analysis of WF-FMMs is better understood by using the proposed procedure which computes accurately the machine parameters.
Detecting potholes using simple image processing techniques and real-world footage
Nienaber, S.; Booysen, Marthinus J.; Kroon, R. S.
Potholes are a nuisance, especially in the developing world, and can often result in vehicle damage or physical harm to the vehicle occupants. Drivers can be warned to take evasive action if potholes are detected in real-time. Moreover, their location can be logged and shared to aid other drivers and road maintenance agencies. This paper proposes a vehicle-based computer vision approach to identify potholes using a window-mounted camera. Existing literature on pothole detection uses either theoretically constructed pothole models or footage taken from advantageous vantage points at low speed, rather than footage taken from within a vehicle at speed. A distinguishing feature of the work presented in this paper is that a thorough exercise was performed to create an image library of actual and representative potholes under different conditions, and results are obtained using a part of this library. A model of potholes is constructed using the image library, which is used in an algorithmic approach that combines a road colour model with simple image processing techniques such as a Canny filter and contour detection. Using this approach, it was possible to detect potholes with a precision of 81.8% and recall of 74.4.%.
Detection of reckless driving in the Sub-Saharan informal public transportation system using acceleration-sensing telematics
(IEEE -- Institute of Electrical and Electronics Engineers, 2013-07) Schietekat, Justin M.; Booysen, Marthinus J.
Many lives are lost annually in Sub-Saharan Africa’s unique and vibrant informal public transportation system due to accidents caused by reckless driving, fatigue, and illegal overloading. Fleet management has been used extensively to determine the location of mobile assets in the event of theft, or as part of operational management. One of the main objectives of the work presented in this paper, is to build on existing fleet management systems to improve safety and drastically reduce road accidents and the unnecessary loss of lives. Through a thorough literature survey it was concluded that existing work on vehicle tracking and reporting systems, do not use accelerometers to monitor or detect reckless driving, despite the obvious advantages. Similar to other tracking devices, this project uses global positioning to determine position and velocity, but this project also incorporates the use of a 3-axis accelerometer augmented by a theoretical behavioral model to detect and report reckless behavior to a central online server. The accelerometer results show a clear difference between safe and reckless driving.

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