Thesis (PhD (Electric and Electronic Engineering))--University of Stellenbosch, 2009. / Keywords: position sensorless control, torque control, synchronous machines The work in this thesis deals with energy e cient torque control and rotor position estimation in the full speed range, for a family of synchronous machines that should be used more often in the near future. This family consists of the permanent magnet synchronous machine (PMSM), the reluctance synchronous machine (RSM), the interior-PMSM and the PMassisted- RSM. By designing and controlling these synchronous machines correctly, better performance and higher energy e ciency can be expected compared to the performance and e ciency of an industry standard induction machine. However, applications are limited to variable speed drives (VSD) in a certain power range, e.g. below 100kW. With the growing concern and necessity of a better utilization of energy, it is becoming standard to use electronically controlled power converters between the electricity grid and electrical machines. Therefore, there is a very large scope for the implementation of this synchronous machine technology. For traction applications like electrical vehicles, the optimally controlled synchronous machine technology has a very strong position. Very compact and robust synchronous machines with a very high power density can be designed that may out-perform the induction machine by far. However, one major requirement for most applications is position sensorless control, i.e. rotor position estimation in the whole speed range. To achieve energy e cient torque control, maximum torque per Ampere (MTPA) control should be implemented. It is possible to achieve MTPA control at low speed, but above the rated speed of the machine, eld weakening needs to be performed. The question is how to implement MTPA and e ective eld weakening for any value of speed and DC bus voltage and for any machine within this family of synchronous machines. In this thesis a method is explained to achieve this goal using results from nite element (FE) analysis directly. The scheme may be implemented within a very short period of time. The contribution of this thesis is a general understanding of the problems at hand, with an in-depth view into the mathematical representation of synchronous machines, a generic method of energy e cient torque control and a thorough study of rotor position and speed estimation methods.

Thesis (PhD (Electric and Electronic Engineering))--University of Stellenbosch, 2005. / A tunable X-band PIN diode switch, implemented in evanescent mode waveguide, is presented. To allow in-situ tuning of resonances after construction, a novel PIN diode mounting structure is proposed and verified, offering substantial advantages in assembly costs. Accurate and time-effective modelling of filter and limiter states of the proposed switch is possible, using an evanescent mode PIN diode and mount model. The model is developed by optimizing an AWR Microwave Office model of a first order switch prototype with embedded PIN diode, to simultaneously fit filter and limiter measurements of four first order prototypes. The model is then used in the design of a third order switch prototype, achieving isolation of 62 dB over a 8.5 to 10.5 GHz bandwidth in the limiting state, as well as reflection of 15.73 dB and insertion loss of 1.23±0.155 dB in the filtering state over the same bandwidth.

Thesis (PhD)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: The engineering of dependable real-time systems for mission critical applications is a resource intensive and error prone process. Achieving dependability requires a general consensus on the correctness of a system with regard to its intended function. For a consensus to be achieved, the properties of the system must be well understood which, in turn, requires consensus on a rigorously defined computational architecture. There is currently no single agreed upon computational architecture at the application level which can serve as a common denominator for the design and implementation of real-time systems. It is the thesis of this dissertation that a rigorous computational architecture, applicable from design to implementation, enables engineers to better understand software for real-time systems. To substantiate this claim, the real-time data flow architecture RDF with its notation allowing the description of complete systems from design to implementation will be explored. Four distinct research areas for improving the engineering process of real-time systems are dealt with in the dissertation: 1) the development of an architecture for real-time systems being suitable for design and implementation in software and hardware, 2) the consolidation of a number of graphical languages into a graphical notation for functional specification, design and construction of real-time systems, 3) the development of a simple processor architecture for the execution of real-time applications, and 4) and the evaluation of the architecture in the framework of a microsatellite case study. In particular, the following original contributions are made: 1) the firing semantics of data flow systems are expanded to include disjunctive firing semantics in a novel way in addition to the classical conjunctive firing semantics, 2) the inherent real-time data flow property, Le. that a receiving task must be ready to receive the next incoming message when it is sent, is extended to the synchronous data flow model, 3) a notation for describing all properties of real-time systems is defined 'with the real-time data flow language RDF as base language, 4) two hardware processor architectures are introduced that offer one-to-one correspondence between design and implementation and, thus, reduce the semantic gap between design language and program execution, and 5) the class of systems that can be modelled with data flow architectures is shown to include control systems and data flow systems. The language set and processor architecture were applied to certain aspects of the SUNSAT microsatellite project. / AFRIKAANSE OPSOMMING:Die skep van betroubare intydsestelsels vir missie kritiese toepassings is 'n proses wat baie hulpbronne verg en waarin maklik 'n fout gemaak kan word. Om 'n betroubare stelsel te skep vereis 'n konsensus oor die korrektheid van 'n stelsel, wat bereik word wanneer die eienskappe van die stelsel goed verstaan word. Dit vereis op sy beurt weer 'n konsensus oor 'n goed gedefinieerde berekenings argitektuur. Daar is tans geen enkel ooreengekome berekenings argitektuur op die toepassingsvlak wat kan dien as 'n gemeenskaplike voertuig vir die ontwerp en implementering van intydsestelsels nie. Dit is die hipotese van die proefskrif dat 'n berekenings argitektuur met 'n streng basis, wat toegepas kan word vanaf ontwerp tot implementering, ingenieurs in staat sal stel om intydsestelsels beter te kan verstaan. Die hipotese word ondersoek deur die intydse datavloei argitektuur, RDF, te gebruik om 'n stelsel vanaf ontwerp tot implementering te beskryf. Daar is vier spesifieke navorsings areas ter verbetering van die ingenieurswese proses vir intydsestelsels, wat in die proefskrif aangespreek word: 1) die ontwikkelling van 'n argitektuur vir intydsestelsels wat geskik is vir die ontwerp en implementering in programmatuur en apparatuur, 2) . die konsolidering van 'n aantal grafiese tale in 'n grafiese notasie vir die funksionele spesifikasie, ontwerp en implementering van intydsestelsels, 3) die ontwikkelling van 'n eenvoudige verwerker argitektuur vir die uitvoering van intydse toepassings en 4) die evaluering van die argitektuur in die konteks van 'n mikrosatelliet gevallestudie. Die volgende oorspronklike bydraes word gemaak: 1) die sneller voorwaardes vir datavloei stelsels word uitgebrei met 'n disjunktiewe patroon saam met die tradisionele konjunktiewe patroon, 2) die inherente intydse datavloei eienskap, n.l. dat'n taak wat boodskappe ontvang, alle verwerking wat met 'n vorige boodskap gepaard gegaan het moet afhandel, voordat 'n volgende boodskap ontvang word, word uitgebrei na die sinkrone datavloei model, 3) 'n notasie om al die eienskappe van 'n intydsestelsel te beskryf word gedefinieer met RDF as die basis taal, 4) twee apparatuur verwerker argitekture word beskryf wat 'n een-tot-een kartering aanbied tussen die ontwerp en die implementering, en wat gevolglik die semantiese gaping verklein tussen ontwerpstaal en die uitvoeringsargitektuur en 5) die klasse van stelsels wat gemodelleer kan word met RDF sluit beheerstelsels en datavloeistelsels in. Die grafiese notasie en verwerker argitektuur was toegepas op sekere aspekte van die SUNSAT mikrosatelliet projek.

Thesis (PhD (Electronic Engineering))--University of Stellenbosch, 2010. / Contains bibliography and index. / ENGLISH ABSTRACT: Super-resolution imaging is the process whereby several low-resolution photographs of an object are combined to form a single high-resolution estimation. We investigate each component of this process: image acquisition, registration and reconstruction. A new feature detector, based on the discrete pulse transform, is developed. We show how to implement and store the transform efficiently, and how to match the features using a statistical comparison that improves upon correlation under mild geometric transformation. To simplify reconstruction, the imaging model is linearised, whereafter a polygon-based interpolation operator is introduced to model the underlying camera sensor. Finally, a large, sparse, over-determined system of linear equations is solved, using regularisation. The software developed to perform these computations is made available under an open source license, and may be used to verify the results. / AFRIKAANSE OPSOMMING: In super-resolusie beeldvorming word verskeie lae-resolusie foto's van 'n onderwerp gekombineer in 'n enkele, hoë-resolusie afskatting. Ons ondersoek elke stap van hierdie proses: beeldvorming, -belyning en hoë-resolusie samestelling. 'n Nuwe metode wat staatmaak op die diskrete pulstransform word ontwikkel om belangrike beeldkenmerke te vind. Ons wys hoe om die transform e ektief te bereken en hoe om resultate kompak te stoor. Die kenmerke word vergelyk deur middel van 'n statistiese model wat bestand is teen klein lineêre beeldvervormings. Met die oog op 'n vereenvoudigde samestellingsberekening word die beeldvormingsmodel gelineariseer. In die nuwe model word die kamerasensor gemodelleer met behulp van veelhoek-interpolasie. Uiteindelik word 'n groot, yl, oorbepaalde stelsel lineêre vergelykings opgelos met behulp van regularisering. Die sagteware wat vir hierdie berekeninge ontwikkel is, is beskikbaar onderhewig aan 'n oopbron-lisensie en kan gebruik word om die gegewe resultate te veri eer.

Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The use of the quadrature mixing topology has been severely limited in the past due to its sensitivity towards mismatches between its signal paths. In recent years, researchers have suggested that digital techniques can be used to compensate for the impairments in the analogue quadrature mixing front-end. Most authors, however, focus on the modelling and compensation of frequency-independent imbalances, reasoning that this approach is sufficient for narrow band signal operation. This common assumption is, however, becoming increasing less applicable as the use of wider bandwidth signals and multi-channel systems becomes more prevalent. In this dissertation, baseband equivalent distortion models are derived, which model frequency-independent, as well as frequency-dependent contributions towards the imbalances of the front-end. Both lowpass and bandpass imbalances are modelled, which extends current modelling approaches found in literature. The resulting baseband models are shown to be capable of explaining the imbalance characteristics observed in practical quadrature mixing front ends, where existing models fail to do so. The developed imbalance models is then used to develop novel frequency-dependent imbalance extraction and compensation techniques, which directly extract the exact quadrature imbalances of the front end, using simple test tones. The imbalance extraction and compensation procedures are implemented in the digital baseband domain of the transceiver and do not require high computational complexity. The performance of these techniques are subsequently verified through simulations and a practical hardware implementation, yielding significant improvement in the image rejection capabilities of the quadrature mixing transceiver. Finally, a novel, blind imbalance compensation technique is developed. This technique is aimed at extracting frequency-independent I/Q imbalances in systems employing digital modulation schemes. No test tones are employed and the imbalances of the modulator and demodulator are extracted from the second order statistics of the received signal. Simulations are presented to investigate the performance of these techniques under various operating conditions. / AFRIKAANSE OPSOMMING: Die gebruik van die haaksfasige mengtopologie word geweldig beperk deur die sensitiwiteit vir wanbalanse wat mag bestaan tussen die twee analoog seinpaaie. In die afgelope paar jaar het navorsers digitale metodes begin voorstel om te kompenseer vir hierdie wanbalanse in die analooggebied. Meeste navorsers fokus egter op frekwensie-onafhanklike wanbalanse. Hulle staaf hierdie aanslag deur te redineer dat dit ’n aanvaarbare aaname is vir ’n nouband stelsel. Hierdie algemene aanvaarding is egter besig om minder akkuraat te raak, namate wyeband- en multikanaalstelses aan die orde van die dag raak. In hierdie tesis word basisband-ekwiwalente wanbelansmodelle afgelei wat poog om die effek van frekwensie-afhanklike en -onafhanklike wanbalanse akkuraat voor te stel. Beide laagdeurlaat- en banddeurlaatwanbalanse word gemodelleer, wat ‘n uitbreiding is op die huididge modellerings benaderings wat in literatuur gevind word. Dit word aangetoon dat die modelle van hierdie tesis daarin slaag om die karakteristieke van ’n werklike haaksfasige mengstelsel akkuraat te vervat – iets waarin huidige modelle in die literatuur nie slaag nie. Die basisband-ekwiwalente modelle word dan gebruik om nuwe digitale kompensasie metodes te ontwikkel, wat daarin slaag om die frekwensie-afhanklike wanbalanse van die haaksfasige mengstelsel af te skat, en daarvoor te kompenseer in die digitale deel van die stelsel. Hierdie kompensasiemetodes gebruik eenvoudige toetsseine om die wanbalanse af te skat. Die werksverrigting van hiedie kompensasiemetodes word dan ondersoek deur middel van simulasies en ’n praktiese hardeware-implementasie. Die resultate wys daarop dat hierdie metodes daarin slaag om ’n aansienlike verbetering in die beeldonderdrukkingsvermo¨ens van die haaksfasige mengers te weeg te bring. Laastens word daar ook ’n blinde kompensasiemetode ontwikkel, wat gemik is op frekwensie- onafhanklike wanbalanse in digital-modulasie-skama stelsels. Vir hierdie metodes is geen toetsseine nodig om die wanbalanse af te skat nie, en word dit gedoen vanuit die tweede-orde statistiek van die ontvangde sein. Die werksverrigting van hierdie tegnieke word verder bevestig deur middel van simulasies.

Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Utilising future radio interferometer arrays, such as the Square Kilometre Array (SKA), to their full potential will require calibrating for various direction- dependent effects, including the radiation pattern (or primary beam in the parlance of radio astronomers) of each of the antennas in such an array. This requires an accurate characterisation of the radiation patterns at the time of observation, as changing operating conditions may cause substantial variation in these patterns. Furthermore, fundamental imaging limits, as well as practical time constraints, limit the amount of measurement data that can be used to perform such characterisation. Herein three techniques are presented which aim to address this requirement by providing pattern models that use the least amount of measurement data for an accurate characterisation of the radiation pattern. These methods are demonstrated through application to the MeerKAT Offset Gregorian (OG) dual-reflector antenna. The first technique is based on a novel application of the Jaco bi-Bessel series in which the expansion coefficients are solved directly from the secondary pattern. Improving the efficiency of this model in the desired application leads to the development of a different set of basis functions, as well as two constrained solution approaches which reduce the number of pattern measurements required to yield an accurate and unique solution. The second approach extends the application of the recently proposed Characteristic Basis Function Patterns (CBFPs) to compensate for non-linear pattern variations resulting from mechanical deformations in a reflector antenna system. The superior modelling capabilities of these numerical basis functions, which contain most of the pattern features of the given antenna design in a single term, over that of analytic basis functions are demonstrated. The final method focusses on an antenna employing a Phased Array Feed (PAF) in which multiple beam patterns are created through th e use of a beam-former. Calibration of such systems poses a difficult problem as the radiation pattern shape is susceptible to gain variations. Here we propose a solution which is based on using a Linearly Constrained Minimum Varia nce (LCMV) beamformer to conform the realised beam pattern to a physics-based analytic function. Results show that the LCMV beamformer successful ly produces circularly symmetric beams that are accurately characterised with a single-term analytic function over a wide FoV. / AFRIKAANSE OPSOMMING: Die volle benutting van toekomstige radio interferometersamestellings, soos die Square Kilometre Array (SKA), benodig die kalibrering van verskeie rigting-afhanklike effekte, insluitend die stralingspatroon (bekend as die primêre bundel onder radio astronome) van elke antenne in só ’n samestelling. Hierdie benodig ’n akkurate karakterisering van die stralingspatrone op die waarnemingstydstip, aangesien veranderende bedryfskarakteristieke ’n beduidende afwyking in hierdie patrone veroorsaak. Verder, weens fund amentele perke in beeldverwerking, asook praktiese tydbeperkinge, bestaan daar ’n limiet op die hoeveelheid gemeetde data wat benut kan word om die nodige karakterisering mee te doen. Hierin word drie tegnieke ten toon gestel wat gemik is daarop om aan hierdie behoefte te voorsien deur die gebruik van modelle wat ’n minimum hoeveelheid metingdata benodig om ’n akkurate beskrywing van die stralingspatroon te lewer. Die verskeie metodes word aangebied aan die hand van die MeerKAT afset-Gregorian dubbelreflektorantenne. Die eerste tegniek is gebasseer op ’n nuwe toepassing van die Jacobi- Besselreeks waarin die sekondêre stralingspatroon direk gebruik word om die uitsettingskoëffisiënte op te los. Die doelmatigheidsverbetering van hierdie model in die huidige toepassing lei na die ontwikkeling van ’n nuwe versameling van basisfunksies, asook twee voorwaardelike oplossings wat die nodige aantal metings vir ’n akkurate, unieke oplossing verminder. In die tweede tegniek word die toepassing van die onlangs voorgestelde Karakteristieke Basisfunksie Patrone uitgebrei om te vergoed vir die nie-lineêre stralingspatroonafwykings wat teweeggebring word deur meganiese vervormings in die reflektorantenne. Die superieure modelleringsvermoëns van hierdie numeriese basisfunksies, wat meeste van die patroonkenmerke vasvang in ’n enkele term, bo dié van analitiese basisfunksies word gedemonstreer. Die laaste metode fokus op die gebruik van ’n gefaseerde samestellingvoer waarin veelvoudige bundelpatrone geskep word deur die gebruik van ’n bundelvormer. Die kalibrering van sulke instrumente word bemoeilik daardeur dat die patroonvorm gevoelig is vir aanwinsafwykings. Hier stel ons ’n oplossing voor waarin ’n lineêrbegrensde minimumstrooiing bundelvormer gebruik word om die stralingspatroon te pas op ’n fisika-gebasseerde analitiese funksie. Resultate toon dat hierdie bundelvormer sirkelsimmetriese bundels kan skep wat akkuraat beskryf word deur ’n een-term analitiese funksie oor ’n wye gesigsveld.

Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: In this dissertation a number of techniques to design multi-band filters, with specific focus on coupled resonator implementations, is presented. Multi-band transfer functions are constructed from single-band transfer functions using frequency mapping methods. A general class of rational mapping functions is presented that can accommodate arbitrary bandwidth specifications. Multi-band circuits are synthesised directly from multi-band transfer functions and are obtained by applying reactance transformations to single-band prototype circuits. For the direct synthesis of multi-band filters from multi-band transfer functions coupling matrix synthesis methods are employed. The circuits that result from matrix synthesis methods tend to have topologies that are undesirable from a practical perspective and must be simplified using rotations of the coupling matrix. The synthesis of multi-band filters through reactance transformations is both simple and result in filters that have practical topologies for realisation as coupled resonator circuits. Multiple filters are designed using different design methodologies and different transmission line technologies to illustrate the various design possibilities. The designs include both all-pole and cross-coupled filters and employ single-layer stripline, multi-layer stripline as well as coaxial resonators as transmission line technologies for the implementations. / AFRIKAANSE OPSOMMING: In hierdie proefskrif word verskeie ontwerpstegnieke vir multi-band filters aangebied en word daar spesifiek klem gelê op filters wat as gekoppelde resoneerder strukture geïmplimenteer kan word. Multi-band oordragsfunksies word geskep uit enkelband oordragsfunksies deur gebruik te maak van wiskundige afbeeldingstegnieke. ’n Spesiale klas van rasionale funksies word voorgestel wat spesifiek gebruik kan word om multi-band funksies te skep wat ’n arbitrêre bandwydte spesifikasie het. Multi-band stroombane word direk gesintetiseer vanuit multi-band oordragsfunksies en word ook verkry deur die toepassing van reaktansietransformasies op enkelband stroombane. Vir die direkte sintese van multi-band stroombane vanuit multi-band oordragsfunksies word stroombane gesintetiseer as koppelmatrikse. Stroombane wat op hierdie wyse gesintetiseer word is geneig om topologieë te hê wat nie baie gesog is vanuit ’n praktiese perspektief nie en matriks rotasies word dan hier ingespan om die stroombane se topologieë te vereenvoudig. Die sintese van multi-band stroombane deur gebruik te maak van reaktansietransformasies is beide eenvoudig en lei tot stroombane wat praktiese topologieë het vir implimentering as gekoppelde resoneerder strukture. Die ontwerpsmoontlikhede wat die verskillende metodieke bied word geïllustreer deur die ontwerp van verskeie filters op verskillende maniere waar daar gebruik gemaak word van verskeie transmissielyn tegnologië. Die filter ontwerpe sluit filters in waar alle transmissienulle by oneidige frekwensies is, sowel as gevalle waar somige transmissienulle by eindige frekwensies is. Die filters word geïmplimenteer deur gebruik te maak van koaksiale resoneerders sowel as enkellaag en multilaag strooklyn.

139 leaves printed single pages, preliminary pages i-xi and numbered pages 1-127. Includes bibliography and a list of figures and tables. Digitized at 600 dpi grayscale to pdf format (OCR),using a Bizhub 250 Konica Minolta Scanner. / Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: Probability density functions (PDFs) and cumulative distribution functions (CDFs) play a central role in statistical pattern recognition and verification systems. They allow observations that do not occur according to deterministic rules to be quantified and modelled. An example of such observations would be the voice patterns of a person that is used as input to a biometric security device. In order to model such non-deterministic observations, a density function estimator is employed to estimate a PDF or CDF from sample data. Although numerous density function estimation techniques exist, all the techniques can be classified into one of two groups, parametric and non-parametric, each with its own characteristic advantages and disadvantages. In this research, we introduce a novel approach to density function estimation that attempts to combine some of the advantages of both the parametric and non-parametric estimators. This is done by considering density estimation using an abstract approach in which the density function is modelled entirely in terms of its moments or characteristic function. New density function estimation techniques are first developed in theory, after which a number of practical density function estimators are presented. Experiments are performed in which the performance of the new estimators are compared to two established estimators, namely the Parzen estimator and the Gaussian mixture model (GMM). The comparison is performed in terms of the accuracy, computational requirements and ease of use of the estimators and it is found that the new estimators does combine some of the advantages of the established estimators without the corresponding disadvantages. / AFRIKAANSE OPSOMMING: Waarskynlikheids digtheidsfunksies (WDFs) en Kumulatiewe distribusiefunksies (KDFs) speel 'n sentrale rol in statistiese patroonherkenning en verifikasie stelsels. Hulle maak dit moontlik om nie-deterministiese observasies te kwantifiseer en te modelleer. Die stempatrone van 'n spreker wat as intree tot 'n biometriese sekuriteits stelsel gegee word, is 'n voorbeeld van so 'n observasie. Ten einde sulke observasies te modelleer, word 'n digtheidsfunksie afskatter gebruik om die WDF of KDF vanaf data monsters af te skat. Alhoewel daar talryke digtheidsfunksie afskatters bestaan, kan almal in een van twee katagoriee geplaas word, parametries en nie-parametries, elk met hul eie kenmerkende voordele en nadele. Hierdie werk Ie 'n nuwe benadering tot digtheidsfunksie afskatting voor wat die voordele van beide die parametriese sowel as die nie-parametriese tegnieke probeer kombineer. Dit word gedoen deur digtheidsfunksie afskatting vanuit 'n abstrakte oogpunt te benader waar die digtheidsfunksie uitsluitlik in terme van sy momente en karakteristieke funksie gemodelleer word. Nuwe metodes word eers in teorie ondersoek en ontwikkel waarna praktiese tegnieke voorgele word. Hierdie afskatters het die vermoe om 'n wye verskeidenheid digtheidsfunksies af te skat en is nie net ontwerp om slegs sekere families van digtheidsfunksies optimaal voor te stel nie. Eksperimente is uitgevoer wat die werkverrigting van die nuwe tegnieke met twee gevestigde tegnieke, naamlik die Parzen afskatter en die Gaussiese mengsel model (GMM), te vergelyk. Die werkverrigting word gemeet in terme van akkuraatheid, vereiste numeriese verwerkingsvermoe en die gemak van gebruik. Daar word bevind dat die nuwe afskatters weI voordele van die gevestigde afskatters kombineer sonder die gepaardgaande nadele.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2007. / The aim of this project was to design and test a partial attitude determination and control system for a nanosatellite. The reaction wheel system was designed and tested as an actuator for the nanosatellite. This reaction wheel system consists of four reaction wheels mounted in a tetrahedral formation. A rate sensor system was also designed and its viability for this space application was examined. The rate sensor system consists of 3 orthogonally mounted planes, each with three rate sensors mounted on it. Hardware-inthe- loop tests were used along with an air bearing experimentational setup, which created near frictionless circumstances, to prove the effectiveness of the designed reaction wheel setup. The results following from this project were the following: The reaction wheel system proved to be an adequate actuator for this nanosatellite application and the rate sensor systemwhich was analysed proved to be inadequate for a nanosatellite application.

Thesis (MScEng (Electrical and Electronic Engineering))--Stellenbosch University, 2008. / A WSN (wireless sensor network) consists of a collection of small, low power electronic devices that can sense their environment and communicate with each other in order to send data to a base station for logging and monitoring. Research done on WSNs has increased rapidly over the past few years, as the necessary RF hardware has become cheaper and smaller. The wealth of information and hardware available in this field has made it possible to design and deploy networks for a multitude of monitoring purposes, on almost any terrain, without an existing telecommunication infrastructure. This thesis presents research into some major aspects of WSNs and the implementation of a test system with wireless sensor motes, that can be used for environmental monitoring, conservation purposes, impact studies, early warning systems for floods, fires etc. The system also has a wide range of possible uses in agriculture, as more data and better control over crops can increase yield. The power constraint of sensor nodes is one of the biggest concerns, as batteries can be depleted quickly and render a system useless. For this reason, work was focused on reducing power consumption of the hardware by means of various methods. Power use was also simulated very successfully, giving a accurate way of predicting node lifetime with a variety of battery types. The system was implemented on the Tmote Sky hardware platform using the open source sensor network operating system, TinyOS.