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The development of a SQUID-based gradiometerMuller, Benjamin John Frederick 03 1900 (has links)
Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: This thesis presents an attempt at creating a fully functional SQUID for the purposes
of a predefined application. The goal of the work is to provide a method
of development, primarily utilising the facilities of the Engineering Faculty of the
University of Stellenbosch, with minimal assistance from other departments. This
method is then analysed and the successes and failures discussed in order to provide
guidelines and recommendations for future research.
The device consists of a gradiometric SQUID, as well as electronics which provide
the SQUID bias current, output linearisation and output signal filtering. YBCO
is used for the superconducting material, allowing the use of liquid nitrogen as
coolant which eases the operation and portability of the device. Various methods
of creating Josephson junctions are tested, such as constriction bridges using AFM
lithography and step-edge junctions, with and without different buffer layers.
Proof of concept simulations demonstrate the viability of the device. Unfortunately,
a functional device could not be constructed, mostly due to the design
requiring higher levels of resolution and process control than some of the available
facilities can provide. Recommendations are provided for future researchers. / AFRIKAANSE OPSOMMING: Hierdie tesis beskryf ’n poging om ’n volledige funksionele SQUID te vervaardig
vir die doeleindes van ’n vasgestelde toepassing. Die doel van die werk is om
’n metode te voorsien wat hoofsaaklik gebruik maak van die fasiliteite van die
Ingenieurswese Fakulteit van die Universiteit van Stellenbosch, met minimale hulp
van ander departemente. Hierdie metode word dan ondersoek en die suksesse
en mislukkings bespreek om riglyne en voorstellings te voorsien vir toekomstige
navorsing.
Die toestel bestaan uit ’n gradiometriese SQUID, sowel as elektronika wat voorsiening
maak vir voorspanning, uittree-linearisering en ’n uittree-filter. YBCO is as
supergeleidende materiaal gebruik, wat die gebruik van vloeibare stikstof as verkoeler
moontlik maak en dus die hantering en draagbaarheid van die toestel vergemaklik.
Verskillende metodes om Josephson-vlakke te vervaardig is getoets, onder
andere vernouingsbrugvlakke deur middel van AFM litografie en stapvlakke met
en sonder bufferlae.
Bewys van konsep simulasies demonstreer die lewensvatbaarheid van die toestel.
Ongelukkig kon ’n funksionele weergawe van die toestel nie vervaardig word
nie, hoofsaaklik as gevolg van die ontwerp wat hoër resolusievlakke en beter prosesbeheer
benodig as wat sekere van die beskikbare fasiliteite kan voorsien. Aanbevelings
word voorsien vir toekomstige navorsers.
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Electronic voltage regulator technology for rural electrificationSerdyn, J. J. 03 1900 (has links)
Thesis (MScEng (Electrical and Electronic Engineering))--Stellenbosch University, 2008. / ENGLISH ABSTRACT: This thesis discusses the development of a 5 kVA single phase AC voltage regulator,
specifically designed to assist in the reduction of electrification costs in sparsely populated rural
areas. The voltage regulator is based on a solid state auto-transformer tap changer, designed to
be robust and maintenance free.
Electrification cost savings can be realized if the length of the LV network can be extended to
reach more households. To accomplish this, a voltage regulator can be installed onto the
extended LV feeder at the point where the LV voltage will drop below the minimum valid
voltage, thereby boosting the voltage downstream and enabling more customers to be
connected.
A variety of voltage regulator topologies were investigated to obtain the best topology for the
application. The voltage regulator design is discussed in detail with careful attention given to
the power loss incurred, surge voltage protection requirements, protection coordination with the
existing LV network and the thermal design requirements. An electronic controller based on a
digital signal processor together with an appropriate power supply is designed and built. The
software to control the voltage regulator is developed, integrated with the hardware and
debugged. The complete voltage regulator is evaluated through extensive laboratory testing and
field trials are performed to verify the performance of the device. / AFRIKAANSE OPSOMMING: Hierdie tesis bespreek die ontwikkeling van ‘n 5 kVA, enkelfase, wisselstroom spannings
reguleerder, spesifiek ontwerp om koste besparings te bewerkstellig in die elektrifisiëring van yl
bevolkte landelike gemeenskappe. Die spannings reguleerder se ontwerp is gebaseer op ‘n
outo-transformator tap wisselaar met vaste toestand skakelaars, om sodoende robuust en
instandhoudings vry te funksioneer.
Elektrifisiërings koste besparings is moontlik indien die laag spannings distribusie kabel verleng
kan word, om sodoende elektrisiteit aan meer huishoudings te voorsien. Om dit mootlik te
maak kan ‘n spannings reguleerder geinstalleer word op die punt waar die kabel spanning onder
die minimum toegelate spanning daal. Sodoende word die spanning weer verhoog aan al die
huishoudings wat aan die verlengde gedeelte van die kabel verbind is.
‘n Verskeidenheid uiteenlopende spannings reguleerder topologieë is ondersoek om die beste
topologie vir die toepassing te identifiseer. Die ontwerp van die spannings reguleerder is baie
deeglik bespreek en spesifieke aandag is gegee aan die verliese, spits opwelling spannings
beveiliging, sinkronisasie met die huidige laag spannings netwerk se beveiligings meganismes
en die termiese ontwerp van die stelsel. ‘n Elektroniese beheerder, gebaseer op ‘n digitale sein
verwerker, tesame met ‘n toepaslike kragbron is ontwerp en gebou. Die nodige sagteware om
die spannings reguleerder te beheer is ontwikkel, geintegreer met die hardeware en ontfout. Die
volledige spannings reguleerder is ontleed deur intensiewe toetse in die laboratorium en toets
installasies op laag spannings netwerke, om sodoende die nakoming van die werks verrigting
vereistes van die toestel te bevestig.
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A low cost, high precision star sensorJacobs, M. J. 12 1900 (has links)
Thesis (MEng (Electrical and Electronic Engineering))--University of Stellenbosch, 1995. / 189 leaves single sided printed, preliminary pages and numbered pages 1-126. Includes bibliography, list of appendixes, figures, notation and symbols. Digitized at 300 dpi (OCR), using a Bizhub 250 Scanner. / ENGLISH ABSTRACT: The Sunsat microsatellite is being developed at the University of Stellenbosch. It is
equipped with a high resolution earth imager which requires a sophisticated attitude
determination and control system. Precise control of the satellite is impossible without
high precision attitude sensors. The most accurate attitude sensor presently used by
satellites is the star sensor.
The aim 'of this thesis is to develop a low cost, high precision star sensor for the
Sunsat microsatellite. The development included the selection of electronic and
optical hardware followed by the design, construction and testing of the sensor.
Software algorithms were developed and programmed to control the imager, extract
stars from images and match the observed constellations to a star catalogue. A set of
matching observed and reference vectors are passed to the attitude determination and
control system which calculates the three axis orientation of the satellite. / AFRIKAANSE OPSOMMING: Die Sunsat mikrosatelliet word tans by die Universiteit van Stellenbosch ontwikkel.
Dit is toegerus met 'n hoeresolusie aardwaarnemingskamera en vereis 'n gevorderde
orientasiebepaling-en beheerstelsel. Presiese beheer is onmoontlik sonder akkurate
sensore. 'n Stersensor is die mees akkurate tipe sensor waarmee satelliete tans
toegerus word.
Die doelwit van hierdie tesis is die ontwikkeling van 'n hoe resolusie, laekoste
stersensor vir die Sunsat mikrosatelliet. Die ontwikkeling behels die seleksie van
elektroniese en optiese apparatuur wat gevolg is deur die ontwerp, opbou en toets van
die sensor. Programmatuur algoritrnes is ontwerp om die kamera te beheer, sterre in
fotos te herken en waargenome konstellasies in die sterkatalogus te vind. 'n Stel
waargenome en verwysingsvektore stel die orientasiebepaling-en beheerstelsel in staat
om die orientasie van die satelliet te bereken.
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An investigation into control techniques for cascaded plants with buffering, to minimise the influence of process disturbances and to maximise the process yieldGryffenberg, Jolandi 12 1900 (has links)
Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The Coal to Liquid facility, Sasol, Secunda operates as a train of processes. Disturbances
and capacity restrictions can occur throughout the plant and the throughput
fluctuates whenever disturbances occur. When capacity restrictions occur in a subplant
and more substances enter the sub-plant than can be processed, the extra substances
are flared or dumped and therefore lost. To reduce losses and extra costs and
to maximise the throughput of the whole plant, supervisory control is implemented over
the whole plant system.
Each process in the process train is controlled with regulatory controllers and the overall
process is then controlled with a supervisory controller. These two sets of controllers
operate in two different layers of control, with the regulatory controllers the faster inner
layer. The supervisory control is the outer layer of the two control layers. The
supervisory controller takes over the work of the human operator by deciding on the
changes in total throughput as well as the set points for each individual process. These
set points for each process are then followed with the regulatory controllers. For the
regulatory control of the system, different control methods are investigated and compared.
The different control methods that are looked at are PI control, Linearised State
Feedback control, Fuzzy Logic control and Model Reference Adaptive Control.
After an investigation into the various control methods Fuzzy Logic control was chosen
for the regulatory as well as the supervisory control levels. Fuzzy Logic control is a rule
based control method. Fuzzy variables are everyday terms such as very slow or nearly
full. These terms are easy to understand by the operator and multi-variable control is
possible with Fuzzy Logic control without an accurate mathematical representation of
the system. These facts made Fuzzy Logic control ideal for this implementation.
To improve the profit of the Coal to Liquid facility the throughput was maximised. The
combination of regulatory and supervisory controllers minimised losses and rejected
disturbances. This resulted in a smoother output with maximum profit. / AFRIKAANSE OPSOMMING: Die Steenkool-na-Olie fasiliteit, Sasol, Secunda funksioneer as ’n trein van prosesse.
Versteurings en kapasiteit beperkings kan deur die hele aanleg voorkom en die deurset
wissel voortdurend wanneer versteurings voorkom. Wanneer kapasiteit beperkings
voorkom in ’n aanleg en meer stowwe word in die aanleg ingestuur as wat dit kan
verwerk, word die ekstra stowwe gestort en dit gaan verlore. Om verliese en kostes
te verminder en om die deurset van die hele aanleg te vergroot, is oorhoofse beheer
geïmplementeer oor die hele stelsel.
Elke proses in die trein van chemiese prosesse word beheer met regulerende beheerders.
Die totale proses word dan beheer met ’n oorhoofse beheerder. Hierdie twee
tipes beheerders funksioneer in twee lae van beheer met die regulerende beheerders
die vinniger binneste laag. Die oorhoofse beheerder vorm die buitenste laag van die
twee beheer lae en neem die werk van die menslike operateur oor deur die veranderinge
in die totale deurset, sowel as die stelpunte vir elke afsonderlike proses, te
bepaal. Hierdie stelpunte vir elke proses word dan met die regulerende beheerders gevolg.
Verskillende beheer metodes is ondersoek vir die regulerende beheer van die stelsel.
Die verskillende beheer metodes waarna gekyk word, is PI beheer, Geliniariseerde
Toestands Terugvoer beheer, Wasige Logiese beheer en Model Verwysing Aanpassende
beheer.
Na ’n ondersoek na die verskillende beheer metodes is Wasige Logiese beheer gekies
vir die regulerende asook die oorhoofse beheer. Wasige Logiese beheer is ’n reël
gebasseerde beheer metode. Wasige Logika veranderlikes is alledaagse terme soos
baie stadig of byna vol. Hierdie terme is maklik om te verstaan deur die operateur.
Meervoudige-veranderlike beheer is moontlik met Wasige Logiese beheer sonder ’n
akkurate wiskundige voorstelling van die stelsel. Hierdie feite maak Wasige Logiese
beheer ideaal vir hierdie doel.
Om die wins van die Steenkool-na-Olie fasiliteit te verbeter, is die deurset gemaksimeer.
Die kombinasie van regulerende- en toesighoudende beheerders beperk verliese en
verwerp versteurings. Dit lei tot ’n gladder uitset en ’n maksimum wins.
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Evaluation and development of conceptual document similarity metrics with content-based recommender applicationsGouws, Stephan 12 1900 (has links)
Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The World Wide Web brought with it an unprecedented level of information overload.
Computers are very effective at processing and clustering numerical and binary data,
however, the automated conceptual clustering of natural-language data is considerably
harder to automate. Most past techniques rely on simple keyword-matching techniques
or probabilistic methods to measure semantic relatedness. However, these approaches do
not always accurately capture conceptual relatedness as measured by humans.
In this thesis we propose and evaluate the use of novel Spreading Activation (SA)
techniques for computing semantic relatedness, by modelling the article hyperlink structure
of Wikipedia as an associative network structure for knowledge representation. The
SA technique is adapted and several problems are addressed for it to function over the
Wikipedia hyperlink structure. Inter-concept and inter-document similarity metrics are
developed which make use of SA to compute the conceptual similarity between two concepts
and between two natural-language documents. We evaluate these approaches over
two document similarity datasets and achieve results which compare favourably with the
state of the art.
Furthermore, document preprocessing techniques are evaluated in terms of the performance
gain these techniques can have on the well-known cosine document similarity metric
and the Normalised Compression Distance (NCD) metric. Results indicate that a near
two-fold increase in accuracy can be achieved for NCD by applying simple preprocessing
techniques. Nonetheless, the cosine similarity metric still significantly outperforms NCD.
Finally, we show that using our Wikipedia-based method to augment the cosine vector
space model provides superior results to either in isolation. Combining the two methods
leads to an increased correlation of Pearson p = 0:72 over the Lee (2005) document similarity
dataset, which matches the reported result for the state-of-the-art Explicit Semantic
Analysis (ESA) technique, while requiring less than 10% of the Wikipedia database as
required by ESA.
As a use case for document similarity techniques, a purely content-based news-article
recommender system is designed and implemented for a large online media company.
This system is used to gather additional human-generated relevance ratings which we
use to evaluate the performance of three state-of-the-art document similarity metrics for
providing content-based document recommendations. / AFRIKAANSE OPSOMMING: Die Wêreldwye-Web het ’n vlak van inligting-oorbelading tot gevolg gehad soos nog nooit
tevore. Rekenaars is baie effektief met die verwerking en groepering van numeriese en
binêre data, maar die konsepsuele groepering van natuurlike-taal data is aansienlik moeiliker
om te outomatiseer. Tradisioneel berus sulke algoritmes op eenvoudige sleutelwoordherkenningstegnieke
of waarskynlikheidsmetodes om semantiese verwantskappe te bereken,
maar hierdie benaderings modelleer nie konsepsuele verwantskappe, soos gemeet deur
die mens, baie akkuraat nie.
In hierdie tesis stel ons die gebruik van ’n nuwe aktiverings-verspreidingstrategie (AV)
voor waarmee inter-konsep verwantskappe bereken kan word, deur die artikel skakelstruktuur
van Wikipedia te modelleer as ’n assosiatiewe netwerk. Die AV tegniek word aangepas
om te funksioneer oor die Wikipedia skakelstruktuur, en verskeie probleme wat hiermee
gepaard gaan word aangespreek. Inter-konsep en inter-dokument verwantskapsmaatstawwe
word ontwikkel wat gebruik maak van AV om die konsepsuele verwantskap tussen twee
konsepte en twee natuurlike-taal dokumente te bereken. Ons evalueer hierdie benadering
oor twee dokument-verwantskap datastelle en die resultate vergelyk goed met die van
ander toonaangewende metodes.
Verder word teks-voorverwerkingstegnieke ondersoek in terme van die moontlike verbetering
wat dit tot gevolg kan hê op die werksverrigting van die bekende kosinus vektorruimtemaatstaf
en die genormaliseerde kompressie-afstandmaatstaf (GKA). Resultate
dui daarop dat GKA se akkuraatheid byna verdubbel kan word deur gebruik te maak van
eenvoudige voorverwerkingstegnieke, maar dat die kosinus vektorruimtemaatstaf steeds
aansienlike beter resultate lewer.
Laastens wys ons dat die Wikipedia-gebasseerde metode gebruik kan word om die
vektorruimtemaatstaf aan te vul tot ’n gekombineerde maatstaf wat beter resultate lewer
as enige van die twee metodes afsonderlik. Deur die twee metodes te kombineer lei tot ’n
verhoogde korrelasie van Pearson p = 0:72 oor die Lee dokument-verwantskap datastel.
Dit is gelyk aan die gerapporteerde resultaat vir Explicit Semantic Analysis (ESA), die
huidige beste Wikipedia-gebasseerde tegniek. Ons benadering benodig egter minder as
10% van die Wikipedia databasis wat benodig word vir ESA.
As ’n toetstoepassing vir dokument-verwantskaptegnieke ontwerp en implementeer ons
’n stelsel vir ’n aanlyn media-maatskappy wat nuusartikels aanbeveel vir gebruikers, slegs
op grond van die artikels se inhoud. Joernaliste wat die stelsel gebruik ken ’n punt toe aan
elke aanbeveling en ons gebruik hierdie data om die akkuraatheid van drie toonaangewende
maatstawwe vir dokument-verwantskap te evalueer in die konteks van inhoud-gebasseerde
nuus-artikel aanbevelings.
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Combined turbo coding and interference rejection for DS-CDMA.Bejide, Emmanuel Oluremi. January 2004 (has links)
This dissertation presents interference cancellation techniques for both the Forward Error
Correction (FEC) coded and the uncoded Direct Sequence Code Division Multiple
Access (DS-CDMA) systems. Analytical models are also developed for the adaptive and
the non-adaptive Parallel Interference Cancellation (PlC) receivers. Results that are
obtained from the computer simulations of the PlC receiver types confirm the accuracy of
the analytical models that are developed. Results show that the Least Mean Square
(LMS) algorithm based adaptive PlC receivers have bit error rate performances that are
better than those of the non-adaptive PlC receivers.
In the second part of this dissertation, a novel iterative multiuser detector for the Turbo
coded DS-CDMA system is developed. The performance of the proposed receiver in the
multirate CDMA system is also investigated. The developed receiver is found to have an
error rate performance that is very close to the single user limit after a few numbers of
iterations. The receiver is also resilient against the near-far effect. A methodology is also
presented on the use of the Gaussian approximation method in the convergence analysis
of iterative interference cancellation receivers for turbo coded DS-CDMA systems. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2004.
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Combined turbo coding and interference rejection for DS-CDMA.Bejide, Emmanuel Oluremi. January 2004 (has links)
This dissertation presents interference cancellation techniques for both the Forward Error
Correction (FEC) coded and the uncoded Direct Sequence Code Division Multiple
Access (DS-CDMA) systems. Analytical models are also developed for the adaptive and
the non-adaptive Parallel Interference Cancellation (PlC) receivers. Results that are
obtained from the computer simulations of the PlC receiver types confirm the accuracy of
the analytical models that are developed. Results show that the Least Mean Square
(LMS) algorithm based adaptive PlC receivers have bit error rate performances that are
better than those of the non-adaptive PlC receivers.
In the second part of this dissertation, a novel iterative multiuser detector for the Turbo
coded DS-CDMA system is developed. The performance of the proposed receiver in the
multirate CDMA system is also investigated. The developed receiver is found to have an
error rate performance that is very close to the single user limit after a few numbers of
iterations. The receiver is also resilient against the near-far effect. A methodology is also
presented on the use of the Gaussian approximation method in the convergence analysis
of iterative interference cancellation receivers for turbo coded DS-CDMA systems. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2004.
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Performance analysis of cellular networks.Rajaratnam, Myuran. January 2000 (has links)
Performance analysis in cellular networks is the determination of customer orientated grade-of-service parameters, such as call blocking and dropping probabilities, using the methods of stochastic theory. This stochastic theory analysis is built on certain assumptions regarding the arrival and service processes of user-offered calls in a network. In the past, cellular networks were analysed using the classical assumptions, Poisson call arrivals and negative exponential channel holding times, borrowed from earlier fixed network analysis. However, cellular networks are markedly different from fixed networks, in that, they afford the user a unique opportunity: the ability to communicate while on the move. User mobility and various other cellular network characteristics, such as customer-billing, cell· layout and hand·off mechanisms, generally invalidate the use of Poisson arrivals and negative exponential holding times. Recent measurements on live networks substantiate this view. Consequently, over the past few years, there has been a noticeable shift towards using more generalised arrival and service distributions in the performance analysis of cellular networks. However, two shortcomings with the resulting models are that they suffer from state space explosion and / or they represent hand off traffic as a state dependent mean arrival rate (thus ignoring the higher moments of the hand-off arrival process). This thesis's contribution to cellular network analysis is a moment-based approach that avoids full state space description but ensures that the hand-off arrival process is modelled beyond the first moment. The thesis considers a performance analysis model that is based on Poisson new call arrivals, generalised hand-off call arrivals and a variety of channel holding times. The thesis shows that the performance analysis of a cellular network may be loosely decomposed into three parts, a generic cell traffic characterising model, a generic cell traffic blocking model and a quality of service evaluation model. The cell traffic characterising model is employed to determine the mean and variance of hand-off traffic offered by a cell to its neighbour. The cell traffic-blocking model is used to detennine the blocking experienced by the various traffic streams offered to each cell. The quality of service evaluation part is essentially afued-point iteration of the cell traffic characterising and cell traffic blocking parts to determine customer orientated grade-of-service parameters such as blocking and dropping probabilities. The thesis also presents detailed mathematical models for user mobility modelling. Finally, the thesis provides extensive results to validate the proposed analysis and to illustrate the accuracy of the proposed analysis when compared to existing methods. / Thesis (Ph.D.)-University of Natal, Durban, 2000.
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Optimized digital signal processing algorithms applied to radio communications.Carter, Alan James Auchmuty. January 1992 (has links)
The application of digital signal processing to radio communications
has come of age with the advent of low power, high speed microprocessors
and over the past five years, various transceiver architectures,
utilizing this new technology have been extensively researched. Due
to the flexible nature of a software based transceiver, a myriad of
possible applications exist and currently the emphasis is on the
development of suitable algorithms.
The principal aim of this research is the derivation of optimized
digital signal processing algorithms applicable to three separate
areas of radio communications. Optimized, as used by the author within
this dissertation, implies a reasonable compromise between performance,
complexity and numerical processing efficiency. This compromise
is necessary since the algorithms are applied to a portable transceiver
where power consumption, size and weight are limited.
The digital signal processing algorithms described by this research
is as follows:-
1. The derivation and assessment of a multirate speech amplitude
modulation demodulator which exhibits low distortion (typically
less than 2%) for a wide range of modulation indices, carrier
frequency offsets and deviations. The demodulator is processing
efficient and requires only five multiplications and five decisions
for every output sample.
2. The derivation and assessment of a low sampling rate speech
frequency modulation demodulator for signals whose bandwidth exceed
quarter the sampling frequency. The demodulator exhibits low
distortion (typically less than 2%) and is processing efficient
requiring eighteen multiplications and three decisions for every
output sample.
3. The derivation and assessment of a multirate single-sideband
suppressed carrier automatic frequency control system which is a
combination of a simple second order adaptive line enhancer and
a digital phase-locked loop. The processing efficient automatic
frequency control system is suited for low signal to noise power
conditions, in both stationary and mobile communication channels. / Thesis (Ph.D.)-University of Natal, Durban, 1992.
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A gridless, variable perveance Pierce electron gun.Foulis, Bruce David. January 1994 (has links)
This thesis covers the design and development of a modulated Pierce electron gun
used in the construction of experimental travelling wave tube (TWT) amplifiers. The
gun incorporated an open aperture switching electrode, positioned mid-way between
anode and cathode, to pulse the beam. This method of modulation did not have the
same adverse effects on electron trajectories as in the case of a conventional mesh
grid, but rather the electrode could be used to alter the focus conditions within the
gun and subsequently improve certain beam characteristics. Ion focusing effects
could also be eliminated with the electrode, allowing dual mode operation of the guns
without the complications normally associated with such a practice.
The switching electrode was simulated to ascertain its effect on electron trajectories
within the gun, using finite element analysis as well as an electron optics design
program. A test gun was constructed in a glass envelope in order to investigate the
performance of the new design. The glass gun allowed a beam analysis to be
performed, as well as thermal measurements to be made. Results from this gun
compared favourably with earlier simulations. The results of two metal/ceramic
construction TWTs are presented, showing the beneficial effects of the switching
electrode on the performance of the tubes as a whole, and the electrode's potential
to compensate for constructional anomalies.
The joining of metals to ceramic using active brazing techniques is also an important
aspect tackled by the thesis, with several innovative ideas being implemented in the
construction of the devices. A simple yet reliable electrical feed-through was
developed for those guns having a ceramic envelope.
Extensive work was also performed on the manufacture of impregnated tungsten
cathodes for use in the electron guns. Several test diodes, including a water-cooled
demountable test vehicle, were constructed to test the performance of the cathodes.
An analysis was performed on the patchy behaviour of some of the initial cathodes
to improve the preparation methods used in the laboratory. The emission results
obtained from the cathodes are documented, as is the successful incorporation of
several of them into the new modulated gun design. / Thesis (Ph.D.)-Univesity of Natal, Durban, 1994.
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