Thesis (PhD)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: One of the most difficult problems in microwave dielectric heating is the generation
and control of field and heating patterns. A technique allowing the synthesis of
different, pre-determinable heating patterns by interference modulation is proposed.
The proposed concept may be described by the term 'interference modulation'.
Interference modulation is a technique which enables particular patterns, called
features, to be obtained by signals from several sources interfering with each other.
The relative phases of the signals are modulated, by which process known features
may be selected. Weights are assigned to these features, which may be combined
over time to form a new heating pattern. Phase changes may then be used to switch
to specific, known features, with weights which will determine the contribution of
each feature to the desired overall pattern.
In the practical implementation described, magnetron tubes are the sources. Each
of these narrow-band high-power sources was injection locked to a low power
control signal. The control signals are derived from a reference source and their
phase is set to select a corresponding feature.
Calculation and measurement showed that reliable locking occurs with a control
signal power of at least 3% of the magnetron's emitted power.
Measurements of patterns were carried out with materials formed into sheets and
blocks. Some were chemically prepared to reveal the overall heating pattern. The
observed patters, simulations and field measurements concur, thus validating the
concept and operation of the proposed topology. / AFRIKAANSE OPSOMMING: Een van die moeilikste probleme in mikrogolf diëlektriese verhitting is die opwekking
en beheer van veld- en verhittingspatrone. 'n Tegniek wat voorsiening maak vir die
sintese van verskillende, voorafbepaalde verhittingspatrone deur interferensie word
hier voorgestel.
Die voorgestelde beginsel kan beskryf word deur die term "interferensie modulasie".
Interferensie modulasie is 'n tegniek wat spesifieke patrone, genoem kenmerke,
moontlik maak deur seine van verskillende bronne met mekaar te laat interfereer.
Bekende kenmerke kan geselekteer word deur die relatiewe fases van die seine te
moduleer. Gewigte word aan hierdie kenmerke toegeken wat oor tyd gekombineer
kan word om nuwe verhittingspatrone te vorm. Faseveranderings kan dan gebruik
word om na 'n spesifieke, bekende kenmerk te skakel met gewigte wat die bydrae
van elke kenmerk van die verlangde algehele patroon bepaal.
Magnetrons word gebruik as bronne in die praktiese implimentering wat beskryf word.
Elkeen van hierdie nouband, hoë drywing bronne is injeksie-gesluit met 'n lae
drywing beheersein. Die beheerseine is afgekoppel van 'n verwysingsbron en hul
fases is gestelom 'n ooreenstemmende kenmerk te verkry.
Berekening en meting toon dat betroubare sluiting voorkom wanneer die beheersein
ten minste 3% van die magnetron se uittree-drywing is. Metings van patrone is
gemaak met materiale wat in lae en blokke gevorm is. Sommiges is met chemikalië
voorberei sodat die algehele verhittingspatroon gesien kan word. Die
waargeneemde patrone, simulasies en veldmetings stem goed ooreen en bevestig
die beginsel en werking van die voorgestelde topologie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/52936 |
| Date | 12 1900 |
| Creators | Meier, Ingolf |
| Contributors | De Swardt, J. B., Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 136 p. : ill. |
| Rights | Stellenbosch University |
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