Microwave dielectric heating through interference modulation with narrow band high power sources

Meier, Ingolf (2002-12)

Thesis (PhD)--Stellenbosch University, 2002.

Thesis

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.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/52936
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