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

[摘要] ENGLISH ABSTRACT: One of the most difficult problems in microwave dielectric heating is the generationand control of field and heating patterns. A technique allowing the synthesis ofdifferent, 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, calledfeatures, to be obtained by signals from several sources interfering with each other.The relative phases of the signals are modulated, by which process known featuresmay be selected. Weights are assigned to these features, which may be combinedover time to form a new heating pattern. Phase changes may then be used to switchto specific, known features, with weights which will determine the contribution ofeach feature to the desired overall pattern.In the practical implementation described, magnetron tubes are the sources. Eachof these narrow-band high-power sources was injection locked to a low powercontrol signal. The control signals are derived from a reference source and theirphase is set to select a corresponding feature.Calculation and measurement showed that reliable locking occurs with a controlsignal power of at least 3% of the magnetron's emitted power.Measurements of patterns were carried out with materials formed into sheets andblocks. Some were chemically prepared to reveal the overall heating pattern. Theobserved patters, simulations and field measurements concur, thus validating theconcept and operation of the proposed topology.

[发布机构] Stellenbosch University