A Study of Some Inherent Causes for Non-Uniform Microwave Heating
Y. F. Tsai1, L. R. Barnett2, H. H. Teng2, C. C. Ko1, K. R. Chu2*
1Department of Entomology, National Taiwan University, Taipei, Taiwan
2Department of Physics, National Taiwan University, Taipei, Taiwan
* Presenter:K. R. Chu
Radio frequency (RF) and microwave heating of dielectric objects is often susceptible to an excessive temperature spread due to uneven energy deposition. The exposure to a non-uniform field is a well-studied cause for this difficulty encountered in numerous applications. There are, however, some less-understood causes, which are inherent in nature in that they persist even in a perfectly uniform field. We present an experimental study on three main inherent causes with rice grains as samples. Experiments are conducted in an applicator, in which samples are irradiated by a 24 GHz microwave. High radiation uniformity (~99%) and polarization control allow a quantitative examination of each cause. Their individual and collective effects are found to be highly significant. In particular, polarization-charge shielding alone can result in a temperature spread of ~18.2% for the samples examined. Physical interpretations are given and an effective method for its mitigation is demonstrated.

Keywords: microwave heating, uniformity, polarization charge shielding