Cavity effects in microwave heating of ceramics

The heating of a ceramic slab in a TE(103) waveguide applicator is modeled in the small Blot number limit. If E(0) is the strength of the incident mode, then the relationship between the temperature and E(0)(2) is shown to be bistable, or s shaped, in this limit. The shape of this response curve is intimately dependent upon the coupling of the microwave to the cavity and upon the effect of the subsequent heating on this coupling. Several examples are presented to illustrate these important effects. Specifically, large aperture openings give rise to an s-shaped response curve which is similar to that of a one-dimensional slab. However, decreasing the aperture past a certain point significantly lowers the upper branch of the response curve. This indicates the detuning of the cavity by the increased electrical conductivity of the heated ceramic. The decrease in the upper branch indicates the existence of an optimal aperture opening which minimizes the power required to achieve a specified temperature. Finally, several examples are presented which demonstrate the effects of changing the sample thickness and position in the applicator.