ABSTRACT. A theoretical investigation of recent microwave heating experiments of cylindrical ZnO powdered samples in nitrogen and air environments is presented. A large discontinuity in the measured temperature was observed when heating in nitrogen atmosphere, while heating in air showed the expected exponentially saturating temperature behavior. The microwave power is mostly absorbed in a narrow, localized region that is moving radially outward as a propagating heat wave. It was assumed that this behavior is caused by the anomaly in the temperature dependence of the permittivity, and the simulations verified this assumption. This phenomenon was investigated using a newly developed 2-D code, and the results are in good agreement with experiments. The width of the microwave absorbing layer is ~1 mm and the radial velocity of the heat wave is inversely proportional to the square of the radius, with a maximum of 20 mm/min.

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