Dielectric properties and electromagnetic wave transmission performance of polycrystalline mullite fiberboard at 2.45 GHz

Abstract

Refractory lining is an indispensable part of high temperature microwave heating equipment, and its wave transmission performance exerts an important impact on the mode and efficiency of microwave heating, while the complex dielectric constant (dielectric constant and dielectric loss) of the material is the decisive factor in determining the wave transmission performance of the material. In this work, we measured the complex dielectric constant of polycrystalline mullite fiber board (PMF) in the temperature range of 25–1000 °C, and the effect of temperature on dielectric constant and dielectric loss was analyzed; The wave-transmission properties of the material were calculated according to the theory of electromagnetic wave transmission line, and the effects of temperature, material thickness, polarization modes of electromagnetic wave and incident angle on the wave transmission performance were analyzed. The results reveal that the dielectric constant of PMF does not change much with the increase of temperature, which is about 1.6; The dielectric loss does not change much within 200 °C, but when the temperature is higher than 200 °C, the change presents approximately exponential increase with the rise of temperature. The wave transmission performance fluctuates with the increase of the thickness, and there are maximum value and minimum value, and the overall wave transmission performance decreases with the increase of the material thickness. In a transverse electric (TE) field, the overall wave transmission performance decreases with the increase of the incident angle, and better wave transmission performance can be obtained by priority selection of vertical incidence of electromagnetic wave. In a transverse magnetic (TM) field, with the increase in the incident angle, the wave transmission performance firstly climbs up then declines, and there is an optimal incident angle where total transmission can occur. Finally, this work selected the thickness corresponding to different temperature as the preferred thickness. This work is of important theoretical significance for understanding the mechanism of the dynamic change of the wave transmission performance of the thermal insulation materials in microwave heating, and provides important practical guidance for the design and optimization of microwave heating equipment.