Dielectric properties and electromagnetic wave transmission performance of aluminium silicate fibreboard at 915 MHz and 2450 MHz

Refractory lining is an important part of microwave heating equipment, and its wave-transparent effect significantly influences microwave heating efficiency. The complex dielectric constant of the material is the main factor determining its wave-transparent properties. In this study, with aluminium silicate fibreboard (ASF) as the study object, the complex dielectric constant of this material was investigated at temperatures ranging from 25 °C to 1000 °C at 915 MHz and 2450 MHz, respectively. Based on the theory of transmission lines, the wave-transparent properties of the material during the entire microwave heating process were calculated and analysed. It has been found that the dielectric constant and loss factor at both frequencies increase significantly when the temperature exceeds 700 °C; the wave-transparent properties of this material decrease with increasing temperature and present a fluctuating trend as the material thickness increases, with maximum and minimum values; in TM polarization mode, there is an optimal angle of incidence for total transmission, which contributes to a better overall wave-transparent effect of the material in TM polarization mode than that in TE polarization mode. Finally, this study provides the preferred thickness values at different working frequencies and temperatures under vertical incidence of electromagnetic waves for reference. This study is of certain theoretical significance to the research on the change mechanism of the material's dielectric and wave-transparent properties and has practical guidance on the optimization of microwave heating equipment and the selection of the technological parameters of furnace linings.