Abstract: The power density of electromagnetic energy loss is deduced from the Maxwell＇s equations, which is dominated by the factors as the imaginary component of relative dielectric constant, of magnetic permeability, external field frequency and the square of field strength. Based on the electromagnetic energy loss, we analyze the principles of microwave heating, and present the thermal energy balance equation in microwave field. This work contributes to improve the understanding of interactions between the electromagnetic field and material, and has some directive meanings to the relative theory research and technological applications.

Key words: Maxwell＇s equations, electromagnetic energy loss, microwave heating