Deep understanding of impedance matching and quarter wavelength theory in electromagnetic wave absorption

It is of great significance for absorber designers to correctly understand impedance matching and its related calculation methods, because excellent impedance matching effect is an important prerequisite for absorber to consume electromagnetic wave (EMW). However, there are some problems in literatures, such as the lack of deep understanding of impedance matching and application conditions of Eq. (3) for the calculation of reflection loss (RL). Based on the transmission line theory of electronic circuit, this paper expounds the definition, symbol, property of various impedances and their influence on impedance matching effect. On the basis of simplifying the actual situation in the process of EMW absorption to the correct transmission line model, the original transmission line model of RL calculation formula and its limitation are pointed out. The doubts about the validity of the quarter wavelength theory in literatures are explained from three aspects: the reduction of EMW length, the multiple reflection and the impedance transformation of absorber.