A physics investigation on impedance matching theory in microwave absorption film—Part I. Theory

Liu, Y. ORCID: https://orcid.org/0000-0001-9862-5786, Drew, M. G. B. ORCID: https://orcid.org/0000-0001-8687-3440 and Liu, Y. ORCID: https://orcid.org/0000-0001-5924-9730 (2023) A physics investigation on impedance matching theory in microwave absorption film—Part I. Theory. Journal of Applied Physics, 134 (4). 045303. ISSN 1089-7550 doi: 10.1063/5.0153608

Abstract/Summary

The mechanism for microwave absorption in a film has previously been numerically verified from the theoretical formula for RL and attributed to angular and amplitude effects with a simple geometrical representation from energy conservation unique to the film. Starting from the case where |RL| = 0, using basic transmission-line theory and mathematics, it is confirmed theoretically here that the mechanism for absorption mechanism in a film, responsible for the minima of the reflection loss RL/dB, is best explained by wave cancelation theory rather than by impedance matching theory. This theoretical proof also reveals that the mechanisms for a film and material are different. The flaws of neglecting the phase effects of interfaces in a film in quarter-wavelength theory are also quantitatively discussed from transmission-line theory. Contrary to the theory held currently, the reported minima of RL/dB originate from phase effects in the film rather than from the resonance peaks for the intrinsic frequencies of a material.