Reflection loss is usually calculated and reported as a function of the thickness of microwave absorption material. However, misleading results are often obtained since the principles imbedded in the popular methods contradict the fundamental facts that electromagnetic waves cannot be reflected in a uniform material except when there is an interface and that there are important differences between the concepts of characteristic impedance and input impedance. In this paper, these inconsistencies have been analyzed theoretically and corrections provided. The problems with the calculations indicate a gap between the background knowledge of material scientists and microwave engineers and for that reason a concise review of transmission line theory is provided along with the mathematical background needed for a deeper understanding of the theory of reflection loss. The expressions of gradient, divergence, Laplacian, and curl operators in a general orthogonal coordinate system have been presented including the concept of reciprocal vectors. Gauss’s and Stokes’s theorems have been related to Green’s theorem in a novel way.

The quarter-wavelength-mode has been widely used in microwave absorption material research for many years. Based on wave-cancellation method, it is proved in the first part of this work that the model fails for most cases. It is interesting that the principles underlining this work are not beyond those covered by fundamental college courses even though the improper model has been dominant in the field for long without correction. In the second part of this work, the correctness of results obtained are verified by formulae well-known to material scientists. The improper commonly used practice of characterizing material by reflection loss and impedance matching has been highlighted and replaced by the method of wave-cancellation for film.

The quarter-wavelength model states that the reflection of microwaves is minimized if the thickness of the film is mλ /4 where m is an odd integer and λ is the wavelength within the film . In part 1 of this work, published previously, it was shown that the theory behind this model is flawed and that it needs to be replaced using a wave superposition approach involving principles not beyond physics at college level. Through the verification of the results from formulae familiar to material scientists, it is shown here that many other concepts in current mainstream microwave absorption theory are used inappropriately including that reflection loss RL has been used to characterize microwave absorption from material instead of film and also that the results have been rationalized incorrectly by impedance matching theory. Impedance matching theory is developed from transmission-line theory for scattering parameter s ₁₁ but cannot be applied to RL which is an innate property only for metal-backed film.