Abstract
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.
Highlights
There is considerable research interest in ferromagnetic resonance[1,2,3] and microwave absorption.[4,5] there are problems from contemporary popular measurements[6,7,8,9,10,11,12,13,14] when reflection loss from microwave absorption material is characterized
In the conventional method, reflection loss is incorrectly reported as a function of sample thickness calculated with respect to the position within the measured material
The value of reflection loss from the conventional calculations can be artificially adjusted by sample thickness
Summary
There is considerable research interest in ferromagnetic resonance[1,2,3] and microwave absorption.[4,5] there are problems from contemporary popular measurements[6,7,8,9,10,11,12,13,14] when reflection loss from microwave absorption material is characterized. In the conventional method, reflection loss is incorrectly reported as a function of sample thickness calculated with respect to the position within the measured material. It is demonstrated here that the problems are caused by confusing the characteristic impedance of the material with the input impedance of the circuit. It is proved theoretically (Eqs. 33, 44, and 49 below) that reflection loss for microwave absorption has the same meaning as the scattering parameter s11 which is called return loss in microwave engineering if it is expressed in decibel units (dB).[17,18,19] The theoretical background is presented here succinctly and . The novel section in this Appendix involves the inclusion of the concept of reciprocal vectors and the way in which Green’s theorem is connected with Gauss’s and Stokes’s theorems
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