Determination of Reference-Plane Invariant, Thickness-Independent, and Broadband Constitutive Parameters of Thin Materials

We propose an effective microwave method for reference-plane-invariant and thickness-independent constitutive parameters measurement of thin materials. A function depending only on the interface reflection coefficient to facilitate fast computations of constitutive parameters is derived. In addition to the extraction of sample thickness, the method can also be applied to unique retrieval of constitutive parameters whose electromagnetic properties are yet unknown. We have performed an uncertainty analysis to examine how the accuracy of the method can be improved. Finally, we have compared the proposed method with other similar methods in the literature using measurements of distilled water and a thinner Plexiglas sample (1 mm). From the comparison, we note that the accuracy of our proposed method is not affected by any inaccurate knowledge of reference-plane positions and the sample length (or both) while those of compared methods are seriously decreased.