Comments on "A Unique Extraction of Metamaterial Parameters Based on Kramers-Kronig Relationship"

Abstract

The paper presents a numerical procedure for extracting the effective constitutive parameters of metamaterials. From the fact that the imaginary part of the refractive index is explicitly given by the magnitude of the transmission coefficient, while the real part is ambiguously defined by the phase of the transmission coefficient, the method above enforces causality to calculate the real part of the refractive index from its imaginary part by numerically integrating the Kramers-Kronig relation over a prescribed frequency range. The refractive index thus calculated for a metamaterial composed of split-ring resonator (SRR)-wire unit cells shows some discontinuities appearing on the covered frequency interval.