Fig. 1: The dielectric response models for conventional dielectric materials and for metamaterials.
From: 2nd-Order Debye relaxation in electromagnetic metasurfaces for wideband dispersion engineering
For conventional dielectric materials, there are three types of polarization models: the Drude model for collective oscillation of free electrons, the Lorentz model for local resonance of electric dipoles, and the Debye model for the relaxation process of dipole orientation. In contrast, for metamaterials, there are only two models: the Drude model for infinitely long wires and the Lorentz model for resonant structures (e.g., short metallic wires and split-ring resonators (SRRs)). The relaxation model is absent in metamaterial research
