On the inapplicability of a negative-phase-velocity condition as a negative-refraction condition for active materials

TL;DR

This paper demonstrates that a negative-phase-velocity condition used for passive materials cannot be applied as a negative-refraction criterion for active materials, highlighting a fundamental limitation in current theoretical approaches.

Contribution

The study clarifies the inapplicability of a specific negative-phase-velocity condition to active materials, emphasizing the need for revised criteria in negative refraction analysis.

Findings

Negative-phase-velocity condition is invalid for active materials.

Current negative-refraction criteria do not extend to active media.

Highlights the necessity for new theoretical frameworks for active materials.

Abstract

A negative-phase-velocity condition derived by Depine and Lakhtakia [Microwave Opt Technol Lett 41 (2004) 315] for isotropic, homogeneous, passive, dielectric-magnetic materials is inapplicable as a negative-refraction condition for active materials.