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

A negative-phase-velocity condition derived by Depine and Lakhtakia (Microwave Opt Technol Lett 41 (2004) 315–317) for isotropic, homogeneous, passive, dielectric-magnetic materials is inapplicable as a negative-refraction condition for active materials. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1230, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24289