A New Condition to Identify Isotropic Dielectric–magnetic Materials Displaying Negative Phase Velocity

Non–dissipative mediums with both simultaneously negative permittivity and permeability were first investigated by Veselago [1] in 1968. These mediums support electromagnetic wave propagation in which the phase velocity is antiparallel to the direction of energy flow, and other unusual electromagnetic effects such as the reversal of the Doppler effect and Cerenkov radiation. After the publication of Veselago’s work, more than three decades went by for the actual realization of artificial materials that are effectively isotropic, homogeneous, and possess negative real permittivity and permeability in some frequency range [2, 3].