Material equations and Maxwell’s equations for isotropic media; waves with negative group velocity and negative values of ε (ω) and μ(ω)

Abstract

The frequently used Maxwell’s equations that contain E, B, D, and H fields are only substantiated in the framework of linear material equations and for isotropic media alone. We have shown that accounting for the deviation of magnetic permittivity μ (ω) from unity in the usually employed dispersion equation implies a false precision. Therefore, if spatial dispersion is disregarded, transverse waves only exist in the energy region where ε(ω) > 0 and have a positive group velocity.