Perfect electromagnetic conductor
  In differential-form representation, the Maxwell equations are represented by simple differential relations between the electromagnetic two-forms and source three-forms while the electromagnetic medium is defined through a constitutive relation between the two-forms. The simplest of such relations expresses the electromagnetic two-forms as scalar multiples of one another. Because of its strange properties, the corresponding medium has been considered as nonphysical. In this study such a medium is interpreted in terms of the classical Gibbsian vectors as a bi-isotropic medium with infinite values for its four medium parameters. It is shown that the medium is a generalization of both PEC (perfect electric conductor) and PMC (perfect magnetic conductor) media, with similar properties. This is why the medium is labeled as PEMC (perfect electromagnetic conductor). Defining a certain class of duality transformations, PEMC medium can be transformed to PEC or PMC media. As an application, plane-wave reflection from a planar interface of air and PEMC medium is studied. It is shown that, in general, the reflected wave has a cross-polarized component, which is a manifestly nonreciprocal effect. 
Ismo V. Lindell, Ari Sihvola