Equivalent Circuit Analysis of Super-Planckian Emission into Far Field
  Using our recently developed equivalent circuit model of radiative heat transfer we analyze the far-field thermal emission from bodies of constrained dimensions. We prove that the power radiated by a hypothetical metamaterial emitter which is conjugate matched with all the harmonics of the emitted field at a given wavelength can be infinitely higher than the power emitted by an ideal black body of the same radius. However, for optically large bodies, fulfilling the conjugate match conditions for higher-order harmonics is not a trivial task, which effectively limits the far-field radiated power by the well-known Planck law. 
Stanislav I. Maslovski, Constantin R. Simovski
physics.optics