  In this paper we demonstrate, for the first time, selective thermal emitters
based on metamaterials perfect absorbers. We experimentally realize a narrow
band mid-infrared (MIR) thermal emitter. Multiple metamaterial sublattices
further permit construction of a dual-band MIR emitter. By performing both
emissivity and absorptivity measurements, we find that emissivity and
absorptivity agree very well as predicted by Kirchhoff's law of thermal
radiation. Our results directly demonstrate the great flexibility of
metamaterials for tailoring blackbody emission.
