  In this work, we numerically demonstrate an infrared frequency-tunable
selective thermal emitter made of graphene covered SiC deep gratings. Full-wave
simulation shows temporally-coherent emission peak associated with magnetic
polariton, whose resonance frequency can be dynamically tuned within the phonon
absorption band of SiC by varying graphene chemical potential. An analytical
inductor-capacitor circuit model is introduced to quantitatively predict the
resonance frequency and further elucidate the mechanism for the tunable
emission peak. Moreover, by depositing multiple layers of graphene sheets onto
the SiC deep gratings, a large tunability of 8.5% in peak frequency can be
obtained to yield the coherent emission covering a broad frequency range from
820 1/cm to 890 1/cm. The novel tunable met-amaterial could pave the way to a
new class of tunable thermal sources in the infrared region.
