  Motivated by the idea of smart metasurfaces, we will demonstrate a
graphene-based tunable absorber in which perfect absorption can be achieved for
all angles of incidence, only by tuning the Fermi level of graphene. We place
an unpatterned graphene sheet on a mushroom-type high impedance surface whose
resonant frequency is stable for all incident angles. For TM-polarization,
perfect absorption can be realized from normal to grazing incidence at the same
frequency when modulating the Fermi level of graphene from 0.18 eV to 1 eV.
