  Switchable metamaterials offer unique solutions for efficiently manipulating
electromagnetic waves, particularly for terahertz waves, which has been
difficult since naturally occurring materials rarely respond to terahertz
frequencies controllably. However, few terahertz modulators demonstrated to
date exhibit simultaneously low attenuation and high modulation depth. In this
letter we propose a new class of electrically-tunable terahertz metamaterial
modulators employing metallic frequency-selective-surfaces (FSS) in conjunction
with capacitively-tunable layers of electrons, promising near 100% modulation
depth and < 15% attenuation. The fundamental departure in our design from the
prior art is tuning enabled by self-gated electron layers that is independent
from the metallic FSS. Our proposal is applicable to all possible electrically
tunable elements including graphene, Si, MoS2, oxides etc, thus opening up
myriad opportunities for realizing high performance switchable metamaterials
over an ultra-wide terahertz frequency range.
