  Metamaterials bring sub-wavelength resonating structures together to overcome
the limitations of conventional materials. The realization of active
metadevices has been an outstanding challenge that requires electrically
reconfigurable components operating over a broad spectrum with a wide dynamic
range. The existing capability of metamaterials, however, is not sufficient to
realize this goal. Here, by integrating passive metamaterials with active
graphene devices, we demonstrate a new class of electrically controlled active
metadevices working in microwave frequencies. The fabricated active metadevices
enable efficient control of both amplitude (> 50 dB) and phase (> 90{\deg}) of
electromagnetic waves. In this hybrid system, graphene operates as a tunable
Drude metal that controls the radiation of the passive metamaterials.
Furthermore, by integrating individually addressable arrays of metadevices, we
demonstrate a new class of spatially varying digital metasurfaces where the
local dielectric constant can be reconfigured with applied bias voltages.
Additionally, we reconfigure resonance frequency of split ring resonators
without changing its amplitude by damping one of the two coupled metasurfaces
via graphene. Our approach is general enough to implement various metamaterial
systems that could yield new applications ranging from electrically switchable
cloaking devices to adaptive camouflage systems.
