  Dynamic polarization control of light is essential for numerous applications
ranging from enhanced imaging to materials characterization and identification.
We present a reconfigurable terahertz metasurface quarter-waveplate consisting
of electromechanically actuated micro-cantilever arrays. Our anisotropic
metasurface enables tunable polarization conversion cantilever actuation.
Specifically, voltage-based actuation provides mode selective control of the
resonance frequency, enabling real-time tuning of the polarization state of the
transmitted light. The polarization tunable metasurface has been fabricated
using surface micromachining and characterized using terahertz time domain
spectroscopy. We observe a ~230 GHz cantilever actuated frequency shift of the
resonance mode, sufficient to modulate the transmitted wave from pure circular
polarization to linear polarization. Our CMOS-compatible tunable
quarter-waveplate enriches the library of terahertz optical components, thereby
facilitating practical applications of terahertz technologies.
