Reflection-enhanced terahertz beam steering via a backside-driven metasurface enabled by dielectric-superstrate matching

Actively tuned metasurfaces have emerged as a key enabling technology for terahertz (THz) beam steering, owing to their outstanding capability for dynamic and flexible wavefront modulation. However, most existing devices feature a metal-dielectric-metal configuration from front to back, which imposes constraints on structural simplicity and active control integration. Here, a backside-driven active metasurface is proposed for reflected THz beam steering, composed of a dielectric superstrate and rear-mounted meta-atoms integrated with vanadium dioxide (VO₂) switches. Based on transmission line theory, its interface impedances in the ON and OFF states are analyzed to realize both enhanced reflection and large-range phase modulation using single-layer meta-atoms. By matching the thickness of the dielectric superstrate, this design achieves a 1-bit phase shift of 180° around 0.34 THz through toggling the VO₂ switches. With array arrangements according to specific 1-bit coding sequences, the experiment demonstrates that the THz beam can be accurately reflected towards designated angles and subsequently redirected to specular reflection when all VO₂ switches transition to the ON state. This work presents a simplified architecture that allows backside control integration without disturbing the front-side beam steering, providing a meaningful step forward in THz metasurface-assisted communications, detections, and imaging.