Design of a 1-Bit, 28-GHz Liquid-Metal Reflective Metasurface for Anomalous Beam Steering

Abstract

5G-and-beyond wireless networks may require passive or active reflective metasurface (RM) technologies to overcome high path loss and increased scattering at mm-wave frequencies. Traditional RMs provide a low-power and scalable solution to the integration challenges of devices in massive input multiple-output (MIMO) communication systems. As such, liquid metals (LMs) have recently been investigated as a viable phase-tuning mechanism for passive RMs, offering high amounts of reconfigurability. However, current LM RM designs rely on precisely maintained operating conditions, limiting practical implementation. This work presents a 1-bit LM RM, designed for 28-GHz operation, that achieves two metastable states with 180° of phase difference. Constant-volume Galinstan slugs are positioned in sealed microfluidic channels to control phase. Thus, phase control of individual unit cells is achieved without the need for continuous external stimuli or varying injection volumes. A fabricated 8 × 8 array demonstrates an anomalous reflection angle of 38° ± 4°, closely matching simulations which predict a main azimuthal beam at 40°. Additionally, in a virtual line-of-sight blockage scenario, the LM RM improves reception by a maximum of 13 dB compared to a standard reflective surface. Thus, a practical design addressing the limitations of previous LM RMs is presented.