Hybrid VO2-graphene bi-functional digital metasurface for beam steering and dual-band absorption

The evolution of sixth-generation wireless communications demands advanced metasurfaces capable of precise beam steering and adaptive electromagnetic (EM) wave absorption to enhance signal quality and mitigate interference. In this work, we present a programmable and reconfigurable digital THz-metasurface, engineered through the integration of metal patch, graphene wire grid, and a vanadium dioxide (VO2)-based square ring to switch between dynamic beam steering (ON-state) and EM wave absorption (OFF-state). In the former state, without physically altering the patch dimensions to create a required phase gradient in the metasurface, here the idea of digitally increasing the patch dimensions only by changing the crystallization level of the VO2 ring is proposed. Consequently, a programmable and reconfigurable coding metasurface by digitally changing the arrangement of coding sequence is achieved that can shift the mainlobe of the reflected EM wave from 0° to 40°. Remarkably, in the OFF-state, a dual-band EM wave absorption is observed based on a dual mechanism including tunable crystallinity level of the VO2 ring, and the Fermi energy of the patterned graphene. In addition, in the OFF-state, the performance of the absorber is investigated by increasing the angle of incidence. The results of detailed full-wave simulations are compared and verified by analytical modeling based on an array antenna theory and an equivalent electric circuit model. The presented structure is a strong candidate for integration into future Reconfigurable Intelligent Surfaces platforms, sensing and imaging systems in the THz band.