Ultra-broadband Tunable Terahertz Absorber Based on Hollow Fan Patterned VO<sub>2</sub> Metamaterials

A novel design of ultra-broadband tunable terahertz (THz) absorber based on hollow fan patterned VO<sub>2</sub> metamaterials is proposed and investigated. Our designed metamaterial absorber (MA) is aimed at expanding the absorption bandwidth, simplifying the structure and reducing the volume as much as possible. It is really proved from simulation results that the proposed MA has not only simple structure and small volume but also ultra-broadband absorption above 90% ranging from 2.92 THz to 10.05 THz. Comparing with previous studies, the proposed MA greatly improved its performances in several aspects of absorption bandwidth, tunable range, simple structure and small volume. Increasing the VO<sub>2</sub> conductivity from 200 S/m to 2×10<sup>5</sup> S/m, the absorption rate of proposed MA rapidly increases from 1.2% to 99.2%, thus the proposed MA has the high tuning performance with maximum modulation depth of 98.8%. We also investigate the absorption origin of proposed MA by using the electric field distributions. The proposed MA achieves the ultra-broadband absorption by the fundamental resonance and high-order resonances of hollow fan VO<sub>2</sub> pattern. In addition, all the influences of polarization angle, incidence angle and geometrical parameters on the ultra-broadband absorption are analyzed in detail. Our designed MA may be widely utilized for practical applications of THz technology.