Design and theoretical analysis of a tunable bifunctional metasurface absorber based on vanadium dioxide and photoconductive silicon

A tunable bifunctional metasurface absorber based on vanadium dioxide (VO2) and photoconductive silicon (PSi) is proposed in terahertz (THz) band. When the conductivities of VO2 (vo2) and PSi (PSi) are 10 S/m and 1×105 S/m, the designed absorber has a function of dual-broadband absorption. The absorptivity over 90% is in the dual-broadband of 2.47-3.71 THz and 8.90-10.62 THz, corresponding relative bandwidths (RBs) are 40.13% and 17.62%, respectively. When vo2 and PSi are equal to 2×105 S/m and 1×105 S/m, the proposed design has a function of single-broadband absorption. More than 90% absorptivity is achieved in 4.69-7.72 THz (RB=48.83%). Furthermore, the absorptivity under dual- and single-broadband is manipulated by changing PSi. Impedance matching theory, equivalent transmission-line (TL) model and electric field distribution are used to reveal the tunable bifunctional absorption mechanism. The influences of structure parameters, polarization mode and incidence angle on the dual- and single-broadband absorption are investigated. The dual- and single-broadband absorption performance is maintained within the incident angles of 55° and 60°, which also possesses polarization insensitivity. The proposed absorber has a potential application value in multifunctional devices such as modulation, sensing and electromagnetic (EM) stealth.