Design of Metasurface Absorber with Four Unequal Rectangular Rings for Ultrawide THz Bandwidth

In this paper, a metamaterial absorber (MA) is proposed based on vanadium dioxide (VO2) having high absorption performance and high bandwidth in terahertz (THz) frequency range. The proposed metamaterial absorber has absorption efficiency over 90% in the frequency range from 2.45 THz to 7.23 THz with a bandwidth of 4.78 THz and the average absorption rate is 95.88% and the relative absorption bandwidth (RAB) is 98.76%. The proposed metamaterial absorber features a design with four rectangular rings of VO2 symmetrically arranged on a SiO2 dielectric substrate. We perform all numerical analyses keeping the phase-changing material VO2 in the metallic state. Our simulation results demonstrate that a larger bandwidth can be achieved in a significant way through structural parameter design and optimization. In order to determine the absorption performance of the proposed absorber, the electric-field distributions at different frequencies are observed, and the physical process underlying the absorber's performance is examined using interference cancellation and impedance matching theory. By adjusting the conductivity of VO2 from 200 S/m to 2 × 105 S/m, the design provides a broad tunable range from 6% to 100%, enabling reconfigurable features that are essential for flexible metamaterial absorbers. Additionally, for transverse electric (TE) mode and transverse magnetic (TM) mode polarizations, the absorber exhibits effective wide-angle absorption and polarization insensitivity. With its high bandwidth, polarization insensitivity, and tunability features, the proposed design is promising for various THz applications, such as in sensing and imaging technologies.