Tunable four-band metamaterial absorber and sensor based on a stacking double-ring Dirac Semimetal structure design

We proposed a novel fourfold narrow-band terahertz absorber based on a double-ring Dirac semimetal (BDS) layout. The designed structure exhibits a three-layer pattern of a double-ring layer of BDS, a SiO2 dielectric layer and a perfect electric conductor (PEC) layer. The BDS-based absorber is highly tunable, its conductivity can be tuned by varying the applied bias voltage, which subsequently alters the field distribution and absorption feature. By employing the Finite Element Method (FEM) of CST STUDIO SUITE, the absorption characteristics are thoroughly investigated. The simulation results revealed that the absorber exhibited remarkable absorption performance, with nearly perfect absorption rates of 99.9 %, 98.7 %, 99.4 %, and 99.9 % at frequencies of 6.836 THz, 7.700 THz, 8.728 THz, and 9.362 THz, respectively. The quality factor (Q) values of the four absorption modes are calculated as 227.9, 167.4, 101.48, and 102.9, respectively. The influence of various factors, including geometric structural parameters and the incident angle of electromagnetic waves, is comprehensively studied. The absorber exhibited excellent polarization insensitivity owing to its structural symmetry. When the Fermi energy of the BDS is tuned from 80 to 100 meV, the absorption frequencies could be tuned within a specific range, resulting in an excellent absorption effect. Additionally, the refractive index sensitivity (S) is defined, and for the four absorption modes, it is determined to be 503.2 GHz/RIU, 871.0 GHz/RIU, 696.0 GHz/RIU, and 122.0 GHz/RIUwhen the refractive index varies within a specific range. Our design achieves superior refractive index sensitivity (871.0 GHz/RIU) and maintains four-band absorption without structural complexity, enabling multifunctional sensing applications.This high-performance absorber holds great potential in the frontier fields of biochemical sensing and environmental detection.