A dynamically tunable four-narrowband terahertz absorber based on Dirac semimetal for perfect absorption and high sensitivity

Multi-band terahertz metamaterial absorbers are essential in modern scientific research and practical applications, with broad usage in areas such as biomedical sensing, high-precision spectroscopy. This study presents a four-band tunable narrowband terahertz absorber utilizing Dirac semimetal (BDS), offering dynamic tuning capabilities and high absorption efficiency. It is demonstrated that the absorber achieves over 96 % perfect absorption across four bands in the range of 0.1-2.4 THz, with two peaks exceeding 99 % absorption. The designed absorber exhibits excellent dynamic tunability, enabling adjustment of the absorption frequencies and rates of the four modes by modulating the Fermi energy level of BDS. The absorption mechanism is studied through impedance matching theory and near-field distribution, while coupling and perturbation theories are used to analyze how the top layer's structure affects the resonance frequency. Additionally, for refractive index detection of analytes, the results show that the narrowband absorber exhibits excellent capabilities with a sensitivity of up to 145 GHz/RIU and a quality factor (Q) of 77. These features enable the absorber suitable for broader applications, including stealth technology, medical diagnostics, and terahertz communications.