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A four-band terahertz metamaterial absorber is proposed in this paper. The metamaterial absorber is based on a traditional "sandwich" structure, with structural units arranged in a honeycomb periodic arrangement in a plane. By using resonant structures of different sizes and selecting the appropriate array mode, the effect of multi-band absorption can be realized. This solves the limitation of poor frequency selectivity and low sensitivity of a single narrow-band absorption peak in terahertz detection applications. The electromagnetic properties of the metamaterial were calculated numerically by the finite element method, and four narrow-band perfect absorption peaks were obtained after parameter optimization. The results show that the absorption rates of the incident electromagnetic wave at 0.208 THz, 0.393 THz, 0.519 THz and 0.697 THz reach 97.27%, 96.69%, 99.37% and 99.33%, which has the characteristics of narrow absorption band and high absorption rate. According to the equivalent medium theory and the surface current mode analysis method, the physical mechanism of narrowband absorption is analyzed. The sensing performance of the metamaterial is significantly improved, with the figure of merit (FoM) reaching 4.55 and the Q value reaching 25. It has good polarization stability due to the high symmetry of the elements. And in the case of large incidence angle, it has good angular stability. Compared with the reported performance of metamaterial sensors, the sensing performance of the metamaterials proposed in this paper has been significantly improved, and it has potential application value in sensing, detection, etc.
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