Multi-band Polarization-insensitive Terahertz Metamaterial Absorber Based on Composite Circular Ring Structure

In this paper, we demonstrate a multi-band and polarization insensitive terahertz metamaterial absorber (MA) using flexible polyimide material. Based on metal-insulator-metal (MIM) configuration, a novel composite circular ring structure is proposed, and five absorption bands are generated. Due to the high symmetry of the structure, the designed absorber is insensitive to polarization. The proposed MA achieves absorption rates of 80.92%, 85.81%, 99.57%, 99.53%, and 99.44% at 0.681 THz, 0.715 THz, 0.815 THz, 0.947 THz, and 0.977 THz, respectively, under normal TE and TM polarized incidence. Impedance matching theory is applied to explain the physical mechanism of the absorption peak. The retrieved effective impedance is analyzed, and the results are consistent with each absorption peak. Compared with other reported structures, the proposed absorber achieves more absorption bands on a single-layer substrate.