Broadband terahertz metamaterial absorber based on simple multi-ring structures

Single-layer metallic rings are the effective structure cell which are widely used to design single-band and multiband perfect metamaterial absorbers owning to their electromagnetic resonance. However, the absorbers based on the single-layer metallic rings have a common shortcoming, that is the narrow absorption bandwidth. To overcome the limitations, here we proposed a single-layer, flexible and broadband terahertz metamaterial absorber, which consists of four sub-cells with multiple metal rings and a metal ground plane separated by a dielectric layer. By enhancing the coupling response between adjacent metallic rings and merging the adjacent resonant peaks of multi-resonators, we experimentally observed broadband characteristics at the terahertz band. The average absorption of 88% from 0.63 to 1.34 THz and the relative absorption bandwidth of 95% at the incident angle of 15o for TE polarization. Correspondingly, for TM polarization the absorption of more than 80% from 0.61 to 1.1 THz with the relative absorption bandwidth of 80% were also observed. The results went far beyond the previous single-layer absorbers based on metal rings and were much better than the fractal-cross structure reported recently [Kenney et al., ACS Photonics 4, 2604 (2017)]. We had reason to believe that the presented terahertz metamaterial absorber with broad absorption bandwidth and simple structure can find important applications in communication, stealth, energy harvesting systems and so on. (C) 2018 Author(s).