A tunable polarization insensitive ultra-broadband absorber based on the plasma metamaterial

In this article, we proposed a tunable polarization insensitive ultra-broadband absorber (TPIUA) in THz band make use of the plasma metamaterial, which is the solid state plasma. Because the foments of solid state plasma can be controlled by the external voltage, such an absorber can reach tunability. With different resonators being energized, different absorption states can be realized. When all the resonators are at excited state (state 1), the proposed TPIUA can reach an ultra-broadband absorption and the absorption region which is over 90% is from 7.18 THz to 14.29 THz. The corresponding relative bandwidth is 66.2%. If the middle and out resonators are energized (state 2), the proposed absorber can form an absorption region which is 8.42-12.81 THz (the absorptivity is above 90%), and its relative bandwidth is 41.4%. Besides, if all the resonators are nonenergized, the TPIUA can form four absorption frequency points whose absorptivities exceed 90%. And these absorption frequency points are 8.14 THz, 12.12 THz, 14.09 THz and 14.35 THz. Their absorptivities are 98.0%, 98.5%, 95.7% and 93.9%. If the incident angle is not larger than 20 degrees, the absorber can achieve the stable absorption. The surface current distributions of such a TPIUA are shown to expound the physical mechanism. Besides, to analyzing the absorption mechanism of the TPIUA, we also give the electric fields and power loss densities. The reconfigurable device can be realized by tailoring the state of the solid state plasma.