Polarization-insensitive and absorption-tunable ultra-broadband terahertz metamaterial absorbers based on multiple resonant rings

A polarization-insensitive and absorption-tunable ultra-broadband terahertz metamaterial absorbers based on multiple split resonance rings (SRRs) are designed. The single-layer structure is composed of top metal SRRs, intermediate dielectric layer and bottom metal plate. The mechanism of perfect absorption is explained by analyzing the distribution of electric field and surface current at the resonance points. The ultra-broadband absorption is realized by superposing numerous continuous single-band absorption. By optimizing the structural parameters, the results show that the designed structure can realize ultra-broadband absorption with average absorptance of 95.1% in the frequency range of 1.33 to 2.43 THz, with the bandwidth 1.1 THz. The absorptance of proposed absorber hardly changes under different polarization angles of the incident wave, which shows that the proposed asymmetric structure can also have the characteristics of polarization-insensitive. The absorption-tunable characteristic is obtained by replacing the bottom metal plate with phase change material VO2. By changing the ambient temperature in the range of 338 K to 358 K, in which the VO2 can be changed between the metal phase and the insulated phase, so as to realize the tunability of absorption. The results show that the designed absorbers can be widely used in many fields, such as terahertz switches and temperature sensors.