A bi-layered quad-band metamaterial absorber at terahertz frequencies

In this work, a quad-band metamaterial absorber is proposed and experimentally demonstrated at terahertz frequency using a bi-layer isotropic structure. The absorber is designed by distributing four metallic square loops with different lengths on two polyimide layers (PI). The backside of PI is covered by an opaque gold film to eliminate the transmission of terahertz waves. The proposed absorber exhibits almost unity absorptions at 0.51, 0.69, 1.05, and 1.34 THz under the normal illuminance. As the incident angle increases from 0° to 50°, the absorption intensities remain above 95%, and the absorption frequencies almost keep stable for both transverse-electric and transverse-magnetic polarizations. The absorption mechanism is interpreted by giving the electromagnetic field distributions at each absorption peak. Experimental results show good agreement with numerical simulations both in the frequency and strength of the four absorption peaks.