An ultra-broadband terahertz metamaterial absorber based on split rings array and island-shape structures

An ultra-broadband absorber is achieved by constructing novel island-shape structures on a single-layered broadband absorber. The single-layered absorber contains four same sized metallic split rings with different heights of the base. Its absorption goes beyond 98% from 1.82 THz to 3.70 THz and the full width at half maximum (FWHM) is 102.3% (from 1.47 THz to 4.55 THz), much better than these achieved by assembling multiple nested resonators. Then, by stacking novel island-shape structures over the single-layered absorber, we can excite 1-order magnetic response to precisely add a new peak near the broadband and enhance the bandwidth. The multi-layered absorber covers a bandwidth of 3.51 THz (the absorption over 90% from 1.23 THz to 4.74 THz) and the FWHM is up to 139.7%, far larger than previous reported results. It also performs well at considerably large oblique incident angles. Moreover, the island-shape structures have the potential to be applied in some other single-layered absorbers to widen their bandwidth.