simplified design of quad-band terahertz absorber based on periodic closed-ring resonator

Multiple-band metamaterial absorbers as an important branch of metamaterial-based resonant devices have shown considerable application prospects in real life. however, current designs have many shortcomings in the realization of multiple-band absorption, including complex pattern structure, time-consuming fabrication steps, and strong interaction between sub-elements. herein, a simple design of multiple-band metamaterial absorber based on single metallic resonator is presented. basic cell of the multiple-band absorption is formed by a square metallic patch (cut by a concentric air gap) placed on a metallic mirror separated by an insulating medium material. the metamaterial structure can interact strongly with the incident beam to produce the fundamental mode resonance, third-order resonance, and two other resonances resulted from the concentric air gap introduction. the combining effect of the four discrete resonance modes provides the ability to achieve quad-band absorption. the quad-band absorption shows great dependence on the structure dimensions. based on this, we further design a kind of multiple-band absorption having the adjustable number of absorption peaks by introducing photosensitive silicon material in the initial area of the air gap. the number of resonance peaks can be tuned flexibly from quad-band absorption to dual-band absorption by changing the conductivity (i.e., material property) of photosensitive silicon material.