Dual-band perfect absorbers based on the magnetic resonance and the cavity resonance

An infrared (IR) absorber based on the metamaterial structure is proposed theoretically and numerically. The near-unity absorption can be achieved at a certain wavelength by optimizing geometrical parameters of the structure. Moreover, we can switch a single-band absorber to dual-band absorber by decreasing the thickness of top metallic layer which is perforated by an air-filled ribbon. At the same time, we confirm that the mechanism of this two absorption bands is completely different. The simultaneous effects of the magnetic resonance and the cavity resonance occur at our proposed structure. Besides according to the control of polarization direction, the absorption peaks occur at the two constant wavelengths, and the superposed value of this two absorption peaks is always close to a constant. Based on this phenomenon, a simple dual-band absorber is designed when the thickness of top shaped metallic film is relatively large. The cavity response is not the existence in this condition. These results that we obtain may provide some promising applications such as sensors, thermal imagers, and IR detectors.