Metamaterial-based Tunable Absorber in the Infrared Regime

In this paper, we present a design for a narrowband absorber based on metamaterials in the infrared wavelengths for wavelength-selective uncooled hyperspectral imaging systems. The proposed narrowband absorber integrated with microbolometer focal plane arrays has the potential to increase the detection sensitivity of the microbolometers. The design of the metamaterial unit cell consists of a resonant metallic 'cross' structure which has a resonance in the IR wavelengths and is placed on a dielectric substrate with a metal back plate. In order to achieve a very high absorption of the electromagnetic radiation, the designed metamaterial needs to have minimal transmission and reflection within its spectral response window. Minimal reflection is achieved through impedance matching of the metamaterial with the free space whereas zero transmission is ensured through the metal back plate. Moreover, for the purpose of hyperspectral imaging, the metamaterial structure is combined with a tunable electro-optic material, namely, liquid crystal. Tunability can be achieved upon applying a voltage across the combined liquid crystal and metamaterial structure thus bringing about a shift in the resonant frequency. In our simulated model, where losses of metal and dielectric substrate materials were taken into account, we noted more than ninety percent of absorption can be achieved in a narrow spectral window for the designed metamaterial structure.