Design of a Four-Band and Polarization-Insensitive Terahertz Metamaterial Absorber

We present a four-band and polarization-insensitive terahertz metamaterial absorber formed by four square metallic rings and a metallic ground plane separated by a dielectric layer. It is found that the structure has four distinctive absorption bands whose peaks are over 97% on average. The mechanism of the four-band absorber is attributed to the overlapping of four resonance frequencies, and the mechanism of the absorption is investigated by the distributions of the electric field. In particular, the frequency of each absorption peak can be flexibly controlled by varying the size of the corresponding metallic ring. The proposed concept is applicable to other types of absorber structures and can be readily scaled up to the structures that are working in the microwave frequency range. Moreover, the characteristic of the design can be used to design a five-band metamaterial absorber by adding one more metallic ring. The proposed absorber has potential applications in detection, imaging, and stealth technology.