An Novel Ultra-thin Triple-band Polarization-insensitive Compact Metamaterial Absorber

An ultra-thin triple band polarization-insensitive metamaterial absorber has been presented in this paper. The unit cell of the proposed structure consists of two square rings in the top layer of metal-backed dielectric substrate and there are four gaps loaded on each ring symmetrically, what's more, through holes are used to connect the metal ground and the rings, so each ring is divided into four RC resonators. The incident wave in space will be restricted in the RC resonators and the energy will be absorbed by the dielectric substrate. It is shown that the absorber exhibits three distinct near-unity absorption peaks, which are distributed across S, C, X bands. We can just change the widths of the gaps to adjust the absorption frequency without changing other parameters. Owing to the symmetry, the absorber is insensitive to the polarization of the incident radiation. In addition, the absorber shows excellent absorption performance over wide oblique incident angles for both transverse electric and transverse magnetic polarizations. Simulated surface current and field distributions at the three absorption peaks are demonstrated to understand the absorption mechanism. Furthermore, parameter analyses are made to see how the dimensions of the absorber structure influence the frequencies and strength of the peaks of the absorption curve. The proposed ultrathin (similar to 0.0125 lambda(0), lambda(0) corresponding to the lowest peak absorption frequency) compact (0.125 lambda(0) x 0.125 lambda(0) corresponding to the area of a unit cell) absorber enables potential applications such as stealth technology, electromagnetic interference and spectrum identification.