Polarization insensitive eye-shape enclosed split ring resonator-based multi-band metamaterial absorber/sensor for S, C, X, Ku, and K-band microwave applications

This article proposes an eye-shape enclosed split ring resonator (ESE-SRR) based metamaterial absorber for multi-band microwave applications with high absorption levels. Four-fold rotational symmetric eye-shaped electrical resonators form the structure of the proposed metamaterial absorber (MMA) to achieve polarisation-insensitive characteristics. Eight near-unity absorption peaks between S, C, X, Ku, and K-band are achieved, where peak absorptions are attained at 3.349 GHz, 5.06 GHz, 6.829 GHz, 9.178 GHz, 14.54 GHz, 17.96 GHz, 18.89 GHz, and 20.4 GHz with absorption levels of 99.8%, 99.7%, 92.9%, 99.1%, 96.4%, 93.3%, 91.3%, and 99.35%, respectively. The electrical dimension of the unit cell is 0.112 lambda min x 0.112 lambda min x 0.018 lambda min, making it a subwavelength compact structure for oblique incident angle stable absorption behaviour. The absorption characteristics are also investigated with metamaterial properties, surface current, and electromagnetic field distributions. The designed MMA is validated by prototype fabrication and measurement, which shows good agreement with simulation results. Finally, the proposed MMA shows an electrically compact structure with eight near-unity absorption peaks and polarisation insensitivity, which makes it an attractive candidate for absorption, sensing, radar cross-section reduction, etc.