Dual-layer ultra-thin polarization-insensitive metamaterial for ultra-wideband microwave absorption

This work proposes a dual-layer ultra-thin polarization-insensitive metamaterial for ultra-wideband microwave absorption. The proposed metamaterial absorber (MMA) consists of two resistive frequency selective surfaces (RFSS) constructed in a grounded dielectric substrate. The two RFSSs, although with the same unit cell periodicity, have different geometric patterns and significantly different surface impedances, resulting in distinct reflection, transmission and absorption properties. The independent electromagnetic simulations of the two RFSSs provide their reflection and transmission coefficients. Leveraging these simulation results, a detailed theoretical analysis based on interference theory predicts that the MMA can achieve ultra-wideband absorption. Numerical simulations demonstrate that the MMA achieves over 90% absorption from 4.3 to 31.3 GHz under normal incidence of arbitrarily polarized waves. Its total thickness is merely 5.3 mm, thus yielding a high bandwidth-to-thickness ratio (BTR) of 11.35. Moreover, the MMA exhibits good angular stability, for incident angle up to 60°, its absorptivity under TM wave incidence remains above 97% across the frequency band of 8.7-33.7 GHz. Finally, experimental measurements on a fabricated sample further validate the absorption performance of the MMA. Overall, the proposed MMA can achieve ultra-wideband absorption and has a higher BTR compared to numerous previous designs, making it highly attractive in practical applications.