Experimental and analytical investigations on a wide-angle, polarization-insensitive, and broadband water-based metamaterial absorber

In this work, a wide-angle, polarization-independent, and broadband superstrate-assisted water-based metamaterial absorber (SWMA) covering the whole X-band is theoretically and experimentally demonstrated. Our SWMA design is a copper-backed structure comprising a thin substrate of distilled water, an FR-4 lossy layer, and a magneto-electric anisotropic metamaterial to boost achieving broadband and wide-angle features. The absorptivity of the proposed SWMA has been elaborately assessed in a full analytical framework involving oblique illuminations and both transverse electric (TE) and transverse magnetic (TM) polarizations. Numerical results demonstrate that exploiting magneto-electric anisotropy, the impedance matching between air and SWMA has been remarkably improved for both major polarizations, especially at near grazing angles. Owing to the end-to-end analytical design, the designed SWMA does not suffer from the drawbacks associated with the traditional designs including intricate particle geometries and brute-force optimizations. As a proof of concept, the proposed SWMA is fabricated and its absorptivity is measured in an anechoic microwave chamber between 8 and 12 GHz. The experimental results depict good conformity with the numerical simulations and the theoretical predictions, elucidating that our design retains its strong absorptivity over the whole X-band and for a wide angular range up to near grazing angles for both TE- and TM-polarizations.