Polarization-insensitive and thin stereometamaterial with broadband angular absorption for the oblique incidence

A novel and thin stereometamaterial composed of an orthogonal double-split-ring microstructure, a plane ground with five hemispherical metric surfaces and a coating substrate is proposed and demonstrated to obtain a polarization-insensitive and broadband angular absorption. The mechanism of absorbing electromagnetic wave has been interpreted and investigated by the anti-reflection theory and the surface loss density for the oblique incidence. The absorbing characters have been improved by the five hemispherical metric grounds. The insensitive polarization is proved by the surface current distributions and the angular absorption. It exhibits a broadband angular absorbing range from 6.05 to 13 GHz with the absorption larger than 80 % at the incident angles of 45° theoretically and experimentally. For verification, a stereometamaterial sample with 576 cells is fabricated and measured. Consistent numerical and experimental results have both validated the broadband angular absorption. The design yields advantages of polarized insensitivity, broadband angular absorption and thin microstructure.