Optically Transparent Broadband Microwave Absorption Metamaterial By Standing-Up Closed-Ring Resonators

Optically transparent metamaterial microwave absorbers (MMAs) developed so far unexceptionally encounter an intrinsic contradiction between extending the absorption bandwidth and improving optical transparency, hindering their practical applications. This work, in its experiment and calculation, demonstrates an MMA with both broadband microwave absorption and excellent optical transparency by standing-up closed-ring resonators (CRRs) in an indium tin oxide backed Plexiglas board. The as-designed MMA shows a strong microwave absorption of 85% covering a wide frequency of 5.5-19.7 and 22.5-27.5 GHz up to a large incident angle of 70(o) due to the electric and magnetic resonances caused by the standing-up arrangement of the CRRs, as well as the multiple reflection mechanism. Moreover, in sharp contrast to the widely adopted stacking multiple layers at the expense of greatly reduced optical transparency, it has an optical transmittance of around 82%, as calculated by a transfer matrix method. The standing-up MMA proposed here provides an effective way to achieve broadband microwave absorption and high compatibility with optical transparency, enabling wide applications in window glass of stealth armament and electromagnetic compatible buildings/facilities.