Optically Transparent 3-Octave Microwave Absorber Designed with Slotted-Annular Metasurfaces

A broadband optically transparent slotted-annular metasurface microwave absorber (SAMMA) is proposed and demonstrated to work in the C, X and Ku bands (6–18 GHz). Its absorbing mechanism is attributed to the new slotted-annular metasurface structures designed on the top indium tin oxide resistive film, which exhibit interesting dual-resonant-absorptions at 7.28 and 16.54 GHz, respectively. By further optimizing the metasurface structure, the dual-resonant-absorptions evolve to desirable broadband characteristics covering 5.98–17.96 GHz. The SAMMA is ultra-thin such that its total thickness is only 3.8 mm or 0.076λ_L, where λ_L is the wavelength at 5.98 GHz. In addition, the new 3-octave absorber is polarization-insensitive and can work for wide-angle oblique incidences up to ± 45°. The SAMMA is all made of transparent materials, which can be well integrated with current optical windows, providing good transmission for visible light and meanwhile screening from unwanted microwave interferences.