Angular- and Polarization-insensitive Ultrathin Double-layered Metamaterial Absorber for Ultra-wideband Application

We proposed an ultra-thin polarization-insensitive metamaterial absorber (MMA) for ultra-wideband and wide incident angle operation. The MMA is composed of double-layer symmetric split rings (SSRs) connected with two orthogonally-arranged bars and the ground metallic plane separated by two identical substrates. Multiple metallic layers and scalabilities are employed to provide broadband absorptivity based on the cooperated mechanisms of the Ohmic loss and the Fabry-Perot interference. To further broaden the absorption bandwidth, four lumped resistors are loaded with the SSRs on the top metallic layer. By this means, an ultra-wideband absorbance is achieved nearly in 4~22 GHz, two gentle slope belts with absorptivity over 60% and 80% in 4~12 GHz and 12~22 GHz, respectively. The whole structure is with an ultrathin thickness of 2.4 mm, which is 0.032λ_low and 0.176λ_high corresponds to the lowest and highest absorption frequency separately. Meanwhile, the symmetric structure enables the MMA of satisfactory stability for polarization and wide incident angles. Numerical and experimental results prove the capability of the proposed MMA for ultra-wideband absorbance.