Numerical study of a wide incident angle- and polarisation-insensitive microwave metamaterial absorber based on a symmetric flower structure

In this study, we propose a wide incident angle- and polarisation-insensitive metamaterial absorber covered with structures comprising a metallic flower shape layer, a dielectric layer and a metallic ground plane. The influences of the structural parameters on the absorptivity are investigated numerically. The proposed absorber exhibits polarisation insensitivity as the number of symmetric petals of a flower shape reaches as high as 4, 6 and 8. Particularly, the absorber based on 8 petals shows an absorptivity of above 90% for wide incident angles up to 70° under transverse electric and transverse magnetic polarisations. The physical mechanism of these observations is clarified by investigating the electric, power loss density and induced current distributions, which is also supported by the retrieved constitutive electromagnetic parameters. That is, the absorption phenomenon is considerably affected by magnetic resonance. By modifying the petals into hollow shapes, the absorber becomes effective in confining the magnetic resonance and can thus minimise the resonant frequency variation to 0.22% without affecting the absorption performance. In comparison with other reported metamaterial absorbers, our design shows considerable practical feasibility in terms of resonant frequency stability, wide incident angle and polarisation insensitivity, thereby making it suitable for various applications in microwave frequency region.