numerical study of an ultra-broadband and polarization independence metamaterial cross-shaped fractal absorber

A three-dimensional cross-shaped fractal metamaterial absorber with ultra-wide wavelength band, polarization-independence and wide-angle, is numerically investigated by the finite-difference time-domain method. in this absorber, the solar energy is trapped by the cross-shaped fractal of the upper layer, and the si-ring filled with iron in the middle layer and the wavelength band can be broadened by the self-similarity of fractal structure. the absorber exhibits absorptivity higher than 91% for the wavelengths from 400 to 2000 nm and an absorption bandwidth of about 133%. furthermore, the proposed absorber realizes polarization independence, and the maximum incident angle is 76°. however, as the iron material applied in the nano-metamaterial absorber (nma) can be easily oxidized and rusted, it is replaced by nickel with characteristics such as corrosion resistance and high-temperature resistance; thus, an improved nma is obtained. the improved absorber not only eliminates the corrosion-prone defects of the above proposed structure but also maintains polarization independence and high absorption and widens the angle of incidence up to 79° and thereby can be applied in many areas, such as solar energy harvesting.