Effect of FeCoB-SiO $_2$ -Film-Based Fractal Frequency Selective Surface on the Absorption Properties of Microwave Absorbers

The effects of FeCoB-SiO₂ -film-based fractal frequency selective surface (FSS) on the absorption properties of multilayer microwave absorbers (MMA) were investigated in detail. These magnetic films were prepared in argon pressure by radio frequency magnetron sputtering targets of SiO₂ and Fe₄₀Co₄₀B₂₀. Laser etching was used to fabricate FSS samples using the prepared magnetic films (SFSS) and comparative nonmagnetic aluminum film (AFSS). The reflection properties of the MMAs were measured in the range 2-18 GHz. The combined samples decreased the reflectivity by 50% and increased the bandwidths under -5 dB by 100% by substituting SFSS for AFSS, with the absorbing peak frequencies almost kept unchanged. The 0.67-mm-thick MMA samples that SFSS and AFSS both used could further enhance the minimum peak vale to -9.84 dB and broaden the bandwidth under -5 dB to 5.36 GHz. As a consequence, magnetic-film-based fractal FSSs are able to strongly improve absorption characteristics in microwave absorbers.