We have proposed a novel double-layer microwave absorber based on spinel ferrite Ni0.8Co0.2Fe2O4 nanofibers (NCFO NFs) and Ni-C hybrid NFs prepared via a facile electrospinning method combined with subsequent heat treatment. Electromagnetic and microwave absorption properties of the double-layer microwave absorbers, together with those of the single-layer ones, were systematically investigated in the frequency range of 2–18 GHz. The double-layer absorbers consisting of 50 wt% NCFO NFs/paraffin composite and 5 wt% Ni-C NFs/paraffin composite show superior microwave absorbing performance with stronger absorption and broader bandwidth as compared with the corresponding single-layer ones and many reported double-layer ones. As 1.5 mm thick NCFO NFs composite is used as the matching layer and 0.8 mm thick Ni-C NFs composite is employed as the absorption layer, the optimal reflection loss (RL) of the absorber reaches −84.9 dB at 17.0 GHz with an effective absorption bandwidth below −10 dB of 7.4 GHz ranging from 10.6 to 18 GHz. The enhancement of microwave absorption in the double-layer absorbers should be mainly ascribed to the improvement of impendence matching characteristics due to the efficient coupling and synergistic effect between two layers. These excellent properties demonstrate that our double-layer structures offer a new route to design microwave absorbers with lightweight and high absorption performance over a broad frequency range.
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