Microwave absorption properties of single- and double-layer absorbers based on electrospun nickel-zinc spinel ferrite and carbon nanofibers

Ni-Zn spinel ferrite nanofibers (NFs) with the chemical formula M-2x Ni0.5-x Zn0.5-x Fe2O4 (M = Co or Cu, and x = 0 or 0.1) and carbon nanofibers (CNFs) were fabricated through electrospinning technique and subsequent thermal treatment processes. Microwave absorption properties of single-layer and double-layer absorbers based on M-2x Ni0.5-x Zn0.5-x Fe2O4 NFs and CNFs were investigated in the frequency range of 2-18 GHz. The single-layer absorbers based on Ni-Zn spinel ferrite NFs show strong microwave absorbing abilities, and the minimum reflection loss (RL) for Ni0.5Zn0.5Fe2O4, Co0.2Ni0.4Zn0.4Fe2O4 and Cu0.2Ni0.4Zn0.4Fe2O4 NFs is - 77.5, - 57.8 and - 69.8 dB with a matching thickness of 5.0, 4.5 and 5.5 mm, respectively. The double-layer absorbers exhibit better absorption performances with a stronger microwave absorption and a wider effective absorption bandwidth (RL < - 10 dB) in comparison with the single-layer absorbers at the same thickness. The optimized double-layer absorber with a total thickness of 3 mm has an optimal RL value less than - 115.9 dB and a maximum absorption bandwidth of 12.4 GHz ranging from 5.6 to 18 GHz. While the corresponding single-layer absorber with a thickness of 3 mm has a minimum RL value of - 21.2 dB and an effective absorption bandwidth of 9.8 GHz. The significantly enhanced microwave absorption performance for double-layer absorbers should be attributed to the good cooperation effect of Ni-Zn spinel ferrite NFs (with high magnetic loss) and CNFs (with strong dielectric loss) as well as the improved impedance matching characteristics. It is expected that our double-layer absorbers can be a good reference for the design of new high performance microwave absorbing materials.