Electromagnetic Wave Absorption Properties of Core Double-Shell Structured α-Fe(Si)@Fe3O4@SiO2 Composites

Core double-shell hierarchical structured α-Fe(Si)@Fe3O4@SiO2 (FFS) microwave absorbing composites have been fabricated by high-temperature mechano-chemical method. Heterogeneous interfaces of Fe/Si, α-Fe(Si)/Fe3O4, Fe3O4/SiO2 and high-density defects were formed by coupling the controlled temperature field and mechanical force. A dramatic reduction in the average particle size of the composite powder was caused by increasing ball-to-powder ratio. Electromagnetic wave absorption (EMWA) performance of the FFS composites was investigated in the 2–18 GHz frequency range. A balance of impedance matching and strong attenuation characteristics was achieved due to the asymmetric charge distribution at the heterogeneous interfaces, high-density defects, natural resonance, and exchange resonance of the FFS composites. When the ball-to-powder ratio is 40:1, the minimum reflection loss (RLmin) of the FFS composite is −47.04 GHz at a frequency of 5.28 GHz with an absorption layer thickness of 3.1 mm. A broad effective absorbing bandwidth (EAB, RL < −10 dB) of 5.6 GHz (12.4–18 GHz) with a thickness of 1.3 mm covers almost the entire Ku-band. After annealing at 1173 K in an argon atmosphere, the FFS composite with 30:1 ball-to-powder ratio shows excellent EMWA performance in the S-band, where the RLmin reaches −50.18 dB at 2.88 GHz with a thickness of 5.0 mm.