Carbonyl iron/graphite microspheres with good impedance matching for ultra-broadband and highly efficient electromagnetic absorption

Composite microspheres with carbonyl iron cores and graphite shells are prepared by a mechanical ball milling method. The microwave absorption properties of these microspheres are investigated in terms of complex permittivity and permeability, impedance matching property, and reflection loss. The morphology and conductivity of the graphite can be well tuned by controlling the milling time to achieve the improvement in its impedance matching characteristics. In addition, by integration of the composition and unique structure, the carbonyl iron/graphite microspheres possess better absorption properties than milling graphite. The microspheres show highly strong electromagnetic wave (EMW) absorption with a minimum reflection loss (RL) of −55.2 dB, which could be attributed to the good impedance matching and effective complementarities between magnetic and dielectric components. More importantly, the qualified frequency bandwidth of the absorber is up to 9.7GHz (8.3-18GHz) with a matching thickness of 2.1mm. The results indicate that carbonyl iron/graphite microspheres may be excellent candidate materials for EMW absorption applications.