Fe3O4@C 3D foam for strong low-frequency microwave absorption

Low-frequency microwave absorbing materials have been challenging for many years. Three-dimensional dielectric/magnetic porous materials are beneficial for improving the low-frequency microwave absorbing performance because of natural resonance and improved impedance matching. In this study, Fe3O4@C 3D foam was prepared by carbothermal reduction method and the microwave attenuation performances and mechanisms were studied. By adjusting the content of Fe3O4@C 3D foam in paraffin composites, the low-frequency microwave attenuation capacity could be effectively optimized. The minimum reflection loss (RLmin) of paraffin composite with 40% (in mass fraction) loading exhibits −54.7 dB at 4.1 GHz for a thickness of 4.0 mm. Surprisingly, the paraffin composite with 50% (in mass fraction) loading could almost cover 2–4 GHz (S-band) in the thickness range of 3.5–5.5 mm. The strong low-frequency microwave attenuation property of Fe3O4@C 3D foam is mainly attributed to excellent low-frequency impedance matching, natural resonance, interfacial/dipole polarization, multiple reflection and scattering. This method provides a new perspective for preparing lightweight and high performance low-frequency microwave absorbing materials.