Ultra-wide microwave absorption with thin thickness in multi-layered Fe3O4-coated FeSiCr composites

Abstract

A fully understand the role of impedance matching and loss capability in obtaining ultra-wide microwave absorption with thin thickness is extremely important. The influence of morphology and microstructure evolution of Fe₃O₄-coated FeSiCr powder on microwave absorption performances are analyzed for revealing the roles of impedance matching and loss capability. When milling time reaches more than 5 h and NaOH solution is adopted, FeSiCr powders transform from flaky structure coated by incomplete Fe₃O₄ layer to multilayered structure with complete Fe₃O₄ layer. By utilizing multiple reflections in multilayered structure, as well as the complete magnetic-dielectric interface provided by Fe₃O₄ layer, good impedance matching is achieved to promote microwaves into composites as much as possible. Due to the dual dielectric relaxations and dual magnetic resonances originating from FeSiCr nanoflakes and complete Fe₃O₄ layers, loss capability is enhanced at broad frequency. Paraffin with 40 wt% multilayered Fe₃O₄-coated FeSiCr delivers optimal effective absorption bandwidth (EAB) of 8.64 GHz covering 9.36–18 GHz with 1.4 mm and the optimal reflection loss of −37.00 dB at 2.32 GHz with 4.3 mm. Furthermore, constructing macroscale gradient metamaterial integrates macroscopic wavelength resonance and electromagnetic loss of composites, thereby generating an ultrabroadband EAB of 14.67 GHz with only height of 4 mm. Radar cross section values are below 10 dB·m² in 9.36–18 GHz, implying the attenuation of wideband EM wave in practical application.