Epoxy/ferrite nanocomposites as microwave absorber materials: effect of multilayered structure

In the present work, different ferrite-type nanoparticles (Ni_0.5Zn_0.5Fe₂O₄, NiFe₂O₄ and Fe₃O₄) were incorporated into an epoxy resin to obtain composites loaded with 20 and 40 wt% of filler. The morphology of these monolayered composites was investigated by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM), which allow identifying a fractal structure of the ferrite-based filler with rough surface. The electromagnetic properties of the monolayer composites with 1 mm thickness were evaluated by the transmission line method in X-band (8.2–12.4 GHz), whose better response in terms of reflection loss was obtained for the composite filled with Ni_0.5Zn_0.5Fe₂O₄. Epoxy-based composites containing 20 and 40 wt% of Ni_0.5Zn_0.5Fe₂O₄ in the form of plaques were arranged in two types of three-layered structures: (i) stacked monolayers and (ii) low dielectric spacer sandwiches between monolayers (air, honeycomb and foam), whose structure sequence was built based on the reflectivity simulation. The best system, designed by mathematical simulation and experimental results, consisted of ER/NiZn(40)–honeycomb–ER/NiZn(20) arrangement, which presented RL of around − 40 dB at a frequency of 8.75 GHz. Broadband with > 90% attenuation (minimum of − 10 dB) with band width of around 1.2 GHz and minimum RL ≈ 20 dB (E_abs ≈ 99%) was achieved for both three-layered structures contain in PU foam or honeycomb as low dielectric spacer. The ferrite-based multilayer structures with only 6 mm of thickness constitute promising absorbing materials for applications in both civil and military fields.