Abstract
Two different sizes of Fe3O4 nanoparticles were synthesized by hydrothermal (H-Fe3O4, ≈100nm) and co-precipitation (C-Fe3O4, ≈20nm) methods. Further, Fe3O4/polypyrrole (Ppy) composites were prepared by polymerizing the conductive monomer, pyrrole on the surface of Fe3O4. In addition, we also synthesized Fe3O4/Ppy/carbon nanotube (CNT) composites by blending the CNTs with Fe3O4/Ppy composites. Epoxy resin-based microwave absorbers were prepared at different thicknesses (1, 2 and 3mm) by mixing 20% by weight of the as-prepared composites and the complex permittivity (ε′−jε″) and permeability (μ′−jμ″) were measured in the 2–18GHz frequency range. The composites exhibited significant improvement in microwave absorption (reflection loss⩽−10dB) with a bandwidth from 8 to 12.5GHz (X-band) by matching the magnetic properties of Fe3O4 and the dielectric properties of Ppy and CNTs for 20wt% of fillers in 3-mm thickness absorbers. The addition of CNTs into H-Fe3O4/Ppy composites further enhances the minimum reflection loss from −15.8 to −25.9dB. The present results can pave the way to construct microwave absorbers with a desired reflection loss at a target frequency and thus, the efficient complementarities between complex permittivity and permeability of the nanocomposites can be achieved.
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