Microwave absorbing characteristics of flake-shaped FeNiMo/epoxy composites

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Abstract
Water atomized Fe16Ni82Mo2 (wt. %) alloy powder with spherical-like form was processed in a planetary mill for 2 h and 4 h, respectively. The complex permittivity (ε′−jε″) and permeability (μ′−jμ″) are measured using the transmission/reflection method in the frequency range of 2–18 GHz for FeNiMo/epoxy composites with 70 wt. % of magnetic fillers. The results show that all ε′, ε″, μ′, μ″ substantially increase due to the increase of aspect ratios. The magnetic susceptibility (μ′−1) of FeNiMo/epoxy absorber is negative above 5 GHz due to the natural magnetic resonance. The frequency dispersion of μ″ of flake-shaped FeNiMo composite shows a higher resonance frequency which exceeds the Snoek's limit in the gigahertz range as a result of large shape anisotropy. For composite absorbers with 2 mm thickness, the calculated reflection loss reaches −12.1 dB at 14.6 GHz without milling, −20.4 dB at 13.0 GHz for 2 h milling, and −13.1 dB at 11.0 GHz for 4 h milling.

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