Abstract
Flexible, lightweight, conductive materials, having both high rf losses and high permeability, are extremely desirable for applications as electromagnetic (EM) shielding. Gas atomized spherical FeSi-based ferromagnetic metallic particles, having a mean diameter of 14.6 μm with a standard deviation of 7.3 μm, were measured to have a room temperature saturation magnetic flux density of 1.49 T with a coercivity of 160 A/m. Ball milling of the amorphous particles led to aspect ratios from 1:1 (spherical) to > 100:1 (flake-like). Flake-like particles, suspended in paraffin, were found to not only increase the surface area of fillers enhancing the polarization mechanism but also increase the complex permeability and complex permittivity, and thus provide broadband shielding effectiveness. A loading factor of 40 vol.% of the ∼15 μm diameter powders provided the largest ΔWRL = -20 dB of 9.49 GHz (i.e., 6.55<f<16.04 GHz) at a coating thickness of 2 mm. Overall, powder composites show a wide absorption potential above 18 GHz for < 1.5 mm thicknesses. The optimized flake-based composites exhibit strong EM wave absorption with an SE of -40 dB and SE<-10 dB of 17.57 GHz at 40 vol.% filler at a thickness of 1.6 mm.
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