Microwave absorbing properties of flaky Fe-Si-Al alloy powder-rubber composites

The frequency profile of complex permeability (mu(r)) and permittivity (epsilon(r)) and their relationship with microwave absorbing properties are investigated in soft magnetic metal-polymer composite materials. The Fc-Si-Al alloy powder was forged by an attrition mill to get the flaky shape. The composite sheet was fabricated in which the flaky powder was dispersed in the polymer and aligned in the direction perpendicular to the electromagnetic wave propagation. We found that dielectric loss (epsilon(r)") spectra for composite sheets can be controlled by combining the aspect ratio of the flaky powder and the contents of the filler. The permittivity (epsilon(r)), of magnetic composite was increased with attrition milling time. The maximum attenuation peak of reflection loss is shifted to lower frequency ranges as the aspect ratio increased, while the value of the maximum attenuation peak gets smaller gradually. From these results, we could design a noise absorber sheet (t=1.0 MM) for a quasi-microwave band, which is impedance matched at 1.8 GHZ with respect to -7.7 dB reflection loss.