Electromagnetic and microwave absorption properties of Alnico powder composites

A novel application of Alnico powder as a thinner microwave absorbing material was investigated. The flake-like Alnico fine powder was found to have excellent complex permeability μ=μ′-jμ″μ=μ′-jμ″ and permittivity ε=ε′-jε″ε=ε′-jε″ in the frequency range of 2–18 GHz. The powder was made from extremely brittle ribbons which were produced using a single roller melt spinning technique. The dependences of the absorption characteristics on the frequency, thickness, and both the dielectric permittivity and magnetic permeability were obtained based on a model in which an electromagnetic wave is incident normal to the surface of the absorbing material backed by a perfect conductor. The samples have the largest values of μ′μ′ and μ″μ″ at 2 GHz. A minimum reflection loss of −11.4 dB is obtained at 2 GHz for composite with volume fraction 60% of Alnico powder and absorber thickness of 1.8 mm. The results show that flake-like Alnico powder composites can be applied as thinner microwave absorbers in S-band (2–4 GHz).