Gigahertz range electromagnetic wave absorbers made of amorphous-carbon-based magnetic nanocomposites

Nanocomposite magnetic materials α - Fe ∕ C ( a ) , Fe 2 B ∕ C ( a ) , and Fe 1.4 Co 0.6 B ∕ C ( a ) were prepared by mechanically grinding α - Fe , Fe 2 B , or Fe 1.4 Co 0.6 B with amorphous carbon [ C ( a ) ] powders. Complex permittivity, permeability, and electromagnetic wave absorption properties of resin compacts containing 40 - vol % composite powders of α - Fe ∕ C ( a ) , Fe 2 B ∕ C ( a ) , and Fe 1.4 Co 0.6 B ∕ C ( a ) were characterized according to a conventional reflection/transmission technique. The real part ( ε r ′ ) and imaginary part ( ε r ″ ) of the relative permittivity are low and almost independent of frequency between 0.05 and 40 GHz . The Imaginary part ( μ r ″ ) of the relative permeability exhibited wide peaks in the 1 - 9 - GHz range for α - Fe ∕ C ( a ) , in the 2 - 18 - GHz range for Fe 2 B ∕ C ( a ) , and in the 18 - 40 - GHz range for Fe 1.4 Co 0.6 B ∕ C ( a ) owing to their different magnetocrystalline anisotropy field ( H A ) values. Consequently, the resin compacts of 40 - vol % α - Fe ∕ C ( a ) , Fe 2 B ∕ C ( a ) , and Fe 1.4 Co 0.6 B ∕ C ( a ) powders provided good electromagnetic (em) wave absorption performances (reflection loss < − 20 dB ) in ranges of 4.3 - 8.2 GHz ( G band), 7.5 - 16.0 GHz ( X band), and 26.5 - 40 GHz ( Q band) over absorber thicknesses of 1.8-3.3, 1.2-2.2, and 0.63 - 0.82 mm , respectively. Our experimental results demonstrate that the amorphous-carbon-based magnetic nanocomposites are promising for the application to produce thin and light EM wave absorbers.