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

摘要

Nanocomposite magnetic materials α-Fe/C(a), Fe_2B/C(a), and Fe_(1.4)Co_(0.6)B/C(a) were prepared by mechanically grinding α-Fe, Fe_2B, 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_2B/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_2B/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_2B/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.