Optimal electromagnetic-wave absorption by enhanced dipole polarization in Ni/C nanocapsules

Electromagnetic-wave (EMW) absorption by Ni/C nanocapsules with similar permeability but different permittivity mainly due to differences in the graphite-shell thickness has been investigated. The optimal working frequency could appear at S-band and C-band and considerable strong EMW absorption was achieved. For the optimal Ni/C nanocapsules, a reflection loss exceeding -20 dB was reached from 2.6 to 8.2 GHz with a maximum value of -40 dB at 3 GHz. The improved absorption can be attributed to an optimal electromagnetic match and an enhanced dipole polarization upon increasing of shell thickness.

Frequency dependence of microwave reflection loss (RL). (a-c) RL of S1, S2 and S3 with different d values. (d) the dependence of the RL peak value and RL peak frequency on t_shell for d = 5.4 mm, 4.4 mm and 3.8 mm.

Enhancement of complex permittivity due to the thickening of the graphite shell. The inset shows an equivalency between core/shell structure (with complex permittivity ε₁ and ε₂) and uniform structure (with an equivalent complex permittivity γε₁). An agreement between experimental and theoretical ε_effeff(t_shell) is obtained.