Core/shell/shell-structured nickel/carbon/polyaniline nanocapsules are prepared by a modified arc-discharge method and a chemical polymerization method, and their microwave absorbing properties are evaluated in the 2-18 GHz range covering the full S-Ku bands of microwaves. The bandwidth-broadening effect in various core/shell/shell material phases of the nanocapsules leads to Debye-type multidielectric polarizations in complex permittivity, a broad magnetic natural resonance of 2-8 GHz in complex permeability as well as extended absorbing bandwidth and absorber thickness range. A 3 mm-thick paraffin-bonded nanocapsule absorber shows an optimal reflection loss (RL) of -9.3 dB at 6.2 GHz with an extremely broad -5 dB-bandwidth of 3.4-18 GHz in almost the whole S-Ku bands as well as a very large absorber thickness range of down to 1 mm without deteriorating RL by 10%.
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