The carbon-coated Ni(C) nanocapsules were prepared by a modified arc-discharge method in methane atmosphere. Its electromagnetic parameters were measured at 2–18GHz. It is observed that the natural resonance which appeared at 5.5GHz is dominant among microwave absorption properties of Ni(C) nanocapsules, as the consequence of the increased surface anisotropic energy for nanosized particles. The measured relative complex permittivity indicates that a high resistivity existed in Ni(C) nanocapsules samples. The maximum reflection loss of Ni(C) nanocomposites can reach 32dB at 13GHz with 2mm in thickness. The microwave absorptive mechanisms of Ni(C) nanocapsule absorbent were discussed.

Carbon-coated Fe [Fe(C)] nanocapsules were synthesized by a modified arc-discharge method, and their microstructure and electromagnetic (EM) properties (2–18 GHz) were investigated by means of transmission electron microscopy, Raman spectroscopy and a network analyser. The reflection loss R of less than −20 dB was obtained in the frequency range 3.2–18 GHz. A minimum reflection loss of −43.5 dB was reached at 9.6 GHz with an absorber thickness of 3.1 mm. The in-depth study of relative complex permittivity and permeability reveals that the excellent microwave absorption properties are a consequence of a proper EM match in microstructure, a strong natural resonance, as well as multi-polarization mechanisms, etc.

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Carbon-coated Cu [Cu(C)] nanocapsules were prepared by a DC arc discharge method in a methane (CH4) atmosphere, and characterized by x-ray diffraction (XRD), thermal gravimetric analysis (TGA), scanning differential thermal analysis (SDTA), transmission electron microscopy (TEM) and Raman spectroscopy. The results show that the as-made product consists of carbon-coated Cu nanocapsules and giant onion-like fullerenes (GOLFs) in the diameter range of 20–50 nm. The graphite outer shells effectively protect the Cu cores from environmental oxidation, and have a greater defect density in comparison with bulk graphite and carbon nanotubes (CNTs). Its relatively complex permittivity (εr = ε′+iε′′) is also measured at 2–18 GHz. The values of ε′ and ε′′ reach 14.5 and 4.1, respectively, exhibiting excellent electromagnetic wave loss ability.