Tunneling-induced negative permittivity is attributed to the low frequency plasmonic state in tunneling networks, where nickel nanoparticles are still isolated geometrically but connected electrically.

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Carbon-based composites have shown excellent electromagnetic wave-absorption properties. In this work, an extremely facile and green method was developed to prepare Fe@Fe3C/C nanocomposites by carbonizing the bulrush impregnated with Fe­(NO3)3 solutions. The core–shell Fe@Fe3C was generated from carbothermal reductions and interfacial reactions. The minimum reflection loss exceeded −50 dB with absorbers thickness almost no more than 2.00 mm. The widest absorption bandwidth was up to 4.57 GHz with a thickness only 1.43 mm. Meanwhile, the absorption performance with RL < −10 dB could be observed in a bandwidth of about 15 GHz as absorbers thickness varied from 1.00 to 5.00 mm. The excellent wave-absorbing properties could be attributed to the synergistic effect of dielectric loss and magnetic loss of Fe@Fe3C/C nanocomposites. Also, the optimized impedance matching and high attenuation abilities of absorbers contributed to the absorption performance. This work provides a new way of recycling the abundant natural herbage waste to be used in electromagnetic applications.

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