In this work, a hydrosoluble matrix is used for the first time to prepare flexible membranous composites, in order to improve their environmental friendliness and simplify the processing. Modified graphene (GR) sheets are distributed in polyvinyl alcohol (PVA) solution to achieve flexible GR/PVA metacomposites. As graphene content increases, an interconnected graphene network is eventually formed among the PVA matrix, and the resulting composites present a conductor‐like behavior. Interestingly, the Drude‐like negative permittivity is obtained in the composites with 20 wt% graphene, which is ascribed to the plasma oscillation. Meanwhile, the absolute values of negative permittivity decrease by several orders of magnitude due to the moderate electron density of graphene. It is demonstrated that the negative permittivity is dependent on the inductive character. This work provides a novel and versatile approach based on water‐soluble matrices to prepare flexible membranous metacomposites, which can be applied in wearable cloaking, thin‐film capacitors, and flexible and stretchable devices.

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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.

The study on novel physical properties of structural ceramics or ceramic composites could make them more conducive to be function‐ and structure‐integrated materials. Herein, titanium nitride‐alumina (TiN–Al2O3) duplex ceramics were prepared and the dielectric spectra of the ceramics were studied from 10 MHz to 1 GHz. Negative permittivity appeared when TiN content exceeded 40 wt% due to the induced plasmonic state of massive delocalized electrons in connected TiN grain networks. Meanwhile, alternating current conduction behaviors of the duplex ceramics were discussed with percolation theory. Furthermore, the analysis of reactance by equivalent circuit models indicated that negative permittivity ceramics exhibited inductive character. This work realized negative dielectric behaviors in TiN–Al2O3 duplex ceramics and would promote the study of electromagnetic functionalization in wave shielding or attenuation for structural ceramics.