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Equivalent electric circuits allowing the simulation of the behavior of nanocomposites based on thermosetting resin and nanocarbon filler are presented. The electric circuits are constructed by employing a multistep simple procedure in which the values and number of the parameters are adjusted until a suitable criterion, based on the comparison between simulated and experimental frequency spectra is satisfied. A resistance–capacitance (RC) simple parallel branch in parallel with a variable number of RC series branches is shown to be capable to reproduce the frequency response of a prepercolative carbon black and two carbon nanotube (CNT) nanocomposites with CNT concentration close to the percolation threshold. The obtained equivalent circuits may be employed for the interpretation of the physical mechanisms underlying the electromagnetic (EM) behavior. Moreover, they can be used in circuit simulators for first-approximation design of EM devices based on such composites. [ABSTRACT FROM PUBLISHER]

A novel lightweight onion-like carbon (OLC)-based polymer composite with high electromagnetic (EM) shielding properties is presented. OLC have been produced via the large-scale production technology based on the annealing of detonation nanodiamond under vacuum conditions (or in inert atmosphere). EM shielding effectiveness has been tested in the frequency range of 26–37 GHz. The highest EM attenuation at 36.6 GHz reaching −34 dB was observed for polymethylmethacrylate films comprising 20 wt.% of OLC. The shielding effectiveness data collected for microwave frequencies were found to correlate well with the electrical resistivity measurements by four-probe method as well as conductivity measurements provided by the broadband dielectric spectroscopy (20 Hz–3 GHz). It was proved experimentally that OLC EM shielding capacity can be optimized by varying the nanoonion cluster size and nanodiamond annealing temperature so that effective EM coatings can be produced. Both the experimental observations and theoretical simulations demonstrate that even small (smaller than percolation threshold) additions of OLC particles to a polymer host can noticeably modify the composite response to EM radiation. [ABSTRACT FROM AUTHOR]