Epoxy matrix-based composite materials filled with various carbon additives, such as natural, artificial and exfoliated graphites (EGs), activated carbons, and thick graphene, were fabricated. Results of their broadband dielectric spectroscopy in wide frequency range, from a few hertz to a few terahertz are reported. The lowest percolation threshold (below 1.5 wt. %) as well as the highest electromagnetic interference (EMI) shielding capacity are observed for composites containing EG. Using an original random resistor-capacitor-diode network model, we proved theoretically that 2 wt.% of EG in the epoxy host is an optimal composition, as it provides high EMI shielding efficiency at the level of 17 dB for a 1.4-mm-thick polymer slice, and at the same time, does not lead to a significant decrease of other important physical properties of epoxy. © 2015 IEEE.

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