Experimental and computational study of shielding effectiveness of polycarbonate carbon nanocomposites

The electrical and electromagnetic interference shielding effectiveness (EMI SE) properties of composites with a polycarbonate matrix and varying amounts of three different types of carbon fillers (carbon black, carbon nanotubes, and graphene nanoplatelets) are analyzed experimentally and theoretically over the 8.5-12 GHz frequency range. A finite element model is also used to study the EMI shielding mechanisms. The theoretical study predicts that the carbon fillers' concentration, sample thickness, incident angle, polarization type, and frequency are the main parameters that have effect on shielding effectiveness of a sample that is confirmed by the experimental and simulation results. Permittivity and related alternating current (AC) conductivity measurements in the above mentioned frequency range are presented for these three types of composites, providing an appropriate way to design a shield. Experimental, theoretical and simulation results indicate that both permittivity and conductivity have significant effects on the SE. It is found that the electrical conductivity, which itself needs a percolating (connected) path, is not the only criterion for shielding and that the connectivity of fillers (and, hence, higher conductivity) does not necessarily lead to a higher SE.