ELECTRICAL CHARACTERIZATION AND ELECTROMAGNETIC INTERFERENCE SHIELDING PROPERTIES OF HYBRID BUCKYPAPER REINFORCED POLYMER MATRIX COMPOSITES

In recent years, there has been a growing interest in the utilization of carbon nanotubes (CNTs) to enhance electromagnetic interference (EMI) shielding capabilities within aerospace structures. Buckypaper (BP), which is an electrically conductive thin membrane made of highly cross-linked CNTs, provides an effective way to enhance the EMI shielding properties of carbon fiber reinforced polymer (CFRP) composites. However, limited work has been reported in predicting the frequency dependent electrical conductivity as well as EMI shielding effectiveness (SE) of hybrid BP/CFRP composites. In this paper, a novel quantum tunneling based equivalent circuit approach, in conjunction with Monte Carlo simulations, is employed to characterize the electrical properties of unidirectional CFRP plies. A frequency range of 1 GHz to 12 GHz corresponding to the L to X band frequency spectrum was considered for this study. It was observed that at 12 GHz the longitudinal conductivity decreases to similar to 3,300 S/m from a DC conductivity level of 40,000 S/m, while the transverse conductivity concurrently rises from almost nil to similar to 12.67 S/m. Subsequently, these results are integrated as effective lamina properties into Ansys High Frequency Structure Simulator (HFSS) to predict SE by simulating the transmission of electromagnetic waves across a semi-infinite shield representative volume element. The numerical simulations illustrate that the inclusion of BP leads to significant improvement in the SE. For an incident radiation at 12 GHz, the incorporation of a single BP interleaf enhances the SE of a 90,0] laminate by up to similar to 64% while the incorporation of two BP interleaves in a [90,0,+/- 45,0,90] balanced symmetric laminate enhances its SE by similar to 20%. This enhancement can be attributed to the high conductivity of BP at high frequencies.