The composite materials (CMs) with mixed conductive/dielectric fillers were found to be perspective for creating low mass, high permittivity materials . The electromagnetic shielding properties of epoxy composites filled with mixed filler carbon nanotubes/barium titanate (CNT/BT) at CNT concentrations of 1, 2, 3, 4, 5 wt.% and 34 wt. % of BT were measured using waveguide spectroscopy in the frequency range from 26 GHz to 37.5 GHz.
While the transmission index was found to decrease monotonically with increase of CNT content, the reflection loss dependence is different (Fig. 1). Increasing the CNT content enhances the conductivity, resulting in increase of the EMR reflection at the interface air-composite as well as EMR absorption inside of the composite. The increase of the shields’ thickness (up to 2.5mm) leads to the increase of shielding efficiency (SET ≈ 30dB for 5%CNT) due to higher EMR absorption inside, while the changes of the reflection index versus frequency depend on CNT content and composite thickness.
The BT primary role in CMs with conductive fillers is to move the percolation threshold further for conductive filler, increasing its real part of permittivity.
1. Z. Wang, K. Nelson, M. Jianjun, R. Linhardt, L. Schadler, IEEE Transactions on Dielectrics and Electrical Insulation., 2012, 3, 960.