Microwave properties of epoxy composites with mixed filler carbon nanotubes/BaTiO3

The microwave properties of composite materials (CMs) based on epoxy resin and mixed filler carbon nanotubes/barium titanate (CNT/BT) at CNT concentrations up to 5 wt% and 34 wt% of BT were investigated. The complex permittivity of epoxy composites was measured in the frequency range 1–67 GHz via vector network analyzer. The CNT/BT/epoxy composite showed the increase of permittivity with the increase of CNT content in CM. The electromagnetic shielding properties of developed CMs were measured using waveguide spectroscopy in the frequency range from 26 to 37.5 GHz. Increasing of CNT content enhances the conductivity, resulting in an 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 2.5 mm) leads to the increase of shielding effectiveness for transmission up to 30 dB for sample with 5% CNT content due to higher EMR absorption inside, while the changes of the reflection index versus frequency depend on CNT content and composite thickness. The reflection loss (RL) of composites was calculated for various thicknesses using the complex permittivity and the obtained results show that composite 2 wt% CNT/BT/epoxy exhibits superior absorptive properties in the frequency range 10–67 GHz. The BT primary role in such CMs (with conductive fillers) is to move the percolation threshold further for conductive filler, increasing its real part of permittivity.