Negative permittivity and permeability of polyethylene-based composites with segregated filler network in microwave range

In this paper, the microwave permittivity and permeability were investigated in the frequency range 26-40 GHz in percolative three-phase graphite nanoplatelets (GNPs)/magnetic particles (Fe,Co₃O₄)-polyethylene composites with segregated filler network. When GNPs content increases up to 5wt.% GNPs particles are in close contact, and a 3D segregated highly conductive network is formed and generates metal-like conductivity. For this case, the Drude type negative permittivity behavior is obtained due to plasma oscillation of free electrons within the conductive filler network. The observed relatively high dielectric loss in the composites was mainly induced by the high leakage current through GNPs and magnetic particles. In addition, the negative imaginary part of magnetic permeability was observed for developed three-phase composites. Higher GNPs content leads to an increase in absolute values of negative imaginary permeability. The comparative analysis of microwave shielding properties of polyethylene composites filled with GNPs and various additional magnetic particles, micron-sized Fe or nanosized Co₃O₄ showed the higher shielding ability of GNP-Fe-filled composites compared with GNP/Co₃O₄ ones. The increase of GNPs content promotes the enhancement of electromagnetic shielding due to both reflection SE_R and absorption SE_A although the electromagnetic reflection index R is much higher compared with absorption index A.