Negative Permittivity Of Conductor/Epoxy Composite

Electromagnetic functional materials have important application backgrounds in stealth materials, wave-transmitting materials, electronic components and so on. In recent years, research of negative permittivity becomes a hot topic. Research shows that negative permittivity can be realized in conductor-insulator composite materials near percolation threshold.Epoxy resin is selected as matrix, different conductive phases are mixed with the matrix by cryomilling. Negative permittivity is successfully realized in radio frequency band in percolative resin matrix composite. The composition and microstructure of the composites are characterized using X-ray diffraction (XRD) and Scanning Electron Microscope (SEM). The dielectric property of the composites is tested using impedance analyzer. Finally, the negative permittivity mechanism of the percolative resin matrix composite is analyzed using Drude model, the percolation phenomenon, etc.Fe-Si-B/epoxy, Fe-Si-Ni/epoxy, Fe-Si-Cr/epoxy and Ag /epoxy composites were fabricated with epoxy as matrix, cryomilling was used to uniformly disperse the conductive phases. The results indicated that, for composites with low metal content, metal is basically isolated phase, permittivity is positive, and the conductivity increases with increasing frequency as hopping conduction. For the composites with high metal content, metal become continuous phase, permittivity is negative, and the conductivity decreases with increasing frequency due to the skin effects. Composites exceeded percolation threshold can be treated as weak metallic conductor which is diluted by the insulative matrix. The plasma oscillation of delocalized electrons in the current loops leads to the negative permittivity.Cu with different spherical particle sizes were dispersed in epoxy matrix using cryomilling. For composite with same conductive phase content, permittivity of the Cu (1μm)/epoxy composite is higher than the Cu (5μm)/epoxy composite, indicating that particle size can produce an effect on percolation threshold and permittivity. Negative permittivity was achieved in radio frequency band for Cu (1μm)/epoxy composite, and the mechanism was similar to Fe-Si-B/epoxy and Fe-Si-Ni/epoxy composites.