Dielectric behavior of laminate-structure Cf/Si3N4 composites in X-band

Dielectric properties of laminate-structure Cf/Si3N4 composites as a function of frequency and surface density of short carbon fibers (SCFs) were studied. Results show that as the surface density of SCFs is up to 0.85 mg/cm2, an abrupt increase both in real and imaginary part of permittivity occurs. Taking conduction current into consideration, a revised Cole-Cole model of permittivity has proposed to reveal the mechanism of dielectric behavior. The best fitting results indicate that conduction loss played an important role in dielectric behavior of laminate-structure Cf/Si3N4 composites after percolation. Further more, the mean relaxation time is slightly smaller than characteristic relaxation time, which leads to continuous increase of the imaginary part of permittivity with frequency increased.