Anisotropic dielectric properties of short carbon fiber composites

Dielectric materials based on short carbon fiber (C_sf) dispersed inside epoxy resin (EP) matrix composites were prepared. The complex permittivity of two types of distributions over the frequency range from 2.6 GHz to 8.2 GHz was reported. The effects of orientation with different content and length of carbon fibers on dielectric properties were investigated. It is found that axial permittivity of carbon fibers is several times larger than their radial permittivity. The real and imaginary parts of complex permittivity increase gradually with increasing the C_sf contents in the composites, and the fiber length also affects the anisotropic property greatly. The two layered transmission line model is used to explain the phenomena.