Microwave radial dielectric properties of carbon fiber bundle: Modeling, validation and application

The radial dielectric spectroscopy of the carbon fiber bundle (CFB) array/epoxy resin composites have been performed over the frequency range from 8.2 to 12.4 GHz. The complex permittivity of the composite increases with the volume fraction, which is attributed to the increase of polarization, and decrease with the CFB diameter along the electric field direction which is ascribed to the increase of depolarization field. A revised Wiener model is proposed for the calculation of the effective permittivity of the composite, and used to extract the radial permittivity of the CFB. The proposed model is validated by the experimental measurements. The proposed model is further applied to derive the radial permittivity of cylinder carbon fiber and analyze the effect of the bundle geometry on the effective permittivity.