The effects of temperature and frequency on the dielectric properties, electromagnetic interference shielding and microwave-absorption of short carbon fiber/silica composites

The dielectric spectroscopy of short carbon fiber/silica composite in the frequency range from 8.2 to 12.4 GHz at temperatures between 30 and 600 degrees C has been performed. The composite was prepared by conventional ceramic processing. The real part of the permittivity increases with increasing temperature, which is attributed to the shortened relaxation time of electron polarization, and the imaginary part also increases which is ascribed to the increasing electrical conductivity of the carbon fibers. The effect of frequency is found in reflection coefficient and absorption coefficient, and the corresponding mechanisms for the effect are proposed. Results indicate that the composite has good electromagnetic interference shielding property. By calculating the microwave-absorption as a single-layer absorber, we find that the reflection loss varies with the changes of thickness and temperature, due to the deviation of impedance matching condition. (C) 2009 Elsevier Ltd. All rights reserved.