Influence of pyrolytic carbon coatings on complex permittivity and microwave absorbing properties of Al2O3 fiber woven fabrics

The pyrolytic carbon (PyC) coatings were fabricated on Al2O3 fiber fabrics by the method of chemical vapor deposition (CVD). The microstructures of Al2O3 fibers with and without PyC coatings were characterized by SEM and Raman spectroscopy. The influence of deposition time of PyC on the DC conductivity (sigma(d)) of Al2O3 filaments and complex permittivity of fabrics at X band (8.2-12.4 GHz) were investigated. The values of sigma(d) and complex permittivity increase with increasing deposition time of PyC. The electron relaxation polarization and conductance loss were supposed to be contributed to the increase of epsilon' and epsilon '', respectively. In addition, the reflection loss (RL) of fabrics was calculated. The results show that the microwave absorbing properties of Al2O3 fiber fabrics can be improved by PyC coatings. The best RL results are for 60 min-deposition sample, of which the minimum value is about -40.4 dB at about 9.5 GHz and the absorbing frequency band (AFB) is about 4 GHz.