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 Al ₂O ₃ fiber fabrics by the method of chemical vapor deposition (CVD). The microstructures of Al ₂O ₃ fibers with and without PyC coatings were characterized by SEM and Raman spectroscopy. The influence of deposition time of PyC on the DC conductivity (σ _d) of Al ₂O ₃ filaments and complex permittivity of fabrics at X band (8.2σ12.4 GHz) were investigated. The values of σ _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 ε′ and ε″, respectively. In addition, the reflection loss (RL) of fabrics was calculated. The results show that the microwave absorbing properties of Al ₂O ₃ 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.