Abstract: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 (σ_d) of Al₂O₃ filaments and complex permittivity of fabrics at X band (8.2−12.4 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 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.

Key words: complex permittivity; pyrolytic coating; Al₂O₃ fiber fabric