Dielectric and Microwave-absorbing Properties of the Carbon/Alumina/Silica Coating

The permittivity and microwave-absorbing properties of carbon black or carbon fiber filled alumina/silica coating were investigated in X-band. The results indicate that both the real and imaginary part of the complex permittivity increase with the increasing content of carbon absorber. With the same content of carbon absorber, the coatings filled with carbon fiber show higher complex permittivity than the coatings filled with carbon black. As the absorber contents increase to 2wt%, the complex permittivity of the coatings decrease with the increase of frequency, which is so-called frequency-dependence dielectric response. The minimum reflection loss of the coatings shifts to low frequency region as their thickness increasing. The results of the microwave absorbing properties show that good microwave absorption ability (below -10 dB) can be obtained in the frequency range from 9.2 GHz to 12.4 GHz for the coating with 2wt% carbon black and 2 mm in thickness.