Study on microwave-absorbing properties of carbon-fiber-reinforced cement-based composites

The reflectivity of carbon-fiber-reinforced cement-based composites (CFRC) in the frequency ranges of 4 to 8 GHz and 8 to 18 GHz was measured using the naval research laboratory (NRL) testing system when the carbon fiber content was 0.2wt%, 0.4wt%, 0.6wt%, 0.8wt%, and 1.0wt%, respectively. The reflectivity data in two different frequency ranges were compared when the fiber content kept constant. The variation of reflectivity in the same frequency range was discussed when carbon fiber content increased. Results show that the reflectivity is less than -10 dB in the lower frequency range and the composites exhibit microwave-absorbing properties. However, the reflectivity is above -10 dB in the higher frequency range after the percentage of 0.6wt% and they exhibit the microwave-reflecting properties. As the fiber content rose, the reflection loss at different frequency ranges varied differently: the minimum reflectivity in the lower frequency range was -15.0 dB at 0.6wt%, while that in the higher frequency range was -19.4 dB at 0.4 wt%.