Complex permittivity and microwave absorbing properties of SiC fiber woven fabrics

A comparative investigation of electric conductivity, complex permittivity, and microwave absorbing properties of KD-1 and Nicalon-202 fibers in the form of fabrics within the range of 8.2–12.4 GHz (X band) has been carried out. The electric conductivity value of KD-1 filaments is two orders larger than Nicalon-202. Both the values of real part (e′) and imaginary part (e″) of KD-1 fabrics are larger than their counterparts of Nicalon-202 especially the imaginary part, which is in agreement with larger DC conductivity (σd). The surface morphology and chemical component were characterized by SEM, EDS, Raman spectroscopy and XRD, which shows that both the KD-1 and Nicalon-202 SiC fibers are rich in carbon, while there is rich carbon layer on the surface of the former and the degree of order in the free carbon phase is higher compared with the latter. In addition, the amount of amorphous Si–C–O phase of KD-1 fibers is higher while the SiC crystal is smaller than Nicalon-202. The free carbon on the surface of KD-1 fibers can establish electric conductivity network. The larger e″ and e′ of KD-1 fabrics are believed to be mainly caused by conductive network established by rich carbon outer layer and relaxation polarization enhanced by more Si–C–O phase. The reflection loss of KD-1 and Nicalon-202 fabrics is −3.5 to 0.7 and −5.1 to −4.3 dB, calculated according to tested complex permittivity.