Controllable dielectric properties and strong electromagnetic wave absorption properties of SiC/spherical graphite-AlN microwave-attenuating composite ceramics

Fully dense SiC/spherical graphite-AlN microwave-attenuating composite ceramics were manufactured via hot-pressing sintering, in which, apart from the primary SG (spherical graphite) attenuating agent, 5-30 wt% semiconductive alpha-SiC was employed as the second attenuating agent. The incorporation of SiC contributed to a slightly decreasing electrical conductivity and enhanced polarization relaxation. Controllable complex permittivities were obtained, namely, both the real and imaginary permittivities exhibit first a decrease and then an increase with the SiC addition, and which delivers an optimized impedance matching of the composites. RLmin values below -10 dB (more than 90% absorption) were achieved by all the composites containing 5-20 wt% SiC with the sample thickness of 1-1.4 mm, and the absorption performance characteristics were significantly tunable by controlling the of SiC content at 8.2-12.4 GHz. Impressively, a superior reflection loss of -46 dB (1.1 mm) and wide effective absorption bandwidth of 2.1 GHz were achieved at a 5 wt% SiC content, respectively, rendering SiC/SG-AlN composites a potential ultra-thin and highly efficient microwave-attenuating ceramic candidate.

Automated summary

Fully dense SiC/spherical graphite-AlN microwave-attenuating composite ceramics were prepared, where the addition of SiC led to a decrease in electrical conductivity and enhanced polarization relaxation. The absorption performance characteristics of the composites could be significantly tuned by controlling the SiC content, resulting in optimized impedance matching and superior absorption at certain frequencies.