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 α-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. RL_min 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.