Gradient multilayer structural design of CNTs/SiO2 composites for improving microwave absorbing properties

Multilayered carbon nanotubes/silicon dioxide (CNTs/SiO2) electromagnetic wave absorbing ceramic matrix composite material was fabricated by hot-pressed sintering. The gradient layer structure was designed to improve its absorbing properties. The multilayered CNTs/SiO2 composite was shaped by adding five kinds of mixed powders with different CNTs contents (0 wt%, 2.5 wt%, 5 wt%, 7.5 wt% and 10 wt%) to the graphite die in turn, and its average CNTs content was 5 wt%. Meanwhile, a single layered composite with the same content of CNTs (5 wt%) was fabricated as a contrast sample. The electromagnetic interference (EMI) shielding effectiveness (SE) and reflecting effectiveness (RE) were studied with insertion loss (IL) and return loss (RL) measurements in the range of 8–12 GHz. The results showed that the gradient multilayered sample had a better absorbing effectiveness and its absorbance was 1.5 times as high as the single layered sample’s, while their SEs were almost the same.