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. (C) 2011 Elsevier Ltd. All rights reserved.