Electromagnetic characteristic and microwave absorption properties of carbon nanotubes/epoxy composites in the frequency range from 2 to 6 GHz

The preparation and characterization of carbon nanotubes (CNTs)/epoxy composites were studied for microwave absorption, which frequency is from 2 to 6 GHz. The absorbing coating with a loading of 15 wt % CNTs/epoxy resin, which thickness is 3 mm, exhibited an absorbing peak of 10.5 dB at 3.85GHz. After being treated by HNO3–H2SO4 acid at the temperature of 100 °C, the real and imaginary part values of permittivity of CNTs have a larger increase in quantity, and the absorbing peak position moves to lower frequency of 3.35 GHz showing an increasing the dielectric loss in lower microwave frequency. Two-layer coating with CNTs/epoxy resin and graphite/epoxy resin composites have been also investigated in order to widen the frequencies range of CNTs microwave sorbent in the low microwave frequency application. The results indicated that two-layer coating (15 wt % loading CNTs/epoxy resin and 9 wt % loading graphite/epoxy resin) can obtain 2.4 GHz broad frequencies band for absorption of 5.0 dB. The absorbing p...