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 HNO(3)-H(2)SO(4) acid at the temperature of 100 degrees 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 peak intensity and position can be adjusted by changing the thickness of each layer coating in the case of fixed total thickness. The two-layer coating of 15 wt % loading CNTs/epoxy resin (d(top)=2 mm) and 9 wt % loading graphite/epoxy resin (d(bottom)=1 mm) has a strong absorbing peak at 5.52 GHz and achieves an absorbing value of 20.79 dB.