Electromagnetic wave absorption property of carbon microcoils in 12-110 GHz region

The electromagnetic (EM) wave absorption properties in the gigahertz region (12-110 GHz) of carbon microcoils (CMCs) with a three-dimensional-helical/spiral chiral structure (1-10 mum coil diameter and 0.1-10 mm coil length) were examined using the open space method. It was found that the target value of reflection loss, over -20 dB (above 99% absorptivity) necessitated for commercial applications, could be obtained for EM absorption composites of only 1-2 wt % addition of CMCs in a polyurethane matrix for the 30-35, 50-55, 75-80, and 95-100 GHz bands. A CMCs addition of more than 3 wt % resulted in a decrease of the EM wave absorptivity, because of the increase in the reflection of the EM waves. Multilayer absorption composites showed a higher EM absorptivity than that of single-layer composites. The longer the coil length, the higher the absorptivity could be obtained. The absorption mechanism of the EM waves by CMCs is discussed. (C) 2003 American Institute of Physics.