Effective Properties of Carbon Fiber Composites: EM Modeling Versus Experimental Testing

This paper discusses the critical issues related to the practical application of Maxwell-Garnett approach to the electromagnetic modeling of the effective electric permittivity of dilute carbon fiber reinforced composites. In fact, recent studies have highlighted the interest in the use of such composites as lossy sheet in broad-band dielectric absorbing screen in the gigahertz range. The a.c. electrical conductivity of carbon fibers embedded in epoxy resin is determined from the best-fit between the data obtained from the experimental tests and the ones obtained from the electromagnetic modeling. Two different manufacturing processes of the test samples are investigated: pouring and dipping. It results that, in the frequency-range from 9 GHz to 12 GHz, carbon fibers having length of a few millimeters embedded in epoxy resin, are characterized by a constant value of the a.c. electrical conductivity only in case of sample preparation by pouring.