Shielding effectiveness density theory for carbon fiber/nylon 6,6 composites

We present a simple density theory based on first principles that predicts the shielding effectiveness of composite matrix materials at filler loadings near or above the percolation threshold. Such a model has practical applications in electromagnetic interference and radio frequency interference, and is validated here for Fortafil 243 carbon fiber within nylon 6,6. In brief, the theory predicts that the most important parameter on the shielding effectiveness of a sample is the carbon fiber volume percent. At very high filler loadings, experimental results show a weak dependence on the frequency of the wave to be shielded, which may be attributed to enhanced reflection from multiple, coherent scatterers (carbon fiber network). These effects are not considered in our model. Nevertheless, advantages of this model are ease of use and improved predictive capabilities when compared to models previously reported in the literature. Our model performs very well over an electrical resistivity range from 1015 ohm‐cm (at low filler loading levels below the percolation threshold) down to 10−1 ohm‐cm (at high filler loading levels well above the percolation threshold), and can be used to determine filler loadings needed to provide a certain level of shielding of electromagnetic waves. POLYM. COMPOS. 26:671–678, 2005. © 2005 Society of Plastics Engineers