Microwave properties of carbon black-epoxy resin composites and their simulation by means of mixture laws

This article reports on a study of the dielectric properties of carbon blac k dispersions in an insulating epoxy matrix at microwave frequencies. Measu rements showed that the complex permittivity of the composites depends stro ngly on the nature and concentrations of the conducting medium. The experim ental values of the complex permittivity were compared to those obtained by using different mixing laws. We show that effective medium theories correc tly account for the experimental results at low conducting particle concent rations. At concentrations higher than a few percent, these laws fail to in terpret experimental results and all tentative results must take into accou nt parameters such as the particle size, their distribution, and the existe nce of agglomerates. (C) 1999 John Wiley & Sons, Inc.