Complex permittivity measurements and mixings laws of alumina composites

The effect of microstructure on the complex permittivity of alumina composites was studied. Three different algebraic mixing laws (Maxwell-Garnett, effective medium approximation, and the Landau-Lifshitz-Looyenga formula) inaccurately predicted the measured complex permittivities of alumina/silicon carbide and alumina/copper oxide composites. The imaginary part of the complex permittivity of the four-phase composites depends significantly on the absorbed water and microstructure. Accurate calculations require that the microstructure of the composite be examined and incorporated into the electrostatic model. Incorporating the general physical characteristics of the composites enabled a three-dimensional electrostatic model to accurately predict the permittivities of four-phase composites with different microstructures. (C) 2001 American Institute of Physics.