Determination of microwave complex permittivity of particulate materials

Abstract

A practical method for determining the broadband microwave complex permittivity of particulate materials is described. In this method, particulate materials are dispersed randomly in paraffin wax; thin disc samples are prepared for measurement from the particle-wax mixtures. During measurements, the samples are backed by a conducting plane, and an open-ended coaxial probe is used to determine the permittivity of the samples. A mixture equation is used to calculate the permittivity of the particulate materials from the permittivity of the samples. The validity of six well known mixture equations is examined. The experimental results indicate that only the QCA-CP and Bruggeman mixture equations can accurately describe the microwave permittivity of the particle-wax mixtures over the wide particle concentration range. To validate this described method, the complex permittivities of PbTiO₃ and Pb(Zr_0.53Ti_0.47)O₃ particles are determined over a frequency range of 0.2 to 6 GHz. The determined results are found to be in agreement with the coaxial transmission/reflection measurement results. The advantages and limitations of this method are also discussed in this paper.