Correction of Geometric Influence in Permittivity Determination

Determination of relative permittivity of dielectric materials is generally done with a rather low accuracy, in the order of several percent. This is in a sharp contrast to the accuracy of measurements of the dissipation factor, both usually being determined in the same measurement. A common understanding for the inferior accuracy in permittivity measurements is the effects of electrode edges. However, further studies indicate that geometric effects, arising from electrode shielding box, guard ring, electrode supporting materials, etc., also influence the accuracy significantly if the responding voltage present at the measuring electrode is non-negligible. With help of the Finite Element Method (FEM), geometric correction factors are estimated from an electrode model to increase the accuracy. This study is specially focused on the application of contact-free electrode arrangement using the air reference method. In this paper, a few examples of how geometric influences affect results are presented as well as a comparison of experimental results. From these insights, we discuss how to minimize and compensate the geometric effects.