Error Analysis and Correction of Relative Permittivity Measured by Three-electrode System

To improve the accuracy of the measured relative permittivity based on three-electrode system, a three-dimensional model for relative permittivity measurement is established and solved with consideration of real electrode system’s material properties and dimension by means of the finite element analysis software Comsol for multiple physical fields. In view of the nearly rotational symmetry of the electrodes system, the model is simplified to two-dimensional one to reduce computation amount. Comparison of the computation results between the 3D and 2D models verifies the reliability of the latter. Subsequently, the potential, electric field and surface charge distributions are obtained, and the error of the relative permittivity calculated by the method in a standard is calculated. The influences of sample’s thickness, relative permittivity and area (radius) on the accuracy of the calculated relative permittivity are systematically investigated, and the key factors influencing the accuracy are determined. Employing the 2D model with the sample’s thickness ranging from 0.2 to 10 mm and relative permittivity ranging from 1 to 100, the errors of relative permittivity are obtained, which are all less than zero. The relationship among sample thickness, measured relative permittivity and real value of relative permittivity is obtained, and the 2D interpolation method is used to correct the measured relative permittivity. In addition, the proposed correction method is validated by simulation and is applied to relative permittivity measurement of an insulating material