Design of an Electrochemical Impedance Test Cell with Servomechanically Adjustable Cell Constant

This paper presents the design of an electrochemical impedance test cell for which the cell constant can be precisely varied so as to enable accurate, calibration-free measurements of the dielectric constant and conductivity of liquids and gases. This impedance test cell uses spherical electrodes separated by an adjustable small gap ranging from less than 1 mum up to 50 mum. Accurate material property measurements can be obtained by leveraging the dimensional accuracy of the spheres and the mechanical accuracy of the positioning mechanism. The accuracy of this impedance cell has been demonstrated in measurements of the dielectric constant of air and methanol.