Calibration-free measurement of liquid permittivity and conductivity using electrochemical impedance test cell with servomechanically adjustable cell constant

Abstract

This paper presents a technique and a device for measuring the permittivity and conductivity of liquids and gases that does not require prior calibration by a reference sample. The technique involves precisely controlling the separation between two closely spaced spherical electrodes to make electrical impedance measurements of the sample media as a function of electrode separation. By leveraging the geometrical accuracy of the spheres and precise control of the electrode separation, the permittivity and conductivity of the sample can be extracted using a simple geometrical model of the electrode. Calibration using a reference sample is replaced by mechanical calibration of the sphere diameter and separation control mechanism, which can be engineered simply and accurately using standard components and processes. The electrode separation is adjusted using a flexure stage and a servomechanical actuator, which enables control of the electrode separation with 0.25 nm resolution with a 50 mum range. Permittivity and conductivity measurements within 1% of established values have been demonstrated.