Four‐Electrode Null Techniques for Impedance Measurement with High Resolution

TLDR: In this article, a null technique was used to measure the voltage across the sample and to obtain the required precision at low frequencies, at which the normally difficult measurement of the dielectric properties of conducting materials is severely compromised by electrode polarization.

Abstract: At low frequencies, the normally difficult measurement of the dielectric properties of conducting materials is severely compromised by electrode polarization. This problem at the electrode‐sample interface arises from the modulation of the normal dc boundary potential by the passage of alternating current. A solution, permitting a conductance resolution of 1:105 for frequencies between 10 cps and 1 kc, is to use a second noncurrent‐carrying pair of electrodes to measure the voltage across the sample and to employ a null technique for obtaining the required precision. Several four‐electrode null techniques are proposed, each having certain relative merits. In all cases the resolution in capacitance is shown to be governed by a combination of the resolution in conductance, the sample properties, and the frequency of the measurement.