Two- and four-electrode, wide-bandwidth, dielectric spectrometer for conductive liquids: Theory, limitations, and experiment

Dielectric spectroscopy is used to measure the dielectric properties of liquids. Two-electrode measurements are common but have resolution difficulties because of electrode polarization and small measured phase angles, particularly for solutions with high ionic content. Four-electrode measurements have been used in previous attempts to overcome these problems. The electrical responses of two- and four-electrode dielectric cells are derived with appropriate circuit analysis to yield expressions for the measured phase angle. The theory demonstrates that an ideal four-electrode measurement cannot resolve the permittivity of the liquid and that polarization effects will still be present in the measured characteristics. A two- and four-electrode experimental cell with a bandwidth of 100 Hz to 40 MHz was constructed and used to measure the electrical properties of water and salt solutions. Electrode polarization and conductivity effects are present in both two- and four-electrode measurements. Parasitic impedance from the potential-sensing electrodes and operational amplifiers additionally affects the four-electrode measurements.