Non-linear dielectric measurements in conducting media using a frequency sampling technique

Abstract

A technique is described for measuring non-linear dielectric effects (NDE) in conducting media using a frequency sampling technique. The medium under investigation is contained in a dielectric cell which is part of the tuned circuit of an oscillator. The change in frequency of the oscillator on application of a square pulse of electric field is measured using a commercial computing counter. The averaging facility of the counter allows up to 10⁴ determinations in one sequence. The measured effect is shown to be the sum of the NDE plus a Joule heating effect due to the conductance of the liquid. The true NDE is determined by extrapolation of the data to zero pulse width while the rate of change of the total effect plus a residual effect after the pulse gives information on the heating. It is shown that the heating of the liquid between the electrodes is an adiabatic process, the time of diffusion of the heat to the rest of the cell being large compared with the time of the experiment. Illustrative results are given for acetone, hexanol and dodecanol. In addition the precise measurements of the heating effect can be used for the determination of high field conductivities and thermometric, calorimetric etc. measurements in suitable cases.