Characterization of non-linearities in permittivity and conductivity of soils

Abstract

Ground impedance is characterized by the frequency and current-density dependent soil parameters; permittivity and conductivity. The non-linearities in these parameters have been elucidated through laboratory tests on a carefully controlled-conductivity medium that is representative of in situ soil. A new test cell, that achieves near uniform current distribution in the electrolyte, and a test and measurement system, for accurate measurement of conduction current and applied voltage phasors, has been designed and commissioned for the evaluation of the complex impedance of ionic conductive media bounded by metal electrodes. A variety of test media have been studied including deionized water, Na2SO4 solutions of different concentrations and sand with varying moisture content. The effect of different electrode materials on the electrode-electrolyte interface and its effect on measured impedance has been investigated with copper and stainless steel. In addition to the developed in-house test and measurement system, two proprietary test systems have been used to study particular features and to provide a platform for results validation. The impedance data has been analyzed using bode and Nyquist plots, and the conduction characteristics have been described, and compared with published literature. Furthermore, effective conductivity and permittivity parameters have been determined from the impedance data sets and compared with published literature. Theoretical models describing the physical behaviors of the conduction mechanisms have been derived and compared with the experimental data. In addition, equivalent circuit models, consisting of a parallel RC branch in series with a constant-phase element, are proposed and fit well with the experimental data.

Date of Award	Dec 2019
Original language	American English