Anomalous reactance behaviour during the impedance analysis of time-varying dielectric systems

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Abstract
Any real dielectric material deviates from ideal behaviour by exhibiting residual electrical conductivity, particularly at high fields and elevated temperatures. This conductivity is usually non-ohmic and often time-varying. During the a.c. impedance analysis of such a system, anomalous reactance behaviour may be observed including negative capacitance and low-frequency dispersion. We con-sider the characterization of dielectrics displaying time-varying conductivity and discuss their interpretation in terms of equivalent-circuit components. The situation is shown to be analogous to the Debye treatment of dielectric relaxation but with time-varying conductivity in place of time-varying permittivity. Quantitative relationships between the time-varying differential conductivity and the measured frequency-domain behaviour are derived and the origins of negative capacitance, low-frequency dispersion and related anomalous reactance effects are elucidated.