Broadband dielectric measurements at high AC voltage on thin polymer films show a temperature dependent non-linear increase in the dielectric loss. This non-linear behavior is due to the non-linear dependence of a frequency independent loss, namely, the nearly constant loss (NCL). Below the glass transition of the polymer, only the increase in the NCL contributes, while above the glass transition temperature, also the DC conductivity contributes to the increase in the dielectric loss. We point out that the NCL observed at high AC voltages is consistent with the NCL observed for low AC voltage and very high frequencies in dielectric materials. Using the same theoretical framework used to interpret the NCL at low voltages, we provide an interpretation of the observed non-linear behavior. This behavior is important since it can provide a new way to characterize NCL in materials where it is too small to be measured and, thus, help expand our understanding of this phenomenon. From a technological point of view, this unexpected increase in the AC losses needs to be considered in the selection of dielectric materials for systems operating at large AC voltages. Further understanding of the nature of the NCL would be useful in material design for large AC voltage applications.
R. Casalini (Thu,) studied this question.