Estimation of the dynamic leakage current of a supercapacitor in energy harvesting powered autonomous wireless sensor nodes

The supercapacitor is a candidate energy storage component for energy harvesting powered autonomous wireless sensor node aiming to achieve battery replacement-free, “fit and forget” sensor node in low-power IoT applications. The leakage current of the supercapacitor provided by the manufacturer is tested long after post-charge, raising a concern relating to the uncertainty of the dynamic leakage current in the IoT applications where the supercapacitor frequently charges and discharges. This paper investigates the charge redistribution process which causes an equivalent capacitance change of the supercapacitor in a full IoT measurement period, and then proposes an experiment design to measure the dynamic leakage current of a supercapacitor for an IoT application. The results showed that the charge redistribution process is completed long before the end of the sleep period due to the low ratio of the amount of discharge in an active period to the total amount of charge the supercapacitor holds. It also showed that the average dynamic leakage current in an entire measurement period corresponds to the value provided by the manufacturer, indicating that leakage current is not an issue when supercapacitors is used for low-power IoT applications.