Leakage-Aware Lifetime Estimation of Battery-Free Sensor Nodes powered by Supercapacitors

Battery-free sensor nodes rely solely on energy harvested from the environment and thus employ supercapacitors as energy storage to allow perpetual operation in absence of ambient energy. To guarantee that the sensor nodes can survive in periods where no harvested energy is available, it is crucial to accurately estimate the lifetime of these devices. However, as we show experimentally in this paper, an accurate lifetime estimation is non-trivial due to the supercapacitors' complex discharge characteristics (e.g., leakage currents) and large capacitance tolerances. After showing that empirical data capturing the supercapacitors' characteristics is essential towards an accurate estimation of the system's lifetime, we introduce an enhanced leakage model that is computationally lightweight and evaluate its accuracy experimentally.