CapDYN : Adaptive Self-Scaling Energy Storage for Powering Batteryless IoT

Battery-free devices collect the harvested ambient energy in their energy storage capacitors. The size of the storage capacitor is one of the main factors affecting the device’s active time and power failure rate. In fact, a larger capacitor ensures energy autonomy for longer operations, while a smaller capacitor charges faster and shrinks inefficient cold starts. This paper presents CapDYN, a new energy storage architecture that can self-adapt its capacity based on incoming ambient energy. CapDYN automatically reconfigures the size of its capacitor bank to both speed up charging and improve execution rate. CapDYN reduces the startup time by up to 98% and can schedule tasks up to 38% faster, compared to a fixed-size capacitor. CapDYN operates in a fully autonomous manner consuming down to 11.6 µW in its simplest implementation and replaces the power-hungry microcontroller governing the switching operation with a dedicated ultra-low-power circuit built with COTS components. Its power consumption improves the previous state of the art by 73%, all the while featuring uncompromising reactivity. CapDYN can instantly react to sudden power transients without incurring extra power draw by foregoing MCU-driven reconfiguration used in state-of-the-art dynamic energy storages.