When they are not listening: Harvesting power from idle sensors in embedded systems

Ambient energy harvesting is a well-known technique in wireless sensing systems. To minimize energy consumption, such systems are typically designed to be heavily duty-cycled with long idle times and are characteristically lightweight in computation. Often, these systems contain a dedicated energy harvesting transducer that is independent of the sensing sub-system. As a result, any output energy from the sensor ends up being unused (and hence, lost) when the system is in idle state. This work proposes a novel system architecture and corresponding hardware platform, Senergy, in which the energy harvested from a sensor during idle time is utilized to power the system. Senergy is based on an ultra-low power charge pump circuit that boosts input voltages as low as 330mV. We successfully demonstrate our proposed architecture with an RF-capable (2.4GHz ISM band) sensing platform utilizing a photovoltaic sensor as the sole energy source. We evaluate our approach on two applications, namely adaptive transmission of sensor data and providing an uninterrupted power supply to an on-board real time clock.