Energy-Aware Approaches for Energy Harvesting Powered Wireless Sensor Nodes

Intensive research on energy harvesting powered wireless sensor nodes (WSNs) has been driven by the needs of reducing the power consumption by the WSNs and increasing the power generated by energy harvesters. The mismatch between the energy generated by the harvesters and the energy demanded by the WSNs is always a bottleneck as the ambient environmental energy is limited and time varying. This paper introduces a combined energy-aware interface with an energy-aware program to deal with the mismatch through managing the energy flow from the energy storage capacitor to the WSNs. These two energy-aware approaches were implemented in a custom developed vibration energy harvesting powered WSN. The experimental results show that, with the 3.2-mW power generated by a piezoelectric energy harvester under an emulated aircraft wing strain loading of <inline-formula> <tex-math notation="LaTeX">$600~\mu \varepsilon $ </tex-math></inline-formula> at 10 Hz, the combined energy-aware approaches enable the WSN to have a significantly reduced sleep current from <inline-formula> <tex-math notation="LaTeX">$28.3~\mu \text{A}$ </tex-math></inline-formula> of a commercial WSN to <inline-formula> <tex-math notation="LaTeX">$0.95~\mu \text{A}$ </tex-math></inline-formula> and enable the WSN operations for a long active time of about 1.15 s in every 7.79 s to sample and transmit a large number of data (388 B), rather than a few ten milliseconds and a few bytes, as demanded by vibration measurement. When the approach was not used, the same amount of energy harvested was not able to power the WSN to start, not mentioning to enabling the WSN operation, which highlighted the importance and the value of the energy-aware approaches in enabling energy harvesting powered WSN operation successfully.