Energy harvesting during human walking to power a wireless sensor node

Abstract

The continuous progress made in wearable energy harvesting technology is delivering sophisticated devices with increasing power output, which are possible to provide sustainable energy supply for body sensors to achieve an energy-autonomous wireless sensing system. This paper reports the development and characterisation of a wearable energy harvesting powered wireless sensing system with system-level strategies to address the challenges in energy harvesting, power conditioning, wireless sensing and their integration into a system. The system comprises four parts: (1) a magnetically plucked wearable knee-joint energy harvester (Mag-WKEH) to scavenge energy from knee-joint motion during human walking, (2) a power management module (PMM) with maximum power point tracking (MPPT), (3) an energy-aware interface (EAI) for dealing with mismatch between energy generated and energy demanded, and (4) an energy-aware wireless sensor node (WSN) for data sensing and transmitting. Experiments were performed with a human subject wearing the system walking on a treadmill at different speeds. The experimental results showed that as the walking speed increased from 3 to 7 km/h, the power output of the Mag-WKEH increased from 1.9±0.12 to 4.5±0.35 mW, and the generated power was able to power the WSN to work at a duty cycle from 6.6±0.36% to 13±0.5% with an active time of 2.0±0.1s. In each active time, the WSN was able to sample 482 readings with an interval of 10 ms from the sensors and transmit all data to a base station at a distance of 4 m.