This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.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.The authors gratefully acknowledge financial support from the Engineering and Physical Sciences Research Council (EPSRC) in the UK through funding of the research into ‘smart multifunctional architecture & technology for energy aware wireless sensors’ (EP/K017950/2)

This letter presents a piezoelectric bimorph with auxetic (negative Poisson’s ratio) behaviors for increased power output in vibration energy harvesting. The piezoelectric bimorph comprises a 2D auxetic substrate sandwiched between two piezoelectric layers. The auxetic substrate is capable of introducing auxetic behaviors and thus increasing the transverse stress in the piezoelectric layers when the bimorph is subjected to a longitudinal stretching load. As a result, both 31- and 32-modes are simultaneously exploited to generate electric power, leading to an increased power output. The increasing power output principle was theoretically analyzed and verified by finite element (FE) modelling. The FE modelling results showed that the auxetic substrate can increase the transverse stress of a bimorph by 16.7 times. The average power generated by the auxetic bimorph is 2.76 times of that generated by a conventional bimorph.