Harvesting energy from the motion of human limbs: the design and analysis of animpact-based piezoelectric generator

Abstract

Vibration energy harvesters can replace batteries and serve as clean and renewable energysources in low-consumption wireless applications. Harvesters delivering sufficientpower for sensors operating in an industrial environment have been developed, butdifficulties are encountered when the devices to be powered are located on the humanbody. In this case, classical harvester designs (resonant systems) are not adaptedto the low-frequency and high-amplitude characteristics of the motion. For thisreason, we propose in this paper an alternative design based on the impact ofa moving mass on piezoelectric bending structures. A model of the system ispresented and analysed in order to determine the parameters influencing thedevice performances in terms of energy harvesting. A prototype of the impactharvester is experimentally characterized: for a generator occupying approximately25 cm3 and weighing 60 g,an output power of 47 µW was measured across a resistive load when the device was rotated by180° eachsecond. 600 µW were obtained for a 10 Hz frequency and 10 cm amplitude linear motion. Furtheroptimization of the piezoelectric transducer is possible, allowing a large increase inthese values, bringing the power density for the two cases respectively to 10 and120 µW cm−3.