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

TLDR

Vibration energy harvesters can replace batteries in low‑consumption wireless devices, yet classical resonant designs fail to capture the low‑frequency, high‑amplitude motion of the human body. This study proposes an impact‑based piezoelectric generator that uses a moving mass striking bending structures to harvest energy from limb motion. A mathematical model is developed and analyzed to identify the key parameters that govern the harvester’s performance. Experimental tests show the prototype delivers 47 µW at 1 Hz rotation and 600 µW at 10 Hz linear motion, with potential power densities up to 10 and 120 µW cm⁻³ after transducer optimization.

Abstract

Vibration energy harvesters can replace batteries and serve as clean and renewable energy sources in low-consumption wireless applications. Harvesters delivering sufficient power for sensors operating in an industrial environment have been developed, but difficulties are encountered when the devices to be powered are located on the human body. In this case, classical harvester designs (resonant systems) are not adapted to the low-frequency and high-amplitude characteristics of the motion. For this reason, we propose in this paper an alternative design based on the impact of a moving mass on piezoelectric bending structures. A model of the system is presented and analysed in order to determine the parameters influencing the device performances in terms of energy harvesting. A prototype of the impact harvester is experimentally characterized: for a generator occupying approximately 25 cm3 and weighing 60 g, an output power of 47 µW was measured across a resistive load when the device was rotated by 180° each second. 600 µW were obtained for a 10 Hz frequency and 10 cm amplitude linear motion. Further optimization of the piezoelectric transducer is possible, allowing a large increase in these values, bringing the power density for the two cases respectively to 10 and 120 µW cm−3.