Performance Enhancement of Piezoelectric Bending Beam-Based Human Knee Energy Harvester

Biomechanical energy harvesters can capture biomechanical energy from human motion and generate electricity for powering wearable and portable electronics. Thanks to that, the widely used body-worn devices can be battery-free and eliminate battery capacity limitations. This article develops a lightweight piezoelectric bending beam-based human knee energy harvester to generate electricity during walking. To enhance the performance, especially in the stance phase, we propose a new design and introduce free vibration in the stance phase to improve the output voltage and power. Specifically, one end of the bending beam is released and moves freely, such that the bending beam experiences free vibration in the stance phase. While in the swing phase, the bending beam still undertakes forced motion. Besides, a proof mass is mounted on the bending beam to tune the free vibration. Experimental results indicate that compared with the previous design, the free vibration can improve the average output power by 52.3%. When walking at 7 km/h on a treadmill, the average power output can reach 43.4 mW. This work significantly facilitates the further development of biomechanical energy harvesters. The output power is improved by 10 to 100 times compared with the existing works.