Biomechanical energy harvesting technologies for wearable electronics: Theories and devices

Wearable biomechanical energy harvesting devices have received a lot of attention recently, benefiting from the rapid advancement of theories and devices in the field of the micro electromechanical system (MEMS). They not only fulfil the requirements for powering wearable electronic devices but also provide an attractive prospect for powering self-powered flexible electronic devices when wearing. In this article, we provide a review of the theories and devices of biomechanical energy harvesting technology for wearable applications. Three different forms of biomechanical energy harvesting mechanisms, including the piezoelectric effect, electromagnetic effect, and electrostatic effect, are investigated in detail. The fundamental principle of converting other types of energy from the biomechanical environment into electrical energy, as well as the most commonly-used analytical theoretical models, are outlined for each process. Therefore, the features, properties, and applications of energy harvesting devices are summarized. In addition, the coupled multi-effect hybrid energy harvesting devices are listed, showing the various possibilities of biomechanical energy harvesting devices for serving as sources, sensors, and actuators. Finally, we present perspectives on the future trends of biomechanical energy harvesting devices for wearable electronics applications.