Mechanical modulations for enhancing energy harvesting: Principles, methods and applications

Mechanical kinetic energy harvesting, which converts the mechanical motions and vibrations that are commonly available in the surrounding environment to electrical energy, can realize self-power sensing, control and actuation, with the advantages of convenience, energy saving, ecofriendliness and sustainability. It has broad application prospects in the fields of aerospace, biomedical engineering, environmental monitoring and military engineering. The forms of mechanical energy in the ambient are various and may be time-varying, and its direct conversion to electrical energy may result in low output power, low conversion efficiency, and even damage to the device. In order to improve the performance of energy harvester, the mechanical energy can be mechanically modulated and then be converted to electrical energy. In this paper, the key roles of mechanical modulations for energy harvesting are emphasized. The methods and principles of mechanical modulations and their applications to energy harvesting systems are reviewed and classified into three categories: excitation type conversions, frequency up-conversions, force/motion amplifications. The prospects of the research on mechanical modulation based energy harvesting are also presented.