Footwear for piezoelectric energy harvesting: A comprehensive review on prototypes development, applications and future prospects

The extreme consumption of non-renewable energy sources poses serious concerns of environment pollution and energy crisis across the globe, which stimulate the research on exploration of alternative energy technologies capable of harvesting available energy in the ambient environment. Mechanical energy is ubiquitously available in the ambient environment, which can be converted into electrical energy using piezoelectric energy harvesters (PEH) based on piezoelectric effect. PEH have evolved as a non-conventional, feasible and clean solution to meet energy requirement worldwide and played an important role in powering of several portable electronic devices, wireless sensor nodes, and medical implants. PEH enables self-powered functioning of devices along with a longer lifespan. The merits of this technology lies in its easy implementation, miniaturization, and high energy conversion efficiency. The utilization of waste mechanical energy available from the human body (e.g., natural movements of humans) in piezoelectric energy harvesters is one of the prime interests of researchers. The footwear equipped with piezoelectric material is one such novel innovation in the area of piezoelectric energy harvesting which utilizes the vibration generated during human body movements, thereby converting direct mechanical impacts into useful energy. This review article starts with providing the basic fundamental information on piezoelectric effect, piezoelectric materials and piezoelectric energy harvesting technology. The prime objective of this article is to provide the comprehensive review of recent developments made in designing footwear prototypes for piezoelectric energy harvesting and their emerging applications. Interestingly, this review also discusses the important patented technologies based on piezoelectric footwear energy harvesting. At last, this review discusses the merits and limitations of available footwear prototypes for piezoelectric energy-harvesting and provides the new directions for researchers in this innovative area of energy harvesting.