Design of Piezoelectric Energy Harvesting Shoes for Charging Phones

In spite of great advances in cell phone technology, the rapid discharge of phone batteries remains a widespread problem. One solution may be recharging phones with movements of the body, such as with energy harvesting shoes. Soft-soled impact-absorbing shoes are best for the feet and for general health. Energy harvesting from shoes have been of interest for decades, but the technology is still in the research phase. Piezoelectric voltage generation at shoes is made more feasible with recent advances in flexible piezoelectric materials. The characteristics of energy conversion at shoes have been studied. Shoes connected through wires on the legs to power electronics can charge a phone at the waist. An extra battery source at the power electronics would be an inconvenience, and a simple full wave rectifier with filter is proposed for initial testing. The resulting large time constant implies the need for a large capacitor. The design considerations in this paper may be the basis of further research and experimentation, and possible commercial implementation.