Possible applications include doormats which can generate power when someone walks over them. Shoes with piezo-electric soles which can generate power with every step. Applications in the field of medicine include power supplies for pacemakers in heart patients. Pacemakers which are implanted in the body require power supplies which are surgically fitted inside the body. This include regular surgical operations to renew the power supplies. Piezo-electric sheets which can be implanted inside the body can be used to power the pacemakers from the force exerted during breathing.
(Image Courtesy: Frank Wojciechowski/Princeton University)