The piezoelectric effect is one way of converting mechanical energy to useful electrical energy.
The video (link below) shows that many of the mechanical motions around us, such as handwriting and foot pressure, can be used to obtain useful electrical energy and signals.
The Physical Electronics and Nanotechnology research group is based at Campus Norrköping and led by senior lecturer Omer Nour.
Eiman Satti’s thesis: Low-Frequency Self-Powered Footstep Sensor Based on ZnO Nanowires on Paper Substrate