How Energy-Generating Sidewalks Work

WIRED 

These innovative pavings convert the kinetic energy of footsteps into clean electric energy. We walk here, we walk there, we walk everywhere. Maybe you're headed to work or to lunch in a busy city. You're expending energy, and the exercise is good for you. But what if, on top of that, we could recapture all that freely supplied energy and convert it to usable electricity?