Researchers at the University of Wisconsin-Madison have come up with a way to produce electricity from just about the most renewable source known to man -- his own breath. It's all thanks to a plastic microbelt developed by engineers Xudong Wang, Chengliang Sun and Jian Shi. Made of a material known as polyvinylidene fluoride (PVDF), this belt produces an electric charge whenever low-speed airflow passes over it and causes it to vibrate -- a result of that vaunted piezoelectric effect. Eventually, Wang and his team were able to tinker with their system to the point where it could produce enough current to charge small electronic devices. "The airflow of normal human respiration is typically below about two meters per second," Wang explained. "We calculated that if we could make this material thin enough, small vibrations could produce a microwatt of electrical energy that could be useful for sensors or other devices implanted in the face." The researchers say their technology could be used to power smaller biomedical devices like blood monitors and pacemaker batteries, which typically don't demand vast amounts of energy. No word yet on when this system could make its way to the mainstream, but we'll be waiting with bated breath.