Energy harvesting from human respiration

Using breath to generate a microwatt to power small devices

By Nick Flaherty www.flaherty.co.uk

One of the strangest ways to harvest energy to power small devices has come from engineers at the University of Wisconsin-Madison. Materials Science and Engineering Assistant Professor Xudong Wang, postdoctoral Researcher Chengliang Sun and graduate student Jian Shi have created a plastic microbelt that vibrates when passed by low-speed airflow such as human respiration.
By making the belt of a piezoelectric material such as polyvinylidene fluoride (PVDF), an electric charge accumulates in response to applied mechanical stress, and the researchers engineered PVDF to generate sufficient electrical energy from respiration to operate small electronic devices.

Graduate Student Jian Shi and Materials Science and Engineering Assistant Professor Xudong Wang demonstrate a material that could be used to capture energy from respiration

Although it sounds strange, the engineering is sound. “Basically, we are harvesting mechanical energy from biological systems. The airflow of normal human respiration is typically below about two meters per second,” says Wang. “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 microbelt generator

Wang’s team used an ion-etching process to carefully thin material while preserving its piezoelectric properties. With improvements, he believes the thickness can be controlled down to the submicron level. Because PVDF is biocompatible, he says the development represents a significant advance toward creating a practical micro-scale device for harvesting energy from respiration. This then could be used to develop biomedical devices that could monitor blood glucose for diabetics or keep a pacemaker battery charged so that it would not need replacing.