Human Motion Seen as Potential Alternative Energy Source

Alternative energy sources are very much in demand as a means to power next-generation electronic devices. Penn State materials scientists and electrical engineers, through the funding of electronics company Samsung, have developed a mechanical energy transducer that could harvest unused mechanical energy in the environment, including wind, ocean waves, and human motion.

Ambient mechanical energy could be converted to electricity and power wearable electronics and biomedical devices. These devices efficiently operate at frequencies higher than 10 vibrations per second. Lower frequencies, however, don't perform as effectively.

"Our concept is to specifically design a way to turn low-frequency motion, such as human movement or ocean waves, into electricity," said Qing Wang, professor of materials science and engineering at Penn State. "That's why we came up with this organic polymer p-n junction device."

In their research 'Flexible Ionic Devices for Low-Frequency Mechanical Energy Harvesting' that was published in the journal Advanced Energy Materials, the research team developed an ionic diode made of two nanocomposite electrodes with oppositely charged mobile ions separated by a polycarbonate membrane.

The electrodes are a polymeric matrix filled with carbon nanotubes and infused with ionic liquids that enhance the conductivity and mechanical strength of the electrodes. The ions diffuse across the membrane, creating a continuous direct current when a mechanical force is applied. The complete cycle operates at a frequency of one-tenth Hertz, or once every 10 seconds.

Using this new source of mechanical energy by touching a screen, human motion could power a tablet or wearable electronic device. "Because the device is a polymer, it is both flexible and lightweight," Wang explained. "When incorporated into a next-generation smart phone, we hope to provide 40 percent of the energy required of the battery. With less demand on the battery, the safety issue should be resolved."