Engineers are testing a device that converts low-frequency motion into electricity to power electronics. The idea is to harvest wasted energy, like that from a finger tapping on a screen, to power a phone or tablet.
“Right now, at low frequencies, no other device can outperform this one.”
“Our concept is to specifically design a way to turn low-frequency motion, such as human movement or ocean waves, into electricity,” says Qing Wang, professor of materials science and engineering at Penn State.
Devices that harvest ambient mechanical energy and convert it into electricity are widely used to power wearable electronics and medical devices. The most common of these devices, based on the piezoelectric effect, operate most efficiently at high frequency, greater than 10 vibrations per second. But at lower frequencies their performance falls off dramatically.
“Right now, at low frequencies, no other device can outperform this one,” says Wang. “That’s why I think this concept is exciting.”
How the new device works
Called an ionic diode, the device is composed 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. The nanotubes enhance the conductivity and mechanical strength of the electrodes.
When a mechanical force is applied, the ions diffuse across the membrane, creating a continuous direct current. At the same time, a built-in potential that opposes ion diffusion is established until equilibrium is reached.
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The complete cycle operates at a frequency of one-tenth Hertz, or once every 10 seconds.
“Because the device is a polymer, it is both flexible and lightweight,” Wang says. “When incorporated into a next-generation smartphone, we hope to provide 40 percent of the energy required of the battery.”
The team describes the device in Advanced Energy Materials. Future work will involve further optimization and integration into smartphones and tablets.
Samsung, the China Scholar Council, and the National Natural Science Foundation of China supported the project.
Source: Penn State
