Researchers from Penn State University have developed a new technology that can harness the movements of a user's fingers against a touch screen to generate electricity. In time, the team hopes the technology could provide as much as 40 percent of the energy required by a next-gen smartphones and tablets.
The research was funded in part by electronics giant Samsung. For obvious reasons, Samsung is exploring alternative energy sources to help power next-gen electronic devices.
So far, there's been some success in harnessing mechanical energy – devices that convert mechanical energy into electricity are already widely used to help power wearable electronics, biomedical devices and things in the growing "Internet of Things".
Commonly, these inventions are based on the piezoelectric effect – the ability of certain materials and substances to generate an electrical charge in response to mechanical stress, such as being compressed, twisted or distorted.
The problem with piezoelectric energy conversion is that it works best at high frequencies – greater than 10 vibrations per second. Performance tends to fall off dramatically at lower frequencies. And such high frequency movements are relatively hard to find in nature, where lower frequency movements are much more commonly seen.
Electrical engineering professor Qing Wang says that the project was squarely aimed at addressing this challenge. "Our concept is to specifically design a way to turn low-frequency motion into electricity," he says.
The multidisciplinary research team decided to try to find a way to match the operating efficiency of transducers, which convert one form of energy to another, to that of the vibrational sources for the sake of efficient energy conversion. If successful, this approach could substantially raise the level of energy harvested from ambient sources.
The solution they arrived at is a mechanical energy transducer based around a new kind of flexible, organic, ionic diode. It's made up 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 improve the conductivity and mechanical strength of the electrodes.
The magic happens when a mechanical force, such as the press of a finger is applied. The ions diffuse across the membrane, creating a continuous direct current. At the same time, a built-in potential is established that opposes ion diffusion until equilibrium is reached. The complete cycle operates at a frequency of one-tenth Hertz, or once every 10 seconds.
The research team says the peak power density of the device is, in general, larger than or comparable to those of piezoelectric generators operating at their most efficient frequencies.
"Right now, at low frequencies, no other device can outperform this one," says Wang. "That's why I think this concept is exciting."
The researchers believe their device could pave the way to a scalable energy harvester that could help power next-gen electronic devices. Their next steps are to further improve the concept and integrate it into smartphones and tablet devices.
"Because the device is a polymer, it is both flexible and lightweight," Wang said. "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 [battery] safety issue should be resolved."
You can read a paper about the new device at the journal Advanced Energy Materials.
Source: Penn State University
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