(Image courtesy of Lotte Grønkjær, Creative Commons).
The mechanical energy involved in touching a smartphone screen or being struck by a raindrop could be converted into electricity using a new energy harvesting concept devised by Penn State researchers. It contrasts from other methods of harvesting energy from motion, which normally generate current from constant vibrations.
The scientists say that they have built a device to capture energy from gentler and more infrequent motions, like scrolling through a news article on a smartphone. They described the device in a paper published in the journal Advanced Energy Materials, a transducer made out of an organic polymer that creates electricity when compressed.
The study gives a twist to the field of energy harvesting, which typically depends on piezoelectric materials that harvest electricity from frequent vibrations or mechanical stress. In recent years, engineers have increasingly tried to exploit this piezoelectric effect, resulting in devices like a sound sensor that only uses power when actually hearing noises.
Their device is known as an ionic diode, which contains two electrodes filled with ions almost like batteries. When a mechanical force is applied, the ions spread out on the membrane, creating a continuous direct current that imparts microwatts of power to the main battery.
“Because the device is a polymer, it is both flexible and lightweight," said Qing Wang, a materials science and engineering professor at Penn State, in a statement. “When incorporated into a next-generation smartphone, we hope to provide 40 percent of the energy required of the battery.”
The charge dissipates once the ions settle down. The complete cycle occurs once every ten seconds, as opposed to devices drawing energy from the piezoelectric effect, which operates most efficiently a hundred times faster, or around 10 vibrations per second.
The device adds to the list of technologies trying to prolong the life of devices like smartphones, wearables, and wireless sensors. Earlier this year, a Georgia Institute of Technology team reported a tiny generator that could allow fitness bands and smart watches to harvest energy from running and walking. Other innovations involve soaking up power from stray radio waves.
Though the transducer is targeted at smartphones, there are many applications that would benefit from harvested energy. It could be used in biomedical devices pasted onto hospital patients or sensor tags for livestock powered by muscle contractions.
The device could also gather energy from wind or ocean waves as “a source of abundant, environmentally benign and sustainable power,” the researchers wrote in their paper.