Energy-generating sheet folds for more firepower

The material actually becomes more powerful when folded(Credit: Michigan State University)

We've seen quite a few experimental systems that can generate energy from movement, each designed with the objective of powering our increasingly mobile lives in mind. A new device developed at Michigan State University (MSU) is the latest take on this problem, consisting of an energy-producing film-like system that increases its output when folded into up into a smaller package.

Advanced backpacks, shoes, insoles and fabrics are just a few examples of systems developed over the past few years that can harness energy from motion. But engineering researchers from MSU have come up with a particularly flexible solution in more ways than one, in the form of a bendable, film-like device no thicker than a piece of paper.

Called a biocompatible ferroelectret nanogenerator, or FENG for short, the device might be slimline but its packs a fairly complex mix of materials within. It begins with a wafer of silicon, with layers of silver, polymide and polypropylene ferroelectret on top. Ions are distributed throughout so that when these layers are compressed through human motion, each layer yields charged particles.

Along with being flexible, lightweight and biocompatible, the device is rather versatile in that the sheet can be cut to size depending on the task at hand. A version was used to successfully power a flexible keyboard, a smaller palm-sized version to power a bank of 20 LED lights, and another the size of a finger to power an LCD touchscreen. This worked simply by touching or applying pressure to the film and without help from a battery pack.

And FENG has another neat trick up its sleeve too, with the ability to become more powerful when folded.

"Each time you fold it you are increasing exponentially the amount of voltage you are creating," says Nelson Sepulveda, project lead. "You can start with a large device, but when you fold it once, and again, and again, it's now much smaller and has more energy. Now it may be small enough to put in a specially made heel of your shoe so it creates power each time your heel strikes the ground."

The team says that FENG could one day find its way into a range of mobile electronics, such as wireless headsets, cell phones and other touchscreen devices. Right now, it is working on technology that can harness the power created by a heel striking the ground and transmit it to device like a wireless headset.

"What I foresee, relatively soon, is the capability of not having to charge your cell phone for an entire week, for example, because that energy will be produced by your movement," says Sepulveda.

The following videos show the technology in action, and the team's research was published in the journal Nano Energy.

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