Materials

Paper-Thin Material Can Generate Power and Morph Into a Foldable Loudspeaker

Researchers have developed a nano-scale technique for converting electrical energy into mechanical energy — and vice-versa.

Like a traditional loudspeaker, this sheet-like, flexible device can transmit sound. | Michigan State University
Like a traditional loudspeaker, this sheet-like, flexible device can transmit sound. | Michigan State University

Look inside any loudspeaker, headphone, or even earbud and what you'll find is a surprisingly straightforward analog operation. Electricity moving through a magnet thumps vibrations to a diaphragm, which amplifies the signal into audible sound waves. It works like a drum, basically.

Researchers at Michigan State University are proposing an entirely new kind of speaker setup in which energy is manipulated on the nano scale, radically switching up basic design principles that have endured for decades. If all goes well, the new technology will result in foldable speakers that you can pull from your pocket and slap on a wall.

The paper-thin material is called a ferroelectret nanogenerator, or FENG, and it works by converting electrical energy to mechanical energy on a very precise and very small scale.

The technology is bidirectional, too. Run in “reverse,” the material can turn mechanical energy back into electrical energy. As such, FENG materials can work as a microphone, converting physical energy of sound waves back into electrical impulses.

Researcher Nelson Sepulveda said the material was originally developed as a fabric that would generate power from repetitive movement.

“The first intention was to harvest electricity from human motion and use it to power wearable devices,” said Sepulveda, associate professor of electrical and computer engineering at Michigan State University. “Later, we came up with these extensions of the work, which allows for the device to be used as a flexible, portable microphone or loudspeaker.”

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To demonstrate that device’s loudspeaker potential, the MSU research team threaded FENG material into a Michigan State Spartan flag. Music ported in from an iPad essentially turned the flag into a speaker, pumping out the Michigan State fight song.

Sepulveda said that, with the flag experiment, the output was slight, but definitely audible.

“You fold it once, twice, three times, you're improving substantially the amount of energy you're getting from the loudspeaker,” he said.

Working in the other direction, the FENG material can be used to design new kinds of voice-activated devices. In fact, FENG-powered flexible microphones are sensitive enough to identify specific frequencies in an individual voice, according to the research team. To demonstrate this aspect of the technology, the developers designed a voice-recognition security patch affixed to a personal computer.

As to the nuts and bolts, FENG materials are built on a silicone wafer base with microscopically thin layers of additional elements including silver, polyimide, and polypropylene ferroelectret. The material is then showered with ions so that each layer contains electrically charged particles.

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Sepulveda hopes that the nanogenerator technique, published today in the journal Nature Communications, will inspire other researchers to find even more applications for the technology. 

“We have just opened the door,” he said. “We're hoping for the scientific community to engage and expand on these ideas. The number of things that can be done with this device, it's really just too much for one group to handle.

“There's plenty of room here to do fun stuff.”

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