FENG device next to a loudspeaker
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Paper-thin device generates energy from motion; turns flag into loudspeaker

Image credit: Michigan State University

Nanotechnology researchers at Michigan State University have developed a paper-thin device which generates energy from human motion and behaves as a microphone and loudspeaker.

The device is the first ultra-thin, flexible, scalable transducer which can convert motion to electrical energy and vice versa. The researchers suggest that this could make foldable loudspeakers and talking newspapers a reality.

The device, which is known as a “ferroelectret nanogenerator” (FENG), had previously been used by the researchers to power simple devices with swipe of a finger or light pressing motion. The mechanical energy of the movement was converted to electrical energy.

The FENG works using a silicone wafer formed of layers of environmentally friendly materials such as silver and polyimide. Ions are added so that each layer of the device contains charged particles. When the device is compressed by movement, electrical energy is created.

More recently, the Michigan State University researchers discovered that the FENG is capable of more than just converting between human motion and electrical energy. They found that the material can act as a microphone by capturing the mechanical energy of sound waves and converting it into electrical energy or as a loudspeaker by converting electrical energy into sound waves.

Writing in Nature Communications, the researchers describe an experiment to demonstrate the sheet-like device’s utility as a microphone by developing a FENG security patch which uses voice recognition to access a computer. The patch was successful in protecting a computer from other users.

“The device is so sensitive to the vibrations that it catches the frequency components of your voice,” said Professor Nelson Sepulveda of Michigan State University, who led the study.

The researchers also demonstrated the loudspeaker effect by embedding the FENG into a Michigan State University athletics flag. They played music from an iPad through an amplifier and into the flag.

“The flag itself became the loudspeaker,” said Professor Sepulveda. “So we could use it in the future by taking traditional speakers, which are big, bulky and use a lot of power, and replacing them with this very flexible, thin, small device.”

Professor Sepulveda says that it could be possible in the future for a public speaker to take a tiny FENG-based device out of their pocket and use it to project their speech to a roomful of people.

“Imagine a newspaper,” he added. “Where the sheets are microphones and loudspeakers. You could essentially have a voice-activated newspaper that talks back to you.”

Other potential applications, according to the researchers, could include tiny megaphones to allow public speakers to fill a room with their projected voice, noise-cancelling sheeting, or a voice-protected health-monitoring wristband.

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