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See how a flag blasts sound like a loudspeaker

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A paper-thin, flexible device can not only generate energy from human motion, but also act as a loudspeaker and microphone, report researchers.

The audio breakthrough could eventually lead to products like a foldable loudspeaker, a voice-activated security patch for computers, and even a talking newspaper.

“You could essentially have a voice-activated newspaper that talks back to you.”

“Every technology starts with a breakthrough and this is a breakthrough for this particular technology,” says Nelson Sepulveda, associate professor of electrical and computer engineering at Michigan State University and primary investigator of the project.

“This is the first transducer that is ultrathin, flexible, scalable, and bidirectional, meaning it can convert mechanical energy to electrical energy and electrical energy to mechanical energy.”

In late 2016, Sepulveda and his team successfully demonstrated their sheet-like device—known as a ferroelectret nanogenerator, or FENG—by using it to power a keyboard, LED lights, and an LCD touch-screen. That process worked with a finger swipe or a light pressing motion to activate the devices—converting mechanical energy to electrical energy.

The current breakthrough extends the FENG’s usability. The researchers discovered the high-tech material can act as a microphone (by capturing the vibrations from sound, or mechanical energy, and converting it to electrical energy) as well as a loudspeaker (by operating the opposite way: converting electrical energy to mechanical energy).

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To demonstrate the microphone effect, the researchers developed a FENG security patch that uses voice recognition to access a computer. The patch was successful in protecting an individual’s computer from outside users. “The device is so sensitive to the vibrations that it catches the frequency components of your voice,” Sepulveda says.

Sepulveda and foldable keyboard
Nelson Sepulveda created an ultra-thin, foldable keyboard that can harvest energy from human motion. (Credit: G.L. Kohuth/Michigan State)

To demonstrate the loudspeaker effect, researchers embedded the FENG fabric into a flag. An iPad piped music through an amplifier and into the flag, which then reproduced the sound flawlessly. “The flag itself became the loudspeaker,” Sepulveda says. “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.”

Imagine a day when someone could pull a lightweight loudspeaker out of their pocket, slap it against the wall, and transmit their speech to a roomful of people, Sepulveda says.

“Or imagine a newspaper,” he adds, “where the sheets are microphones and loudspeakers. You could essentially have a voice-activated newspaper that talks back to you.”

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Wei Li, an engineering researcher and lead author of the paper in Nature Communications, says other potential applications of the FENG include noise-cancelling sheeting and a health-monitoring wristband that is voice-protected.

“Many people are focusing on the sight and touch aspects of flexible electronics,” Li says, “but we’re also focusing on the speaking and listening aspects of the technology.”

The process of creating the FENG starts with a silicone wafer, which is then fabricated with several layers, or thin sheets, of environmentally friendly substances including silver, polyimide, and polypropylene ferroelectret. Ions are added so that each layer in the device contains charged particles. Electrical energy is created when the device is compressed by human motion, or mechanical energy.

The National Science Foundation funds this research. Other coauthors are from Michigan State and Georgia Tech.

Source: Michigan State University