Engineers at Michigan State University have created a paper-thin, flexible device that is able to generate energy from human motion, and act as a loudspeaker and microphone as well.
This breakthrough in nanotechnology could eventually lead to foldable loudspeakers, a voice-activated security 'patch' for computers, and even print publications capable of emitting sounds and spoken words.
Nelson Sepulveda is a Michigan State University associate professor of electrical and computer engineering, and primary investigator in the project. He and his team first successfully demonstrated their sheet-like device in late 2016.
"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," he explained.
In their first demonstration, the team used the device, known as a ferroelectret nanogenerator (FENG), to power a keyboard, LED lights and a LCD touch-screen. The FENG is able to convert mechanical energy, such as a finger swipe or a light pressing motion, into electrical energy to activate the devices.
The most recent breakthrough extends the useability of the FENG device. They found that the material is able to act as a microphone, by capturing the vibrations from sound and then converting it to electrical energy. By reversing the conversion and transforming electrical energy into mechanical energy, the same device is able to act as a loudspeaker.
To demonstrate the microphone effect, the researchers developed a security patch that uses voice recognition to access a computer. The FENG patch is so sensitive to vibrations, it is capable of catching the frequency vibrations of an individual's voice, successfully protecting a computer from other users.
The team also demonstrated the loudspeaker effect by embedding the FENG fabric into a flag, then piping music through an amplifier into the device, reproducing the sound flawlessly.
"The flag itself became the loudspeaker," Sepulveda said. "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."
Other potential applications of the FENG include noise-cancelling sheeting and a health-monitoring wristband that is voice-protected. This would allow flexible electronics to not just have sight and touch aspects, but also speaking and listening capabilities.
FENG is created from a silicone wafer. The wafer 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.
[Photo: G.L. Kohuth]
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