At the end of last year researchers from Michigan State University (MSU) demonstrated a way to harvest energy from motion using a paper-thin flexible material—known as a ferroelectret nanogenerator, or FENG. Using the low-cost material they built a flexible keyboard powered entirely by touch without any batteries or other power source.
Now the same researchers have managed to extend the technology, allowing the FENG to act both as a microphone and a loudspeaker.
Built out layers of thin sheets of ionised silicon, silver, and polymide, and then covered with a foam called polypropylene ferroelectret, as the FENG is compressed it produces electrical energy.
“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.”
Originally the team—lead by Nelson Sepulveda, an associate professor of Electrical and Computer Engineering at MSU—thought the material could be used to make garments that could harvest the motion of the wearer to charge their gadgets. However as they continued to research it they discovered that it was much more sensitive to vibrations than they thought. Sensitive enough that even sound waves were enough to produce small amounts of electricity—it could be used as a microphone. The researchers went on to prototype a security patch that would restrict access a computer based on an individual’s unique voice pattern.
“The device is so sensitive to the vibrations that it catches the frequency components of your voice,” said Sepulveda.
The material proved equally effective in reverse, converting electrical energy back to sound. To demonstrate the effect the team went ahead and embedded the FENG fabric into an MSU Spartan’s flag, and piped the team’s fight song to the material using an iPad outputting the music through an amplifier.
The work could eventually lead to foldable loudspeakers, stick on microphones, and talking newspapers, all powered by vibration.
“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,” said Sepulveda.
However the new work doesn’t rule out using the material for its originally intended purpose, so you could also imagine clothing that could charge your phone while at the same time also act as a microphone and speaker.