Scientists have created a paper-thin, flexible device that can generate energy from human motion and could one day lead to foldable loudspeakers or even talking newspapers.
The audio breakthrough can act as a loudspeaker and a microphone at the same time.
"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," said Nelson Sepulveda, associate professor at Michigan State University in the US.
Last year, the reseachers had successfully demonstrated their sheet-like device - known as a ferroelectret nanogenerator (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 that the 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 converting electrical energy to mechanical energy).
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 said.
To demonstrate the loudspeaker effect, the FENG fabric was embedded into a flag. Music was piped from a tablet through an amplifier and into the flag, which then reproduced the sound.
"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," he said.
"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 said.
"Or imagine a newspaper where the sheets are microphones and loudspeakers. You could essentially have a voice-activated newspaper that talks back to you," he said.