New Fibers Can See, Hear, Speak
Would you want to wear a shirt that you could talk to? Would you mind if it talked back?
Right now the fibers require an external
power source to sense sound and light or produce sound. That could soon change. Click to enlarge
Research Laboratory of Electronics at MIT/Greg Hren Photograph
Clothing that can see, hear and even talk
is being developed by scientists from the Massachusetts Institute of Technology.
By adding light- and sound-sensitive
materials to synthetic fibers, the researchers are creating a new class of intelligent
materials that could have a huge range of potential applications, from undetectable
microphones to sophisticated medical sensors.
"Fibers are, for the most part,
static," said Yoel Fink, a scientist at MIT and a co-author of the Nature
Materials paper that describes the research.
Cotton, polyester, wool and other
materials look good and feel comfortable, but that's about all they can do. They are, in
other words, dumb. "We want to see how sophisticated a fiber can become to see how
many different functions we can put into it," said Fink.
The key to Fink's fibers is a special
manufacturing process that is remarkably similar to how saltwater taffy is made.
To create the sound-sensitive fibers the
scientists first make a thick rod, or preform. Inside that preform are thick layers of
graphite electrodes, a plastic piezoelectric commonly found in microphones and
light-sensitive materials. The MIT scientists heat up the rod and stretch it into miles of
nanometer-sized fibers with thin layers that, besides their size, are otherwise identical
to the original preform.
Here's the trick: Ordinarily, heating up
these materials would cause them to mix, separating the layers and rendering the fibers
useless. Fink and his colleagues have created a unique way to stretch those fibers without
destroying the underlying architecture.
It's a simple tweak, but one that has
enabled Fink to create an ever expanding class of fibers with new and unique abilities.
"He's certainly gotten a lot of
mileage out of it," said Eli Yablonovitch, a scientist at the
Last year Fink and his colleagues used
this technique to create fibers that can see. By incorporating piezoelectric materials
into the fibers, he has created a fiber that can hear and speak as well as see.
The new research details the addition of a
piezoelectric material, which creates an electrical current in response to pressure. When
a sound wave hits Fink's new fiber, it bends and produces electricity. By measuring the
electrical current, the MIT scientists can listen to sound and pressure waves, ranging
from loud, megahertz sized waves to inaudible ultrasonic waves.
Fink's fibers can also work in reverse.
When an electrical current is pumped into the piezoelectric fibers they create a similar
range of sound and pressure waves.
"Ultimately, we want each part to
function together," said Fink. "It's like moving from a circuit board to an
integrated circuit, just in a fiber."
The range of applications for such an
integrated fibers is huge.
Some are obvious: hidden microphones
embedded in clothes or shirts that can change into loudspeakers when necessary. Other
applications are more subtle. The narrow fibers could be threaded through blood vessels to
monitor blood flow. They could image organs, like the lungs, that are otherwise difficult
to see with ultrasound.
Right now the fibers require an external
power source. That could soon change, said Fink. By tweaking the piezoelectric fibers to
maximize power output when they are flexed, it could be possible to create a fabric that
could power not only itself, but other electrical devices as well.
The U.S. Army has already tested the
light-sensitive materials as a means of communications between soldiers, said Fink in an
interview last year. (Fink's research is funded by DARPA at MIT's Institute for Soldier
Niche markets like the military and
medicine will most likely develop uses for the new fibers first, said Yablonovitch,
followed by more civilian applications over the next 10 years.
"This is a trend that we will see
more and more in the future: our clothes becoming very high-tech," said Yablonovitch.
"But we also have to ask ourselves if all of our clothes need a plug."