[FoRK] MIT researchers create fibers that can detect and produce sound
Stephen D. Williams
sdw at lig.net
Tue Jul 13 11:49:05 PDT 2010
Now that is cool. The applications are endless. Extensions into movement
and robotics would be cool too: flagella, etc.
> The heart of the new acoustic fibers is a plastic commonly used in
> microphones. By playing with the plastic's fluorine content, the
> researchers were able to ensure that its molecules remain lopsided —
> with fluorine atoms lined up on one side and hydrogen atoms on the
> other — even during heating and drawing. The asymmetry of the
> molecules is what makes the plastic "piezoelectric," meaning that it
> changes shape when an electric field is applied to it.
> In a conventional piezoelectric microphone, the electric field is
> generated by metal electrodes. But in a fiber microphone, the drawing
> process would cause metal electrodes to lose their shape. So the
> researchers instead used a conducting plastic that contains graphite,
> the material found in pencil lead. When heated, the conducting plastic
> maintains a higher viscosity — it yields a thicker fluid — than a
> metal would.
> Not only did this prevent the mixing of materials, but, crucially, it
> also made for fibers with a regular thickness. After the fiber has
> been drawn, the researchers need to align all the piezoelectric
> molecules in the same direction. That requires the application of a
> powerful electric field — 20 times as powerful as the fields that
> cause lightning during a thunderstorm. Anywhere the fiber is too
> narrow, the field would generate a tiny lightning bolt, which could
> destroy the material around it.
> Despite the delicate balance required by the manufacturing process,
> the researchers were able to build functioning fibers in the lab. "You
> can actually hear them, these fibers," says Chocat, a graduate student
> in the materials science department. "If you connected them to a power
> supply and applied a sinusoidal current" — an alternating current
> whose period is very regular — "then it would vibrate. And if you make
> it vibrate at audible frequencies and put it close to your ear, you
> could actually hear different notes or sounds coming out of it." For
> their /Nature Materials/ paper, however, the researchers measured the
> fiber's acoustic properties more rigorously. Since water conducts
> sound better than air, they placed it in a water tank opposite a
> standard acoustic transducer, a device that could alternately emit
> sound waves detected by the fiber and detect sound waves emitted by
> the fiber.
> In addition to wearable microphones and biological sensors,
> applications of the fibers could include loose nets that monitor the
> flow of water in the ocean and large-area sonar imaging systems with
> much higher resolutions: A fabric woven from acoustic fibers would
> provide the equivalent of millions of tiny acoustic sensors.
> Zheng, a research scientist in Fink's lab, also points out that the
> same mechanism that allows piezoelectric devices to translate
> electricity into motion can work in reverse. "Imagine a thread that
> can generate electricity when stretched," he says.
> Ultimately, however, the researchers hope to combine the properties of
> their experimental fibers in a single fiber. Strong vibrations, for
> instance, could vary the optical properties of a reflecting fiber,
> enabling fabrics to communicate optically.
> SOURCE <http://www.eurekalert.org/pub_releases/2010-07/miot-mr071210.php>
More information about the FoRK