CARBON-nanotube speakers may help to reveal the secrets of the deep seas. Engineers have created an underwater speaker using thin sheets of nanotubes, which they hope could provide a lightweight alternative to the sound projectors used in long-range sonar.
The team knew that passing an alternating current through carbon-nanotube sheets could mimic the vibrations of a speaker cone, as the sheet quickly heats and cools the surrounding air.
Now 鈥榮 team at the NanoTech Institute, University of Texas at Dallas, has shown that the speakers work surprisingly well underwater. Water鈥檚 high heat capacity and low thermal expansion would normally absorb any temperature fluctuations. But the nanotubes鈥� hydrophobic properties result in an air pocket around the sheet which expands and contracts as the sheet heats and cools, pushing the surrounding water in and out as a piston would (Nano Letters, ).
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The sheets can generate a wide range of frequencies, including those below 4 kilohertz, which are used for long-range sonar and are traditionally generated using heavy sound projectors, says Aliev. There is a high demand for lighter devices, he adds.
