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Speakers made from carbon nanotube sheets a fraction of the width of a human hair can generate sound and cancel out noise at the same time, which is perfect for submarine sonar to probe the ocean depths, while making it invisible to enemies.
Thin films of nanotubes can generate sound waves via a thermoacoustic effect, said Ali Aliev, Ph.D. of the MacDiarmid NanoTech Institute at the University of Texas at Dallas. Every time an electrical pulse passes through the microscopic layer of carbon tubes, the air around them heats up and creates a sound wave.
Chinese scientists first discovered that effect in 2008, and applied it in building flexible speakers. The Chinese nanoscientists stuck a sheet of nanotubes onto the side of a flag, and attached it to an mp3 player. They used the nanotube-coated flag to play a song while it flapped in the breeze. But they did not test its ability to operate under water.
Taking the next step, Aliev’s group showed nanotube sheets produce the kind of low-frequency sound waves that enable sonar to determine the location, depth, and speed of underwater objects.
They also verified speakers can tune into to specific frequencies to cancel out noise, such as the sound of a submarine moving through the depths.

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