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Now nanotubes make music

05 November 2008

Chinese researchers at Tsinghua University in Beijing, say that sheets made of carbon nanotubes behave like a loudspeaker when zapped with an AC current.
Shoushan Fan and his research team believe that the discovery could lead to a new generation of cheap, and very thin loudspeakers. Video content is available for this story.

The New Scientist is reporting that the team, working with colleagues from Beijing Normal University, created a thin sheet by roughly aligning lots of 10-nm-diameter carbon nanotubes. When they sent an audio frequency current through the sheet, they discovered it acted as a loudspeaker.

Fan and his team first speculated that the nanotube speaker worked the same as a normal loudspeaker with a vibrating surface disturbing surrounding air molecules and creating pressure waves, which the human ear detects as sounds. However, measurements conducted with a vibrometer indicated that whilst the nanotube speaker produced sound, its surface was totally static.

Instead, they believe that it functions as a thermostatic device. When an AC current passes through the sheet, its temperature fluctuates between around room temperature and 80 degrees C. These oscillations in temperature cause the pressure to change in the air near the film, causing pressure waves that the ear can pick up.

This is in fact not a new phenomenon. In the 19th century, two different observers recorded similar behaviour in thin metal foils, but the sounds produced were very weak. The differences in thermal properties between metals and carbon nanotubes mean that the new version could be 20-30 decibels louder.

According to Kaili Jang, one of Fan’s team, the new technology has several advantages over standard loudspeakers, including resistance to damage, and the ability to be made into complex shapes. In fact, a stretched carbon nanotube film is transparent, and could even be placed over an LCD screen to replace standard speakers (see video).

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