Carbon nanotubes could act as an efficient music speaker

Nov 03, 2008 by Lisa Zyga weblog
Nanotube speaker
Excerpt from a video of Lin Xiao´s nanotube music speaker. The speaker produces sound when a current passes through, due to a thermoacoustic effect. Credit: Lin Xiao, et al.

(PhysOrg.com) -- While carbon nanotubes are widely praised for their strength and electrical properties, no one has thoroughly investigated their acoustic properties, until now. A team of Chinese researchers has found that zapping sheets of carbon nanotubes with an electric current causes the nanotubes to emit sound.

The team, which consists of scientists Shoushan Fan and colleagues at Tsinghua University in Beijing, China, and Beijing Normal University, hope that the discovery could lead to the development of cheap, flat loudspeakers. Examples of carbon nanotubes´ musical abilities can be heard here and here.

To create the nanotube speaker, the researchers sent an audio frequency current through a thin sheet of carbon nanotubes, generating a sound. Unlike standard loudspeakers that generate sound by vibrations in the surrounding air molecules, the nanotube speaker doesn´t emit vibrations. The team used a laser vibrometer to detect vibrations in the sheet, but found nothing.

Instead, the nanotube speaker likely works as a thermoacoustic device: when an alternating current passes through the sheet, the sheet experiences rapid temperature oscillations alternating between room temperature and 80 °C (176 °F). These temperature oscillations cause pressure oscillations in the surrounding air, producing the sound, while the nanotube sheet remains static. One advantage of this method is that, even if part of the nanotube sheet breaks, it should continue to emit sound, unlike conventional speakers.

This thermoacoustic phenomenon was actually discovered in the late nineteenth century, when scientists passed a current through a thin foil to produce sound, leading to the invention of the "thermophone." Although the principle is the same, however, the nanotube sheet acts much more efficiently than foil because it doesn´t require nearly as much applied heat to increase its temperature. Specifically, the nanotube sheet´s heat capacity is 260 times smaller than platinum foil, making nanotubes 260 times more efficient and able to produce a louder sound.

The Chinese researchers envision several interesting applications for the nanotube speakers. Because the nanotube sheets can be stretched to be visually transparent and still produce sound, they might be fitted over the front of an LCD screen to replace conventional speakers. Another possibility is incorporating the nanotube speakers into textiles to create musical clothes.

More information: Xiao, Lin, et al. "Flexible, Stretchable, Transparent Carbon Nanotube Thin Film Loudspeakers." ASAP Nano Lett., ASAP Article, 10.1021/nl802750z.

© 2009 PhysOrg.com

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User comments : 6

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ZeroDelta
5 / 5 (1) Nov 03, 2008
If I could wear a shirt whose fibers both generate power and emmit sound...that would be great.

Oh yeah, it should change color, display images,compute and glow too !!
MGraser
5 / 5 (2) Nov 03, 2008
Sound coming from "thin air" would be interesting.

I'm not against the clothes idea, but I can now see us getting entertained continuously by kids turning up the bass on their shorts, instead of hearing it as they pass by in their cars. Thump! Thump! Uh oh, I'm starting to get old... :-(
earls
not rated yet Nov 03, 2008
MGraser, it does raise an interesting question about how "they" would regulate this sort of technology in schools...
jeffsaunders
not rated yet Nov 03, 2008
noisy cloths? not for me. But thermophone speakers? Looks like the old will be new again.

We are working towards flexible notebooks and soon maybe solid state speakers. If only we can get rid of the fans.
RocketScience
not rated yet Nov 03, 2008
Since this is a ThermoAcoustic device can it lead to a more efficient form of cooling for, say microchips or even small refrigeration units?
earls
not rated yet Nov 04, 2008
Rocket, you could probably use them for cooling, but being "thermoacoustic" I doubt they'll do it quietly. :)

I've got my hopes set on thermoelectric cooling devices that recapture the wasteful heat, or better yet, devices with features of "superconductors" that don't produce heat in the first place!

I can dream. :(

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