Thin films of carbon nanotubes can be made into flexible loudspeakers that have no moving parts
Carbon nanotubes are moving into the music business. Kaili Jiang, Shoushan Fan and co-workers at Tsinghua University and Beijing Normal University1 have made high-performance loudspeakers from nothing but a thin film of nanotubes.
The researchers drew out films just a few tens-of-nanometres thick from an array of nanotubes. The films conduct electricity well, and can be made to emit sound simply by applying an audio-frequency voltage.
The nanotube thin-films were built into a flat loudspeaker the size of A4 paper and a cylindrical loudspeaker that can emit sound in all directions. The loudspeakers have excellent acoustic performance and require no moving parts or magnets. In fact the film itself does not vibrate. Instead the nanotubes — which have an extremely low heat capacity — are periodically heated and cooled by the alternating current, exciting a pressure oscillation in the surrounding air.
The nanotube films can be bent or stretched without losing performance, raising the prospect of applications such as musical clothes. They are also transparent, and thus could be placed in front of a display screen for a combined sound and image device. One drawback with the loudspeakers is that they produce double the frequency of the input voltage, and so require a different type of amplifier from present devices.
References
Xiao, L. et al. Flexible, stretchable, transparent carbon nanotube thin film loudspeakers. Nano Lett. 10.1021/nl802750z (2008).
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Reid, T. Nanotube noise. Nature Nanotech (2008). https://doi.org/10.1038/nnano.2008.345
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DOI: https://doi.org/10.1038/nnano.2008.345