Carbon Nanotube Speakers Promise Applications Outside of Audio Equipment

Property of CNT-based speakers producing sound through heat could prove useful in heating applications

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Carbon Nanotube Speakers Promise Applications Outside of Audio Equipment
Photo: Mahsa Asgarisabet

It’s been some time since we covered the use of nanomaterials in audio speakers. While not a hotly pursued research field, there is some tradition for it dating back to the first development of carbon nanotube-based speakers in 2008. While nanomaterial-based speakers are not going to win any audiophile prize anytime soon, they do offer some unusual characteristics that mainly stem from their magnet-less design.

Now a group of researchers at Michigan Technological University (MTU) have continued this tradition of tinkering with carbon nanotubes and speakers and walked away winning the Best of Show Award at SAE International’s Noise and Vibration Conference and Exhibition.

While the MTU researchers have continued the trend of demonstrating a fairly rudimentary speaker design using the carbon nanotubes (CNTs), the real potential of their research may be in applications outside of audio. The team invesigated how CNTs produce sound with heat, which they think could ultimately prove useful in applications such as de-icing helicopter blades and heating filaments for back windshield defrosters.

Nonetheless, the idea of a novel speaker technology seems irresistible.

“Traditional speakers use a moving coil [attached to a diaphram and interacting with a permanent magnet], and that’s how they create sound waves,” said Troy Bouman, one of the MTU researchers, in a press release. “There are completely different physics behind carbon nanotube speakers.”

With the different physics come unique operating properties. CNT films can heat up and cool down up to 100,000 times per second, which causes air near the film to expand and contract, pushing air molecules around and leading to sound waves. Minus the magnet, these CNT-based speakers are also incredibly light.

“A little wind gust across them, and they would just blow away,” said Andrew Barnard, an assistant professor of mechanical engineering at MTU, in the press release. “But you could shake them as much as you want—since they have such low mass, there is virtually no inertia.”

Despite their attractive qualities, CNT-based speakers have the problematic property of doubling every frequency that is put into them so that what we hear initially is a bit of a jumbled mess. But Bouman figured out how to process this noise so that the sound you hear is more intelligible. You can listen to how this processing works in the audio file below:

The potential for other applications depends on getting accurate models of how the CNT-based speakers operate. Mahsa Asgarisabet, another of the MTU researchers, has been developing a thorough thermal model of the speakers to assist her in developing active noise control solutions.

The researchers believe that this extensive modeling will lay the groundwork for developing new applications for the underlying technology.

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