Nanotube speakers outperform sonar equipment

Lightweight carbon nanotube speakers could replace traditional sonar equipment because of their strong performance underwater, according to new research.

Scientists at the NanoTech Institute in Dallas showed that nanotube speakers worked just as well in water as they did in air and could also cancel out unwanted noise.

The University of Texas at Dallas research team, led by Dr Ali Aliev, found the nanotubes were more efficient at producing the low-frequency sound waves used to scan the ocean than the existing sonar equipment.

The nanotubes’ success in producing sound in the ocean was due to the fact they repel water slightly and form a layer of air along their perimeter.

Instead of producing sound vibrations like traditional speakers, nanotubes heat and cool very quickly when alternating current is passed through them, producing a pressure wave that can be detected as sound.

An experimental setup measures acoustic sound projection in liquids from a sheet of carbon nanotubes
An experimental setup measures acoustic sound projection in liquids from a sheet of carbon nanotubes

Water needs more energy than air to change its temperature and doesn’t expand as much when heated. But the layer of air around the nanotubes meant they could still produce this ‘thermoacoustic’ sound in the ocean.

Traditional sonar equipment can also be heavy and expensive so nanotubes could provide an attractive alternative when mounted on underwater vehicles.

‘Nanotube sheets can easily be deployed on curved surfaces, such as the hull of a sub,’ said Aliev. ‘They’re very light, about 20 microns thick and they’re 99 per cent porous.

‘Layers of nanotube sheets can be built up, each with a different function, for sonar projector applications or for control of the boundary layer losses for marine vehicles.’

The team also confirmed previous studies that showed nanotube speakers tuned to the correct frequency could cancel out noises such as the rumble of a submarine.

‘These underwater sound generators could cancel out the sonar signal being sent out by another sub, leaving the friendly sub undetected,’ added Aliev.

The research was partially sponsored by the National Science Foundation, the Office of Naval Research and the Air Force Office of Scientific Research.