The thin films of carbon nanotubes create sound through a thermoacoustic effect, turning electrical pulses into tiny sound waves via heat generated in the air around the nanotubes when the pulses pass through. This effect was discovered and demonstrated back in 2008, as seen below, but it wasn’t tested underwater.

Now, researchers including a team from UT Dallas have demonstrated that sheets of nanotubes can produce low-frequency sound ideal for mapping out the ocean depths with sonar, and those frequencies can be fine-tuned to cancel out other background noise, like the sound of the submarine itself moving through the water. That capability should help subs pinpoint the depth, location, and speed of other undersea objects — like enemy subs — without revealing their own positions.

[Eurekalert]