What's the News: Scientists have already bent light to make invisibility cloaks and manipulated sound to hide underwater objects from sonar. Now, researchers have come up with a preliminary design for a mesh shield that would let submarines stealthily maneuver through the seas without leaving any wake, they report in a study published online last week. How the Heck:
When something moves through water, it pulls water along with it, creating drag, and leaves a turbulent wake behind it, where more water rushes in to fill the newly vacated space.
To get an object to glide through water wake-free, the researchers propose coating it in a porous mesh of man-made metamaterial. Tiny pumps scattered throughout the mesh would help push water through with variable amounts of force. "The goal is make it so the water passing through the porous material leaves the cloak at the same speed as the water surrounding by the vessel," Yaroslav Urzhumov, one of the researchers, said in a press release. "In this way, the water outside the hull would appear to be still, relative to the vessel." The mesh would also reduce drag, letting a cloaked sub or ship cut through the water more efficiently than a traditional vessel.
The researchers modeled this technique on a sphere, simulating 10 layers of mesh to show how the shield would function. Essentially, the shield would speed up water at the front of the sphere, then slow the water to about its initial speed as it flows around the back.
Not So Fast:
This mesh is still just a simulation; the researchers haven't actually built a wake-free sphere, much less a full-size submarine, yet.
So far, the cloak design would only work for small objects moving at a slow pace. For something four-tenths of an inch wide to stay wake-free, for instance, it would have to move at less than half an inch per minute.
The Future Holds:
Even with its limitations, the cloak could prove useful, Urzhumov suggests. Tiny cloaked robots made to look like fish could stealthily dart through the depths, sending back information on enemy vessels without being detected.
The mesh could also improve ships' efficiency and reduce drag, even if it didn't fully erase their wake.
Reference: Yaroslav A. Urzhumov and David R. Smith. "Fluid Flow Control with Transformation Media." Physical Review Letters, August 11, 2011. DOI: 10.1103/PhysRevLett.107.074501
Image courtesy of the United States Navy