Invisibility cloaks could take sting out of tsunamis — but not by hiding from them:
The first working invisibility cloak, built in 2006, guided microwaves around a small, flat copper ring as if it wasn’t there. By October 2007, a device repeated the trick for harder-to-handle visible light, and some progress is reported on the yet more complex task of making cloaks to hide 3D objects.Now Stefan Enoch at the Fresnel Institute in Marseille, France, says that established cloaking principles could be applied to ocean waves, which are essentially two-dimensional.
So the idea does not involve an invisibility cloak at all, just the concept behind it, which involves manipulating two-dimensional waves:
To prove it, the researchers have built a prototype 10 centimetres across (see image, right) for testing in a wave tank. Concentric rings of rigid pillars form a labyrinth of radial and concentric corridors.It may look like waves could pass easily along the radial corridors to the cloak’s centre. But they interact with the pillars, producing forces that pull water along the concentric corridors instead.
“Basically, the cloak behaves like a whirlpool,” says Sebastian Guenneau at the University of Liverpool, UK, and a member of Enoch’s team. “The further you go into the whirlpool, the faster you rotate.”
The spinning rate increases close to the cloak’s centre where the concentric corridors are narrower, making the forces greater, he explains.
As the water whizzes around the cloak, the waves are flung out again along the radial corridors. “If you imagine water entering the cloak from the north, some leaves the cloak to the east, and some leaves to the west, but most is thrown out at the south,” says Guenneau.
The waves exiting the cloak travel as if they have not been disturbed at all, he says.
Perfect for protecting oil rigs — or seasteads.