Physicists introduce a "cloak of silence"

In 2006, invisibility cloaks took the world by storm, thanks to a joint effort by mathematicians, physicists and Harry Potter.

This year, however, the physicists have another surprise: you can be invisible AND silent!

Two independent teams of scientists came up the plans for a “cloak of silence,” a device which will be able to create a pocket of silence around an object by redirecting sound waves. Some physicists used to think such a device was mathematically impossible, but the two teams, one from Duke and the other from the Hong Kong University of Science and Technology, say their equations check out. (Image courtesy of Duke.)

The technology can be used by engineers to build better concert halls or hide submarines from sonar, but it’s unlikely that the scientists will come up with a cloak you can throw over your neighbor’s noisy dog. (And if a tree fell in the forest and everyone was wearing an acoustic cloak, would it make a noise?)

A Spanish physicist has taken up the task of actually building a cylindrical acoustic cloak.

From the physicsworld article:

The considerable challenge of building an acoustic cloak has been taken up by José Sánchez-Dehesa and colleagues at the Polytechnic University of Valencia in Spain. The team has calculated that a cylindrical cloak can be made by surrounding the region to be cloaked with a matrix of cylindrical rods (to be published in New Journal of Physics). By choosing rods with the right elastic properties and by varying the radius and spacing of the rods , Sánchez-Dehesa believes that cloaking can be achieved over a wide range of acoustic frequencies. The team are now looking for an appropriate material for the rods.

Sánchez-Dehesa told physicsworld.com that the theoretical breakthroughs in the US and Hong Kong mean that it should be possible to build a spherical cloak by surrounding a region with a matrix of spheres in a manner consistent with the recipe proposed by Cummer, Chen and Chan.