Metamaterials are very interesting materials that can be used to cloak things from the naked eye and hide the sounds produced by things like submarines when in the water. So far, these exotic metamaterials are in the realm of scientific research and theory but they certainly hold a lot of promise for applications other than the obvious military uses of hiding troops and machinery.
Previously the metamaterials that were being studied for hiding the sound produced by things like a submarine would only work underwater. A team of researchers from Duke University have created a new metamaterial that will work in air to hide sound. The team has been successful in creating and demonstrating a small acoustic cloak so far.
The cloak was designed by Steven Cummer and his team and the prototype was created by layering ordinary strips of perforated plastic. When the sound waves hit the plastic and penetrated most of them appeared to have traveled all the way down to the flat surface under the triangular block. The team believes that a version that would cover a 3D object is possible, but that is a long way off.