Acoustic cloak could hide ships, noisy neighbors

Imagine a material so dense it could block sonar waves looking for warships or on a more pedestrian level, soundproof your apartment from the noisy neighbors.

That’s just a couple of the applications researchers say are possible with new materials that could create an acoustic cloak  over large or small noise-makers. The fabric, known as metamaterial is defined by its unusual man-made cellular structure, researchers said. For example, researchers from the Wave Phenomena Group at the Polytechnic University of Valencia, calculated how metamaterials constructed with sonic crystals, solid cylinders in an array that can scatter sound waves, could be used in a multilayered structure to divert sound completely around an object.

The researchers performed multiple simulations to test their theory. They investigated the optimum number of layers required to completely divert sound and how thin the materials could be made to maintain their use but also ensure that they are easy to implement. Results were very encouraging, showing that optimum cloaking requires approximately 200 layers of the metamaterial. While that may amount to inches of material, researchers say they are looking at creating much thinner materials to handle the same job.

Researchers said their work builds on recent theoretical work at Duke University in North Carolina which sought ways to produce materials that can hide objects from sound, sight and x-rays. To an observer it looked like the microwaves had passed straight through the cylinder.

There is also work being done within DARPA’s MetaMaterials Program where scientists are working to demonstrate engineered magnetic nanocomposites with enhanced energy products. If they are successful, it is believed that magnets 50 to 100% more powerful than today's magnetic materials will be available. The demonstration of these materials is a major step toward demonstrating electric drive and propulsion for our future military platforms, according to scientists.

Researchers are also looking at optical cloaking technology that could hide objects. Purdue researchers using nanotechnology last year created a theoretical design that uses an array of tiny needles radiating outward from a central spoke. The design, which resembles a round hairbrush, would bend light around the object being cloaked. Background objects would be visible but not the object surrounded by the cylindrical array of nano-needles.

In addition Carnegie Mellon University researchers say they have come up with an invisibility cloak for nanoparticles.   

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