March 12, 2014
3D Acoustic Cloak That Hides Objects From Sound
Lee Rannals for redOrbit.com - Your Universe Online
Engineers at Duke University have demonstrated the world’s first three-dimensional acoustic cloaking device.The scientists reported in the journal Nature Materials that they have created a new device that reroutes sound waves to create the impression that the cloak and whatever it covers is not there. This technology could one day be used by the US Navy as a way to avoid sonar detection.
According to the researchers, the acoustic cloaking device works no matter which direction the sound is coming from or where the observer is located.
“The particular trick we’re performing is hiding an object from sound waves,” Steven Cummer, professor of electrical and computer engineering at Duke University, said in a statement. “By placing this cloak around an object, the sound waves behave like there is nothing more than a flat surface in their path.”
The team used a combination of natural materials in repeating patterns in order to help them achieve unnatural properties in this device. The materials manipulating the behavior of sound waves are simply plastic and air. When the device is constructed, it looks like several plastic plates with a repeating pattern of holes poked through them.
In order to avoid sound waves, the cloak alters the waves’ trajectory to match what they would look like as if an object wasn’t there.
“The structure that we built might look really simple,” said Cummer. “But I promise you that it’s a lot more difficult and interesting than it looks. We put a lot of energy into calculating how sound waves would interact with it. We didn’t come up with this overnight.”
The researchers covered up a small sphere with the cloak and “pinged” it with short bursts of sound from various angles. They mapped out the waves to see how they responded and created videos of them traveling through the air.
After this, the team compared the videos to those created with both an unobstructed flat surface and an uncloaked sphere blocking the way. They found that the cloak actually makes the device appear as though the sound waves reflected off an empty surface.
The device is not yet ready for use in commercial applications, but the team is confident that it will be used in plenty of fields.
“We conducted our tests in the air, but sound waves behave similarly underwater, so one obvious potential use is sonar avoidance,” said Cummer. “But there’s also the design of auditoriums or concert halls—any space where you need to control the acoustics. If you had to put a beam somewhere for structural reasons that was going to mess up the sound, perhaps you could fix the acoustics by cloaking it.”