Mar.12, 2014

Admit it. You'd love to own an invisibility cloak. Well, scientists have some good news for you. Using little more than a few perforated sheets of plastic and a staggering amount of number crunching, Duke engineers have demonstrated the world's first three-dimensional acoustic cloak.

Using 3D printed metamaterials scientists has built a 3D acoustic invisibility cloak that interacts with sound waves to create the impression that both the cloak and anything beneath it are not there.

Steven Cummer, professor of electrical and computer engineering and his colleagues at Duke University turned to metamaterials. These tiny structures are smaller than the wavelength of light. If properly constructed, they guide rays of light around an object - much like a rock diverting water in a stream.

In the case of the new acoustic cloak, the materials manipulating the behavior of sound waves are simply plastic and air. The pastic sheets were created using 3D printer. Once constructed, the device looks like several plastic plates with a repeating pattern of holes poked through them stacked on top of one another to form a sort of pyramid.

The trick is to hide an object from sound waves, said Cummer. "By placing this cloak around an object, the sound waves behave like there is nothing more than a flat surface in their path."

Graduate student Bogdan Popa shows off the 3D acoustic cloak he helped design and build as a member of Steven Cummer's laboratory.

To give the illusion that it isn't there, the cloak must alter the waves' trajectory to match what they would look like had they had reflected off a flat surface. Because the sound is not reaching the surface beneath, the device needs to slow down the speed of the sound waves to compensate.

To test the cloaking device, researchers covered a small sphere with the cloak and "pinged" it with short bursts of sound from various angles. They then mapped how the sound waves responded using a microphone. The team then produced videos of them traveling through the air and compared them to those created with both an unobstructed flat surface and an uncloaked sphere blocking the way. The results show that the cloak makes it appear as though the sound waves reflected off an empty surface.

In addition the acoustic cloaking device works in all three dimensions, no matter which direction the sound is coming from or where the observer is located.

The whole idea might sound simple. But Cummer said, "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."

Cummer sees several applications for the technology:"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."

The details of the team's acoustic cloak is published in the journal Nature Materials.


Posted in 3D Printing Applications


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René wrote at 4/25/2015 5:57:33 PM:

Is there any way to acquire a template for one to print on a Makerbot 3D printer?

Julio wrote at 3/12/2014 3:12:02 PM:

This should be classified, but it's too late now.

akka69 wrote at 3/12/2014 2:25:19 PM:

I wonder how such experiment could be used to make totally sound proof buildings, so no external noise could penetrate the building.

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