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World's first 3D acoustic cloaking device created

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March 11, 2014

The acoustic cloak was constructed from several sheets of plastic plates dotted with repea...

The acoustic cloak was constructed from several sheets of plastic plates dotted with repeating patterns of holes (Photo: Duke Photography)

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Metamaterials are already being used to create invisibility cloaks and "temporal cloaks," but now engineers from Duke University have turned metamaterials to the task of creating a 3D acoustic cloak. In the same way that invisibility cloaks use metamaterials to reroute light around an object, the acoustic cloaking device interacts with sound waves to make it appear as if the device and anything hidden beneath it isn't there.

Steven Cummer, professor of electrical and computer engineering, and his colleagues at Duke University constructed their acoustic cloak using several sheets of plastic plates dotted with repeating patterns of holes. The plastic sheets, which were created using a 3D printer, were stacked on top of each other to form a device that resembles a pyramid in shape. The geometry of the sheets and the placement of the holes interact with sound waves to make it appear as if the device and anything sitting underneath it isn't there.

Despite its apparent simplicity, the device's construction was far from a haphazard affair, with a lot of time and research going into calculating how sound waves would interact with it. As Cummer puts it, "we didn't come up with this overnight."

Research scientist Bogdan Popa with a 3D acoustic cloaking device constructed with compone...
Research scientist Bogdan Popa with a 3D acoustic cloaking device constructed with components created in a 3-D printer (Photo: Duke Photography)

To work effectively, the cloak needs to alter the trajectory of the sound waves so they behave as if they had reflected off a flat surface. To achieve this, the device needs to slow down the speed of the sound waves to compensate for the fact that they aren't traveling as far.

To test the effectiveness of the cloak, the researchers took a small sphere and covered it with the cloak. They then "pinged" the sphere with short bursts of sound from various angles and mapped how the sound waves responded using a microphone. The team then produced videos of the sound waves traveling through the air and compared them to videos produced with the cloak removed and another showing the sound wave behavior with an unobstructed flat surface.

The results showed that the acoustic cloak made it appear as if the sound waves were being reflected off a flat surface with no sign the sphere was there. Unlike the "silence cloak" developed at Germany's Karlsruhe Institute of Technology that worked only in two-dimensions, this held true no matter which direction the sound originated from or where the observer was located, prompting the team to call their creation the "world's first 3D acoustic cloaking device."

Cummer believes the technology has numerous potential commercial applications.

"We conducted our tests in the air, but sound waves behave similarly underwater, so one obvious potential use is sonar avoidance,” he said. "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 team's acoustic cloaking device is detailed in a letter published in the journal Nature Materials.

Source: Duke University

About the Author
Darren Quick Darren's love of technology started in primary school with a Nintendo Game & Watch Donkey Kong (still functioning) and a Commodore VIC 20 computer (not still functioning). In high school he upgraded to a 286 PC, and he's been following Moore's law ever since. This love of technology continued through a number of university courses and crappy jobs until 2008, when his interests found a home at Gizmag.   All articles by Darren Quick
7 Comments

Wow, this has the potential to piss off a lot of bats & dolphins! Great work guys! ☺

MzunguMkubwa
12th March, 2014 @ 06:35 am PDT

Wow! This reminds me of working with Pierre Heftler, the Ford Family Attorney who put up Ren Cen in Detroit and was on many of the Boards in town. He had a masters in EE and worked on Sonar in WWII in similar attempts concerning Sonar. Apparently the issue was Submarines in the Channel and apparently the Germans were working with rubber coatings with slots to absorb the ping.

Pete was concerned about the Ford Auditorium In Detroit and to my surprise he hired Dr. Vern Knudsen from Berkley, (I believe) and P.H. Parkin from London. It turned into a very interesting project of controlling Sound waves and it was a delight to see Dr. Knudsen clap his hands to "read" a space to determine how to control the sound within it.

To be sure, there were folk trying to promote assisted resonance but Pete would have none of it. And insisted on the Pure transmission of sound. This was a most interesting and clever project and it was unbelievable for me to sit in Pete's home in Grosse Pointe and watch him calculate the cables, and design a hoist mechanism for it including the gear ratios and winch design strictly and accurately in conversation only... no sketches, no slide rule... strictly from the mind.

Bravo and great advance!

The story of the Demise of the Auditorium is both sad and disgusting illustrating what happens when lesser lights start meddling.

Bill Dickens, Architect

Lewis M. Dickens III
12th March, 2014 @ 08:55 am PDT

I feel like I've seen this structure before somewhere. But in building form. And sometimes on the cover of National Geographic.

Daniel Gregory
12th March, 2014 @ 12:51 pm PDT

i didn't hear about this, first, here

ash
12th March, 2014 @ 05:10 pm PDT

Buck Henry is probably a little bummed. He missed it by THAT much. Not the Cone of Silence, but the Pyramid of Silence.

Gadgeteer
12th March, 2014 @ 05:12 pm PDT

Very cool stuff, but with the shape of the surfaces and the myriad tiny and precisely spaced holes of these metamaterials being so critical, won't dust and other airborne contaminants degrade their performance? And unfortunately, dust and gunk seem to be at least as inevitable as death and taxes...

xenocog
14th March, 2014 @ 06:59 am PDT

"The results showed that the acoustic cloak made it appear as if the sound waves were being reflected off a FLAT SURFACE with no sign the sphere was there."

The above is quoted from the article. If so they went to a lot of trouble for nothing. They could use a simple cube or box with FLAT SURFACES.

Critical Condition
18th March, 2014 @ 09:38 pm PDT
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