Acoustic 'cloaking device' shields objects from sound


Graphs showing acoustic 'cloaking' Reflections of sound off a surface (top), off an object on it (middle) and off a cloaked object (bottom)

Scientists have shown off a "cloaking device" that makes objects invisible - to sound waves.

Such acoustic cloaking was proposed theoretically in 2008 but has only this year been put into practice.

Described in Physical Review Letters, the approach borrows many ideas from attempts to "cloak" objects from light.

It uses simple plastic sheets with arrays of holes, and could be put to use in making ships invisible to sonar or in acoustic design of concert halls.

Much research has been undertaken toward creating Harry Potter-style "invisibility cloaks" since the feasibility of the idea was first put forward in 2006.

Those approaches are mostly based on so-called metamaterials, man-made materials with properties that do not occur in nature. The metamaterials are designed such that they force light waves to travel around an object; to an observer, it is as if the object were not there.

But researchers quickly found out that the mathematics behind bending these light waves, called transformation optics, could also be applied to sound waves.

"Fundamentally, in terms of hiding objects, it's the same - how anything is sensed is with some kind of wave and you either hear or see the effect of it," said Steven Cummer of Duke University. "But when it comes to building the materials, things are very different between acoustics and electromagnetics.

"The thing you need to engineer into the materials is very different behaviour in different directions that the wave travels through it," he told BBC News.

In 2008, Dr Cummer first described the theory of acoustic cloaking in an article in Physical Review Letters, and earlier this year a group from the University of Illinois Urbana-Champaign demonstrated the first practical use of the theory in an article in the same journal.

That work showed acoustic invisibility in a shallow layer of water, at ultrasound frequencies above those we can hear.

Now, Dr Cummer and his colleagues have shown off an acoustic cloaking technique that works in air, for audible frequencies between one and four kilohertz - corresponding to two octaves on the higher half of a piano.

Acoustic cloaking device The cloaking shell is made of easily-manufactured sheets of plastic with holes through them

It works by using stacked sheets of plastic with regular arrays of holes through them. The exact size and placement of the holes on each sheet, and the spacing between the sheets, has a predictable effect on incoming sound waves.

When placed on a flat surface, the stack redirects the waves such that reflected waves are exactly as they would be if the stack were not there at all.

That means that an object under the stack - in the team's experiments, a block of wood about 10cm long - would not "hear" the sound, and any attempts to locate the object using sound waves would not find it.

"How the sound reflects off this reflecting surface with this composite object on it - which is pretty big and has a cloaking shell on it - really reflects... just like a flat surface does," Dr Cummer said.

Hole poking

Ortwin Hess, a director of Imperial College London's Centre for Plasmonics and Metamaterials, called the work "a really remarkable experimental demonstration".

"It shows very nicely that although acoustic and electromagnetic waves are very different in nature, the powers of transformation optics and transformation acoustics are [similar] - I'm quite pleased that there's activity on both ends."

Professor Hess pointed out that the demonstration was for very directed sound waves, and only in two dimensions, but the most notable aspect of the approach was its simplicity.

"It's almost like someone could take a pencil and poke holes in a particular way in the plastic," he told BBC News.

"It's a bit more challenging for three dimensions. I don't see any reason why it shouldn't be possible but it won't be just an afternoon's work."

The work shows that an object can be hidden from sonar, and protected from incoming sound, but the same principles could be applied in the other direction - that is, containing or directing the sound within a space, for instance in soundproofing a studio or fine-tuning the acoustics of a concert hall.

http://www.bbc.co.uk/news/science-environment-13905573

Views: 49

Comment

You need to be a member of 12160 Social Network to add comments!

Join 12160 Social Network

Comment by Nikki on June 25, 2011 at 9:12pm
Did they get this idea from Harry Potter?

"Destroying the New World Order"

TOP CONTENT THIS WEEK

THANK YOU FOR SUPPORTING THE SITE!

mobile page

12160.info/m

12160 Administrators

 

Latest Activity

Doc Vega posted blog posts
47 minutes ago
kacang99 commented on tjdavis's photo
Thumbnail

The Name Game

"very nice, main di kacang99 demo situs slot kasih akun demo gratis"
2 hours ago
Doc Vega commented on Doc Vega's blog post Plausible Explanation Behind Recent Cryptid Sightings in the Wild!
"cheeki kea I was wrong Emperor Penguins are big and powerful but still alive but this,  A size…"
3 hours ago
Doc Vega commented on Doc Vega's blog post Plausible Explanation Behind Recent Cryptid Sightings in the Wild!
"Cheeki kea here's another that they say there have been modern sightings of!  The name of…"
3 hours ago
Doc Vega commented on Doc Vega's blog post Plausible Explanation Behind Recent Cryptid Sightings in the Wild!
"cheeki kea, did you ever hear of the giant Imperial Penguins? They were about 6 feet tall and could…"
3 hours ago
Doc Vega commented on Doc Vega's blog post Plausible Explanation Behind Recent Cryptid Sightings in the Wild!
"cheeki kea I do not think these giant two legged birds would need to have a bad attitude as long as…"
3 hours ago
Olivia Brooks updated their profile
9 hours ago
kacang99 updated their profile
11 hours ago
John Miller was featured
12 hours ago
tjdavis's 2 blog posts were featured
12 hours ago
Zfort Group's blog post was featured
12 hours ago
Doc Vega's 6 blog posts were featured
12 hours ago
Burbia commented on tjdavis's video
Thumbnail

“What’s His Motive?” - Inside The Mind of George Soros

"Trump calls for George Soros and son to face federal…"
17 hours ago
Burbia commented on tjdavis's photo
17 hours ago
Profile Iconkacang99, Seeta Sathe and Olivia Brooks joined 12160 Social Network
18 hours ago
tjdavis posted a video

Mossad, Terrifying CIA Technology, Blackwater & The Most Secret CIA Unit | John Kiriakou

John Kiriakou served 15 years in the CIA as a Case Officer (Spy) and as CIA's Head of Counterterrorism Operations in Pakistan where he lead the raid that cap...
yesterday
tjdavis posted a photo
yesterday
tjdavis posted a video

A Critique of the Tavistock Institute - The Mother Of All Conspiracy Theories

An examination of the Tavistock Institute, a theory which seeks to explain how Western societies have been brainwashed by a cabal of social scientists and th...
Sunday
tjdavis posted a video

“What’s His Motive?” - Inside The Mind of George Soros

In this short clip, Patrick Bet-David, Sebastian Gorka Adam Sosnick, and Tom Ellsworth George Soros and what motivates him to do the things he does. FaceTime...
Thursday
Doc Vega posted blog posts
Aug 27

© 2025   Created by truth.   Powered by

Badges  |  Report an Issue  |  Terms of Service

content and site copyright 12160.info 2007-2019 - all rights reserved. unless otherwise noted