The invisibility cloak for SOUND: Plastic pyramid could hide objects from sonar
Engineers from Duke University in North Carolina, claim the acoustic cloaking device works no matter which direction the sound is coming from
The device reroutes sound waves to create the impression that both the cloak and anything beneath it are not there
A refined version of the technology could one day be used for sonar avoidance and to refine noise in concert halls
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The 'invisible' pyramid: The world's first 3D acoustic cloak (pictured) was created by U.S. engineers using just a few perforates sheets of plastic and a great deal of number crunching. The device reroutes sound waves to create the impression that both the cloak and anything beneath it are not there
HOW DOES THE SOUND-CLOAKING PYRAMIDWORK?
The engineers used metamaterials - a combination of materials with special light-scattering qualities; in this case in repeating patterns - to achieve unnatural properties.
The pyramid is constructed using plastic plates with a repeating pattern of holes that are stacked on top of one another.
Its design means that sound waves can be manipulated by plastic and air.
The cloak alters the sound waves’ trajectory to match what they would look like had they had reflected off a flat surface.
Because the sound waves are not penetrating the pyramid, they are travelling a shorter distance, which in turn affects the wave's speed.
The device then reroutes these slower sound waves to create the impression that both the cloak and anything beneath it are not there.
Engineers from Duke University in Durham, North Carolina, claim that unlike other efforts, the acoustic cloaking device works in all three dimensions, no matter which direction the sound is coming from.
The materials manipulating the behaviour of sound waves in the plastic pyramid, which is constructed using plastic plates with a repeating pattern of holes that are stacked on top of one another, are simply plastic and air.
The cloak alters the sound waves’ trajectory to match what they would look like had they had reflected off a flat surface.
Because the sound waves are not penetrating the pyramid, they are travelling a shorter distance, which in turn affects the wave's speed.
The device then reroutes these slower sound waves to create the impression that both the cloak and anything beneath it are not there.
‘The structure that we built might look really simple,’ said Professor 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,’ he said.
‘The particular trick we’re performing is hiding an object from sound waves,’ said Steven Cummer, professor of electrical and computer engineering.
‘By placing this cloak around an object, the sound waves behave like there is nothing more than a flat surface in their path,’ he explained.
To achieve the effect, Professor Cummer and his colleagues used metamaterials, which are materials with light-scattering properties.
His device uses a combination of materials in repeating patterns to achieve unnatural properties, according to the study which is published in the journal Nature Materials.
To test the cloaking device, the researchers covered a small sphere with the cloak and ‘pinged’ it with short bursts of sound from various angles.
