Acoustic Circulator.

The UT Austin team disclosed to wise labs that realized the same principles could apply from sound waves traveling in air sonic theory. This led to the team's building of a first-of-its-kind three-port acoustic circulator. This means it could use this proposed concept. Like wise were able to create one-way communication for sound traveling through air,' Professor Alu said. As a refined version of the technology could one day be used in sonar avoidance and to refine noise in concert halls. The invisibility cloak for sound used a plastic pyramid, this could hide objects from sonar. It might look like a quirky plastic model of an ancient Egyptian pyramid. This model is in fact a 3D 'acoustic cloak', created using just a few perforated sheets of plastic.
The device reroutes sound waves to create the impression that both the cloak and anything beneath, meaning it is not there. As Engineers from Duke University in North Carolina, claim the acoustic cloaking device works no matter which direction the sound is coming from. This 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. 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.  ‘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.

Engineers from Duke University in Durham, North Carolina such as Bogdan Popa who is pictured with the pyramid, 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. 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. The scientists conducted their tests in the air, but sound waves behave similarly underwater, so the device could one day be used for sonar avoidance. Sonar is used by the military to find objects underwater (pictured) and cloaking devices are expected to evolution surveillance and warfare.

Using a microphone, they mapped how the waves responded and produced videos of them travelling through the air. Professor Cummer and his team then compared the videos to those created with both an unobstructed flat surface and an uncloaked sphere blocking the way. The results clearly show that the cloaking device makes it appear as though the sound waves reflected off an ‘empty’ surface. Although the experiment is a simple demonstration showing that the technology is possible, concealing an evil genius’ underwater lair is a long ways away, according to Professor Cummer.

However, he believes that the technique has several 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 centre of the acoustic circulator, pictured, is fitted with three specially positioned fans that change the flow of air through the separate chambers Spies around the world could soon be able to listen in on secret conversations without any fear of being found out thanks to the first ever one-way sound machine. Sound waves traditionally travel forward before bouncing back, and with sound this means you can speak, hear yourself speak, and hear any responses. The inspiration for the device came from current three-port electronic circulators that are typically used in communication devices and radars. In these electronic circulators, when one of the ports isn’t being used, the system acts as an isolator, letting signals to flow from one port to the other, but not back.