Engineers have invented the world’s first acoustic circulator, a device that stretches the rules of physics by controlling the direction of sound waves so that the user can hear without being heard.

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The acoustic circulator prototype is pretty complex but essentially contains a resonant ring cavity, three small computer fans that circulate air at a particular velocity and three separate ports that record sound, according to the University of Texas at Austin. With that setup, electrical and computer engineering associate professor Andrea Alù and his colleagues were able to direct sound from one port to another. This in very unusual, since sound travels in waves in all directions from a source that same way that water ripples out in all directions when a stone is tossed into a pond. Causing the sound to move in only one direction is no small feat. Hat tip Gizmag.

You might ask why anyone would want to create one-way communication like this since most of us want to be heard. But agencies doing surveillance definitely don’t, so the device could have useful applications in that area. The U.S. Defense Threat Reduction Agency and the Air Force Office of Scientific Research supported this research.

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The device has potential civilian uses as well. I asked Alù whether city-dwellers could use this to avoid hearing a loud neighbor and he responded that there are easier ways to achieve that. Instead, the acoustic circulator could mean creating communications systems and inexpensive smartphones that don’t require mined magnetic components. And maybe even the ultimate noise-canceling headphones.

The work was led by UT Austin electrical and computer engineering associate professor Andrea Alù, who I suspect might actually be a wizard in disguise based on his previous cloaking tech. Alù, along with PhD student Romain Fleury and a team of engineering researchers from the University, detailed the acoustic circulator in the journal Science (abstract).

Photo (top) Credit: Filipe Varela, Flickr Creative Commons. Inset: The acoustic circulator core built by engineers at the University of Texas at Austin. Credit: Science / AAAS