Bond-style one-way sound device developed

Scientists have developed a new 'Bond-style' device that may allow spies to listen to someone without having to worry about being heard.
Researchers at The University of Texas at Austin's Cockrell School of Engineering have built the first-ever nonreciprocal circulator for sound that is able to break sound wave reciprocity.
Experiments with the device successfully prove that the fundamental symmetry with which acoustic waves travel through air between two points in space can be broken by a compact and simple device.
"Using the proposed concept, we were able to create one-way communication for sound travelling through air," said Andrea Alu, who led the project.

"Imagine being able to listen without having to worry about being heard in return," said Alu.
An electronic circulator, typically used in communication devices and radars, is a nonreciprocal three-port device in which microwaves or radio signals are transmitted from one port to the next in a sequential way.

When one of the ports is not used, the circulator acts as an isolator, allowing signals to flow from one port to the other, but not back.
The team realised the same functionality is true for sound waves travelling in air, which led to the team's building of a first-of-its-kind three-port acoustic circulator.

Romain Fleury, the papers first author said the circulator "is basically a one-way road for sound. The circulator can transmit acoustic waves in one direction but block them in the other, in a linear and distortion-free way."
The scientific knowledge gained from successfully building a nonreciprocal sound circulator may lead to advances in noise control, new acoustic equipment for sonars and sound communication systems, and improved compact components for acoustic imaging and sensing, researchers said.
"More broadly, our paper proves a new physical mechanism to break time-reversal symmetry and subsequently induce nonreciprocal transmission of waves, opening important possibilities beyond applications in acoustics," Alu said.

"Using the same concept, it may actually be possible to construct simpler, smaller and cheaper electronic circulators and other electronic components for wireless devices, as well as to create one-way communication channels for light," said Alu.
This research may eventually allow for an "acoustical version of one-way glass," said acoustics expert Preston Wilson.