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In the words of Romain Fleury, a PhD student who worked with professor Alù on the project, the device "can transmit acoustic waves in one direction but block them from another." Professor Alù and his team exploited this design, applying it to the medium of sound and creating the first non reciprocal sound circulator. When one of the ports of the circulator was left unused, it had the effect of working as an isolator, preventing the signals from heading back the way they came. The traditional definition of an electronic circulator is a three-port device through which microwaves/radio signals are sent consecutively from one port to another. That is until now.Īndrea Alù, the engineer who led the project, stated that "using the proposed concept, we were able to create one-way communication for sound traveling through air." The device itself takes the form of a circulator. If a sound wave goes in one direction it can also travel in the other – hence, if you can hear, you can always be heard. There is a fundamental underpinning of symmetry called "time reversal symmetry" in the transfer of acoustic waves through the medium of air between two points in space. The simple, compact device, which controls the direction of sound waves, allows the user to hear without being heard.
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A team of researchers at the University of Texas At Austin's Cockrell School of Engineering has effectively disproved the adage that, “if you can hear you can be heard” by creating the world's first one-way acoustic circulator.