An acoustic circulator, which makes one-way sound transmission possible.
Scientists have created a one-way sound machine.
The device, called an acoustic circulator, breaks the fundamental principle that sound, and other types of waves, are a two-way street.
The findings, published today (Jan. 30) in the journal Science
, could lead to the sound equivalent of a one-way mirror
. With such a device, people can hear someone talking, but they themselves cannot be heard.
All waves - whether visible light, sound, radio or otherwise - have a physical property known as time reversal symmetry. What that means is that a wave sent one way can always be sent back.
"If I am able to talk to you, you should be able to talk to me back," said study co-author Andrea Alù, an electrical engineer at the University of Texas at Austin.
For radio waves
, researchers figured out how to break this rule using magnetic materials that set electrons spinning in one direction. The resulting radio waves detect the difference in the material in one direction versus the other, preventing reverse transmission. As a result, transmission towers can broadcast the top 40 hits, without having the radio waves bounce back.