Physicists Generated Sound Waves That Travel In One Direction Only

An anonymous reader quotes a report from ScienceAlert: Imagine three people huddled in a circle so when one speaks, only one other hears. Scientists have created a device that works like that, ensuring sound waves ripple in one direction only. The device, developed by scientists at ETH Zurich and the Swiss Federal Institute of Technology Lausanne, is made up of a disk-shaped cavity with three equally-spaced ports that can each send or receive sound. In an inactive state, sound transmitted from port 1 is audible to ports 2 and 3 at equal volumes. Sound waves bounce back to port 1 as an echo as well. When the system is running, however, only port 2 hears port 1’s sounds.

The trick is to blow swirling air into the cavity at a specific speed and intensity, which allows the sound waves to synchronize in a repeating pattern. That not only guides the sound waves in a single direction, but gives more energy to those oscillations so they don’t dissipate. It’s kind of like a roundabout for sound. The scientists say their technique may inform the design of future communications technologies. New metamaterials could be made to manipulate not just sound waves but potentially electromagnetic waves too. “This concept of loss-compensated non-reciprocal wave propagation is, in our view, an important result that can also be transferred to other systems,” says senior researcher Nicolas Noiray. The research was published in the journal Nature Communications.