Researchers manage to direct sound in only one direction

An unexpected breakthrough in sound wave management has been achieved. At ETH Zurich, researchers have discovered a way to guide sound waves in only one direction.


Typically, light and sound waves propagate in multiple directions. This characteristic is useful for communication, but in some technical applications, it would be preferable for waves to move in only one direction to avoid unwanted reflections.

Ten years ago, scientists had already succeeded in stopping the reverse propagation of sound waves, but that also dampened their forward motion. Today, the team led by Nicolas Noiray at ETH Zurich, in collaboration with Romain Fleury from EPFL, has developed an innovative method to prevent the backward propagation of sound waves while maintaining their forward motion.

This breakthrough is based on the concept of self-oscillations, a phenomenon where a dynamic system repeats its behavior periodically. Nicolas Noiray, who has spent much of his career studying these phenomena, discovered that these oscillations could be used in a controlled way to allow sound waves to move in only one direction without energy loss.

The key device, a circulator, works thanks to a disk-shaped cavity through which swirling air flows. When air is blown at a certain speed, a whistling sound is created in the cavity. This whistling, however, is generated by a rotating wave rather than a standing wave.

After years of theoretical modeling and development, the researchers were able to experimentally demonstrate that their approach works.

When the researchers sent a sound wave of 800 Hertz into the first waveguide of the device (which contains three), this wave was able to move through the circulator and exit via the second waveguide. However, this same wave could not continue its path to the third waveguide.

This discovery could have future applications well beyond simple sound waves. Indeed, this method could be transposed to electromagnetic waves, potentially improving microwave management in radar systems and enabling the development of new topological circuits for communications.