Synopsis

One-Way Sound Transport

Physics 12, s4
An array of air channels behaves as an “acoustic Chern insulator” in which sound waves travel only around the edges and only in one direction.
Y. Ding/Nanjing University

Topological phases are defined by geometric constraints, which makes them especially robust against environmental influences. Although typically an electronic phenomenon, topological phases can also occur in acoustic systems. Researchers have now assembled an array of air channels to create the acoustic version of a topological phase known as a Chern insulator. Their acoustic device limits the propagation of sound waves to a single direction, which could benefit medical ultrasound and the control of environmental noise.

Some of the first acoustic topological systems were periodic arrays of scattering elements that blocked sound propagation except along their edges—similar to what happens for electronic transport in topological insulators. In these acoustic prototypes, the edge propagation was time-reversible, meaning sound waves could travel both forwards and backwards. The advantage of going to time-irreversible propagation is that edge-traveling sound waves would be less susceptible to scattering losses from defects.

To create their time-irreversible acoustic material, Jianchun Cheng from Nanjing University in China and co-workers connected several time-irreversible units, or “atoms,” via waveguides to make a hexagonal array. Each atom consisted of a ring cavity in which air was spun around at high speed. Previous work with single atoms had shown that sound waves enter and exit the cavity in only one direction. Cheng and co-workers managed to synchronize the acoustic modes of multiple atoms by relying on high-order acoustic resonances within each atom. They observed time-irreversible sound wave propagation along the edges of the array and verified that these one-way edge modes were immune to defects, such as cavities in which air spins the wrong way or not at all.

This research is published in Physical Review Letters.

–Michael Schirber

Michael Schirber is a Corresponding Editor for Physics based in Lyon, France.


Subject Areas

AcousticsTopological InsulatorsMetamaterials

Related Articles

Manipulating Objects Using Air Bubbles and Sound Waves
Acoustics

Manipulating Objects Using Air Bubbles and Sound Waves

Centimeter-scale objects in liquid can be manipulated using the mutual attraction of two arrays of air bubbles in the presence of sound waves. Read More »

A Parametric Oscillator for Phonons
Quantum Physics

A Parametric Oscillator for Phonons

A newly demonstrated device could lead to the creation of entangled pairs of phonons. Read More »

Metamaterials Control the Shape of Water Waves
Metamaterials

Metamaterials Control the Shape of Water Waves

A water wave incident on a grooved wall is shown to be analogous to electromagnetic waves called surface plasmon polaritons. Read More »

More Articles