UM Researchers Discover Spiral Sound Beams Shift Sideways in Acoustic Hall Effect

Spiral sound beams can be nudged sideways as they pass through a specially engineered surface, an Ole Miss research team has experimentally confirmed for the first time, publishing their findings in Physical Review Letters.

Likun Zhang, associate professor of physics and astronomy and senior scientist at the National Center for Physical Acoustics in Oxford, led the team behind the discovery. Using vortex beams, sound that spirals forward rather than traveling in a straight column, Zhang's group passed the beams through a designed surface and observed the beam's angular momentum shift, deflecting it slightly to the side. The phenomenon is now experimentally identified as the acoustic orbital Hall Effect.

The Hall Effect has a long history in physics: when something traveling forward, traditionally an electric current, encounters an external influence such as a magnetic field, it deflects to the side. Zhang's group spent roughly five years building toward this acoustic version of that principle.

"About five years ago, our group extended the concept of the Hall Effect to acoustics, where we predicted that this would be the case," Zhang said. "But this follow-up is the first time that we've been able to say, experimentally, 'Here is that shift, and we can prove that it's there.'"

The study, published in Physical Review Letters, a premier journal for physics research, marks the first measurement of the Hall Effect as it applies to acoustics. No prior experimental proof existed for the lateral deflection of acoustic vortex beams, despite the theoretical prediction having circulated for years.

The practical stakes reach well beyond the laboratory. Zhang pointed to biomedical engineering as one promising direction, where precise control of spiral sound could mix fluids or move micro-particles within cells or tissue. The same principle could improve acoustic communication in underwater environments, where conventional signal propagation faces significant limitations.

The University of Mississippi's National Center for Physical Acoustics, situated on the Oxford campus, has positioned itself as a national hub for this kind of fundamental acoustics research. The Zhang group's work adds an experimentally verified building block to what had previously been a theoretical framework, opening a new class of acoustic tools whose precision depends on understanding not just where sound goes, but exactly how its path can be steered.