Researchers at the Institute of Science and Technology Austria (ISTA) have made significant advancements in the field of acoustic levitation, overcoming a fundamental limitation known as “acoustic collapse.” Published in the Proceedings of the National Academy of Sciences on December 2, 2025, their findings could lead to groundbreaking applications in materials science, robotics, and microengineering.
Acoustic levitation has long fascinated scientists due to its ability to make objects float using sound waves. While effective for a single particle, the technique struggles when multiple particles are introduced, causing them to clump together instead of remaining separate. This phenomenon, termed “acoustic collapse,” has limited the technique’s potential for studying complex interactions among particles.
Scott Waitukaitis, an assistant professor at ISTA, first became interested in using acoustic levitation for fundamental research in 2013. He observed that while other researchers were applying the technique for practical applications, its capabilities for exploring basic physical phenomena had not been fully realized. “I had the impression that the technique could be used for much more fundamental purposes,” he stated.
The research team, including Ph.D. student Sue Shi, aimed to address the issue of particle clumping. Initially, they sought to separate levitated particles to facilitate crystal formation. However, they discovered that the key to overcoming acoustic collapse lay in introducing electrostatic forces to counteract the attractive forces created by sound scattering. “By counteracting sound with electrostatic repulsion, we are able to keep the particles separated from one another,” explained Shi.
The researchers developed a method to charge the particles, allowing them to explore a range of configurations. These configurations included completely separated particles, fully collapsed systems, and hybrid formations that exhibited both states. By adjusting the charge, the team could manipulate the levitation setup effectively, enabling a deeper investigation into the behavior of particles in different arrangements.
Unexpected Discoveries and Implications
During their experiments, the team observed complex behaviors that hinted at “non-reciprocal” interactions—a phenomenon that deviates from traditional physics principles, including aspects of Newton’s third law. Some particle arrangements began to spontaneously rotate, while pairs of particles appeared to chase each other. Although Newton’s third law technically holds, the additional momentum gained by the particles is transferred back to the sound waves, illustrating a fascinating interplay between sound and motion.
Waitukaitis noted that previous theoretical work had suggested such effects could exist in acoustically levitated systems, but they had not been observed until now due to the issue of particle collapse. “By introducing electrostatic repulsion, we can now maintain stable, well-separated structures. This finally gives us a controllable platform to investigate these subtle non-reciprocal effects,” he said.
The implications of this research extend beyond academic interest. The ability to manipulate matter in mid-air could revolutionize fields that require precise control of small building blocks, such as micro-robotics and advanced materials science. Shi expressed that despite initial frustrations with unexpected particle dynamics, the results opened new avenues for exploration. “The most interesting discoveries often come from the things that don’t go as planned,” she remarked.
As the team continues to investigate these novel interactions, their method may pave the way for innovative applications that leverage the unique properties of acoustically levitated materials. The journey from conceptualization to realization highlights the dynamic nature of scientific inquiry, where unexpected findings can lead to substantial advancements in understanding and technology.
The research conducted at ISTA marks a notable milestone in the field of acoustic levitation, demonstrating the potential of combining sound and electrostatics to explore uncharted territories in physics and engineering.
