Researchers at the Institute of Science and Technology Austria (ISTA) have successfully addressed a fundamental limitation of acoustic levitation, a technique that uses sound to suspend objects in mid-air. They achieved this breakthrough by employing electric charge to prevent multiple levitated particles from clumping together, a phenomenon known as “acoustic collapse.” The findings were published in the prestigious journal, Proceedings of the National Academy of Sciences, on December 2, 2025.
Acoustic levitation functions effectively for single particles but struggles when multiple particles are involved. As particles scatter sound waves, they create attractive forces that cause them to collapse into clusters. This limitation has hindered the technique’s potential applications in various scientific fields.
Scott Waitukaitis, an assistant professor at ISTA, recognized the broader implications of acoustic levitation back in 2013, when few research groups delved into its fundamental aspects. “Acoustic levitation was being used in acoustic holograms and volumetric displays, but I felt it could serve more fundamental purposes,” he explained.
To combat the issue of acoustic collapse, Sue Shi, a Ph.D. student in Waitukaitis’s group and the lead author of the study, and her team introduced electric charge into their experiments. They discovered that by applying electrostatic repulsion, they could maintain separation between levitated particles. “By counteracting sound with electrostatic repulsion, we are able to keep the particles separated from one another,” said Shi.
The researchers developed a method to charge the particles, allowing them to manipulate various configurations of levitated matter. They could create completely separated systems, fully collapsed ones, and hybrid configurations that combined both states. This flexibility provided a unique platform for studying the interactions of individual particles without the interference of clustering.
New Insights into Particle Behavior
The team’s findings also led to unexpected behaviors among the particles. Some arrangements exhibited “non-reciprocal” interactions, suggesting phenomena that challenge traditional understanding, such as Newton’s third law. For instance, certain particles began to rotate spontaneously or chase each other across the levitation setup.
While the researchers had not anticipated these behaviors, they are now viewed as exciting avenues for further exploration. “You can’t study how individual particles interact when you can’t keep them apart,” Waitukaitis noted. With electrostatic repulsion, the team can maintain stable, well-separated structures, enabling them to investigate these subtle interactions more thoroughly.
The implications of this research extend to various fields, including materials science and micro-robotics. The ability to manipulate particles mid-air can lead to the development of controlled, dynamic structures from small components. Shi reflected on her initial frustrations with the unexpected particle behaviors, stating, “At first, it was frustrating… they were preventing me from getting the clean, stable crystalline structures I was aiming for.” However, presenting her results at conferences helped her appreciate the significance of these phenomena.
As the team continues to explore these non-reciprocal effects, they are poised to unlock new potential for acoustic levitation in scientific research and technological applications. The journey from addressing the limitations of the technique to discovering new phenomena illustrates the unpredictable nature of scientific inquiry, where the most fascinating discoveries often arise from unforeseen challenges.
For more information, refer to the original study: Sue Shi et al, “Electrostatics overcome acoustic collapse to assemble, adapt, and activate levitated matter,” Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.2516865122.
