Single-sided ultrasonic Bessel beam levitates objects six times farther away

Sound waves can do something that looks like magic: hold small objects suspended in midair, untouched by any physical support. This phenomenon, known as acoustic levitation, has been a laboratory curiosity and a practical tool for decades, used to handle fragile materials, contamination-sensitive samples, and hazardous substances without ever touching them. Yet the technique has always suffered from a frustrating constraint. Conventional systems trap objects only within enclosed regions between opposing sound sources or between a source and a reflector, while the single-sided alternatives that eliminate the need for enclosures have been limited to levitating objects in the immediate vicinity of the transducer. Now, researchers at the University of Tsukuba, working in collaboration with the University of Bristol, have shattered that limitation, demonstrating stable levitation of objects at distances of up to approximately 40 centimeters from a single sound source, roughly six times farther than previously possible with single-sided acoustic traps.

The breakthrough, published in Physical Review Letters on 24 August 2026, hinges on a clever choice of ultrasound beam geometry. Conventional acoustic levitation relies on standing waves, in which objects settle at low-pressure nodes surrounded by high-pressure regions. In single-sided systems, the restoring force that keeps an object stable diminishes as the distance from the sound source increases, and eventually the force becomes repulsive, pushing the object away rather than holding it in place. This fundamental decay of the trapping mechanism has been the central obstacle to long-range, open-air acoustic manipulation, effectively confining levitation to a narrow shell of space near the emitter.

The Tsukuba team, led by Assistant Professor Tatsuki Fushimi of the Institute of Library, Information and Media Science, together with Yusuke Koroyasu of the Doctoral Programs in Informatics, Graduate School of Comprehensive Human Sciences, turned to a different kind of acoustic field: the zero-order Bessel beam. Unlike ordinary focused beams that spread out and lose intensity as they propagate, a zero-order Bessel beam maintains a narrow, high-intensity central core over long distances. This self-sustaining structure arises from the beam’s conical wave components, which continuously reconstruct the central pressure profile as the beam travels. By exploiting this property, the researchers were able to trap objects directly within the beam’s high-pressure core, using ultrasound emitted from only one side of the apparatus.

This approach represents a striking inversion of the conventional trapping paradigm. Instead of confining objects at pressure nodes flanked by high-pressure zones, the new method holds them within the high-pressure region itself. Although acoustic levitation within a high-pressure region had previously been predicted theoretically, this study provides the first experimental demonstration of stable three-dimensional acoustic levitation under such conditions. The distinction matters because high-pressure trapping had long been considered unsuitable for stable confinement; the Bessel beam’s persistent central core changes the force landscape in a way that keeps the restoring force attractive even far from the source.

The experimental results are compelling. The team achieved stable levitation of a 1.5-millimeter-diameter expanded polystyrene sphere at distances of up to approximately 40 centimeters from the sound source, approximately six times farther than the range achieved with conventional single-sided acoustic traps. Beyond simply holding the sphere in place, the researchers demonstrated that the levitated object could be manipulated in three dimensions using ultrasound from only one side, a capability that transforms the technique from a static suspension trick into a genuine tool for contact-free transport and positioning in open space.

The versatility of the method extends further. The researchers showed that their system could levitate multiple objects simultaneously, handle non-spherical objects whose shapes would destabilize conventional traps, and even levitate objects located beyond physical obstacles placed between the sound source and the target. This last capability is particularly significant for real-world applications, because it means the acoustic beam can reach around or through obstructions that would block mechanical grippers or optical tweezers, opening scenarios in which samples must be retrieved from enclosed or cluttered environments without any physical intrusion.

To appreciate why this matters, consider the broader landscape of non-contact manipulation technologies. Optical tweezers, which earned the 2018 Nobel Prize in Physics, trap particles using tightly focused laser light, but they require transparent media and work best at microscopic scales. Acoustic levitation, by contrast, works in air, exerts forces sufficient for millimeter-scale objects, and imposes no transparency requirements on the sample. Its contactless nature makes it ideal for handling fragile materials, contamination-sensitive samples such as pharmaceutical compounds or biological specimens, and hazardous substances that must never touch container walls or human hands. The chief drawback has always been the enclosed, short-range geometry of practical systems, and it is precisely this drawback that the Bessel beam approach eliminates.

The physics behind the advance rewards a closer look. A zero-order Bessel beam is characterized by a bright central lobe surrounded by concentric rings of decreasing intensity, and its defining feature is nondiffracting propagation: the central core regenerates itself from the conical superposition of plane-wave components, so the high-pressure region persists over an extended axial distance. When a small object is placed in this core, the acoustic radiation forces arising from the pressure and velocity fields produce a restoring effect that pulls the object back toward the beam axis and toward an equilibrium position along it. Because the core remains intense far from the transducer, the trap does not collapse with distance, which is exactly the failure mode of conventional single-sided traps. The result is a stable, three-dimensional potential well that exists in open, unconfined space, generated entirely from one side.

The potential applications suggested by the researchers span automated experimentation and three-dimensional displays. In automated laboratories, long-range acoustic traps could move reagents, droplets, or sensitive samples between stations without tubing, robotic arms, or physical contact, reducing contamination risks and enabling entirely new workflow geometries in which objects travel through open air along programmable paths. In display technology, levitated particles could serve as physical voxels, suspended and steered in three-dimensional space to form volumetric images that viewers can walk around and inspect from any angle, a concept that has been explored with shorter-range systems but now gains the working volume needed to become practical.

The research was supported by the Japan Science and Technology Agency through the Adopting Sustainable Partnerships for Innovative Research Ecosystem (ASPIRE) program under Grant Number JPMJAP2330, JST SPRING Grant Number JPMJSP2124, Japan Society for the Promotion of Science KAKENHI Grant Number JP25KJ0674’s companion award JP25KJ0673, and the Engineering and Physical Sciences Research Council Grant Number EP/Z534171/1. The work was also fostered by the JST ASPIRE program, which promoted and strengthened personnel and technical exchange, centered on early-career researchers at the University of Tsukuba, through the international research collaboration between the University of Tsukuba and the University of Bristol. As acoustic levitation steps out of its enclosure and reaches across tens of centimeters of open air, the boundary between laboratory demonstration and deployable technology grows thinner, and the prospect of manipulating matter with nothing but sound moves measurably closer to everyday reality.

Subject of Research: Single-sided acoustic levitation of objects in the high-pressure core of a zero-order Bessel ultrasound beam

Article Title: Ultrasonic beam extends acoustic levitation range sixfold

Article References: Ultrasonic beam extends acoustic levitation range sixfold. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: acoustic levitation, ultrasound, Bessel beam, University of Tsukuba, Physical Review Letters, non-contact manipulation, acoustic radiation force, three-dimensional manipulation, automated experimentation, 3D displays, photonics-free trapping, open-air levitation