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A research team at University of Tsukuba and the University of Bristol has experimentally demonstrated, for the first time, stable three-dimensional acoustic levitation within the high-pressure core of a zero-order Bessel beam. Using a specially designed ultrasonic beam emitted from a single side, the researchers successfully levitated and translated millimeter-scale objects in midair without physical contact over distances of up to approximately 40 cm. This working distance is approximately six times greater than that achieved using conventional single-sided acoustic levitation methods.

Tsukuba, Japan—Acoustic levitation is a technique that uses the acoustic radiation forces generated by sound waves, particularly ultrasound, to suspend objects in midair without physical contact. Because the object remains untouched, the technique is well suited for handling fragile materials, contamination-sensitive samples, and hazardous substances. Conventional acoustic levitation systems typically rely on standing waves generated between opposing sound sources or between a sound source and a reflector, confining objects within enclosed regions of the apparatus. Although single-sided approaches have been developed to eliminate the need for such enclosures, they have generally been limited to levitating objects only in the immediate vicinity of the sound source.

These limitations arise from the underlying trapping mechanism. In conventional acoustic levitation, objects are typically confined at low-pressure nodes surrounded by high-pressure regions. In single-sided systems, however, the restoring force that stabilizes the object decreases with increasing distance from the sound source and eventually becomes repulsive, thereby preventing long-range levitation. In the present study, the researchers employed a zero-order Bessel beam—an ultrasonic beam that maintains a narrow, high-intensity central core over long distances. By exploiting its unique properties, they successfully trapped objects directly within the beam's high-pressure core using ultrasound emitted from only one side. Using this approach, they achieved stable levitation of a 1.5-mm-diameter expanded polystyrene sphere at distances of up to approximately 40 cm from the sound source—approximately six times farther than those achieved using conventional single-sided acoustic traps. The levitated object could also be manipulated in three dimensions using ultrasound from only one side. Furthermore, the researchers demonstrated the levitation of multiple objects, non-spherical objects, and objects located beyond physical obstacles.

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. Because it enables long-range, non-contact manipulation in open, unconfined environments, the method is expected to find applications in automated experimentation and three-dimensional displays.

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This work was supported by Japan Science and Technology Agency (JST) as part of Adopting Sustainable Partnerships for Innovative Research Ecosystem (ASPIRE) Grant Number JPMJAP2330, JST SPRING Grant Number JPMJSP2124, Japan Society for the Promotion of Science (JSPS) KAKENHI Grant Number JP25KJ0673, and Engineering and Physical Sciences Research Council (EPSRC) Grant Number EP/Z534171/1.
This 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.

Original Paper

Title of original paper:

Midair Single-Sided Acoustic Levitation in High-Pressure Regions of Zero-Order Bessel Beams

Journal:

Physical Review Letters

DOI:

10.1103/pfkh-4x7j

Correspondence

Assistant Professor FUSHIMI Tatsuki
Institute of Library, Information and Media Science, University of Tsukuba

KOROYASU Yusuke
Doctoral Programs in Informatics, Graduate School of Comprehensive Human Sciences, University of Tsukuba

Related Link

Institute of Library, Information and Media Science