Narrow ultrasonic beam enables stable 3D levitation six times farther than before

Scientists have developed a novel acoustic levitation technique that employs an ultrasonic beam capable of suspending small objects in midair over distances six times greater than previously possible. The research, conducted by teams from the University of Tsukuba in Japan and the University of Bristol, was recently published in the journal Physical Review Letters.

Acoustic levitation, which suspends objects using sound waves without physical contact, holds promise for handling delicate materials, sensitive samples, and hazardous substances.

Conventional acoustic levitation systems utilize sound waves generated within an enclosed space. However, the new technique represents a significant breakthrough as it is the first single-sided design to demonstrate stable three-dimensional levitation. Professor Bruce Drinkwater of the University of Bristol explained that conventional levitators rely on sound waves from opposing directions to stabilize objects.

In single-sided levitators, the force that holds the object steady diminishes with distance, eventually pushing the object away. This limitation renders long-distance levitation unfeasible.

To overcome this challenge, the researchers utilized a specialized ultrasonic beam known as a zero-order Bessel beam. Unlike conventional sound beams, a Bessel beam maintains a narrow focus and preserves a high-intensity central core over extended distances. By harnessing the unique properties of this beam, the researchers successfully achieved stable levitation of a 1.5 mm-diameter polystyrene sphere at a distance of up to 40 cm from the sound source, approximately six times farther than any previously accomplished using single-sided acoustic traps.

The team demonstrated the versatility of their technique, manipulating the levitated object in three dimensions using ultrasound emanating from a single side. Furthermore, the method successfully levitated multiple objects, non-spherical objects, and objects situated between other physical barriers. Professor Tatsuki Fushimi from the University of Tsukuba highlighted the potential applications of this technique, including automated experiments, three-dimensional displays, handling fragile materials, and working with hazardous substances.

The study, titled "Midair Single-Sided Acoustic Levitation in High-Pressure Regions of Zero-Order Bessel Beams," was authored by Yusuke Koroyasu et al. The findings were published in Physical Review Letters, with the DOI of 10.1103/pfkh-4x7j.