Sound Waves Levitate Objects From Reflective Surfaces in New Method Developed by Japanese Engineers

Engineers from Tokyo Metropolitan University in Japan developed a new technology for levitating and manipulating small objects using sound waves. Researchers used ultrasound transducers to produce 3D acoustic levitation that trapped and lifted a small polystyrene ball from a reflective surface.

Although this might sound like magic, scientists from different disciplines like chemistry, biology, and technology have been using optical trapping for many years to help them move microscopic objects using light. But the use of light also has its limits on the type of objects it can only move.

The new method of using sound waves could help unlock the potential of manipulating physical objects using only sound waves that can be beneficial in various fields, like biomedical engineering, nanotechnology, and pharmacology, Science Alert reported.

Sound Waves Can Be a Powerful Tool to Levitate and Move Objects

Levitating objects without touching them is nothing new in the field of science. Scientists were able to levitate objects using optical tweezers in the past that uses lasers to generate sufficient radiation pressure that can pick up and move tiny particles.

Meanwhile, acoustic tweezers can also be used to move particles. They use sound waves generated from pressure and could potentially be a more powerful tool than optical tweezers.

Acoustic tweezers were discovered in the 1980s, but limitations of acoustic tweezers have prevented their use in broad practical applications. For instance, sound waves need to be "trapped" for this technology to be used.

Scientists have used hemispherical arrays of acoustic transducers in the past to trap sound waves, but it is still tricky to control them in real-time because they still need to produce the right amount of sound field to levitate an object and move it from the transducers. More so, the past method was even trickier when there is a surface that reflects sound as it complicates the sound field.

But engineers Shota Kondo and Kan Okubo have developed a method to make a hemispherical acoustic array that can levitate a 3mm polystyrene ball from a reflective surface. They propose a multi-channel hemispherical ultrasound transducer array to levitate small objects.

"The phase and amplitude of each channel are optimized using the sound reproduction method. This creates an acoustic trap at only the desired position, and pick-up can thus be realized on the rigid stage. To the best of our knowledge, this is the first study to demonstrate non-contact pickup using this approach," they wrote in their paper.

New Method Uses Sound Waves to Levitate and Move Objects on Reflective Surfaces

Shondo and Okubo's new method involves splitting the hemispherical array into manageable blocks and use an inverse filter that looks for the optimal phase and amplitude to trap sound waves at some distance from transducers; SciTech Daily reported. It was unlike previous methods that involved complex addressing of individual elements.

They were able to change the position of their target field by adjusting how they drive the blocks over time. As a result, they were able to lift the millimeter-sized particle they have trapped. This supports the simulations done using 3D acoustic fields that are created by arrays and polystyrene balls.

But challenges still loom for this technology, especially in keeping particles trapped and stable. Nonetheless, this exciting new technology opens new doors towards transforming acoustic tweezers into a practical tool in the laboratory and various industries.

The team published their paper, titled "Mid-air Acoustic tweezers for non-contact pick up using multi-channel controlled ultrasonic transducer arrays," in the Japanese Journal of Applied Physics.

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