Lifting things with sound waves

Watch a hemisphere of ultrasound transducers that create sound waves, lifting a polystyrene ball off a reflective surface. Credit: Tokyo Metropolitan University

Researchers have created a technology that uses sound waves to move small objects without touching them.

You may have heard of optical tweezers, which use light to build molecules and move microscopic things around without physical contact. This new method, dubbed “acoustic tweezers”, uses the same logic with sound waves, and can move much larger things. It’s previously been used to move microparticles around, but a team of researchers based at Tokyo Metropolitan University, Japan, have figured out a way to lift objects several millimetres in diameter – like a polystyrene ball.

The acoustic tweezers work inside a 120mm-diameter hemisphere, which is lined with 180 small transducers (devices which convert energy from one form to another – in this case, into sound). The transducers emit sound waves which, when they converge, can create an “acoustic trap” that moves objects within a small area inside the hemisphere.

This technique has previously needed very complicated, individual sound waves coming from each transducer to work, but the researchers developed a method which optimised and simplified the sound waves required. It also meant that they could position their device on a reflective surface: previously, reflective surfaces have bounced sound waves around too much to make this possible.

The researchers point out that while they could pick up a polystyrene ball several times, and film it happening, the method wasn’t perfect and it didn’t work every time.

“When we move a particle, it sometimes scatters away,” they write in their paper describing the device, published in the Japanese Journal of Applied Physics.

“In future studies, the robustness of the proposed method will be improved for practical use of non-contact pick-up,” they add.

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