Tweezers of Sound: Lifting Objects Without Touching Them

Scientists in Japan have experimented successfully in raising objects using only sound. The aim is to use this technology in a wide range of places – including Space.

Such “acoustic tweezer” technology promises completely contactless, contamination-free manipulation of small objects.

Last year, Dr Shota Kondo and Associate Professor Kan Okubo from Tokyo Metropolitan University had success with the contactless lift and movement of millimeter-sized particles using a hemispherical array of small, ultrasound transducers. The transducers would be driven individually according to a unique algorithm, allowing them to set up fields of sound pressure which ultimately lifted and moved objects. However, the stability of their “acoustic tweezers” remained an outstanding issue.

Now, the same team have come up with a way of using the same setup to achieve significant enhancements in how they can lift particles from rigid surfaces. There are two “modes” in which the transducers can be driven, where opposing halves of their hemispherical array are driven in and out of phase.

The team’s new insight is that different modes are more suited to doing certain things. Starting with a particle on a surface, an “in-phase” excitation mode is better at lifting and moving the particle close to the surface, with accurate targeting of individual particles only a centimeter apart.

Meanwhile, an “out-of-phase” mode is more suited to bringing the lifted particle into the center of the array. Thus, using an adaptive switching between the modes, they can now leverage the best of both modes and achieve a well-controlled, stable lift, as well as more stability inside the trap once it is lifted.

This is an important step forward for a futuristic technology that could one day be deployed to manipulate samples which need to be kept strictly contamination free. The team also hopes that it might find practical application in space one day, where competing against gravity is not an issue.

The work was partially funded by the Murata Science Foundation and the results published in the paper ‘Improved mid-air acoustic tweezers using adaptive phase and amplitude control’ in the Japanese Journal of Applied Physics

(left) An illustration of the array of transducers and the lifting of a small particle. (middle) The different fields of sound generated by the array as a particle is lifted. (right) “Acoustic tweezers” lifting a particle and keeping it in place as the whole array is moved by hand. Image: Tokyo Metropolitan University

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