Tokyo team adds stability to acoustic tweezer technology

The ‘acoustic tweezers’ could already lift things from reflective surfaces without physical contact, but stability remained an issue. Now, using an adaptive algorithm to fine-tune how the tweezers are controlled, the team at Tokyo Metropolitan University have considerably improved how stably the particles can be lifted. With further miniaturisation, this technology could be deployed in numerous environments, including space, for contactless, contamination-free manipulation of small objects.

In 2021, Dr Shota Kondo and Associate Professor Kan Okubo from Tokyo Metropolitan University realised contactless lift and movement of millimetre-sized particles using a hemispherical array of ultrasound transducers. The transducers would be driven individually according to a unique algorithm, allowing them to set up fields of sound pressure which lifted and moved objects. Despite this success, the stability of their 'acoustic tweezers' remained problematic.

Now, the same team have devised 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 centimetre apart. An 'out-of-phase' mode is more suited to bringing the lifted particle into the centre of the array. Using 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.

The technology is described in the Japanese Journal of Applied Physics.