An innovative method allows researchers to move objects using ultrasound waves

"We have known for a while that waves and light and sound can manipulate objects. What sets our research apart is that we can manipulate and trap much bigger objects if we make their surface a metamaterial surface, or a 'metasurface,'" said Ognjen Ilic, senior author of the study and the Benjamin Mayhugh Assistant Professor in the University of Minnesota Department of Mechanical Engineering.

"When we place these tiny patterns on the surface of the objects, we can basically reflect the sound in any direction we want. And in doing that, we can control the acoustic force that is exerted on an object."

It not only pushes but also pulls the objects

The technique not only enabled the researchers to move an object forward, but also pull it in the direction of a source. This could be especially useful in manufacturing or robotics industries.

"Contactless manipulation is a hot area of research in optics and electromagnetism, but this research proposes another method for contactless actuation that offers advantages that other methods may not have," said Matthew Stein, first author of the paper and a graduate student in the University of Minnesota Department of Mechanical Engineering.

"Also, outside of the applications that this research enables, expanding upon our knowledge of physics is just a very exciting thing to do in general!"

The research team is now planning to test the method with higher wave frequencies on objects of different materials and sizes in the future.

"In a lot of fields of science and engineering, robotics especially, there is the need to move things, to transfer a signal into some sort of controlled motion," Ilic said.

"Often this is done through physical tethers or having to carry some source of energy to be able to perform a task. I think we're charting in a new direction here and showing that without physical contact, we can move objects, and that motion can be controlled simply by programming what is on the surface of that object. This gives us a new mechanism to contactlessly actuate things."

The study was published in the journal Nature Communications.

Abstract:

Waves impart momentum and exert force on obstacles in their path. The transfer of wave momentum is a fundamental mechanism for contactless manipulation, yet the rules of conventional scattering intrinsically limit the radiation force based on the shape and the size of the manipulated object. Here, we show that this intrinsic limit can be broken for acoustic waves with subwavelength-structured surfaces (metasurfaces), where the force becomes controllable by the arrangement of surface features, independent of the object's overall shape and size. Harnessing such anomalous metasurface scattering, we demonstrate complex actuation phenomena: self-guidance, where a metasurface object is autonomously guided by an acoustic wave, and tractor beaming, where a metasurface object is pulled by the wave. Our results show that bringing the metasurface physics of acoustic waves, and its full arsenal of tools, to the domain of mechanical manipulation opens new frontiers in contactless actuation and enables diverse actuation mechanisms that are beyond the limits of traditional wave-matter interactions.