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The technique, developed at the University of Minnesota, builds on previous demonstrations that showed how light and sound waves can manipulate objects. Unlike the previous work, the Minnesota researchers said their method can move objects that are larger than the wavelength of sound or light – typically nanometres to millimetres.
The Minnesota method moves larger objects using the principles of metamaterial physics. Metamaterials include materials that are artificially engineered to interact with waves, like light and sound.
By placing a metamaterial pattern on the surface of an object, the researchers were able to use sound to steer it in a certain direction without physically touching it. A video shows a comb-like structure moving in response to an inaudible ultrasound signal.
“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 assistant professor 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.”
Using this technique, the researchers can not only move an object forward but also pull it toward a source, not unlike sci-fi style tractor beams.
The method could be useful for moving objects in sectors like manufacturing or robotics, the researchers said.
“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 on the paper and a graduate student.
Describing the study as more of a demonstration of the concept, the researchers now hope to test higher-frequency waves, and different materials and object sizes.
“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 research was supported by the Minnesota Robotics Institute and the US Air Force Office of Scientific Research.
The study was published in Nature Communications.
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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.