A team of scientists in Zurich, Switzerland, have developed a method of acoustic levitation that allows them to float several objects next to each other and move them around. Using sound waves, scientists at the Swiss Federal Institute of Technology in Zurich have made water droplets, instant coffee crystals, Styrofoam flakes, and a toothpick, among other objects; hang in mid-air, move along a plane, and interact with each other. The acoustic levitator was originally developed for NASA to simulate microgravity conditions.
Unlike the acoustic levitator developed at the US Department of Energy’s Argonne National Laboratory, which is able to suspend droplets in mid air between two small speakers, the new technology allows the movement of suspended droplets and objects to be controlled. From this, scientists can mix multiple droplets in mid-air and transport other objects.
The knowledge that acoustic waves can exert a force – the acoustic radiation pressure effect – on an object to keep it in suspension, was discovered more than 100 years ago. However, until now, no one had been successful in controlling the motion of objects riding on acoustic waves.
Being able to manipulate matter without touching it promises a wealth of applications, from material sciences to biology. For instance, nucleic acids can be introduced into cells – a process known as DNA transfection – without fear of contamination. “You can basically play with cells in a droplet. This is a toy. I hope that it can be useful for something,” said engineer Daniele Foresti, the study’s lead author. In a video, he captured how the two droplets mix and the pigment begins to glow.
Research published in the Proceedings of the National Academy of Sciences, describes how objects placed between two horizontal surfaces, the bottom one emitting high-pitched sound waves and the top one reflecting the waves back, can be levitated and manipulated.
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