Scientists have been able to use the power of sound to levitate incredibly small items, like for exmaple, small insects and fish for decades now, but now thanks to a new study, researchers in Switzerland have figured out how to move bigger objects around, and doing so in midair. The breakthrough discovery in acoustic levitation will pave the way for scientists and allow scientists explore and to unlock “a huge amount of applications for this very powerful method,” including in pharmaceutical and electronics manufacturing, according to the author and mechanical engineer Dimos Poulikakos of ETH Zurich, a science and technology university located in Switzerland.
The study, which was proudly published online in the Proceedings of the National Academy of Sciences notes that Poulikakos’s team performed a number of midair experiments to truely test the boundaries of the finding, such as combining water droplets or chemical solutions, inserting DNA into cells and even making a tiny portion of instant coffee. They also levitated a wooden toothpick, which they noted was something that had never been done before prior to this experiment, in which they quickly found rotating and moving forward and backward in midair.
So how exactly does it work? Well, according to the scientists involved, sound waves exert pressure when they hit a surface, but the effects are usually too small to notice. But if the intensity is cranked up high enough, sound has the ability to counteract the effects of gravity. Poulikakos and his colleagues used levels of about 160 decibels; that’s louder than standing near a rocket launch and is enough to rupture a human eardrum. But they were able to work without ear protection. They took advantage of the fact that the frequency of sound, which involves the physical property that gives it a pitch. Using 24,000 hertz, a level comparable to a dog whistle, they were unaffected by the noise. The upper range of human hearing is approximately only 20,000 Hz.
“The tricky part was figuring out how to move things from square to square carefully, without damaging them”, said lead author Daniele Foresti, also a mechanical engineer at ETH Zurich. When studying the sound waves, Foresti found that balance was the key to successfully mastering the levitation. According to Foresti, if you push too hard, and the sound waves will cause a water droplet to explode, and . if you don’t push hard enough, and the droplet will fall and take a natural gravity-induced route. Eventually, Foresti discoverd that the way to succeed was to slowly lower the sound intensity of the “giving” square while increasing that of the “receiving” one. Poulikakos compares the previous state of acoustic levitation — without the airborne motion control — to a luxury car kept permanently in park. “We could walk around it and enjoy it, but we could not drive it,” he said. “Now we can drive it.”
Physicist Rick Weber of Argonne National Laboratory outside Chicago commended the authors for developing “a highly innovative approach” that furthers the capabilities of acoustic levitation.
Poulikakos’s advance over motionless levitation will no doubt assist many professional fields, particularly in the pharmaceutical industry where the new discovery will allow scientists to mix solutions in midair without the potential for contamination from a container, Weber said. The team, along with many other scientists is confident that the same methodology could be adapted to in-water particle manipulation in approximately one year and they hope that soon after, it could be adapted for use in biological tissue. Additionally, the technology could also facilitate hands-off construction of delicate microelectronic components, says coauthor Asier Marzo, a computer scientist at the Public University of Navarre in Pamplona, Spain. Or it could be used in manipulating levitated particles into free-floating, 3-D images to create futuristic displays.