The two platforms face each other, emitting high-energy sound waves toward each other. Where the sound waves off the two surfaces overlap, they cancel out and can trap materials in place, researchers at the Swiss Federal Institute of Technology in Zurich reported Tuesday.
Since the sound waves must be extremely powerful to levitate even tiny drops of liquid, the researchers chose ultrasound frequencies above the range of human hearing to protect their ears as the experiments run.
While acoustic levitators are not a new concept, this is the first such device capable of both moving and controlling the material being levitated, researcher Daniele Foresti said.
"We have total control of the acoustic field inside," he told BBC News.
Moving objects such as particles or droplets of a liquid freely in mid-air makes it possible to investigate processes while avoiding any disruptive contact with a surface, which might compromise a chemical reaction or biological process, the researchers said.
"This method of moving levitated objects could have a wide range of possible applications," including industrial processes, Foresti said.