Employees of the University of Tokyo and the Nagoya Institute of Technology managed to set small objects in motion using a complex acoustic levitation system: sound waves moved polystyrene particles with a diameter of 0.6 to 2 mm in three-dimensional space. Previously, objects using the same system were able to move only in two dimensions.
It took four rows of speakers to move water droplets, polystyrene particles, small pieces of wood, and even screws through the air. These objects were moved in all directions within the limits allowed by the experimental conditions. Movement in this case is caused by standing ultrasonic waves.
The literature describes an experiment that can be performed at home: by placing a strip of paper held in your hand over the ultrasonic generator so that its free end is 3-5 mm above the end of the rod, you need to press the button of the generator - and the tip of the paper under the influence of a sound wave will go up and hover motionlessly over the rod.
The apparatus used in the experiment is much more complicated than the generator: sound waves with a frequency of more than 20 kHz, inaudible to the human ear, emanate from four sides and intersect inside a limited space. Thus, they form a movable focus, in which a small object seems to be clamped and hovered in space.
The direction of the waves can be arbitrarily changed, while the object is moving. Sound levitation is a way to overcome gravity, scientists say. Therefore, organizations such as NASA are already using devices for acoustic levitation.