Researchers of the University of Tokyo and Nagoya Institute of Technology managed to move small objects with the help of a complex system of acoustic levitation: sound waves moved polystyrene particles with a diameter of 0.6 to 2 mm in three-dimensional space. Earlier moving items using the same system was possible in only two dimensions.
To move through the air drops of water, polystyrene particles, small pieces of wood and even screws, four rows of speakers were needed. These objects were moving in all directions within the limits permitted by the experimental conditions. Motion in this case was caused by ultrasonic standing waves.
The literature describes an experiment that can be made at home: holing a slip of paper over the ultrasonic generator so that its free end was 3-5 mm above the end of the rod, you need to press the generator, and the tip of the paper will go up and will hang over the rod under the influence of a sound wave.
The apparatus used in the experiment is much more complicated than the generator: sound waves with a frequency of above 20 kHz, which are not audible to the human ear, come from four sides and intersect inside the confined space. Thus, they form a movable focus, in which small objects hang in the air.
The direction of the waves can vary arbitrarily, while the object is moving. Sound levitation is a way to overcome gravity, scientists say. So even now acoustic levitation devices are used by organizations such as NASA.