Ultrasonic levitation, also known as acoustic levitation, has been demonstrated a few times already. However, until recently it has not been possible to manipulate the suspended objects in free space. The levitation suspends objects in air by exploiting the properties of a standing wave. While most animations of waves show them moving through space, with the maximum and minimum values changing, the standing wave appears as if it is not moving at all, with the maximum and minimum peaks staying in one place. This is where one can define the nodes, the minimum pressure areas, and the anti-nodes, the high pressure areas. The nodes are the area of the wave where an object will levitate, given that the density of the object is small enough for the upward pressure to overcome the downward effects of gravity.
Granules floating in air due to ultrasonic sound. Animals hate it. (via 3DOF)
With that said researchers Yoichi Ochiai, Takayuki Hoshi, and Jun Rekimoto from the University of Tokyo have used an array of ultrasonic sound to suspend an object in air, and then move the object around in the horizontal plane. The arrays used to generate the high frequencies consisted of 285 specialized speakers which were made to produce waves above 20KHz (inaudible for humans). Some of the waves are fixed in position to produce the upward pressure to keep object levitating in space. On the other hand, additional waves are used which can be adjusted to change the position of the levitating object in the horizontal axis.
The applications of levitation are scarce at the moment, but there exists some uses in chemistry and biology in which it can pose an advantage. Levitation can be used to carry out chemical reactions without exposing them to any containers or materials. This can keep the chemicals from being exposed to contamination or any type of surface contact. In fact, scientists have already used levitation to demonstrate sodium reacting with water. Although the levitation is unnecessary for the demonstration, it is an awesome way to utilize it.
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