Researchers at the University of Tokyo (UoT) have created a technique of offsetting the effects of gravity to simulate levitation using sound.
The paper entitled, “Three-dimensional Mid-air Acoustic Manipulation by Ultrasonic Phased Arrays”, reads: “Our manipulation system has two original features. One is the direction of the ultrasound beam, which is arbitrary because the force acting toward its [center] is also utilized. The other is the manipulation principle by which a localized standing wave is generated at an arbitrary position and moved three-dimensionally by opposed and ultrasonic phased arrays.”
Using an ultrasound standing wave (USW) the team was able to suspend “small particles” in mid-air.
These polystyrene particles were manipulated “at the third node along one of the acoustic axes from the intersection of the ultrasound beams. They set the sound pressure to 70 percent, and were able to move the tiny particle in several directions.”
During the experiments, it was shown that size matters.
The paper explains: “There are some factors to be considered in choosing the manipulation target, namely the size and material. The size of the manipulation target is determined by the distribution of the potential energy, and a light material is required. The internal force is also an important factor in selecting the material; for example the electrostatic force determines the maximum number of particles that can be at a single node, and the surface tension of the fluid determines the size of droplets that can be levitated.”
The conclusion of the paper states: “We have demonstrated an extended acoustic manipulation by which millimeter-sized particles can be levitated and moved three-dimensionally by localized ultrasonic standing waves generated by ultrasonic phased arrays.”
The paper concedes that the scientists have not glossed over the fact that this “method for levitation under gravity suggests the possibility of developing a technology for handling objects under microgravity.”
In space, where low-gravity is an issue, this technique could prove useful.
Another application may be that corporations use “invisible waves to improve existing technology.”
For example, an ultrasonic windshield would repel water, thereby making it safer for the driver in extremely wet conditions.