Practical levitation is something that has been eluding scientists for decades. However, a recent development in Tokyo may help bring practical levitation out of science fiction and into reality.
Scientists from the University of Tokyo have succeeded in creating a levitation rig that utilizes the power of sound, specifically ultrasonic standing waves, to levitate and suspend small objects in midair. While levitating small objects has been done before using a variety of methods such as magnetism, the recent Tokyo experiment has succeeded in actually moving the suspended objects around in a controlled fashion.
Like magnetic levitation, sound-based levitation has also been around for a while. However, previous experiments involved the use of in-line speakers that reflect sound off of a sound-reflecting surface to levitate objects. The recent experiment uses a very different approach. Instead of using speakers arranged in a straight line, the Tokyo-based scientists use four speaker arrays all facing each other. Since the speakers are arranged in this manner, the sounds emanating from the array converge into a single "ultrasonic focal point." It is this focal point that allows the scientists to manipulate the suspended objects. By moving the focal point left to right and up or down, the scientists were also able to move the suspended objects. This is accomplished by varying the output of each speaker.
"In the present study, we considered extended acoustic manipulation whereby millimetre-sized particles were levitated and moved three-dimensionally by localised ultrasonic standing waves, which were generated by ultrasonic phased arrays," said the team in a published report. "Our manipulation system has two original features. One is the direction of the ultrasound beam, which is arbitrary because the force acting toward its centre is also utilised. The other is the manipulation principle by which a localised standing wave is generated at an arbitrary position and moved three-dimensionally by opposed and ultrasonic phased arrays."
While the rig allows the levitation of relatively small objects for now, it serves as an important proof of concept for future studies and experiments. For now, it also serves as a confounding display of science in action. For the average Joe, it appears to be a good example of Arthur C. Clarke's third law in practice, that "any sufficiently advanced technology is indistinguishable from magic."
