You may have heard of acoustic levitation, the process of suspending something in mid air with sound. In the process, two waves of sound are fired at each other and where they meet they produce "standing waves." These waves have peaks that oscillate between high and low pressure, and can be used to bounce an object up against the force of gravity.
For years, we have been experimenting with levitating small objects, like water droplets and tiny, lightweight balls. Until now, we were unable to levitate anything larger than the acoustic wavelength, as it would fall out of the standing wave.
Now, scientists have levitated an object 3.6 times larger than what we could do previously.
"In our paper, we demonstrate that we can combine multiple ultrasonic transducers to levitate an object significantly larger than the acoustic wavelength," one of the researchers, Marco Andrade from the University of São Paulo in Brazil, said.
"We could increase the maximum object size from one quarter of the wavelength to 50 mm, which is approximately 3.6 times the acoustic wavelength."
In order to levitate the larger object, a tripod structure of ultrasound transducers were used. Having the three sound outputs allowed the ball to be buffered on three sides, producing a standing wave between the transducers and the object.
So rather than catch a small item inside the standing wave, they produce the wave below the object and sort of bounce it upward like a super fast, barely moving ping-pong ball.
Very cool; here it is in action.