The levitation of a polystyrene sphere has been presented by researchers in recent times which is larger than the acoustic wavelength- a world first.
By means of illustrations of small objects being levitated through ultrasonic waves, the notion behind acoustic levitation has been around for several years. A unique property of sound is the course via which acoustic levitation is attained. The property is capable of empowering objects to remain suspended atop specific pressure regions. The apparatuses of acoustic levitation are incredibly simple and include two major components, one of them is “Transducers” and the other is “Reflectors”. The sound is provided by the transducer which is directed towards the reflection where it is then reflected back to the source. The device is arranged in such a way that a standing wave is produced, thereby generating constructive and destructive interference. The object is capable of levitating when it enters a region of low pressure with a high-pressure underneath. As we are familiar with the fact that the force is directly proportional to the pressure, therefore the force is greater in the high-pressure region, creating a net force in the upwards direction, enabling the object to be pushed up. Levitation is attained if the upwards force can be matched with the force of gravity.
But, a fundamental problem is that there is a restriction as to how big the object can be. While telling Phys.org, Andrade said:
“Acoustic levitation of small particles at the acoustic pressure nodes of a standing wave is well-known, but the maximum particle size that can be levitated at the pressure nodes is around one quarter of the acoustic wavelength. This means that, for a transducer operating at the ultrasonic range (frequency above 20 kHz), the maximum particle size that can be levitated is around 4 mm. In our paper, we demonstrate that we can combine multiple ultrasonic transducers to levitate an object significantly larger than the acoustic wavelength. In our experiment, 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.”
A paper has been published lately on the acoustic levitation demonstration and their unique approach that makes them capable of levitating objects much larger than previously possible by researchers Marco Andrade and Julio Adamowski at the University of São Paulo in Brazil, alongside Anne Bernassau at Heriot-Watt University in Edinburgh, UK. A similar standing wave is generated between the sphere and the transducers with the help of a tripod configuration. By producing another axis of acoustic radiation, a force was created that was able to sustain a load 3.6 times larger than the wavelength.
In medical applications where the risk of bacterial contamination is great, this technology might have potential uses. Despite the fact that the experiment marks another milestone in acoustic levitation, it will probably not see use in any levitating vehicles anytime in the near future.