Scientists levitate objects with sound

Scientists levitate objects with sound

Scientists levitate objects with sound

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The first real “acoustic clamp” was produced in 2016 by CNRS researchers: a complex system based on sound waves, composed of emitters and reflectors, which manages to trap a particle and lift it! This device was then recreated around the world, then improved many times. I don’t like the acoustic levitation, which keeps an object in the air previously deposited where it should levitate, this technique causes the object to take off from a reflective surface. Although they had already made such a device last year, this time the researchers from the University of Tokyo decided to improve its stability, more precisely that of the particle once it is lifted. The details of their project were presented in a study, published in Japanese Journal of Applied Physics.

Improvement of the device called “acoustic gripper” for handling objects without contact. © TMU, YouTube

The acoustic clamp, evolution of acoustic levitation

Their device of acoustic clamp is based on the use of ultrasonic transducers, or devices that convert an input signal into ultrasound. For the 180 transducers used, the frequencies output were at 40 kHz. At this frequency, the human ear is no longer able to hear the signal. The whole was positioned in the form of a hemispherical network, with the aim of encircling the target particle. But how can sound waves “trap” a particle? Everything rests on pressure acoustic radiation: i sound waves exert pressure on the environment in which they spread.

Using either more sources of the same frequency that combine or are reflected, or just one that is reflected, it is possible to generate what is called a standing wave: a wave that contains some points called ” knots “, So the amplitude remains constant over time, and between these nodes of the” belly “where vice versa the amplitude varies over time.

At the level of the nodes, the width does not vary. Therefore, by adjusting it so that the force exerted by the waves compensates for gravity, it is possible to immobilize a particle at the level of the acoustic pressure nodes. It’s here acoustic levitation ! For the acoustic clamp, it is more complicated. The emitters must be tuned so that the particle moves, taking advantage of a continuous variation of the emission frequency. “A particle levitates at the nodes of a standing wave. Therefore, the modification of the frequency of the signal coming from the transducers allows the transfer of a particle “, describe the researchers. The nodes are thus gradually moved and the levitating particle will follow these nodes. However, the move is one-sided.

Two modes, “in phase” and “out of phase”, to bring the particle to its destination

The acoustic clamp developed by the researchers is based on a hemispherical network of ultrasonic transducers. The manipulated particles are of the order of a millimeter and move following the acoustic pressure field created by this network. But within that field, the particle fluctuated until they updated their acoustic tweezers: A major concern when shooting objects using the strength of acoustic radiation is the reflection effect caused by the scene. Since the sound field is disturbed by this reflection, it is not possible to keep the object stable “, explain the researchers. A problem that scientists have solved “A block and a phase and amplitude control upon excitation of a transducer network”.

More precisely, they use a switching adaptive between excitations of opposite phase and in phase “. The particle is first captured from the ground by phase excitation, not all transducers are used. Then the shift towards the center is carried out in an out of phase mode (in the opposite phase), this time of the entire network, and is then maintained using the whole network, always in phase opposition. The signal thus created allows the particle to be gently lifted, then moved and held in a central position. This type of device might have app in various fields, in particular in those in which the manipulation of components could be carried out without contact: electronics or chemistry. Such an experiment can also be more easily reproduced in thespacewhere gravity no longer needs to be compensated for.

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