Audio technology: how pieces of plastic are moved using ultrasound and why it is needed

    The technology of acoustic tweezers has been known since 1986. It is based on the phenomenon of acoustic levitation and uses ultrasonic waves to lift objects a few millimeters in size. Until recently, scientists could only manipulate a single plastic ball. Now it is possible to levitate many objects at once and manage their movement separately. On Habré there was an article which is devoted to the principles of work of technology. We will tell about its potential and analogues.

    Photo by Morgan / CC BY

    Briefly about what technology is

    Researchers from the University of Navarre in Spain and the University of Bristol in the UK have created an installation in the form of a kind of “box”, inside which are arrays of ultrasonic emitters above and below. In total, the system uses 512 speakers with a diameter of less than a centimeter, emitting waves at a frequency of 40 KHz.

    With the help of special reflectors, engineers can form so-called standing waves . They have the same amplitude and frequency, but differ in phase. So, between the sound waves formed "empty" areas of the same size with zero sound pressure, they keep objects in the air. These objects can be both pieces of plastic and liquid droplets. The movement of individual objects independently of each other occurs due to a change in the phase of standing waves. A special algorithm based on the back-propagation method is responsible for this . The authors of technology compare it with fingers that capture and move objects within the field. Using 512 speakers, the researchers were able to control 12 foam balls.

    What is the potential

    According to the authors, acoustic levitation ("acoustic tweezers") can replace another technology - " optical tweezers ", for the discovery of which in 2018 was awarded the Nobel Prize in Physics. Optical tweezers use a laser beam to move microscopic objects (molecules and particles).

    But this approach has a drawback - it is expensive , plus the laser can harm cells or living organisms on contact. Acoustic tweezers of these shortcomings are devoid of. Therefore, it is proposed to use in medicine and biological research. For example, acoustic tweezers will help guide the drug molecules to the desired area of ​​the patient’s body or do microsurgery.

    Another possible use- the creation of 3D-displays and holograms from voxels , or three-dimensional pixels. The existing solutions for the generation of 3D projections are based on the phenomena of light reflection, and therefore such holograms are visible only at a certain angle. Ultrasound will help to form three-dimensional images of material particles, which will not compromise the viewing angles of the “screens”.

    Also, acoustic tweezers are suggested for use in the production of microelectronics. With the help of ultrasound, you can move small particles and automate the creation of devices that were previously assembled only manually.

    While the technology can work only in the air environment, but in the future, the authors plan to evaluate the possibilities of acoustic tweezers in a liquid.

    Similar developments

    There are several other developments based on the principle of acoustic levitation. The first one is the “liquid seal” that was created at Harvard.

    The invention is a printer with a special nozzle, which is embedded in the generator of standing waves. The sound forms liquid drops of the same given size and applies them to the substrate. The device is proposed to be used in pharmaceuticals, the manufacture of optical materials and other areas where the exact dosage of a substance is important.

    Another project was presented by engineers from the National Autonomous University of Mexico. Their setup uses acoustic levitation in conjunction with laser-spark emission spectrometry to detect heavy metals in water.

    The analyte is irradiated with a laser and transferred to the plasma state . By measuring the spectral radiation of a plasma, it is possible to determine the concentration of individual elements in it. The University of Mexico used acoustic levitation to hold a drop of water in one position. This makes it possible to obtain more accurate and high-quality analysis results.

    Photo by Gaetano Virgallito / CC BY-ND

    Also, the decision of the developers allowed to conduct research outside the equipped laboratory using portable spectrometers. This will help with the study of the composition of water in regions with a poor environmental situation, because it will be possible to carry out analyzes more often.

    The third solution from German scientists usesacoustic levitation to create an ultrasound field of a certain shape. This allows you to build physical particles in the desired order. It is expected that the system will find application in medicine - it will help to improve the treatment with ultrasound, for example, to restore damaged muscles more effectively due to the directional effect of the field.

    In general, the potential of acoustic levitation is extensive. It can be used both in production, for example for moving hot objects, and in medicine for carrying out precise operations. In the near future we can expect that new ways of applying the technology will be proposed.

    Further reading - our world of Hi-Fi and an n-microformat about the sound: the InSight first recorded sounds of the Martian wind Eight audio technologies that fall into TECnology Hall of Fame in 2019 How to turn your computer into a radio, and other ways to extract music from calc. systems

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