By Paul Cromwell

Researchers have created a single sided sonic manipulator. Asier Marzo, Sue Ann Seah, Bruce W. Drinkwater, Deepak Ranjan Sahoo, Benjamin Long & Sriram Subramanian used an array of micro-speakers to first build a single sided acoustic levitator. The researchers then developed algorithms to enable them to rotate, push, pull, and squeeze the levitated objects. The manipulator is sufficiently powerful to work while facing any direction.

Traditional acoustic levitators work by trapping objects in the nodes between two sound waves that have combined to create a standing wave. The nodes are pockets of air surrounded by higher pressure air. Traditionally, in previous work, the standing wave is created by two sound waves that are traveling in opposite directions, either from two speakers or other acoustic devices, or by bouncing the wave off of a surface. The surface then becomes the second acoustic device. These levitators can be upscaled to utilize many additional pairs of acoustic devices, including pairs at right angles to the original wave, which would allow them more degrees of freedom to move the object by changing the frequency of the wave.

This new breakthrough sonic manipulator works as a single-sided stand-alone device, it doesn't need to have a paired device facing it. The researchers first created an array by essentially taking the second speaker and placing it next to first speaker, facing the same direction as the first speaker, and then gradually adjusting the timing of the frequency and the angles of the two speakers to recreate a standing wave, this time from the same side. This was then scaled up to include 64 speakers, all creating waves with an intersecting node.

The next step for the researchers was to create algorithms for each speaker to adjust the timing and frequency of their output. This results in the sound waves' nodes being able to move according to the whims of the operator. Using different algorithms alters the size, shape, and characteristics of the nodes. The algorithms can allow the levitated object to be spiraled, spun, and moved in any 3d direction: left, right, up, down, forward, backward, diagonal. When several objects are being levitated at once, it should be possible for the device and the algorithms to be programmed to bring all of the objects together, like a black hole, or spread apart, like an explosion.

Currently the device can manipulate small, light weight, polystyrene balls, but the algorithms and processes allow for the device to be scaled to levitate larger, smaller, or heavier objects by varying the operating frequency and the decibel level of the speakers. Higher frequencies will create smaller nodes and will manipulate smaller objects. Heavier objects can be manipulated by increasing the decibel level.

The researchers' plans and goals for the technology are to miniaturize the device even further and create algorithms with a higher precision of control to allow the device to be able to be used for medical purposes such as non-invasive surgery.

The original work was published under Creative Commons Attribution 4.0 in Nature Communications as Marzo, A. et al. Holographic acoustic elements for manipulation of levitated objects. Nat. Commun. 6:8661 doi: 10.1038/ncomms9661 (2015).

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