Scientistsat the Public University of Navarra and the University ofBristol have developed an intriguing "sound tweezer" device thatcoordinates the tiny mechanical forces exerted by five hundredminiature speakers to levitate and manipulate dozens of small objectsat the same time through nothing but thin air.

Justtwo months ago, 96-year-old Arthur Ashkin was awarded a Nobel Prizein Physics for his work on optical tweezers, which can harness the radiation pressure of light tomanipulate microscopic objects. Since that initial discovery in 1970,scientists have managed to transfer the same principles to the realmof sound.

Sofar, we've seen sound tweezers used for an array of nifty but hardlypractical applications, from home gadgets that levitate small water droplets to sonic tractor beams and even rudimentary levitating displays. The technology, however, could really come into its ownwhen applied to surgical applications. In this area, it holds manycrucial advantages over its optical counterpart: most importantly, itcan easily operate through opaque materials (such as human organs)and it runs on much lower power, meaning there is little risk ofdamaging delicate living tissue.

ResearcherAsierMarzo Pérez and professor Bruce Drinkwater have now taken animportant step in this direction by developing a way to finelymanipulate dozens of small, levitating particles independently usingsound waves alone.

Two arrays of speakers (top and bottom) can generate the acoustic fields needed to manipulate multiple objects suspended in a 3D space Iñaki Zaldúa, Asier Marzo, and Bruce Drinkwater (UPNA)

Theydid so by creating two arrays of 16 by 16 sound transducers (inessence, small speakers) that generate sound waves at a frequency of40 kHz, outside the human hearing spectrum,and an algorithm that adjusts the output of each speaker 90 times asecond to make the object move as needed. The result is a device thatcan simultaneously and independently control the movement of up to 25smallobjects up to 2.5 cm (1 in) in diameter in a three-dimensional space.

Todemonstrate theperformance of their system, the scientists attached two smallspheres to the ends of a thread and used their acoustic tweezers to"sew" the thread onto a piece of cloth. The team is confidentthat the technique could soon adapt to the handling of such taskswhile submerged in water and, shortly after that, to use onbiological tissue with the goal of allowing new means to perform noninvasive surgery.

The sound tweezer could have important applications for noninvasive surgery Iñaki Zaldúa, Asier Marzo, and Bruce Drinkwater (UPNA)

Asidefrom medical applications, this advance could also be used to createa new form of highly interactive 3D displays where physical "pixels"move about to form evolving shapes and could be seen from any angle.

"Weare accustomed to the two-dimensional pixels in our monitors, but wewould like to see a technology where the objects are formed bytangible pixels that float in the middle of the air," saidMarzo.

The advance is described in an open-access paper for the scientificjournal Proceedings of the National Academy of Science.Youcan get a better feel for the degree of precision achieved (includinga levitating "sewing" demonstration) by taking a look at thevideo below.

Source: Universidad Pública de Navarra