Watch Researchers Use Sound to Move Multiple Objects With Precision

A team of researchers at Aalto University in Finland has devised a method for the controlled movement of multiple objects using a single sound source, a development which may find use in manufacturing everything from pharmaceuticals to computer chips.

As detailed in the above video and a paper published Friday in Nature Communications, the researchers were able to manipulate objects with such precision that they could spell out words on the surface. To make this happen, they carefully constructed melodies where the frequency of the notes would cause the objects to move in a predictable manner along nodal lines specific to that frequency.

"We are very excited about the results because this probably is a new world record of how many independent motions can be controlled by a single acoustic actuator," said Quan Zhou, a professor of nanorobotics at Aalto and lead author of the paper.

The work of Zhou and his colleagues makes use of a curious property discovered by Ernst Chladni, the father of acoustics, back in 1787. While observing the movement of sand on a vibrating plate, Chladni noticed that the sand tended to move toward a predictable handful of points depending on the frequency the plate was vibrating at.

These spots, called nodal lines, are the areas of the vibrating plate which are not experiencing vibration because they exist at the boundary of two regions of the plate that are vibrating in opposite directions, canceling one another out. Since Chladni published his observations in Discoveries in the Theory of Sound in 1787, the prevailing view has been that while the movement of particles on a vibrating plate toward nodal lines can be predicted based on the frequency of the plate's vibration, the movement of particles outside these nodal lines is essentially random.

The randomness of particles outside of nodal lines meant that the movement of these particles could not be controlled. This is what make Zhou and his colleagues' work such a big deal: they've demonstrated that object movement outside of nodal lines can be predicted and multiple objects can be manipulated with a high degree of precision.

"We have shown that the [object's] motion is also predictable away from the nodal lines," said Zhou. "Now that the object does not have to be at a nodal line, we have much more freedom in controlling its motion and have achieved independent control of up to six objects simultaneously using just one single actuator."

Zhou and his team placed a motion-tracking camera above the vibrating plate, which would feed the movement of the object on the plate to a computer. This computer would then query a database of music notes to determine which note is most likely to move the objects in a given direction.

Once this note is played and the object moves in the direction determined by the note's frequency, the computer recalibrates and picks another note that will continue to move the object along the desired path. By the time the objects, which included everything from water droplets to pieces of candy, have made it to their destination, the string of notes used to move the object creates something that kind of sounds like music.

"The basic idea should be transferrable to other kinds of systems with vibration phenomena," said Zhou. "For example, it should be possible to use waves and ripples to control floating objects in a pond using our technique. Some of the practical applications we foresee include conveying and sorting microelectronic chips, delivering drug-loaded particles for pharmaceutical applications or handling small liquid volumes for lab on chips,"