Engineers Use the Power of Acoustics to Move Multiple Objects Simultaneously

Artificial omni-directional sound source in an anechoic chamber.

Listen up!

Researchers of Aalto University have made a breakthrough in controlling the motion of multiple objects on a vibrating plate with a single acoustic source. By playing carefully constructed melodies, the researchers can simultaneously and independently move multiple objects on the plate towards desired targets.

This has enabled them to write words consisting of separate letters with loose metal pieces on the plate by playing a melody.

In 1878, the first studies of sand moving on a vibrating plate were done by Ernst Chladni, known as the father of acoustics. Chladni discovered that when a plate is vibrating at a frequency, objects move towards a few positions, called the nodal lines, specific to that frequency. Since then, the prevailing view has been that the particle motion is random on the plate before they reached the nodal line.

Computer-controlled melodies enabled the researchers to control the movement of objects on a vibrating plate. (Image courtesy of Quan Zhou/Aalto University.)

"We have shown that the motion is also predictable away from the nodal lines, said professor of electrical engineering and automation, Quan Zhou, who led the research. “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. 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."

The objects to be controlled were placed on top of a manipulation plate and imaged by a tracking camera. Based on their detected positions, an algorithm goes through a list of music notes to find the note that is most likely to move the objects towards the desired directions.

After playing the note, the new positions of the objects are detected and the control cycle is restarted. This cycle is repeated until the objects have reached their desired target locations. The notes played during the control cycles form a sequence, a bit like music, though not nearly as pleasant.

The research has been published in the journal Nature Communications.

The new method has been applied to manipulate a wide range of miniature objects, including electronic components, water droplets, plant seeds, candy balls and metal parts.

Engineers were able to move multiple objects simultaneously on a metal plate by playing a carefully chosen melody. (Image courtesy of Quan Zhou/Aalto University.)

"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," said Zhou. "Also, the basic idea should be transferrable to other kinds of systems with vibration phenomena. For example, it should be possible to use waves and ripples to control floating objects in a pond using our technique."

For more news from the world of acoustics research, read about detangling the complexity of waves with acoustic voxels.