Acoustic levitation: Bayreuth researchers make luminous shapes float in the air

For several years, research on acoustic levitation has been able to trap solid particles with a size of about two millimeters in so-called "acoustic traps" and influence their movements in the air. However, before the particles actually move along the desired paths at high speeds and produce colored, seemingly floating forms in space, numerous experiments based on "trial and error" were required for each individual shape. The phase and spatial orientation of the sound waves used to control the particles had to be adjusted again and again.

The "OptiTrap" system developed by researchers at the University of Bayreuth now marks a fundamental advance: for the first time, it is possible to calculate the positioning of the acoustic traps in advance with high precision so that the trapped particles actually "behave" and reliably move along the respective predetermined paths. In addition, the new algorithm allows for a wide variety of trajectories, that could not be demonstrated before. Complex objects with sharp edges, and/or significant changes in curvature are now part of the repertoire of elements that can make up the paths. Thus, the particles illuminated by colored LEDs that travel along these paths create the outlines of animals, plants, or everyday objects. Their speed is so high in all cases that the human eye does not notice the single particle moving, but only perceives the full luminous shape floating in mid-air. "OptiTrap" is therefore perfect for exciting visual effects in films and theater performances.

In August 2022, the first author of the new study from Bayreuth, Viktorija Paneva M.Sc., presented the "OptiTrap" levitation system at the SIGGRAPH international conference in Vancouver, Canada. "Our numerical approach, which is the basis of "OptiTrap", has aroused strong interest among experts. In addition to the aesthetics of the luminous effects we can achieve with it, from a mathematical and physical point of view, our system has been taken up as a significant innovation on the way to a deeper understanding of acoustic levitation. We will continue to refine it and make it even more powerful in the coming years," says Paneva.

Research funding:
The study, which has now been published, emerged from the EU project "Levitate," in which the University of Bayreuth collaborated with three other universities: the University of Glasgow, University College London and Chalmers University of Technology in Gothenburg. The Ultraleap company was also involved in the research.

Video:
Part of the presentation of "OptiTrap" in Vancouver was this video made by Viktorija Paneva M.Sc.: https://www.youtube.com/watch?v=RM4V2GV8Yls

Publication:
Viktorija Paneva, Arthur Fleig, Diego Martínez Plasencia, Timm Faulwasser, Jörg Müller: OptiTrap: Optimal Trap Trajectories for Acoustic Levitation Displays. ACM Transactions on Graphics (2022), DOI: https://doi.org/10.1145/3517746