Major limitation in acoustic levitation, the tendency of multiple levitated particles to collapse into a clump in mid-air (acoustic collapse), is solved

https://www.eurekalert.org/news-releases/1108105

"sound scattered off them creates attractive forces, causing them to snap together into single clump...  introducing/ tuning electric charge to particles leverages electrostatic repulsion to keep particles separated, achieving stable configurations ranging from completely separated systems to fully collapsed ones, and hybrids in between, including non-reciprocal: particle arrangements that spontaneously rotate/ pairs of particles that chase each other... stable mid-air manipulation: material science, micro- robotics/ engineering"