Electrostatics overcome acoustic collapse to assemble, adapt, and activate levitated matter

Abstract

Acoustic levitation provides a unique method for manipulating small particles as it completely evades effects from gravity, container walls, or physical handling. These advantages make it a tantalizing platform for studying complex phenomena in many-particle systems. In most standing-wave traps, however, particles interact via acoustic scattering forces that cause them to merge into a single dense object. Here, we introduce a complementary approach that combines acoustic levitation with electrostatic charging to assemble, adapt, and activate complex, separated many-particle systems. The key idea is to superimpose electrostatic repulsion on the intrinsic acoustic attraction, rendering a so-called “mermaid” potential where interactions are attractive at short range and repulsive at long range. By controlling the attraction–repulsion balance, we can levitate expanded structures where all particles are separated, collapsed structures where they are in contact, and hybrid ones consisting of both expanded and collapsed components. We find that collapsed and expanded structures are inherently stable, whereas hybrid ones exhibit transient stability governed by acoustically unstable dimers. Furthermore, we show how electrostatics allow us to adapt between configurations on the fly, either by quasistatic discharge or discrete up/down charge steps. Finally, we demonstrate how large structures experience selective energy pumping from the acoustic field—thrusting some particles into motion while others remain stationary—leading to complex dynamics including coupled rotations and oscillations. Our approach establishes a design space beyond acoustic collapse, offering possibilities to study many-particle systems with complex interactions, while suggesting pathways toward scalable integration into materials processing and other applications.