Demonstration of topological acoustic tweezing for robust mass transport.

Acoustic tweezers harness the mechanical effects of ultrasound to achieve contact-free manipulation of micro/nanoparticles. In acoustofluidics, standing-wave tweezers were widely adopted for particle trapping and translation due to their facile implementation and on-chip integrability. However, those conventional standing-wave fields, typically generated by transducer pairs, exhibit limited manipulation flexibility owing to their simplistic field configurations. Here, we demonstrate topological mass transport along arbitrarily designed trajectories by constructing localized and tunable standing-wave fields based on valley interface states. Precise phase modulation of incident waves enables efficient particle conveyance through continuous displacement of standing-wave pressure nodes or antinodes, leveraging the radiation forces from topologically protected standing waves in scattering systems. Experimental results confirm that such topological tweezing and circulating effect enables robust mass transport, showing antibackscattering characteristics and immunity against various structural defects such as sharp corners or cavities. Our work establishes a foundational paradigm for investigating the radiation forces in topological acoustic fields and advances the development of acoustofluidics technologies.