Broad tunability of ultrasonic tweezer for multi‑droplet manipulation.

Abstract

Controllable droplet manipulation is essential for applications from biochemical analysis to soft robotics. Despite significant advances, existing methods struggle to achieve broadly tunable, asynchronous control of multiple droplets, limiting their efficiency in three-dimensional and dynamic environments. Here, we introduce a droplet ultrasonic tweezer (DUT), which leverages broadly tunable acoustic control to enable three-dimensional multi-droplet manipulation and enhance condensing surface renewal. The DUT generates a twin-trap acoustic field from a single phased-array focal point, allowing droplet coalescence and confinement at five specific trapping positions. Leveraging this capability, we demonstrate synchronous directional transport of three droplets and asynchronous control of their relative positions. Moreover, the DUT's vertically extensible twin trap enables synchronous manipulation of droplets across double-layer surfaces. Beyond transport, programmable spatial modulation of the acoustic field enhances microdroplet coalescence and suppresses merged-droplet detachment, increasing the droplet detachment size and expanding the swept area for more effective surface renewal. Our results establish a robust paradigm for applications in optical surface self-cleaning, condensation heat transfer, and atmospheric water harvesting, offering a scalable solution for precise droplet control.