Dynamic Water-Wave Tweezers

Abstract

Following a recent demonstration of stable trapping of floating particles by stationary (monochromatic) structured water waves [Nature 638, 394 (2025)], we report dynamic water-wave tweezers that enable controllable transport of trapped particles along arbitrary trajectories on the water surface. We employ a triangular lattice formed by the interference of three plane waves, which can trap particles, depending on parameters, either at intensity maxima or at intensity zeros (vortices). By introducing small frequency detunings between the interfering waves, we control 2D motion of the lattice and trapped particles. This approach is robust and effective over a relatively broad range of particle sizes and wave frequencies, offering remarkable new possibilities for noncontact manipulation of floating (e.g., biological and soft-matter) objects in fluidic environments.

Figures (5)

• Figure 1: Schematics of the interference of three plane waves with time-varying frequencies $\omega+\delta\omega_i(t)$, $|\delta\omega_i| \ll \omega$. This produces a near-triangular lattice in the elevation wavefield $Z(x,y)$ (its intensity is shown by the gray surface), which traps and transports a floating particle with a local velocity ${\bf u}(t)$.
• Figure 2: (a) Top view of the experimental setup. (b) Measured complex field $Z({\bf r})$ within the dashed yellow square in (a) for stationary three-wave interference with central frequency $f = 6\;$Hz. Brightness and hue colors represent the field amplitude and phase, respectively. A particle of diameter $d=9.5\;$mm, trapped at a field zero (vortex), is shown schematically. (c--f) Transport of trapped particles achieved by modulating the frequencies of the interfering waves; see also Supplemental Movies 1--4, Fig. \ref{['Fig_freq']}, and Supplemental Fig. S1 SM1. All scalebars throughout the paper correspond to 2 cm.
• Figure 3: Temporal dependencies of the frequencies $f_i(t) = \omega_i(t)/2\pi$ corresponding to particle transport along the letter-"H" trajectory shown in Fig. \ref{['Fig_exp']}(c) and Supplemental Movie 1 (see also Supplemental Fig. S1 SM1).
• Figure 4: Trapping of a particle with diameter $d=9.5\;$mm in monochromatic three-wave interference fields at different frequencies $f=4\!-\!7\;$Hz [the case of $f=6\;$Hz is shown in Fig. \ref{['Fig_exp']}(b)]. (a--c) Stable trapping at a wave-intensity maximum. (d) Transition regime with orbital motion around a vortex (field zero). (e,f) Stable trapping at a vortex.
• Figure 5: Stability of particle transport at different parameter values. (a--d) Particle of diameter $d=9.5\;$mm in frequency-modulated fields at different central frequencies $f=3.5\!-\!7\;$Hz (see also Supplemental Movies 12--19 and Supplemental Fig. S3 SM1). (a,d) Unstable regimes. (b,c) Stable trapping at an intensity maximum and transport along an L-shaped path. (e,f) Controllable transport in a field with $f=6\;$Hz, similar to Fig. \ref{['Fig_exp']}(c), but for particles with diameters $d=8.0$ and 6.2 mm (see also Supplemental Movies 20 and 21).