Chinese researchers have developed a new way to manipulate objects on solid surfaces using specially structured vibrations, allowing particles and other small objects to be confined, moved in circular paths, or rotated without the complex electronic control systems normally required to generate such motion.
The new approach essentially builds the instructions for creating these specialized vibration patterns directly into the structure of a thin plate. The approach works across multiple size scales, from submillimeter particles to lightweight centimeter-scale structures. The study was published in Advanced Science on September 19.
Structured wave fields offer a promising means of object manipulation on solid surfaces, with potential applications in micromechanics, microrobotics, and intelligent manufacturing. One particularly useful type is a vortex wave, in which the wave forms a swirling pattern around a central point. These waves have helical phase profiles and carry orbital angular momentum (OAM), which can be transferred to objects to induce rotational and orbital motion.
However, conventional vortex-field generation often relies on multichannel phased arrays or dynamically controlled wavefront systems, requiring complex electronics and precise phase synchronization.
To address this challenge, a research team led by Prof. ZHAO Liuxian and Prof. YANG Jun from the Institute of Acoustics (IOA) of the Chinese Academy of Sciences (CAS), in collaboration with Prof. BI Chuanxing from Hefei University of Technology, developed a passive subwavelength-encoded platform for generating flexural-wave vortices and using them to manipulate objects on solid surfaces.
The platform uses labyrinthine subwavelength units as local phase modulators. Instead of electronically controlling the phase of the waves, the researchers encoded the azimuthal phase profile required to produce a target vortex directly into the spatial arrangement of these structures.
As a result, flexural-wave vortices with prescribed topological charges can be generated on a thin plate using only single-channel excitation, without electronic phase modulation.
Experiments revealed clear azimuthal phase winding, a low-amplitude vortex core, and a phase singularity, confirming the formation of the desired vortex field. The field’s nonuniform amplitude distribution creates an effective tendency toward radial confinement, helping keep objects within a particular region. At the same time, the OAM associated with the azimuthal phase gradient provides tangential driving through momentum transfer. Together, these effects allow objects to be confined, transported along orbital paths, or rotated.
The platform also enabled manipulation of objects across multiple scales, from submillimeter and millimeter-scale particles to lightweight centimeter-scale structures. Submillimeter particles could be confined near the vortex core or transported along orbital paths in the surrounding region, while millimeter-scale particles exhibited stable bounded orbital motion. Lightweight centimeter-scale structures could also undergo sustained rotation under the vortex field.
The researchers also found that the direction of motion could be controlled at the design stage. Reversing the sign of the structurally encoded topological charge reverses the azimuthal phase gradient and the OAM direction, switching the particles’ orbital motion from clockwise to counterclockwise or vice versa. The results demonstrate a clear correspondence between structural phase encoding, OAM, and object motion.
According to the researchers, the study demonstrates a passive elastic-wave manipulation scheme based on structural pre-encoding, single-channel excitation, and vortex-field reconstruction, extending structure-encoded flexural-wave vortices from wave-field generation to the manipulation of objects on solid surfaces.
They added that the approach may provide new opportunities for surface particle transport, micromechanical actuation, intelligent structures, and lab-on-a-surface systems.
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