The new concept of wave-based liquid-interface metamaterials opened new ways of engineering to surface flows with tunable properties at macroscopic scale. The liquid-interface metamaterials is generated by the superposition of two orthogonal standing surface waves. Such surface waves possess a polarisation: fluid particles exhibit different types of trajectories depending on the phase shift between the two orthogonal waves. Circular orbits can be created when the two orthogonal waves are phase shifted by 90 degrees.

The liquid-interface metamaterials are periodic arrays of unit cells, analogues to optical lattices. The analogy with optics, triggered recent investigation into the trapping of active particles within the surface metamaterials, namely magnetic spinning particles (spinners). A floating spinner can be guided by changing the spinning frequency and the spin direction. A single spinner exhibits stable orbits in a unit cell. The orbital motion arises from the coupling between the spinner angular momentum and the wave angular momentum. Furthermore, multiple spinners tend to self-organize into stable configurations around the centre of the unit cells. The results offer novel methods of manipulation and confinement of actively moving particles at the fluid interfaces using waves and suggest new analogies between surface wave physics and confinement of nano- and micro-particles and atoms by optical fields.

Jean-Baptiste Gorce is a PhD student in the CPF department at the ANU. He obtained a Bachelor degree in physics from the French ENS and a Master’s degree in Microfluidics from UP6 in Paris. His research interest lie in the capillary interaction between 2 fluids at microscopic scales.