Remote control of a liquid metal slug through transient magnetohydrodynamic interactions

We investigate the motion of a liquid metal slug actuated by transient magnetohydrodynamic (MHD) forces generated by a rotating magnetic field. A centimeter-scale Galinstan slug is immersed in an electrolyte solution and subjected to a rotating magnetic field. Driven by localized Lorentz force induced by the MHD interaction, the slug exhibits a stable revolving motion along the container wall. This Lorentz force is induced by the interaction between the rotating magnetic field and the eddy current within the conductive slug. The spatiotemporal distribution of the Lorentz force in the slug is characterized by experiments and multiphysics simulations. We also propose a scaling law that links various parameters, such as magnetic flux density and slug mass, to the velocity of the slug, which is derived based on energy balance. The proposed scaling relation successfully predicts the slug velocity measured from experiments and simulations in various conditions. Our results highlight how transient MHD interaction can be utilized to enable controllable, electrode-free manipulation of conductive liquid bodies, with potential implications in soft robotics, drug delivery and thermal management.