Liquid metal slug actuated by an unsteady magnetic field

The dynamics of a liquid metal slug driven by electromagnetic induction under an unsteady magnetic field are investigated through experiments and numerical simulations. When a Galinstan slug is subjected to a rotating magnetic field in a circular container filled with an electrolyte solution, it exhibits regular circular revolutions along the circumferential edge of the container. To reveal the spatiotemporal distribution of the electromagnetic field within the slug and the temporal profile of the Lorentz force acting on the slug, we develop a numerical framework that fully resolves the coupled transient phenomena in the multi-physics and multi-phase system. The periodic magnetic field induces locally intensified eddy currents within the slug, which interact with the magnetic field to generate a pulse-like Lorentz force per magnet rotation cycle, eventually promoting the revolving motion of the slug. The maximum magnitude of the Lorentz force acting on the slug increases with the rotational speed of the permanent magnet, and the duration of the strong Lorentz force within the magnet rotation cycle increases with the mass of the slug. Based on the energy balance, a scaling relation that characterises the motion of the slug is developed. Experimental and numerical comparisons demonstrate that the proposed scaling relation predicts the angular velocity of the slug with reasonable accuracy. Our findings highlight a strategy for the remote manipulation of liquid metals, offering insights into soft actuation.