Electromagnetic Field Induced Transformation of Liquid Metal

Abstract

Unlike using a single external electric field, simultaneous administration of both electrical and magnetic fields would induce rather complex transformation behaviors of liquid metal. Along this direction, the present lab (Wang and Liu in Electromagnetic rotation of a liquid metal sphere or pool within a solution, 471:20150177, 2015, [1]) demonstrated a group of transformational behaviors of liquid metal electric motors. The machine system is composed of a pair of concentric ring electrodes, permanent magnet, and electrolyte solution. A liquid metal galinstan sphere, along with NaOH solution, is stimulated to rotate centrifugally around the central electrode and the rotating speed increases with the voltage. The NaOH solution serves to remove the oxide on the liquid metal surface in time, reduce the motion friction, and provide impetus to the liquid metal. As the liquid metal is added to 12.16 g to form a kidney like body, its rotating speed appears more controllable and the effect of the electrolytic action in the NaOH solution becomes weak in the range of 0–1.82 V. As the liquid metal is increased to 18.20 g to form a circular ring-shaped body, the ideal voltage range for controlling the rotating motion of the liquid metal is 0–0.81 V. The metal fluid rotates at a speed of 1.9 rpm even at an extremely low voltage of 0.03 V. Further, with the administrated increased electrical field, a variety of surface folding patterns of rotational liquid metal like wheel shape, dual concentric ring shape, and so on were found to occur (Wang and Liu in Liquid metal patterns induced by electric capillary force, 108:161602–161605, 2016, [2]), which refreshes the basic understanding of classical fluid kinematics. The knowledge obtained and the liquid metal electric motor, thus, established can find important applications in realizing certain future rotating soft machine. This chapter presents the typical phenomena of the electromagnetic field induced transformation of liquid metal.