A Stepwise Control of Multiple Magnetic Millirobots for Flow Manipulation Applications

Small-scale magnetic robots are extensively recognized as promising untethered devices that can be controlled externally for numerous microscale applications. This study is proposed to address the independent control of multiple magnetic millirobots using an array of electromagnetic coils. Herein, each of the fabricated magnetic millirobots is magnetized with a dissimilar magnetization profile. Further, these millirobots are independently controlled using the mentioned magnetization strategy in addition to the supply of controlled current to each electromagnetic coil. To explore the physics of this combined stepwise approach in controlling the millirobots, theoretical and numerical investigations are carried out that further ensure the practical significance for broad applications. For demonstration purposes, three different shear-induced flow manipulation experiments, including the particle manipulation task, fluid color transition task, and micromixing task, are conducted using more than one millirobot with distinct motions. A maximum of three millirobots controlled with different motions are employed in the micromixing task, and further, it is observed to achieve nearly 80% mixing efficiency within 45 s. The presented work with the introduced actuation system and motion control strategies can strengthen the existing methods of small-scale robots for various applications, particularly for tasks that demand multiple millirobots.