Selective Locomotion Control of Magnetic Torque-Driven Magnetic Robots Within Confined Channels

The use of global magnetic fields—typically produced by pairs of Maxwell and Helmholtz coils—offers the advantage of generating uniform magnetic fields and magnitude uniform gradient distributions over extensive volumes, while ensuring easy control. However, achieving selective control of multiple magnetic microrobots under such global fields remains problematic. In this study, we utilize a magnetic focus field generated by a pair of Maxwell coils to impede the magnetic torque-based movement of magnetic robots confined within channels. Although the magnetic field is null at the focus field’s center, it increases linearly in all directions. This exerts magnetic forces that push robots, which are situated away from the center, toward the channel walls. This not only restricts their positioning but also reduces their responsiveness to additional fields. By introducing uniform dc magnetic fields to the focus field, we can change the controlled robot. This mechanism for selective locomotion has been empirically validated with the selective movement of two helical magnetic robots and swarms of magnetic microparticles. Furthermore, leveraging the same focus field, we present a novel separation mechanism for magnetic particle swarms, enhancing the aforementioned selective locomotion mechanism. The practical implications of our proposed locomotion mechanism have been showcased in targeted delivery, drilling, and improved magnetic heating experiments.