Three-sphere magnetic swimmer in a shear flow.

We consider a low-Reynolds-number swimmer made from three spheres linked by two slender arms, and explore its motion in a shear flow. This rodlike three-sphere swimmer finally follows the direction dictated by the shear flow. To overcome this shortcoming, we propose a model in which the two outer spheres have permanent magnetic moments along the arms. This magnetic swimmer can be navigated to a desired direction by applying an external static and uniform magnetic field.