ESPCI web site
The physics of force-based microswimmers
As paradigmatic systems of active matter, self-propelled microswimmers came recently in focus of numerous theoretical and experimental studies in the field of fluid dynamics at low Reynolds numbers. Most models are based on the pre-defined stroke exhibited by device. However, such approaches underestimate the role of the hydrodynamic interactions, which can be rectified by employing a propulsion mechanism based on applied external or internal forces. Naturally, these forces acting on the swimmer, need to sum to zero at each instance of time or within a cycle. Such swimmers where realized experimentally in a number of occasions. We are particularly motivated by devices consisting of paramagnetic beads on the water-air interface that are actuated by a magnetic field. Using this as a motivation, we construct a family of bead-spring devices, which we model using a perturbative approach. This allows us to study the the physics underyling this type of propulsion and discuss the implication on the interactions of the swimmer with its viscous environment, and between swimmers.