Manufacturing and near wall swimming of helical thin magnetic ribbons

In this study, we employed micro manufacturing techniques to fabricate magnetic helical micro ribbons, which consist of a nickel layer sandwiched between two SiN layers. Then the ribbons are placed inside a chamber filled with isopropyl alcohol on top of a microscope glass. Three pairs of Helmholtz coils generated a rotating magnetic field around the chamber, exerting a magnetic torque on the ribbon, causing it to rotate synchronously with the field. Additionally, a piezo actuator was attached to the microscope glass and driven at frequencies of 1 and 10 kHz during the experiments. Forward and lateral velocities of the ribbons are obtained from recorded images. According to experimental results, lateral velocities of the ribbons decreased, and forward velocities improved when the vibration is induced by the piezo actuator. To analyze the swimming behavior, we also developed a three-dimensional CFD model, assuming steady Stokes flow around the swimmer due to both its rotation and translation. In the simulations, we varied the distance between the swimmer and the bottom wall. The CFD model provided valuable insights to understand the effect of vibration on the swimming behavior of the helical ribbons which exhibit sliding behavior near the wall when the gap between the swimmer and the wall is minimal. This sliding behavior is due to a large pressure gradient around the nip region when the swimmer almost touches the wall.