Fast, repeatable and precise magnetic actuation in ambient environments at the micrometer scale

This work aims at increasing the velocity of micrometer scale particles controlled by non contact magnetic actuation systems. The particles are placed in an ambient environment (i.e. in air) to minimize the drag forces. However this approach raises two major issues: the repeatability and the precision of position are difficult to obtain in ambient environments due to the adhesion force between the substrate and the particle. This work proposes to use first a magnetic torque to provoke in-plane rotation of the particle to overcome adhesion between the particle and the substrate. Then a magnetic force is applied to induce the movement of the particle. To ensure that the static friction is broken and that the position of the particle can be controlled precisely a current pulse actuation mode is used. A dedicated closed loop control law which controls both the amplitude and the duration of the current simultaneously is proposed to ensure accurate positioning of the particle. Speed during pulse can reach 176 mm/s (more than 350 body lengths per second) in open loop on silicon substrates. Adhesion is overcome in 95% of the tests using the magnetic torque, compared to 66% using classical approaches. Precision of positioning of less than 20% of the size of the particle can be reached. The approach proposed in this paper is generic so that it can be easily transposed to other systems in the literature. The large number of experimental tests provides a deep understanding of the possibilities and challenges of magnetic actuation in ambient environments.