Electromagnetic Microactuator Realized by Ferrofluid-Assisted Levitation Mechanism

This paper reports a highly simple and robust levitation method realized by ferrofluid for micromotor applications. A layer of ferrofluid is self-sustained on a permanent magnet to serve as liquid bearing that lifts the magnet up on the substrate, enabling low-friction movements of the magnet. A levitation height of ~500 μm is observed with a 1.6-mm-sized NdFeB magnet. The load carrying capacity and friction force of the ferrofluid-levitated magnet are measured to be ~2.9 g and 14 μN, respectively. The levitated magnet is electromagnetically driven by microfabricated planar coils to demonstrate a linear micromotor. The dynamic responses of the magnet slider are characterized in detail and shown to match well with the results from electromagnetic simulations of the driving coil. The actuation force of 386 μN or greater is obtained. Using the electromagnetic rail track that contains a micropatterned array of planar coils, continuous actuation of the slider along the array is achieved with the average velocity of 19 mm/s. The feasibility of stepping displacements between two adjacent coils is demonstrated by controlling power distribution to the two coils.