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In this article, an electromagnetic actuator with a movable non-magnetic disc immersed in a ferrofluid that is exposed to a non-uniform magnetic field generated by permanent magnets is presented. The position of the levitated disc is stably controlled by the current in a command coil. Numerical simulations and experimental tests show that the actuator has linear transfer characteristics force versus current and displacement versus current. The device can ensure the highest ratio of force/size and the best energy efficiency for the actuators using a non-magnetic body immersed in a ferrofluid. Examples of possible applications are precision positioning systems and semi-active vibration dampers.

The paper studies an actuator based on magnetofluidic forces acting on a non-magnetic disc plunged into a ferrofluid that is exposed to a non-uniform magnetic field generated by magnetic inductor(s). The input output equations (force -current and displacement -current) that describe the behaviour of two types of actuators are established. The expression of the force generated on the nonmagnetic disc is determined analytically for the particular conditions imposed by the two actuator configurations: a) simple, with one magnetic inductor; b) differential, with two inductors. The derived relations enable a comparative study of the two types of actuators. The results show the superior performance of the differential actuator. The latter was tested as a current to displacement transducer in an electropneumatic converter.