An actuator includes an inner element coupled to an outer element by a linear-motion bearing that provides a single degree of translational movement of the inner element with respect to the outer element along a longitudinal axis. The inner element includes a permanent magnet and the outer element includes a conductive winding with a first coil wound in first direction around a first pole of the permanent magnet and a second coil wound in a second direction around a second pole of the permanent magnet.
