Abstract: With variable airgap reluctance actuators problems arise due to the relationship between actuator mass and displacement range. By providing opposed surfaces in the actuator stator core and armature which have undulations typically in the form of grooves, slots and projections, a greater displacement range can be achieved whilst maintaining performance above a rated displacement force characteristic. In such circumstances by establishing a necessary rated displacement force characteristic, an actuator can be tailored and designed to meet that characteristic over a desired displacement range which has significantly less mass in comparison with a prior actuator arrangement having flat surfaces.