Combdrive Configuration for an Electromagnetic Reluctance Actuator

This paper presents a novel combdrive configuration of a linear magnetic microactuator. We discuss in detail the influence of the air-gap geometry on the plunger motion and give design rules to avoid pull-in behavior. This analysis results in a new configuration, which is, so far, only known for electrostatic actuators. The magnetic flux is guided over several interdigitating comb structures with moderate large gap width of 25 mum instead of one single plunger, as reported for earlier designs. This results in larger forces, scaling with the number of comb fingers, until the material reaches saturation. The new configuration linearizes the characteristics and saves driving power without sacrificing fabrication stability, which would arise from small air-gap widths. Several combdrive actuators featuring one, two, and eight comb fingers were fabricated in LIGA technology, simulated, and tested. For a driving current of 40 mA, the achievable stroke is measured to increase by 800% for eight comb fingers in comparison to one finger. Alternatively, for a given stroke, a reduction of the driving current of more than 50% is measured.