Abstract
The equation that describes the relationship between the applied voltage and the resulting electrostatic force within comb drives is often used to assist in choosing the dimensions for their design. This paper re-examines how some of these dimensions—particularly the cross-sectional dimensions of the comb teeth—affect this relationship in vertical comb drives. The electrostatic forces in several vertical comb drives fabricated for this study were measured and compared to predictions made with four different mathematical models in order to explore the amount of complexity required within a model to accurately predict the electrostatic forces in the comb drives.
Highlights
If connected to a circuit that can measure the change in capacitance produced by the variance in overlapping area between their fixed and Sensors 2014, 14 movable comb teeth as an external force is applied to the movable combs, comb drives can be used as sensors—such as accelerometers [1,2,3]
Besides allowing an estimate to be made of the complexity of the mathematical model required to accurately predict the electrostatic forces within vertical comb drives, the collection of measured electrostatic forces was valuable in another way: it indicated that the first comb drive fabricated for this study will only generate about half the electrostatic force for any given voltage than that predicted by Equation (4)—the equation traditionally used to determine the dimensions of the comb teeth required for a particular force-voltage relationship
The equation that describes the relationship between the applied voltage and the resulting electrostatic force within comb drives is often used to assist in choosing the dimensions for their design
Summary
Comb drives are often used as switches and micropositioners, controlling the position of MEMS components such as mirrors and microlenses [4,5,6] They can be used as force-compensation mechanisms, in, for instance, interfacial force microscopes. With a probe attached to their movable combs, a feedback circuit can apply a voltage difference between their fixed and movable combs so that the electrostatic force generated between them balances the interfacial forces felt by the movable combs as the probe interacts with a sample surface. The vertically-offset combs of vertical comb drives have the potential to apply electrostatic forces on the movable combs in both the upwards and downwards directions, allowing them to compensate for both attractive and repulsive interfacial forces acting on the attached probe. The result is compared to electrostatic forces measured in several vertical comb drive prototypes
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