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Unformatted text preview: Actuators – 1 An actuator, like a sensor, is a device that converts energy from one form to another. In the case of an actuator, we are interested in inducing action. Actuating mechanisms include the following: electrostatic, electromagnetic, piezoelectric, thermal, memory alloy, etc. The first three methods are the most common ones and we are going to discuss them in more details here. 1. Electrostatic Actuators One of the advantages that a MEMS device has is the easy integration of electronic and mechanical devices. Using electrostatic energy to actuate a MEMS mechanical device is the most common approach. 1.1 Continuum Theory Electrostatic charges arise from buildup or deficit of free electrons in a material. An electrically charged material can exert an attractive force on oppositely charged objects or a repulsive force on similarly charged ones. Applying a voltage, V, across the two electrodes shown in Figure 1, the electrostatic potential energy stored between them is E e = - 1 2 CV 2 = - e r e o xyV 2 2 z i ^ j ^ k ^ (1) ^ ^ ^ k j i z xy C o r ε ε = (2) Here ε r is the relative permittivity and ε o is the permittivity in vacuum. x and y represent the real dimensions in the X and Y directions respectively. z represents the real dimension of the separation between the electrodes, which is along the Z direction. + + + + + + + + + E- - - - - - - - - - - - Figure 1 Illustration of the Electrostatic Field Therefore, the electrostatic force introduced by the electrodes is insulator Z X Y V E F e = - E e = - ( x E e i ^ + y E e j ^ + z E e k ^ ) = - x (- e r e o xyV 2 2 z ) i ^ + y (- e r e o xyV 2 2 z ) j ^ + z (- e r e o xyV 2 2 z ) k ^ = e r e o yV 2 2 z i ^ + e r e o xV 2 2 z j ^- e r e o xyV 2 2 z 2 k ^ (3) For a pair of electrodes with width = w in the X direction and length = l in the Y direction, and the separation =...
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This note was uploaded on 02/02/2008 for the course AME 455 taught by Professor Han during the Spring '08 term at USC.
- Spring '08