MECH466-Lecture-8 - MECH 466 Microelectromechanical Systems...

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1 MECH 466 Microelectromechanical Systems University of Victoria Dept. of Mechanical Engineering Lecture 8: Electrostatics - Cont. June 4th, 2007 Mech 466, N. Dechev, UVic 2 Electrostatic Interdigitated Finger Capacitors (Comb-Drives) Electrostatics Overview Mech 466, N. Dechev, UVic
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Diagram of Comb-Drive: 3 Interdigitated Finger Capacitors Mech 466, N. Dechev, UVic L o t L c w t x o One Side of Comb Other Side of Comb Modeling of Comb-Drives 4 Interdigitated Finger Capacitors Mech 466, N. Dechev, UVic One Comb is Anchored K m Mechanical Connection Between Combs C Cf Where: C - Normal Capacitance Between Beams C f - Fringe Capacitance (Highly Non-linear) A mechanical spring constant, Km, represents the stiffness of the compliant mechanism between the two combs The two types of capacitance, C, and Cf, both have substantial contributions to the overall capacitance of the device.
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5 The total capacitance of the system is given by: For the previous diagram: There are two main types of Comb-Drives: - Transverse - Longitudinal Mech 466, N. Dechev, UVic Interdigitated Finger Capacitors 6 The design of the flexture mechanism will determine the system stiffness and hence axis of motion Mech 466, N. Dechev, UVic Transverse Comb-Drive High Stiffness K m (y-axis) K m (x-axis) Low Stiffness Anchor Points Flexible Beams (a) Deflected Beams (b) ! x
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7 When the upper comb is deflected to the right, the capacitance will change between the fingers as follows: Mech 466, N. Dechev, UVic Transverse Comb-Drive x y L o
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MECH466-Lecture-8 - MECH 466 Microelectromechanical Systems...

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