Electrostatic Actuators and Sensors Flashcards
Why do electrostatics work well for MEMs devices
SA/Vol ration is higher for micro devices and the electrostatic effect is based on SA, while mass is based on volume
Capacitance is governed by ___
- Distance between plates
- overlapping area between plates
- permittivity of the material between the plates
Two cases for using electric charge to generate force
Attractive force
Repulsive force
Principles of an electrostatic micromotor
- central rotor with one charge
- radial stator poles with opposite charge
- The stator phases are turned off / on in sequence to rotate the rotor
Electrostatic comb-drive
- creates a linear motion
- combs are charged push / pulling one another
Benefits of Electrostatic devices
- simplicity
- very low power use
- fast response
- deflection can be accurately controlled
Disadvantages of electrostatic transducer
- require drive voltages in the 100-150V range
- sensors require carefully designed circuits to measure capacitance change in the presence of noise and interference
- large SA required for comb drive to generate forces equivalent to other microactuators
Capacitance is defined as
electric energy stored per volt
permittivity of a material can be influenced by
- humidity
- chemical reactions
- temp
orientation, overlap or distance between plates can be changed by
- static pressure
- acceleration
- other physical phenomenon
Equilibrium of electrostatic devices has two points
1) stable point:
2) meta stable point:
Pull in voltage
A critical point of equilibrium at which the mechanical force is equal to the electrical force. This is the last voltage where the actuator can be controlled
What happens if V pull in is exceeded?
The device will snap-in and may be damaged, or burnt out
When V = Vpull how much displacement is seen?
The plate can be displaced up to 1/3 of the separation distance between the plates
Beam stiffness can be added in__
series
