Acuators in MEMS

1. Amjad Althabit
210101422
Prof. Fathi O. Hareb

2.  It statnds for micro electro mechanical
systems.
 It is the integration of elements sensors
actuators and electronics on a common
silicon substrate.
 Micro fabrication technology for making
microscopic devices.

3.  The actuator is an element which
applies a force to some object
through a distance
 Various actuation mechanisms :
1. Electrostatic actuation.
2. Thermal actuation.
3. Piezoelectric actuation.
4. Magnetic actuation.

5.  A voltage is applied between metal plates to
induce opposite charges and coulomb
attraction.

6.  Electrostatic micro-actuator consist of many
fingers that ate actuated by applying a
voltage.
 The thickness of the fingers is small in
comparison to their length and width.
 The attractive forces are mainly due to the
fringing fields rather than the parallel plate
fields.
Firing Curves

7.  Electrostatic energy :
 Electrostatic Force :
◦ Coulomb’s Law: Force between two point charges

8.  Low power dissipation.
 Can be designed to dissipate no power while
exerting a force.
 High power density at micro scale.
 Easy to fabricated

9.  Scaling
 Noise & efficiency
 Range of force, motion and frequency
 Repeatability
 Nonlinearity

11.  Assume that the electrical field is uniform
between the plates of the capacitor and zero
outside.
 Uniform electric field between the plates has
the magnitude.
 Voltage across the capacitor is the product of
E-field and the gap.
 The capacitance is the ratio of the charge and
the voltage

12.  When the capacitor plates are fixed the stored
energy is given by :
 Fixed gap – increasing charge

13.  At zero gap, the electrical energy is zero.
 The force between two plates with opposite charges
+Q and –Q depends on electric fields setup by
charges
 The field is : ɛ=Q/ɛA
 The corresponding force is :
 F=(Q/2) ɛ=Q²/2ɛA
 Now we pull upper plate by distance g
 W(g)=F*g=Q²g/2ɛA
 Charge fixed – increasing gap

14.  Micromotor, Microshutter, Micromirror,
Microrelay, Micropump

15.  Micro pumps play a significant role in micro
fluid systems of MEMS.
 Micro pumps were started in middle 1980s.
 Before 1990s, mechanical pumps were mainly
studied. After 1990s, non-mechanical pumps
were introduced.
 Presently most micro pumps aim to fluid
pumping.

16. Goodness:
Low power, good control of
actuation and short response time.
Weakness:
High actuation voltage, small stroke.