2. It stands for micro electro mechanical
It is the integration of elements sensors
actuators and electronics on a common
Micro fabrication technology, for making
3. The actuator is an element which applies a
force to some object through a distance
Various actuation mechanisms:
- Electrostatic actuation
5. A voltage is applied between metal plates to
induce opposite charges and Coulomb
α fringing field factor Normally the flux lines inside
the capacitor are uniform and
parallel. But at the edges, the
flux lines are not straight and
bend slightly upward due to
the geometry. This is known as
6. Electrostatic Micro-actuator consists of many
fingers that are actuated by applying a voltage.
The thickness of the fingers is small in
comparison to their lengths and widths.
The attractive forces are mainly due to the
fringing fields rather than the parallel plate
7. Electrostatic energy :
W= ½ CV2 = αƐ0ƐrWL V2/2d
Electrostatic Force :
Coulomb’s Law: Force between two point
8. Low power dissipation.
Can be designed to dissipate no power while
exerting a force.
High power density at micro scale.
Easy to fabricate.
Noise & Efficiency
Range of force, motion and frequency
11. assume that the electrical field is uniform
between the plates of the capacitor, and
uniform electric field between the plates has
where A is the area of one capacitor plate, and Q is the
magnitude of the charge on each plate
voltage across the capacitor is the product of
the E-field and the gap
V = gE = gQ /ƐA
the capacitance is the ratio of the charge
C=Q/V = ƐA/ g
12. When the capacitor plates are fixed
The stored energy in the capacitor is given by
13. Charging the capacitor at zero gap and
At zero gap, the electrical stored energy is zero
The force between two plates with opposite charges +Q
and –Q depends on electric field setup by charges
This field is
The corresponding force is
F= (Q/2)Ɛ =Q2/2ƐA This force is independent of g
Now we pull upper plate by distance g
W(g) = F*g
14. • Stored energy
• Force is derivative of energy with
respect to pertinent dimensional
• Plug in the expression for capacitor
• We arrive at the expression for
15. As the voltage bias increases from zero
across a pair of parallel plates, the distance
between such plates would decrease until
they reach 2/3 of the original spacing, at
which point the two plates would be
suddenly snapped into contact.
This behavior is called the pull-in effect.