TABLE OF CONTENTS An important aspect of MEMS devices is the ability to generate mechanical motion the application of a force over a distance. There are several classes of actuators, which are grouped according to the means by which motion is generated, amongst which the following are the most common:
Electrostatic actuators:
The attraction or repulsion between charges generates a force;
Shape memory alloy actuators:
A phase change of a material produces a physical change in local atomic bonding that produces a change in volume of the material and hence a force;
Thermal actuators:
The expansion of a material when heated produces a force;
Piezoelectrics:
The application of an electric field to a piezoelectric material causes a deformation of the crystal lattice and hence a change in dimension which generates a force;
Magnetic actuators:
The application of a magnetic field produces a force on a magnetic material or moving charge.
The critical parameters to consider in choosing a method of actuation for a particular system are:
the magnitude of the force that can be produced compared with the distance over which it can be applied or more fundamentally, the maximum stress and strain;
the minimum step change in displacement that can be produced, known as the strain resolution;
the maximum frequency of operation;
the temperature of operation;
the volume and density of the actuator relative to the power that can be produced and
the efficiency of the device (power out relative to power...
