Working principles of MEMS sensors and actuators

Sensors (physical quantity to electrical signal)

Principle	How it works	Example
Piezoresistive	Strain changes the resistance of a diffused resistor in a bridge	Pressure sensor with a silicon diaphragm
Capacitive	Motion changes the gap or overlap, so capacitance changes	Accelerometer, microphone
Piezoelectric	Stress generates charge	Ultrasound transducer, vibration sensor
Thermal	Temperature changes resistance or voltage	Flow sensor, thermopile

Actuators (electrical signal to motion or force)

Principle	How it works	Example
Electrostatic	Attraction between charged plates, F = εAV²/(2g²)	Comb-drive resonator, micromirror
Thermal	Joule heating causes expansion; a bimorph bends	Thermal microgripper
Piezoelectric	Applied voltage deforms the film	Micropump diaphragm, inkjet head
Electromagnetic	Current in a magnetic field gives a Lorentz force	Micro relay, magnetic microvalve

Example: capacitive accelerometer

A proof mass hangs on springs between fixed plates. Acceleration moves the mass, one capacitor gap shrinks and the other grows, and the capacitance difference gives the acceleration.

Exam tip

Give one clear row each for sensor and actuator, name the transduction principle, and add one real device.