MEMS Sensors

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1 Introduction to MEMS sensors

Micro Electro Mechanical Systems (MEMS) are devices that are built and operate at a micron (or micrometer) scale. They are bigger than nanoscale devices but smaller than anything else. They can be both electrical and mechanical.

Market applications[1]

Healthcare
Transportation
  • Tire pressure
  • Airbags
  • Indy car crash safety
  • Aircraft and watercraft position and attitude determination
  • Cell phones and PDAs
  • Pedometers
  • Video Games
  • Laptops - lock the hard drive a fraction of second before a dropped laptop makes impact
  • Optical communications
  • Health and Safety of structure - buildings, bridges, etc.

1.1 Actuators

Devices whose principal aim is to produce mechanical motion[2]

  • micro-tweezers
  • micro-engines

1.2 Sensors

Devices whose principal aim is to produce an output which is dependent upon their environment[3]

  • pressure sensors
  • accelerometers
  • gyroscopes (gyros)

1.3 Passive devices

Devices whose principal aim is to respond passively to their environment without producing an output signal[4]

  • hinges
  • micro-lenses
  • linkages

2 Sensing Components[5]

Major advantages of microsensors over traditional macro sensors

  1. High surface area to volume ratio typically leads to unprecedented levels of sensitivity
  2. Small size allows for very localized measurements
  3. Microsystems allow for the integration of signal processing into a sensor resulting in improved signal-to-noise

2.1 Mechanical Sensors

There are 2 categories of mechanical sensor (1) non-resonant and (2) resonant. For non-resonant devices deflection is measured through Optical, Capacitive, or Piezoresistive detection schemes. Resonant devices measure the change in velocity and amplitude of acoustic waves created by the resonating of some micro object. Resonating devices measure the change in acoustic waves through Piezoelectrics.

2.2 Other sensor types

Optical sensors use photodiodes.

Thermal sensors comes in 4 flavors.

  1. Microbolometers: detect infrared radiation
  2. Thermocouples: measure a difference in potential across to different materials in "intimate" contact
  3. Resistors and thermistors: exploits the fact that most metals change resistance with temperature
  4. Semiconductor devices: exploits the current-voltage characteristics which are temperature dependent in many semiconducting devices

3 MEMS Gyros

3.1 Disk Resonating Gyro (DRG)

TODO

TODO
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3.2 Tuning Fork Gyro (TFG)

TODO

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4 MEMS Accelerometers

TODO

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5 References

Gaura, E., and Newman, R 2006 Smart MEMS and Sensor Systems. 1st. Imperial College Press. ISBN 0860944930

5.1 Notes

  1. Gaura & Newman, pp. 3-7
  2. Gaura & Newman, pg. 32
  3. Gaura & Newman, pg. 32
  4. Gaura & Newman, pg. 32
  5. Gaura & Newman, pp. 42-48