The MEMS Accelerometer – A Device that Permeates the World Around Us

You may have never heard of an accelerometer, but they are found in many areas of our everyday lives. Accelerometers retract the read/write heads of a hard disk when a laptop is dropped as well as detect impact in accidents and deploy automobile airbags. They are used in pedometers for more accurate measurement of distance and in washing machines to detect excessive vibration. They also enable a handheld display to be switched between portrait and landscape modes when the unit is turned.

What is Meant by MEMS?
MEMS stands for micro electromechanical systems and are tiny mechanical devices that are built onto semiconductor chips. Research began on these devices in the 1980s and began to appear in commercial products in the 1990s. Sometimes the terms nanotechnology and MEMS are used interchangeably because they both deal with microminiaturized objects. However, MEMS deals with devices measured in micrometers while nanotechnology deals with manipulating atoms at the nanometer level.

Acceleration and Accelerometers
Acceleration is the rate of change of the speed of an object. However, measuring acceleration is more complex than that and accelerometers are used to measure acceleration forces. These forces can be static, such as the constant force of gravity, or dynamic, such as those that are moving or vibrating the accelerometer itself.

Initially, accelerometers were based on piezo-electric crystals and contained microscopic crystal structures that get stressed by accelerative forces which cause the generation of a voltage. However, these were too big and clumsy, and researchers then looked to something smaller and turned to the field of microelectronics. As a result, the MEMS accelerometer was developed.

How a MEMS Accelerometer Works
MEMS accelerometers use two capacitors in a moveable plate held between two fixed plates. The two capacitors are equal under a net-zero force but when a change is forced is applied, the moveable plate will move closer to one of the fixed plates, increasing its capacitance, and further away from the other so that its capacitance is reduced. This difference in capacitance is detected and amplified to produce a voltage proportional to the acceleration which translates to the acceleration force.
The latest generation of the MEMS accelerometer is being incorporated into more and more personal electronic devices and has enabled innovative new products in dozens more markets around the world.

Watson Industries has more than 35 years of experience in the sensor applications industry. For information about the company’s products, go to www.watson-gyro.com.

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