MEMS accelerometers are used wherever there is a need to measure linear motion, either movement, shock or vibration but without a fixed reference. They measure the linear acceleration of whatever they are attached to. Acceleration is measured in m/s-2, but the convention for accelerometers is in ‘g’, or units of gravity, 1g being 9.81m/s-2.
All accelerometers work on the principle of a mass on a spring, when the thing they are attached to accelerates then the mass wants to remain stationary due to its inertia and therefore the spring is stretched or compressed, creating a force which is detected and corresponds to the applied acceleration.
In Silicon Sensing’s Gemini® MEMS dual-axis accelerometer, and also the accelerometer in its CMS combi-sensor MEMS combi-sensor, precise linear acceleration detection in two orthogonal axes is achieved by a pair of silicon MEMS detectors formed by sprung ‘proof’ masses. Each mass provides the moving plate of a variable capacitance formed by an array of interlaced ‘fingers’.
When the sensor is subjected to a linear acceleration along its sensitive axis the proof mass tends to resist motion due to its own inertia, therefore the mass and its fingers become displaced with respect to the fixed electrode fingers. Gas between the fingers provides a damping effect. This displacement induces a differential capacitance between the moving and fixed silicon fingers which is proportional to the applied acceleration.