A mechanical element — e.g. a proof mass suspended on silicon spring beams — is etched into silicon. Its motion under acceleration or rotation changes a measurable quantity, most commonly the capacitance between moving and fixed comb electrodes. Gyroscopes use a vibrating mass and the Coriolis effect to measure angular rate. An integrated read-out circuit (ASIC) converts the signals into digital data. In MEMS microphones a membrane deflects under acoustic pressure, and in scanning LiDAR an electrostatically actuated micromirror steers the laser beam. Signals from multiple sensors (e.g. accelerometer + gyroscope in an IMU) are combined via sensor fusion, typically a Kalman filter.
Classic inertial, pressure and acoustic sensors were large, expensive and power-hungry, preventing mass deployment in mobile devices and robots. MEMS miniaturise the mechanics to chip scale and integrate them with electronics in a single silicon process, drastically reducing size, cost and power consumption.
