A device that detects acceleration and tilt. Built using MEMS technology, accelerometers detect impact and deploy automobile airbags as well as retract the hard disk's read/write heads when a laptop is dropped. Digital cameras employ them in their image stabilization circuits. They are used in washing machines to detect excessive vibration and in pedometers for more accurate distance measurement. They also enable a handheld display to be switched between portrait and landscape modes when the unit is turned.
Springs, Bubbles, Capacitance and Crystals
MEMS accelerometers initially used a microminiaturized cantilever-type spring, which converted force into a displacement that was measured. Subsequent MEMS devices use a heated gas bubble with thermal sensors that functions like the air bubble in a construction level (see MEMS
). Other types of accelerometers use microstructures that change their capacitance or microscopic crystals that generate a voltage when stressed.
Accelerometers, Gyroscopes and Magnetometers
An accelerometer measures a change in velocity and position, whereas a gyroscope measures rotational changes, and a magnetometer measures compass direction. All three are used in an "inertial measurement unit" (IMU) in airplanes, spacecraft and satellites, and mobile devices use accelerometers and magnetometers.
Dual-Axis Thermal Accelerometer
This MEMS unit works like the air bubble in a construction level. The square in the middle of the chip is a resistor that heats up a gas bubble. As the device is tilted or accelerated, surrounding thermal couples sense the bubble's location. (Image courtesy of MEMSIC, Inc.)
An iPhone Level
Because of its built-in accelerometer, smartphones can be turned into a digital level with apps such as this one from PosiMotion (www.posimotion.com).
The device at the bottom left with the C-shaped wings is an accelerometer. Built one metal layer at a time, Microfabrica's EFAB system was the first MEMS foundry process to quickly turn customers' CAD files into micromachines. (Image courtesy of Microfabrica Inc., www.microfabrica.com)