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accelerometer

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).






Microfabrica Accelerometer
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)






MEMS

(MicroElectroMechanical Systems) Tiny mechanical devices that are built onto semiconductor chips and are measured in micrometers. In the research labs since the 1980s, MEMS devices began to materialize as commercial products in the mid-1990s. They are used to make pressure, temperature, chemical and vibration sensors, light reflectors and switches, as well as accelerometers for vehicle airbags, smartphones, tablets and games (see accelerometer).

MEMS technology is also used to make inkjet print heads, microactuators for read/write heads and all-optical switches that reflect light beams to the appropriate output port.

MEMS and MOEMS
When optical components are included in a MEMS device, it is called a micro-opto-electromechanical system (MOEMS). For example, adding a photonic sensor to a silicon chip constitutes a MOEMS device. See micromachine, MEMS mirror, DLP and optical switch.

MEMS Vs. Nanotechnology
Sometimes MEMS and nanotechnology are terms that are used interchangeably, because they both deal with microminiaturized objects. However, they are vastly different. MEMS deals with creating devices that are measured in micrometers, whereas nantotechnology deals with manipulating atoms at the nanometer level.




MEMS-based Optical Switch
In an all-optical switch, MEMS mirrors reflect the input signal to an output port without regard to line speed or protocol. This technology is expected to be the dominant method for building photonic switches.






Sample Micromachines
Microfabrica's EFAB system was the first MEMS foundry process to accept CAD files as input, turning customer designs into micromachines much faster than traditional methods. EFAB builds the devices one metal layer at a time. In this image, the square at the top is a microfluidics device with internal passageways used for a "lab on a chip." The multi-arm device (center) is a fuel injection nozzle. Bottom left is an accelerometer, and bottom right is an inductor used in RF circuits. (Image courtesy of Microfabrica Inc., www.microfabrica.com)







MEMS-Based Accelerometer
MEMSIC's dual-axis thermal accelerator is a MEMS-based semiconductor device that works conceptually 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. The next larger squares contain thermal couples that sense the location of the heated bubble as the device is tilted or accelerated. (Image courtesy of MEMSIC, Inc.)






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