Accelerometer

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An accelerometer is a device for measuring acceleration. An accelerometer inherently measures its own motion (locomotion), in contrast to a device based on remote sensing.

One application for accelerometers is to measure gravity, wherein an accelerometer is specifically configured for use in gravimetry. Such a device is called a gravimeter.

Accelerometers are used along with gyroscopes in inertial guidance systems, as well as in many other scientific and engineering systems. One of the most common uses for micro electro-mechanical system (MEMS) accelerometers is in airbag deployment systems for modern automobiles. In this case the accelerometers are used to detect the rapid negative acceleration of the vehicle to determine when a collision has occurred and the severity of the collision.

Accelerometers are perhaps the simplest MEMS device possible, sometimes consisting of little more than a suspended cantilever beam or proof mass (also known as seismic mass) with some type of deflection sensing and circuitry. MEMS Accelerometers are available in a wide variety of ranges up to thousands of g_n's. Single axis, dual axis, and three axis models are available.

The widespread use of accelerometers in the automotive industry has pushed their cost down dramatically.

There is currently research investigating using accelerometers to help estimate the location of devices. The Global Positioning System can only provide information to a device where the device can receive signals. When a device is in a tunnel, it can make use of an accelerometer to infer its position.

1 Types of accelerometer
2 In biology
3 Applications
4 See also
5 External links

[edit] Types of accelerometer

Piezo-film or piezoelectric sensor
Surface Micromachined Capacitive (MEMS) — Analog Devices, Freescale, Honeywell, Systron Donner (BEI)
Thermal (submicron CMOS process) — MEMSIC
Bulk Micromachined Capacitive — VTI Technologies
Bulk Micromachined Piezo Resistive
Electromechanical Servo (Servo Force Balance)
Null-balance
Strain gauge
Resonance
Magnetic induction
Optical
Surface Acoustic Wave (SAW)
Laser Accelerometer

[edit] In biology

Many aquatic invertebrates use statocysts, special cellular structures with pendulous weights and enervated sensory organs to measure acceleration and gravity.

In humans, the vestibular apparatus in the inner ear provides information about acceleration to the brain, used for coordination and balance. In people whose sense of balance is injured or defective, this function may someday be regained through the use of a wearable MEMS-based sensor.

[edit] Applications

The Wii Remote for the Nintendo Wii console contains accelerometers for measuring movement and tilt to complement its pointer functionality. In addition, the "nunchuk" peripheral contains accelerometers as well. One confirmed use for this is to simulate the winding of a reel of fishing line in the fishing mini-game within The Legend of Zelda: Twilight Princess, as well as controlling a shield for the same game and a boxer's left hand for a fighting game.

Within the last several years, Nike, Polar and other companies have produced and marketed sports watches for runners, that include footpods, containing accelerometers to help determine the speed and distance for the runner wearing the unit.

More recently, Apple Computer and Nike have combined the footpod technology and Apple's iPod nano to provide real-time audio feedback to the runner on his/her pace and distance. [1]

A small number of modern notebook computers feature accelerometers to automatically align the screen depending on the direction the device is held (this feature is only relevant in Tablet PCs.)

Some laptop's hard drives utilize an accelerometer to detect when falling occurs. If the laptop is dropped, the accelerometer signals the drive to move the read/write head away from the inner drive platters, thus protecting the data.