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• Joseph Diong

# Accelerometers: How do they work?

Every year, airbags save many lives, preventing fatal consequences. Airbags deploy within a fraction of a second after a crash, but how is it that such crashes can be detected in almost an instant?

Crashes involve high speed collisions that generate a lot of force and acceleration in a vehicle. Using a sensor called an accelerometer, accelerations and forces can be detected. How does this sensor work though?

Acceleration is defined as the rate of change of velocity over time, mathematically defined as change of velocity divided by total time taken to change velocity. The type of acceleration being measured by the accelerometer would be called “proper acceleration”, or commonly known as G-force. Simply put, it is the force and acceleration felt by an object.

There are many types of accelerometers, but in this article the focus will be on a single type: piezoelectric accelerometers. “Piezoelectric” implies a conversion of kinetic energy into electrical energy. An example would be if I were to slap something hard that is piezoelectric, a voltage would be produced. The amount of force is proportional to the voltage generated; acceleration can be inferred from the voltage reading.

A piezoelectric crystal is a type of crystal that produces a voltage when it experiences a force. There is a tiny mass that is connected to the piezoelectric crystal, and as a force is experienced by the sensor, the mass moves. The mass hits the crystal, and a voltage is produced. This voltage is then measured by a sensor, which is then relayed to other devices that may read this voltage. The voltage created by the crystal is very small and must be amplified to a higher magnitude.

The applications of accelerometers are wide, and has been used in many fields and devices such as smartphones, drones and numerous other devices. Different types of accelerometers have been created for specific situations, such as miniaturized versions of accelerometers called MEMS accelerometers, used in smartphones and tablets.