Piezoresistive type
A piezoresistor is installed at the support of a weight to detect the strain caused by acceleration. This simple structure allows for easy miniaturization.
Accelerometers
Accelerometers are sensors that measure the rate of change in velocity per unit time. If there is no change in velocity per unit time, the acceleration is zero. By acquiring the acceleration information, information such as change in velocity per unit time, motion, and impact/shock can be obtained.
This section presents the features of accelerometers and examples of their applications.
What Is an Accelerometer?
Accelerometers are sensors that detect the rate of change in velocity per unit time due to motion, gravity, vibration, impact/shock, and other forces, and output it as acceleration data.
Angular rate sensors (gyro sensors) detect the rate of change in angle per unit time relative to acceleration, and the two types of sensors are increasingly being used in combination.
By integrating a 3-axis accelerometer and a 3-axis gyro sensor, it is now possible to detect the overall movement of objects.
Accelerometers Using MEMS
There are three types of MEMS accelerometers: piezoresistive, capacitive, and thermal sensing.
Capacitive type
In this sensor, changes in capacitance are detected between a fixed part and a movable part. The part that detects the capacitance has a comb-type structure, providing high accuracy and excellent temperature characteristics. Major applications include vibration suppression and orientation control in automobiles.
Thermal sensing type
A heater is used to generate hot air flow in the sensor, and convection currents that change with acceleration are detected by thermal resistance and other means. Although the measurement frequency bandwidth is narrow, the sensor has no moving parts, making it superior in shock resistance, and it is often used in locations subject to vibrations and shocks.
Application Examples of Accelerometers
Familiar applications of accelerometers include controlling the orientation of smartphone screens and correcting the map orientation control according to the direction of travel in navigation applications. They are also used in sensors that detect collisions for activating airbags. Furthermore, they are also used in wearable devices such as AR and VR headsets, and are essential sensors in devices that are expected to grow even more in coming years.