There are three types of mature MEMS accelerometers: piezoelectric, capacitive, and thermal. Piezoelectric MEMS accelerometers use the piezoelectric effect. Inside, there is a mass supported by a rigid body. When there is movement, the mass will generate pressure, and the rigid body will generate strain, which will convert acceleration into electrical signal output.
There is also a mass inside the capacitive MEMS accelerometer. From a single unit point of view, it is a standard flat capacitor. The change in acceleration drives the moving mass to change the distance between the two poles of the plate capacitor and the area directly facing it. The acceleration is calculated by measuring the change in capacitance.
There is no mass inside the thermal MEMS accelerometer. There is a heating body in the center, a temperature sensor in the periphery, and a closed air cavity. When working, the gas forms a hot air mass in the interior. The specific gravity of the mass is different from the surrounding cold air. The change in the thermal field formed by the movement of the inertial hot air mass makes the sensor sense the acceleration value.
Due to the rigid body support inside the piezoelectric MEMS accelerometer, usually, the piezoelectric MEMS accelerometer can only sense "dynamic" acceleration, but not "static" acceleration, which is what we call gravity acceleration. . Capacitive and thermal sensing can sense both "dynamic" acceleration and "static" acceleration.
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