There is also a mass inside the capacitive MEMS accelerometer. From a single unit point of view, it is a standard plate capacitor. The change in acceleration drives the movement of the active mass to change the distance and the area facing the two poles of the plate capacitor, and the acceleration is calculated by measuring the amount of change in capacitance.
The thermal MEMS accelerometer does not have any mass inside. It has a heating body in the center, a temperature sensor around it, and a closed air cavity inside. Under the action of the heating body during operation, the gas forms a hot air mass inside. 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 causes the sensor to sense the acceleration value.
Because there is a rigid body support inside the piezoelectric MEMS accelerometer, under normal circumstances, the piezoelectric MEMS accelerometer can only sense "dynamic" acceleration, but not "static" acceleration, which is what we call gravity acceleration. The capacitive and thermal sensors can sense both "dynamic" acceleration and "static" acceleration.
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