There are three types of mature MEMS accelerometers: piezoelectric, capacitive, and thermal. Piezoelectric MEMS accelerometers use a piezoelectric effect with a rigid body-supported mass inside. In the case of motion, the mass will generate pressure, the rigid body will generate strain, and the acceleration will be converted into an electrical signal output.
There is also a mass inside the capacitive MEMS accelerometer, which is a standard plate capacitor from a single unit. The change of acceleration drives the movement of the moving mass to change the spacing and the facing area of the two poles of the plate capacitor, and the acceleration is calculated by measuring the amount of capacitance change.
There is no mass inside the thermal MEMS accelerometer. It has a heating body in the center, a temperature sensor in the periphery, and a closed air cavity inside. Under the action of the heating body, the gas is in the air. A hot air mass is formed inside, and the specific gravity of the hot air mass and the surrounding cold air are different, through inertia.
The thermal field change caused by the movement of the hot air mass causes the sensor to sense the acceleration value. Since the piezoelectric MEMS accelerometer has the existence of rigid body support, usually,Piezoelectric MEMS accelerometers can only sense "dynamic" acceleration, but can not sense "static" acceleration, which is what we call gravity acceleration, while capacitive and thermal sensing can sense "ld"; Dynamic & rdquo; acceleration, and can sense "static" acceleration.
Generally, when the orientation is measured by a capacitive and thermal accelerometer, the acceleration measured by the accelerometer includes the gravity component of the gravitational acceleration on each axis and the acceleration component caused by the dynamic motion. I think that when we use this type of accelerometer for orientation, we must remove the dynamic acceleration (it is more difficult); when performing the motion of the detection chip, the acceleration of gravity must be removed.