Dynamic Capacitance Extraction of a Triaxial Capacitive Accelerometer

Capacitive sensing is widely used in micromachined sensors, such as accelerometers, pressure sensors, gyroscopes, etc. In order to achieve desired performance, the capacitance variation according to external excitation must be evaluated carefully. However, obtaining the analytical result is not easy, especially for complicated deformations. This problem can be solved in ANSYS by building the electrostatic model according to a structural analysis result, then extracting capacitance through CMATRIX. However, rebuilding the model manually is not efficient and is sometimes very difficult, given a complex model. In this paper, a dynamic capacitance extraction method is presented to solve this problem. This method is based on automatic mesh updating and physics environments. The analysis procedure is to first create the structural and electrostatic physics environment, then do the structural analysis in the structural environment, updating the mesh according to the result, and, lastly, extract capacitance through CMATRIX in an electrostatic environment. A triaxial capacitive accelerometer is used as an example to evaluate this method. The analysis results show that this method is efficient to achieve capacitance variation versus external excitation relation.

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