Fixed Electrodes

Fixed electrodes are precision-engineered stationary conductive plates or surfaces within capacitive accelerometers that form part of a differential capacitor arrangement. They maintain a fixed position relative to the accelerometer housing while interacting with movable proof masses or seismic masses. When acceleration occurs, the movable mass deflects, changing the distance between it and the fixed electrodes, thereby altering capacitance. This capacitance change is measured and converted into an electrical signal proportional to acceleration. Fixed electrodes are critical for maintaining measurement stability, linearity, and sensitivity in MEMS (Micro-Electro-Mechanical Systems) and capacitive accelerometers used across various precision measurement applications.

Fixed electrodes operate on the principle of variable capacitance sensing. They form one plate of a parallel-plate capacitor system, with the movable proof mass acting as the other plate. Under acceleration, the proof mass moves relative to the fixed electrodes, changing the gap distance between them. This alters the capacitance according to C = εA/d, where ε is permittivity, A is overlapping area, and d is gap distance. The capacitance change is detected by integrated circuitry (often using AC excitation or charge amplification), converted to a voltage signal, and processed to determine acceleration magnitude and direction. Differential configurations with multiple fixed electrodes cancel common-mode noise and improve sensitivity.