Actuation Distortion
Capacitive force actuators generate mechanical translation through electric fields established between conductive surfaces. The electrostatic force non-linearity refers to the inverse-square relationship between the attractive force and the distance separating the capacitive plates. This physical characteristic limits the stable operating region of electrostatic actuators and sensors to a fraction of the total gap.
Beyond this critical displacement, the system experiences instability or pull-in failures.
Deflection Mechanism
Voltage inputs produce forces that grow rapidly as the gap between the plates decreases. Such feedback loops cause the moving electrode to accelerate toward the fixed electrode beyond the structural balance point. The mechanical restoring spring cannot compensate for this force increase.
This acceleration restricts the linear dynamic range of capacitive microphones and pressure sensors.
Control Method
Closed-loop feedback systems using force-balance techniques counteract the non-linear voltage response. By continuously adjusting the bias voltage to maintain a constant gap, the sensor remains in its linear operational region.
System Calibration
Automated profiling of the force versus voltage curve enables software compensation in the downstream digital signal processor. Optical interferometers measure the displacement of the actuator across a series of applied voltages to map the deviation from the ideal square-law curve. The resulting dataset is used to build polynomial lookup tables that correct the non-linear voltage outputs in real time.
This procedure is verified during factory testing to guarantee that the residual distortion remains below specified thresholds.
