High Accuracy Capacitive Displacement Transducer for the Position Local Control Loops at the Adaptive Secondary

The thin faceplate adaptive secondary mirrors are controlled by means of electromagnetic force actuators, which seem to be a suitable choice in terms of stroke, accuracy and cost [Del Vecchio, Gallieni et al.; Biasi, Gallieni et al. in this Conference]. Those actuators need a local control loop to achieve a linear position response. The position sensor is definitely a crucial component of this control loop: both high sensitivity and high speed have to be achieved at same time.