Finite element analysis of eddy current displacement sensor for contactless thin adaptive mirror

Adaptive optics is the key technology of large-aperture optical telescopes to eliminate the effects of atmospheric interference on optical imaging. In adaptive optical systems, the distortion of the optical system is detected by the wavefront sensor and corrected by the deformable mirror to improve the resolution and image quality of telescopes. The contactless thin adaptive mirror is considered as the most competitive solution for the large-aperture optical telescope, which uses voice coil motors to drive the deformable mirror and capacitive displacement sensors to measure the mirror shape for feedback control. However, capacitive displacement sensor is very expensive and sensitive to environmental contaminants, such as dust, moisture, etc. In this paper, eddy-current displacement sensor is proposed for the shape measurement of contactless thin adaptive mirror in harsh environment. The structural design and working principle of the single unit with a voice coil motor and an eddy-current displacement sensor are explained. A complete model is built for the simulation of magnetic field interference among the voice coil motor, eddy-current displacement sensor, and other components. The influence of voice coil and permanent magnet on the performances of detecting coil is analyzed. The influence of the detecting coil, conductive target, and other components on the actuation of voice coil is also estimated. The simulation results indicate that the influence of eddy-current displacement sensor on the voice coil motor is limited. But the voice coil motor has a significant influence on the eddy-current displacement sensor, for which special attention should be considered.