EMC design for the actuators of FAST reflector

Abstract: The active reflector is one of the three main innovations of the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The deformation of such a huge spherically shaped reflector into different transient parabolic shapes is achieved by using 2225 hydraulic actuators which change the position of the 2225 nodes through the connected down tied cables. For each different tracking process of the telescope, more than 1/3 of these 2225 actuators must be in operation to tune the parabolic aperture accurately to meet the surface error restriction. It means that some of these actuators are inevitably located within the main beam of the receiver, and the Electromagnetic Interference (EMI) from the actuators must be mitigated to ensure the scientific output of the telescope. Based on the threshold level of interference detrimental to radio astronomy presented in ITU-R Recommendation RA.769 and EMI measurements, the shielding efficiency (SE) requirement of each actuator is set to be 80dB in the frequency range from 70MHz to 3GHz. Therefore, Electromagnetic Compatibility (EMC) was taken into account in the actuator design by measures such as power line filters, optical fibers, shielding enclosures and other structural measures. In 2015, all the actuators had been installed at the FAST site. Till now, no apparent EMI from the actuators has been detected by the receiver, which proves the effectiveness of these EMC measures.