Radio frequency shielding effectiveness of carbon-nanotube-based x-ray filters

Optical and thermal blocking filters are critical components in X-ray space observatories, their primary function is to minimize unwanted radiation that could reduce the performance of highly sensitive detectors. As detector sensitivity advances, the demand for filters with superior X-ray transparency and out-of-band rejection increases, while ensuring the necessary mechanical robustness to withstand launch stresses. A novel technology under investigation within ESA research contracts involves the use of carbon nanotube (CNT) pellicles. A thin membrane, composed of CNT bundles, is coated with metal to provide the requisite filtering characteristics. The ultra-thin nature of high-performance filter membranes necessitates a support structure; silicon or metal meshes are often used to support the membranes, but CNT technology enables the creation of supporting meshes from the same material as the membrane. This innovation results in filter supports composed solely of carbon, offering the dual benefits of minimal high-energy X-ray obscuration and the absence of extraneous absorption lines, except for those related to carbon and the metal coating. While the membrane itself handles EUV to infrared radiation rejection, metal meshes have been previously used to enhance the radio frequency (RF) shielding effectiveness of filters. Electromagnetic RF interference, produced in a spacecraft primarily from antennas and secondarily from onboard electronics, poses a significant challenge for sensitive detectors like the transition-edge sensors in the ESA mission Athena’s X-IFU instrument. Given CNTs’ potential electrical conductivity—contingent on the production process—this study explores the shielding effectiveness of all-carbon filters and benchmarks them against state-of-the-art filters featuring an Al-coated polyimide membrane with a metal mesh support.