The measurements are being made using ground-based millimetre-wave telescopes, whose receivers are cooled to cryogenic temperatures to reduce noise, boosting sensitivity. The latest generation of instruments are so sensitive that any amount of stray light can degrade the image and decrease its sensitivity.
The team therefore looked for a solution to suppress this stray light, no mean feat at such low temperatures. They found the answer lay in low-cost absorbing tiles made from a combination of polyurethane and carbon particles.
The injection-moulded tiles, manufactured from a carbon-loaded TPU with a 25% loading, absorb more than 99% of millimetre wave radiation and, importantly, retain these absorptive properties at –272°C, just above absolute zero. The TPU used to make the tiles is a commercially available electromagnetic interference shielding material, and sold as Conductive TPU Compound by Yushuo New Material.
Another problem that needed to be overcome was the fact that the surface of the tiles also reflected a significant amount of radiation before it could be absorbed. This was fixed by adding an anti-reflective coating. The resulting tiles had excellent reflectance properties with low scattering, and absorbed almost all of the incoming photons.
‘Because the tiles can be made by injection-moulding commercially available materials, they are an economic, mass-producible and easy-to-install solution to what has been a long-standing problem,’ Xu said. ‘With this technology, the Simons Observatory will transform our understanding of the universe from many aspects, including the beginning of the universe, the formation and evolution of the galaxies, and the ignition of the first stars.’
The work has been published in the journal Applied Optics.