Material survey for millimeter-wave absorber using 3-D printed mold

Abstract

Radio absorptive materials (RAMs) are key elements for receivers in the millimeter-wave range. For astronomical applications, cryogenic receivers are widely used to achieve a high-sensitivity. These cryogenic receivers, in particular the receivers for the cosmic microwave background, require that the RAM has low surface reflectance ($\lesssim 1\%$) in a wide frequency range (20--300 GHz) to minimize the undesired stray light to detectors. We develop a RAM that satisfies this requirement based on a production technology using a 3D-printed mold (named as RAM-3pm). This method allows us to shape periodic surface structures to achieve a low reflectance. A wide range of choices for the absorptive materials is an advantage. We survey the best material for the RAM-3pm. We measure the index of refraction ($n$) and the extinction coefficient ($\kappa$) at liquid nitrogen temperature as well as at room temperature of 17 materials. We also measure the reflectance at the room temperature for the selected materials. The mixture of an epoxy adhesive (STYCAST-2850FT) and a carbon fiber (K223HE) achieves the best performance. We estimate the optical performance at the liquid nitrogen temperature by a simulation based on the measured $n$ and $\kappa$. The RAM-3pm made with this material satisfies the requirement except at the lower edge of the frequency range ($\sim$20 GHz). We also estimate the reflectance of a larger pyramidal structure on the surface. We find a design to satisfy our requirement.

arXiv comment8 pages, 10 figures

References in corpus (5)

• The Simons Observatory: Science goals and forecasts
• A 3D-printed broadband millimeter wave absorber
• Development of Multi-Fourier Transform interferometer :Fundamental
• The Simons Observatory: Metamaterial Microwave Absorber (MMA) and its Cryogenic Applications
• Production Method of Millimeter-Wave Absorber with 3D-Printed Mold

Cited by in corpus (3)

• Planar near-field measurements of specular and diffuse reflection of millimeter-wave absorbers
• Optimization procedure of the baffle of the GroundBIRD Telescope to mitigate stray light
• Mitigating Cosmic Microwave Background Shadow Degradation of Tensor-to-scalar Ratio Measurements through Map-based Studies