Appl Opt. 2023 Mar 20;62(9):2317-2328. doi: 10.1364/AO.478842.
The development of radiation-absorbent materials and devices for millimeter and submillimeter astronomy instruments is a research area of significant interest that has substantial engineering challenges. Alongside a low-profile structure and ultra-wideband performance in a wide range of angles of incidence, advanced absorbers in cosmic microwave background (CMB) instruments are aimed at reducing optical systematics, notably instrument polarization, far beyond previously achievable specifications. This paper presents a metamaterial-inspired flat conformable absorber design operating in a wide frequency range of 80-400 GHz. The structure comprises a combination of subwavelength metal-mesh capacitive and inductive grids and dielectric layers, using the magnetic mirror concept for a large bandwidth. The overall stack thickness is a quarter of the longest operating wavelength and is close to the theoretical limit stipulated by Rozanov's criterion. The test device is designed to operate at a 22.5° incidence. The iterative numerical-experimental design procedure of the new metamaterial absorber is discussed in detail, as well as the practical challenges of its manufacture. A well-established mesh-filter fabrication process has been successfully employed for prototype fabrication, which ensures cryogenic operation of the hot-pressed quasi-optical devices. The final prototype, extensively tested in quasi-optical testbeds using a Fourier transform spectrometer and a vector network analyzer, demonstrated performance closely matching the finite-element analysis simulations; that is, greater than 99% absorbance for both polarizations, with only a 0.2% difference, across the frequency band of 80-400 GHz. The angular stability for up to ±10 has been confirmed by simulations. To the best of our knowledge, this is the first successful implementation of a low-profile, ultra-wideband metamaterial absorber for this frequency range and operating conditions.
毫米和亚毫米波天文仪器辐射吸收材料和器件的发展是一个极具工程挑战性的研究领域。除了在宽入射角范围内具有低轮廓结构和超宽带性能外，宇宙微波背景（CMB）仪器中的先进吸收体旨在降低光学系统，特别是仪器极化，远远超出以前可实现的规格。本文提出了一种基于超材料的平面共形吸收器设计，工作频率范围为 80-400GHz。该结构由亚波长金属网电容和电感栅格以及介电层组成，采用磁镜概念实现大带宽。总堆叠厚度为最长工作波长的四分之一，接近 Rozanov 准则规定的理论极限。测试设备设计用于 22.5°入射角。详细讨论了新超材料吸收器的迭代数值-实验设计过程以及其制造的实际挑战。已经成功地采用了成熟的网格滤波器制造工艺来制造原型，这确保了准光学热压器件的低温操作。最终原型在准光学测试台上进行了广泛的测试，使用傅里叶变换光谱仪和矢量网络分析仪，其性能与有限元分析模拟非常匹配；也就是说，在 80-400GHz 的频带内，两种偏振的吸收率都大于 99%，仅相差 0.2%。通过模拟确认了高达±10 的角稳定性。据我们所知，这是首次在这种频率范围和工作条件下成功实现低轮廓、超宽带超材料吸收器。
