Integrating tunable characteristics and multiple functions into a single metasurface has become a new scientific and technological undertaking that needs to deal with huge challenges, especially in the terahertz frequency region. The multifunctional design combining the broadband absorption and broadband polarization conversion using a single switchable metasurface is proposed in this paper. The switchable performance can be realized by treating the insulation to metal phase transition properties of vanadium dioxide (VO₂). At high temperature (74 °C), the proposed metasurface can be used as a broadband absorber which consists of a VO₂ square ring, polyimide (PI) spacer, and VO₂ film. Simulated results show that the terahertz wave absorption can reach above 90% with the bandwidth ratio of 75% in the frequency range of 0.74 THz-1.62 THz. This absorber is insensitive to polarization resulted from the symmetry structure and also shows a good performance at large incident angles. Once the temperature is lower than the cooling phase transition temperature (about 62 °C) and VO₂ is in insulation state, the metasurface can be transformed into a broadband linear-to-circular polarization converter. Numerical simulation depicts that the ellipticity reaches to -1 and the axis ratio is lower than 3 dB from 1.47 THz to 2.27 THz. The designed switchable metasurface provides the potential to be used in the fields of advanced research and intelligent applications in the terahertz frequency region.

中文翻译：

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基于太赫兹波的单个超表面设计的二氧化钒辅助宽带吸收和线到圆极化转换

将可调谐特性和多种功能集成到单个超表面中已成为一项新的科学技术任务，需要应对巨大的挑战，尤其是在太赫兹频率区域。本文提出了一种利用单个可切换超表面将宽带吸收和宽带极化转换相结合的多功能设计。通过处理二氧化钒（VO ₂）的绝缘到金属的相变特性，可以实现可切换的性能。在高温（74°C）下，建议的超表面可以用作宽带吸收器，该吸收器由VO ₂方环，聚酰亚胺（PI）垫片和VO _2组成电影。仿真结果表明，在0.74 THz-1.62 THz的频率范围内，太赫兹波吸收率可以达到90％以上，带宽比为75％。该吸收剂对由对称结构引起的极化不敏感，并且在大入射角下也显示出良好的性能。一旦温度低于冷却相变温度（约62°C）并且VO ₂处于绝缘状态，超表面就可以转换为宽带线性至圆偏振转换器。数值模拟表明，椭圆率达到-1，轴比从1.47 THz到2.27 THz低于3 dB。设计的可切换超表面提供了在太赫兹频率范围内的高级研究和智能应用领域中使用的潜力。