基于柔性基底动态调焦石墨烯超表面聚焦反射镜的仿真研究

Simulation on tunable graphene metasurface focusing mirror based on flexible substrate

焦距范围可调的超薄聚焦反射镜在片上太赫兹光谱和成像等紧凑型系统中有重要应用价值。通过改变几何尺寸和调节化学势可以使石墨烯亚波长反射结构获得0~2π的相位,结合聚二甲基硅氧烷(PDMS)柔性基底的动态拉伸可以实现大动态范围的超薄太赫兹聚焦反射镜。本文设计了一个工作频率为1.0 THz,宽度为12 mm,焦距为60 mm,厚度为75μm的柔性基底动态调焦石墨烯超表面聚焦反射镜。首先在基底自然状态下通过掺杂调节单元石墨烯条的化学势和改变宽度使其反射相位覆盖0~2π相位,并按照预定设计的相位空间分布达到反射聚焦效果。然后通过横向拉伸柔性基底实现反射镜焦距的动态调节。仿真结果表明:柔性基底长度在100%~140%内范围变化时,反射镜的焦距由53.4 mm增加到112.1 mm,动态调焦范围可达到最小焦距的109.7%,同时聚焦效率从69.7%减小到46.8%。此外,本文还研究了该反射镜在宽频带范围的工作性能。仿真结果表明:其对于在0.85~1.0 THz范围内的入射平面波都能实现良好的动态聚焦。

Ultra-thin focusing mirror with adjustable focal length has important applications in compact systems,especially for on-chip terahertz spectroscopy,imaging systems and communication systems.By changing the geometric size and adjusting the chemical potential,the graphene subwavelength reflective structure can achieve a phase of 0~2π.Combined with the above properties and the dynamic stretching of polydimethylsiloxane(PDMS)flexible substrate,the ultra-thin terahertz focusing reflector with large dynamic adjustment range can be realized.In this paper,a dynamic focusing graphene metasurface focusing reflector based on flexible substrate with a working frequency of 1.0 THz,a width of 12 mm,a focal length of 60 mm and a thickness of 75μm is designed and investigated.Firstly,by adjusting the chemical potential and width of the graphene unit strips,the reflective phase covers the 0~2π,and the reflective focusing effect can be achieved according to the predesigned phase spatial distribution.Then,the dynamic adjustment of the focal length of the reflective mirror can be realized by laterally stretching the flexible substrate.The simulation results demonstrate that when the length of the flexible substrate varies from 100%to 140%,the focal length of the reflective mirror increases from 53.4 mm to 112.1 mm,the dynamic focus range can reach 109.7%of the minimum focal length,and the focus efficiency decreases from 69.7%to 46.8%.In addition,the performance of the reflective mirror in a wide frequency range has also been investigated,and the simulation results demonstrate that the good dynamic focusing for incident plane waves in the frequency range of 0.85~1.0 THz can be achieved.The proposed tunable metasurface design is highly versatile in the development of ultrathin,multifunctional and tunable terahertz devices for various applications.