具有二维聚焦特性的柱形超表面透镜设计

Design of cylindrical metasurface lens with two-dimensional focusing characteristics

针对柱面共形情形下的透射聚焦问题,提出了一种在圆柱周向和轴向均有聚焦效果的共形透镜设计。为了使进入柱形区域内部的透射射线以相同的相位汇集于预设焦点处,在射线分析模型的基础上,得到了柱面共形超表面透镜应满足的透射相位补偿量。结合超表面单元结构实际的周期尺寸,对透射相位补偿量进行离散近似,并通过不同内部尺寸的单元结构将其映射至圆柱表面。在TE极化和TM极化平面电磁波照射下,柱面共形超表面透镜在预设焦点处均可产生明显的聚焦斑点,在11 GHz附近,预设焦点处电场幅值下降3 dB的带宽分别为24.3%和27.3%,结果表明了该透镜沿圆柱周向和轴向的二维聚焦能力。

A conformal lens design with the focusing effect along both circumferential and axial directions of a cylinder was proposed to address the transmissive focusing issue in cylindrical conformal situations.In order to concentrate the transmitted rays entering the cylindrical region to the predefined focal point with the same phase,the transmissive phase compensation required for the cylindrical conformal metasurface lens was derived based on the ray analysis model.According to the actual periodicity of the metasurface unit cell,a discrete approximation of the transmissive phase compensation was adopted.Then the discrete phase values were mapped onto the cylindrical surface through the unit cells of different internal dimensions.Under the illumination of a TE-or TM-polarized plane electromagnetic wave,the cylindrical conformal metasurface lens can generate an obvious focal spot at the predefined focus.The bandwidths corresponding to a 3 dB drop in the electric field amplitude at the focal point around 11 GHz are 24.3%and 27.3%,respectively.The results indicate the two-dimensional focusing capability along both the circumferential and axial directions of the cylinder.