Tunable Gradient Index Fishnet Structures based on Liquid Crystals for Beam Steering Applications

本课题的目标是设计和研究一种基于液晶（LC）的可调梯度指数渔网结构，用于波束导向应用的发射阵列。其目的是首次应用一种非均匀调谐电压分布与入射光束传播方向相反的鱼网结构。利用液晶作为电压可调介质，实现梯度的调谐。这样，就可以对渔网结构的色散特性进行调谐，从而实现发射波束的转向。由于鱼网结构是在宽方向上激发的，因此制造的技术挑战相对较小，可以应用成熟的LC技术制造可调谐平面微波元件。研究表明，鱼网结构可以应用到光学领域。加上连续可调谐LC应用到太赫兹区域是可能的。该项目由两部分组成：可调谐渔网单元单元元件的设计和研究以及由这些可调谐单元单元元件组成的阵列的设计。由于鱼网结构作为有效梯度材料的应用和表征是一个新的研究领域，因此将对有效材料和布洛赫参数的适用性、单位胞各向异性和近场耦合进行基础研究。为了引入LC层的电压可调性，我们将设计一种偏置策略，并研究其移相特性。在这些结果的基础上，将制作阵列来演示梯度折射率渔网结构的波束导向能力。鱼网阵列本身的总体尺寸在几个自由空间波长范围内，但也包含比自由空间波长小得多的几何细节。这导致了很大的模拟复杂性。因此，在这个项目中需要考虑一种时间和内存效率高的模拟技术。

The objective of this project proposal is the design and investigation of a tunable gradient index fishnet structure based on liquid crystal (LC) for the application as transmit array for beam steering applications. It aims for the first time application of a fishnet structure with a non-uniform tuning voltage distribution transversal to the propagation direction of the incident beam. The tuning of the gradient will be realized by applying liquid crystals as voltage tunable dielectric. That way, the dispersion characteristics of the fishnet structure can be tuned in order to realize a steering of a transmitted beam. As the fishnet structure is excited in broadside direction the technological challenges for the fabrication are relatively small and well established LC technology as used for the fabrication of tunable planar microwave components can be applied. It has been shown that the fishnet structure can be applied up to the optical region. Together with the continuously tunable LC applications up to the THz region are possible.The project consists of two parts: the design and investigation of a tunable fishnet unit cell element and the design of an array consisting of these tunable unit cell elements. As the application and characterization of the fishnet structure as effective gradient material is a new field of study, basic investigation redarding the applicability of effective material and Bloch parameters, the unit cell anisotropy, and nearfield coupling will be carried out. To introduce a voltage tunability of the LC layer a biasing strategy will be designed and the phaseshift properties will be investigated. Based on these results the array will be fabricated to demonstrate the beam steering capability of the gradient index fishnet structure. The fishnet array itself has an overall size in the range of several freespace wavelengths but also contains geometrical details which are much smaller than the freespace wavelength. This results in large simulation complexity. Thus, a time- and memory efficient simulation technique needs to be conceived within this project.