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

本项目提案的目的是设计和研究一种基于液晶（LC）的可调梯度折射率渔网结构，用于波束控制应用的发射阵列。它的目的是第一次应用的渔网结构与非均匀的调谐电压分布的入射光束的传播方向的横向。利用液晶作为电压可调介质，实现了梯度的调谐。这样，可以调谐渔网结构的色散特性，以便实现透射光束的转向。由于渔网结构在宽边方向上被激励，因此制造的技术挑战相对较小，并且可以应用用于制造可调谐平面微波部件的成熟LC技术。结果表明，渔网结构可以应用到光学区域。该项目包括两个部分：可调谐渔网单元元件的设计和研究以及由这些可调谐单元元件组成的阵列的设计。由于渔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Bloch参数的适用性、单胞各向异性和近场耦合进行基础研究。为了引入LC层的电压可调谐性，将设计偏置策略并研究相移特性。基于这些结果，阵列将被制造以展示梯度折射率渔网结构的波束转向能力。渔网阵列本身具有在几个自由空间波长范围内的总体尺寸，但也包含比自由空间波长小得多的几何细节。这导致大的模拟复杂度。因此，一个时间和内存效率的模拟技术需要在这个项目中构思。

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.