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

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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.