Measurement of Dielectric Properties of Nematic Liquid Crystals at Millimeter Wavelength
Measurement of Dielectric Properties of Nematic Liquid Crystals at Millimeter Wavelength
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DOI：
10.1109/tmtt.2010.2054332
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发表时间：
2010-12-01
影响因子：
4.3
通讯作者：
Fernandez, F. Anibal
中科院分区：
文献类型：
--
作者：
Bulja, Senad;Mirshekar-Syahkal, Dariush;Fernandez, F. Anibal
液晶具有大的双折射和较低的损耗，是一种很有前途的介质，可用于开发各种可重构毫米波器件。为了优化可调谐毫米波器件的设计，需要精确的介电常数和弹性常数，以及LC的损耗角正切值。然而，在毫米波频率下的LC的表征是一个非常具有挑战性的和苛刻的task.In这项工作中，传输线的方法被用于在30-60 GHz的频率范围内的宽带表征的MEMS LC。为此，提出了一种独特的LC单元，并使用该LC单元测量了包括E7、K15、E44、E63和MDA-00-3506在内的五种不同的双相LC，并提取了它们的电参数和机械参数的值。从测量中提取这些参数涉及使用两个有限元计算机程序的优化最近开发的预测的LC分子的局部取向和测试cell.The最高值的介电双折射和最高值的损耗角正切的测试单元内的波传播记录为E44和MDA-00-3506。随着频率的增加，所有LC的损耗角正切都呈现出总体下降的趋势，这在可重构毫米波器件的开发中是一个有用的特性。
Due to their large birefringence and moderately low loss, liquid crystals (LCs) are a promising dielectric media for development of a variety of reconfigurable millimeter-wave devices. In order to optimize the design of tunable millimeter-wave devices, accurate values of the dielectric and elastic constants, as well as the loss tangents of LCs, are needed. However, characterization of LCs at millimeter-wave frequencies is a very challenging and demanding task.In this work, a transmission line method is used for the broadband characterization of nematic LCs in the frequency range of 30-60 GHz. For this purpose, a unique LC cell is proposed and using this, five different nematic LCs, including E7, K15, E44, E63, and MDA-00-3506, are measured and the values of their electrical and mechanical parameters are extracted. The extraction of these parameters from the measurements involves an optimization using two finite-element computer programs recently developed by the authors for the prediction of the local alignments of LC molecules and the wave propagation within the test cell.The highest values of the dielectric birefringence and the highest values of the loss tangents are recorded for E44 and MDA-00-3506. The loss tangent for all the LCs shows a general downward trend as the frequency increases, which is a useful characteristic in the development of reconfigurable millimeter-wave devices.