Research On Electrically Tunable Terahertz Device Based On Liquid Crystal

Due to the excellent characteristics of high penetrativity,directivity and wide range bandwidth,Terahertz(THz)wave has been applied to the field involving national security,security examination imaging,ultra-high-speed wireless communication,medical instruments,space exploration and so on.Over the past decade,the semiconductor material technology and the micro-processing techrnology are developing rapidly,which have made the progress of the stable THz transmitter and the technology of detector.Therefore,THz wave are increasingly paid attention and related terahertz wave transmission control devices have also been developed rapidly.Liquid crystals(LCs)are one of the most promising materials for constructing tunable devices in the THz regime,thanks to its excellent tunable dielectric properties and wide tuning range.The use of LCs has been proposed as an alternative way for electrically controllable THz devices.In this dissertation,we design,analysis and fabricate some electrically tunable THz devices,and set up a measurement system for testing and analysis for measuring THz transmission devices.The main contributions of this dissertation are described as follow.1.A testing platform was established for measuring the THz transmission devices in order to avoid the interference and inaccuracy for the measurement results.Based on the vector network analyzer,the remote control and measurement system was devised by LabVIEW,which can be used for the reflection,transmission and multi-angle incident measurement of the device.2.An electrically tunable THz phase shifter for reflectarray systems was designed,fabricated and tested.The electromagnetic reflecting characteristics of unit cell with two parallel dipoles of unequal length were simulated and analyzed.The performance of the proposed phase shifter was validated in an array consisting of 30x30 patch elements.The maximum phase shift of 331° is achieved at 330 GHz.For improving the orientation of the liquid crystal layer,a novel electrode was designed for applying bias electric field for liquid crystal phase shifter.3.A tunable LC-based THz metamaterial absorber has presented designed,fabricated and measured in this dissertation.The proposed absorber has been analyzed both numerically and experimentally analysis.In the 4x4 cm2 quartz substrate,a 25x25 structure unit metamaterial absorber has been fabricated.The proposed absorber is measured at F frequency band and the resonant frequency shift from 110.9 GHz to 103.8GHz with the frequency tenability of 6.4%by adjusting of the bias voltage.The absorptivity of the proposed absorber was measured,and it was higher than 90%for all bias voltage.