Design And Research Of Liquid Crystal Dielectric Parameter Measurement And Test System

From the discovery and naming of liquid crystal materials,liquid crystals are intermediate phases between a solid phase and a liquid phase,which have some characteristics such as fluidity of liquid and anisotropy of crystal.Liquid crystal materials have many unique physical properties,including dielectric anisotropy,birefringence,and liquid crystal molecules having dielectrically tunable size for electric and magnetic fields.In addition to exhibiting excellent photoelectric characteristics as a display field.liquid crystals are also used to form a series of liquid crystal microwave devices such as liquid crystal phase shifters,liquid crystal reconfigurable antennas,delay lines,and liquid crystal filters.All of these applications are inseparable from the dielectric properties of liquid crystal materials,so studying the dielectric properties of liquid crystal materials in the microwave field has always been a major issue.This paper first introduces the physical properties of liquid crystal materials and the theory related to microwave measurement,including the basic theory of measurement and the theory related to transmission line.Then,three different methods are used to measure the dielectric constant of liquid crystal and the corresponding testing system is built.Due to the unique properties of liquid crystal materials,which can be tuned by dielectric parameters in the applied electric field and magnetic field,we tested the liquid crystal materials and applied magnetic field to the liquid crystal by ridgeland-waveguide cavity resonance perturbation method respectively.By changing the size of the static magnetic field and the direction to tuning,LCD liquid crystal molecules under the action of magnetic field deflects,we through the ridge waveguide cavity under the odd mode TE direction of electric field and pointing in the direction vector of the relationship between liquid crystal molecules,respectively to measure the liquid crystal molecules dielectric parameters under two kinds of limit state,and liquid crystal material anisotropy value is calculated.Then,we and microstrip resonant method is used to test the LCD and tuned by voltage,liquid crystal molecules will deflect as the size of the applied voltage,the equivalent dielectric constant of the LCD and change through HFSS simulation and specific experimental results fit the LCD of the relationship between dielectric constant and the voltage of liquid crystal dielectric parameters testing system is established.Finally,by using coaxial terminal open circuit method to test the dielectric constant of liquid crystal,a suitable coaxial probe was designed to test the dielectric constant of several liquid crystal materials under normal conditions.Each of the three systems has its own advantages and disadvantages.The ridgeline waveguide method requires that the sample is cylindrical and cannot be applied with electrodes,so it cannot be charged for testing,and this method is more convenient to apply magnetic field.In order to test the dielectric anisotropy of liquid crystal,it is necessary to conduct orientation treatment for liquid crystal molecules first,and give a predip Angle so that all liquid crystal molecules will turn in the same direction under the action of electric field,and the liquid crystal molecules will return to the original state when the electric field disappears.In this case,the microstrip resonance method can meet the above requirements.Coaxial terminal open circuit method has many advantages such as continuous measurability of bandwidth and simple measurement procedure.In this paper,various liquid crystal dielectric constant testing systems are set up under the conditions of testing theory and hardware to test the liquid crystal materials.After obtaining the test results,error analysis is required to verify the accuracy of the measurement results.