Electrolyte Solution Detection Technique Based On Microwave Resonant Cavity

In recent years,microwave detecting technology has attractedmany people's attention and been widely researchedfor its unique characteristicssuch as non-contact,no injury,no pollution,and fast speed.With the diversification of its application,microwave detecting technology has caused interests in interdisciplinary research.At the same time,electrolyte solution concentration detection is a very normal and necessary job in biochemical field,and the commonly existing methods such as spectrophotometric method,chemical method,chromatography,infrared absorption spectroscopy and optical refractive index method is more or less some deficiencies attached.Under this background this thesis proposesto use the microwave detecting method to determine the concentration of electrolyte solution,mainly using the change of the resonance frequency and quality factorbefore and after the measured liquid is loaded to detect concentration,finally the feasibility of this method are verified through the experimental measurement.This thesis mainly contains the following aspects of research works:1.This thesishas deeply studied the microwave cavity perturbation theory and dielectric constant of electrolyte solution theory,the former one can explain the relationship between the complex dielectric constant and the resonance frequency and quality factor,and thelatter one gives the relationship between the complex dielectric constant and the concentration of electrolyte solution,so the cavity detection of electrolyte solution concentration method can bedeveloped when combiningthe two theories.2.Microwave cavity is a multimode multi-resonant system,but the resonant cavity perturbation method requires the cavity work with a single mode,so the cylindrical cavity's resonant mode and field distribution has been introduceddetailed in this thesis,two kind structureslike TE₀₁₁ mode and TM₀₁₀ mode cylindrical cavities have been chosenas preliminary selections to finish the experimental simulation.The operation mode,the resonance frequency and the structuresize are all determined by the cavity's work mode pattern,the HFSS software is used to optimize the coupling structure to find the best coupling condition,and the resonant frequency shifts when the measured dielectric permittivity changes has been simulated.By comparing the two kinds of the cavity structure's complexity and processing cost finally the optimized TM₀₁₀ modestructureis sent to the professional microwave instrument manufacturer for processing.3.The network analyzer?NA?can be used to measure the related parameters of the cavity,in order to improve efficiency and reduce the disturbance of human activity,a network automatic control programbased on LabVIEW platform is proposed in this thesis,data transmission realizes through GPIB interface.Experiments show that the program can greatly improve the efficiency of the measurement,and is capable for complicated measurement which is time-consuming and timing-necessary.4.Finally a typical electrolyte solution:NaCl ischosento finish the measurement,a series of data operations such as statistical analysis,theory comparison and data correction are operated and the errors caused byexperimental theory error,temperature and machining precision are analyzed.After allthe conclusion thatusing microwave resonator to measure the concentration of electrolyte solution is an effective and feasible way isverified.