Research On Microwave Sensor For Microfluidic Electromagnetic Parameter Detection

The microwave measurement technology based on Maxwell's electromagnetic theory has the characteristics of stable test signal,strong anti-interference ability,high test accuracy,non-contact measurement and simple and safe operation.It is widely used in radar detection,communication systems,industrial processing,biomedicine and so on.The core component of microwave measurement technology is microwave sensor,which has the advantages of high precision and high sensitivity as a microwave sensor.The perturbation method is widely used in actual microwave measurement.It can link the resonance frequency with the material parameters of the material to realize the mutual transformation of non-electrical parameters and electrical parameters.In this thesis,the electromagnetic parameters of microfluidic solution in microwave cavity based on perturbation method are studied.The microwave cavity and coupling structure are designed.The microwave cavity solution test system is built,and the solution concentration and microwave cavity are finally obtained.The relationship between the resonant frequencies and the microwave resonator is tested for solution concentration.Firstly,the principle of the perturbation method is elaborated.The relationship between the resonant frequency of the microwave cavity and the dielectric constant of the sample and the cavity parameters is derived by using Maxwell's equations and related vector calculation formulas.The distribution of the electric and magnetic fields obtained is analyzed,and the theoretical calculation formula of the resonant frequency of the resonant cavity and the dielectric constant of the sample is obtained.Secondly,according to the resonant frequency and resonant mode of the cylindrical cavity,the geometric parameters of the cavity are designed.By studying the coupling structure of the cavity,it is determined that the cylindrical cavity uses magnetic coupling based ring in this thesis.The HFSS electromagnetic simulation software is used to optimize the geometric parameters and coupling structure of the designed cavity,which is mainly to optimize the sample tube size,coupling ring radius and coupling structure position at the center of the cavity,and optimize the cavity.A simulation experiment was carried out to load the sample medium,and the relationship between the resonance frequency and the dielectric constant of the sample was obtained.According to the optimized cavity parameters,the cylindrical cavity and the coupling structure are designed and fabricated,and then the solution test system is built to test and analyze the performance of the cylindrical cavity.Finally,the reentrant resonant cavity and the coaxial resonant cavity are designed,and the corresponding solution testing system is built.The two microwave resonators are tested and analyzed.According to the cylindrical cavity parameters,a conductor column is added to form a reentrant cavity;the coaxial cavity is formed by a coaxial line of RG401.By comparing the results of three kinds of microwave sensors on different concentrations of glucose solution,the relationship between resonance frequency and solution concentration was verified,and the measurement of solution concentration by microwave sensor was realized.