System Of Integrated LC Passive Wireless Sensor For Microfluidic Droplet Characterization

Microdroplets are widely used in multiphase system,analytical chemistry,molecular biology,digital PCR and single-cell analysis.Therefore,the rapid and accurate detection of droplet generation rate,size and quantity has drawn more and more attention recently.Existing droplet detection technique are limited by their low portability and high cost,which limit their application scenarios in harsh environments,such as confined spaces,mechanical rotating structures,and high temperature and pressure environments.Therefore,a droplet characterization method based on LC(inductor-capacitor)passive wireless sensor was proposed in this thesis,and a microfluidic droplet characterization chip and its integrated system based on LC passive wireless sensor was designed to achieve wide detection dynamic range and high system integration of droplet characterization in order to ensure high-repeatability detection.The main research contents include:1.A theoretical model of droplet characterization was proposed.In the model,the parallel plate capacitor in an LC resonant circuit was used as the capacitance sensing unit,and a full range of droplet characterization from spherical shape to flat shape was realized in the center of the dielectric layer of the parallel plate capacitor.When the droplet passes through the capacitor insulating dielectric layer,the dielectric constant of the capacitor insulating dielectric layer changes,causing the variation of capacitance value of the flat capacitor,and thus leading to the change of the resonant frequency of the LC resonant circuit.The relationship between the resonant frequency variation and the droplet volume was established by the equivalent capacitance method to characterize the droplet volume variation.The calculation formula of droplet generation velocity was established by using the starting time difference of resonant frequency variation.2.An integrated LC passive wireless microfluidic droplet characterization chip was designed and fabricated,and features droplet generation microfluidic structure and LC resonant circuit structure.Spherical-,drum-and flat-shaped droplets were produced in the droplet generation microfluidic structure by controlling the flow rates.The resonant frequency of LC resonant circuit was detected by means of near field coupling between inductor coil and readout coil.In addition,a rapid and efficient method was proposed to fabricate the capatcitor and inductor in the microfluidic chip,in which liquid conductive material was injected into the microchannels to form the LC resonant circuit.3.Finite element modeling and simulation of droplet generation and droplet characterization was completed.In the finite element simulation study of droplet generation,three different shapes of droplets,i.e.,spherical,drum and flat shapes,were generated by controlling the velocity ratio of two-phase flow,and a 3D finite element model was established to characterize the droplet in the finite element simulation study.In the finite element simulation of droplet characterization,the curvilinear relationship between the volume of spherical,drum and flat droplet and the change value of the resonant frequency of LC resonant circuit is firstly fitted.The rationality of the approximate calculation formula of droplet formation velocity was verified.4.A full range measurement of droplets in the center of the dielectric layer of the parallel plate capacitor from spherical shape to flat shape was realized.In the experiment,three different shapes of droplets,i.e.,spherical,drum and flat shapes,were successfully generated.The dynamic range of droplet size characterization reached3.814?58.722 n L,and the resolution reached 0.260 nL.