| Oil pollution is one of the important factors of equipment failure.The micron-sized particle contaminants in the oil contain rich tribological information and corrosion information of equipment,which reflects the running condition and the fault conditions of equipment.The rapid,accurate detection technology for contaminants in oil can not only diagnose the fault location of the system,but also monitor the condition and forecast the working life of mechanical equipment.It is of great significance for modern fault diagnosis and prediction theory based on information fusion.Based on the National Natural Science Foundation of China,this thesis presents a multi-parameter micro-impedance analysis method on microfluidic chip.Distinguished detection of ferromagnetic metal particles,non-ferromagnetic metal particles and non-metallic particles in oil can be obtained by common detection and analysis of multiple parameters through a single micro-impedance chip.The main research contents and conclusions are as follows:(1)The mechanism of the impedance change caused by metal particles and non-metal particles has been analyzed.For the metal particles,the Maxwell equations are firstly used to calculate the change of the magnetic vector potential in the whole space,which caused by the spherical particles magnetized by the harmonic magnetic field;and then combined with the magnetic field distribution generated by the coil excited by harmonic source.Finally,a inductance change formula of single coil caused by metal particles at any position is obtained,and the ferromagnetic and non-ferromagnetic metal particles can be distinguished through the direction of the inductance change.While for non-metallic particles,the complex permittivity model of the particle-oil mixture is studied in a parallel plate capacitor excited by a harmonic source.Which reveals the root cause of the change in capacitance,and the non-metallic particles can be distinguished by the direction of the inductance change.(2)Based on the mechanism of impedance change caused by particles,a multi-parameter micro-impedance analysis method is proposed.A solenoid coil chip and a planar coil chip based on dual-coil structure are designed,which both have two modes of inductance detection and capacitance detection.The inductance principle is analyzed in terms of the structure of the dual-coil.Firstly,the calculation formula about self-inductance of the coil and the mutual inductance of the two coils are deduced.Then,combined with the inductance change of the single coil caused by the particles in the metal particle magnetization model,the equivalent inductance formula of the double coil caused by the metal particles in harmonic magnetic field and space arbitrary position is obtained.For the principle of capacitance detection,two single-layer coils are equivalent to a pair of circular capacitor plates for reasonable simplification.The Schwarz-Christoffel transform is applied to obtain the capacitance calculation formula involving edge effect of capacitor.Together with the complex permittivity model about the mixture of non-metallic particles and oil,the expression formula of complex capacitance change caused by particles is finally obtained.After comparing and analyzing the theoretical detection capabilities of the two micro-impedance chips,it is concluded that the detection sensitivity of the solenoid coil chip is higher than that of the planar coil chip.(3)Experimental studies on the solenoid coil chip and planar coil chip were carried out.According to the influencing factors of inductance detection in the theoretical analysis,the inductance experiment about the excitation frequency and the coil turns was first carried out on the solenoid coil chip,and the parameters are optimized based on the theoretical analysis.Making use of the optimal parameters through different particle size of the metal particles to calibrate the inductance amplitude of the two types of chips.As the floor level of inductance detection,the solenoid coil chip could detect 40?m iron particles and 110?m copper particles;the planar coil chip could detect 80?m iron particles and 150?m copper particles.According to the influencing factors of the capacitance detection in the theoretical analysis,the detection experiments were also carried out from the two aspects of excitation frequency and coil turns,and these two parameters were optimized in the theoretical analysis.Then using different diameters of water droplets and bubbles to calibrate the capacitance amplitude of the two types of chips by optimal parameters.As the floor level of capacitance detection,the solenoid coil chip can detect 110?m water droplets and 180?m air bubbles;the planar coil chip can detect 180?m water droplets and 240?m air bubbles.(4)Based on the characteristics of the two detection chips,the studies were conducted to optimize sensitivity and throughput of the chips.Sensitivity optimization based on the principle of core enhanced magnetic field is introduced.Firstly,the micro-impedance chips with iron core were designed and fabricated according to the previous two kinds of chips;electromagnetic field simulation about two kinds of chips with iron core was carried out by COMSOL software,and the mechanism of improving sensitivity was analyzed;then the relevant experiments were carried out to analyze and theoretically verify the detection effect of the chips.The floor level of chips was enhanced,the planar coil chip with iron core could detect 33?m iron particles,90?m copper particles,100?m water droplets and 180?m air bubbles;the solenoid coil chip could detect 18?m iron particles and 75?m copper particles,but the detection limit of the capacitor did not change.The second was based on the sensitivity optimization of LC resonance principle.A dual-coil micro-impedance chip with a LC oscillation circuit was proposed,and the detection mechanism was analyzed.Combined with the experiment,the frequency characteristics of the chip were comprehensively analyzed,and the optimal detection frequency of iron particles and copper particles was obtained.10?m iron particles and 50?m copper particles were successfully detected at the optimum excitation frequency.In order to solve the problem of low throughput of microfluidic chip,combined with the detection characteristics of inductance and capacitance methods,the microchannel structure of chip was changed.A circular ring cross-area microchannel was designed to increase the theoretical flux by 8 times without reducing the sensitivity of detection. |
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