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Study On The Permittivity Measurement Of Lubricant Based On Quartz Crystal Microbalance

Posted on:2019-02-22Degree:MasterType:Thesis
Country:ChinaCandidate:C L LiuFull Text:PDF
GTID:2428330596461343Subject:Instrumentation engineering
Abstract/Summary:PDF Full Text Request
The quality of oil is an important factor that affects the performance of the engine.The permittivity of oil is the key factor to measure the quality of oil.The detection method of permittivity is insensitive and cannot be monitored in real time.Therefore,a sensor with high sensitivity and real-time monitoring is urgently needed.Quartz crystal microbalance(QCM)is a high-precision resonant sensor,which is widely used as biosensor and chemical sensor because of its high accuracy,sensitivity and low cost.The traditional QCM with its electrodes located on both sides of crystal is based on thickness field excitation and it's mainly used to detect trace mass.The lateral field excited QCM with its electrodes located on the same side can be used for detection of liquid permertivity and conductivity because the electric field can enter the liquid.In this paper,the basic characteristics of quartz crystal are firstly elaborated in detail.Based on vibration theory,the equation of QCM mass effection is deduced and the mechanism of QCM for detecting trace mass is explained.The mechanism of the measurement of QCM in the liquid and its equivalent circuit are analyzed.The theoretical relationship between the water content of the oil and the permertivity is analyzed,and the feasibility of using quartz crystal microbalance to detect the permertivity of the oil is ensured.Through theoretical analysis,it is found that the frequency response of LFE-QCM is influenced by the mechanical and electrical properties of the liquid.Therefore,a LFE-QCM structure with dual resonantor is put forward.A reference resonantor is designed to eliminate the influence of liquid mechanical characteristics and ambient temperature.The LFE-QCM chip is made by MEMS process.The structure of flow cell is designed to load the LFE-QCM chip,and a set of high precision testing system is formed with the flow injection technology.Multiple LFE-QCM chips with different sizes carry out many groups of experiments.The Q value in air and warter is over thirty thousand and one thousand,which indicates the frequency stability of the chip.The tests in organic solution have proved the theory of structure design.And they also verify the relationship between frequency shift and permertivity.Through some tests that different types of floating electrodes and different widths of gap are compared,they provide reference for the optimization of LFE-QCM.Based on the analysis of experimental data,a permittivity circuit model of LFE-QCM in liquid is proposed.Finally,the feasibility of measuring the permertivity of the oil by LFE-QCM is determined through the experiment of the water content of the lubricating oil.
Keywords/Search Tags:quartz crystal microbalance, lateral field excitation, permittivity, dual resonantor, flow injection
PDF Full Text Request
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