Design And Implementation Of Test Circuit For QCM Liquid-phase Detection

Since its birth,quartz crystal microbalance(QCM)has attracted extensive attention because of its high sensitivity and high accuracy.At present,the detection of QCM is mainly realized by oscillation circuit.The circuit structure of this implementation method is simple and the cost is low,and it is often used in various QCM application research.However,the phenomenon of vibration stop often occurs in large damping liquid.In order to avoid great influence on the measurement results,the laboratory network analyzer can be used for measurement under the condition of large damping,but it has the disadvantages of large volume,high cost,etc.Therefore,this thesis proposes a passive test method based on sweep frequency method.According to this method,a QCM test circuit is designed.The test circuit uses a sweep frequency source to scan the frequency near the resonant frequency of the QCM,and then directly samples and calculates the voltage amplitude of the signals to be measured at both ends of the QCM.Finally,the QCM test circuit was verified by glycerol solution test and fibrinogen thrombin mixed process test.The test system designed based on the sweep frequency passive test method proposed in this thesis will not stop vibration under the condition of large damping,and has a simple structure,which can realize miniaturization integration.The main work of this thesis is as follows:1.A method to correct the resistance frequency effect is proposed.The QCM is simulated according to the electrical equivalent model of the QCM.By analyzing the influence of parameter changes in the equivalent model on the QCM,a specific method to correct the resistance frequency effect is designed.2.The design of sweep frequency source and mixer circuit of the test circuit.The sweep frequency source in this thesis is realized by Si5351 clock signal generator.The frequency mixing circuit mixes the response signals at both ends of the QCM to the k Hz level,so the voltage acquisition circuit can meet the design requirements by using the ADC chip with low sampling rate.3.Data acquisition and control circuit design of test circuit.The data acquisition circuit in this thesis is realized by audio codec chip.The voltage signal is collected by audio sampling rate,and the controller calculates the voltage sampling signal by FFT,so as to calculate the amplitude information of signals at both ends of QCM.4.Using the test circuit designed and realized in this thesis,the test system is built,and the fluctuation of the detection frequency of the test circuit is tested.In this thesis,we designed two liquid phase detection experiments,the experiment pair of different concentrations of glycerol detection experiment,experiment two for the fibrinogen thrombin experiment.The performance of QCM liquid test circuit and its feasibility for liquid test and thrombin test were verified.According to the proposed passive test method based on sweep frequency method,this thesis designs a QCM test circuit which has the advantages of simple structure and miniaturization integration without vibration stop under the condition of large damping,and verifies the index and feasibility of the test circuit through experiments.Compared with the measurement methods based on oscillation circuit and network analyzer,the test circuit based on sweep frequency method in this thesis has lower cost,is conducive to integration,and has a good prospect.