A Design Of QCM Liquid Detection System Based On Mode Locking And Phase Locking

Quartz Crystal Microbalance(QCM)is a high-precision measuring instrument with the advantages of easy portability and simple structure,and is widely used in biomedicine,high-end chemistry,environmental testing and other related fields.Oscillating circuit method and sweep frequency analysis method are commonly used in QCM for detection.The oscillating circuit method puts the sensor in the frequency selection network,which can detect quickly,but in the liquid environment,the high damping brought by the liquid will cause it to appear mode hopping even the phenomenon of stopping the vibration brings great difficulties to the actual measurement.The sweep frequency analysis method completes the measurement by applying excitation signals of different frequencies to the QCM sensor to measure the impedance,phase and other information,and the sweep frequency analysis method does not need to design the vibration circuit,which avoids vibration stop and mode hopping,but this method requires the use of expensive and bulky equipment,which is mostly used in laboratories.In this paper,on the basis of studying the existing detection methods,combined with the characteristics of phase-locked loop and quartz crystal,a QCM liquid detection scheme based on mode-locked and phase-locked is proposed,and the construction and debugging of the detection system are completed.Finally,the liquid concentration experiments and blood coagulation experiments were used to test the function of the system.The main content of this thesis is as follows:1.Analyze the working principle and corresponding advantages and disadvantages of common QCM measurement methods,the frequency impedance characteristics of quartz crystals,and the working principle of phase-locked loops.And then propose the mode-locked phase-locked detection scheme.At the same time,in order to ensure the scheme can complete the measurement of QCM,based on simulation software such as ADS,the proposed detection system is simulated to verify the feasibility of the scheme.2.Realization of the detection system by functional modules.The frequency source module is built with AD9834,the phase detection module is built with AD8302,and the control processing module is built with STM32.After the hardware system is realized,the frequency control scheme is given and the detection system program is written.3.The no-load experimental test of the system proves that the detection system can lock the resonant frequency of the QCM sensor through the phase information;the liquid detection experiment verifies that the system can be used for the detection of the liquid environment.Compared with the oscillating circuit method,the mode-locked phase-locked QCM detection scheme designed in this paper avoids the situation of mode hopping and vibration stop.And compared with the frequency sweep analysis method using a network analyzer,it has low cost,small size,and easy operation features.