Design And Implementation Of Quartz Crystal Microbalance Array System Based On Quadrature Demodulation

Quartz crystal microbalance(QCM),as a device to measure little mass change with high sensitivity to nanogram,has been widely applied in the fields of microchemistry,molecular biology,environmental science etc.for its advantages of simple structure,high stability and fast response.The QCM instrument develops very rapidly and has experienced from the early ordinary quartz crystal microbalance to flowing quartz crystal microbalance,the quartz crystal microbalance with dissipation(QCM_D)and quartz crystal microbalance array.Compared with other types of QCM,quartz crystal microbalance array can greatly improve the detection efficiency for its advantages of detecting multiple samples at the same time.Quartz crystal microbalance array is consistent with the development trend of the sensor array,and it is a new direction for the development of QCM instrument.In this paper,we design and implement a system of quartz crystal microbalance array based on the principle of quadrature demodulation.The system can connect up to 6 channels at most,and the resonance frequency and dissipation factor can be measured simultaneously.Multichannel time sharing measurement method is adopted in this system,and the maximum measurement speed of each channel is 15 data points per second.To improve the measurement speed and precision of the dissipation factor,a novel method is put forward to measure the dissipation factor by using the phase information of the quartz crystal,by which fast measurement of dissipation factor can be realized.In order to obtain the phase information,it is necessary to compensate the static capacitance.Therefore,a static capacitance compensation circuit based on the principle of quadrature demodulation is designed to realize the automatic compensation of the static capacitance.The process of data acquisition,storage and processing is controlled by a host computer.The host computer communicates with the slave computer through USB interface.The control interface and data storage program of the host computer are developed with LabVIEW.The host computer can simultaneously collect the data from 6 channels,and real-time display the resonance frequency and dissipation factor.In order to test the performance of the system,following tests are carried out:(1)The stability of the system is tested in air and in water,which shows that the system frequency drift is within ±2Hz in 5 minutes.(2)The effectiveness of the system is verified by the experiments of ethanol volatile and rosin quality measurement.The measurement error is within 2% compared with the theoretical value,and the causes of the error are analyzed.(3)The high efficiency of the QCM array is verified through the test of various concentrations of glycerol aqueous.The measurement process of twelve concentrations of glycerol aqueous solution is completed with only two sets of experiments.The experimental results are consistent with the well-known Kanazawa-Gordon equation.