Piezoelectric Sensor Signal-to-noise Ratio Data Research And Application Of New Methods

Frequency measurement is very important in the applications of piezoelectric sensors. Oscillation circuit and impedance analyzer are the two main ways for the frequency measurements of the piezoelectric sensors. Advance impedance analyzer is employed in the impedance analysis method, which can provide multi-dimension information for the piezoelectric sensors. Quartz crystal microbalance (QCM) is the most important piezoelectric sensor. However, the impedance analyzers made by Agilent Co. are not specially designed for QCM. Agilent Co. does not provide software for data treatment for QCM. It is difficult to use the impedance for continuous QCM measurements. In addition, the noise level of the impedance analyzer is quite large. In this dissertation, the data treatment methods that can improve the signal-to-noise ratio of the QCM was edited in the software for communication between the impedance analyzer and computer. The main works were given below.1) Based on the equivalent circuit model of the QCM, the resonant frequency of the QCM was theoretically derived. The relationship between the resonant frequency and the center and span of the conductance peak at a given height was discussed. The averaged resonant frequencies were proposed and measured in an impedance scan. The influence of the peak height for measurement on the value and noise level of the resonant frequency was tested. By using the averaged resonant frequency from 100 height at the conductance peak, the signal-to-noise ratio of the QCM can increase 6 times. This is a simple and efficient way to decrease the random noise during the QCM measurement. The proposed method was applied to the data treatment for QCM in the adsorption experiment. In the adsorption experiment, a polystyrene film was prepared on the surface of the QCM. The adsorbed mass changes during the adsorption of a cationic surfactant, CPC, on the polystyrene film were monitored in real time by the QCM. The adsorption rate constant and adsorption equilibrium constant were estimated from the frequency shifts of the QCM. The influence of the ionic strength on the adsorption of CPC was tested.2) According to the phase-frequency spectra of the QCM, the theoretical expression...