The Theoretical Analysis And Test Verification Of QCM Detection In Liquid Phase

QCM sensor technology is a new detection technology, it can do the specific high precision detection combined with the biological, chemical and physical technology. In 1980 s, QCM began to be used in liquid detection, but it has encountered great obstacles in theoretical modeling and practical tests, such as the QCM will stop vibrating in liquids, nonlinear modeling is difficult to achieve, test results have large deviation compared with the theoretical results and so on, which attracts a large number of scholars at home and abroad to do the related research.Now, when QCM is used for liquid detection, since its structural characteristics may lead to different vibration in different areas, the inconsistent between displacement and potential of the particle will increase the difficulty in theoretical modeling. It also makes the uneven distribution of the quality sensitivity, which may lead the low duplication during the detection process, then affects the accuracy of detection. In addition, since the classical liquid detection theory doesn’t considered the effects of the quality layer on the QCM in the theoretical modeling, the liquid detection results always have larger deviation. The existence of these problems seriously limit the application of QCM in practical research.Aiming at these problems, this paper deeply studied the QCM liquid phase detection mechanism and put forward the corresponding improvement measures for each problem. The main work of this paper is:1.From the point of constitutive equation of quartz crystal, we have deduced the vibration equation of QCM, and analyzed the electrode area, part of the electrode area and the non-electrode area specifically, revealed that although the particles of each region have displacement equation, but it can formally use a unified expression, and just need to determine the parameters according to different regions. The expressions of the displacement and the QCM surface potentials were normalized.2.Deeply analysed the quality detection principle of QCM and mass sensitivity, point out that we can analyze the mass sensitivity on the base of the amplitude of particle displacement on the surface of QCM. The distribution of mass sensitivity of the QCM was similar to Gauss, and the distribution is extremely uneven. The mass sensitivity has higher sensitivity only near the electrode center. Aiming at these problems, this paper has designed a new probe, which greatly improved the consistency of the distribution of mass sensitivity. Then achieved the reproducible measurement of QCM in a certain extent, and improved the accuracy of the test results.3.Since the traditional liquid phase detection theory didn’t considered the influence of the liquid flexible adsorption on QCM vibration, we add a mass layer during the theoretical modeling progress to make up the loss, and on the basis of the existing theory, the modified BVD equivalent circuit model is deduced in detail, then put forward the test method for the viscosity and density of the unknown solution.4.Made the analysis of viscosity and density test of the water and alcohol, verified the accuracy of the modified BVD equivalent circuit model, and made a comparative with the traditional theory. During the test progress, the S parameter was obtained using the network analyzer and then translated it into admittance spectrum. Meanwhile, the frequency offset was also measured. Combined these two parameters, we can get the half frequency. Finally, according to the theoretical formula, we calculated out the viscosity and density of the solution.