Research On Quartz Crystal Microbalance Based On Spectrum Analysis Method

QCM ( Quartz Crystal Microbalance) is a new type of highly precise micro-mass sensor and is getting more and more attention in biology, medicine, chemistry, environment testing and aeronautics areas for its advantages of higher precision(10^-9), better stability, smaller size and wider working temperature range. At present QCM is usually operated with the oscillator method, however there are some serious limitations associated with the oscillator method: (1) the series resonant frequency is the only parameter; (2) the oscillator does not function in certain situations, such as highly viscous damping. On the other hand, vibration coupling occurs sometimes because of the high frequency complex vibration modes, which will damage the single vibration mode so as to lead to the decrease of the value of Q and cause the resonant frequency away from the true value.This dissertation brings up a spectrum analysis method based on circuit and realizes the experimental platform including software and hardware, which can solve these limitations of the oscillator method. And a new design of the QCM structure based on energy trapping theory and finite element analysis provides a useful methodology to suppress vibration coupling and decrease the vibration energy in the non-electrode area.As the important part of the "Quartz Crystal Microbalance" subject supported by Innovation Fund of China, No. 06C26222200129, the main points of this dissertation can be summarized as follows:1. The background, the research status and the development trend of QCM are systematically reviewed. The theory basis, work theory and realization method of QCM are discussed along with the analysis of the advantages of the spectrum analysis method.2. The vibration theory of QCM is systematically summarized, and the reasons of vibration couplings are analyzed. In the end the methods for suppressing vibration coupling in this dissertation are present.3. Based on energy trapping and finite element analysis, the research has been studied about how the thickness and the radius of the electrode affect the vibration displacement of QCM so as to optimize the design of the electrodes. And a design method with a platform on the surface of the quartz is provided, which can strengthen the energy trapping.4. The six resonant frequencies are deduced based on the equivalent circuit of unperturbed QCM and the variety trend of the spectrum characteristics with the change of the equivalent element parameters is studied. And the equivalent circuit of QCM under mass and liquid loading is discussed based on the analysis of the mechanical impedance, which gives the theory references for circuit design.5. It is one of the top concerns to design a high-quality and steady platform including software and hardware, because the useful signal of QCM is very weak compared with the high frequency output signal. Circuits, electrodes, clamp and the software of DSP and PC have been reasonably designed in this dissertation, which serve as concrete basis for the stable and reliable operation of the system and also the accurate acquisition of the signal. The designs of the QCM vibration drive and the vibration signal collection based on the correlation theory are the most important part of the circuit design, which has applied for two patents and has obtained the new practical patent. No. of the new practical patent is ZL200320124230.6 and no. of the invention patent is 200310112847.0).6. Experiments are conducted for testing the validity of the QCM system. By the verification experiments, the validity of the clamp and the electrodes designs has been proved. And the measurement precision is calculated half-quantificationally with the measurement experiments. In addition, the reasons of the error of the liquid experiments are discussed detailedly and the improving methods are proposed in the end.