Phase compensated Quartz Crystal Microbalance for Simultaneous Measurement of Bio-mass loading and liquid damping
Date Issued
2007
Date
2007
Author(s)
Chen, Chun-Kuang
DOI
zh-TW
Abstract
The application of Quartz Crystal Microbalance (QCM) in the liquid phase condition usually subjected to two major problems. The first one is the extra damping in liquid phase that causes the mechanical quality factor drop to a level that may induce unstable oscillation frequency. The second one is the self oscillation zero phase condition will be lost due to the shunt capacitance effect. In this study, a novel phase compensated quartz crystal oscillation circuit is proposed and will try to resolve these problems.
According to the traditional theoretical analysis, the prediction of frequency change is done by using the series resonance frequency as a reference. However, the general oscillation circuit is designed and operated at the actual resonance frequency condition. The difference between the two above-mentioned frequencies became even larger in the high damping liquid environment, and will lead to errors on bio-medical samples measurement. To hold self oscillation operated on the series resonance frequency accurately, a negative capacitance compensation circuit is proposed to cancel out the shut capacitance of the quartz crystal. It was shown that the simple self oscillation circuit will lead to accurate series resonant frequency oscillation no matter it is in liquid phase or not. The experimental result of the impedance analysis shows that the method is successful and work well to stabilize the oscillation and eliminate the measurement errors in liquid phase. A new bridge oscillation circuit to enhance the circuit loop quality factor and to sustain the constant voltage cross the quartz was also developed in this study. It also helps to further stabilize the oscillation in liquid phase.
The new compensated oscillation circuit not only fix the phase error in the liquid phase, but also can be used to get the capacitance and damping values by using a control loop design. With all these developmnets, not only the bio-mass loading but also the damping coefficient can be measured on the circuit simultaneously. With the improved stability and precision on the new QCM system, it will be shown that protein conformation changes and bio-mechanisms can then be examined.
Subjects
石英
微質量天平
Q值
負導抗
振盪電路
構形變化
Quartz
Mirco Balance
Quality Factor
Negative Immittance
Oscillator Circuit
Conformation Change
Type
thesis