同時解析分子質量與液相阻尼之相位補償式石英微質量天平

Phase compensated Quartz Crystal Microbalance for Simultaneous Measurement of Bio-mass loading and liquid damping

陳俊光(Chun-Kuang Chen)

指導教授 ： 李世光

國立臺灣大學/工學院/應用力學研究所/博士(2007年)

https://doi.org/10.6342/NTU.2007.00363

摘要

石英微質量天平在液相中應用時，面臨到Q值大幅下降以致影響振盪頻率穩定度，以及電容效應導致相位零點的振盪條件消失，所以本論文乃針對此兩大難題提出相位補償式的石英振盪電路以茲解決。
本研究從石英的基本特性分析切入，並從現有的理論模型得知，其理論所依據的參考頻率為串聯諧振頻率，然一般振盪電路其回授振盪乃是操作在相位零點的諧振頻率，而當石英在高阻尼的流體環境時，此兩頻率的差異也就越大，因此一般振盪電路所量測到的頻率與理論值也就存在更大的誤差，容易造成在生物質量分析上的誤判，所以本論文提出以負電容的方式以消除石英的並聯電容值，使其振盪頻率能夠準確地操作在串聯諧振頻率，使石英微質量天平在生物的量測應用中得到更精準地分析。
本論文從各種振盪電路的分析研究中，提出創新式的橋式振盪電路，使其振盪電路能夠具有額外的環路Q值增益，並且維持石英端的電壓恆定，使其整體振盪頻率的穩定度提升。
新的相位補償式振盪電路，除了可以修正在液相中振盪相位所產生的頻率誤差, 更可透過控制得知石英在液相中所受到的電容值之變化與阻尼狀況，因此本論文所開發的相位補償式石英微質量天平，可量測的參數除了頻率之外，還有電容值與阻尼值可提供生物應用時的分析，因此具有同時解析分子質量與液相阻尼之功能，故對於生物研究可以進一步了解其構形變化與力學特性。

關鍵字

石英 ； 微質量天平 ； Q值 ； 負導抗 ； 振盪電路 ； 構形變化

並列摘要

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.

並列關鍵字

Quartz ； Mirco Balance ； Quality Factor ； Negative Immittance ； Oscillator Circuit ； Conformation Change

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