Analysis of the Radial Dependence of Mass Sensitivity for Modified-Electrode Quartz Crystal Resonators

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• 作者：Fabien Josse and ; Youbok Lee ; Stephen J. Martin ; and Richard W. Cernosek
• 刊名：Analytical Chemistry
• 出版年：1998
• 出版时间：January 15, 1998
• 年：1998
• 卷：70
• 期：2
• 页码：237 - 247
• 全文大小：133K
• 年卷期：v.70,no.2(January 15, 1998)
• ISSN：1520-6882

文摘

The radial dependence of mass sensitivity of the sensingsurface is analytically calculated for two examples of"modified-electrode" quartz crystal resonators (QCR).Theterm "modified-electrode" QCR is used here withrespectto the conventional QCR which has two identical circularand concentric electrodes. For these QCRs, thesensingsurface is divided into a fully electroded, a partiallyelectroded, and an unelectroded region, and the efficiencyof each region is evaluated in terms of the electrode massloading factor. Such QCRs are typically investigatedforsensor applications in which the electrical properties ofthe liquid load or the coating deposited on the sensingsurface (electroded and partially electroded regions) arebeing measured in addition to mass loading. Whilemodified-electrode QCRs can be viewed as a simplecapacitance sensor in those applications, the use of apiezoelectric crystal resonator in the narrow range offrequencies near resonance and antiresonance allows fora direct measurement of the capacitance through theantiresonant frequency, provided that the device damping(motional resistance) is not too high or that theresonancequality factor, Q, is high enough for a stablevibrationunder the load. It is shown that, for some values oftheelectrode mass loading factor, the off-electrodeefficiency(partially electroded and unelectroded region efficiency)can still have a significant contribution to the overallsurface area mass sensitivity. Knowledge of theefficiencies is needed to determine the loading area required forstable QCR sensor operation. This is becauseadditionaldissipation of energy into the load can occur, especiallyfor cases where the sample load extends to the unelectroded surface, which has a nonnegligible particle displacement amplitude. It is also shown that, for someapplications involving a liquid load and for some valuesof the electrode thickness, the shear particledisplacementprofile is such that compressional wave generation cancontribute significantly to device damping, thus makingthe device unstable. Experimental measurements of themass sensitivity profile on the surface are also performedfor those QCRs and compared to theory.