Authors: A. Arnau, J.V. García, Y. Jiménez, V. Ferrari, M. Ferrari
Event: 19th International Congress on Acoustics – ICA07. Madrid, september 2-7 (2007)
The classical quartz crystal microbalance (QCM) is no longer only a microbalance; it has got a place as an acoustic sensor in a broad range of applications such as: fluid physical characterization, viscoelastic study of polymers, charge transfer analysis in electrochemical processes, and detection of biological components in fluid media, among other applications. In this paper, the basic operation of an AT cut quartz crystal resonator is extended to the fluid environment. In these applications the resonator is submitted to a heavy load which strongly affects the sensor response, making especially difficult the characterization of the main sensor parameters. The problem associated with the electronic interfaces for sensor characterization is introduced along with a brief reviewing and some recent improvements. After this description, an improved electronic interface is introduced in detail. The design is an interface based on a phase locked loop system which permits an accurate monitoring of the series resonant frequency and the motional resistance of the quartz crystal resonator sensor. A continuous and automatic compensation of the sensor parallel capacitance makes this possible. The report of experimental results shows the benefit of the new system, especially for heavy load QCM applications.
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