Broadband spike excitation method for in-liquid QCM sensors

A Quartz Crystal Microbalance (QCM) is a highly sensitive device based on the measurement of the resonance parameters of a thickness-shear piezoelectric resonator, which classical application is the detection of attached mass per unit area. Although the most economical ways of driving these sensors make use of oscillator circuits, other electronic interfaces are also well-established, i.e., electrical impedance analysis and impulse excitation/decay methods. Impulse excitation and decay methods are founded on the same principle, but in practice only the latter has been exploited. The present work explores the suitability of a broadband spike excitation technique (up to 0.25 GHz) as an interface electronic system for QCM sensors. The principles of measurement—including the processing of signals—are described in detail and illustrated for liquids with different mechanical shear impedances. The proposed mode of operation has proved some advantageous characteristics: both resonant frequency and energy dissipation can be simultaneously determined in a wide range of frequencies; it is appropriate for in-liquid sensing applications (including highly viscous liquids); it can be easily automated for continuous monitoring and integrated with other external circuitry (such as multiplexing for sensor arrays).