Commonly, the frequency of oscillation is measured. The usage of QCM as a sensor can be applied to both gas and liquid phases. We summarize the measured parameters that are most frequently used for different types of applications in Figure 1 below. However, some measurement technique is required to extract this parameter, unlike resonant frequency, which can be estimated by the QCM oscillating frequency (if an oscillator circuit was used). If the attached film is not rigid but viscous, its viscoelasticity property can also be deducted from QCM as a Q-factor. Although other acoustic devices such as a SAW (Surface Acoustic Wave) device or FBAR (Film Bulk Acoustic Resonator) can be used to detect mass, the high Q-factor characteristic of QCM enables the detection of a subtle frequency shift in comparison with those devices even if the device structure and measurement setup are simple. It can detect very slight mass changes, around a nanogram in real-time only using a simple measurement setup. Moreover, not only mass but other parameters are detected by QCM. Its capability to detect the mass makes the acoustic resonator a universal transducer. Since mass is the fundamental property of an analyte, it can be monitored using acoustic devices. The first application of quartz crystal was not a sensor but a resonator, mainly used in communications and oscillator circuits. Lastly, we review some theoretical models to describe QCM behavior with various models.įor more than 40 years, the Quartz Crystal Microbalance (QCM) has been one of the choices amongst many acoustic sensors due to its stability and sensitivity. Furthermore, we describe the experiment on QCM with viscous loading and its interpretation based on the Mason equivalent circuit. Then, we present various existing QCM electronic measurement methods. We show the behavior of QCM with a viscous film based on the acoustic wave equation and Mason equivalent circuit. Then, the conventional equations that govern QCM behaviors in terms of resonant frequency and resistance are described. Next, the theory of QCM is introduced by using piezoelectric stress equations and the Mason equivalent circuit, which explains how the QCM behavior is obtained. Then, we explain some of the recent QCM applications both in gas-phase and liquid-phase. Since a new researcher may seek to understand QCM sensors, we provide an overview of QCM from its fundamental knowledge. At present, this is not an issue, mainly due to the advancement of oscillator circuits and dedicated measurement circuits. Without coating materials, its selectivity and sensitivity are not obtained. However, it is necessary to coat QCM with a sensing film. It has found wide applications in chemical and biosensing fields owing to its high sensitivity, robustness, small sized-design, and ease of integration with electronic measurement systems. It is the most popular and widely used acoustic transducer for sensor applications. Quartz Crystal Microbalance (QCM) is one of the many acoustic transducers.
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