Uniformization of QCM’s Mass Sensitivity Distribution by Optimizing its Metal Electrode Configurations

The quartz crystal microbalance (QCM) is an ultra-sensitive measuring device and has been commonly used in many specific applications. The mass sensitivity distribution curve of m-m type QCM (QCM with symmetrical electrode) is a Gaussian distribution. However, achieving highly accurate and repeatable measurements requires the uniform distribution of mass sensitivity. To improve the uniformity of QCM mass sensitivity while ensuring high absolute mass sensitivity, the double-ring electrode geometry is designed. This study improves the size design of the double-ring electrode, and reveals the rules for varying sensitivity and electrode parameters based on a mathematical model. Through analyzing the mass sensitivity distribution of different electrode structures of QCMs, the uniformity of the double-ring electrode QCM is proved. The effects of mass sensitivity distribution of QCM are studied using the finite element method (FEM) by the variation of the size of electrodes, and an optimal size of electrode was discovered. Our results show that the double-ring type QCM has better uniformity of the mass sensitivity distribution and it can maintain the high mass sensitivity when the size of the inner ring of the double-ring electrode is close to half of the size of the outer ring. Meanwhile, there is an optimal outer radius that enables us to obtain an ideal and desirable displacement distribution. The numerical simulation results provide design ideas for the physical design of the double-ring type QCM.