Detecting Spurious Modes in Quartz Plates by Measuring Surface Charges

In this paper, we describe a method for detecting weak spurious modes in quartz plates. This method picks up the weak modes by measuring the frequency characteristics of high-frequency charge voltages, which are excited at resonant frequencies, at many points on the plate surface. The measured results for two strip AT-cut quartz resonators show that this method can detect very small resonance modes undetectable by conventional methods.