Method and a simple apparatus for rapid simultaneous measurement of resonance frequency and Q factor of a quartz crystal

Abstract

The quartz crystal microbalance is finding many novel uses beyond its traditional utility as a thin film deposition controller. In many situations where the quartz crystal is immersed in a viscous fluid, it is desirable to measure the crystal’s Q factor in addition to its resonance frequency. Here, we describe a simple method for simultaneous measurement of the resonance frequency, the quality factor, and the activity or relative amplitude of oscillation of a quartz crystal in vacuum and in gaseous environment. The hardware, comprising of a synthesized sine wave generator and a phase detector, passively interrogates the crystal to determine its resonance frequency and activity. The passive measurement system can detect a resonance even when the crystal is heavily damped. Representative measurement results for an AT-cut quartz crystal in a number of gases at various pressures are presented. The methodology described here may be readily applied to quartz crystals immersed in a liquid.