Study on the behavior of oscillation circuit for QCM gas sensor

Abstract

A quartz resonator with its electrode coated with sensing film is used as gas sensor and its output is resonance frequency shift due to mass loading effect. It is possible to measure frequency shift by impedance analyzer. However, the method to measure the shift using oscillation circuit is more often used for simplicity. The oscillation frequency shift deviates from that of resonance frequency due to dependency of active impedance upon its load change when viscoelastic effect accompanied with film coating of vapor sorption occurs. Then we established analysis method of oscillation frequency shift, taking dependency of active impedance upon change of load into account. Furthermore, we determined the condition of load parameters within which oscillation frequency shift agrees with resonance frequency one.