Quartz crystal microbalance sensor for NH3 gas with compensation of humidity drift

Abstract

A quartz crystal microbalance (QCM) sensor coated with a sensing film has been studied as a gas-sensing device with high gas selectivity and high sensor sensitivity. One of the problems to be solved for practical applications is that the resonant frequency of a QCM sensor drifts due to the influence of humidity. We investigated a method for compensating the humidity drift of a QCM sensor for NH3 gas by using an element coated with a reference film that was prepared by modifying the phosphate group of zirconium phosphate in the sensing film with sodium hydroxide. The response characteristics of the reference element were measured. The results showed good agreement with the humidity response of the sensor element when not responding to ammonia gas. It was found that compensation of the humidity drift was successfully accomplished by calculating the frequency difference between the sensor element and the reference element. An application to small QCM (1.3 × 0.9 mm) is also presented.