Digital ammonia gas sensor based on quartz resonator tuned by interdigital electrode coated with polyaniline film

摘要

This paper reported an ammonia gas sensor which was constructed by an interdigital electrode (IDE) coated with PANI thin film connected to quartz resonator in series. The sensor could convert concentration change of ammonia into frequency shift of the quartz resonator through the frequency tuning effect of IDE. Test result showed that the digital ammonia gas sensor exhibited a large frequency shift approximately 1500 Hz in ammonia concentration range of 20-1200 ppm, namely the proposed sensor showed higher frequency change compared with the majority of QCM ammonia sensors. The experiment suggested that the resistance of IDE coated with PANI film increased and meanwhile its capacitance decreased with increasing of ammonia gas concentration. Simulation on Butterworth-van Dyke (BVD) circuit of the sensor revealed that the capacitance of IDE coated with PANI played a major role in tuning of the quartz resonator although the capacitance changed little, while the resistance tuning effect was relatively weak. Compared with the traditional QCM gas sensors, the proposed sensor had a very fast response speed and a good anti-interference ability to pollutants and electromagnetic fields due to encapsulation of quartz crystal.