Megahertz characteristics of thick film PZT resonators for gas sensing applications

Research in sensors for toxic and flammable gas detection is an increasing activity. A reliable gas sensor should be sensitive, selective and stable. A low cost ultrasonic gas sensor using a quartz resonator as ultrasound generator was developed and compared red its resonant characteristics with a thick film piezoelectric PZT ceramic resonator. PZT resonators were sere en printed using inks formulated in CITEI. The sensor is based on ultrasonic resonance of gas flowing through a cell. A piezoelectric resonator generates ultrasonic waves within a cell cavity. Stationary waves an established when distance between a vibrating surface and the opposite parallel reflecting wall is an integer multiple of half vibration wavelength of the oscillator. The compound oscillator is formed by the vibrating surface and surrounding gas. For this purpose, the electromechanical behavior in thickness mode must be adequate to use a simple electronic oscillator with the PZT thick film ceramic resonator. The impedance characteristic of such device presents a high capacitance to low inductance transition: near resonance, which is inadequate to get stable oscillation in its thickness resonance mode. Some ways to overcome this situation are studied.