Ultrasonic PZT gas sensor using thick film technology

A new low cost ultrasonic gas sensor for human environment pollution monitoring was developed using a thick film piezoelectric PZT ceramic resonator. The working principle of this kind of sensor is based on ultrasonic resonance of gas flowing through a cell. A PZT piezoelectric ceramic resonator generates ultrasonic waves within the cell cavity. Stationary waves are generated if distance between a vibrating surface and the opposite parallel reflecting wall, is an integer multiple of half vibration wavelength of the compound oscillator, formed by the vibrating surface and surrounding gas. In this way, resonance is induced in the gas and an important amount of vibration energy is absorbed by the gas, so changes can be measured on oscillation amplitude. Sensors based on this principle were designed using quartz crystals as ultrasound generators. Nevertheless in resonance condition the quality factor of quartz is much better than of PZT ceramic used in this case, several advantages are remarkable: low cost due to thick film technology, much higher tolerance to temperature variations and the possibility of PZT ceramic fine mechanical adjusting. The resonating cell's wall could be adjusted by using PZT elements as piezoelectric actuators, which control the cavity gap.