CMUT Based Air Coupled Transducers for Gas-Mixture Analysis

This paper demonstrates the ability of air-coupled capacitive micro-machined ultrasonic transducer (CMUT) to monitor binary gas mixtures. The method consists of sensing simultaneously the variations of both the ultrasonic velocity and the ultrasonic attenuation. Then, by inverse problem resolution, the concentration of each gas mixture components can be found. A specific measuring cell was fabricated, which is made of two CMUTs facing each other, in order to perform ultrasonic time of flight and attenuation measurements. The total size of the emitter and receiver were fixed by the final application. To validate the general principle of the proposed detection method, helium/air gas mixture with varying concentration was studied. A shift in the time of flight and a significant variation in the attenuation were clearly observed.