Gas discrimination by simultaneous sound velocity and attenuation measurements using uncoated capacitive micromachined ultrasonic transducers

Chemically functionalized or coated sensors are by far the most employed solution in gas sensing. However, their poor long term stability represents a concern in applications dealing with hazardous gases. Uncoated sensors are durable but their selectivity is poor or non-existent. In this study, multi-parametric discrimination is used as an alternative to selectivity for uncoated capacitive micromachined ultrasonic transducers (CMUTs). This paper shows how measuring simultaneously the attenuation coefficient and the time of flight under different nitrogen mixtures allows to identify hydrogen, carbon dioxide and methane from each other and determine their concentration along with identification of temperature and humidity drifts. Theoretical comparison and specific signal processing to deal with the issue of multiple reflections are also presented. Some potential applications are monitoring of refueling stations, vehicles and nuclear waste storage facilities.

Automated summary

Chemically functionalized or coated sensors are commonly used in gas sensing, but their poor long term stability is a concern. This study proposes a multi-parametric discrimination approach for uncoated CMUTs to achieve selectivity. By simultaneously measuring the attenuation coefficient and time of flight under different nitrogen mixtures, hydrogen, carbon dioxide, and methane can be identified and their concentrations can be determined, along with temperature and humidity drifts. The study also presents theoretical comparisons and signal processing techniques to address the issue of multiple reflections.