Abstract
Functionalized films are commonly used in gas sensing to target a particular gas. This is due, in part, to their usually high capability to detect very low concentrations and their high selectivity. However, their poor stability over time remains a challenge when dealing with applications that require the sensing to remain reliable without frequent recalibration. For this reason, uncoated gas sensors have become increasingly popular regardless of their lower sensitvity and their often non-selective characteristics. There exist different approaches for gas sensing without a functionalized film. One possibility is to use an uncoated resonating sensor and tracking its resonant properties which depend on its surrounding environment. The easy integration capability of capacitive micromachined ultrasonic transducers (CMUTs) makes them great candidates for uncoated gas sensing. Moreover, they are able to reach very high resonant frequencies and, therefore, allow for a shorter response time. In this article, a method to detect gas by following the value of the admittance of an uncoated silicon nitride CMUT array at either the resonant or at the anti-resonant frequency is presented and tested. This chemical detection is purely based on the change of the physical properties of the gas mixture (the mass density and the viscosity). A general model describing the impact of the electrical and mechanical properties of the CMUT in the sensitivity is presented, validated and applied to carbon dioxide and methane detection.
Highlights
In gas sensing, coating a device with a thin film tailored to chemically interact with the target analyte is by far the most common approach (Göpel, 1994; Park et al, 2007; Lee et al, 2011; Qiu et al, 2015)
This means that this sensing method would be more suitable to detect gases that would induce an important change in the gas mass
An analytical model of the influence of the bias voltage in the sensitivity when measuring the value of the normalized admittance at either the resonance or the antiresonance of a capacitive micromachined ultrasonic transducers (CMUTs) was presented
Summary
In gas sensing, coating a device with a thin film tailored to chemically interact with the target analyte is by far the most common approach (Göpel, 1994; Park et al, 2007; Lee et al, 2011; Qiu et al, 2015). It has been shown that both the resonant frequency and the quality factor of uncoated resonant sensors such as microcantilever resonators depend on physical properties of the fluid surrounding them (Sader, 1998; Abdolrazzaghi and Daneshmand, 2016) This has been used previously for characterizing liquids (Heinisch et al, 2015) and even gases, despite the fact that their mass density and viscosity are much smaller. Gas detection such as hydrogen, carbon dioxide, argon, helium and methane detection have already been demonstrated using uncoated resonant sensors (Tétin et al, 2010; Boudjiet et al, 2014; Rosario and Mutharasan, 2014; Iglesias et al, 2019). The principle, which is based on the measurement of the value of the admittance at the resonance and anti-resonance and not on the corresponding frequency shifts, along with an analytical model of the impact of a change in the gas composition, are presented and verified under mixtures of nitrogen and either carbon dioxide (CO2) or methane (CH4) as an example
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
