Determination of gas composition within ultrasonic devices

One of the goals addressed by the 2030 Agenda for Sustainable Development is the implementation of affordable clean energy. To achieve this, it is necessary to move from fossil natural gas to blends containing increasing amounts of renewable or green gases, such as hydrogen and biomethane. Consequently, the presence of a gas sensor capable of assessing the composition of gas mixtures on grid becomes crucial. In this regard, acoustic sensors that use ultrasonic technology possess unique advantages: they are cost-effective, consume low power, have a long service life, and adapt well to various environments. In this thesis, an ultrasonic gas sensor device is built placing two piezoelectric transducers inside a plexiglass tube at a fixed distance, where a chosen gas can be inserted and evacuated. Measuring the time of flight of an ultrasound travelling between the transducers, the speed of sound is computed, and from that the molar mass of the mixture is obtained, providing information about the gas composition. The device has been tested with a series of gases and gas mixtures, including also combustible gases. The results have revealed up to now great accuracy and resolution for this device, with a relative difference between experimental and literature values below 0.8%.