Noninvasive pressure determination in vacuum vessels using frequency-domain measurements

Pressure determination in vessels plays a crucial role in many industrial applications, such as manufacturing, food processing, oil & gas industry, nuclear, chemical industry, material science, and others. There are numerous types of vessels used, some with very complicated geometries and levels of layering, varying from vacuum chambers, cryostats and cry-coolers to vacuum flasks and different systems used for vacuum packaging. It is not always practical, often even undesirable, to have a vacuum and/or pressure gauge directly attached to the system. Here we are using an acoustics-based approach, with measurements performed in the frequency-domain. Two piezoelectric transducers are mounted on the outside of the vessel, and the measurements are performed in-situ, without disturbing the structural integrity of the vessel. Frequency-domain measurements present several advantages over the typical time-domain measurements. Since the whole vessel will resonate at very specific frequencies, i.e., mechanical resonances, air-gaps and other coupling issues do not preclude obtaining vibrational information. Some of these resonances are sensitive to the internal pressure of the vessel. As typical vacuum vessels have very complicated shapes/internal structures, determination of these resonances can be very challenging. Machine learning is used to simplify their identification and monitoring and provide a path forward to a quantitative measurement of internal pressure.