In-Line Temperature Monitoring by Ultrasonic Waveguide-Based Distributed Sensor

Ultrasonic waveguide techniques are most familiar to monitor fluid level, viscosity, corrosion, and temperature for hostile environments. The potential advantage of using waveguides is to monitor various condition monitoring applications because the transducer could be placed outside the hostile or in-access areas. And also, a single waveguide could be used as multiple sensors by incorporating echogenic features (notches) in appropriate lengths. Here, stainless steel strip waveguide comprising reflectors at appropriate gauge length was fabricated to monitor temperatures at multiple locations. A shear wave transducer (0.5 MHz) was used in the pulse-echo technique to propagate S0 wave mode in the strip waveguide. Reference reflections from the notches are considered as time of flight (TOF) which could be collected at various temperature instances. The strip waveguide sensor and the co-located thermocouples are calibrated using the resulting time-of-flight shift (δTOF) from the reflectors. A machine learning model was used to extract a best-fit calibration equation with a heating cycles. The obtained calibration equation can be used to extract the temperatures at various spots on the structure where the waveguide sensor is placed. The developed single strip waveguide sensor, designed for measuring temperature at multiple locations, is easy to use, durable, and affordable. It is suitable to tracking the temperatures in the hostile and difficult to access areas.