Development of an air-coupled ultrasonic sensor for high pressure, and temperature applications

The focus of this investigation is to develop an Ultrasonic Position Indication System (UPIS) that is capable of determining one-dimensional target location in a steel-contained pressurized gaseous medium. The combination of the very high acoustical impedance of steel (45.4 MRayl) and the very low impedance of air (0.0004 MRayl) causes extremely high-energy losses upon transmission. In addition to the energy loss, propagation through a steel plate produces many internal reflections in the plate. The strategy of this investigation is to develop a self-contained ultrasonic transducer that is capable of replacing a small portion of a high temperature-pressure boundary. In building such a transducer, sufficient acoustic matching layers for the steel-gas interface, a mechanically and acoustically competent housing, a sufficient piezoelectric element, and backing materials are all developed and tested. The results include a successful housing design, high-temperature acoustic matching layers, and subsequent successful waveforms. Target location through 9.6 inches (24.5 cm) of ambient air was successful, with a steel pressure boundary 0.4566 inches (1.1598 cm) thick, and using one matching layer.