Ultrasonic Sensor for High Temperature Gas Filled Vessels

The focus of this paper is an Ultrasonic Position Indication System (UPIS) that is capable of determining one-dimensional target location in a high temperature steel-container with gaseous medium. The combination of the very high acoustical impedance of steel (45.4MRayl) and the very low impedance of air (0.0004MRayl) 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 was 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” (24.5cm) of ambient air was successful, with a steel pressure boundary 0.4566” (1.1598cm) thick, and using one matching layer. In addition to the experimental results, this investigation includes numerical simulations. Sample waveforms were predicted one-dimensionally with the Mason model using MatLab, and two-dimensionally with a Coupled Acoustic Piezoelectric Finite Element Method (CAPA) program. The Mason model program predicts waveform changes as the wave travels through various interfaces. CAPA is a finite element program that predicts waveforms based on the equations for ultrasonic wave propagation.