Developing high temperature broadband fiber optic acoustic sensor with flat response

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In the pyrometallurgical industry, smelting vessels are subjected to extreme heat stress, as well as chemical andabrasive reactions. The lining of the vessels suffer from severe degradation over time. Early detection ofdegradation in the refractory lining is essential to avoid sudden vessel failures and to prevent unscheduledshutdowns. The acoustic ultrasonic-echo (AU-E) technique is widely used to detect the refractory degradationand remaining thickness of smelting vessels. This technique uses a piezoelectric transducer (PZT) for manualimpact detection of the signal reflected from the shell of the vessels, in order to determine the remainingthickness of the refractory lining. These reflections are caused by local changes of material properties such asvoids or interfaces between different materials. The reflected waves are analyzed in both the time andfrequency domains to determine the condition of the vessels. However, the PZT detection system has lowsensitivity with single frequency ability, thus requiring manual impact with multiple PZTs to cover variousfrequency ranges. This represents the company-specific problem.The primary objective of this project is to design broadband acoustic sensors with a flat response over a broadfrequency range, that operate at temperatures >300°C. Following the successful design of the flat-responsebroadband acoustic sensor, we will explore the option of high-temperature fiber coating for high acousticresponse. In collaboration with Hatch Ltd., we will then develop a transmitter and receiver for ultrasonicsignals, capable of generating and receiving a frequency sweep pulse (chirp) in the 1 kHz - 250 kHz range (astandard non-destructive testing (NDT) acoustic generator). The joint transmitter and receiver unit will detectthe weak receiver signal at minimal loss. This innovative research will lead to promising applications inacoustic sensing instrumentation and NDT detection.