High-temperature damage detection via liquid metallic laser-ultrasound transmitter and shielded AlN receiver

In this study, a high-temperature (HT) damage-sensing method using a laser-ultrasound transducer was demonstrated. Laser ultrasound is a technique that generates structural waves at remote locations using lasers. In recent years, ultrasound wave signals have been intensified using laser-ultrasound transducers instead of projecting laser onto a bare surface. However, the application of laser-ultrasound transducers, particularly for damage sensing, is restricted to room-temperature or relatively low temperature conditions (e.g., <100°C). Therefore, we investigated a liquid metallic laser-ultrasound transducer for HT (>400°C) damage sensing using Lamb waves. The laser-ultrasound transducer was composed of the liquid phase of Field’s metal and its container. Meanwhile, the wave receiver was fabricated with a bulk aluminum nitride single crystal coated with ZrO 2 . The performance of the sensing unit was confirmed based on electric impedance responses with respect to temperature increases up to 1100°C. Next, the operation frequency and wave modes were selected based on numerical simulation results. The HT damage sensing system combined with 532-nm pulse laser successfully detected the damage of a steel beam at HTs up to 1000°C within an error of approximately 7%. The results obtained in this study provide technical benefits not only for damage sensing but also for other HT sensing applications.