Lamb Wave Sensor Based on a Near-Stoichiometric LiNbO ₃ Piezoelectric Crystal for High-Temperature Structural Health Monitoring

The development of ultrasonic guided wave sensors is of great significance for structural health monitoring (SHM). In this work, a Lamb wave (fundamental symmetric (S₀) and antisymmetric (A₀)) sensor based on the near stoichiometric lithium niobate (NSLN) piezoelectric single crystal was demonstrated. The NSLN crystal exhibited superior piezoelectric properties, which were attributed to its finer domain structure and higher domain density. An optimum crystal cut for NSLN was designed, resulting in an enhanced piezoelectric coefficient d₃₂' of -34.3 pC/N at room temperature. This result was equivalent to 16.3 times the original value of -2.1 pC/N. The NSLN-based ultrasonic-guided wave sensors utilizing the optimum cut were proficient in transmitting and receiving Lamb waves. Under the driving voltage of 100 V, the signal voltages of the NSLN-based Lamb wave sensor were found to be on the orders of 227.3 and 3.0 mV at room temperature and high temperature of 650 °C, respectively. Moreover, the NSLN-based Lamb wave sensor showcased its better defect localization ability, and the signal-to-noise ratio (SNR) was evaluated to be 23.2 dB at a high temperature of 650 °C. To sum up, the Lamb ultrasonic-guided wave sensor based on the NSLN crystal demonstrated higher potential applications under in situ SHM at elevated temperatures.