Airborne ultrasonic technique to measure leaky Lamb waves with narrowband and low-frequency excitation

Abstract

Air-coupled non-destructive testing has become very valuable because eliminates the use of liquid couplants and enables a contactless fast inspection of structures. Multimodal leaky Lamb waves can be excited and sensed with this technology in plate-like specimens varying the excitation frequency and the inclination of the transducers. To reduce undesired effects, as the existence of unwanted modes, narrowband and low-frequency excitation signals can be used. In this paper, the generation and detection of ultrasonic leaky Lamb waves in a metallic plate with capacitive air-coupled transducers have been performed. Theoretical and experimental data have been matched, showing good correlation.