ScholarWorks@성균관대학교

초록

In this study, an ITO thin-film-based thermoacoustic air-coupled ultrasonic transducer is fabricated as a non-contact ultrasonic source, and the A0 Lamb wave excitation characteristics in an aluminum plate are investigated through experiments and COMSOL Multiphysics-based finite element analysis. Dispersion analysis showed that only the A0 and S0 modes exist at 40 kHz. In addition, the phase and group velocities of the A0 mode were determined to be 613.6 m/s and 1192.5 m/s, respectively. Based on these results, Snell's law was applied to determine the optimal incident angle for A0 mode excitation. The Lamb wave response was measured as a function of incident angle and showed that the maximum response occurred near 34.0 degrees in both the experiments and finite element analysis. This is in good agreement with the theoretically derived excitation condition. In addition, the group velocity was calculated from the arrival times of Lamb waves measured over the frequency range of 20 similar to 100 kHz. The velocity was compared with the theoretical dispersion curves, confirming that the excited Lamb waves corresponded to the A0 mode. Furthermore, the array spacing was designed to be 18.5 mm by considering the A0 mode wavelength of 15.34 mm at 40 kHz and the optimal incident angle, and the response characteristics were evaluated as a function of the number of array elements. As a result, the maximum Lamb wave response with a four-element array increased by up to 4.1 times compared with that of a single element. These results indicate that thermoacoustic air-coupled ultrasonic transducer arrays can be effectively used for non-contact Lamb-wave excitation and guided-wave-based nondestructive testing.

키워드