Frequency dependence of the thermosonic effect

The thermosonic nondestructive evaluation technique employs an infrared (IR) camera to image defects which are excited via ultrasonic waves. The dissipation of ultrasonic energy at the faces of the defect causes an increase in temperature in the vicinity of the defect, which is imaged by the IR camera. The defect is seen as a bright IR source within a dark background field. It has been learned that the coupling of high-power sound into a solid object is highly nonlinear. However, it is never clear whether it is the fundamental frequency or some harmonic that is most effective in heating the crack. Results of the study frequency dependence of the thermosonic effect with both 20 and 40 kHz are presented in this article, along with vibrational information in the vicinity of a crack.