Resonant ultrasonic imaging of defects for advanced non-linear and thermosonic applications

Abstract

An efficient wave–defect interaction is the key to high non–linear and thermal responses of flaws to be applied in ultrasonic imaging for non–destructive material evaluation. To selectively enhance defect vibrations a concept of local defect resonance is developed and applied to ultrasonic activation of defects. The frequency match between the defect resonance frequency and the probing ultrasonic wave results in a substantial rise of the defect non–linear response and its local temperature. The non–linear applications of this concept demonstrated in this paper cover both the higher harmonic and frequency mixing modes. The defect resonance is shown to be accompanied by depletion of the excitation frequency vibration due to non–linear frequency conversion to higher harmonics. The local generation of higher frequency components provides a high thermal defect response in such acoustically non–linear thermosonic mode.