Acoustic non-linearity for defect selective imaging.

Non-linear acoustic effects are of increasing interest in close-to-application research in which mostly ultrasonic frequencies above 1 MHz are used. If the excitation frequency is reduced, one can use high power excitation performed locally by a piezoceramic stack actuator that provides much higher vibration amplitudes. The combination of this excitation with a scanning laser interferometer provides a system for rapidly imaging non-linearities and thereby selectively detecting defects in most kinds of materials. This contribution presents various experimental results showing the potential of this new technique.