Micro-crack detection using a collinear wave mixing technique

• A collinear wave mixing technique is proposed for detection of micro-cracks.
• Driving frequency strongly affects the performance of defect detection.
• The optimal driving frequency corresponded to maximum amplitudes of SDF sidebands.
• The time-delay dependence of the SDF sidebands allowed the location of defects.

A collinear wave mixing technique was developed to detect micro-cracks in samples by measuring the mixing of two ultrasonic sinusoidal waves. The bispectrum was used to process the nonlinear response. Experiments were conducted to investigate the influence of excitation parameters, such as driving frequency and time delay, on intermodulation among ultrasonic waves and defects. Mixing components were tracked for varying frequency or time delay, and the nonlinear response was measured at fixed frequencies and time delay. The driving frequency was found to strongly affect micro-crack detection; the optimal driving frequency corresponded to maximum amplitudes of sum and difference frequency sidebands. The time-delay dependence of the amplitude of mixing components allowed the location of defects throughout a sample.