Detection of crack in a shallow layer of mortar by using a harmonic component of very high intensity aerial ultrasonic waves

We developed a noncontact, nondestructive method of imaging defects in solid objects with high-intensity aerial ultrasonic waves and optical equipment. The method detects defects in the imaged area by analyzing the velocity distribution on the surface of an object continuously irradiated with aerial ultrasonic waves. In this study, we attempted to detect a crack in a shallow layer of mortar. We used the nonlinearity of high-intensity sound waves and we imaged a rectangular defect imitating a crack (width: 1 mm) using harmonic components of the vibration velocity. Our method successfully imaged the rectangular defect, showing the possibility of its application to the detection of actual cracks.