Study on non contact acoustic imaging method for concrete defect detection

We propose a new non-contact acoustic imaging method for nondestructive inspection using a Scanning Laser Doppler Vibrometer (SLDV) and a Long Range Acoustic Device (LRAD). In this method, vibration velocities on concrete surface, which is generated by air borne sound, is measured by using SLDV. In our past study, we had already confirmed that cavity defects in concrete can be clearly imaged from a distance of approximately 5 m. This time, two kinds of experiments were performed. The purpose of first experiment was examination of angular dependence, and the purpose of second experiment was test to confirm whether cracks in concrete can be detected or not. As a result of the first experiment, the limits of radiation angle of a sound wave and a laser beam were understood respectively. Meanwhile a result of second experiment yielded that cracks in concrete can be detected as well as cavity defects.