Study on non contact acoustic imaging method for concrete structures

We propose a new non-contact acoustic imaging method for nondestructive inspection using a high-power directional sound source and a S canning Laser Doppler Vibrometer (SLDV). In this method, vibration velocities on concrete surface, which is generated by an air borne sound, is measured with the SLDV. As a high-power directional sound source, an LRAD (Long Range Acoustic Device) is employed. Near a targeted concrete surface, very high sound pressure is required to excite the concrete wall. However, while the sound wave is emitted, the SLDV is vibrated by the sound wave. Thus, the vibration of the SLDV affects the signal-to-noise ratio. This paper describes about tone burst wave method for an improvement of the signal-to-noise ratio. Consequently, the signal to noise ratio of 12 dB was improved than using a chirp wave.