Long distance measurement over 30m by high-speed non-contact acoustic inspection method using acoustic irradiation induced vibration

Abstract

The noncontact acoustic inspection method has been studied using a laser Doppler vibrometer (LDV) of high sensitivity and a sound source which can generate big sound pressure at a long distance. However, the inspection at the long distance over 10 m was carried out only with the concrete test object. Therefore, for an actual concrete bridge in Japan, the long distance measurement experiment over 30 m was conducted this time. Long range acoustic device (LRAD) was used as the excitation sound source and a scanning laser Doppler vibrometer (SLDV) was used as a measurement LDV, both of which were located at a distance of about 34 m from the surface of target under the bridge. Multi tone burst wave was used as the emitted sound wave. Since the same experimental result using hammer method was obtained, it was confirmed that this method can detect defects even at a distance exceeding 30m.