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| | Abstract | | The hammer method is still used for the non-destructive test of the concrete structures. However, difficulty had followed on the inspection of the high place. Therefore, the long distance non-contact acoustic inspection method with defective detection accuracy comparable as the hammer method has been examined. This is the technique of having combined a scanning laser Doppler vibrometer (SLDV) and a long-distance acoustic device (LRAD). It is suitable for searching a comparatively narrow region precisely taking advantage of plane excition ability of LRAD, and the two-dimensional scanning capability of SLDV. On the other hand, since the two-dimensional scanning performance by SLDV needs to take alignment of laser light in the state where it was stood still, it is not suitable for measurement while moving. And although the directional characteristics of the LRAD itself are excellent in 1 kHz with plus minus 15 degree, there are problems, such as angular dependence nature to a subject and noise to the circumference at the time of considering practical use. Then, the case where a strong ultrasonic sound source and LDV for a single point were combined as the 2nd construction of the non-contact acoustic inspection method was examined. |
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