| 研究概要 |
Preliminary mobile prototype of the system has been assembled. Optical layout is close to the real system design. The system prototype has been tested in the laboratory and filed conditions.
In laboratory, the system has demonstrated capability of detection of laser-initiated vibration. Special samples with inner defect were used as test specimens. The system could recognize inner defect even if the sample was moving imitating bouncing structure.
However, working with speckled radiation puts some limitations on the system performance. Instability of speckled leads to fluctuation of the laser signal power after spatial filtering. Despite of comparatively slow movement of bouncing structures – several hertz only – signal power after spatial filtering is fluctuating with frequency up to 80 kHz. Time windows where the signal is comparatively stable are shorter than one observed in the preliminary experiments with using corner cubes in the probing points. The algorithm of inspection should take this fact into account.
After laboratory tests, the system prototype was delivered to the field experiment site. Under real bridge loaded with heavy traffic, signal instability due to speckle movement was lower than in laboratory – up to 12 kHz. But it also overlapped the range of expected vibration frequency. Anyway, there still exist time windows when the vibration measurement procedure can be started and completed. In the next field tests, the system will be examined with laser impact.
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