11 June 2002 Nondestructive inspection of concrete structures with the use of photorefractive two-wave mixing
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We present a technique of remote non-destructive inspection of concrete structures and location of inner defects. The technique is based on detection of ultrasonic vibration in concrete with the use of laser interferometer. The interferometer uses principles of dynamic holography via two-wave mixing in photorefractive crystal and homodyne detection. The use of the dynamic hologram of the inspected surface excludes possibility of wave front mismatch between interfering signals, one of which (probing signal) has speckle structure due to the roughness of the inspected surface. Bismuth Silicon Oxide (BSO) photorefractive crystal is used as a nonlinear medium for the recording of the dynamic hologram. CW YAG:Nd laser radiation of 532 nm wavelength is used for detection. Results of detection are verified by piezoelectric sensor. Vibration in concrete is initiated by hammering or laser impact. For completely remote operation, vibration should be initiated by laser impact. In purpose of reliable detection, we analyze both shape of propagating ultrasonic wave and its spectrum. Spectrum of low frequency (1-10 kHz) vibration provides information of the presence or absence of inner defects. Analysis of propagating ultrasonic wave of higher frequency (10-100 kHz) allows to locate the defect more precisely.
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Oleg Kotiaevy, Oleg Kotiaevy, Shigeaki Uchida, Shigeaki Uchida, "Nondestructive inspection of concrete structures with the use of photorefractive two-wave mixing", Proc. SPIE 4702, Smart Nondestructive Evaluation for Health Monitoring of Structural and Biological Systems, (11 June 2002); doi: 10.1117/12.469882; https://doi.org/10.1117/12.469882

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