Experimental Study on Remote Non-contact Detection of concrete structure cavities based on Laser Doppler Vibrometry technology and acoustic excitation

Abstract This study investigates a non-contact detection method that combines Laser Doppler Vibrometry (LDV) with acoustic excitation to efficiently identify the locations of cavities within tunnel linings. By comparing the vibration response characteristics of hammer excitation and acoustic excitation, it is found that acoustic excitation is better than traditional hammer excitation in terms of vibration stability, frequency distribution range and non-damaging. The study further examined the vibration behaviour of specimens containing cavities of different sizes, depths, and measurement distances. The results show that the increase of cavity size leads to a significant increase in vibration amplitude and a decrease in bending resonance frequency, while the increase of depth leads to a decrease in vibration amplitude and an increase in characteristic frequency, showing obvious correlation with geometric parameters. Furthermore, in long-distance detection scenarios, while vibration amplitude exhibits exponential decay with distance, the resonance frequency shift remains consistently small. This demonstrates that frequency characteristics can serve as a stable defect identification criterion. Ultimately, velocity analysis enables precise detection of void boundaries, validating the method's effectiveness. This study provides a high-precision, non-contact technical solution for diagnosing hidden defects in concrete structures. Experimental data shows its cavity recognition accuracy rate is notably high, demonstrating significant engineering application value.