Research on improving defect detection performance using noise reduction processing during movement measurement with noncontact acoustic inspection method

Abstract Noncontact acoustic inspection method using airborne sound waves and laser Doppler vibrometer (LDV) has been studied to detect internal defects in structures due to aging. To improve the inspection efficiency, fundamental experiments were conducted on movement measurement using a cart equipped with a sound source and LDV. The experimental results confirmed that the LDV resonated when the excitation sound pressure was increased to improve the signal-to-noise ratio. Therefore, an attempt was made to reduce the effects of LDV resonance by subtraction processing using vibration waveforms measured in the healthy part first. Next, a study was conducted on further improvements to defect detection performance by combining several noise reduction processes. As a result, it was revealed that even with movement measurements, defect with a diameter of 300 mm and a depth of 100 mm can be detected at average travel speed of 0.26 m s −1 .