Abstract
The authors previously developed two non-destructive inspection methods for concrete structures using an ultrasonic sensor. One was based on a multi-reflected wave model and the other on a stationary wave model. For the former, only a method in time domain was developed. The method required a cumbersome parameter adjustment in the use, since the fundamental reflected wave was difficult to extract from the raw sensor output contaminated with large noises. The paper proposes a method based on a frequency analysis in the framework of the multi-reflected wave model and demonstrates that cracks at any arbitrary depth from 40mm to 500mm are easily detected with the method.
