Fundamental study on ultrasonic measurement system to detect penetration of boulders using cepstrum analysis

Generally, ultrasonic method and an elastic impact wave method are mentioned as examples representing the nondestructive test method. However, the ultrasonic method is known for the investigation of shallow depth becoming very shallow because of its small input. And the elastic impact wave method uses for example, a hammer for the discrimination of the reflection wave produced by minute cracks existing in the object, which is difficult. Theoretically, if it becomes possible to input the vibration of an ultrasonic domain into artificial structures such as a concrete and a boulder with strong amplitude, deeper investigation of depth and higher precision will be attained. The authors have developed a new ultrasonic method by using ultrasonic wave of the chirp signal, using the input of this system and using auto correlation and cepstrum as the analysis methods. In this paper, the experiment is classified into Pattern 1 and Pattern 2. In Pattern 1, the experiment of receiving the reflection wave was carried out using the concrete block with a width of 1300 mm and the down chirp signal from 50 kHz to 40 kHz. In Pattern 1, a reflection wave was clearly detected, and the length of the concrete block was calculated using auto correlation analysis, and was obtained as 1311.76 mm. In Pattern 2, the experiment of receiving the reflection wave was carried out using the same concrete block and the down chirp signal from 150 kHz to 130 kHz. In Pattern 2, the direct wave and the reflection wave were mixed, therefore it was not possible to presume the length from the obtained waveform. So cepstrum analysis method was used, and the traveling time of the reflection wave was obtained. In this result, the length of the concrete block was given as 1278.25 mm.