부산대학교 도서관

Ultrasonic Pulse Echo Technique has been used successfully as a practical modality for nondestructive testing of concrete to localize defects which cause critical infrastructure problems. However, in this highly attenuating medium, only limited penetration can be obtained using high frequency ultrasonic signals. Furthermore, ultrasonic signals from defects are corrupted by the echoes from randomly distributed scatterers, which generally result in significant background noise. Therefore, even when sufficient penetration is achieved, it is often cumbersome, if not impossible, to distinguish flaw signals from the background microstructure noise, corresponding to complex, dispersive and nonhomogeneous reflectors. To enhance flaw visibility, a well-known frequency diversity technique, namely Split Spectrum Processing (SSP) is employed. This paper presents experimental results obtained using transducers with center frequencies of up to 1 MHz in different types of concrete to demonstrate SSP's noise reduction and defect detection capabilities. Experimental data from concrete samples such as mortar, with and without defects, and other concrete specimens using transducers with 0.25 0.5 and 1 MHz center frequencies are shown.