LI Qiufeng1,3  SHI Lihua2  LIANG Dakai3

(1 Key Laboratory of Nondestructive Test of Ministry of Education, Nanchang Hangkong Univ. 330063)

(2 Engineering Institute of Corps of Engineers, PLA University of Sci. and Tech. Nanjing  210007)

(3 College of Aerospace Engineering, Nanjing University of Aeronautics and Astronautics  Nanjing 210016)

Received Jul. 25, 2008

Revised Sept. 5, 2008

Abstract Two signal processing approaches are presented to improve imaging resolution in ultrasonic NDT of concrete structures. When low-frequency B-scan data are processed by Synthetic Aperture Focusing Technique (SAFT), wavepacket will be further elongated because low-frequency detection signal covers a relative long period. Wavepacket Decomposition Technique (WDT) is introduces here to solve this problem. This method uses a few parameters to describe the original signal so that it can avoid the processing of the whole time history of signals. In practical measurement, ringing of commercial ultrasonic transducers also effect the discrimination of the detected signal. A method based on digital filtering is processed to build the compensation model of transducer system. By eliminating the ringings with the filter, the spatiotemporal resolution of ultrasonic imaging is improved. The efficiency of the methods has been proved by numerical simulation and experimental results. Imaging resolution is improved obviously and the embedded object in a test specimen is located accurately.  　 　

PACS numbers: 43.60