IMPROVED ULTRASONIC INSPECTION SYSTEM USING MULTIBIT DIGITAL SIGNAL CORRELATORS

A MAJOR AND PRESSING PROBLEM IN NONDESTRUCTIVE EVALUATION (NDE) OF MATERIAL USING ULTRASOUND IS THE DETECTION OF MICROSTRUCTURAL ECHOES OF LOW SIGNAL-TO-NOISE RATIO (SNR). THE LOSS OF SIGNAL BY SCATTERING AND ABSORPTION IMPOSES A LIMIT ON THE DETECTION CAPABILITY OF ULTRASONIC SYSTEMS. THIS PROBLEM OFTEN ARISES IN EXAMINING COMPOSITES, CERAMICS, CAST COMPONENTS, WELDS OR ANY THICK SECTION OF MATERIALS. ONE METHOD OF OBTAINING HIGH SNR IS THE APPLICATION OF A CORRELATION RECEIVING SYSTEM. IN PHASE I OF THIS RESEARCH PROPOSAL, WE PROPOSE TO DEVELOP AND EVALUATE AN ULTRASONIC INSPECTION SYSTEM USING GOLAY CODES AND MULTIBIT SIGNAL CORRELATORS. THIS SYSTEM TRANSMITS LARGE TIME-WIDTH RADOM CODES AND ACHIEVES PULSE COMPRESSION THROUGH THE CORRELATOR WHICH RESULTS IN TREMENDOUS SNR. THE HARDWARE DESIGN WILL INCLUDE FEATURES TO EASE INTERFACING THE CORRELATOR SYSTEM WITH THE PC-BASED WORKSTATION FOR POST-PROCESSING THE ACQUIRED DATA. IT IS OUR OBJECTIVE TO EVALUATE THE ABILITY OF THE CORRELATOR TO CHARACTERIZE THE STRUCTURE OF COMPOSITES AND OTHER MATERIALS OF IMPORTANCE TO DOD.