STEPPED FREQUENCY ULTRASONIC HOLOGRAPHY FOR FLAW CHARACT.

ULTRASONIC IMAGING SYSTEMS OF VARIOUS TYPES ARE PRESENTLY UNDER DEVELOPMENT FOR NONDESTRUCTIVE TESTING. ALL OF THEM REQUIRE A TWO-DIMENSIONAL APERTURE TO BE SCANNED BY A TRANSDUCER, OR FILLED WITH MULTIPLE TRANSDUCERS. A PARTICULARLY INTERESTING SYSTEM IS ONE BASED ON HOLOGRAPHIC PRINCIPLES. IN MANY REACTOR LOCATIONS IT IS VERY DIFFICULT TO IMPLEMENT EITHER A SCANNER OR A LARGE ARRAY OF TRANSDUCERS. RECENT WORK HAS SHOWN THAT UNDER SOME CIRCUMSTANCES IT IS POSSIBLE TO USE FREQUENCY SWEEPING TO GENERATE A SYNTHETIC APERTURE IN ONE DIMENSION. THIS ALLOWSA SINGLE DIMENSIONAL CROSS-SECTIONAL IMAGE TO BE MADE FROM ONE FIXED TRANSDUCER, OR A TWO-DIMENSIONAL IMAGE FROM A LINE ARRAY OF TRANSDUCERS. IN THIS RESEARCH, WE WILL ADAPT THE SWEPT FREQUENCY METHOD TO OUR STANDARD HOLOGRAPHIC SYSTEM TO ACHIEVE THIS TYPE OF IMAGING.