PROCESSING AND CHARACTERIZATION OF HIGH T-C MAGNETIC-SHIELDS AND FLUXTRANSFORMERS

The use of high T-c SQULD (HTSQUID) magnetometers for magnetocardiogra phy (MCG) and nondestructive testing (NDT) requires effective shieldin g from magnetic noise fields. We have investigated the shielding chara cteristics of high-T-c superconducting (HTS) material and developed a compact, portable system consisting of several HTS components. A proce ss for fabricating these components out of Bi-Pb-Sr-Ca-Cu-O has been d eveloped. Tubes and disks of various sizes have been formed by Cold Is ostatic Pressing (CIP) and sintered at reduced oxygen pressures. The H TS tubes exhibit shielding factors of up to 10(3) at low frequencies. A novel technique for fabricating superconducting flux transformers (s pecifically, first-order gradiometers) has also been developed. The fl ux transfer efficiencies of these first-order gradiometers have been e valuated. The tubes, gradiometers, and flux focusers have been incorpo rated into an HTSQUID setup. We find that the low-frequency noise reje ction obtained in our setup is very promising for potential MCG and ND T applications in an unshielded environment.