High-sensitivity gradiometer based on three high-T c SQUID magnetometers

An operating prototype model of an electronic gradiometric system based on three high-sensitivity high-T c (HTS) SQUID magnetometers is developed, fabricated, and studied. A dynamic range of 140 dB implemented in the system provides its stable operation in an unshielded space with a sensitivity level of about 8 fT/cm 2 Hz 1/2 . The ultimate sensitivity of the system, which can be attained either at large distances from man-made noises or in a weakly shielded space, is 4 fT/cm 2 Hz 1/2 . This value is equivalent to 100 fT/Hz 1/2 reduced to the sensitivity of a single SQUID magnetometer. The operating frequency band of the system is from 1 Hz to 15 kHz. The developed system, which is based on three HTS SQUIDs, can be successfully used in its present configuration in geophysical studies performed under field conditions and in magnetometric methods of nondestructive evaluation of materials.