ELECTRONIC HIGH-TEMPERATURE RADIO-FREQUENCY SUPERCONDUCTING QUANTUM INTERFERENCE DEVICE GRADIOMETERS FOR UNSHIELDED ENVIRONMENT

This article will discuss improved electronically formed gradiometers based on high-temperature radio frequency (rf) superconducting quantum interference device (SQUID) magnetometers. For gradiometer balancing, a system of adjustable superconducting plates was developed. This tec hnique was used to build first- and second-order, axial gradiometers w ith adjustable baselines, which operate at 77 K. Each magnetometer com bines a washer rf-SQUID with bulk or a thin-film flux concentrator in Aip chip geometry. In an unshielded environment, the magnetic field se nsitivity in the white noise region is about 80 fT/Hz for first-order and 150 fT,/Hz for second-order gradiometer. Common mode rejection cou ld be balanced to better than 10(4) for uniform background fields and better than 200 for gradient fields. (C) 1997 American Institute of Ph ysics.