HIGH-T-C 3-AXIS DC SQUID MAGNETOMETER FOR GEOPHYSICAL APPLICATIONS

A prototype three-axis magnetometer has been developed, intended for geophysical applications, involving high-transition temperature dc superconducting quantum interference devices (SQUIDs). Each SQUID was fabricated from a thin film of YBa2Cu3O7-x deposited on a SrTiO3 bicrystal to form two Josephson junctions, and was directly coupled to a single-turn pickup loop patterned in the same film. The three orthogonally mounted sensors were immersed in liquid nitrogen in a fiberglass Dewar and operated in separate flux-locked loops. In nominally zero ambient magnetic field, the best magnetic field resolution was 170 fT Hz-1/2 in the white noise, increasing to 225 fT Hz-1/2 at 1 Hz. The dynamic range was ±1.6×106 Hz1/2 in the white noise, and the highest slew rate achieved was 1.6 mT s-1, at 900 Hz. The 3 dB point in the frequency response was about 90 kHz. The three channels were mutually orthogonal to about 1%. The three-axis magnetometer was also operated outside the laboratory in the presence of 60 Hz and radio-frequency noise. © 1994 American Institute of Physics.