A first-order axial gradiometer has been constructed using two high-critical-temperature superconducting-quantum-interference-device magnetometers having a double-pickup loop configuration on bicrystal substrates. The magnetometer, which had a slot-type structure but no weak links on the pickup loops, can be operated steadily in an unshielded environment after in situ cooling. The gradiometer was formed by connecting the feedback and the compensation coils of the two magnetometers in series using a normal conductive wire. Sufficiently high noise reduction (31 dB at 1 Hz) was achieved without any need for adjustments and low-noise magnetocardiograms were obtained with the gradiometer in a moderately magnetically shielded room.
ASJC Scopus subject areas
- Physics and Astronomy (miscellaneous)