There has been recently considerable progress in the development of Superconducting Quantum Interference Devices (SQUIDs) fabricated from thin films of high transition temperature superconductors. For marine applications where the signal extends to very low frequencies (due to the opacity of sea water at higher frequencies), the level of 1/f noise is of particular interest. This noise may be inherent to the junctions where it arises from critical current fluctuations or it may arise from the motion of vortices trapped in the body of the SQUID. It is possible to reduce the contribution of the first mechanism substantially by applying modulation schemes to the DC SQUID, whereas the latter mechanism cannot be reduced in this way. In this paper, we present firstly a synthesis of important parameters of SQUIDs, read-out schemes and noise reduction techniques, noise analysis and measurements. Finally, considerations are given on the use of superconducting magnetometers in marine non shielded environment.
ELF monitoring at sea with vectorial high sensitivity magnetometers
1997
Seiten, 2 Quellen
Conference paper
English