Superconducting Quantum Interference Device Magnetometer System for Geomagnetic Field and VLF Field Measurements

Superconducting quantum interference device (SQUID) is a macro quantized high-sensitivity magnetic flux detector based on Josephson tunnel effect and flux quantization effect. The low-temperature SQUID takes the advantages of low noise down to fT/Hz
^1/2
and wide frequency bandwidth from DC to GHz. It is widely used in basic research, material science, geophysics, astrophysics, life science and other fields. The earth's magnetic field can be approximated as a magnetic dipole, but the weak fluctuation of the earth's magnetic field contains rich information, which can reflect the solar wind activity, the earth's ionospheric activity and even earthquake precursors, and has great research value. This paper reports a liquid helium cooled low noise DC SQUID based 3-axis magnetometer and discusses the detection results of long-term geomagnetic fluctuations and Schumann resonance signal as well as some very low frequency (VLF) measurements observed by the SQUID system.