Weak magnetic fields in human body

The ability of SQUID (Superconducting Quantum‐Interference Device) magnetometers to measure magnetic fields weaker than $10−9$ gauss has made possible the study of the very weak magnetic fields induced in human beings by biochemical current flow or by the presence of small quantities of ferromagnetic contaminants. The SQUID is basically a superconducting loop with a weak link that behaves as a Josephson junction. One can monitor the intrusion of individual flux quanta $(h/e≈2×10−11 gauss‐meters2)$ as they force their way through the weak link into the superconducting loop. The first SQUID magnetometers were built in 1967 by James Zimmerman and his colleagues at the Ford Scientific Research Lab.