An Introduction to the Use of SQUID Magnetometers in Biomagnetism

Abstract

The advent of magnetometers with superconducting quantum interference device (SQUID) sensors has brought about a major breakthrough in magnetic field measurement. SQUID magnetometers have permitted field determinations which are orders of magnitude more sensitive than previous measurements. They have also been used in magnetometers designed to measure the magnetic moments of small specimens, such as the standard rock cylinders used in paleomagnetism and biological samples which may contain minute quantities of magnetite, of interest to biomagnetists. In the absence of an inducing field, the remanent moment of the specimen is measured. In the presence of a field, the induced moment can be measured giving the susceptibility. SQUIDs have also been used in gradiometers to obtain magnetocardiograms and magnetoencephalograms. In the latter application, fields of the order of femtoteslas (microgammas) are measured!