ABSTRACT
Superconducting quantum interference devices (SQUIDs) have been a key factor in the development and commercialization of ultrasensitive magnetic measurement systems. Because of their superconducting nature, SQUID sensors operate at cryogenic temperatures. The SQUID can act as a magnetometer by allowing flux to directly penetrate the SQUID loop. A unique advantage of SQUIDs is that they can be used to make magnetic field sensors with direct current response and sensitivities well below environmental noise levels. This has allowed noninvasive measurements of electrophysiological activity and a number of other magnetic sensing methodologies not possible with conventional electromagnetic sensing systems. SQUID magnetometers may provide diagnostic capabilities in areas where there is no present measurement technique. The use of bioelectric signals as a diagnostic tool is well known in medicine, for example, the electrocardiogram for the heart and the electroencephalogram for the brain. The SQUID magnetometer is sensitive enough to noninvasively detect the fetal magnetocardiogram.
