Fig. 12.1. Magnetic signals produced by various sources. Biomagnetic signals: MCG = magnetocardiogram, MMG = magnetomyogram, MEG = magnetoencephalogram, MOG = magneto-oculogram Noise fields: static field of the Earth, geomagnetic fluctuations, laboratory noise, line frequency noise, radio frequency noise Equivalent input noise: commercial flux-gate magnetometer, ring-core flux-gate (NASA), induction coil magnetometer, SQUID-magnetometer. Thermal noise fields: eddy current shield, the human body.