A Review of Magnetic Field Emissions From the Human Body: Sources, Sensors, and Uses

It has long been common practice to capture the electric fields emanated by the human body as a means of detecting and/or monitoring diverse health conditions. However, these electric fields are strongly impacted by the complex permittivity of biological tissues which deteriorates their waveforms and limits their diagnostic capabilities. As an alternative, recent progress has been made in the measurement of bio-magnetic fields occur from the natural currents flowing through the body. The advantage in this case is, since tissues are non-magnetic, magnetic fields propagate in an uninterrupted manner towards the skin surface where they are eventually collected. This unveils game-changing opportunities for future medical diagnostics. Nevertheless, a major challenge associated with sensing these naturally emanated magnetic fields is that they are extremely weak, and in fact orders of magnitude smaller than those generated by the Earth. To this end, extensive efforts have been pursued to realize sensing technology that is sensitive enough to collect bio-magnetic fields. Example fields of use include magnetomyography (MMG), magnetocardiography (MCG), magnetoencephalography (MEG), and Magnetoneurography (MNG) (including magnetospinography (MSG)). This review will provide an overview of technologies used to sense bio-magnetic fields, list their merits and limits in a critical manner, and discuss clinical applications.