Magnetic field fluctuations arising from thermal motion of electric charge in conductors

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Abstract
A model is developed for the source of magnetic field fluctuations emanating from thermal agitation of electric charge in conductors. The calculation of the thermal magnetic noise with the model involves the solution of a general volume conductor forward problem. Frequency-dependent equations for this problem are derived from Maxwell’s equations. The model is applied to calculate the magnetic noise generated by infinite conducting slabs. A good agreement between theoretical predictions and experimental results were found. Thermal magnetic noise fields inside magnetically shielded rooms are estimated and noise in biomagnetic measurements is discussed.