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This paper presents an integral equation and method of moments (MoM) solution to the problem of TM transmission by a metallic conducting shield at extremely low frequencies (ELF). In order to accurately compute the total fields interior to the shield, equivalent problems are formulated which avoid the numerically difficult problem of computing the total fields as the sum of the incident plus scattered fields. In particular, the total electric field on the interior surface of the shield is obtained by a volume current equivalent problem, and then the total magnetic field interior to the shield is formulated in terms of equivalent magnetic surface currents flowing on the interior surface of the shield replaced by a perfect conductor.

Recently there has been increasing concern regarding the effects of low-frequency magnetic fields on humans and livestock. A portable magnetometer is essential for monitoring the field dose encountered. There are some devices currently available for this purpose which use the induced EMF technique. The field sensitivity for these devices depends on the number of turns of coil used. This limits the minimum size of devices with reasonable performance. The magnetometer considered in this paper overcomes this size limitation by using a highly magnetostrictive material, Terfenol-D, as the magnetic field sensor. The primary focus of this paper is to determine the magnetic field spectral characteristics using digital signal processing. A survey of spectral estimation techniques are presented, followed by their application to the Terfenol-D magnetic field signal. The estimators are compared using data obtained from a magnetometer hardware prototype. Using these methods it was possible to detect signal for a field strength of 20 milligauss.