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A small, extremely simple magnetometer has been developed for use in metal detecting devices. It is a ring-core fluxgate type employing a small Permalloy-tape bobbin core purchased commercially. When the magnetometer is used in low ambience or as a dc field null detector, the intrinsic noise can be as low as 0.1 gamma in a one hertz passband. For additional details, see Digests of the 1972 Intermag Conference (available from IEEE Headquarters).
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Robert Brown (1972) studied this question.
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