Patent ID: 7659717

Claim:
A sensor for measuring the magnetic moment of a sample material comprising: two or more pick-up coils for generating pick-up signals, wherein said pick-up coils comprise a first pick-up coil having a first set of windings and a second pick-up coil having a second set of windings, said first and second sets of windings being spaced apart from one another along an axis of the coils, the windings of one of the second pick-up coil being positioned outside the windings of the first pick-up coil, wherein: said first and second pick-up coils are arranged to have an equal sensitivity with respect to a background field; and said first and second pick-up coils are arranged to have a different sensitivity with respect to a field generated by the sample material positioned inside said first set of windings; and said first and second pick-up coils are arranged to have an equal sensitivity with respect to deviations of the sample material from a center position of the first and second pick-up coils; and signal combining means for combining signals picked-up by said first and second sets of pick-up coils such that: since said pick-up coils have an equal sensitivity with respect to said background field, background signal components due to the background field will cancel each other; since said pick-up coils have a different sensitivity with respect to the field generated by the sample material, sample field signal components due to the field generated by the sample material will yield a difference signal indicative of said field; and since said pick-up coils are arranged to have an equal sensitivity with respect to deviations of the sample material from the center position, differences in said sample material signal components resulting from deviations from center will cancel each other.