Opposed coil magnet calculations for large sample and unilateral nuclear-magnetic resonance

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Abstract
A magnet configuration has been devised, consisting of two nested coaxial coils with the current in the inner coil circulating in an opposite sense from that in the outer coil. The magnetic field generated by such an opposed pair exhibits a small region of homogeneity outside of the magnet itself, creating the possibility of constructing a unilateral nuclear‐magnetic‐resonance device capable of examining an object from only one side. Calculations on one special case, the inside‐out Helmholtz configuration, indicate a volume of 10 cm3 with homogeneity of ±1% for a coil of outer radius 10 cm, and 0.1 cm3 with 100‐ppm homogeneity. A second special case, consisting of two sets of opposed solenoids arranged in a quasi‐Helmholtz manner, offers homogeneity comparable to a conventional Helmholtz pair of similar diameter but with an increase in separation of as much as a factor of 2.