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

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.

Mobile single-sided NMR

“…This is why CFG NMR is less sensitive than PFG-NMR. But it does not require sophisticated equipment [228,335,336], in particular, when high gradients of the order of several tens of Tesla per meter are in demand. Such gradients can easily be generated in the stray fields of superconducting [333] and permanent magnets [46,162].…”

“…Instead of a hole a second magnet can be placed in the hole and its position varied [224]. This concept has been used some time ago in the design of electromagnets for unilateral NMR [228]. A discrete version of the barrel magnet is the NMR-MOLE (MObile Lateral Explorer, Fig.…”

An Open Magnet Utilizing Ferro-Refraction Current Magnification

“…The dependence of Eq. [5] upon l m is less significant, since x max is bounded between h/ √ 2 and h as l m → 0 to ∞. Utilizing the parameters above, B m = B z (x max ) is calculated to be 39.4 G. This value may be doubled to reflect the contribution of image currents.…”

“…The first of this type of magnet was used in an industrial application and provided an external radial field (4). Other monohedral designs have been proposed (5)(6)(7)(8)(9)(10)(11). Clearly the primary advantage of monohedral magnets over bihedral magnets is their openness.…”

A Two-Spiral Flat Coil for Detecting 14N NQR Signals

“…As is well known (for example, see [12]), the coil with current has a wide effective directivity pattern; as a consequence, the spiral coil with the density of windings increasing toward the external coil radius will have low spatial selectivity and large noise level. The flat spiral coil with uniform winding [8,11] has still a greater number of disadvantages than the coil with non-uniform winding.…”