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Description
Several unique coil configurations have been developed which have applications in nuclear magnetic resonance. These include a number of designs which are appropriate for use as rf surface coils, and two configurations which have been developed as NMR magnets. The magnetic field profiles have been calculated for each of these designs, from which field strength and homogeneity information have been obtained. The rf coil configurations which have been modelled include the opposed loop, opposed half loop, bicycle wheel, opposed bicycle wheel, and semi-toroid. The opposed loop design has been studied in detail in terms of the theoretical spatial sensitivity and selectivity which it offers. A number of NMR experiments were performed to test the validity of these theoretical calculations. This configuration produces a field which is substantially reduced near the coil itself, compared with the field produced by a single loop surface coil, but which rises to a maximum along the coil axis yielding a somewhat homogeneous region which may be used to achieve a degree of spatial localization. several comparison schemes are used to evaluate the relative advantages and disadvantages of both the single loop and the opposed loop coil. These comparisons include the spatial sensitivity expected with each coil from both single pulse and depth pulse experiments. The opposed loop coil offers an advantage over the single loop coil in terms of spatial localization. Additionally, the region of relatively homogeneous field may be utilized for multiple pulse experiments to an extent not possible with a conventional surface coil. The use of opposed coils of larger size, and at higher frequencies, required the development of a unique parallel wiring scheme, which is also presented. The opposed coil concept also has been applied to the design of magnets. The results of calculations on the homogeneity and field strength possible with an opposed solenoid magnet are presented. In a manner analogous to the opposed loop coil, this configuration produces a region of homogeneous field external to the magnet itself, which has been studied as the possible source of static field for a unilateral NMR device. One special configuration, the "Inside-out Helmholtz," offers a substantial increase in the size of the homogeneous region when compared to an opposed solenoid magnet. Another special configuration, the "quasi-Helmholtz," consists of a pair of opposed solenoids, and produces a region of homogeneity comparable to that of a conventional Helmholtz configuration, but with substantially increased separation.
