ABSTRACT
Most two-dimensional (2-D) images have been obtained either by rotating the sample with one pair of gradient coils, or by using two sets of gradient coils. In designing gradient coils, the desired magnitude of the gradient, linearity, sample volume, and sample access need to be taken into account. Calculation of the magnetic-field gradient is nontrivial for coils with finite dimensions. The magnitude of the gradient desired and the limited space available between the pole caps and the cavity may prevent the use of optimum coil dimensions for a single pair of anti-Helmholtz coils. The use of two sets of coils merely increases the number of degrees of freedom that can be used to optimize the linearity of the gradient. Power supply requirements for gradient coils depend on the wire size. For electron paramagnetic resonance imaging one needs a larger magnetic-field gradient than for nuclear magnetic resonance imaging.
