Coil winding for quadrupolar fields

Abstract

A coil is constructed such as that required in NMR imaging apparatus and in some NMR analytical applications, gradients can be established on selected axes within a uniform magnetic field. The windings of the coil also constitute an electrostatic screen which isolates the high-frequency coupling coil from the sample. The coil comprises a pair of similar quadrupole windings uniformly interpolated on the circumference of a cylindrical surface which encloses the sample volume. The winding of each pole includes conductors lying longitudinally on the cylindrical surface and distributed symmetrically over a quadrant of the circumference, the number of conductors per radian being proportional to cos 2.theta. where .theta. is the displacement from the center of the quadrant. Adjacent pole windings belonging to different quadrupoles thus overlap and the winding density is chosen so that the outer conductors of the two windings can be interlaid to form an effectively continuous electrostatic screen. The quadrupole windings are independent and can be energized to set up the required gradients on two axes perpendicular to each other in a uniform magnetic field directed perpendicular to the cylindrical axis. A high frequency coil can be wound helically over the field gradient windings without further shielding.