Cylindrical induction coil to accurately imitate the ideal magnetic dipole

In this work, we optimize the geometry of a cylindrical induction coil in order to improve the imitation of the ideal dipole field. First, we analyze a single-layer coil and find that for an optimum length-to-diameter ratio (LID) of 0.86:1 the imitation error, computed for a four radii distance front the coil's center, is reduced by a factor of similar to12 (from 9.4 down to 0.73%) relative to a single-turn coil. Second, we analyze two different types of multilayer coils: one having for all the layers the same 0.86:1 optimum LID (a coil with a trapezoidal cross section of the winding); and another having for each layer a different LID (a coil with a rectangular cross section of the winding). The imitation error in this case is reduced by a factor of similar to22 and similar to33, correspondingly. We finally show that optimizing the multilayer coil makes the imitation error practically negligible (<0.28%) even at as short as four radii distances from the coil's center. Employing such optimized coil allows one to use the simple dipole model with a high degree of accuracy. It also relieves the system of having to spend extra time for computing the exact values of the coil field. (C) 2004 Elsevier B.V. All rights reserved.