Patent ID: 7427908
Filing Date: 2008-09-23
Classification: G01R

Abstract:
1. A shim assembly for improving magnetic field uniformity in an electromagnet having a central axis, a central bore which is aligned with said central axis and which is bounded by a cylindrical wall, a mid-plane which is orthogonal to said central axis, a z-axis lying along said central axis, an x-axis lying in said mid-plane and orthogonal to said z-axis, and a y-axis lying in said mid-plane and orthogonal to said z-axis and said x-axis, said shim assembly comprising: a. an A circuit having an A circuit loop which surrounds the −x axis; b. wherein the majority of said A circuit loop lies on the −z side of said mid-plane; c. a B circuit having a B circuit loop which surrounds the −x axis; d. wherein all of said B circuit loop lies on said −z side of said mid-plane; e. a C circuit having a C circuit loop which surrounds said y axis; f. wherein the majority of said C circuit loop lies on the −z side of said mid-plane; g. a D circuit having a D circuit loop which follows the same path as said C circuit, except that said D circuit is translated in the −z direction with respect to said C circuit so that all of said D circuit lies on the −z side of said mid-plane; h. an E circuit having a first E circuit loop and a second E circuit loop, wherein said first E circuit loop surrounds the +z-axis and said second E circuit loop surrounds the −z-axis; i. wherein said first E circuit loop lies on the +z side of said mid-plane and said second E circuit loop lies on said −z side of said mid-plane; j. an F circuit having a first plurality of F circuit loops, a second plurality of F circuit loops, and a third plurality of F circuit loops; and k. wherein said first plurality of F circuit loops lies on said +z side of said mid-plane, said second plurality of F circuit loops lies proximate said mid-plane, and said third plurality of F circuit loops lies on said −z side of said mid-plane.