Principles of active acoustic control in gradient coil design.

The new principles of active acoustic control in gradient coil design are introduced and theoretical expressions are developed for the far field acoustic output for a coil system comprising four or more flat rectangular coil sectors. Each sector consists of a split plate arrangement in which are embedded two windings, an outer primary winding and a narrow inner re-entrant loop control winding immediately adjacent to and surrounding the split or air gap. The wire spacing of the control winding is made small so as not to affect substantially the magnetic field created by the primary winding. Experimental results are produced for one sector which show an average difference in acoustic output of 34.9 dB when the control winding is appropriately driven. The theoretical expressions developed are used to fit the experimental data and indicate good agreement with regard to the form of the output response.