Improvement in the Magnetic Detecting Power of Iron-cored Search Coils

Abstract

SLOWLY changing magnetic fields have usually been measured by means of search coils with iron or mumetal cores, connected either to fluxmeters or to galvanometers. In this communication the term ‘coiled rod’ is employed and means a straight ferromagnetic rod about which a detector-coil is wound. The sensitivity or detecting power of the coiled rod is usually defined as the total number of flux linkages of the winding produced in the coiled rod by a spatially uniform magnetic field of one oersted and is measured in Maxwell-turns per oersted. The advantage of mumetal over iron for the core of the coiled rod has been its high permeability in low magnetic fields, low electrical losses and low coercive force. Any further increase in sensitivity of coiled rods has been obtained either by lengthening the rod and so reducing its demagnetizing factor or by winding on more turns—the latter case being accompanied by a rapid increase in inductance and by increased resistance unless the diameter of the wire in the coil is correspondingly increased, which in turn affects the overall diameter.