Patent ID: 6595419
Filing Date: 2003-07-22
Classification: G01V,G06K

Abstract:
A detector for sensing the presence of a magnetic tag having an easy axis of magnetisation, which detector comprises:i) two assemblies of permanent magnets, each assembly comprising a central magnet and at least one other secondary magnet disposed either side of the central magnet, the two assemblies being arranged such that each magnet of one assembly directly faces a magnet of the other assembly, thereby defining a gap through which, in use, the magnetic tag is passed with the easy axis of the tag oriented in the direction of travel; ii) one or more pair(s) of receiver coils connected in antiphase, the coils being arranged to receive dipole radiation which is emitted by the tag as it is passed through the gap, wherein the magnets from each assembly which directly face each other are arranged such that their like poles are directed towards the gap, and wherein the magnetic orientations of the secondary magnets of each assembly are opposite to that of the corresponding central magnet.