Patent ID: 6268723
Filing Date: 2001-07-31
Classification: G06K

Abstract:
An apparatus comprising:an exciter coil having a coil axis;a plurality of magnetic field detection coils spaced apart from one another along said coil axis on opposite sides and in proximity of said exciter coil;said exciter coil being operative to emit an excitation magnetic field that stimulates a transponder located in the direction of said coil axis, but beyond said plurality of detection coils and said exciter coil therebetween, to emit a response magnetic field; andsaid plurality of magnetic field detection coils being operative to detect said response magnetic field emitted by said transponder, and being arranged and electrically differentially coupled with one another to produce a composite, transponder-discriminating electrical output, in which responses of said magnetic field detection coils to said excitation magnetic field are canceled, but being representative of the difference in said response magnetic field emitted by said transponder as detected by said plurality of magnetic field detection coils.