Device for detecting magnetic fields and method of making same

Claim 1

Apparatus for detecting a magnetic field in a region comprising a magnetoresistive element responsive to a DC energizing current, means for applying an alternating magnetic field of predetermined frequency and phase to the element, said element being responsive to the magnetic field in the region and the alternating magnetic field so that the fields are combined in the element to modulate the energizing current, whereby the energizing current in the element has an AC component at the predetermined frequency and a phase determined by the phase of the alternating magnetic field and the field in the region, and means for comparing the predetermined phase with the phase of the AC component to detect the field.

Claim 25

A method of making an apparatus for enabling fringing magnetic fields established by magnetic bars having parallel longitudinal axes on documents to be read, said fringing fields extending in opposite directions to the magnetic polarization directions of the bars, the apparatus including an array of magnetoresistive elements adapted to be responsive to a DC energizing current, at least one of said elements being provided for each of the fields, said elements being adapted to be positioned to be responsive to the fringing fields, a conductor effectively forming a single turn coil adapted to apply an alternating magnetic field of predetermined frequency and phase to each of the elements, said alternating magnetic field being superimposed on the fringing field coupled to each element so that the alternating and fringing fields are combined in each element to modulate the energizing current at the predetermined frequency with a phase determined by the phase of the alternating magnetic field and the fringing field direction, a non-magnetic, dielectric substrate carrying corresponding conductors and elements in registration, said conductors and elements being mutually insulated metal films on the substrate; the method comprising the steps of depositing the conductors as a thin conductive layer over an entire area of the non-magnetic dielectric substrate, etching the conductive layer to form in it, in a single operation, mutually parallel conductive layers and interconnections for groups of the parallel layers to terminals situated at a first edge of the substrate and to a common point situated at a second edge of the substrate, depositing on a part of the conductive layer an insulating layer so only the terminals and the common point are exposed, depositing the elements as a magnetoresistive layer extending over the part of the insulating layer covering the conductive layers, depositing a conductive layer in two parts, each of said parts partially overlapping an edge of the magnetoresistive layer having an orientation perpendicular to that of the underlying line of conductive layers, etching the magnetoresistive layer and the two parts of the conductive layer to form in them bands having magnetoresistive parts aligned with the underlying conductive layers, depositing an insulating layer over the area covered by said bands, etching openings in the insulating layer on either side of the underlying magnetoresistive layers, said openings being aligned in staggered groups in directions perpendicular to that of the bands, the openings being consecutive in each group on one side and spaced apart by the number of bands corresponding to the number of magnetoresistive layers in each group on the other side, depositing a conductive layer over the insulating layer contacting the transverse bands through the openings, and etching the last named conductive layer into bands extending to one edge of the substrate.

Claim 26

A method of making an apparatus for enabling fringing magnetic fields established by magnetic bars having parallel longitudinal axes on documents to be read, said fringing fields extending in opposite directions to the magnetic polarization directions of the bars, the apparatus including an array of magnetoresistive elements adapted to be responsive to a DC energizing current, at least one of said elements being provided for each of the fields, said elements being adapted to be positioned to be responsive to the fringing fields, a conductor effectively forming a single turn coil adapted to apply an alternating magnetic field of predetermined frequency and phase to each of the elements, said alternating magnetic field being superimposed on the fringing field coupled to each element so that the alternating and fringing fields are combined in each element to modulate the energizing current at the predetermined frequency with a phase determined by the phase of the alternating magnetic field and the fringing field direction, a non-magnetic, dielectric substrate carrying corresponding conductors and elements in registration, said conductors and elements being mutually insulated metal films on the substrate; the method comprising the steps of depositing the conductors as a thin conductive layer over an entire area of the non-magnetic dielectric substrate, etching the conductive layer to form in it, in a single operation, mutually parallel conductive layers and interconnections for groups of the parallel layers to terminals situated at a first edge of the substrate and to a common point situated at a second edge of the substrate, depositing on a part of the conductive layer an insulating layer so only the terminals and the common point are exposed, depositing the elements as a magnetoresistive layer extending over the part of the insulating layer covering the conductive layers, depositing a conductive layer in two parts, each of said parts partially overlapping an edge of the magnetoresistive layer having an orientation perpendicular to that of the underlying line of conductive layers, etching the magnetoresistive layer and the two parts of the conductive layer to form in them bands having magnetoresistive parts aligned with the underlying conductive layers, depositing an insulating layer over the area covered by said bands, etching openings in the insulating layer on either side of the underlying magnetoresistive layers, said openings being aligned in staggered groups in directions perpendicular to that of the bands, the openings being consecutive in each group on one side and spaced apart by the number of bands corresponding to the number of magnetoresistive layers in each group on the other side, depositing a conductive layer over the insulating layer contacting the transverse bands through the openings, and etching the last named conductive layer into bands extending to one edge of the substrate.