Permanent magnet assembly with MR sensor drift compensation

摘要

A magnetic assembly (60) for detection and authentication of magnetic documents (11). The magnetic assembly (60) includes a permanent magnet (PM) (62), first and second magnetically soft high permeability pole pieces (64,66) shaped to form a tapered, variable gap size magnetic circuit with the permanent magnet (62). The PM (62)is located at a first gap (g) between the first and second pole pieces (64,66). A magnetoresistive (MR) sensing element (68) is located at or near the center of a second gap (G) between said first and second pole pieces (64,66). The second gap (G) and MR sensing element (68) are proximate a magnetic document (11) to be sensed. An electrical conductor (80) is adjacent to the MR sensing element (68), but is electrically insulated therefrom. <IMAGE>