Magnetic field sensing apparatus for sensing the proximity of a member having high magnetic permeability without requiring an external field source

TLDR: In this paper, a bias magnetic field is generated by a magnetoresistive element in a direction perpendicular to one of the main current conducting paths and which is sensed by the element, whereby an output signal is produced from the junction in the element as a function of the relative positions of leading and trailing edges of the member with respect to the magnetic element.

Abstract: Apparatus is provided for producing an output signal upon sensing the proximity of a member having relatively high magnetic permeability. The apparatus includes a magnetoresistive element which is comprised of an insulating substrate upon which first and second ferromagnetic strips are provided. The ferromagnetic strips define first and second main current conducting paths which are respectively perpendicular to each other. The strips are connected in series to define a junction therebetween from which an output signal is derived. Current supply terminals are provided for furnishing an energizing current to the magnetoresistive element, which energizing current flows in a direction from one to the other of the current supply terminals. A bias magnetic field is provided in a direction perpendicular to one of the main current conducting paths and which is sensed by the element. A portion of this bias field is received by a member having a relatively high magnetic permeability which is proximate the element, thereby altering the distribution of the received portion of the bias field to produce a composite field which can be considered a vector formed of the bias field and the field attributed to the permeable material. The composite field is a function of the spacing between the element and the member and the longitudinal positioning of the member with respect to the element. This composite magnetic field is sensed by the element, whereby an output signal is produced from the junction in the element as a function of the relative positions of leading and trailing edges of the member with respect to the magnetoresistive element.