Patent ID: 7977937
Filing Date: 2011-07-12
Classification: G01R

Abstract:
1. method for detecting the presence of a small magnetized particle proximate to a planar sensor having a magnetic configuration, wherein the magnetization of said small magnetized particle is accomplished by subjecting said particle to an applied magnetic field, wherein said magnetic field has all in-plane field components in the plane of said sensor substantially eliminated, wherein said applied magnetic field produces a magnetic stray field in the vicinity of said particle, wherein said stray field has an in-plane component and wherein said magnetic configuration of said sensor is affected by said in-plane component of said stray field and wherein said detecting of said presence of said small magnetized particle is accomplished by monitoring said affected magnetic configuration of said sensor, said method comprising said substantial elimination of said in-plane component of said applied field by positioning at least one planar magnetic keeper layer proximate to, at least coextensive with and parallel to said sensor.