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Eddy Current-Induced Stray Magnetic Field Cancellation Technique for B-H Loop Applications

IP.com Disclosure Number: IPCOM000046728D
Original Publication Date: 1983-Aug-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 3 page(s) / 57K

Publishing Venue

IBM

Related People

Hamaker, RW: AUTHOR [+3]

Abstract

The use of hysteresigraphic techniques to characterize the magnetic properties of both thick and thin film samples is well known in the literature [1-4]. Such techniques provide both a rapid and a reasonably accurate method for determining the B-H loop characteristics of a film sample. One common B-H loop measurement procedure is to introduce a magnetic film sample into a sense coil, whose output had previously been nulled by a similar coil (bucking coil) in series with the sense coil prior to sample introduction. The resultant output signal is differentially amplified and integrated, then displayed on a CRT screen, as shown schematically in Fig. 1. The differential mode of sample detection has an inherent advantage over the single-ended sense coil mode of operation.

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Eddy Current-Induced Stray Magnetic Field Cancellation Technique for B-H Loop Applications

The use of hysteresigraphic techniques to characterize the magnetic properties of both thick and thin film samples is well known in the literature [1-4]. Such techniques provide both a rapid and a reasonably accurate method for determining the B-H loop characteristics of a film sample. One common B-H loop measurement procedure is to introduce a magnetic film sample into a sense coil, whose output had previously been nulled by a similar coil (bucking coil) in series with the sense coil prior to sample introduction.

The resultant output signal is differentially amplified and integrated, then displayed on a CRT screen, as shown schematically in Fig. 1. The differential mode of sample detection has an inherent advantage over the single-ended sense coil mode of operation. In the differential bucking mode, common-mode noise is cancelled directly between a closely matched pair of coils. In addition, elaborate electronic filtering schemes may be required to suppress external electromagnetic noise sources in the single-ended sense coil mode of operation. If mutual inductive coupling effects between the two coils are minimized in the differential mode, then much less complex electronic circuitry will be required over the single-ended mode. In general, magnetic film samples to be characterized are deposited on flat glass slides or other dielectric substrates. Such substrates are non-conductive; hence, there is no detectable coupling between the exciting magnetic field and the substrate. On the other hand, metallic or other conductive materials are sometimes used as film substrates. In such instances, the exciting magnetic field will induce eddy currents within the substrate. Such eddy currents will, in turn, generate stray and unpredictable magnetic fields that may produc...