1988-02-01

A New Era of Application for the Wiegand Effect 880406

This paper is presented to explain and demonstrate the most recent gains made in application techniques of the Wiegand Effect. “Wiegand Wire” is a small diameter wire drawn from a magnetic alloy such as Vicalloy and secondarily processed by cold working so as to cause a gradient of magnetic hardness from its center to exterior. When exposed to magnetic fields of proper orientation, intensities, and sequence, substantial flux jumps will occur within the wire. These flux changes may be converted to an electrical pulse by interposing an inductive pick up-coil.Being a bistable magnetic threshold device with a firing point of approximately 20 oersteds, the Wiegand Effect may be used to create self-powered pulsers which are essentially insensitive to speed and immune to most ambient magnetic field disturbances.In addition to the extremely successful application as an encoding technique for “Access Control Cards”, the Wiegand Effect has been applied in numerous commercial and industrial pulser designs where low speed, temperature extremes, and power considerations have made other technologies impractical.Although a wide variety of magnetic field shapes and intensities will cause Wiegand Effect flux jumps, it has become apparent that certain field shaping techniques and packaging designs have advantages over others from the aspect of output pulse amplitude, general physical size of components, and immunity from permanent disruption by strong external magnetic fields. In order to best utilize the inherent advantages of the Wiegand technology, it is important that the optimal application techniques be identified and understood.To this end, a great deal of development time has been devoted to investigating various magnetic excitation schemes and evaluating their results. The outcome was: 1. a three to four fold improvement in pulse amplitude under symmetric drive conditions; 2. a general reduction in physical component size; and 3. relative immunity from external magnetic field interference.This paper will summarize the laboratory findings, demonstrate optimal field shaping techniques, and suggest designs for practical, cost effective pulsers.

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