Deactivatable E.A.S. marker having a step change in magnetic flu

Details Deactivatable E.A.S. marker having a step change in magnetic flu Deactivatable E.A.S. marker having a step change in magnetic flu

1987-11-04

1990-12-25

Swann, III, Glen R.

Communications: electrical

Condition responsive indicating system

Specific condition

340572, G08B 1324

Patent

active

049806700

ABSTRACT:
A magnetic marker is formed from a magnetic material having a hysteresis characteristic which is such that upon subjecting the material to an applied alternating magnetic field, the magnetic flux of the material undergoes a regenerative step change in flux at a threshold value when the field increases to the threshold value from substantially zero and undergoes a gradual change in flux when the field decreases from the threshold value to substantially zero. For increasing values of applied field below the threshold, there is substantially no change in the magnetic flux of the material. The aforesaid hysteresis characteristic of the marker is achieved by causing the material to have domains with a pinned wall configuration. Deactivation of the marker is realized by disabling the pinned walls from returning to their pinned condition via application of a deactivation field of high frequency and/or amplitude.

REFERENCES:
patent: 4581524 (1986-04-01), Hoekman et al.
patent: 4660025 (1987-04-01), Humphrey
patent: 4686516 (1987-08-01), Humphrey
Yamasaki, J. et al., "Domain Wall Induced Anisotropy During Annealing in Amorphous Ribbons," IEEE Transactions on Magnetics, vol. Mag.-20, No. 5, Sep. 1984.

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