Magnetostrictive element for use in a magnetomechanical surveillance system
AssigneeSensormatic Electronics Corporation
InventorNen-Chin Liu
Life of this patent
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Abstract
A magnetostrictive element for use in a magnetomechanical article surveillance marker formed by first annealing an amorphous metal alloy, such alloy comprising iron and cobalt with the proportion of cobalt being in the range of about 5 to about 45 atomic percent, in the presence of a saturating magnetic field and then second annealing the alloy in the absence of the saturating magnetic field.
Claims34
A magnetostrictive element for use in a magnetomechanical electronic article surveillance marker formed by first annealing a strip of amorphous metal alloy, said alloy comprising iron and cobalt with the proportion of cobalt being in the range of about 5 to about 45 atomic percent, in the presence of a saturating magnetic field so that said strip has a characteristic upon completion of said first annealing such that, upon application of a biasing magnetic field to said strip, said strip is mechanically resonant at a resonant frequency in response to exposure to an alternating magnetic field at said resonant frequency, said resonant frequency being subject to variation in dependence on changes in said biasing magnetic field and, subsequent to said first annealing, second annealing said strip to reduce a rate at which said resonant frequency varies in dependence on changes in said biasing magnetic field.
A marker for use in a magnetomechanical electronic article surveillance system comprising an amorphous magnetostrictive strip formed by first annealing an amorphous metal alloy, said alloy comprising iron and cobalt with the proportion of cobalt being in the range of about 5 to about 45 atomic percent, in the presence of a saturating magnetic field so that said strip has a characteristic upon completion of said first annealing such that, upon application of a biasing magnetic field to said strip, said strip is mechanically resonant at a resonant frequency in response to exposure to an alternating magnetic field at said resonant frequency, said resonant frequency being subject to variation in dependence on changes in said biasing magnetic field and, subsequent to said first annealing, second annealing said strip to reduce a rate at which said resonant frequency varies in dependence on changes in said biasing magnetic field.
A magnetomechanical electronic article surveillance system comprising (a) generating means for generating an electromagnetic field alternating at a selected frequency in an interrogation zone;
- (b) a marker comprising an amorphous magnetostrictive strip formed by first annealing an amorphous metal alloy, said alloy comprising iron and cobalt with the proportion of cobalt being in the range of about 5 to about 45 atomic percent, in the presence of a saturating magnetic field so that said strip has a characteristic upon completion of said first annealing such that, upon application of a biasing magnetic field to said strip, said strip is mechanically resonant at a resonant frequency in response to exposure to an alternating magnetic field at said resonant frequency, said resonant frequency being subject to variation in dependence on changes in said biasing magnetic field and, subsequent to said first annealing, second annealing said strip to reduce a rate at which said resonant frequency varies in dependence on changes in said biasing magnetic field and a biasing element to cause said magnetostrictive strip to be mechanically resonant when exposed to said alternating field;
- and (c) detecting means for detecting said mechanical resonance of said magnetostrictive strip.
Dependencies are inferred from the claim text.