Transverse magnetic field annealed amorphous magnetomechanical elements for use in electronic article surveillance system and method of making same
AssigneeSensormatic Electronics Corporation
InventorsNen-chin Liu, Ming-Ren Lian, Jimmy Cantey
Life of this patent
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Abstract
A ribbon-shaped strip of an amorphous magnetic alloy is heat treated, while applying a transverse saturating magnetic field. The treated strip is used in a marker for a pulsed-interrogation electronic article surveillance system. A preferred material for the strip is formed of iron, cobalt, silicon and boron with the proportion of cobalt exceeding 30% by atomic percent.
Claims53
A marker for use in a magnetomechanical electronic article surveillance system, comprising an amorphous magnetostrictive strip formed of an alloy of iron and cobalt in which the proportion of cobalt is at least 30% by atomic percent.
A method of fabricating a marker for use in a magnetomechanical electronic article surveillance system, comprising the steps of:
- providing an amorphous magnetostrictive element formed of an alloy of iron and cobalt in which the proportion of cobalt is at least 30% by atomic percent;
- and
- mounting the magnetostrictive element in a mounting means in proximity to a biasing element which provides a dc magnetic biasing field for the magnetostrictive element so that the magnetostrictive element has a predetermined magnetomechanical resonant frequency.
A magnetomechanical electronic article surveillance system comprising:
- (a) generating means for generating an electromagnetic field alternating at a selected frequency in an interrogation zone, said generating means including an interrogation coil;
- (b) a marker secured to an article appointed for passage through said interrogation zone, said marker including an amorphous magnetostrictive element formed of an alloy of iron and cobalt in which the proportion of cobalt is at least 30% by atomic percent, said marker also including a biasing element located adjacent to said magnetostrictive element, said biasing element being magnetically biased to cause said magnetostrictive element to be mechanically resonant when exposed to said alternating field;
- and
- (c) detecting means for detecting said mechanical resonance of said magnetostrictive element.
A method of fabricating a marker for use in a magnetomechanical electronic article surveillance system, the method comprising the steps of:
- applying a saturating magnetic field to an amorphous magnetic element;
- heating said element at a temperature in the range of 460.degree. to 540.degree. C. for at least 5 minutes during application of said magnetic field;
- and
- allowing the annealed element to cool to room temperature.
A marker for use in a magnetomechanical electronic article surveillance system, comprising a magnetostrictive element formed by annealing an amorphous magnetic member by applying a saturating magnetic field to said member while heating said member at a temperature in the range of 460.degree. C. to 540.degree. C. for at least 5 minutes.
A magnetomechanical electronic article surveillance system comprising:
- (a) generating means for generating an electromagnetic field alternating at a selected frequency in an interrogation zone, said generating means including an interrogation coil;
- (b) a marker secured to an article appointed for passage through said interrogation zone, said marker including an amorphous magnetostrictive element formed by annealing an amorphous magnetic member by applying a saturating magnetic field to said member while heating said member at a temperature in the range of 460.degree. C. to 540.degree. C. for at least 5 minutes, said marker also including a biasing element located adjacent to said magnetostrictive element, said biasing element being magnetically biased to cause said magnetostrictive element to be mechanically resonant when exposed to said alternating field;
- and
- (c) detecting means for detecting said mechanical resonance of said magnetostrictive element.
A marker for use in a magnetomechanical electronic article surveillance system, comprising:
- (a) an amorphous magnetostrictive element;
- (b) a biasing element located adjacent to said magnetostrictive element;
- (c) said magnetostrictive element and said biasing element being contained within a housing;
- (d) the overall thickness of said housing being less than 0.065 inches.
A method of making a marker for use in a magnetomechanical electronic article surveillance system, the method comprising the steps of:
- (a) applying a saturating magnetic field to an amorphous magnetostrictive element formed of an alloy that comprises iron and at least 30% cobalt by atomic percent;
- (b) heating said element at a temperature in the range of 300.degree. to 540.degree. C. for at least 5 minutes during application of said magnetic field;
- (c) allowing the annealed element to cool to room temperature;
- and
- (d) mounting said cooled magnetostrictive element and a biasing element within a housing that has an overall thickness of less than 0.065 inches.
A magnetomechanical electronic article surveillance system comprising:
- (a) generating means for generating an electromagnetic field alternating at a selected frequency in an interrogation zone, said generating means including an interrogation coil;
- (b) a marker secured to an article appointed for passage through said interrogation zone, said marker including an amorphous magnetostrictive element and a biasing element located adjacent to said magnetostrictive element, said magnetostrictive element and said biasing element being contained within a housing, the overall thickness of said housing being less than 0.065 inches, said biasing element being magnetically biased to cause said magnetostrictive element to be mechanically resonant when exposed to said alternating field;
- and
- (c) detecting means for detecting said mechanical resonance of said magnetostrictive element.
A marker for use in a magnetomechanical electronic article surveillance system, comprising:
- (a) an amorphous magnetostrictive element;
- (b) a biasing element located adjacent said magnetostrictive element;
- and
- (c) said magnetostrictive element having a hysteresis loop characteristic such that said magnetostrictive element does not produce detectable harmonic frequencies when in an alternating electromagnetic field.
A method of making a marker for use in a magnetomechanical electronic article surveillance system, the method comprising the steps of:
- (a) making an amorphous magnetostrictive element;
- and
- (b) mounting said magnetostrictive element adjacent to a biasing element;
- said magnetostrictive element having a hysteresis loop characteristic such that said magnetostrictive element does not produce detectable harmonic frequencies when in an alternating electromagnetic 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, said generating means including an interrogation coil;
- (b) a marker secured to an article appointed for passage through said interrogation zone, said marker including an amorphous magnetostrictive element and a biasing element located adjacent to said magnetostrictive element, said magnetostrictive element having a hysteresis loop characteristic such that said magnetostrictive element does not produce detectable harmonic frequencies when in an alternating electromagnetic field, said biasing element being magnetically biased to cause said magnetostrictive element to be mechanically resonant when exposed to said alternating field at said selected frequency;
- and
- (c) detecting means for detecting said mechanical resonance of said magnetostrictive element.
A method of forming a magnetostrictive element, the method comprising the steps of:
- (a) providing an amorphous magnetic material;
- and
- (b) heat treating said material in the presence of a saturating magnetic field, said heat treating being performed so as to smooth a hysteresis characteristic of said material.
A method of making a magnetostrictive element for use as a marker in a magnetomechanical electronic article system comprising:
- (a) selecting an amorphous magnetic material;
- (b) cutting the said material to a strip having a fixed uniform length preselected to ultimately make the strip mechanically resonant at a desired frequency;
- (c) annealing the said strip at a temperature between 300.degree. C. and 540.degree. C. for a period of time between 2 and 60 minutes in a transverse magnetic field having a strength of at least 500 oersteds;
- and
- (d) cooling said strip to room temperature for a period of not less than two minutes in a transverse magnetic field having a strength of at least 500 oersteds;
- whereby said strip exhibits magnetostrictive properties having the said desired mechanical resonant frequency and has a unique detectable signal during a ring down period.
A marker for use in a magnetomechanical electronic article surveillance system, comprising a magnetostrictive element made by selecting an amorphous magnetic material, cutting said material to a strip having a fixed uniform length preselected to ultimately make the strip mechanically resonant at a desired frequency, annealing the said strip at a temperature between 300.degree. C. and 540.degree. C. for a period of time between 2 and 60 minutes in a transverse magnetic field, and cooling said strip to room temperature over a period of not less than two minutes in a transverse magnetic field having a strength of at least 500 oersteds;
- wherein said strip exhibits magnetostrictive properties having the said desired mechanical resonant frequency and has a unique detectable signal during a ring down period.
A magnetomechanical electronic article surveillance system comprising:
- (a) generating means for generating an electromagnetic field alternating at a selected frequency in an interrogation zone, said generating means including an interrogation coil;
- (b) a marker secured to an article appointed for passage through said interrogation zone, said marker including a magnetostrictive strip made by selecting an amorphous magnetic material, cutting said material to a strip having a fixed uniform length preselected to ultimately make the strip mechanically resonant at said selected frequency, annealing the said strip at a temperature between 300.degree. C. and 540.degree. C. for a period of time between 2 and 60 minutes in a transverse magnetic field having a strength of at least 500 oersteds and cooling said strip to room temperature over a period of not less than two minutes in a transverse magnetic field having a strength of at least 500 oersteds, said marker also including a biasing element located adjacent to said magnetostrictive strip, said biasing element being magnetically biased to cause said magnetostrictive strip to be mechanically resonant when exposed to said alternating field, said magnetostrictive strip having a unique signal during a ring down period;
- and
- (c) detecting means for detecting said unique signal of said magnetostrictive strip.
Dependencies are inferred from the claim text.