Magnetostrictive element having optimized bias-field-dependent resonant frequency characteristic
DCFirst Claim
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1. A magnetomechanical electronic article surveillance marker comprising:
- a magnetostrictive element for use as an active element in said marker;
said element being a strip of amorphous metal alloy, said element having been annealed so as to relieve stress in said element, said element having a resonant frequency that varies according to a level of a bias magnetic field applied to said element and having a bias-field-dependent resonant frequency characteristic such that the resonant frequency of said element varies by a total of no more than 800 Hz as the bias field applied to said element varies in the range of 4 Oe to 8 Oe.
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Abstract
A magnetostrictive element for use in a magnetomechanical marker has a resonant frequency characteristic that is at a minimum at a bias field level corresponding to the operating point of the magnetomechanical marker. The magnetostrictive element has a magnetomechanical coupling factor k in the range 0.28 to 0.4 at the operating point. The magnetostrictive element is formed by applying current-annealing to an iron-nickel-cobalt based amorphous metal ribbon, or by cross-field annealing an iron-nickel-cobalt alloy that includes a few percent chromium and/or niobium.
33 Citations
35 Claims
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1. A magnetomechanical electronic article surveillance marker comprising:
- a magnetostrictive element for use as an active element in said marker;
said element being a strip of amorphous metal alloy, said element having been annealed so as to relieve stress in said element, said element having a resonant frequency that varies according to a level of a bias magnetic field applied to said element and having a bias-field-dependent resonant frequency characteristic such that the resonant frequency of said element varies by a total of no more than 800 Hz as the bias field applied to said element varies in the range of 4 Oe to 8 Oe. - View Dependent Claims (2, 3, 4)
- a magnetostrictive element for use as an active element in said marker;
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5. A magnetomechanical electronic article surveillance marker, comprising:
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an active element in the form of a strip of amorphous magnetostrictive metal alloy; and means for applying a magnetic bias at a level HB to said active element, HB being greater than 3 Oe; said active element having been annealed to relieve stress therein, and having a resonant frequency that varies according to a level of the bias magnetic field applied to said element;
said active element having a bias-field-dependent resonant frequency characteristic such that the resonant frequency of said active element varies by a total of no more than 600 Hz as the bias field applied to said active element varies in the range of HB minus 1.5 Oe to HB plus 1.05 Oe. - View Dependent Claims (6, 7, 8)
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9. A magnetomechanical electronic article surveillance marker comprising:
- a magnetostrictive element for use as an active element in said marker;
said element being a strip of amorphous metal alloy, said element having been annealed so as to relieve stress in said element, said element having a resonant frequency that varies according to a level of a bias magnetic field applied to said element and having a bias-field-dependent resonant frequency characteristic that has a slope of substantially zero at a point in the range of bias field levels defined as 3 Oe to 9 Oe.
- a magnetostrictive element for use as an active element in said marker;
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10. A magnetomechanical electronic article surveillance marker, comprising:
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an active element in the form of a strip of amorphous magnetostrictive metal alloy; and means for applying a magnetic bias at a level HB to said active element, HB being greater than 3 Oe; said active element having been annealed to relieve stress therein, and having a resonant frequency that varies according to a level of the bias magnetic field applied to said element;
said active element having a bias-field-dependent resonant frequency characteristic that has a slope of substantially zero at a point in the range of bias field levels defined as 3 Oe to 9 Oe.
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11. A magnetomechanical electronic article surveillance marker comprising:
- a magnetostrictive element for use as an active element in said marker;
said element being a strip of amorphous metal alloy, said element having been annealed so as to relieve stress in said element, said element having a resonant frequency that varies according to a level of a bias magnetic field applied to said element and having a bias-field-dependent resonant frequency characteristic such that the resonant frequency of said element is at a minimum level at a point in the range of bias field levels defined as 3 Oe to 9 Oe.
- a magnetostrictive element for use as an active element in said marker;
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12. A magnetomechanical electronic article surveillance marker, comprising:
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an active element in the form of a strip of amorphous magnetostrictive metal alloy; and means for applying a bias magnetic field at a level HB to said active element, HB being greater than 3 Oe; said active element having been annealed to relieve stress therein, and having a resonant frequency that varies according to a level of the bias magnetic field applied to said element;
said active element having a bias-field-dependent resonant frequency characteristic such that the resonant frequency of said active element is at a minimum level at a point in the range of bias field levels defined as HB minus 1.5 Oe to HB plus 1.5 Oe.
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13. A magnetomechanical electronic article surveillance marker comprising:
- a magnetostrictive element for use as an active element in said marker, said active element having been formed by heat-treating a strip of amorphous metal alloy while applying an electrical current along said strip, said alloy having a composition consisting essentially of Fea Nib Coc Bd Sie, with 30≦
a≦
80, 0≦
b≦
40, 0≦
c≦
40, 10≦
d+e≦
25. - View Dependent Claims (14, 15)
- a magnetostrictive element for use as an active element in said marker, said active element having been formed by heat-treating a strip of amorphous metal alloy while applying an electrical current along said strip, said alloy having a composition consisting essentially of Fea Nib Coc Bd Sie, with 30≦
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16. A method of forming a magnetostrictive element for use in a magnetomechanical EAS marker, comprising the steps of:
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annealing an amorphous metal alloy strip; and during said annealing step, applying an electrical current along a length of said strip; wherein said alloy has a composition consisting essentially of Fea Nib Coc Bd Sie, with 30≦
a≦
80, 0≦
b≦
40, 0≦
c≦
40, 10≦
d+e≦
25. - View Dependent Claims (17, 18)
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19. A method of forming a magnetostrictive element for use in a magnetomechanical EAS marker, comprising the steps of:
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annealing an amorphous metal alloy strip during application of a magnetic field directed transverse to a longitudinal axis of said strip; and subsequent to said annealing step, applying an electrical current along said longitudinal axis of said strip; wherein a magnetic field is applied along said longitudinal axis of said strip during said current-application step. - View Dependent Claims (20, 21)
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22. A magnetomechanical electronic article surveillance marker comprising:
- a magnetostrictive element for use as an active element in said marker, said active element having been formed by heat-treating a strip of amorphous metal alloy and then, after said heat-treatment, applying an electrical current along said strip;
wherein said heat-treatment of said strip is performed in the presence of a magnetic field directed transversely to a longitudinal axis of said strip to induce a transverse anisotropy in said strip. - View Dependent Claims (23)
- a magnetostrictive element for use as an active element in said marker, said active element having been formed by heat-treating a strip of amorphous metal alloy and then, after said heat-treatment, applying an electrical current along said strip;
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24. A magnetomechanical EAS marker, comprising
an active element in the form of a strip of amorphous magnetostrictive metal alloy having a composition essentially of Fea Nib Coc Crd Nbe Bf Sig ; - and
means for applying a magnetic bias at a level HB to said active element, HB being greater that 3 Oe; said active element having been annealed to relieve stress therein and having a magnetomechanical coupling factor k, such that 0.28≦
k≦
0.4 at the applied bias level HB ;with 69≦
a+b+c≦
75;
26≦
a≦
45;
0≦
b≦
23;
17≦
c≦
40;
2≦
d+e≦
8;
0≦
d;
0≦
e;
20≦
f+g≦
23;
f≧
4g. - View Dependent Claims (25, 26, 27)
- and
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28. A magnetomechanical electronic article surveillance marker comprising:
- a magnetostrictive element for use as an active element in said marker;
said element being a strip of amorphous metal alloy, said element having been annealed so as to relieve stress in said element, said element having a magnetomechanical coupling factor k in a range of about 0.28 to 0.4 at a bias field level that corresponds to a minimum resonant frequency of said element, said alloy including iron, boron and no more than 40% cobalt. - View Dependent Claims (29, 30, 31)
- a magnetostrictive element for use as an active element in said marker;
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32. A magnetomechanical electronic article surveillance system comprising:
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(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 strip of magnetostrictive amorphous metal alloy, said alloy strip having been annealed so as to relieve stress in said alloy strip, said alloy strip having a resonant frequency that varies according to a level of a bias magnetic field applied to said alloy strip, said alloy strip also having a bias-field-dependent resonant frequency characteristic such that the resonant frequency of said alloy strip varies by a total of no more than 800 Hz as the bias field applied to said alloy strip varies in the range of 4 Oe to 8 Oe;
said marker also including means for applying a magnetic bias to said alloy strip so that said strip is magnetomechanically resonant when exposed to said alternating field at said selected frequency; and(c) detecting means for detecting said magnetomechanical resonance of said alloy strip. - View Dependent Claims (33, 34, 35)
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Specification