Method, system and apparatus for magnetic surveillance of articles
First Claim
1. In a method for effecting article surveillance by the use of a time-varying signal establishing a magnetic field, the steps of providing first and second diverse magnetic materials, the first for application to articles under surveillance and the second for shielding said field, and preselecting said first and second magnetic materials to have respective diverse timewise responsivity to said magnetic field.
2 Assignments
0 Petitions
Accused Products
Abstract
Surveillance of magnetically tagged articles in a control zone is effected in a noisy environment by so shielding an antenna establishing a front magnetic field in the control zone as to reduce field strength in the back field rearwardly of the control zone. Shield magnetic material has response to the field which is detectably distinct from tag material response to the field.
39 Citations
50 Claims
- 1. In a method for effecting article surveillance by the use of a time-varying signal establishing a magnetic field, the steps of providing first and second diverse magnetic materials, the first for application to articles under surveillance and the second for shielding said field, and preselecting said first and second magnetic materials to have respective diverse timewise responsivity to said magnetic field.
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13. A method for determining the presence of a magnetic article surveillance tag selectively in a control zone, said method comprising the steps of:
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(a) selecting an alternating transmitting excitation signal for establishing a magnetic field for such surveillance and having current peaks at positive and negative levels and a zero-crossover therebetween; (b) selecting tag magnetic material of character responsive to said magnetic field in maximum amplitude near such zero-crossovers; (c) selecting magnetic shielding material of character responsive to said magnetic field in maximum amplitude other than at such zero-crossovers; (d) disposing magnetic shield members comprised of said magnetic shielding material at side margins of said control zone; (e) establishing said magnetic field locally interiorly of said shield members; and (f) processing signals received from said shielding material and said tag material in manner suppressing surveillance output alarm indication for received signal content attributable to such shielding material and generating surveillance output alarm indication for received signal content attributable to said tag material. - View Dependent Claims (14, 15, 16, 17, 18)
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19. A system for use in determining the presence of a magnetic article surveillance tag selectively in a control zone, said system comprising:
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(a) means for establishing an alternating magnetic field in said control zone by use of an excitation signal having current peaks at positive and negative levels and a zero-crossover therebetween; (b) magnetic shielding material of character responsive to said magnetic field in maximum amplitude other than near such zero-crossovers; (c) magnetic shield members at side margins of said control zone and comprised of said magnetic shielding material; and (d) processing means for receiving signals from said shielding material and processing same in manner suppressing surveillance output alarm indication for received signal content attributable to such shielding material. - View Dependent Claims (20, 21, 22, 23, 24, 25, 26, 27, 28)
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29. Shielding apparatus for use in a system for determining the presence of magnetic article surveillance tags selectively in a control zone, said system employing a time-varying signal of preselected frequency to establish a magnetic field in said control zone, said shielding apparatus comprising:
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(a) a first shield including magnetic material having a skin depth minimizing eddy current generation in said first shield responsively to said magnetic field; and (b) a second shield including electrically conductive material having a skin depth effecting eddy current generation in said second shield responsively to signals generated by said tags responsively to said magnetic field. - View Dependent Claims (30, 31, 32, 33)
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34. Apparatus for use in a system for determining the presence of a magnetic article surveillance tag selectively in a control zone, said system being of type including means for generating a magnetic field by use of alternating excitation signal having current peaks at positive and negative levels and a zero-crossover therebetween, said apparatus comprising:
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(a) a shielding member including magnetic shielding material of character responsive to said excitation signal in maximum amplitude other than near such zero-crossovers; (b) a transmitting antenna juxtaposed with said shielding member and adapted for establishing a magnetic field responsively to said excitation signal; and (c) a receiving antenna juxtaposed with said shielding member and adapted to be responsive to perturbations induced in said magnetic field by said shielding member and said tag. - View Dependent Claims (35, 36, 37, 38, 39, 40, 41)
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42. An electronic article surveillance system to detect the presence of a magnetic article surveillance tag in a control zone, comprising:
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(a) transmitter means for transmitting alternating magnetic energy into said control zone; (b) receiving means for detecting perturbations of said magnetic energy caused by the presence of magnetic tags within said control zone; (c) signal processing means connected to said receiving means to cause an alarm condition when said active tag is in said control zone; (d) a shield member located at a side margin of said control zone; (e) said shield member comprising magnetic shield material being of composition to reduce the intensity of magnetic energy in the back field located in a zone behind said shield member to lessen the probability of objects in said back field causing an alarm condition; (f) said magnetic shield material being of composition to produce principal perturbations of said magnetic energy which are detectably distinguishable from the perturbations caused by said magnetic tag; (g) said signal processing means being adapted to suppress said principal perturbations caused by said magnetic shield material to preclude an alarm condition from said magnetic shield perturbations. - View Dependent Claims (43, 44, 45, 46, 47, 48, 49, 50)
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Specification