Magnetic detection of security articles
First Claim
1. A method for detecting the presence of magnetic elongated particles which function as security elements in a substrate which functions as a security document, the base material of said substrate having magnetic properties substantially differing from the corresponding magnetic properties of the elongated particles, said elongated particles having such a long and thin form that their demagnetisation factor N is smaller than 1/250, a diameter being smaller than 30 micrometer, a magnetic saturation field greater than 100 A/m and a magnetic saturation flux density being greater than 0.1 Tesla, said method comprising the following steps:
- (a) emitting an electromagnetic source signal of one or more particular base frequencies to said substrate so that any present magnetic elongated particles go into a non-linear part of their B-H curve for at least part of a cycle of the source signal;
(b) detecting an electromagnetic detection signal emanating from said substrate;
(c) testing the detection signal for the presence of particular higher harmonics of said base frequencies or of any linear combination of said base frequencies and of said harmonics, said particular higher harmonics being indicative of the presence of said magnetic elongated particles.
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Abstract
A method for detecting the presence of magnetic elongated particles in a substrate the base material of which has magnetic properties substantially differing from the corresponding magnetic properties of the elongated particles. The elongated particles have such a long and thin form that their demagnetisation factor N is smaller than 1/250, they have a diameter smaller than 30 micrometer and a magnetic saturation field greater than 100 A/m. The method comprising the following steps:
(a) emitting an electromagnetic source signal of one or more particular base frequencies to the substrate so that any present magnetic elongated particles go into a non-linear part of their B-H curve for at least part of a cycle of the source signal;
(b) detecting an electromagnetic detection signal emanating from the substrate;
(c) testing the detection signal for the presence of particular higher harmonics of the base frequencies or of any linear combination of the base frequencies or of the harmonics, the particular higher harmonics being indicative of the presence of the magnetic elongated particles.
24 Citations
44 Claims
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1. A method for detecting the presence of magnetic elongated particles which function as security elements in a substrate which functions as a security document, the base material of said substrate having magnetic properties substantially differing from the corresponding magnetic properties of the elongated particles, said elongated particles having such a long and thin form that their demagnetisation factor N is smaller than 1/250, a diameter being smaller than 30 micrometer, a magnetic saturation field greater than 100 A/m and a magnetic saturation flux density being greater than 0.1 Tesla, said method comprising the following steps:
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(a) emitting an electromagnetic source signal of one or more particular base frequencies to said substrate so that any present magnetic elongated particles go into a non-linear part of their B-H curve for at least part of a cycle of the source signal; (b) detecting an electromagnetic detection signal emanating from said substrate; (c) testing the detection signal for the presence of particular higher harmonics of said base frequencies or of any linear combination of said base frequencies and of said harmonics, said particular higher harmonics being indicative of the presence of said magnetic elongated particles. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. A method for detecting the presence of magnetic elongated particles which function as security elements in a substrate which functions as a security document, the base material of said substrate having magnetic properties substantially differing from the corresponding magnetic properties of the elongated particles, said elongated particles having such a long and thin form that their demagnetisation factor N is smaller than 1/250, a diameter being smaller than 30 micrometer and a magnetic saturation field greater than 100 A/m, the combination of shape, composition and structure of the magnetic elongated particles is such that they have:
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i) a saturation field range being greater than 100 A/m; ii) a saturation flux density being greater than 0.1 Tesla; iii) a magnetic dynamic permeability ranging from 10 to 10000, said method comprising the following steps; (a) emitting an electromagnetic source signal of one or more particular base frequencies to said substrate so that any present magnetic elongated particles go into a non-linear part of their B-H curve for at least part of a cycle of the source signal; (b) detecting an electromagnetic detection signal emanating from said substrate; (c) testing the detection signal for the presence of particular higher harmonics of said base frequencies or of any linear combination of said base frequencies and of said harmonics, said particular higher harmonics being indicative of the presence of said magnetic elongated particles.
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- 19. A magnetic elongated particle for being incorporated in a base material of a substrate, said base material having magnetic properties differing substantially from the corresponding magnetic properties of said particle, said particle having such a long and thin form that its demagnetisation factor N is smaller than 1/250, a diameter being smaller than 30 micrometer, a magnetic saturation field greater than 100 A/m and a magnetic saturation flux density being greater than 0.1 Tesla.
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27. A magnetic elongated particle for being incorporated in a base material of a substrate, said base material having magnetic properties differing substantially from the corresponding magnetic properties of said particle, said particle having such a long and thin form that its demagnetisation factor N is smaller than 1/250, a diameter being smaller than 30 micrometer, a magnetic saturation field greater than 100 A/m and a D.C. magnetic remanence which is smaller than 0.3 Tesla.
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28. A magnetic elongated particle for being incorporated in a base material of a substrate, said base material having magnetic properties differing substantially from the corresponding magnetic properties of said particle, said particle having such a long and thin form that its demagnetisation factor N is smaller than 1/250, a diameter being smaller than 30 micrometer, a magnetic saturation field greater than 100 A/m and wherein the combination of shape, composition and structure of the magnetic particle is such that it has:
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i) a saturation field range from 100 to 1000 A/m; ii) a saturation flux density being greater than 0.1 Tesla; iii) a magnetic dynamic permeability μ
d ranging from 10 to 10000.
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- 29. A substrate comprising a base material and elongated particles inside said base material, the magnetic properties of said elongated particles differing from the corresponding magnetic properties of said base material, the elongated particles having such a long and thin form that their demagnetisation factor N is smaller than 1/250, their diameter being smaller than 30 micrometer, their magnetic saturation field greater than 100 A/m and wherein said elongated particles have a magnetic saturation flux density being greater than 0.1 Tesla.
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43. A substrate comprising a base material and elongated particles inside said base material, the magnetic properties of said elongated particles differing from the corresponding magnetic properties of said base material, the elongated particles having such a long and thin form that their demagnetisation factor N is smaller than 1/250, their diameter being smaller than 30 micrometer, their magnetic saturation field greater than 100 A/m and wherein the combination of shape, composition and structure of the magnetic elongated particles is such that they have:
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i) a saturation field range from 100 to 1000 A/m; ii) a saturation flux density being greater than 0.1 Tesla; iii) a magnetic dynamic permeability μ
d ranging from 10 to 10000.
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44. A substrate comprising a base material and elongated particles inside said base material, the magnetic properties of said elongated particles differing from the corresponding magnetic properties of said base material, the elongated particles having such a long and thin form that their demagnetisation factor N is smaller than 1/250, their diameter being smaller than 30 micrometer, their magnetic saturation field greater than 100 A/m and wherein said magnetic elongated particles have a D.C. magnetic remanence which is smaller than 0.3 Tesla.
Specification