US4660025A
Expired / Lapsed
US
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Article surveillance magnetic marker having an hysteresis loop with large Barkhausen discontinuities
Assignee: Sensormatic Electronics Corp
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Filing: 1984-11-26
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Granted: 1987-04-21
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Expires: 2004-11-26
Abstract
Abstract A marker for an electronic article surveillance system is disclosed comprising a body of magnetic material with retained stress and having a magnetic hysteresis loop with a large Barkhausen discontinuity such that, upon exposure of the marker to an external magnetic field whose field strength in the direction opposing the instantaneous magnetic polarization of the marker exceeds a predetermined threshold value, there results a regenerative reversal of the magnetic polarization of the marker. An electronic article surveillance system and a method utilizing the marker are also disclosed. Exciting the marker with a low frequency and low field strength, so long as the field strength exceeds the low threshold level for the marker, causes a regenerative reversal of magnetic polarity generating a harmonically rich pulse that is readily detected and easily distinguished.
Inventors
- 👤 Floyd B. Humphrey
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-06 03:31
CPC Classifications
G; G08; G08B; G08B13/00; G08B13/22; G08B13/24; G08B13/2402; G08B13/2428; G08B13/2437; G08B13/244; G08B13/2442
Claims Analysis
Total Claims: 48
Claim 1
Independent Claim
108 words
A marker for use in an article surveillance system in which an alternating magnetic field is established in a surveillance region and an alarm is activated when a predetermined perturbation to said field is detected, said marker comprising a body of magnetic material with retained stress and having a magnetic hysteresis loop with a large Barkhausen discontinuity such that exposure of said body to an external magnetic field, whose field strength in the direction opposing the magnetic polarization of said body exceeds a predetermined threshold value, results in regenerative reversal of said magnetic polarization, and means for securing said body to an article to be maintained under sureveillance.
Claim 2
Dependent Claim
108 words
A marker for use in an article surveillance system in which an alternating magnetic field is established in a surveillance region and an alarm is activated when a predetermined perturbation to said field is detected, said marker comprising a body of magnetic material with retained stress and having a magnetic hysteresis loop with a large Barkhausen discontinuity such that exposure of said body to an external magnetic field, whose field strength in the direction opposing the magnetic polarization of said body exceeds a predetermined threshold value, results in regenerative reversal of said magnetic polarization, and means for securing said body to an article to be maintained under sureveillance.
Claim 3
Dependent Claim
18 words
A marker according to claim 1, characterized in that said body comprises a length of amorphous metal wire.
Claim 4
Dependent Claim
33 words
A marker according to claim 2, characterized in that said wire has a diameter within the range of 0.09 to 0.15 mm and a length within the range of 1 to 10 cm.
Claim 5
Dependent Claim
21 words
A marker according to claim 3, characterized in that the demagnetizing factor for said length of wire does not exceed 0.000125.
Claim 6
Dependent Claim
18 words
A marker according to claim 3, characterized in that said wire has a diameter of approximately 1/8 millimeter.
Claim 7
Dependent Claim
16 words
A marker according to claim 5, characterized in that said wire is approximately 7.6 cm long.
Claim 8
Dependent Claim
16 words
A marker according to claim 3, characterized in that said wire is approximately 7.6 cm long.
Claim 9
Dependent Claim
21 words
A marker according to claim 2, characterized in that the demagnetizing factor for said length of wire does not exceed 0.000125.
Claim 10
Dependent Claim
37 words
A marker according to claim 2, characterized in that the metallurgical composition of said wire is essentially given by the formula Fe 81 Si 4 B 14 C 1 , where the percentages are in atomic percent.
Claim 11
Dependent Claim
33 words
A marker according to claim 9, characterized in that said wire has a diameter within the range of 0.09 to 0.15 mm and a length within the range of 1 to 10 cm.
Claim 12
Dependent Claim
21 words
A marker according to claim 10, characterized in that the demagnetizing factor for said length of wire does not exceed 0.000125.
Claim 13
Dependent Claim
52 words
A marker according to claim 2, characterized in that the metallurgical composition of said wire is essentially given by the formula Fe 85-x Si x B 15-y C y , where the percentages are in atomic percent, x ranges from about 3 to 10, and y ranges from about 0 to 2.
Claim 14
Dependent Claim
12 words
A marker according to claim 12, characterized in that x=4 and y=0.
Claim 15
Dependent Claim
12 words
A marker according to claim 12, characterized in that x=7.5 and y=0.
Claim 16
Dependent Claim
27 words
A marker according to claim 1, characterized in that said body comprises a length of amorphous metal ribbon supported in a magnetic Barkhausen discontinuity inducing strained condition.
Claim 17
Dependent Claim
42 words
A marker according to claim 15, characterized in that said ribbon when restrained in a flat position has a helical easy axis of magnetization resulting from annealing said ribbon while twisted to relax helical stresses resulting from said twisting and thereafter untwisting.
Claim 18
Dependent Claim
28 words
A marker according to claim 16, characterized in that said length of ribbon is about 0.025 mm thick, about 2 mm wide, and 3 to 10 cm long.
Claim 19
Dependent Claim
28 words
A marker according to claim 15, characterized in that said length of ribbon is about 0.025 mm thick, about 2 mm wide, and 3 to 10 cm long.
Claim 20
Dependent Claim
51 words
A marker according to claim 1, characterized in that the perturbation accompanying said regenerative reversal of said magnetic polarization is in the form of a pulse having a duration of less than about 400 μSec. when said body is exposed to a magnetic field of about 1.2 oersteds at 20 hertz.
Claim 21
Dependent Claim
19 words
A marker according to claim 1, characterized in that said predetermined threshold value is no greater than 1.0 oersted.
Claim 22
Dependent Claim
38 words
A marker according to claim 1, characterized that said body comprises a length of amorphous metal wire which, due to its manufacturing history, contains locked in strain giving rise to said large Barkhausen discontinuity in said hysteresis loop.
Claim 23
Dependent Claim
33 words
A marker according to claim 21, characterized in that said wire has a diameter within the range of 0.09 to 0.15 mm and a length within the range of 1 to 10 cm.
Claim 24
Dependent Claim
18 words
A marker according to claim 22, characterized in that said wire has a diameter of approximately 1/8 millimeter.
Claim 25
Dependent Claim
16 words
A marker according to claim 23, characterized in that said wire is approximately 7.6 cm long.
Claim 26
Dependent Claim
52 words
A marker according to claim 21, characterized in that the metallurgical composition of said wire is essentially given by the formula Fe 85-x Si x B 15-y C y , where the percentages are in atomic percent, x ranges from about 3 to 10, and y ranges from about 0 to 2.
Claim 27
Dependent Claim
12 words
A marker according to claim 25, characterized in that x=4 and y=0.
Claim 28
Dependent Claim
12 words
A marker according to claim 25, characterized in that x=7.5 and y=0.
Claim 29
Dependent Claim
12 words
A marker according to claim 25, characterized in that x=4 and y=1.
Claim 30
Dependent Claim
65 words
A marker according to claim 1, in combination with a low frequency generator, a field generating coil assembly coupled to an output of said generator, a field receiving coil, a high pass filter, and means coupled to an output of said filter for detecting the presence of a series of frequency components above a predetermined frequency and above a pre-set amplitude for activating an alarm.
Claim 31
Dependent Claim
52 words
A marker according to claim 15, characterized in that the metallurgical composition of said ribbon is essentially given by the formula Fe 85-x Si x B 15-y C y , where the percentages are in atomic percent, x ranges from about 3 to 10, and y ranges from about 0 to 2.
Claim 32
Dependent Claim
12 words
A marker according to claim 30, characterized in that x=4 and y=0.
Claim 33
Dependent Claim
12 words
A marker according to claim 30, characterized in that x=7.5 and y=0.
Claim 34
Dependent Claim
12 words
A marker according to claim 30, characterized in that x=4 and y=1.
Claim 35
Dependent Claim
77 words
A marker for use in an article surveillance system in which an alternating magnetic field is established in a surveillance region and an alarm is activated when a predetermined perturbation to said field is detected, said marker comprising a body of magnetic material characterized in that the magnetic polarity thereof commences and completes reversal when the magnitude of strength of said field attains a given value, without need for increase in field strength above said given value.
Claim 36
Dependent Claim
77 words
A marker for use in an article surveillance system in which an alternating magnetic field is established in a surveillance region and an alarm is activated when a predetermined perturbation to said field is detected, said marker comprising a body of magnetic material characterized in that the magnetic polarity thereof commences and completes reversal when the magnitude of strength of said field attains a given value, without need for increase in field strength above said given value.
Claim 37
Independent Claim
139 words
A method for detection of the presence of an article in an interrogation zone comprising the steps of: a. generating an incident alternating low frequency magnetic field within an interrogation zone; b. securing a marker to an article, said marker being selected to comprise a body of magnetic material with retained stress and having a magnetic hysteresis loop with a large Barkausen discontinuity such that upon exposure of said body to an external magnetic field, whose field strength in the direction opposing the magnetic polarization of said body exceeds a given threshold value, there results a regenerative reversal of said magnetic polarization; and c. detecting perturbations of the magnetic field in said interrogation zone having a frequency higher than the 30th harmonic of the incident alternating low frequency magnetic field when said marker is present in said interrogation zone.
Claim 38
Independent Claim
139 words
A method for detection of the presence of an article in an interrogation zone comprising the steps of: a. generating an incident alternating low frequency magnetic field within an interrogation zone; b. securing a marker to an article, said marker being selected to comprise a body of magnetic material with retained stress and having a magnetic hysteresis loop with a large Barkausen discontinuity such that upon exposure of said body to an external magnetic field, whose field strength in the direction opposing the magnetic polarization of said body exceeds a given threshold value, there results a regenerative reversal of said magnetic polarization; and c. detecting perturbations of the magnetic field in said interrogation zone having a frequency higher than the 30th harmonic of the incident alternating low frequency magnetic field when said marker is present in said interrogation zone.
Claim 39
Independent Claim
27 words
The method of claims 35 wherein perturbations in excess of the seventy-fifth harmonic of the incident alternating low frequency magnetic field are detected in said step c.
Claim 40
Dependent Claim
27 words
The method of claim 35 wherein perturbations in excess of the ninetieth harmonic of the incident alternating low frequency magnetic field are detected in said step c.
Claim 41
Dependent Claim
47 words
The method of claim 35 wherein said incident alternating low frequency magnetic field is selected at a frequency of less than 100 hertz, and wherein perturbations of the magnetic field in excess of the thirtieth harmonic of incident magnetic field frequency are detected in said step c.
Claim 42
Dependent Claim
25 words
The method of claim 38 wherein the lowest intensity of the magnetic field in the interrogation zone is selected to be less than 1.2 oersted.
Claim 43
Dependent Claim
159 words
An article surveillance system for detection of the presence of an article in an interrogation zone comprising: a. low frequency generator means for generating an incident alternating low frequency magnetic field within an interogation zone having a magnetic field intensity throughout said interrogation zone in excess of a predetermined threshold value; b. a marker secured to an article, said marker comprising a body of magnetic material with retained stress and having a magnetic hysteresis loop with a large Barkhausen discontinuity such that upon exposure of said body to an external magnetic field, whose field strength in the direction opposing the instaneous magnetic polarization of said body exceeds said predetermined threshold value, there results a regenerative reversal of said magnetic polarization; c. receiving means for detecting perturbations of the magnetic field in said interrogation zone having a frequency higher than the 30th harmonic of the incident alternating low frequency magnetic field when said marker is present in said interrogation zone.
Claim 44
Dependent Claim
159 words
An article surveillance system for detection of the presence of an article in an interrogation zone comprising: a. low frequency generator means for generating an incident alternating low frequency magnetic field within an interogation zone having a magnetic field intensity throughout said interrogation zone in excess of a predetermined threshold value; b. a marker secured to an article, said marker comprising a body of magnetic material with retained stress and having a magnetic hysteresis loop with a large Barkhausen discontinuity such that upon exposure of said body to an external magnetic field, whose field strength in the direction opposing the instaneous magnetic polarization of said body exceeds said predetermined threshold value, there results a regenerative reversal of said magnetic polarization; c. receiving means for detecting perturbations of the magnetic field in said interrogation zone having a frequency higher than the 30th harmonic of the incident alternating low frequency magnetic field when said marker is present in said interrogation zone.
Claim 45
Dependent Claim
27 words
The article surveillance system of claims 40 wherein the marker produces detectable perturbations in excess of the seventy-fifth harmonic of the incident alternating low frequency magnetic field.
Claim 46
Dependent Claim
27 words
The article surveillance system of claim 40 wherein the marker produces detectable perturbations in excess of the ninetieth harmonic of the incident alternating low frequency magnetic field.
Claim 47
Dependent Claim
46 words
The article surveillance system of claim 40 wherein the incident alternating low frequency magnetic field operates at a frequency of less than about 100 hertz, and the receiving means detects perturbations of the magnetic field in excess of the thirtieth harmonic of incident magnetic field frequency.
Claim 48
Dependent Claim
25 words
The article surveillance system of claim 43 wherein the lowest intensity of the magnetic field in the interrogation zone is less than about 1.2 oersteds.
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| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
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| 3.5 Years (Year 4) | 1990-04-20 | 1990-10-20 | 1991-04-21 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1994-04-20 | 1994-10-20 | 1995-04-21 | $3760.00 | Window Closed / Lapsed |
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