EP0457078A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Electro-magnetic desensitizer
Assignee: 3M Co
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Filing: 1991-04-25
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Granted: —
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Expires: 2011-04-25
Abstract
Abstract The invention is related to a process of deactivating a magnetic security marker of an article surveillance system, wherein the security marker is detected by simulating conditions normally present in such a system, e.g., by creating between a transmitter and a receiver a sinewave electromagnetic field and the deactivating the security marker by means of the electronically switchable magnetizing apparatus in response to the detection of the magnetic field which corresponds to the magnetization of the security marker in the surveillance zone. It is the object of the invention to enable the magnetic security marker to be deactivated using any alternating power line. To this end, the magnetic system is automatically connected to a power line without circuit change when the security marker is detected. The magnetizing apparatus gradually builds up a magnetic field by rectifying the flow current, monitoring it by a current sensor and increasing it at each change of phase until the current reaches a level to which the sensor is set as effecting deactivation. Thereafter, the magnetizing apparatus is electronically disconnected from the power line.
Inventors
- 👤 Werner 3M Laboratories Schwarz (Europe) Gmbh
- 👤 Josef 3M Laboratories Graessle (Europe) Gmbh
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-04 13:25
CPC Classifications
G; G08; G08B; G08B13/00; G08B13/22; G08B13/24; G08B13/2402; G08B13/2405; G08B13/2408; G08B13/2411
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
284 words
A method for magnetizing a magnetically responsive marker of an electronic article surveillance system in which an alternating magnetic field is produced within an interrogation zone for interrogating a said marker and a characteristic response produced by an activated marker in said zone is detected and used to produce an appropriate alarm signal, said marker comprising at least one magnetizable element which when magnetized causes a different response to be produced, said method comprising the steps of a) positioning a said marker within a first magnetic field corresponding to that produced by said system for interrogating a said marker, detecting the response from the marker and producing an active marker signal in the event the response corresponds with the characteristic response required by the system to produce a said alarm signal, b) applying a second magnetic field identified by its flux density to said magnetizable element to change the magnetic state thereof, thereby altering said response, and c) applying said first magnetic field to said marker, detecting the response therefrom and producing a deactivated marker signal when said altered response is detected, said method being characterized by the steps of responding to a said active marker signal by electronically closing a switch so as to apply a source of alternating electrical power via a rectifier to said coil to gradually build up said second magnetic field, which is directionally constant, sensing said current and using said sensed current to drive electronic control means to increase said current until a current level is reached corresponding to a magnetic field intensity level at which said characteristic response will be altered, and electronically opening said switch to disconnect the source of alternating electrical power from the coil.
Claim 2
Dependent Claim
373 words
An apparatus for performing the method according to claim 1, comprising means for producing within an interrogation zone an alternating magnetic field for interrogating a said marker and means for producing an appropriate alarm signal when a characteristic response produced by an activated marker in said zone is detected, said marker comprising at least one magnetizable element which when magnetized causes a different response to be produced than that resulting when the magnetizable element is unmagnetized, said deactivating apparatus comprising a) electronic article surveillance system simulation magnetizing means comprising a wave generator (1) including a coil (2) for generating a first magnetic field corresponding to that produced by said system for interrogating said marker, within which first field said marker may be positioned, means (8, 16) for detecting the response from the marker and for producing an active marker signal in the event the response corresponds with the characteristic response required by the system to produce a said alarm signal, b) means (3) for generating within said coil a second magnetic field identified by its flux density, and for applying said second field to said magnetizable element to change the magnetic state thereof, thereby altering said response, and c) means (9) for applying a said first magnetic field to said marker detecting the response therefrom and (20) for producing a deactivated marker signal when said altered response is detected, said apparatus being characterized by electronic switch means (13, 15) responsive to said active marker signal for applying current through a rectifier means (12) directly from a source of alternating electrical power thereby applying said unidirectional current to said coil to gradually build up said second magnetic field, which is directionally constant, means (14) for sensing the current in said coil, electronic evaluator and control means (17, 18) responsive to said sensed current for gradually increasing said current so as to reach a current level at which the intensity of said second magnetic field corresponds to that level at which said characteristic response will be altered, and electronic control means (18) for electronically opening said switch means (13, 15) to disconnect the source of alternating electrical power from the coil when the intensity of said second magnetic field is sufficient to alter said response.
Claim 3
Dependent Claim
21 words
An apparatus according to claim 2, further characterized by a wave generator (1) for generating a substantially sinusoidal first magnetic field.
Claim 4
Dependent Claim
57 words
An apparatus according to claim 2, further characterized by said coil further including a yoke (5) of ferromagnetic material and a coil (2) short-circuited by a full wave bridge rectifier (12) connected directly to said source of electrical power, with said current sensor (14) and said electronic switch (17, 18) being connected in series in said short-circuit.
Claim 5
Dependent Claim
54 words
An apparatus according to claim 2, characterized in that the apparatus further comprises a yoke (5) and a coil (2) short-circuited by an antiparallel diode connected by another rectifier diode to the source of electrical power, with said current sensor (14) and said electronic switch (17, 18) being connected in series in said short-circuit.
Claim 6
Independent Claim
39 words
An apparatus as in claims 4 and 5, characterized by said yoke (5) being configured to create a relatively wide air gap, with the yoke (5) and coil (2) being adopted to be mounted underneath a table top (6).
Claim 7
Independent Claim
41 words
An apparatus as in claims 4, 5 and 6, characterized by said yoke (5) having a substantially U-shaped configuration such that the magnetic flux density required for deactivating the magnetic security element is provided above the legs of said U-shaped configuration.
Claim 8
Dependent Claim
35 words
An apparatus as in claim 2, characterized by the magnetic flux density required for deactivating the magnetic security element being built up by a plurality of rectified voltage pulses from the source of electrical power.
Claim 9
Dependent Claim
37 words
An apparatus as in Claim 2, characterized by the maximum current level to which said current sensor (14) is set corresponds to a magnetic flux density amouting to three times the magnetic flux density required for deactivation.
Claim 10
Dependent Claim
34 words
An apparatus according to claim 2, characterized in that said magnetic flux density can be set by the current sensor (14) in the range of 300 to 1000 G (30 - 100 mT (milli-Tesla)).
Claim 11
Dependent Claim
54 words
An apparatus as in claim 3, characterized in that both terminals of said coil (2) are connected through impendance matching and decoupling capacitors (11) to a wave generator (1) and in that a switch (13) included in the short-circuit loop of the magnetic system prevents the transmit signal from being short-circuited in said loop.
Claim 12
Dependent Claim
22 words
An apparatus as in claim 2, characterized by yoke (5) of electromagnetic coil (2) consisting of a relatively low coercive force material.
Claim 13
Independent Claim
31 words
An apparatus as in any of claims 2-12, characterized in that the magnetizing, apparatus 4 comprising coil 2, yoke 5 and power section 3 is mounted under a table top 6.
Claim 14
Independent Claim
30 words
An apparatus as in any of claims 2-12, characterized in that the magnetizing apparatus 4' comprising coil 2', yoke 5' and power section 3 is mounted in a handheld unit.
References Cited (Backward Citations)
No citation records indexed.
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